United States Department of Agriculture

Forest Rocky Mountain General Technical

Service Research Station Report RMRS-GTR-346 August 2016

Classification and Description of 

World Formation Types 

Don Faber-Langendoen, Todd Keeler-Wolf, Del Meidinger, Carmen Josse, 

Alan Weakley, David Tart, Gonzalo Navarro, Bruce Hoagland, 

Serguei Ponomarenko, Gene Fults, Eileen Helmer 
Faber-Langendoen, D.; Keeler-Wolf, T.; Meidinger, D.; Josse, C.; Weakley, A.; Tart, 

D.; Navarro, G.; Hoagland, B.; Ponomarenko, S.; Fults, G.; Helmer, E. 2016. 

Classification and description of world formation types. Gen. Tech. Rep. 

RMRS-GTR-346. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 222 p.

Abstract

An ecological vegetation classification approach has been developed in which a combination of vegetation attributes (physiognomy, structure, and floristics) and their response 

to ecological and biogeographic factors are used as the basis for classifying vegetation 

types. This approach can help support international, national, and subnational classification efforts. The classification structure was largely developed by the Hierarchy Revisions 

Working Group (HRWG), which contained members from across the Americas. The 

HRWG was authorized by the U.S. Federal Geographic Data Committee (FGDC) to develop a revised global vegetation classification to replace the earlier versions of the structure 

that guided the U.S. National Vegetation Classification and International Vegetation 

Classification, which formerly relied on the UNESCO (1973) global classification (see 

FGDC 1997; Grossman and others 1998). This document summarizes the development of the upper formation levels. We first describe the history of the Hierarchy 

Revisions Working Group and discuss the three main parameters that guide the classification—it focuses on vegetated parts of the globe, on existing vegetation, and includes 

(but distinguishes) both cultural and natural vegetation for which parallel hierarchies are 

provided. Part I of the report provides an introduction to the overall classification, focusing on the upper formation levels. Part II provides a description for each type, following 

a standardized template format. These descriptions are a first preliminary effort at global 

descriptions for formation types, and are provided to give some guidance to our concepts. 

Cover photos of Cool Temperate Forests from around the world. Clockwise from 

top left:

1. Western Eurasian Forest & Woodland division: European beech (Fagus sylvatica) 

forest in Czech Republic (by Scott Franklin) 

2. Eastern North American Forest & Woodland division: Eastern Hemlock-Sugar 

Maple (Tsuga canadensis-Acer saccharum) forest in central Wisconsin, United States 

(by Don Faber-Langendoen).

3. Eastern Asian Forest & Woodland division: Oak-pine / bamboo forest in Foping 

National Nature Reserve, Shaanxi Province, China (by Scott Franklin) 

4. Valdivian Forest division: Southern beech (Nothofagus spp.) forest in Altos de Lircay 

National Reserve, Chile (by Bruce Young)

5. Southeast Australian Cool Temperate Forest & Woodland division: Australian Alps - 

mainly Mountain Ash (Eucalyptus regnans) (by Andy Gillison)
Classification and Description of 

World Formation Types 

Don Faber-Langendoen, Todd Keeler-Wolf, Del Meidinger, Carmen Josse, 

Alan Weakley, David Tart, Gonzalo Navarro, Bruce Hoagland, 

Serguei Ponomarenko, Gene Fults, Eileen Helmer 

Hierarchy Revisions Working Group

FGDC Vegetation Subcommittee

Forest Rocky Mountain General Technical

Service Research Station Report RMRS-GTR-346 August 2016

United States Department of Agriculture

i
ii

Authors

(in order of authorship)

Don Faber-Langendoen: NatureServe, Conservation Science Division, 

Arlington, VA

Todd Keeler-Wolf: Biogeographic Data Branch, California 

Department of Fish and Game, Sacramento, CA

Del Meidinger: Meidinger Ecological Consultants Ltd., Victoria 

BC

Carmen Josse: NatureServe, Conservation Science Division, 

Arlington, VA

Alan Weakley: North Carolina Botanic Garden, University of 

North Carolina at Chapel Hill, Chapel Hill, NC

David Tart: USDA Forest Service - Intermountain Region, 

Natural Resources, Ogden, UT

Gonzalo Navarro: Universidad Católica Boliviana “San Pablo, 

Cochabamba, Bolivia 

Bruce Hoagland: Oklahoma Biological Survey and Department 

of Geography, The University of Oklahoma, 

Norman, OK

Serguei Ponomarenko: Ecological Integrity Branch, Parks Canada, 

Gatineau, Québec 

Gene Fults: Natural Resources Conservation Service - West 

National Technology Support Center, Portland, 

OR

Eileen Helmer: USDA Forest Service - International Institute of 

Tropical Forestry, Fort Collins, CO
iii

Acknowledgments

The work produced here was supported by the U.S. National Vegetation 

Classification partnership between U.S. Federal agencies, the Ecological Society 

of America, and NatureServe staff, working through the Federal Geographic Data 

Committee (FGDC) Vegetation Subcommittee. FGDC sponsored the mandate of the 

Hierarchy Revisions Working Group, which included international expertise into the 

process. For that reason, this product represents a collaboration of national and international vegetation ecologists.

We thank Ralph Crawford, chair of the FGDC vegetation subcommittee. We gratefully acknowledge the support of the U.S. Federal agencies that helped fund the work 

of the Hierarchy Revisions Working Group from 2003 to 2012. We appreciate their patience with our slow progress on this effort. Most recently, the U.S. Geological Survey, 

and in particular Alexa McKerrow, has supported the development of the formation 

descriptions that are provided in this document. 

We appreciate the support of the Ecological Society of America Vegetation 

Classification Panel for their peer review of this document. In particular, we thank the 

Panel’s chair, Scott Franklin, for facilitating review among the panel and internationally. Through his efforts, we benefited from international reviewers, including Ken 

Baldwin, John Benson, Sara del Río González, Jesus Izco, David Keith, Ángel Penas 

Merino, Salvador Rivas-Martínez, Michael Rutherford, and Daniel Sánchez-Mata, and 

we thank them for their input. A special thanks to Ángel Penas Merino for creating the 

North American and European macrobioclimate maps for this report.

Over the years, various members of the HRWG have participated for a period of 

time. We thank Sherm Karl, Otto Huber, Jean-Pierre Saucier, and Andy Gray for their 

input at critical stages early on in the development of the formations. 

We thank Mary Russo and Kristin Snow, of NatureServe, for maintaining and 

editing the classification database and producing the Level 1–Level 3 description 

documents for Part II. 
iv
v

Executive Summary

An ecological vegetation (EcoVeg) classification approach has been developed in 

which a combination of vegetation attributes (physiognomy, structure, and floristics) 

and their response to ecological and biogeographic factors are used as the basis for 

classifying vegetation types (Faber-Langendoen and others 2014). This approach can 

help support international, national, and subnational classification efforts. Support for 

many aspects of the development of classification was provided by the U.S. National 

Vegetation Classification (USNVC) partnership, in conjunction with development of 

the International Vegetation Classification (IVC) (FGDC 2008; Faber-Langendoen 

and others 2009; Jennings and others 2009). The classification structure was largely 

developed by the Hierarchy Revisions Working Group (HRWG), which contained 

members from across the Americas. The group was authorized by the U.S. Federal 

Geographic Data Committee (FGDC) Vegetation Subcommittee (chaired by the U.S. 

Forest Service), to develop a revised global vegetation classification to replace the 

earlier versions of the structure that guided the USNVC and IVC, which relied on the 

UNESCO (1973) global classification (see FGDC 1997; Grossman and others 1998). 

This document summarizes the development of the upper formation levels. 

We first describe the history of the Hierarchy Revisions Working Group and discuss 

the three main parameters that guide the classification—it focuses on vegetated parts 

of the globe, on existing vegetation, and includes (but distinguishes) both cultural and 

natural vegetation for which parallel hierarchies are provided.

For natural vegetation, we define three main physiognomic levels: Formation 

Class, Formation Subclass, and Formation; each of the types for all three levels is 

also described. For cultural vegetation, we define and describe four main physiognomic levels: Cultural Class, Cultural Subclass, Cultural Formation, and Cultural 

Subformation. We use a fourth physiognomic level for cultural vegetation because the 

floristic/biogeographic patterns used for natural vegetation at the fourth level are not 

nearly as relevant for cultural vegetation. We provide guidance for developing formation type description and nomenclature. 

The upper levels were not developed in a strictly top down manner. Rather, members of the HRWG had access to draft mid and lower level units (from Division to 

Association) for the United States and parts of Canada and Latin America. A comprehensive master spreadsheet of these draft units was organized under the upper levels 

and was used to critique the overall “naturalness” of the formation units. The HRWG 

reevaluated formation concepts where formations introduced undesirable splits in 

lower units that were otherwise ecologically and floristically similar. Our goal was to 

make splits between upper level types that had good ecological and vegetation support for them. Still, inevitably, given the multi-dimensional and continuous gradients 

affecting vegetation, some criteria for upper levels require splitting otherwise closely 

related floristic and physiognomic types (e.g., open woodland from grassland, floodplain forest from upland forest).
vi

Part I of the report provides an introduction to the overall classification, focusing 

on the upper formation levels. Appendices provide important information on members 

of the working group, a draft set of formation types at all three levels, growth forms 

used to describe the types, and comparisons with other formation level classifications. 

Appendix I provides a key to Level 1. Appendix J introduces examples of the Division 

level, the level immediately below formation. A comprehensive set of Divisions for 

all formations is a key next step in the process of establishing an ecological vegetation 

classification framework.

Part II provides a description for each type, following a standardized template 

format. The HRWG had limited time to develop descriptions, and we focused more 

on developing consistent, meaningful concepts than extensive descriptive text. Thus, 

these descriptions are a first preliminary effort at global descriptions for formation 

types, and are provided to give some guidance to our concepts. Undoubtedly, even 

these preliminary descriptions are biased by our western hemisphere perspective. We 

look forward to engaging with a broader set of ecologists around the globe to continue 

improving both the concepts and the descriptions. We hope such collaboration can 

develop, in part, by identifying vegetation types at the Division level around the globe.
vii

Contents

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Part I: Development of the U.S. National Vegetation Classification Hierarchy . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Hierarchy Revisions Working Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Phase I: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Phase II: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Context for the Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Vegetated – Non-Vegetated: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Existing Vegetation: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Natural and Cultural Vegetation: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

The Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Development of the Upper Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Ecological Approach to Organizing Formation Class Types: . . . . . . . . . . . 13

Terminology for Formation Names: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Zonal and Azonal Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Development of Natural Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Formation Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1. Forest & Woodland (Mesomorphic Tree Vegetation) . . . . . . . . . . . . . . . 14

2. Shrub & Herb Vegetation (Mesomorphic Shrub & Herb Vegetation). . . . 16

3. Desert & Semi-Desert (Xeromorphic Woodland, Scrub & 

Grassland Vegetation)........................................ 16

4. Polar And High Montane Scrub & Grassland (Cryomorphic Scrub, 

Herb And Cryptogam Vegetation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5. Aquatic Vegetation (Hydromorphic Vegetation) . . . . . . . . . . . . . . . . . . . 17

6. Open Rock Vegetation (Cryptogam —Open Mesomorphic Vegetation) . 17

Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Formation Subclass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Formation Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Wetland Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
viii

Summary of Criteria for Natural Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Development of Cultural Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Cultural Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Cultural Subclass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Cultural Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Type Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Upper Level Nomenclatural Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Description Template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Peer Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

A Key to the Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Part II: Description of World Formation Types............................ 35

1. Forest & Woodland (C01) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

1.A. Tropical Forest & Woodland (S17) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

1.A.1. Tropical Dry Forest & Woodland (F003) . . . . . . . . . . . . . . . . . . . . . 42

1.A.2. Tropical Lowland Humid Forest (F020) . . . . . . . . . . . . . . . . . . . . . . 46

1.A.3. Tropical Montane Humid Forest (F004) . . . . . . . . . . . . . . . . . . . . . . 49

1.A.4. Tropical Flooded & Swamp Forest (F029) . . . . . . . . . . . . . . . . . . . . 51

1.A.5. Mangrove (F006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

1.B. Temperate & Boreal Forest & Woodland (S15) . . . . . . . . . . . . . . . . . . . . . . . . 56

1.B.1. Warm Temperate Forest & Woodland (F018) . . . . . . . . . . . . . . . . . . 60

1.B.2. Cool Temperate Forest & Woodland (F008) . . . . . . . . . . . . . . . . . . . 62

1.B.3. Temperate Flooded & Swamp Forest (F026) . . . . . . . . . . . . . . . . . . 66

1.B.4. Boreal Forest & Woodland (F001) . . . . . . . . . . . . . . . . . . . . . . . . . . 68

1.B.5. Boreal Flooded & Swamp Forest (F036) . . . . . . . . . . . . . . . . . . . . . . 72

2. Shrub & Herb Vegetation (C02) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

2.A. Tropical Grassland, Savanna & Shrubland (S01) . . . . . . . . . . . . . . . . . . . . . . . 77

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019) . . . . . . . 79

2.A.2. Tropical Montane Grassland & Shrubland (F017) . . . . . . . . . . . . . . 84

2.A.3. Tropical Scrub & Herb Coastal Vegetation (F024) . . . . . . . . . . . . . . 86

2.B. Temperate & Boreal Grassland & Shrubland (S18) . . . . . . . . . . . . . . . . . . . . . 88

2.B.1. Mediterranean Scrub & Grassland (F038) . . . . . . . . . . . . . . . . . . . . . 89

2.B.2. Temperate Grassland & Shrubland (F012) . . . . . . . . . . . . . . . . . . . . 92

2.B.3. Boreal Grassland & Shrubland (F028) . . . . . . . . . . . . . . . . . . . . . . . 96

2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation (F005) . . . . . . 98
ix

2.C. Shrub & Herb Wetland (S44) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

2.C.1. Tropical Bog & Fen (F002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

2.C.2. Temperate to Polar Bog & Fen (F016) . . . . . . . . . . . . . . . . . . . . . . 103

2.C.3. Tropical Freshwater Marsh, Wet Meadow & Shrubland (F030) . . . 106

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & 

 Shrubland (F013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

2.C.5. Salt Marsh (F035) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

3. Desert & Semi-Desert (C03) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

3.A. Warm Desert & Semi-Desert Woodland, Scrub & Grassland (S06) . . . . . . . . 115

3.A.1. Tropical Thorn Woodland (F039) . . . . . . . . . . . . . . . . . . . . . . . . . . 117

3.A.2. Warm Desert & Semi-Desert Scrub & Grassland (F015) . . . . . . . . 119

3.B. Cool Semi-Desert Scrub & Grassland (S11) . . . . . . . . . . . . . . . . . . . . . . . . . . 120

3.B.1. Cool Semi-Desert Scrub & Grassland (F033) . . . . . . . . . . . . . . . . . 121

4. Polar & High Montane Scrub, Grassland & Barrens (C04) . . . . . . . . . . . . . . . . . . 123

4.A. Tropical High Montane Scrub & Grassland (S16) . . . . . . . . . . . . . . . . . . . . . 125

4.A.1. Tropical High Montane Scrub & Grassland (F022) . . . . . . . . . . . . 127

4.B. Temperate to Polar Alpine & Tundra Vegetation (S12).................. 129

4.B.1. Temperate & Boreal Alpine Vegetation (F037) . . . . . . . . . . . . . . . . 132

4.B.2. Polar Tundra & Barrens (F031) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

5. Aquatic Vegetation (C05) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

5.A. Saltwater Aquatic Vegetation (S09) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

5.A.1. Floating & Suspended Macroalgae Saltwater Vegetation (F052) . . 139

5.A.2. Benthic Macroalgae Saltwater Vegetation (F053) . . . . . . . . . . . . . . 140

5.A.3. Benthic Vascular Saltwater Vegetation (F054) . . . . . . . . . . . . . . . . 142

5.A.4. Benthic Lichen Saltwater Vegetation (F055) . . . . . . . . . . . . . . . . . . 143

5.B. Freshwater Aquatic Vegetation (S13) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

5.B.1. Tropical Freshwater Aquatic Vegetation (F056) . . . . . . . . . . . . . . . 146

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057) . . . . . . . 149

6. Open Rock Vegetation (C06) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

6.A. Tropical Open Rock Vegetation (S02) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

6.A.1. Tropical Cliff, Scree & Other Rock Vegetation (F011) . . . . . . . . . . 156

6.B. Temperate & Boreal Open Rock Vegetation (S04) . . . . . . . . . . . . . . . . . . . . . 157

6.B.1. Temperate & Boreal Cliff, Scree & Other Rock Vegetation (F034) 160

7. Agricultural & Developed Vegetation (CCL01) . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

7.A. Woody Agricultural Vegetation (CSC01) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
x

7.A.1. Woody Horticultural Crop (CFO01) . . . . . . . . . . . . . . . . . . . . . . . . 165

7.A.2. Forest Plantation & Agroforestry (CFO02) . . . . . . . . . . . . . . . . . . . 166

7.A.3. Woody Wetland Horticultural Crop (CFO03) . . . . . . . . . . . . . . . . . 167

7.B. Herbaceous Agricultural Vegetation (CSC02) . . . . . . . . . . . . . . . . . . . . . . . . 168

7.B.1. Row & Close Grain Crop (CFO04) . . . . . . . . . . . . . . . . . . . . . . . . . 169

7.B.2. Pasture & Hay Field Crop (CFO05) . . . . . . . . . . . . . . . . . . . . . . . . 169

7.B.3. Herbaceous Horticultural Crop (CFO06) . . . . . . . . . . . . . . . . . . . . 170

7.B.4. Fallow Field & Weed Vegetation (CFO07) . . . . . . . . . . . . . . . . . . . 171

7.B.5. Herbaceous Wetland Crop (CFO08) . . . . . . . . . . . . . . . . . . . . . . . . 172

7.C. Herbaceous & Woody Developed Vegetation (CSC03) . . . . . . . . . . . . . . . . . 172

7.C.1. Lawn, Garden & Recreational Vegetation (CFO09) . . . . . . . . . . . . 173

7.C.2. Other Developed Vegetation (CFO10) . . . . . . . . . . . . . . . . . . . . . . 174

7.C.3. Developed Wetland Vegetation (CFO11)..................... 175

7.D. Agricultural & Developed Aquatic Vegetation (CSC04) . . . . . . . . . . . . . . . . 175

7.D.1. Agricultural Aquatic Vegetation (CFO12) . . . . . . . . . . . . . . . . . . . . 176

7.D.2. Developed Aquatic Vegetation (CFO13) . . . . . . . . . . . . . . . . . . . . . 178

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Appendix A—Hierarchy Revisions Working Group 

 2010–2012..................................................... 190

Appendix B. Formation level units, Level 1 to Level 3. . . . . . . . . . . . . . . . . . . . . . . . 191

Appendix C. Glossary Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

Appendix D. Growth Form Names, Codes, and Definitions . . . . . . . . . . . . . . . . . . . 200

Appendix E. Growth Forms from Box and Fujiwara (2005) . . . . . . . . . . . . . . . . . . . 204

Appendix F. Comparisons to Other Formation-Level Classifications . . . . . . . . . . . . 206

Appendix G. Example of Descriptive Methods for Describing 

 Physiognomy — Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

Appendix H. Key to bioclimatic maps of the world—Rivas 

 Martinez & Rivas-Saenz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

Appendix I. Key to Formation Class (Level 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

Appendix J. Examples of Divisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
USDA Forest Service RMRS-GTR-346. 2016. 1

Part I: Development of the U.S. National 

Vegetation Classification Hierarchy
2 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 3

Introduction

There is currently no fully suitable classification framework by which vegetation 

ecologists can organize, define, and describe global vegetation patterns at multiple 

scales, from broad physiognomic types to narrowly defined floristic types. Some classification publications provide little more than a name. Others provide very expansive 

descriptions but with only some or little consistency to the classification, and others 

focus solely on either structural or floristic patterns. What is needed is a comprehensive, global vegetation classification approach that is multi-scalar, from broad 

global types to local fine scale types. It should be committed to a rigorous plot-based 

approach while building on the accumulated work of vegetation ecologists over the 

past century, open to ongoing peer review, and able to maintain an authoritative list of 

types at all times that can be used for description, inventory, monitoring, and mapping.

Here, we briefly introduce an ecological vegetation (EcoVeg) classification approach that addresses these needs and then focus on the development and rationale 

for the upper formation levels. These formations, both natural and cultural, provide 

a basic synopsis of the world’s vegetation that is structured by specific criteria with 

sufficient detail to encourage consistent application anywhere in the world and within 

a multi-scale hierarchical structure. Details of the scientific basis for the classification 

approach are provided in Jennings and others (2009) and Faber-Langendoen and others (2014) who build on the integrated “physiognomic-floristic-ecologic,” or EcoVeg, 

approach to vegetation classification (Bohn and others 2000-2003; Brown and others 

1998; Davies and others 2004; Devilliers and others 1991, 1996; Rodwell and others 

2002; Rübel 1930–1931, in Shimwell 1971; Whittaker 1962). Appendices to this 

report contain specific descriptions to each formation and a key to the uppermost 

formation class level, along with comparisons to other global formation level classifications. The classification has been developed to support the U.S. National Vegetation 

Classification (FGDC 2008), other partner classifications, such as the Canadian and 

Bolivian NVC, and constitutes a revision of the International Vegetation Classification 

(Grossman and others 1998) that was based on UNESCO (1973). 

Background

Hierarchy Revisions Working Group

The U.S. National Vegetation Classification (USNVC) emerged through a partnership between Federal agencies and nongovernmental organizations—NatureServe 

and the Ecological Society of America’s Vegetation Classification Panel (hereafter 

Panel)—through the auspices of the Federal Geographic Data Committee Vegetation 

Subcommittee (FGDC 1997), chaired by the U.S. Forest Service. The USNVC 

originally adopted the international structure of UNESCO (1973 see also Appendix 

B in Mueller-Dombois and Ellenberg 1974) for its classification. At the same time 

NatureServe supported applications of the UNESCO-based structure in other countries through the International Vegetation Classification (IVC) (Grossman and others 

1998). Thus, when the USNVC partners agreed in 2003 to undertake a revision to the 

USNVC, an international approach was adopted, reflecting the goals to incorporate 

global classification concepts and to avoid an artificial national perspective on units. 

Our goal was to concentrate on the natural structuring of vegetation world-wide and to 
4 USDA Forest Service RMRS-GTR-346. 2016.

emphasize the physiognomic-structural, floristic and ecological components of vegetation, without relying on a particular emphasis on any single predominant criterion such 

as height, woodiness, cover, environmental schema, or other human uses. To this end, 

the partners agreed to form a Hierarchy Revisions Working Group (HRWG) sponsored 

by FGDC. The work of the HRWG progressed in two phases, the first phase from 

2003–2008, and the second phase from 2010–2013.

Phase I:

The Hierarchy Revisions Working Group (HRWG) was formed in November 

of 2003, co-chaired by representatives of the U.S. Forest Service (USFS) and 

NatureServe. Members were drawn from State and Federal agencies and organizations 

in the United States, Canada, and Latin America. All were chosen based on either their 

familiarity with the USNVC, IVC and related classifications or for their expertise in 

vegetation classification. Members were also encouraged to have their own “teams” 

with which to consult, including the U.S. Forest Service Vegetation Technical Guide 

team that developed an existing vegetation classification and mapping manual (Brewer 

and others 2005; Tart and others 2005a,b), NatureServe staff who developed mesoscale classification units called ‘‘terrestrial ecological systems’’ (Comer and others 

2003; Comer and Schulz 2007; Josse and others 2003), and California vegetation 

ecologists who tested the hierarchy above the alliance level on California’s vegetation 

(see Sawyer and others 2009, Appendix 3). The HRWG interacted regularly with the 

ESA Panel, Federal agencies, and NatureServe staff.

The HRWG process was somewhat formal, consisting of more or less bimonthly 

phone calls between November 2003 and November 2007, and three face-to-face 

meetings (May 3–6, 2004 in Denver, Colorado; May 22–25, 2005 in Washington, DC; 

March 8–10, 2007 in Mojave, California). The result was a suggested eight-level hierarchy to replace the seven-level hierarchy then in use (FGDC 1997). The lower two 

floristic levels, alliance and association, were retained as is, and the top five formation 

levels were compressed into three to make way for three new physiognomic-floristic 

mid-levels. In 2006, FGDC began the formal process for the USNVC revision, 

incorporating both the HRWG suggestions on the full hierarchy and the ESA Panel’s 

work on standards for the lower floristic levels. The HRWG continued to advise the 

USNVC partners through 2007 and 2008, leading to a formal revised FGDC Standard 

(2008). This Standard established the hierarchical framework of the USNVC and the 

processes for establishing and revising USNVC types. At that time, a formal report 

describing the EcoVeg approach that the USNVC is based on was drafted by the 

HRWG (Faber-Langendoen and others 2007), and later published (Faber-Langendoen 

and others 2012). Lower floristic level guidelines were published by Jennings and others (2009). 

The revised standard was a substantial overhaul of the 1997 standard and the classification, as summarized by FGDC (2008):

a. uses vegetation criteria to define all types (de-emphasizing abiotic criteria, such 

as hydrologic regimes in wetland types), 
USDA Forest Service RMRS-GTR-346. 2016. 5

b. provides a clear distinction between natural (including semi-natural) vegetation 

and cultural vegetation wherever these can be observed from broad growth form 

patterns (rather than combining natural and cultural vegetation initially and 

separating them at lower levels), 

c. defines, for natural vegetation, the upper levels of the hierarchy based on broad 

growth form patterns that reflect ecological relationships (rather than detailed 

structural criteria, which are more effectively used in combination with floristic 

criteria in lower levels of the hierarchy), 

d. provides a new set of mid levels for natural vegetation units that bridge the large 

conceptual gap between alliance and formation, 

e. integrates the physiognomic and floristic hierarchy levels based on ecologic 

vegetation patterns, rather than developing the physiognomic and floristic levels 

independently and then forcing them into a hierarchy, 

f. provides detailed standards for plot data collection, type description and 

classification, data management and peer review of natural vegetation, 

g. provides a dynamic content standard for the USNVC that allows the FGDC 

partner agencies and organizations to revise the classification and its component 

vegetation types through a peer review process, and

h. provides, for cultural vegetation, an independent set of levels that addresses the 

particular needs of cultural vegetation.

The structure of the revised hierarchy is a substantial revision of the 1997 hierarchy, 

which relied heavily on the UNESCO (1973) physiognomic hierarchy for all levels 

above the alliance. The newly adopted national vegetation hierarchy consists of eight 

levels, organized into three upper levels, three middle levels, and two lower levels 

(Table 1). See also Table 3, which provides the details on both the natural and cultural 

2008 hierarchies. 

Table 1—Comparison of original 1997 USNVC Vegetation Hierarchy (adapted from UNESCO 

1973) and the 2008 revision.

1997 FGDC Hierarchy 2008 Revised Hierarchy for Natural Vegetation

Division — Vegetation vs. Non- vegetation Upper Levels

Order — Tree, Shrub, Herb, Nonvascular

Level 1 — Formation Class Level 1 — Formation Class

Level 2 — Formation Subclass

Level 3 — Formation Group Level 2 — Formation Subclass

Level 4 — Formation Subgroup — Natural/Cultural

Level 5 — Formation Level 3 — Formation

Middle Levels Level 4 — Division

Level 5 — Macrogroup

Level 6 — Group

Level 6 — Alliance Lower Levels Level 7 — Alliance

Level 7 — Association Level 8 — Association
6 USDA Forest Service RMRS-GTR-346. 2016.

Phase II:

With the completion of the FGDC standard, USNVC partners began implementing revisions to the classification system, but two important issues remained to be 

resolved. First, the 2008 FGDC standard called for a screening/peer review process 

to induct proposed types into the revised USNVC. Thus, in June of 2010, FGDC requested the HRWG to take on the task of reviewing, revising, and describing the pilot 

upper level units (L1 – L3) provided in the FGDC 2008 standard (see Appendix G in 

FGDC 2008). Fortunately, most of the members of the original HRWG stayed with the 

project and new members were added (Appendix A). 

During this phase of development, the HRWG was able to draw on extensive 

testing of the upper level units, which were being used as mid and lower level units 

in the USNVC (usnvc.org) and in Canada (cnvc-cnvc.ca). NatureServe and partners 

also began applying the same approach to revisions to the International Vegetation 

Classification (IVC) through projects in South America (Josse 2011; Navarro 2011) 

and Africa. Testing of the hierarchy in Africa led to one major proposed change: move 

all wetland formations under an expanded Class V – Hydromorphic and Hydrophytic 

Vegetation. This decision was only partly implemented (see below). A draft of world 

grassland types from Formation Class to Division was also published (Dixon and others 2014; Faber-Langendoen and Josse 2010).

The HRWG completed the initial review of the units in October of 2010, having 

found that information from proposed new mid-levels provided good support to the 

upper levels (see Division examples in Appendix J). The suggested revisions to move 

all wetlands under a single large class in Class V was not adopted. Instead, the decision was to move all shrub and herb wetlands under a single subclass, while keeping 

forested wetlands and aquatic vegetation wetlands in other classes (see “Wetlands” 

section below). The HRWG made other modest changes to the 2008 version (e.g., adding a Tropical Thorn Woodland formation, removing cryomorphic and xeromorphic 

rock vegetation formations from the “lithomorphic” or open cryptogam class and 

placing the vegetation within those formations within existing divisions of hydryomorphic and xeromorphic vegetation, modifying various formation names). After further 

consultation with the Ecological Society of America Vegetation Classification Panel 

(hereafter “ESA Panel”), the HRWG submitted a request to FGDC that the USNVC 

partners adopt the 2008 pilot units. FGDC approved the request, based on the process 

used to reach those decisions. The set of units is provided in Appendix B. 

The HRWG then began writing detailed descriptions of each of the L1 – L3 units, 

following the standard description template. In addition, a key to Level 1 was produced (Appendix I). 

Context for the Hierarchy

Several primary categories are helpful in describing the scope of the classification 

and placing it within a broader land cover context: vegetated – non-vegetated, existing 

vegetation, and natural – cultural vegetation. 
USDA Forest Service RMRS-GTR-346. 2016. 7

Vegetated – Non-Vegetated: 

The classification includes all vegetated areas with 1 percent or more of their 

surface area covered by live vegetation. This includes vegetation found on both 

upland environments and in wetlands (rooted emergent and floating vegetation). The 

classification excludes non-vegetated (i.e. less than 1 percent vegetation cover) natural 

lands (e.g., rock, glaciers, some deserts) and waters (e.g., lakes and rivers) and nonvegetated cultural lands (e.g., roads, buildings, mines) and waters (e.g., reservoirs, 

canals), though it can easily be linked to land cover classifications that do include 

these lands to provide a full terrestrial coverage (see “Natural and Cultural Vegetation” 

section below).

Existing Vegetation:

This classification includes only existing vegetation types, as described by FGDC 

(2008): “Existing vegetation is the plant cover, or floristic composition and vegetation structure, documented to occur at a specific location and time, preferably at the 

optimal time during the growing season.” (see also Jennings and others 2009; Tart and 

others 2005a). Abiotic factors, geographic and successional relationships are used to 

help interpret the types. Existing vegetation can provide the basis for describing potential vegetation types.

Natural and Cultural Vegetation:

This classification provides separate categories for natural and cultural vegetation, 

a distinction that is consistent with other vegetation and land cover classifications 

(e.g., Anderson and others 1976; Di Gregorio2005; Küchler 1969). Although cultural 

and natural vegetation are distinguished in the classification, both are subsequently 

classified in a hierarchical framework that emphasizes primarily floristics at the lower 

levels, both physiognomic and floristics at mid levels, and primarily physiognomy at 

upper levels. 

Natural (including semi-natural) vegetation is defined as vegetation where 

ecological processes primarily determine species composition and stand structure; 

that is, the vegetation is comprised of a set of plant species growing spontaneously 

(i.e., with little human influence) and is shaped by both abiotic and biotic processes 

(Küchler 1969; Westhoff and van der Maarel 1973). Cultural vegetation is defined as 

vegetation with a distinctive structure, composition, and development determined by 

regular human activity (cultural vegetation sensu stricto of Küchler 1969). The distinctive physiognomy, floristics, and dependence on human activity for its persistence set 

cultural vegetation apart from natural and semi-natural vegetation. These distinctive 

attributes typically include one or more of the following:

•  Dominant herbaceous vegetation is regularly spaced and/or growing in rows, 

often in areas with substantial cover of bare soil for significant periods of the 

year, usually determined by tillage or chemical treatment.

•  Dominant vegetation has highly manipulated growth forms. Structure is rarely 

the result of natural plant development, but is usually determined by mechanical 

pruning, mowing, clipping, etc.
8 USDA Forest Service RMRS-GTR-346. 2016.

•  Dominant vegetation is comprised of species not native to the site or area that 

have been intentionally introduced by humans and that would not persist without active management by humans.

Recognition of cultural or “anthromorphic” vegetation classes parallels recent calls 

for recognition of an “Anthrosol” order for soils because of intrinsic properties of the 

soil caused by farming, fertilizing, irrigation, and tillage (Bryant and Galbraith 2003; 

Gong and others 2003).

Summary

We identify these fundamental aspects of vegetation using two categorical levels 

(Table 2a). These categories provide the organizing framework for the classification, 

beginning with Level 1. The framework allows the vegetation-ecologic approach to 

be easily extended to a full terrestrial approach by linking these categories to existing 

land cover classification systems, such as FAO Land Cover Classification System 

(Di Gregorio 2005) (Table 2b). Further examples of this approach are provided for 

the USNVC by FGDC (2008, Appendix B - Relationships to the U.S. National Land 

Cover Database (NLCD) (USGS 2001). See also Appendix B.

 Table 2a—Conceptual categories and level one of the hierarchy (from FGDC 

2008, Table 2.1).

Category 1 Category 2 Level 1

Vegetated Semi-natural vegetation Forest & Woodland (Mesomorphic 

Tree Vegetation)

Shrub & Herb Vegetation 

(Mesomorphic Shrub & Herb 

Vegetation)

Desert & Semi-Desert (Xeromorphic 

Woodland, Scrub & Herb Vegetation)

Polar & High Montane Scrub, 

Grassland & Barrens (Cryomorphic 

Vegetation)

Aquatic Vegetation (Hydromorphic 

Vegetation)

Open Rock Vegetation (Cryptogam - 

Open Mesomorphic Vegetation)

Cultural vegetation Agricultural & Developed Vegetation 

(Anthro-morphic Vegetation)

Nonvegetated Not included (see Table 2b).
USDA Forest Service RMRS-GTR-346. 2016. 9

The Hierarchy

The eight levels of the hierarchy for both cultural and natural vegetation are provided in Table 3. The EcoVeg approach treats natural vegetation distinct from cultural 

vegetation; thus, each has similar but differently defined hierarchical levels. This 

allows for a dynamic portrait of all existing vegetation in a way that reflects ongoing 

changes driven by land use, climate change, invasive species and natural processes. 

Tables 4a and 4b provide examples of natural (4a) and cultural (4b) types across all 

levels of the two hierarchies.

Development of the Upper Levels

The upper levels of the classification were based on the formation concept, which 

is prominent in the history of vegetation classification (Appendix F). The definition 

provided by Whittaker (1962 pg. 150) is typical: “a community type defined by dominance of a given growth form in the uppermost stratum (or the uppermost closed stratum)

of the community or by a combination of dominant growth forms.” The UNESCO (1973) 

definition guided much of the earlier work on the EcoVeg approach. The formation is 

“basically physiognomic-structural in character with supplementary ecological information integrated into its various categories and applicable to natural and semi-natural vegetation.” 

Physiognomy can be defined as “the visible structure or outward appearance of a plant 

community as expressed by the dominant growth forms, such as their leaf appearance or 

deciduousness”(Fosberg 1961). Structure is the horizontal and vertical spatial pattern of 

growth forms in a plant community, especially with regard to their height, abundance, 

coverage or biomass within the individual layers (Gabriel and Talbot 1984). 

Table 2b—Optional non-vegetated categories from land cover classifications 

(FAO Land Cover Classification System). See also Appendix B.

Category 1 Category 2 Level 1 FAO (1996)

Non-vegetated Natural Terrestrial: Bare Areas 

Aquatic: Natural Waterbodies, Snow & Ice

Cultural Terrestrial: Artificial Surfaces & Associated Areas

Aquatic: Artificial Surfaces & Associated Areas

Table 3—Hierarchy levels for natural and cultural vegetation.

Natural Hierarchy Level Cultural Hierarchy Level

 L1 – Formation Class L1 – Cultural Class

 L2 – Formation Subclass L2 – Cultural Subclass

 L3 – Formation L3 – Cultural Formation

 L4 – Division L4 – Cultural Subformation

 L5 – Macrogroup L5 – Cultural Group

 L6 – Group L6 – Cultural Subgroup

 L7 – Alliance L7 – Cultural Type

 L8 – Association L8 – Cultural Subtype
10 USDA Forest Service RMRS-GTR-346. 2016.

Table 4a—Hierarchical classification for natural vegetation with examples. 

Natural Vegetation Example

Upper Levels

1 – Formation Class Scientific Name: Mesomorphic Shrub & Herb Vegetation 

Colloquial Name: Shrub & Herb Vegetation

2 – Formation Subclass Scientific Name: Temperate & Boreal Shrub & Herb Vegetation

Colloquial Name: Temperate & Boreal Grassland & Shrubland

3 – Formation Scientific Name: Temperate Shrub & Herb Vegetation

Colloquial Name: Temperate Grassland & Shrubland

 Mid Levels

4 – Division Scientific Name: Andropogon – Stipa – Bouteloua Grassland & 

Shrubland Division

Colloquial Name: Central North American Grassland & Shrubland

5 – Macrogroup Scientific Name: Andropogon gerardii – Schizachyrium 

scoparium – Sorghastrum nutans Grassland & Shrubland 

Macrogroup

Colloquial Name: Central Lowlands Tallgrass Prairie

6 – Group Scientific Name: Andropogon gerardii – Sporobolus heterolepis 

Grassland Group

Colloquial Name: Northern Tallgrass Prairie

Lower Levels

7 – Alliance Scientific Name: Andropogon gerardii – Sorghastrum nutans – 

Sporobolus heterolepis Grassland Alliance 

Colloquial Name: Northern Mesic Tallgrass Prairie

8 – Association Scientific Name: Andropogon gerardii – Hesperostipa spartea – 

Sporobolus heterolepis Grassland 

Colloquial Name: Northern Bluestem Mesic Tallgrass Prairie

Table 4b—Hierarchical classification for cultural vegetation with 

examples. 

 Cultural Vegetation Example

 Upper Levels

 1 – Cultural Class Anthromorphic Vegetation

 2 – Cultural Subclass Herbaceous Agricultural Vegetation 

 3 – Cultural Formation Row & Close Grain Crop

 4 – Cultural Subformation Graminoid Row Crop

 Mid Levels

 5 – Cultural Group [optional] Tropical & Temperate Corn Crop

 6 – Cultural Subgroup Temperate Corn Crop

 Lower Levels

 7 – Cultural Type Maize Corn

 8 – Cultural Subtype [optional] Corn for silage
USDA Forest Service RMRS-GTR-346. 2016. 11

We define growth form1 as the shape or appearance of a plant reflecting growing conditions and genetics (see Appendix C for a glossary of terms). Growth form 

is usually consistent within a species, but may vary under extremes of environment 

(Mueller-Dombois and Ellenberg 1974). A list of growth forms is provided in 

Appendix D as a first approximation for defining upper level types.2 This list is 

structured into two levels: general growth forms and specific growth forms. These lists 

were adapted from Whittaker (1975, pg. 359) and Box (1981), and may reflect a western hemisphere perspective, but the intent is to provide a method for characterizing the 

growth form composition of all formations. For comparison, an extended list of “ecophysiognomic” growth form types developed by Box and Fujiwara (2005) is presented 

in Appendix E. This extended list could provide a stronger basis for the approach 

proposed here but needs further review. Introducing a combination of morphological, 

anatomical and physiological adaptations could allow for finer classification distinctions. Instead, however, we proposed adding diagnostic species at the mid-levels of the 

classification, in addition to growth form descriptors. 

By characterizing the growth forms as part of a vegetation plot, it becomes possible 

to empirically describe the growth form components of a vegetation type and relate 

them to ecological factors. Thus, combinations of growth forms can define xeromorphic (desert) vegetation or hydromorphic (aquatic) vegetation. Some growth forms, 

however, such as “flowering forb” do not show particularly strong ecological relationships, at least not as currently defined. They may be constant growth forms rather than 

diagnostic ones.

As with species in lower level units, a growth form is rarely restricted to one upper 

level formation type. Too often, a single physiognomic criteria has been used alone to 

define a formation (e.g., defining a formation by 25 to 60 percent tree canopy cover). 

Although such criteria may be helpful in a diagnostic key or for particular mapping applications, we suggest that in an integrated classification, the use of differential growth 

forms is more helpful. The same growth forms may appear in multiple units, but it is 

the relative abundance of that growth form, in combination with ecological processes 

and consideration of broad floristic-biogeographic patterns at lower levels, that define 

formation types (Table 5). Thus, tree covered lawns are separated from natural forests 

because of differences in the combination of shrub, herb and tree growth forms and 

in ecological processes, though both may have 25 to 60 percent tree canopy. Just as a 

specified presence and abundance of one or more differential species are primary criteria for defining vegetation types at lower levels, the presence and abundance levels of 

one or more growth forms are primary criteria for defining vegetation types at upper 

levels. 

1 A similar term, life form, is defined as the ecological strategy that a plant uses to complete

its life cycle, e.g., Raunkiaer life forms are defined on the position of the bud or organs from

which new shoots or foliage develop after an unfavorable season. Different life forms may not 

always exhibit clear outward structural differences (e.g., hemicryptophytes and geophytes).

2 The growth form list in the FGDC standard is published as a “normative list,” which may 

require a formal approval process for amending it. In the mean-time, all additions or changes 

could be treated as optional.
12 USDA Forest Service RMRS-GTR-346. 2016.

Finally, growth forms are closely related to plant functional types (PFTs), a grouping of organisms that respond in a similar way to a suite of environmental factors 

(Gitay and Noble 1997). A comparison of PFTs used for broad scale assessments 

shows a very close relationship to the growth forms presented here, and leads to aggregations of functional types that are similar to formations (Leemans 1997). This opens 

up the possibility of modeling responses of formations to disturbances and to climate 

change (Cramer 1997), as earlier developed by Box (1981) who formulated climatic 

envelopes for each of his growth form/plant functional types (Appendix E). See also 

Gillison (2013) for a recent treatment of plant functional types.

The upper levels were not developed in a strictly top down manner. Rather, members of the HRWG had access to draft mid and lower level units (from Division to 

Association) for the United States and parts of Canada and Latin America. In addition, 

comparisons were made with other classifications in which physiognomic or formation types were used to organize floristic types, such as the European vegetation types 

published in Rodwell and others 2002 (see other examples in Appendix F). To test 

relationships between upper and lower levels, a comprehensive master spreadsheet of 

draft units was organized under the upper levels and was used to critique the overall 

“naturalness” of the formation units. The HRWG reevaluated formation concepts 

where formations introduced undesirable splits in lower units that were otherwise 

ecologically and floristically similar. Our goal was to make splits between types that 

had good ecological and vegetation support for them. Still, inevitably, given the multidimensional and continuous gradients affecting vegetation, some criteria for upper 

levels require splitting otherwise closely related floristic types (e.g., open woodland 

from grassland, floodplain forest from upland forest). 

Table 5—Characters used to distinguish Tropical Lowland Humid Forest from Tropical 

Montane Humid Forest (after Whitmore 1984, Table 18.1).

Formation

Formation Criteria Tropical Lowland Humid Forest Tropical Montane Humid Forest

Canopy height 25-45 m 1.5-33 m

Emergent trees Characteristic, to 60 (80) m tall Often to usually absent, to 37 m tall

Pinnate leaves Frequent Rare to very rare

Principle leaf size class of 

woody plantsa

Mesophyll or Macrophyll (or 

Megaphyll)

Mesophyll or microphyll

Buttresses Usually frequent and large Uncommon, small or absent

Cauliflory Frequent Rare to absent

Big woody climbers Abundant Usually none

Bole climbers Often abundant Very few to to abundant

Vascular epiphytes Frequent Frequent to abundant

Nonvascular epiphytes Occasional Occasional to abundant

a For definition of leaf-sizes see Mueller-Dombois and Ellenberg (1974, page 453).
USDA Forest Service RMRS-GTR-346. 2016. 13

In summary, the upper levels of the hierarchy are based on dominant and diagnostic 

growth forms that reflect ecological and anthropogenic drivers at global and continental scales, and their concepts are influenced by consideration of vegetation patterns at 

lower levels. The comprehensive set of formation types for all 3 levels (L1–L3) are 

provided in Appendix B. 

Ecological Approach to Organizing Formation Class Types: 

Formation Class is a vegetation classification unit of high rank (1st level) defined 

by broad combinations of dominant general growth forms adapted to basic ranges of 

moisture, temperature, and/or substrate or aquatic conditions (FGDC 2008; cf. Beard 

1973; cf. “major physiognomic types” of Whittaker 1975). 

A primary concern of the HRWG was to consider the ecological relationships 

among vegetation types rather than simply growth forms alone. We asked ourselves 

what fundamental ecological/environmental and anthropogenic processes order global 

vegetation patterns. Can we identify the characteristics of vegetation that reflect those 

processes? Our concern is a familiar one to those seeking an ecological basis for developing vegetation classifications. For example, Warming (1909, pg. 143) wrote: 

“Why not use each growth form [lichen, moss, herb, dwarf-shrub, 

shrub, tree] as a foundation upon which to build a special class? The 

following classes could then be distinguished: that of forest formations, 

of bush-formations of shrub-formations, of dwarf-shrub formations, 

or perennial-herb formations, of moss-formations, and of algaformations... From a morphological standpoint this would possess a 

certain interest, but from a phytogeographical one it must be dismissed, 

because it would involve the separation of formations that are oecologically closely allied.” 

He goes on to state that formations can be based on either a single or compound 

growth forms, where many growth forms are combined to form a single whole. This 

approach has been echoed by others over the years (Box and Fujiwara 2005, 2013; 

Whittaker 1962, 1975) and was adopted by the HRWG. Here we rely strongly on 

multiple growth forms to define formations types (e.g., including needle-leaved and 

cold deciduous broad-leaved trees together within a temperate and boreal forest subformation; aseasonal or drought deciduous herbaceous growth forms with evergreen 

or drought-deciduous shrubs to define topical grassland, savanna and shrubland 

subformation), wherever these combination of growth forms reflected a more natural 

vegetation unit with respect to macro-ecological gradients. 

Terminology for Formation Names:

Because our growth forms emphasize primarily morphological adaptations we use 

the term “morphic” to name formation types, as in hydromorphic, mesomorphic, xeromorphic (see also Table 4 in Ellenberg 1988). Other researchers have used terms such 

as hydrophyte, mesophyte, and xerophytes (e.g., Warming 1909). But these terms are 

often applied to species, where the combination of morphology, anatomy, physiology, 
14 USDA Forest Service RMRS-GTR-346. 2016.

and even life history strategy define the forms. These terms may be better applied in 

the mid and lower levels of the classification where species are part of the criteria. 

Compounding the issue in North America is use of the term “hydrophyte” or “helophyte” species that depend, to varying degrees, on wet habitats, irrespective of any 

obvious morphologic or anatomical adaptations. For example, Tiner (1998) defines 

hydrophytes as “plants growing in water or on a substrate that is at least periodically 

deficient in oxygen as a result of excessive water content.” Hydrophytic vegetation 

is defined as “the sum total of macrophytic plant life that occurs in areas where the 

frequency and duration of inundation or soil saturation produce permanently or periodically saturated soils of sufficient duration to exert a controlling influence on the 

plant species present” (U.S. Army Corps of Engineers 1987). By contrast, hydromorphic vegetation in our approach is defined by types where rooted and floating aquatic 

growth forms are dominant (i.e., aquatic vegetation).

Zonal and Azonal Vegetation

Zonal vegetation refers to vegetation that reflects a close relation to the current climatic conditions of a region and that develop, without significant human interference, 

on soils with non-extreme properties (Mueller-Dombois and Ellenberg 1974). For 

example, mesic mixed beech-maple forests with Fagus grandifolia (American beech) 

and Acer saccharum (sugar maple) in the northeastern United States and southeastern 

Canada. Azonal vegetation is found on sites subject to “excessive” moisture or drought 

within that climatic region or strong anthropogenic influence; for example, sedge 

meadows, forested swamps and rocky woodlands, as well as corn fields and orchards. 

From the perspective of existing vegetation, we treat zonal and azonal vegetation together as part of extended environmental gradients. Thus, although climate is a strong 

contributor to global environmental gradients, other factors are also notable, including 

substrate (rock, water). The combinations of factors are used when assessing the ecological relationships among formations.

Development of Natural Formations

Formation Class

The formation class is the top level at which users enter the classification; thus, a 

small set of clearly defined types is helpful. The six types are defined by broad combinations of dominant general growth forms associated with basic moisture, temperature, 

and/or substrate or aquatic conditions, often spanning multiple climatic regions (See 

Appendix C for a glossary of terms). 

In addition, practical applications of the classification suggest that we be as clear 

as possible on specifying criteria for what constitutes forest and woodlands versus 

various grassland and shrubland types. Concerns over the precise boundaries of these 

classes require careful attention and are noted in the description. 

1. Forest & Woodland (Mesomorphic Tree Vegetation) 

Concept Summary

Type Concept Sentence: Tropical, temperate and boreal forests, woodlands and 

tree savannas characterized by broadly mesomorphic (including scleromorphic) tree 
USDA Forest Service RMRS-GTR-346. 2016. 15

growth forms (including broad-leaved, needle-leaved, sclerophyllous, palm, bamboo 

trees, and tree ferns), with at least 10 percent cover, irregular horizontal spacing of 

vegetation structure, and spanning humid to seasonally dry tropical to boreal and subalpine climates and wet to dry substrate conditions. Includes native forests as well as 

managed and some plantation forests where human management is infrequent. 

This class contains all mesomorphic tree-dominated vegetation (including scleromorphic tree vegetation) down to 10 percent canopy cover. The HRWG followed the 

FAO recommendations (FAO 2001), which are satisfactory for ecological and floristic 

application in many treed biomes, in both upland and wetland formations. The appropriate boundaries for distinguishing forest and woodland vegetation have been defined 

in many ways. This is further complicated by use of the term savanna (see below). 

However, it is also common to define Forest & Woodland as having greater than 25 

percent tree cover, whereas tree savannas, commonly found in grassland regions of the 

world, have 10 to 25 percent tree cover (see FGDC 1997; Grossman and others 1998; 

UNESCO 1973). Savanna definitions vary widely, from 5 to 30 percent to 10 to 50 

percent (Curtis 1959), 10 to 60 percent cover, or even higher, thus spanning the same 

range as used by others for woodlands. Given the commonality of a lower threshold 

of 10 percent tree cover, we felt it best to initially place tree savannas and woodlands 

together, at least in the temperate zone, then separate them at lower levels. The HRWG 

recognizes that this is not entirely satisfactory from some rangeland perspectives. 

Further review of tropical grasslands, savannas and shrublands by Dixon and others 

(2014) suggests some differences in criteria are needed for tropical versus temperate 

grasslands and tree savannas, namely:

1. a non-wetland formation with at least 10 percent vascular vegetation canopy 

cover;

2. graminoids have at least 25 percent cover (but if less than 25 percent cover, 

graminoids exceed that of other herbaceous and shrub cover),

3. broad-leaved herbs (forbs) may have variable levels of cover and dominance,

4. shrubs have less than 25 percent canopy cover, and

5. trees:

i. in temperate regions, typically have less than 10 percent canopy cover, are 

less than 5 m tall and are single-layered, or 

ii. in tropical regions, typically have less than 40 percent canopy cover, are less 

than 8 m tall, and are single layered. 

The term “savanna” (let alone its spelling, with or without the “h”) has often engendered confusion and debate. In our work, the term is restricted to two broad vegetation 

patterns. For temperate regions, it is applied to grasslands or shrublands with scattered 

trees (typically 10 to 30 percent) and primarily limited to fire-maintained upland types, 

although these vegetation types are also referred to as woodlands, oak openings and 

oak barrens. Temperate grasslands without scattered trees are referred to either as 

grasslands or prairies. For tropical vegetation, savanna is applied in the classical sense 

as interchangeable with tropical grasslands, with or without scattered trees, but sometimes separating out the treed tropical savanna distinct from non-treed tropical savanna 

(tropical grasslands sensu stricto). 
16 USDA Forest Service RMRS-GTR-346. 2016.

A final comment on tree growth forms: scleromorphic tree vegetation is treated here 

as broadly mesomorphic and is the growth form distinctive to the warm-temperate 

formation (level 3) within this class. 

2. Shrub & Herb Vegetation (Mesomorphic Shrub & Herb Vegetation).

Concept Summary

Type Concept Sentence: Grasslands, shrublands, open tree savannas, marshes, bogs 

and fens dominated by broadly mesomorphic (including scleromorphic) shrub and 

herb growth forms (including broad-leaved, needle-leaved, and sclerophyllous shrubs, 

and forb and graminoid herbs) with an irregular horizontal canopy structure, typically 

less than 10 percent mesomorphic tree cover (but see discussion of tropical grasslands 

and savannas above), tropical to boreal and subalpine climates, and wet to dry substrate conditions.

Shrub and herb vegetation is combined here because in many non-forested vegetation types, these two growth forms may occupy the same upper strata, or in some 

cases, grasses may even overtop shrubs (tallgrass prairie, emergent marshes). This can 

lead to strong floristic overlap between shrub and grass types, which supports combining them at the upper levels and separating them at lower levels. 

The primary issue with this class is incorporating both upland and wetland types. 

See discussion on “Wetlands” below. 

3. Desert & Semi-Desert (Xeromorphic Woodland, Scrub & Grassland 

Vegetation)

Concept Summary

Type Concept Sentence: Cool and warm semi-deserts dominated by xeromorphic 

growth forms, including succulent (e.g., cacti, euphorbias) and small-leaved shrubs

and trees, desert grasses and other xeromorphic growth forms, with an irregular horizontal canopy spacing that is often open to very sparse, including very open sandy and 

rocky vegetation with xeromorphic growth forms.

Inclusion of Tropical Thorn Woodland with other warm-desert scrub was a late addition to the hierarchy. The decision was based on the similarity of xeromorphic trees 

to other desert vegetation, although some will prefer that thorn woodland be placed 

next to Tropical Dry Forest (indeed some authors include thorn woodlands in that 

concept [Pennington and others 2006]). Our logic for the placement of Tropical Thorn 

Woodland is based on explicitly defined xeromorophic growth forms (e.g., succulents, 

leafless thorn trees, etc.).

Distinguishing non-vegetated and vegetated areas in deserts will also be difficult, 

given that on a site where vegetation is about 1 percent cover, there may be patches 

that vary between greater than 1 and less than 1 percent, and unbiased plot sampling 

of the site could have some plots with no cover. The few plants occurring at such low 

percentages may also be generalists and not particularly strong diagnostic species. For 

that reason, desert rocky and sandy vegetation are included here, rather than the “Open 

Rock Vegetation” class.
USDA Forest Service RMRS-GTR-346. 2016. 17

4. Polar And High Montane Scrub & Grassland (Cryomorphic Scrub, 

Herb And Cryptogam Vegetation)

Concept Summary

Type Concept Sentence: Tundra, alpine and tropical high montane habitats dominated by cryomorphic growth forms (including dwarf-shrubs, krummholz, associated 

herbs, and cryptograms such as lichens and mosses) with low height and open to 

closed canopy.

The name of this formation class emphasizes the cryomorphic nature of the vegetation. However, in many tropical montane regions that are roughly equivalent with the 

temperate “alpine” zone, the vegetation is not truly cryomorphic. That is, the soils 

do not experience cryoturbation and the vegetation doesn’t experience frost, strong 

winds, and short growing seasons. This is true for parts of the paramo and puna, so 

the HRWG placed them under Shrub & Herb Vegetation (class 2) in Tropical Montane 

Grassland & Shrubland. However, all temperate alpine vegetation is placed in 

cryomorphic. Rocky vegetation dominated by cryptogram and cryomorphic vascular 

vegetation (such as Arctic barrens in polar deserts) is included here.

5. Aquatic Vegetation (Hydromorphic Vegetation)

Concept Summary

Type Concept Sentence: Open freshwater and saltwater wetlands dominated by 

aquatic vegetation, either rooted with leaves rising up to or near the surface, or floating 

freely on the water surface. Stands typically have surface water, generally up to 2 m 

in depth, along ocean, lake, pond, and river margins in non-tidal, tidal, and intertidal 

habitats.

We include rooted and submerged vegetation in this formation class but treat all 

other emergent wetlands under mesomorphic vegetation classes 1 and 2, as many 

emergent wetlands share growth forms with upland vegetation. We expect that this 

aquatic vegetation class will be most useful in wetland situations such as ponds 

(i.e., bodies of water smaller than 8 ha and less than 2 m deep with no wave action; 

Cowardin and others 1979). Where aquatic vegetation forms a component of lakes, 

rivers, and oceans, other classification schemes can provide a more holistic set of 

types, within which various levels of aquatic vegetation types can be included. 

Nonetheless, it is possible to include all vegetated habitats, even seagrasses, in this 

classification. For example, Den Hartog (2003) developed comprehensive marine 

seagrass formations and lower level floristic units for the globe. From a terrestrial perspective, wetlands may seem to be sufficiently distinct from upland types in classes 1 

and 2 to place them here; but, when viewed from the larger aquatic vegetation perspective that includes only floating and submerged freshwater and marine vegetation, they 

are more closely related to those classes (See Wetlands section below).

6. Open Rock Vegetation (Cryptogam —Open Mesomorphic Vegetation)

Concept Summary

Type Concept Sentence: Lichen, bryophyte, alga or fern-dominated rocky habitats 

such as cliffs, talus, scree, pavement, cobble, lava or boulderfields in association with 

open or sparse mesomorphic vegetation.
18 USDA Forest Service RMRS-GTR-346. 2016.

This formation class is restricted to cropytogamic dominated vegetation found on 

consolidated and unconsolidated rocks where mesomorphic vascular plant cover is 

less than 10 percent; there is discussion as to whether non-seed plants such as ferns or 

Selaginella spp. should be excluded from the 10 percent vascular cover limit. The typical habitat is cliff, scree, talus or rock outcrops. Desert rocky or sandy vegetation is 

placed in Class 3, and alpine rock, scree and fellfields are placed in Class 4. There are 

questions to be resolved regarding placement of sparsely vegetated boulder or cobble 

drainages in dry creeks, river beds, or rocky shorelines where nonvascular vegetation 

may be a minor component. Scree vegetation may have more direct contact with soil 

with higher levels of vascular plant cover. The lack of information on rock vegetation 

makes classification and descriptions difficult. 

The concept of this class has been narrowed to regions where climates are milder 

and mesomorphic vegetation is more typical, and cryptogam vegetation is otherwise 

not a typically dominant growth form. Early pilots of this hierarchy included desert, 

polar, and alpine rock vegetation in this class. However, given how open the vascular 

vegetation can be in those habitats, it created too much of an artificial split between 

the very sparse vascular vegetation and the somewhat more open vascular vegetation, 

both of which have substantial cryptogam dominance. 

Wetlands

Wetlands have international significance due to the variety of human and ecological 

values they provide. However, placing wetlands in the hierarchy has been challenging. 

Wetlands are handled in various ways by ecological and vegetation classifications. 

In various global schemes, they are sometimes only noted incidentally, next to the 

main climatically driven types (e.g., Box and Fujiwara 2005; Whittaker 1975). Others 

recognized them as wholly distinct from other vegetation (NWWG 1997). The HRWG 

integrated them more directly into the hierarchical levels, although we struggled with 

their placement, as described below.

Chosen option: Wetlands are placed within various classes, depending on the level 

of distinctiveness of growth forms and their ecological drivers, but are always segregated out at Level 3 (formation).

Alternate option: Wetlands are grouped together into a single large hydromorphic 

and hydrophytic (or helomorphic) vegetation group. It reflected the perspective of 

many who see wetlands as a distinctive set of vegetation types, as well as various wetland publications that identify “wetland” as its own higher category (see the National 

Wetlands Inventory/Cowardin wetland classification, Cowardin and others 1979; and 

the Canadian wetland classification, National Wetlands Working Group 1997). 

Rationale for Chosen Option (wetlands initially dispersed among other classes, 

then individual wetland types recognized at formation level): 

1. It relies more strongly on dominant growth forms rather than diagnostic ones. 

2. It more strongly separates the most distinctive vegetation classes (“more 

orthogonal vegetation criteria”). That is, it is difficult to class all wetlands 

together globally due to their “relative wetness,” because that depends on the 

context of surrounding regional climatic and vegetation patterns. 
USDA Forest Service RMRS-GTR-346. 2016. 19

3. Wetland distinctions vary even at the species level, because many widespread 

species may be considered wetland in some regions but not in other regions; 

e.g., definitions of Facultative and Obligate wetlands differ across U.S. wetland 

regions. 

4. It is less dependent on ecological considerations in defining the class (i.e, a 

wetland/non-wetland distinction).

Rationale for Alternative Option (wetlands grouped with aquatic vegetation as a 

single class, then individual wetland types recognized at formation level):

1. It identifies the wetland criteria up front, overall, rather than repeatedly across 

subclasses. 

2. It groups closely related wetland types together. 

3. It provides a set of wetland subclasses that are clearly identified in many wetland 

classifications (e.g., swamp, bog and fen, marsh).

4. It more strongly integrates ecologically related growth forms, even if not the 

dominant ones.

Rationale for either option:

1. Both do a good job of grouping vegetation patterns. 

2. Both are equally amenable to mapping approaches. 

3. Both provide useful categories for vegetation management.

4. Both recognize the same major wetland types at formation level (Level 3).

The HRWG decided to adopt the chosen option because it was more faithful to the 

criteria required for Level 1. Forested wetlands are placed in the “Forest & Woodland” 

class; shrub and herb wetlands are placed in the “Shrub & Herb Vegetation” class, but 

separated out as a subclass; aquatic wetland vegetation, which has distinctive hydromorphic growth forms, is placed in Class 5 under Aquatic Vegetation. As all major 

wetland types are separated out at Level 3, most users will find few disadvantages to 

the current approach, and they can choose to aggregate all wetlands into their own 

category if so desired. Our approach is a classification of all vegetation, not a classification of wetland and non-wetland, which is more concerned with legal conservation 

and water law issues. 

Formation Subclass

Formation Subclass: A vegetation classification unit of high rank (2nd level) defined 

by combinations of general dominant and diagnostic growth forms that reflect global 

macroclimatic factors driven primarily by latitude and continental position, or that 

reflect overriding substrate or aquatic conditions. (cf. Box and Fujiwara 2005, 2013; 

FGDC 2008; Walter 1985; Whittaker 1975).

Macroclimatic factors have a strong influence on the development of the formation 

subclass, even among substrate-based classes. Few issues arose in developing these 

subclasses. The HRWG worked with vegetation patterns that often correspond to 

broad bioclimatic classes. The work of Rivas-Martinez and others (Rivas-Martinez 

and others 1999a; Rivas-Martinez and Rivas-Sáens 1996–2009) was helpful for global 

scale distinctions, particularly the division of bioclimates into Tropical, Temperate, 

Mediterranean, Boreal, and Polar (Figure 1). Here we review a few of the subclasses, 

where some problems in definition were encountered. In all cases, see additional “classification comments” in the type descriptions in Part II. 
20 USDA Forest Service RMRS-GTR-346. 2016.

Figure 1—Bioclimatic Regions of (a) North America (Rivas-Martinez et al. 1999), (b) Europe (Rivas-Martinez 

et al. 2004), and (c) South America (Rivas Martinez, in press). Mapped distribution of these bioclimatic regions should not be used as definitive linework for actual formation distributions. See text for discussion of 

Mediterranean bioclimate. Maps used with permission (figure produced by Ángel Penas Merino).
USDA Forest Service RMRS-GTR-346. 2016. 21

Figure 1b
22 USDA Forest Service RMRS-GTR-346. 2016.

Temperate, Boreal and Montane Vegetation

Temperate & Boreal vegetation are combined at the subclass level, because they 

share many of the same broad growth forms. They are recognized as distinct at the formation (L3) level based on the simplified set of growth forms and distinctive climate 

found in the boreal forests. Montane forests, shrublands, and grasslands in the temperate and boreal regions do not contain distinctive growth forms from lower elevation 

vegetation until one reaches the alpine zone. Alpine vegetation shares strong growth 

form similarities with polar vegetation, and they are treated together at the subclass 

level (4.B. Temperate to Polar Alpine & Tundra Vegetation).

Temperate and Mediterranean Vegetation

The one bioclimate type of Rivas-Martinez and Rivas-Sáens (1996-2009) that 

does not correspond as closely to our approach is the Mediterranean bioclimate. They 

define this bioclimate to include not only Mediterranean scrub vegetation but also 

vegetation that we place in Cool Semi-Desert, (e.g., in North America, the Great Basin 

Figure 1c
USDA Forest Service RMRS-GTR-346. 2016. 23

vegetation, in South America the Patagonian vegetation, and in Europe the Eastern 

European steppe) (figures 1, 2). In addition, we only use the term “Mediterranean” 

in reference to “Mediterranean Scrub & Grassland” (an L3 formation unit), thus 

restricting the vegetation concept to sclerophyllous and other Mediterranean type 

scrub growth forms within a broadly temperate and boreal subclass. The distinctive 

Mediterranean vegetation around the world has been variously treated either narrowly 

or broadly; here, we use the term narrowly based on growth forms. The sclerophyllous 

and mixed evergreen-deciduous tree growth forms of the European Mediterranean 

region are also found in other warm-temperate climates, and are included in the WarmTemperate Forest class. That formation includes:

•  In Europe, the European Mediterranean cork-oak forests (Quercus suber) of 

Spain and Portugal, fir forests (Abies maroccana) and cedar forests (Cedrus atlantica) in high-mountain areas in Morocco, oak woodlands broadly distributed 

throughout the Mediterranean Basin countries; 

• In South America, the warm temperate forests of Nothofagus macrocarpa, N. 

glauca, N. alessandrii, Austrocedrus chilensis forests, etc.; 

• In Australia, the many Eucalypt forests; and

• In North America, both the Mediterranean California forests and woodlands 

and the Southeast U.S. Coastal Plain forests.

Figure 2—Bioclimatic Regions and Formations and Divisions within North America defined by climate. Lessclimatically driven wetland or substrate formations are not as strongly influenced by these patterns. Mapped 

distribution of these biogeographic regions should not be used as definitive linework for actual formation, 

division or other vegetation type distributions.
24 USDA Forest Service RMRS-GTR-346. 2016.

Our approach here, as throughout, is to emphasize the vegetation patterns, and to 

assess their significance through correlations with broad ecological and biogeographic 

processes. For example, at the level of formation subclass, we typically combine temperate and boreal units, despite the differences in macroclimate, because of their fairly 

strong overlap in dominant and diagnostic growth forms, whereas tropical types are 

much more distinctive from either temperate or boreal. Separate temperate and boreal 

types are recognized at the formation level.

Formation

Formation: A vegetation classification unit of high rank (3rd level) defined by combinations of dominant and diagnostic growth forms that reflect global macroclimatic 

conditions as modified by altitude, seasonality of precipitation, substrates, and hydrologic conditions. (cf. “formation-type” and “biome-type” of Box and Fujiwara 2005; 

FGDC 2008; Walter 1985; Whittaker 1975). 

The formation describes vegetation patterns that reflect the combination of macroclimates and/or substrate and topography. There is no strict parallelism among criteria 

in identifying formations; thus, in a few cases, a subclass is not split any further, 

because no major patterns of variation are evident with respect to the vegetation or 

ecological processes as compared to other types at that level. In addition, bottom-up 

information may also be considered from the Division level. For example, a formation 

split was avoided if it creates two Divisions with overlapping floristics within broadly 

similar growth forms, although tradeoffs are inevitable (e.g., wetland and upland forest 

formations may overlap in floristics and dominants). 

Formation Issues

Tropical humid forest (1.A.2, 1.A.3)

Commonly called tropical rain forests, we chose this term to ensure that users understand that both moist and wet, or seasonal evergreen and aseasonal evergreen rain 

forests are included in the concept.

Temperate and boreal forest and woodland formations (1.B.1 – 1.B.5.)

The distinctive growth forms and climate relations of major forest formations 

draw from a variety of works, including Walter (1985) who separated boreal, cooltemperate, and warm-temperate forests and woodlands. (See the Formation subclass 

discussion under “Temperate and Mediterranean vegetation” for a discussion of warm 

temperate and Mediterranean forest vegetation.) 

Placement of subalpine forests and woodlands is problematic as to whether they 

are more boreal-like or temperate-like in their growth forms and floristics, and corresponding climate. At this time, we treat subalpine forests within the temperate, as they 

often take on some of the characteristics of lower elevation forests, and we restrict 

boreal forests to the high latitude regions of the globe. 

Mediterranean scrub and grassland formation (2.B.1)

See discussion of this vegetation under the Formation Subclass – Warm “Temperate 

and Mediterranean “Vegetation.” 
USDA Forest Service RMRS-GTR-346. 2016. 25

Coastal upland scrub and herb formations (2.A.3, 2.B.4)

Distinctive ecology and substrate of rocky shores, beaches and dunes, somewhat 

reflected in vegetation, are separated out into their own formations. This is one of the 

weaker formation distinctions. Note that coastal salt marshes are treated separately as 

a wetland formation.

Salt marsh (2.C.5)

The vast majority of salt marshes are temperate, but the formation ranges broadly 

enough, both along the coast and inland, that climate regime is identified with it. 

Inland salt marshes are typically separated from coastal salt marshes at the Division 

level. 

Polar tundra and barrens formation (4.C)

Wet Tundra is sometimes defined to include: peaty wet tundra (bogs and poor fens), 

tundra meadows, and marshes. But we treat those as wetland types in 2.C. Shrub & 

Herb Wetland. Thus a separate “Wet Tundra” is not recognized. Cryptogam dominated 

barrens (polar deserts) are also placed here.

Tropical high montane and temperate alpine (4.A.1)

The Tropical Montane Grassland & Shrubland (i.e. paramo and puna) is placed under the Mesomorphic class (2.A.2), differentiating it from the Tropical High Montane 

Scrub & Grassland Formation that has been placed within the Cryomorphic Scrub, 

Herb & Cryptogam Vegetation Class. This split is a result of the key physiognomic 

distinctions such as the ground cover of the formation, which is continuous for the 

tropical montane shrubland and grasslands as compared to the low, semi-open coverage of the tropical cryomorphic formations, and the predominance of mesomorphic 

growth forms (predominantly tussock grasses, large rosette plants, shrubs with 

evergreen coriaceous and sclerophyllous – ericoid leaves, and cushion plants). As for 

environmental drivers, seasonality is related to rainfall rather than temperature. The 

main difference of this formation with its temperate counterpart is the diurnal fluctuation of temperature, which can be 20 °C or more in tropical high mountains (i.e., 

Andes, Africa) with no growth limiting season. 

Cliff, scree and rock formations (6.A.1-6.B.1)

Climate and substrate combinations are used for these formations, but there is little 

literature available to guide us. Vascular components of these rock formations are often helpful. That is, one might find bromeliads on tropical cliffs, deciduous broadleaf 

shrubs on temperate cliffs, and sclerophyllous evergreen shrubs on Mediterranean 

cliffs. We are not aware of how the nonvascular growth forms might differ among 

these formations.

In early pilots of this hierarchy, additional formations existed for desert, polar, and 

alpine rock vegetation but these have now been moved under those classes and subclasses (see discussion above under “6. Open Rock Vegetation”).
26 USDA Forest Service RMRS-GTR-346. 2016.

Wetland Formations

Our approach to defining wetland formations follows a widely used set of 

physiognomic-ecological types and terms that provide a set of wetland units corresponding to broad climatic and edaphic factors. We drew, in particular, on the 

Canadian Wetland Classification system for types and definitions (National Wetlands 

Working Group 1997; see also Mackenzie and Moran 2004) and from Mitsch and 

Gosselink (2000) for ecological processes and functions. The major wetland types 

that inform our formation distinctions are described in Table 6. Most of the wetland 

types are divided into tropical versus temperate wetlands based on the different kinds 

of dominant growth forms (e.g., broad-leaved evergreen trees and palms in tropical 

swamps) (see Appendix B).

Table 6—Major wetland types used to guide formation distinctions. Types, definitions, environmental 

features and growth forms are adapted from the Canadian National Wetlands Working Group (1997) and 

Mackenzie and Moran (2004), with linkage to major wetland types described by Mitsch and Gosselink 

(2000).

Wetland type Definition

Environmental 

features Growth forms

Mitsch & 

Gosselink 

(2000) Type

Forest & 

Woodland (1)

Flooded 

& Swamp 

Forest 

A swamp is a wooded 

mineral (or less often peat) 

wetland on sites with a 

flowing/flooded or fluctuating 

semi-permanent, near 

surface water table. Forested 

swamps have trees occurring 

on elevated microsites. 

Flooded forests occur on 

sites where flooding varies 

from temporary (<7 days) 

to semi-permanent (>180 

days). Trees >2 m have >10 

percent cover. We place 

shrub swamps with marsh 

and wet meadow in Class 2.

Mineral 

soils or wellhumified peat. 

Temporary to 

semi-permanent 

flooding (0.1 to 

2 m deep), or 

freshwater or 

oligohaline tidal 

inundation

Tall shrub, 

broad-leaved 

tree, needleleaved 

tree, forb, 

graminoid, 

hydromorphic 

herb (rarely)

Freshwater 

swamps; 

Riparian 

ecosystems 

(wetland, 

tree)

Mangrove Mangroves occur in the intertidal and brackish backwater 

of estuarine areas in tropical 

regions. Mangroves include 

tree and shrub forms of 

mangrove of all heights.

Intertidal and 

supratidal zones, 

semi-diurnal to 

diurnal, flooding 

by brackish or 

saltwater

Mangrove, 

halophytic 

shrub, 

halophytic 

(succulent) 

forb, 

graminoids

Mangrove 

swamps

(continued)
USDA Forest Service RMRS-GTR-346. 2016. 27

Wetland type Definition

Environmental 

features Growth forms

Mitsch & 

Gosselink 

(2000) Type

Shrub & Herb 

Wetland (2.C.)

Bog Bogs are shrubby, nutrientpoor peatlands with 

distinctive communities 

of ericaceous shrubs 

and hummock-forming 

Sphagnum species, 

sometimes with sedges, 

adapted to high acid and 

oxygen-poor soil conditions. 

Trees >5 m typically have 

<10 percent cover (raised 

bogs may contain some 

forested stands). 

+/- 

ombrotrophic,

pH < 5.5,

>40 cm fibric/

mesic peat

Stunted 

needleleaved tree, 

low shrub, 

dwarf shrub 

(ericaceous), 

sphagnum

Peatland

Fen Fens are peatlands where 

groundwater or stream inflow 

maintains relatively moderate 

to high mineral content 

within the rooting zone. Sites 

are characterized by nonericaceous shrubs, sedges, 

grasses, reeds, and brown 

mosses. Trees >5 m typically 

have <10 percent cover. 

Forested fen is included 

under Swamp Forest.

Groundwater-fed

pH > 5.0

>40 cm fibric/

mesic peat

Low shrub 

(often nonericaceous), 

sedge (often 

fine), grass, 

reed, and 

brown moss, 

with or without 

sphagnum

Peatland

Freshwater 

Marsh, Wet 

Meadow 

& Shrub 

Swamp (nontidal and 

tidal)

A marsh-wet meadow is 

a shallowly flooded or 

saturated wetland dominated 

by emergent grass-like 

vegetation. A fluctuating 

water table is typical in 

marshes and wet meadows, 

with early season high water 

tables and some flooding 

dropping through the 

growing (or dry) season, and 

exposure of the substrate or 

drying of the profile possible 

in late (or dry) season 

or drought years. Shrub 

wetlands (shrub swamps, 

shrub carrs) occupy similar 

sites to wet meadows. Trees 

>5 m have <10 percent 

cover.

Mineral soils or 

well-humified 

peat. Protracted 

shallow flooding 

(0.1 to 2.0 m) 

or prolonged 

soil profile 

saturation, or 

freshwater or 

oligohaline tidal 

inundation. 

Grass, sedge 

(often coarse), 

forb, low 

shrub, tall 

shrub 

Freshwater 

marshes - 

emergent; 

Tidal 

freshwater 

marshes; 

Riparian 

ecosystem 

(wetland, 

herb/shrub) 

Saltwater 

Marsh

Saltwater marshes are 

intertidal to supratidal 

ecosystems that are flooded 

diurnally (or less), sometimes 

with freshwater inputs, and 

are dominated by salttolerant emergent graminoids 

and succulents. Trees >5 m 

have <10 percent cover.

Intertidal and 

supratidal zones, 

semi-diurnal to 

diurnal, flooding 

by brackish or 

saltwater [n.b. 

inland nontidal saline wet 

meadows may 

also be placed 

here]

Grass, 

sedge, forb, 

halophytic 

(succulent) 

forb, 

halophytic 

shrub.

Tidal salt 

marshes

Table 6—(Continued).

(continued)
28 USDA Forest Service RMRS-GTR-346. 2016.

Wetland type Definition

Environmental 

features Growth forms

Mitsch & 

Gosselink 

(2000) Type

Table 6—(Continued).

Aquatic Aquatic 

Vegetation 

(non-tidal 

and tidal)

Aquatic wetlands are shallow 

waters dominated by rooted, 

submerged and floating 

aquatic plants. They are 

associated with permanent 

still or slow-moving waters, 

such as shallow potholes, 

ponds, rivers and lakes. 

Aquatic plants may occur in 

mineral or in well-humified 

sedimentary peat. Emergent 

growth forms <10 percent 

cover, hydromorphic growth 

forms >1 percent cover.

+/-Permanent 

deep flooding 

(0.5 – 2 m), 

substrate can 

be muck, sand, 

marl or rocky 

substrates

Hydromorphic 

(aquatic) herb, 

Emergents 

< 10 percent 

cover

 Freshwater 

marshes - 

aquatic

Summary of Criteria for Natural Formations

We summarize the criteria for these three formation levels in Table 7, and compare 

them with the Division level, which introduces the use of both physiognomic and 

floristic criteria.

Development of Cultural Formations

As with the natural vegetation, physiognomic criteria represent the primary properties of cultural vegetation at the upper levels but are assessed in light of human 

activities that govern these properties. Thus, the arrangement and organizing criteria 

for these units is quite different from natural units, being largely constructed from 

physiognomic and structural considerations driven by human management activities. 

Excluded from these criteria are properties from outside the current vegetation, such as 

explicit habitat factors (e.g., climate, soil type) or land use activities (e.g., grazed pasture versus ungrazed pasture), except as these are expressed in the vegetation growth 

forms and structures. Some types are difficult to classify as natural or cultural vegetation (e.g., forest plantation, pastures), and the user may need to compare both parts of 

the hierarchy to determine the type’s location. 

The upper levels of the hierarchy are based on dominant and diagnostic growth 

forms that reflect anthropogenic drivers at global to continental scales. A comprehensive set of cultural vegetation units are available in pilot form for most levels of 

the hierarchy, based on the U.S. Natural Resources Conservation Service’s National 

Resources Inventory (NRI) (FGDC 2008; Appendix I); thus, we deferred to that 

classification for most of the units but organized them into a hierarchical structure 

consistent with the overall framework. 
USDA Forest Service RMRS-GTR-346. 2016. 29

Table 7—Brief summary of criteria for formation units and division.

Criteria Formation Class

Formation 

Subclass Formation Divisiona

Diagnostic 

Species

-- -- -- Very large set. Many 

character spp., often 

endemic to the division. 

At least some of the 

character species are 

dominant in parts of the 

range of the type.

Growth Forms Broad combinations 

of dominant general 

growth forms and 

specific growth forms

Combinations 

of general and 

specific dominant 

and diagnostic 

growth forms

Combinations of 

dominant and diagnostic 

growth forms, sometimes 

based on individual 

diagnostic growth forms 

(e.g. mangrove)

The same combination 

of growth forms as at the 

formation level

Range of 

Variation

Overlapping general 

growth forms 

(tree, shrub), but 

combinations of 

diagnostic growth 

forms generally nonoverlapping (e.g., 

xeromorphic)

Combinations of 

diagnostic growth 

forms partially nonoverlapping (e.g., 

warm temperate 

forests and tropical 

forests

Combinations of 

diagnostic growth 

forms more strongly 

overlapping (e.g., 

temperate and boreal 

forests), relative 

abundances more 

important

Essentially nonoverlapping floristics

Ecological 

Gradients

Basic moisture, 

temperature, and/or 

substrate or aquatic 

conditions

Global 

macroclimatic 

factors driven 

primarily by latitude 

and continental 

position, or that 

reflect overriding 

substrate (rock 

vegetation) or 

water salinity 

(aquatic 

vegetation)

Global macroclimatic 

conditions in combination 

with landmass and 

edaphic factors, such as 

altitude, seasonality of 

precipitation, substrates, 

and hydrologic conditions

Continental scale 

biogeographic 

differences in 

composition, reflecting 

macroclimate patterns 

modified by the 

continents. Divisions 

within a formation are 

often geographically 

separated. 

aA character species in a Division shows a distinct maximum concentration, either in constancy and/or abundance, in one well-defined 

vegetation type as compared to all others and recognizable at general/global geographic scales (Mueller-Dombois and Ellenberg 

1974).

Cultural Class

Cultural Class: A vegetation classification unit of high rank (1st level) defined by 

broad combinations of dominant general growth forms determined by global scale 

human activities 

Cultural Subclass

Cultural Subclass: A vegetation classification unit of high rank (2nd level) defined 

by combinations of general dominant and diagnostic growth forms that reflect global 

scale human activities. 
30 USDA Forest Service RMRS-GTR-346. 2016.

Cultural Formation

Cultural Formation: A vegetation classification unit of high rank (3rd level) defined 

by combinations of dominant and diagnostic growth forms that reflect global scale 

human activities. 

Type Description 

Many details of type description especially for natural vegetation, are provided in 

FGDC (2008) and Jennings and others (2009), including from plot data preparation 

and data collection, data analysis, interpretation, documentation and archiving, and 

type description, nomenclature, and peer review. That work, however, was focused on 

the lower floristic levels of the natural types, alliances and associations. Additional 

guidance is needed for application across all levels of the hierarchy. Here we summarize our approach to type description of the formations (See also Faber-Langendoen 

et al. 2014).

Upper Level Nomenclatural Rules

The HRWG has adopted and advocated for the approach taken in FGDC (2008) and 

Jennings and others (2009), whereby a scientific name, a translated scientific name 

(from the vernacular plant names available from widely accepted standard taxonomic 

references), and a colloquial name are all provided. Translated names and colloquial 

names are provided in English and a variety of other common languages. The names 

can include both physiognomic terms (forest, grassland, bog, tundra) and species 

names, and may also include a biogeographic term. The HRWG recommends development of a glossary of nomenclatural terms to guide ongoing naming of types.

Formation types at Levels 1-3 are named, defined, and organized by vegetation 

structure and physiognomy, as these are reflected in broad climatic and site factors. 

A convenient aid for naming the formations, and consistent with the goal of using 

common terminology (FGDC 2008), is to use terms based on the habitats that they 

occupy; it should be re-emphasized that habitat factors are not typically used in defining formations (Whitmore 1984, pg. 155). To avoid tendencies towards making the 

name too descriptive, we also provide a one-sentence descriptive summary of the type. 

The result is a set of easily recognized formations with memorable colloquial names 

that communicate the most distinctive vegetation and ecological characteristics of the 

formation. Currently, we apply only English terms to the three formation levels, and 

distinguish scientific and common names only for Level 1.3

Overall Style

All first letters of English words in a vegetation type name are capitalized and, as 

needed, additional words are separated by either a hyphen with spaces ( - ), a comma 

and space (, ) or the “and” symbol with spaces ( & ). 

3 These approaches to nomenclature do not rule out the option of adding a formal Latinized 

name for types at these three levels, as done by Rübel (1930-1931, see Appendix B in Shimwell 

1971). For example, following Rübel, the scientific names for the Desert and Semi-Desert class

could be “Deserta,” the Warm Semi-Desert subclass could be named “Siccadeserta,” and the 

Cool Semi-Desert subclass named “Frigorideserta.”
USDA Forest Service RMRS-GTR-346. 2016. 31

Level 1 (Formation class)

Class names are based on the very broad growth forms that correspond to global 

moisture/temperature regimes. The single name helps identify the broad grouping of 

growth forms that correspond to particular moisture/temperature conditions. A parenthetical set of names is included to guide general users to the main kind of vegetation 

included in the class. The class level is organized by decreasing complexity and cover 

of the vegetation, reflecting increasingly stressful site factors. Given the wide overlap 

in use of the terms “Forest” and “Woodland” we use both terms to indicate that the 

class definition encompasses all mesomorphic (i.e. broad-leaved or needle-leaved) 

trees of varying height and canopy spacing.

Examples: 

•  Mesomorphic Tree Vegetation (Forest & Woodland)

•  Mesomorphic Shrub & Herb Vegetation (Shrub & Herb Vegetation)

•  Xeromorphic Woodland, Scrub & Herb Vegetation (Desert & Semi-Desert) 

•  Hydromorphic Vegetation (Aquatic Vegetation)

Level 2 (Formation subclass)

The subclass name reflects the structure, physiognomy and environmental factors 

that characterize the subclass. The primary environmental factor is macroclimate. 

Physiognomic terms are sometimes more specific than the class name (e.g., scrub versus shrubland where the vegetation may include tall xeromorphic tree-like plants such 

as tall cacti). All such terms, if used, should be defined. 

Examples:

•  Tropical Forest & Woodland

•  Temperate & Boreal Grassland & Shrubland

•  Cool Semi-Desert Scrub & Grassland

•  Saltwater Aquatic Vegetation

Level 3 (Formation)

The formation name reflects the structure, physiognomy and environmental factors 

that characterize the formation. The primary environmental factors are macroclimate 

in combination with soil moisture conditions, elevation and substrate. Physiognomic 

terms are sometimes more specific than the class or subclass name. All physiognomic 

terms should be defined in the vegetation type description. 

Examples:

•  Tropical Lowland Humid Forest

•  Mediterranean Scrub & Grassland

•  Cool Semi-Desert Scrub & Grassland

•  Marine & Estuarine Saltwater Aquatic Vegetation
32 USDA Forest Service RMRS-GTR-346. 2016.

Description Template

The official template for describing types is provided in FGDC (2008) and Jennings 

and others (2009), and is appropriate to all levels of the hierarchy (see also FGDC 

2008, Section 3.2.3). An expanded set of instructions on completing the template is 

available on request from the authors. Following are a few general observations on the 

format of these descriptions:

•  A standard template is used, supplemented with a few additional fields.

•  Concepts for Level 1 types were developed from the expertise of the HRWG 

members. Other levels are more commonly used by other classifications and appropriate citations and synonyms are provided (See Appendix F). 

•  A standard set of growth forms is used (see Appendix D; see also Appendix E in 

FGDC 2008). Growth forms types are placed in italics to remind the reader that 

the terms have specific meanings. Additional growth forms that may be useful 

to add to the list and that are included in the descriptions can also be placed in 

italics, with an asterisk.

These descriptions are a first preliminary effort at global descriptions for formation 

types, and are provided to give some guidance to our concepts. Undoubtedly even 

these preliminary descriptions are biased by our western hemisphere perspective. We 

look forward to engaging with a broader set of ecologists around the globe to continue 

improving both the concepts and the descriptions. We hope such collaboration can 

develop, in part, by identifying vegetation types at the Division level around the globe.

Peer Review

We follow the approach of FGDC (2008) and Jennings and others (2009) for peer 

review. Those documents outline a process based on a dynamic classification standard, 

whereby peer review is an open process conducted by professional organizations in 

collaboration with other interested parties. It is administered by a peer review board 

under the aegis of an institution capable of providing independent reviewers of appropriate experience in vegetation classification. In this case, the ESA Vegetation 

Classification Panel will solicit review of the current set of formations. It is desirable 

to have a panel of international vegetation ecologists oversee the ongoing peer review 

of these global formation types.

A Key to the Formations 

An introduction and key to the Formation Class (Level 1) is provided in Appendix 

I. We note in the introduction to the key, that keying out formations requires attention 

to vegetation strata and growth forms. Many species have only a single or primary 

growth form. Therefore, if a species list and vegetation strata or general growth forms 

are part of the plot description, detailed recording of specific growth forms may not be 

needed (e.g., Mucina and others 2000; Peet and others 1998; Tart and others 2005b). 

If a flora or species list for a state, province, or nation also identifies the species 

growth form(s), then a rollup of species to growth forms will simplify the standard 

field methods. The user need only be aware of those species that have multiple growth 
USDA Forest Service RMRS-GTR-346. 2016. 33

forms, and which growth form is present on the plot. In the United States, the U.S. 

Department of Agriculture (USDA) PLANTS database (2002 version; see http://

plants.usda.gov) lists the general growth form (“growth habit”) of all plant species 

in the United States This list could be supplemented with the specific growth forms 

(Appendix D) of each species. 

Synopsis

We have introduced an ecological vegetation classification approach (the EcoVeg 

approach) by which vegetation ecologists can organize global vegetation patterns at 

multiple scales (Faber-Langendoen and others 2014), and also provide rationale and 

detailed descriptions for each of the upper level units. We believe this framework is 

an important contribution to what is currently available to vegetation ecologists, land 

managers, and conservationists. Many global classifications deal with only broad 

structural patterns, others with only floristics. We provide an introduction to formations, along with the descriptions and key, as a basic synopsis of the world’s vegetation 

structured by specific growth form criteria. Sufficient detail is given to encourage 

consistent application anywhere in the world and within a hierarchical structure that 

includes both floristic and growth form criteria, ultimately at the levels of alliance and 

association. The formations descriptions are not detailed; they rely on a large tradition 

of description and classification for their support, and they seek to provide as concise 

an overview as possible. They are presented here in draft form, and we are aware 

that we have not been able to invest as much effort across all of them. More work is 

needed to reference the many publications that support or improve these concepts. 

In addition, our work is only one, among many, and so establishing crosswalks to 

other classification will increase our understanding of how others have defined and 

described the vegetation.

A real test of these concepts is whether they provide any value in moving to 

the next step, which is supporting description and classification of Divisions and 

Macrogroups within the formations. It is these types that force us to specify very 

clearly in which continents and regions these formations are found and whether the 

summaries of variability so simply described here can account for the variation observed around the globe. Our expertise has primarily come from Western Hemisphere 

vegetation ecologists, though we have also considered vegetation in Africa and 

Europe. We look forward to helping vegetation ecologists achieve consensus on 

these “mid-level” units (see Appendix J for examples of Cool Temperate Forest and 

Grassland Divisions). Such collaboration can help us better understand the ecological 

processes, biogeographic and historical relationships, current threats, and conservation 

status of vegetation types.
34 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 35

PART II: DESCRIPTION OF WORLD 

FORMATION TYPES
36 USDA Forest Service RMRS-GTR-346. 2016.
USDA Forest Service RMRS-GTR-346. 2016. 37

1. Forest & Woodland (C01)

Overview

Database Code: 1 (C01)

Scientific Name: Mesomorphic Tree Vegetation Class

Common Name (Translated Scientific Name): Mesomorphic Tree Vegetation Class

Colloquial Name: Forest & Woodland

Hierarchy Level: Class

Lower Level Hierarchy Units:

1.A. Tropical Forest & Woodland (S17)

1.B. Temperate & Boreal Forest & Woodland (S15)

Concept Summary

Type Concept Sentence: Tropical, temperate and boreal forests, woodlands and 

tree savannas characterized by broadly mesomorphic (including scleromorphic) tree 

growth forms (including broad-leaved, needle-leaved, sclerophyllous, palm, bamboo 

trees, and tree ferns), typically with at least 10 percent cover (but tropical tree savannas up to 40 percent cover, when trees are less than 8 m tall), irregular horizontal 

spacing of vegetation structure, and spanning humid to seasonally dry tropical to 

boreal and subalpine climates and wet to dry substrate conditions. Includes native 

forests, as well as managed, and some plantation forests where human management is 

infrequent.

Classification Comments: Plantations, ruderal, and native forest and woodland 

stands are typically placed in this class. Some plantation forests can be placed here 

rather than in the Agricultural & Developed Vegetation Class (CCL01) despite having 

a canopy layer that may be very regular (spaced in planted rows), if the tree regeneration, shrub and ground layers develop spontaneously with irregular horizontal spacing, 

similar to native forests (i.e., regular human intervention does not occur for these 

layers). However, where plantations have highly regular horizontal structure, with 

regular human intervention in all layers (e.g., through cutting, spraying, ground-layer 

mowing), they may better be placed in the Agricultural & Developed Vegetation Class 

(CCL01).

Similarly, tree-dominated vegetation that has a natural, irregular horizontal spacing 

in the tree layer, but highly regular shrub or herb layers because of human intervention, should be placed in the Agricultural & Developed Vegetation Class (CCL01). For 

example, shade coffee, cacao, and other woody agricultural crops grown under native 

(or exotic) tree species and in which all non-treed strata layers are subject to regular 

human intervention should be placed in that class.

Included in this class are low-statured trees that overtop other growth forms. These 

include tree sapling and seedling stands with trees less than 2 m, where the tree growth 

form is at least 10 percent cover and overtops other growth forms. These include 

subarctic woodlands, and coastal dwarf-tree woodlands that are less than 2 m but 

are single-stemmed with definite crowns. Conversely, treed bogs and fens, with low 

stunted trees and conical canopies, and otherwise sharing the moss and dwarf-shrub 

layers of open bogs and fens, are placed with those types. Where trees share the same 

strata as grasslands and shrublands (e.g., tallgrass brush prairie of 1 to 3 m, with trees 

less than 2 m), the vegetation is placed in the shrub- and herb-dominated classes.
38 USDA Forest Service RMRS-GTR-346. 2016.

Tree cover ranges from 10 to 100 percent, and is inclusive of what are called forests, woodlands, and tree savannas, at least in the non-tropical regions. The class limit 

of 10 percent tree cover (for mesomorphic tree growth forms) follows that of FAO’s 

Global Forest Resources Assessment 2000 (FAO 2001). We exclude stands of trees 

planted primarily for agricultural production (such as fruit tree or forest plantations) 

and typically agroforestry, as well as those in developed lands, such as cities and roadsides (they are placed in Class 7, formation 7.A.2). However, unlike FAO, we do not 

include what FAO calls “temporarily unstocked areas” (such as clearcuts, burnt areas) 

unless the tree growth form is actually present at 10 percent cover—even if in seedling 

or sapling form—and exceeds the height of other growth forms.

Other classifications may limit forests and woodland to a narrower range of tree 

cover. For example, forests and woodlands are sometimes defined as 25 to 100 percent 

cover, and distinguished from tree savannas with 10 to 25 percent cover, which included under broadly defined grassland and shrubland classes (Driscoll and others 1984; 

FGDC 1997; Grossman and others 1998; Minnesota DNR 2005). UNESCO (1973) required that tree savannas also have a strong herbaceous layer (greater than 50 percent 

graminoid cover). Still, a variety of definitions of tree savanna have been published, 

from the 10 to 25 percent cover noted above, to 10 to 30 percent cover in Nelson 

(2005), 10 to 40 percent in UNESCO (1973), and 10 to 50 percent cover in Curtis 

(1959). Blue oak, Engelmann oak, and other woodlands in California Mediterranean 

woodlands are typically between 10 and 60 percent cover, and California State ecologists place these in the Forest & Woodland (Barbour and others 2007). However, 

apart from tree savannas, there are many other forest and woodland types and regions 

where the degree of canopy closure plays less of a role in defining types, for example, 

forested swamps and bogs, longleaf pine woodlands (Peet 2006), eastern pine barrens, 

and subarctic woodlands.

Thus, given the variety of situations, we have chosen a more inclusive definition of 

forest and woodland that encompasses most tree savanna concepts, and rely on lower 

levels of the hierarchy to make distinctions based on a combination of biogeography, 

ecology, and floristics. For example, in the context of the eastern Great Plains tallgrass prairie-forest border, it is common to recognize oak savannas, based on open 

tree cover levels (e.g., 5 to 30 percent tree cover in Nelson 2005), as separate from 

oak woodlands (30 to 80 percent cover) and oak forests (80 to 100 percent cover). 

Savannas may be distinguished from forests or woodlands, but these structural distinctions often correspond to lower level units of the NVC hierarchy (e.g., group, alliance, 

and association). Still, Dixon and others (2014) suggest that there may be good ecological reasons to treat upland tropical tree savannas, with 10 to 40 percent tree cover, 

trees less than 8 m tall, and a substantial graminoid layer as part of 2. Shrubland & 

Grassland (C02), and we allow for that option here.

Similar NVC Types: 

2. Shrubland & Grassland (C02): When grasses and shrubs dominate the ground 

layer and tree cover is near but greater than 10 percent, is clumped, or overtopped by grasses and shrubs, there may be cases where assignment to this 

class is preferable. Short mesomorphic trees that do not overtop shrubs and 
USDA Forest Service RMRS-GTR-346. 2016. 39

herbs are placed in this class. However, in tropical upland savanna regions, 

stands may have 40 percent tree cover, where trees are less than 8 m tall, tree 

regeneration is sparse to absent, and there is a substantial graminoid layer.

3. Desert & Semi-Desert (C03): Occasionally xeromorphic trees may be 

sufficiently dense to form woodland stands (e.g., saguaro, Joshua tree, 

microphyllous-leaved mesquite woodlands, tropical thorn woodlands). The 

dominance of xeromorphic growth forms places these stands in the Desert & 

Semi-Desert class rather than Forest & Woodland.

7. Agricultural & Developed Vegetation (CCL01): Forests found in urban parks 

and lawns may have an irregular horizontal spacing but a highly regular or 

mowed understory and are placed in this developed vegetation class. Forests, 

such as orchards and forest plantations, typically have either a very regularly 

spaced tree canopy (often pruned or trained) and/or plowed or regularly manipulated ground layer (e.g., tree-shaded shrub or herb crops).

Diagnostic Characteristics: Mesomorphic tree growth forms (broad-leaved, needle-leaved, and sclerophyllous trees, palms, bamboo trees, and tree ferns) have greater 

than 10 percent canopy cover, a spontaneous, irregular horizontal canopy spacing, and 

overtop other growth forms, except in tropical upland regions, where trees typically 

have greater than 40 percent cover, are greater than 8 m tall, and the vegetation lacks a 

substantial graminoid layer.

Vegetation

Physiognomy and Structure: Growth Forms: Stands are dominated by mesomorphic trees, including broad-leaved deciduous (including mostly deciduous, 

winter-deciduous, facultatively deciduous), broad-leaved evergreen (including mostly 

evergreen), needle-leaved (deciduous and evergreen), sclerophyllous trees, palms, 

bamboo trees, and tree ferns. Tree growth forms generally have a single main stem 

and more-or-less definite crowns, and may be as low as 2 m (scrub trees) (e.g., tropical 

cloud elfin forest, mesquite woodland). Where growth forms are not easily defined, 

woody plants equal to or greater than 5 m at maturity are considered trees (FGDC 

2008).

Structure: Typical stands have one or more of the tree growth forms exceeding 5 m 

in height, and the canopy has irregular horizontal tree stem spacing, with a minimum 

of 10 percent canopy cover (8 m in height and minimum of 40 percent in tropical 

forests and woodlands, as low as 2 m in subarctic woodlands). A tree regeneration 

layer is often present, along with various associated growth forms (shrubs, herbs, 

nonvasculars). Stands of trees where the tree growth form is short (<5 m) in height but 

overtopping shrub and herb growth forms, may also be placed in this class.

Environment

Environmental Description: Climate: Climates range from humid tropical to 

boreal and subalpine, with fairly moderate moisture and temperature conditions. See 

details under the various forest and woodland subclasses. 

Soil/substrate/hydrology: Dry to wet soils, including those found in swamp forests 

and mangroves.
40 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: Forest and Woodland occurs on all continents, mostly in the 

following ecoregions (Bailey 1989, 1996): the Humid Tropical and Humid Temperate 

Domains, the Subarctic Division of Polar Domain, and Mountain Divisions of Dry 

Domain. It is less common in other divisions of Polar and Dry domains.

Citations

Synonymy: 

= Forest (FAO 2001) [Approximately equivalent. Xeromorphic scrub woodlands are 

probably included here, but otherwise the concepts are very similar.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 26 Aug 2014

1.A. Tropical Forest & Woodland (S17)

Overview

Database Code: 1.A (S17)

Scientific Name: Tropical Forest & Woodland Subclass

Common Name (Translated Scientific Name): Tropical Forest & Woodland 

Subclass

Colloquial Name: Tropical Forest & Woodland

Hierarchy Level: Subclass

Placement in Hierarchy: 1. Forest & Woodland (C01)

Lower Level Hierarchy Units:

1.A.1. Tropical Dry Forest & Woodland (F003)

1.A.2. Tropical Lowland Humid Forest (F020)

1.A.3. Tropical Montane Humid Forest (F004)

1.A.4. Tropical Flooded & Swamp Forest (F029)

1.A.5. Mangrove (F006)

Concept Summary

Type Concept Sentence: Tropical forests found at lowland and montane elevations 

including tropical dry forests, and lowland to montane humid forests (tropical rainforests) and tropical forested wetlands, where frost is essentially absent at sea level.

Classification Comments: Review of tropical monsoon forests is needed, as they 

can vary from dry to moist.

Similar NVC Types: 

1.B. Temperate & Boreal Forest & Woodland (S15): Broad-leaved evergreen trees 

may be common in warm temperate forests, comparable to tropical dry forests 

(i.e., evergreen leaves are typically small), but deciduousness is caused by frost, 

and types are found where a hard frost occurs annually.
USDA Forest Service RMRS-GTR-346. 2016. 41

2.A. Tropical Grassland, Savanna & Shrubland (S01): Where tree cover exceeds 

10 percent, stands are typically placed in the Tropical Forest & Woodland 

(S17). However, in tropical upland savanna regions, stands may have 40 percent tree cover, where trees are less than 8 m tall, tree regeneration is sparse to 

absent, and there is a substantial graminoid layer.

3.A. Warm Desert & Semi-Desert Woodland, Scrub & Grassland (S06): Thorn 

woodlands, with xeromorphic characteristics (aphyllous or very small-leaved 

trees, with succulents), are placed in this subclass, and rainfall is more typically 

between 25 and 100 cm.

7.A. Woody Agricultural Vegetation (CCL01): Tropical Forest & Woodland (S17) 

long-rotation plantations or woody restoration plantings with an irregular 

structure and a largely spontaneous ground layer may initially be similar to 

Woody Agricultural Vegetation (CCL01) in their early stages of development, 

especially if planted in rows and the understory is strongly manipulated.

Diagnostic Characteristics: Tropical Forest & Woodland is dominated by 

broad-leaved, often megaphyll, evergreen trees, broad-leaved drought-deciduous 

or semi-deciduous trees, or small-leaved (micro- to mesophyll evergreen trees). 

Evergreen needle-leaved trees may occur in association with these other growth forms. 

Climates are consistently warm (seasonal daily temperatures with minimal variation), 

and annual rainfall is typically greater than 100 cm.

Vegetation

Physiognomy and Structure: Tropical Dry Forest (typically called Tropical Dry 

Forest or Tropical Seasonally Dry Forest) range in canopy types, including evergreen, 

semi-evergreen (needle-leaved or broad-leaved), or largely or wholly deciduous 

Canopy heights decrease and canopy coverage tends to decrease as the climate dries 

until the forests are reduced to open, short-statured (5 - 15 m) woodlands (Whittaker 

1975). Tree growth forms predominate, with micro- to mesophyll leaves, but succulent 

species may be present. They occur in humid dry tropical climates, typically with a 

pronounced dry season, during which some or all of the trees may lose their leaves, or 

leaves may be moderately small and evergreen sclerophyllous. Some tropical forests 

have a more sustained dry period, with less seasonality. 

Tropical humid forests (including moist and wet forests) occur in the humid tropics 

where rainfall varies from abundant and well-distributed throughout the year to somewhat seasonal. Tree growth forms predominate, are tall, often of numerous species, 

some with buttressed bases, often smooth bark, and evergreen meso- to macrophyll 

leaves. Also present may be tree ferns, large woody climbers or lianas, and both vascular and nonvascular epiphytes, often of greater diversity than the ground layer. Heights 

may exceed 30 m (Whittaker 1975).

Tropical forested wetlands include swamps and mangroves, with hydrophytic plants 

and, in the case of mangrove, distinctive hydromorphic growth forms adapted to saline 

conditions.
42 USDA Forest Service RMRS-GTR-346. 2016.

Environment

Environmental Description: 

Climate: In general, the tropical humid forest has a fairly consistent average annual 

temperature, ranging from 26 to 27 degrees C, and a more variable daily temperature, 

with changes up to 5 degrees C. In the tropical dry forest, average annual temperatures 

range between 20 and 30 degrees C, and daily temperatures change from between 

26 to 28 degrees C. At sea level, frost is essentially absent from the Tropical Forest & 

Woodland (Holdridge 1967). Rainfall ranges from 100 to 450 cm (400 to 180 inches), 

with the rainfall becoming increasingly more seasonal in tropical dry climates, where 

the dry season may extend for 4 to 7 months (Holzman 2008).

Soil/substrate/hydrology: Soils in humid regions are often highly weathered ancient 

soils with high acidity and low nutrient and organic matter content; however, many 

tropical forests occur on rich volcanic or limestone soils. The major soil orders in the 

U.S. system include Oxisols, Ultisols, Inceptisols, and Entisols (Soil Survey Staff 

1999) (see Brady and Weil 2002 for comparison of U.S. soil orders with Canadian 

and FAO systems). Younger and richer soils are found in alluvial habitats or in areas 

influenced by ashes from volcanic activity (Holzman 2008).

Distribution

Geographic Range: Tropical Forest & Woodland is concentrated around the 

equator with tropical humid forest most common between 0 and 10 degrees N and S 

latitude, and tropical dry forest between 10 and 23 degrees N and S, with latitudinal 

limits shaped by frost and drought. Tropical Forest & Woodland is found in three 

major regions: South and Central America and the Caribbean Islands; Africa (west, 

central, and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast 

Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).

Citations

Synonymy: 

= Tropical Forest & Woodland (Holzman 2008)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and E. Helmer

Acknowledgments:

Version Date: 26 Aug 2014

1.A.1. Tropical Dry Forest & Woodland (F003)

Overview

Database Code: 1.A.1 (F003)

Scientific Name: Tropical Dry Forest & Woodland Formation

Common Name (Translated Scientific Name): Tropical Dry Forest & Woodland 

Formation

Colloquial Name: Tropical Dry Forest & Woodland
USDA Forest Service RMRS-GTR-346. 2016. 43

Hierarchy Level: Formation

Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Dry Forest & Woodland is dominated by 

broad-leaved drought-deciduous, semi-deciduous, and small-leaved or sclerophyllous 

evergreen trees where rainfall is lower, often associated with more strongly seasonal, 

tropical climates, rainshadows, or drying winds. At continental scales, the largest areas 

occur between 10 and 23 degrees N and S latitude.

Type Concept: Tropical Dry Forest & Woodland, including most monsoon forests, 

occurs in extensive areas near the equator around the globe between about 10 and 

23 degrees N and S latitude, though it is also be found near windward coasts and on 

the leeward sides of mountains or islands. These forests are dominated by broadleaved drought-deciduous trees or small-leaved (micro- to mesophyll) evergreen trees 

or broad-leaved (meso- to macrophyll) sclerophyllous-leaved trees. Evergreen needleleaved trees may occur in association with these other growth forms. It is a medium to 

high forest varying on average from 15 to 25 m tall, typically with several structural 

levels as complex upper canopy, several subcanopy levels of treelets and shrubs, 

woody vines, and an irregular low herbaceous plant stratum. Canopy heights decrease 

and canopy coverage tends to decrease as the climate dries until the forests are reduced 

to open, short-statured (5 - 15 m) woodlands (more rarely shorter). Included are semievergreen, partially sclerophyllous, semi-deciduous and deciduous, mostly dense to 

semi-dense forests adapted for a distinct period of seasonal winter drought, resulting 

in 4 to 7 months of drought (rainfall 60 mm or less), during which some or all of the 

trees lose their leaves. Annual rainfall ranges from 100 to 200 cm. The considerable 

diversity of dry tropical forests and woodland types are related to the topographic, 

hydric and edaphic variations as well as with the floristic composition and different 

biogeography.

Classification Comments: Mooney and others (1995) suggest that Tropical Dry 

Forest & Woodland may be defined as forest occurring in tropical regions characterized by pronounced seasonality in rainfall distribution, resulting in several months 

of drought. The forests that develop under such climatic conditions share a broadly 

similar structure and physiognomy; they mainly occur on oligotrophic, reddish soils 

(Oxisols, Ultisols), but may also occur on mesotrophic soils. Beyond that, they note 

that these shared characteristics are difficult to define with precision. They may 

either be deciduous or evergreen, though typically small-leaved, and either open- or 

closed-canopy. There are sclerophyllous evergreen broad-leaved (mesophyllous to 

macrophyllous-leaved) Tropical Dry Forest & Woodland in the Brazilian-Bolivian 

Cerrado. But we include here only the most closed form of cerrado (i.e. the cerradão) and the more typical cerrado is placed in 2.A. Tropical Grassland, Savanna & 

Shrubland (S01).

Many authors include thorn woodlands as part of a broadly defined “tropical 

dry forest” or “seasonally dry tropical forest” (SDTF). For example, Pennington 

and others (2006) use a wide interpretation of SDTF in the Neotropics, including 
44 USDA Forest Service RMRS-GTR-346. 2016.

formations as diverse as tall forest on moister sites to cactus scrub on the driest, but 

they exclude the Chaco of Argentina, Paraguay and Bolivia because it receives frost. 

See also Oliveira-Filho and others (2006) who include caatingas and carrascos within 

their broad definition of SDTF, but exclude cerrados and chaco. Here we treat 3.A.1 

Tropical Thorn Woodland Formation (F039) as a separate xeromorphic growth formbased formation that includes, in the Neotropics, caatingas, carrascos, and chaco.

Tropical monsoon forests are sometimes grouped with 1.A.2 Tropical Lowland 

Humid Forest Formation (F020) as “tropical moist forest,” but being deciduous with 

pronounced drought periods, they are better included here with 1.A.1 Tropical Dry 

Forest & Woodland Formation (F003) (Whitmore 1998). Further review of the range 

of variation in tropical monsoon forests is needed, to clarify the transition to Tropical 

Lowland Humid Forest.

Similar NVC Types: 

1.A.2. Tropical Lowland Humid Forest (F020): As seasonality increases, the abundance of drought-deciduous trees increases, and semi-evergreen humid forests 

more closely resemble Tropical Dry Forest & Woodland (F013). Tropical monsoon 

forests are sometimes grouped with Tropical Lowland Humid Forest as “tropical 

moist forest” (Whitmore 1998), but they are here included with Tropical Dry Forest 

& Woodland.

1.B.1. Warm Temperate Forest & Woodland (F018): Broad-leaved evergreen trees may 

be common in this formation, comparable to Tropical Dry Forest & Woodland 

(i.e., evergreen leaves are typically small), but deciduousness is caused by frost, 

and types are found north or south of around 23 degrees N and S latitude.

3.A.1. Tropical Thorn Woodland (F039): Thorn woodlands, with xeromorphic characteristics (aphyllous or very small-leaved trees, with succulents) are placed in 

this xeromorphic woodland formation (F039). Rainfall is between 25 and 100 cm. 

Tropical Dry Forest & Woodland grades to Tropical Thorn Woodland in areas with 

lower annual rainfall and increasing period of seasonal drought (in xeric warm 

bioclimates), while the trees and shrubs become fully deciduous and with a considerable increase of distinct xeromorphic adaptations such as thorns, succulency 

and clearly microphyllous species that instead are scarce or absent in Tropical Dry 

Forest & Woodland.

7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Tropical Dry Forest 

& Woodland (F003) long-rotation plantations or woody restoration plantings with 

an irregular structure and a largely spontaneous ground layer may initially be 

similar in their early stages of development, especially if planted in rows and the 

understory is strongly manipulated.

Diagnostic Characteristics: Tropical Dry Forest & Woodland is dominated 

by broad-leaved drought-deciduous trees or, more rarely, small-leaved (micro- to 

mesophyll) evergreen trees or broad-leaved (meso- to macrophyll) sclerophyllousleaved trees. Thorn forest scrub, and scrubby cerrado are excluded. Evergreen 

needle-leaved trees may occur in association with these other growth forms. Climates 
USDA Forest Service RMRS-GTR-346. 2016. 45

are consistently warm (seasonal daily temperatures with minimal variation), and annual rainfall is strongly seasonal, but average annual rainfall is typically greater than 

100 cm.

Vegetation

Physiognomy and Structure: Tropical Dry Forest & Woodland is dominated 

by broad-leaved drought-deciduous trees or, more rarely, small-leaved (micro- to 

mesophyll) evergreen trees or broad-leaved (meso- to macrophyll) sclerophyllousleaved trees (Lugo and others 2006). Evergreen needle-leaved trees may occur in 

association with these other growth forms. It is a medium to high forest varying on 

average from 15 to 25 m tall, typically with several structural levels as complex upper 

canopy, several subcanopy levels of treelets and shrubs, woody vines, and an irregular 

low herbaceous plant stratum. Canopy heights decrease and canopy coverage tends 

to decrease as the climate dries until the forests are reduced to open, short-statured 

(5 - 15 m) woodlands (more rarely shorter). Included are semi-evergreen, partially 

sclerophyllous, semi-deciduous and deciduous, mostly dense to semi-dense forest 

(Whittaker 1975).

In the Neotropics the lower forest level is often dominated by colonies of clumping 

terrestrial bromeliads. Overall, there is predominance in the canopy of medium-sized 

leaves (mesophyllous) that fall partially or almost completely in the dry season. Tall 

arborescent cacti can be frequent in dry semi-deciduous forest of the Neotropics and 

physiognomically similar arborescent succulent euphorbias in the Paleotropics. In 

western Brazil, eastern Bolivia, and Paraguay, this formation includes large stands 

of medium-low and partially sclerophyllous semi-evergreen forests or “cerradão,” 

with characteristic adaptations to drought and fire, such as very corky bark on twisted 

trunks and xylopodiums (but we exclude the more typical cerrado, which is placed 

with 2.A. Tropical Grassland, Savanna & Shrubland (S01).

Environment

Environmental Description: Climate: Tropical Dry Forest & Woodland occurs 

in areas where the air subsides near the tropics of Cancer and Capricorn and the 

Intertropical Convergence Zone (ITCZ) migrates north and south seasonally, producing the alternating pattern of rainfall and dryness. The average drought season varies 

in length from 3 to 6 months and is generally coincident with the annual lowest 

temperatures. Annual rainfall ranges from 100 to 200 cm (Whitmore 1998), or where 

the annual rainfall is less than 160 cm, with a period of at least 5 to 6 months receiving 

less than 10 cm, during which some or all of the trees lose their leaves (Pennington 

and others 2006). The climate is warm tropical pluviseasonal, subhumid to humid.

Soil/substrate/hydrology: The substrate often includes large areas of highly weathered reddish soils with high iron and aluminum content and low mineral nutrients 

content, as well as frequent development of laterization. The main soil orders in the 

U.S. system associated with Tropical Dry Forest & Woodland are Oxisols, Ultisols and 

Alfisols (Soil Survey Staff 1999) [see Brady and Weil (2002) for comparison of U.S. 

soil orders with Canadian and FAO systems]. More rarely, they occur on mesotrophic 

soils. This type also occurs on limestone substrates in the Caribbean and Mesoamerica 

(Lugo and others 2006).
46 USDA Forest Service RMRS-GTR-346. 2016.

In most areas, Tropical Dry Forest & Woodland supports seasonal regimes of 

fire, both natural and characteristically human induced, which can cause frequent 

pyrogenic secondary savannized or woodland physiognomies. Fires, in conjunction 

with climate, are likely to partially explain the distribution of Tropical Dry Forest & 

Woodland (Bond and others 2005).

Tropical Dry Forest & Woodland tends to occur at lower elevations. However, in 

South America, large more-or-less isolated pockets occur in several valleys of the 

eastern slopes of the Andes, particularly in southern Peru and Bolivia, where they can 

reach altitudes up to approximately 1,200 m.

Distribution

Geographic Range: Tropical Dry Forest & Woodland is concentrated near the 

equator, primarily between 10 and 23 degrees N and S latitude. It is found in three 

major regions: South and Central America and the Caribbean Islands; Africa (west, 

central and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast 

Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).

In the Neotropics, this formation occupies large areas in central South America, 

mainly in eastern Bolivia, central and western Brazil, and eastern Paraguay. Also, in 

the Neotropics, these forests extend across northern South America (Venezuela) and in 

western Mesoamerica (Mexico to Panama), with minor extensions in western Ecuador 

and Peru.

In the Paleotropics, Tropical Dry Forest & Woodland potentially occupies large 

areas in Africa (Sudano-Zambezian and Madagascan regions), India and Southeast 

Asia (Indochinese region), northeastern Australia, and the Pacific Islands, but generally has been extensively degraded by human activity to semi-open woodlands and 

treesavannas.

Citations

Synonymy: 

= Seasonally Dry Tropical Forests (Mooney and others 1995)

= Tropical Dry Forest (Miles and others 2006)

= Tropical Seasonal Forest (Holzman 2008)

= Tropical broadleaf woodland: biome type 8 (Whittaker 1975)

= Tropical seasonal forest: biome type 2 (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: G. Navarro, D. Faber-Langendoen and E. Helmer

Acknowledgments:

Version Date: 26 Aug 2014

1.A.2. Tropical Lowland Humid Forest (F020)

Overview

Database Code: 1.A.2 (F020)

Scientific Name: Tropical Lowland Humid Forest Formation

Common Name (Translated Scientific Name): Tropical Lowland Humid Forest Formation

Colloquial Name: Tropical Lowland Humid Forest
USDA Forest Service RMRS-GTR-346. 2016. 47

Hierarchy Level: Formation

Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)

Lower Level Hierarchy Units

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Lowland Humid Forest is dominated by 

broad-leaved evergreen trees, often with multiple complex strata and growth forms 

in lowland to submontane or premontane elevations with aseasonal to moderately 

seasonal rainfall and warm temperatures.

Classification Comments: Heath forests are a striking variant within this formation, as described by Richards (1996) and Whitmore (1998). They occur on podsolized 

soils developed from siliceous sand, either coastal alluvium or weathered sandstones. 

Although typically found in a rainforest climate and retaining basic growth forms 

characteristic of 1.A.2 Tropical Lowland Humid Forest Formation (F020), the 

nutrient-poor, acidic conditions produce a strikingly distinct physiognomy. Here are 

found dense, often pole-sized trees, a stronger predominance of microphylls over 

mesophylls, with some sclerophylly, and woody climbers that are more often slender. 

The most extensive heath forests are found in the upper reaches of the Rio Negro and 

Rio Orinoco of South America, also in Guyana (wallaba forests of Eperua falcata), 

coastal forests of southeastern Madagascar, Gabon, Cameroon and Ivory Coast, and 

in Kalimantan, Sarawak and Brunei in Borneo (referred to as kerangas), and parts of 

Malaya (Whitmore 1998).

Tropical montane forests may resemble heath forests to some degree (Whitmore 

1998). Tropical monsoon forests are sometimes grouped with Tropical Lowland 

Humid Forest as “tropical moist forest” (Whitmore 1998), but by and large, they are 

included with 1.A.1 Tropical Dry Forest & Woodland Formation (F003). Further 

review is needed of the transition between monsoon forests and humid forests or 

rainforests.

Similar NVC Types: 

1.A.1. Tropical Dry Forest & Woodland (F003): As climate becomes more seasonal, 

increasing numbers of deciduous trees are found. Stands are placed in Tropical 

Dry Forest & Woodland when greater than 25 percent cover of trees are deciduous during a dry period, or where small-leaved (micro- to mesophyll) trees 

dominate. These forests also share some characteristics with the heath forest 

variant of Tropical Lowland Humid Forest.

1.A.3. Tropical Montane Humid Forest (F004): Montane rainforests at highest 

elevations are considerably smaller and heavily covered with bryophytes, 

but lower elevation montane forests (towards 1000 m) share similarities with 

Tropical Lowland Humid Forest.

1.A.4. Tropical Flooded & Swamp Forest (F029): Soils are typically saturated 

to flooded, but many of the growth forms are shared with Tropical Lowland 

Humid Forest.

Diagnostic Characteristics: Tropical Lowland Humid Forest is dominated by 

meso- to megaphyll, broad-leaved evergreen trees (up to 25 percent deciduous trees), 

with a complex multi-layer structure, often exceeding 30 m in height. Climates are 
48 USDA Forest Service RMRS-GTR-346. 2016.

consistently warm (seasonal daily temperatures with minimal variation), and annual 

rainfall is relatively aseasonal and typically greater than 100 cm, with any given month 

rarely less than 60 mm.

Vegetation

Physiognomy and Structure: Tropical Lowland Humid Forest is a dense, multilayered forest, with broad-leaved evergreen trees that can exceed 45 m in height. The 

tree layer is minimally divided into a top stratum with giant emergent trees, over a 

main stratum between 25 and 35 m tall, under which a stratum of shorter trees between 

10 and 25 m occurs. Ground vegetation may be sparse, commonly with small trees 

(treelets). Herbs may be patchy. Individual trees may be deciduous or semi-deciduous, 

but overall comprise less than 25 percent of the main stratum. Evergreenness varies 

from completely evergreen to evergreen seasonal forest (which is mainly evergreen 

but individual trees may lose their leaves) to semi-evergreen seasonal forest (in 

which up to about 25 percent of the main canopy may be deciduous) (Richards 1996). 

Whitmore (1998) notes the following features: buttresses are common, cauliflory 

and ramiflory are occasional to common, pinnate leaves are frequent, leaf blades of 

mesophyll size predominate, big woody climbers (mostly free-hanging) are frequent 

to abundant, bole climbers, shade and sun epiphytes are occasional to frequent, and 

bryophytes are rare (Table 5). These characteristics are lost as forests become drier or 

as elevation increases.

Environment

Environmental Description: Climate: Tropical Lowland Humid Forest (including 

semi-evergreen rainforest) occurs in aseasonal, humid climates where water stress 

is low to absent, with no regular annual dry season (Whitmore 1998). In general, a 

tropical rainforest climate can be defined as one with monthly mean temperatures of 

at least 18 degrees C throughout the year, and an annual rainfall of at least 170 cm 

(and usually above 200 cm) and either no dry season or a short one of fewer than 4 

consecutive months with less than 10 cm rainfall (Richards 1996; Whitmore 1998).

African rainforests are primarily semi-evergreen (where deciduous trees may comprise up to 25 percent of the main canopy), as are Australian rainforests, and various 

parts of other regional rainforest blocks (Whitmore 1998).

Soil/substrate/hydrology: These forests generally occur from sea level to approximately 1,200 m elevation, but the boundary between lowland and montane forests 

occurs at different elevations depending on the “Massenerhebung effect” (Collins 

1990; Richards 1996). This is a phenomenon whereby large mountains and the central 

parts of large ranges are warmer at given elevations than small mountains and outlying 

spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America, 

Madagascar, Australia and Southeast Asia at 910 m, whereas in West Africa the boundary was set at 1200 m, in New Guinea at 1,400 m and in South America at 1800 m.

Soils are often ancient and deeply weathered, with little organic darkening of the 

topsoil and with bright reddish or yellowish colors throughout the subsoil. Few of the 

original rock minerals remain in the upper horizon. Organic content may vary. Soils 

are often clay-like, but weathered sands also occur. Other more recent soils include 

those found on recent volcanic deposits, colluvial and alluvial soils (Richards 1996).
USDA Forest Service RMRS-GTR-346. 2016. 49

Distribution

Geographic Range: Tropical Lowland Humid Forest is concentrated around the 

equator, between the Tropic of Cancer (23 degrees N latitude) and Tropic of Capricorn 

(23 degrees S latitude). It is found in three major regions: South and Central America; 

Africa (west, central and interior) and Madagascar; and the Indo-Asian Pacific (India, 

Southeast Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia). 

In the United States, it is found in Hawaii and in several territories, including Puerto 

Rico and many of its Pacific island territories.

Citations

Synonymy: 

= Lowland tropical rain forest: biome type 1 (Whittaker 1975)

= Tropical Rain Forest (Richards 1996)

> Tropical heath forest (Whitmore 1998) [Heath forests occur on podsolized soils 

developed from siliceous sand, either coastal alluvium or weathered sandstones. The 

nutrient-poor, acidic conditions produce a strikingly different physiognomy of dense, 

often pole-sized trees, stronger predominance of microphylls over mesophylls, with 

some sclerophylly. Woody climbers are more often slender.] 

> Tropical lowland evergreen rain forest (Whitmore 1998) [Whitmore separates out 

tropical semi-evergreen rainforest, which is here combined at the formation level.] 

> Tropical semi-evergreen rain forest (Whitmore 1998) [Whitmore separates out tropical lowland evergreen rainforest, which is here combined at the formation level.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

1.A.3. Tropical Montane Humid Forest (F004)

Overview

Database Code: 1.A.3 (F004)

Scientific Name: Tropical Montane Humid Forest Formation

Common Name (Translated Scientific Name): Tropical Montane Humid Forest 

Formation

Colloquial Name: Tropical Montane Humid Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Montane Humid Forest is dominated by 

broad-leaved evergreen trees, with increasingly small leaves and stems, often gnarly, 

with dense crowns as elevations increase. These forests are generally found within 

23 degrees N and S latitude of the equator between 1,000 and 3,500 m in elevation.
50 USDA Forest Service RMRS-GTR-346. 2016.

Classification Comments: The proportion of precipitation that is from clouds is a 

defining factor, but is difficult to assess. Tropical Montane Humid Forests resemble 

heath forests to some degree (Whitmore 1998), with their wet climate, but have 

smaller stems and leaves.

Similar NVC Types: 

1.A.2. Tropical Lowland Humid Forest (F020): These rainforests are typically much 

taller, with multiple strata and growth forms, but as elevations increase (up 

to 1,000 m), a transition occurs to lower elevation Tropical Montane Humid 

Forest.

Diagnostic Characteristics: Tropical Montane Humid Forest is dominated by 

micro- to mesophyll, broad-leaved evergreen trees (up to 25 percent deciduous trees), 

with a simple or two-layer structure, ranging from 5 to 30 m in height. Climates are 

more often cool, but without frost, with seasonal daily temperatures with minimal 

variation. Annual rainfall is relatively aseasonal and typically greater than 100 cm, 

with any given month rarely receiving less than 60 mm. The proportion of precipitation that is from clouds is a defining factor, but is difficult to assess. Better defining 

characteristics are the amounts of epiphytes and ferns and where the epiphytes occur 

as well as canopy structure.

Vegetation

Physiognomy and Structure: Tropical Montane Humid Forest is dominated by 

broad-leaved evergreen trees, with increasingly small leaves and stems, often gnarly, 

with dense crowns as elevations increase. Lower elevations represent a transition from 

1.A.2 Tropical Lowland Humid Forest Formation (F020) [see Table 5]. At the highest 

elevations, the trees may be less than 10 m tall (sometimes referred to as elfin woodland), and covered in bryophytes, ferns, and other epiphytic plants. Peat may form, 

sometimes with sphagnum mosses (Sphagnum spp.). These in turn may be replaced 

by a kind of “tropical subalpine forest” with very tiny leaves (nanophylls), as found in 

New Guinea and the Andes (Whitmore 1998). Treeline is typically reached between 

3500 and 4000 m, where the vegetation transitions to “tropical high montane grassland 

and shrubland” (tropical “alpine” vegetation).

Environment

Environmental Description: Climate: Climates are more often cool, but without 

frost, with seasonal daily temperatures with minimal variation. Annual rainfall is 

relatively aseasonal and typically greater than 100 cm, with any given month rarely 

receiving less than 60 mm. The proportion of precipitation that is from clouds is a 

defining factor, though this is difficult to know in the field. Better defining characteristics are the amounts of epiphytes and ferns and where the epiphytes occur as well as 

canopy structure.

Soil/substrate/hydrology: Tropical Montane Humid Forest is typically found 

between elevations of 1,000 to 3,500 m, with the treeline typically reached between 

3,500 and 4,000 m. But the boundary between lowland and montane forests occurs 

at different elevations depending on the “Massenerhebung effect” (Collins 1990; 

Richards 1996). This is a phenomenon whereby large mountains and the central parts 
USDA Forest Service RMRS-GTR-346. 2016. 51

of large ranges are warmer at given elevations than small mountains and outlying 

spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America, 

Madagascar, Australia, and Southeast Asia at 910 m, whereas in West Africa the 

boundary was set at 1,200 m, in New Guinea at 1,400 m, and in South America at 

1,800 m.

Distribution

Geographic Range: Tropical Montane Humid Forest is generally found around the 

globe within 23 degrees N and S latitude of the equator, typically between 1000 and 

3500 m in elevation. It is found extensively in Central and South America, especially 

the Andes and parts of the Caribbean, and is uncommon in Africa (Cameroon and the 

eastern fringe of the Congo basin) and many mountain regions throughout the IndoMalayan region.

Citations

Synonymy: 

= Elfinwoods: biome-type 7 (Whittaker 1975)

= Tropical montane rain forests (Whitmore 1998) [Whitmore (Table 2.2) discusses the 

range of variation between lower and upper montane rainforests.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, E. Helmer and J. Sawyer

Acknowledgments:

Version Date: 26 Aug 2014

1.A.4. Tropical Flooded & Swamp Forest (F029)

Overview

Database Code: 1.A.4 (F029)

Scientific Name: Tropical Flooded & Swamp Forest Formation

Common Name (Translated Scientific Name): Tropical Flooded & Swamp Forest 

Formation

Colloquial Name: Tropical Flooded & Swamp Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)

Lower Level Hierarchy Units: 

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Flooded & Swamp Forest is a forested or 

wooded wetland and peatland found in margins of freshwater lakes, alluvial plains, 

rivers and depressions around the globe.

Classification Comments: Forests may vary from deciduous to evergreen. Further 

review is needed of the degree of variation in evergreen versus deciduous-leaved trees 

between floodplains and swamps in tropical dry versus moist-wet climates.
52 USDA Forest Service RMRS-GTR-346. 2016.

Similar NVC Types: 

1.A.2. Tropical Lowland Humid Forest (F020): Overall dominant growth forms 

are similar, but forest structure is more complex in Tropical Lowland Humid 

Forest, and the soils are not saturated or inundated. Tree palms and lianas are 

more common.

1.A.5. Mangrove (F006): As concentrations of salts decline, Mangrove (F006) may 

grade into Tropical Flooded & Swamp Forest.

Diagnostic Characteristics: This formation is dominated by mesophyll, broad-leaved, 

evergreen trees, with soils saturated to flooded for all or parts of the year, varying from 

peat to mineral soil textures. Climates are consistently warm (seasonal daily temperatures with minimal variation).

Vegetation

Physiognomy and Structure: Tropical Flooded & Swamp Forest is a forested or 

wooded wetland and peatland. Structural characteristics that recur in flooded forests 

are presence of monospecific stands such as palm swamp, even-canopied forests, and 

sharp vegetation zonations. It is common to find that trees in flooded tropical forests 

develop sclerophylly (firm, thickened leaves) due to poor nutrition or water limitations, or gas exchange structures (e.g. pneumatophores, lenticels, knees, aerial roots, 

swelling of base of trees, surface or aerial roots) in order to overcome poor soil aeration, or support structures (e.g. plank buttresses and stilt roots) to provide stability in 

muddy or steep conditions. Tree heights can vary greatly, from 1 to 50 m.

Based on the type of dominant species, swamp forests can be conveniently divided 

into two types: forests dominated by broad-leaved evergreen hardwood species and 

those dominated by palms. Dominance by palms becomes stronger with increasing 

hydroperiod or soil moisture conditions. Species richness generally decreases with 

increasing hydroperiod. One formation that covers large areas in western Amazonia 

and in the Orinoco River basin is the often monodominant “aguajales” or Mauritia 

flexuosa stands. These palm swamps may be regularly affected by riverine floods, 

but they mostly occur farther from current river channels, the water-logged condition 

then being maintained by a combination of high precipitation and poor drainage in 

depressional terrain. Other palm-associated (Raphia, Manicaria) swamps are typical 

of the coastal regions of Central America and northern South America along estuarine 

channels, sometimes in mixed stands with a few mangrove species.

Environment

Environmental Description: Soil/substrate/hydrology: Tropical swamp forests can 

be divided into freshwater or brackish swamp or floodplain forest (along rivers and 

lakes) and peat swamp forest (formed behind natural floodplain levees), where peat 

layers may be well in excess of 1 m thick (Whitmore 1984). The floodplain forests are 

found along rivers, streams, coasts and lakes. They have a dynamic water table, with 

seasonal flooding inundating the vegetation for short (<7 days) to long (>1 month) 

periods, leading to an influx of sediment and mineral enrichment during high water 

periods. Information about underlying soils is scarce. 
USDA Forest Service RMRS-GTR-346. 2016. 53

Many floodplain swamp forests are potentially peat-accumulating, but, although 

studies on this subject exist in Southeast Asia, they have apparently never been published for the Amazon basin (Whitmore 1998). Swamps and other types of wetlands in 

the Neotropics have been described in terms of their vegetation composition, structure, 

and geomorphology, but studies have failed to deal with peat formation or detailed descriptions of the underlying soils. There is evidence that at least the Mauritia swamps 

frequently accumulate peat of some kind.

The lowland tropical peat swamps are formed from layers of woody debris too 

waterlogged to fully decompose. Slowly deposited over thousands of years, the 

carbon-rich peat strata have been known to reach a thickness of up to 20 m. In 

Indonesia the ombrogenous peatlands are mostly formed on the inward edge of the 

mangroves. They are usually dome-shaped and several meters thick overlying the 

mangrove mineral soil; the whole sequence taking several thousand years. Periods 

with rising sea levels promote the formation of very deep peat layers up to 20 m 

thickness with the alluvial soil far below present sea levels. Peat domes younger than 

3,000 years do have the alluvial soil at about present mean sea level. 

The initial rate of vegetation growth and peat build up is rapid, as the alluvial mangrove soils are nutrient rich. As the peat accumulates, it builds up above the level of 

the nutrients in the alluvial soils that are accessible for the plant roots. In that case, the 

mineral supply to the vegetation depends on the minerals in the rainwater and available nutrients of the decaying vegetation in the surface layer. As the swamp ages and 

the peat layer increases, nutrients become increasingly scarce, tree growth and litter 

production are reduced, and growth of the whole formation slows down.

Besides its association with mangroves, the lowland Neotropical peatlands are 

associated with palm swamps and open herbaceous marshes. The latter apparently 

are relatively nutrient rich, since surface runoff water easily reaches all parts of the 

swamps. Furthermore, the layer of organic material is usually thin enough for the roots 

of the plants to have direct contact with the underlying mineral soil. In the case of 

palm swamps, they may be regularly affected by riverine floods, but for most of their 

extent they occur farther from current river channels, the water-logged condition then 

being maintained by a combination of high precipitation and poor drainage, which 

makes them ombrogenous types of peatlands. 

Distribution

Geographic Range: Flooded forest systems are a regular feature of the low-lying 

coastal areas in the West Indies, southern Mexico, Central America, and northern 

South America. In South America, the greatest extent of flooded forest occurs in 

Amazonia, and in the basins of other important rivers, such as the Orinoco and the 

Atrato. However, the most complex mosaics of wetlands, savannas, and flooded 

forests are maybe those of the Beni in Bolivia and the Brazilian Pantanal, on very 

extensive flat basins subject to a strong seasonality in the precipitation. Some of the 

extensive floodplains of South America include treed and shrub swamps that are located off the direct influence of the main river channels, usually occupying past, silted 

up river arms or depressed areas with inflows product of runoff and seepage or only 

sporadic, extreme river floods.
54 USDA Forest Service RMRS-GTR-346. 2016.

Citations

Synonymy: 

> Freshwater swamp forest (Whitmore 1998) [Whitmore divides the Tropical Swamp 

& Flooded Forest into two formations based on peat or mineral soils.] 

> Peat swamp forest (Whitmore 1998) [Whitmore divides the Tropical Swamp & 

Flooded Forest into two formations based on peat or mineral soils.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: C. Josse and G. Navarro

Acknowledgments:

Version Date: 26 Aug 2014

1.A.5. Mangrove (F006)

Overview

Database Code: 1.A.5 (F006)

Scientific Name: Mangrove Formation

Common Name (Translated Scientific Name): Mangrove Formation

Colloquial Name: Mangrove

Hierarchy Level: Formation

Placement in Hierarchy: 1.A. Tropical Forest & Woodland (S17)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Mangroves are dominated by broad-leaved evergreen 

trees, with complex aerial root systems, found in estuarine and coastal marine habitats 

that form a typically narrow fringe along the coasts of tropical latitudes worldwide.

Similar NVC Types: 

1.A.4. Tropical Flooded & Swamp Forest (F029): As concentrations of salts decline, Mangrove (F006) may grade into this formation.

2.C.5. Salt Marsh (F035): Dwarf mangroves may grade into tropical salt marshes.

Diagnostic Characteristics: Broad-leaved evergreen trees, with complex aerial 

root systems (including aerial “stilt” roots and pneumatophores), found in tropical 

estuarine and coastal marine habitats.

Vegetation

Physiognomy and Structure: Physiognomically, mangroves vary in size from 

shrubby dwarf trees to tall trees, with mesophyll, evergreen leaves. They have a complex set of aerial roots. Roots may diverge from the tree as much as 2 m above ground 

and penetrate the soil away from the main stem. Secondary roots may branch off, 

creating a “stilt root” structure. They also may contain pneumatophores (root extensions growing up above the water surface) emerging 30 cm or more above the muddy 

surface. Their adaptations to cope with seawater include methods of salt secretion, 

exclusion and accumulation.
USDA Forest Service RMRS-GTR-346. 2016. 55

Environment

Environmental Description: Soil/substrate/hydrology: Mangroves (mangal, 

mangle) are tidal, estuarine forested wetlands that occur along the (sheltered) coasts 

of tropical latitudes of the Earth. They are commonly found on the intertidal mudflats 

along the shores of estuaries, usually in the region between the salt marshes and seagrass beds. Where tidal amplitude is relatively low, they form narrow bands along the 

coastal plains, and rarely penetrate inland more than several kilometers along rivers. 

Where tidal amplitude is greater, mangroves extend farther inland along river courses 

forming extensive stands in the major river deltas. Mangrove cays occur also within 

the lagoon complex of barrier reefs (Stoddart and others 1982). In general, mangroves 

fall within two categories: mangroves of oceanic islands and inland mangroves. 

The latter need to adapt to a pronounced variation in salinity due to the variations in 

freshwater carried from the interior streams, while the former owe the salinity gradient 

to the rate of evaporation in the shallow ponds and mudflats and the rainfall on site, 

especially in the case of small to very small islands.

Gilmore and Snedaker (1993) described five distinct types of mangrove forests 

based on water level, wave energy, and pore water salinity: (1) mangrove fringe 

forests, (2) overwash mangrove islands, (3) riverine mangrove forests, (4) basin 

mangrove forests, and (5) dwarf mangrove forests. Dwarf forests are most commonly 

observed in south Florida, around the vicinity of the Everglades, but occur in all 

portions of the range where physical conditions are suboptimal, especially in drier 

transitional areas.

Rainfall plays an important role in distribution and species composition because 

rainfall regulates salt concentrations in soils and plants, as well as providing a source 

of freshwater for the mangroves. This is an important factor when propagules begin to 

take root and when mature individuals bloom and fruit. If high rainfall occurs over a 

short period and other months of the year are prone to drought, the conditions can be 

considered unfavorable for the growth and distribution of mangroves.

Mangroves provide habitats for commercially important crustaceans; are important 

nursery grounds for juvenile fish; filter and trap pollutants and sediments from land 

runoff thus maintaining estuarine water quality; provide barriers and buffer zones to 

stabilize shorelines and prevent coastal erosion; and are also a major producer of organic material. Mangroves protect the coast against erosion, but monsoons and storms 

cause large waves and winds to erode the coast, destroying many mangrove areas. Sea 

level rise, together with monsoons or hurricanes and storms, accelerates the speed of 

mangrove coastal erosion.

Mangroves cannot tolerate frost, especially in the seedling stage, but mangroves 

are also regulated by sea temperatures, rarely occurring outside the range delimited 

by the winter position of the 20 degree C isotherm (Hogarth 2007). It is not entirely 

clear why mangroves are limited to the tropics. Given their pan-tropical distribution 

and the wide availability of muddy, saline habitats in temperate regions, there would 

seem to be many suitable opportunities to spread into these latitudes. Hogarth (2007) 

suggests that perhaps the combination of being a tree, tolerating salt, and coping with 

waterlogging creates a metabolic cost that is difficult to sustain in lower temperatures 

and shorter day lengths. 
56 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: Mangroves occur along the (sheltered) coasts of tropical 

latitudes of the Earth, typically between the equator and 23 degrees N and S, but mangroves occur considerably southward in southeastern Australia. Mangrove distribution 

appears to be limited by both frost and sea temperatures, rarely occurring outside the 

range delimited by the winter position of the 20 degree C isotherm (Hogarth 2007). 

They are estimated to cover 18 million ha (Spalding and others 1997, in Hogarth 

2007).

Citations

Synonymy: 

= Mangrove vegetation (mangal) (Richards 1996)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: C. Josse

Acknowledgments:

Version Date: 26 Aug 2014

1.B. Temperate & Boreal Forest & Woodland (S15)

Overview

Database Code: 1.B (S15)

Scientific Name: Temperate & Boreal Forest & Woodland Subclass

Common Name (Translated Scientific Name): Temperate & Boreal Forest & 

Woodland Subclass

Colloquial Name: Temperate & Boreal Forest & Woodland

Hierarchy Level: Subclass

Placement in Hierarchy: 1. Forest & Woodland (C01)

Lower Level Hierarchy Units:

1.B.1. Warm Temperate Forest & Woodland (F018)

1.B.2. Cool Temperate Forest & Woodland (F008)

1.B.3. Temperate Flooded & Swamp Forest (F026)

1.B.4. Boreal Forest & Woodland (F001)

1.B.5. Boreal Flooded & Swamp Forest (F036)

Concept Summary

Type Concept Sentence: Temperate & Boreal Forest & Woodland is typically 

dominated by broad-leaved deciduous and needle-leaved trees, with some broadleaved evergreens in warmer regions, and a climate that varies from warm temperate 

with only rare frosts to very cold subarctic conditions. It is found across the globe 

in the mid latitudes, typically between 25 and 60 to 70 degrees N and S latitude, and 

includes boreal, cool temperate, and warm temperate/Mediterranean forests.

Classification Comments: Warm temperate forests and woodlands are defined 

here to include both the classic Mediterranean forests and woodlands and the more 

humid warm temperate forests. Both share increasing levels of broad-leaved evergreen 

trees, including sclerophyllous-leaved trees, as well as evergreen shrubs and herbs, 
USDA Forest Service RMRS-GTR-346. 2016. 57

as compared to other temperate forests and woodlands. Walter (1985) recognizes two 

warm temperate biomes, the “Zonobiome of the Winter-Rain Region with an AridHumid Climate and Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the 

Warm-Temperate Humid Climate” (Zone V), distinct from the cool-temperate biome 

“Zonobiome of the Temperate-Nemoral Climate” (Zone VI) and the boreal biome 

“Zonobiome of the Cold-Temperate Boreal Climate” (Zone VIII). Schultz (1995) also 

recognizes the two warm-temperate regions, which he refers to as: “MediterraneanType subtropics” (with world distribution shown in his Figure 129) and “Humid 

subtropics” (with world distribution shown in his Figure 171).

Similar NVC Types: 

1.A. Tropical Forest & Woodland (S17): There is a strong dominance by broadleaved evergreen trees, and deciduousness is caused by drought rather than 

forest composition.

2.B. Temperate & Boreal Grassland & Shrubland (S18): Tree cover is less than 10 

percent.

7.A. Woody Agricultural Vegetation (CCL01): Long-rotation plantations or woody 

restoration plantings of Temperate & Boreal Forest & Woodland (S15) with an 

irregular structure and a largely spontaneous ground layer may initially be 

similar in their early stages of development to Woody Agricultural Vegetation 

(CCL01), especially if planted in rows and the understory is strongly manipulated.

Diagnostic Characteristics: Temperate & Boreal Forest & Woodland is typically dominated by broad-leaved deciduous and needle-leaved trees, with some 

broad-leaved evergreens in warmer regions (See Table 8). Climate varies from warm 

temperate with only rare frosts and snow to cold subarctic conditions. It is found 

across the globe typically between 25 and 60 to 70 degrees N and S latitude.

Table 8—Characteristics of Boreal and Temperate Forests.

Criterion

Boreal Forest & 

Woodland

(upland and wetland)

Cool Temperate Forest & 

Woodland

(upland and wetland)

Warm Temperate Forest & 

Woodland

(upland and wetland)

Dominant 

Growth Forms

Needle-leaved (usually 

evergreen) conifer, often 

strongly conical-shaped, 

and simple, broad-leaved, 

small mesophyll deciduous 

hardwoods.

Broad-leaved deciduous or 

evergreen needle-leaved conifer, 

alone or in mixes, variable leaf 

and crown shapes, and leave 

sizes typically mesophyll with 

a seasonal green understory 

of herbs. The tall-shrub layer 

is variable, and is often broadleaved deciduous, but the 

short-shrub layer may be heath. 

The moss layer is often sparse, 

but more dominant in cold, rainy 

and/or high montane needleleaved evergreen stands.

Broad-leaved evergreen trees, 

microphyll to small mesophyll 

leaves, sometimes dwarfed 

stems, sclerophyllous or smallleaved trees (e.g., eucalypts, 

sclerophyllous oaks); or various 

combinations of broad-leaved 

deciduous, broad-leaved 

evergreen or evergreen needleleaved conifer trees.

(continued)
58 USDA Forest Service RMRS-GTR-346. 2016.

Criterion

Boreal Forest & 

Woodland

(upland and wetland)

Cool Temperate Forest & 

Woodland

(upland and wetland)

Warm Temperate Forest & 

Woodland

(upland and wetland)

Table 8—(Continued).

Location Northern Hemisphere 

south of the arctic treeline.

Middle latitudes of North 

America, western and fareastern Eurasia, and an isolated 

small area in the middle latitude 

of South America.

Mediterranean Basin and 

Mediterranean and warm 

temperate regions in North 

America (California, Southeast 

Coastal Plain), Chile, South 

Africa, Australia, India and 

Southeast Asia.

Climate Type Cold snow climates, with 

extended cold winters and 

short mild summers, frozen 

soils in winter.

Humid temperate climates with 

distinctive spring, summer, 

autumn, and cool to cold 

winter seasons, with freezing 

temperatures.

Mild (mostly frost-free) winter, 

temperate humid spring, hot-dry 

summer, and mild, often dry 

autumn seasons. Rainy season 

in winter and dry summers 

(Mediterranean).

Temperature Lengthy periods of 

freezing temperatures 

with the coldest month 

isotherm –3 oC, with 

the growing season 

generally averaging 

less than 100 days, 

occasionally interrupted by 

nights of below-freezing 

temperatures.

Freezing temperatures usually 

of moderate duration, although 

of frequent occurrence during 

winter months. Potential growing 

season generally from 100 

to 200 days and confined to 

late spring and summer when 

freezing temperatures are 

infrequent or absent.

Freezing temperatures of short 

duration but generally occurring 

every year during winter months. 

Potential growing season more 

than 200 days with less than 

an average of 150 days a year 

subject to temperatures below 

0 oC or chilling fog.

Precipitation 

Controls

Seasonal shift of polar 

front.

Summer convectional storms, 

Atlantic hurricanes, Asian 

monsoons.

Stationary high-pressure cells in 

summer.

Precipitation 

(annual)

38–50 cm (15–20 inches) 50–125 cm (20–50 inches). 25–100 cm (10–40 inches) 

(Mediterranean).

Dominant SoilForming ProcessPodzolization Podzolization. Severe weathering.

Major Soil 

Orders (Soil 

Survey Staff 

1999)

Gelisols, some Spodosols 

in south.

Alfisols and Ultisols, some 

Spodosols in north.

Various, Ultisols and Alfisols 

common.

Soil 

Characteristics

Sandy ash-colored A 

horizon; accumulation 

of minerals in B horizon; 

generally low in natural 

fertility.

Gray forest soils with 

accumulated silicate clay 

minerals in B horizon; some 

(Alfisols) with relatively high 

natural fertility; more leached 

soils in southern areas (Ultisols) 

due to higher precipitation levels.

Naturally productive soils, some 

regions worn by thousands of 

years of human use.

Biogeographic 

History

Recent-post Pleistocene 

migration of plants and 

animals.

Recent-post Pleistocene to 

ancient Tertiary origins.

Recent to more ancient, some 

regions influenced by thousands 

of years of human use.
USDA Forest Service RMRS-GTR-346. 2016. 59

Vegetation

Physiognomy and Structure: Temperate forests and woodlands include temperate rainforest, temperate deciduous forest, and temperate evergreen forests and 

woodlands. They are dominated by broad-leaved or needle-leaved growth forms. 

Trees typically range in height from 10 to 30 m, but rainforest trees may attain great 

height, exceeding 50 m. Temperate broad-leaved deciduous and needle-leaved forests 

and wooodlands grow in cool temperate continental climates, with summer rainfall 

and cold winters, during which the broad-leaved trees lose their leaves, extending to 

high montane regions, where they resemble boreal forests and woodlands. Temperate 

broad-leaved evergreen forests and woodlands, often mixed with broad-leaved deciduous and needle-leaved trees, occur in warm-temperate climates, with either mild 

winters and moist, warm summers, or winter-rain winters and dry, warm summers 

(Mediterranean). Tree species diversity is low in temperate forests and woodlands 

(Whittaker 1975).

Boreal Forest & Woodland contains primarily needle-leaved evergreen trees, 

with or without boreal broad-leaved deciduous trees. Structure varies from tall, 

closed canopy (but rarely exceeding 15 m) to open, low (<5 m) subarctic woodlands. 

Nonvascular mosses and lichens may predominate in the ground layer. Winters are 

very cold and vary from arid to moist. Temperate high montane forest may resemble 

Boreal Forest & Woodland (Whittaker 1975).

Environment

Environmental Description: Soil orders in Table 8 are described using the U.S. 

soil orders (Soil Survey Staff 1999). See Brady and Weil (2002) for comparison of 

U.S. soil orders with Canadian and FAO systems.

Distribution

Geographic Range: Temperate forests and woodlands range from the giant forests 

of the Pacific Coast of North America, or the Australian temperate rainforests, to New 

Zealand and Chile, to montane forests in various locations. Temperate forests and 

woodlands occur across much of the United States and southern Canada, in limited 

parts of Mesoamerica, Western Europe, Mediterranean regions, Southeast Asia, southern Australia, and limited parts of Chile. Boreal forests and woodlands occur in the 

northern regions of North America and Eurasia. A few isolated areas may occur in the 

Southern Hemisphere.

Citations

Synonymy: 

= Temperate Forest Biomes (Kuennecke 2008) [Kuennecke includes boreal, cool 

temperate, and warm temperate (Mediterranean) formations as part of his “temperate 

forest biomes” concept.] 

= Temperate and boreal woodlands & scrub (Mucina 1997) [Mucina created this type 

as an organizational category for Braun-Blanquet classes and did not define it as a 

formal type.] 

> Temperate broad-leaved forests and scrub (Rodwell and others 2002) [European 

cool and warm temperate forests and floodplain forests are included in the subclass, 

but boreal forests are excluded.]
60 USDA Forest Service RMRS-GTR-346. 2016.

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

1.B.1. Warm Temperate Forest & Woodland (F018)

Overview

Database Code: 1.B.1 (F018)

Scientific Name: Warm Temperate Forest & Woodland Formation

Common Name (Translated Scientific Name): Warm Temperate Forest & Woodland 

Formation

Colloquial Name: Warm Temperate Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Warm Temperate Forest & Woodland is dominated by 

broad-leaved evergreen trees, sometimes with dwarfed stems and small, sclerophyllous 

leaves (in Mediterranean climates), or various combinations of broad-leaved deciduous, broad-leaved evergreen and needle-leaved evergreen conifer trees. Winters are 

mild (mostly frost free) and may be the rainiest season, springs are temperate-humid, 

summers are hot-dry, and autumn is often dry.

Classification Comments: The warm-temperate Mediterranean regions around the 

world typically contain both the classic Mediterranean scrub (2.B.1. Mediterranean 

Scrub & Grassland Formation (F038)), and the forests and woodlands included 

here. Cool-temperate and warm-temperate forests may be difficult to distinguish, 

but cool-temperate forests are more strongly dominated by broad-leaved deciduous 

trees, and broad-leaved evergreen trees are essentially absent. Braun (1950) includes 

at least parts of these warm-temperate forests in her “Deciduous Forest Formation” 

(the “Southeastern Evergreen Forest Region”), but briefly notes a “Subtropical Broadleaved Evergreen Forest” that includes central Florida southward.

Various ecoregional treatments recognize the distinct vegetation and climate of 

the warm-temperate region, e.g., Brown and others (1998) separates cool-temperate 

from warm-temperate vegetation. Walter (1985) recognizes two warm-temperate 

biomes, the “Zonobiome of the Winter-Rain Region with an Arid-Humid Climate and 

Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the Warm-Temperate 

Humid Climate” (Zone V), distinct from the cool-temperate biome “Zonobiome of 

the Temperate-Nemoral Climate” (Zone VI) and the boreal biome “Zonobiome of the 

Cold-Temperate Boreal Climate” (Zone VIII). Similarly, Schultz (1995) recognizes 

the two warm temperate regions, which he refers to as: “Mediterranean-Type subtropics” (with world distribution shown in his Figure 129) and “Humid subtropics” (with 

world distribution shown in his Figure 171). We prefer the term warm temperate to 
USDA Forest Service RMRS-GTR-346. 2016. 61

subtropics. Schultz states that “apart from the driest sites and those with lowest nutrient contents, all the regions of the Mediterranean Type subtropics were originally 

covered by forests of mostly evergreen sclerophyllous species of trees” and in the 

European Mediterranean region, these were mostly evergreen oak, such as Quercus 

ilex. Today, many of these regions are more typically dominated by sclerophyllous 

shrub formations, as described in 2.B.1 Mediterranean Scrub & Grassland Formation 

(F038).

Similar NVC Types: 

1.A.1. Tropical Dry Forest & Woodland (F003): Broad-leaved evergreen trees may 

be common in Warm Temperate Forest & Woodland (F018), comparable to 

Tropical Dry Forest & Woodland (F003) (i.e., evergreen leaves are typically 

small), but deciduousness in Warm Temperate Forest & Woodland is caused by 

frost, and types are found north or south of 23 degrees N and S latitude.

1.B.2. Cool Temperate Forest & Woodland (F008): More strongly dominated by 

broad-leaved deciduous trees; broad-leaved evergreen trees essentially absent. 

Frost regularly occurs, with snow common in the northern parts of the regions.

1.B.3. Temperate Flooded & Swamp Forest (F026): Warm Temperate Forest & 

Woodland (F018) typically contains well-drained soils and lacks any aquatic 

vegetation, peat or muck layer.

2.B.1. Mediterranean Scrub & Grassland (F038): The vegetation is more 

commonly scrub-shrub, typically sclerophyllous, or with open (sometimes annual-dominated) grasslands and forb meadows. Combinations of dwarf scrubby 

trees less than 2 m tall with low shrubs may grade into Warm Temperate Forest.

2.B.2. Temperate Grassland & Shrubland (F012): Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10 percent cover or 

more, are placed in Warm Temperate Forest & Woodland (F108), but may have 

strong floristic similarities to grasslands.

Diagnostic Characteristics: Broad-leaved evergreen trees, sometimes with 

dwarfed stems, microphyll to small mesophyll leaves, sclerophyllous (Mediterranean); 

or various combinations of broad-leaved deciduous, broad-leaved evergreen or needleleaved evergreen conifer trees. Mild (mostly frost-free) winter, temperate humid 

spring, hot-dry summer, and mild, often dry autumn seasons. Rainy season in winter 

and dry summers (Mediterranean).

Vegetation

Physiognomy and Structure: The vegetation varies from (a) dominance by 

broad-leaved evergreen trees, sometimes with dwarfed stems, and microphyll to small 

mesophyll leaves, with varying levels of sclerophylly (Mediterranean) to (b) various 

combinations of broad-leaved deciduous, broad-leaved evergreen or needle-leaved 

evergreen conifer trees. Natural disturbances include wind and fire. 

Environment

Environmental Description: Climate: Freezing temperatures of short duration are 

expected, generally occurring every year during winter months. The potential growing 

season is more than 200 days with less than an average of 150 days a year subject to 

temperatures below 0 degrees C or chilling fog (Brown and others 1998). Spring is 
62 USDA Forest Service RMRS-GTR-346. 2016.

mild, summers are hot-dry, and autumns are mild and often dry. Rainy season in winter is most strong in Mediterranean climates. Average annual precipitation varies from 

25 to 100 cm (10 to 40 inches).

Soil/substrate/hydrology: Soils are often strongly weathered. Soils are various, with 

Ultisols and Alfisols most common, and productive, but in some regions the soils are 

worn by thousands of years of human use (Soil Survey Staff 1999) (see Brady and 

Weil, 2002, for comparison of U.S. soil orders with Canadian and FAO systems). 

Distribution

Geographic Range: Warm Temperate Forest & Woodland is found in the 

Mediterranean Basin and Mediterranean and warm temperate regions in North 

America (California, Southeast Coastal Plain), Chile, South Africa, Australia, India 

and Southeast Asia.

Citations

Synonymy: 

= Warm Temperate Forest and Woodland (Brown and others 1998)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

1.B.2. Cool Temperate Forest & Woodland (F008)

Overview

Database Code: 1.B.2 (F008)

Scientific Name: Cool Temperate Forest & Woodland Formation

Common Name (Translated Scientific Name): Cool Temperate Forest & Woodland 

Formation

Colloquial Name: Cool Temperate Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Cool Temperate Forest & Woodland includes temperate 

deciduous forest and woodland, temperate needle-leaved forest and woodland, and 

temperate rainforest, dominated by broad-leaved or needle-leaved tree growth forms.

Classification Comments: This formation includes a range of conifer and broadleaved hardwood growth forms. The formation is sometimes restricted to “temperate 

broadleaf forest regions,” but even there, pure conifer stands can occur, (e.g., in 

temperate eastern North America, there are pure conifer stands of Tsuga canadensis

and Pinus strobus). Inclusion of western North American conifer forests in this 

cool-temperate formation rather than the Boreal Forest & Woodland follows that of 

Brandt (2009) and others. Warm-temperate and cool-temperate forest and woodland 
USDA Forest Service RMRS-GTR-346. 2016. 63

formations are very similar, but differences are driven by broad climatic patterns. 

Overlap with boreal forests in the western montane region also presents conceptual 

challenges.

Various ecoregional treatments recognize the distinct vegetation and climate of 

the cool-temperate region, e.g., Brown and others (1998) separate cool-temperate 

from warm-temperate vegetation. Walter (1985) recognizes the cool-temperate biome 

“Zonobiome of the Temperate-Nemoral Climate” (Zone VI) distinct from two warmtemperate biomes, the “Zonobiome of the Winter-Rain Region with an Arid-Humid 

Climate and Sclerophyllic Woodlands” (Zone IV) and the “Zonobiome of the WarmTemperate Humid Climate” (Zone V), and from the boreal biome “Zonobiome of the 

Cold-temperate Boreal Climate” (Zone VIII).

Our approach treats the subalpine forests of the Rocky Mountain region as part of 

1.B.2 Cool Temperate Forest & Woodland Formation (F008), rather than as part of 

1.B.4 Boreal Forest & Woodland Formation (F001), such as done by Whittaker (1975) 

and Brown and others (1998). Our decision is in line with a more biogeographic approach for divisions, and corresponds to that of Rivas-Martinez and others (1999b), 

but is debatable from a structural and climatic perspective. As Chris Lea (pers. comm. 

2012) notes, one could retain lowland and lower montane western coniferous forests 

in Cool Temperate, but move high montane and subalpine to the Boreal formation, to 

which they also have strong floristic and environmental similarities (this would require 

a name change of the latter to something like “Boreal & High Montane” or “Boreal 

& Subalpine” formation). This would have minimal impact on lower level units, 

requiring only a transfer of two current western North America groups (G020 and 

G025) to F001, under a new (western North American) division of F001 and eastern 

North America group G024 (requires a new macrogroup and division, but the description of these would be identical with the existing group description). The only major 

new description for Forests and Woodlands would be a new division description for 

“Western North America High Montane & Subalpine Forest,” within formation F001. 

These forests, fairly simply, contain quaking aspen and lodgepole pine on up through 

the Engelmann spruce-fir types. In the Sierra Nevada, Ponderosa pine, Douglasfir, “mixed conifers” (white fir, etc.) represent the upper limits of 1.B.3 Temperate 

Flooded & Swamp Forest Formation (F026). The Shrubland & Grassland class needs 

no formation-level adjustments, but some lower level adjustments might be needed for 

consistency. We will continue to review this issue as we compare our work with that of 

Eurasian treatments of boreal and cool temperate (nemoral) forests.

Similar NVC Types: 

1.B.1. Warm Temperate Forest & Woodland (F018): Has increasing prominence 

of evergreen broad-leaved trees, and shrubs, and evergreen herb ground layer. 

Snow virtually absent, frost is relatively rare.

1.B.3. Temperate Flooded & Swamp Forest (F026): Cool Temperate Forest & 

Woodland (F008) typically contains well-drained soils and lacks any aquatic 

vegetation, peat or muck layer.

1.B.4. Boreal Forest & Woodland (F001): Greatly simplified set of growth forms, 

primarily more conical-shaped spruce, fir and larch, and simple-leaved boreal 

hardwoods of Betula spp. and Populus spp. Moss layer often very prominent. 

Persistence of snow typically greater than 5 months of the year. Frost possible 
64 USDA Forest Service RMRS-GTR-346. 2016.

in almost any season. These conditions also closely describe North American 

subalpine and high montane forests, but those are treated here with Cool 

Temperate Forest & Woodland because of the floristic, biogeographic and ecological similarities with lower elevation forests. See Brown and others (1998) 

who recognize a “Boreal and Subalpine Forest & Woodland” type.

2.B.2. Temperate Grassland & Shrubland (F012): Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10 percent cover or 

more, are placed in Cool Temperate Forest & Woodland (F008), but may have 

strong floristic similarities to grasslands.

7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Long-rotation 

plantations or woody restoration plantings of Cool Temperate Forest & 

Woodland (F008) with an irregular structure and a largely spontaneous ground 

layer may initially be similar in their early stages of development, especially if 

planted in rows and the understory is strongly manipulated.

Diagnostic Characteristics: This formation contains pure or mixed stands of 

broad-leaved deciduous or needle-leaved evergreen tree growth forms, with a seasonal 

green understory of herbs. The tall shrub layer is variable, and is often broad-leaved 

deciduous, but the short shrub layer may be heath. The moss layer is often sparse, but 

more dominant in cold, rainy and/or high montane needle-leaved evergreen stands. 

Snow may be on the ground between 1 to 6 months of the year (8 months in high 

montane temperate examples).

Vegetation

Physiognomy and Structure: In moist climates and habitats, there are commonly 

five strata: (1) a tree stratum, 15 to 35 m (60 to 100 feet) tall, dominated by broadleaved deciduous and/or needle-leaved evergreen forest, often with a substratum of 

small trees (5 to 15 m tall); (2) a small tree and tall sapling layer (between 2 to 5 m); 

(3) a short shrub layer (<2 m); (4) an herb layer of perennial forbs, including an ecological group that bloom primarily in early spring (in deciduous broadleaf-dominated 

examples); and (5) a ground layer of lichens, clubmosses, and true mosses. Lichens 

and mosses also grow on the trunks of trees. Woody vines (lianas) are not common. 

In dry, and fire-dependent climates and regions, the structure may be simple, with a 

tree layer (>10 percent) and a strong grassy or shrubby ground layer. In western North 

America, structure is more variable, reflecting the range of ecological sites, from high 

mountains and valleys, to coastal rainforests with a variety of mesoclimates. Structural 

variability ranges from short-statured conifers, with a sparse understory and heavy 

duff layer, to the tallest and largest trees in the world in moist to wet climates, with 

shrub, herb and moss growth forms prominent (Whittaker 1975).

Many of the genera, previously part of an Arcto-Tertiary Geoflora, are common 

to all three of the disjunct Northern Hemisphere broadleaf expressions of this biome. 

Included among these genera are Quercus (oak), Acer (maple), Fagus (beech), 

Castanea (chestnut), Carya (hickory), Ulmus (elm), Tilia (basswood or linden), 

Juglans (walnut), and Liquidambar (sweetgum). Different species of these genera occur on each continent. In the Southern Hemisphere different sets of genera and species 

are found. Western North America contains a much reduced set of hardwood genera 

and expanded conifer diversity (Abies, Picea, Pinus, Pseudotsuga, Thuja, Tsuga). 

Transitions to the boreal forests are also apparent.
USDA Forest Service RMRS-GTR-346. 2016. 65

The temperate regions of the Southern Hemisphere differ from their northern 

counterparts. Distinctions between warm temperate and cool temperate are much 

contracted (e.g., in parts of the evergreen southern beech Nothofagus forests in South 

America, Australia and New Zealand). 

Environment

Environmental Description: Climate: This formation is associated with cooler 

continental and oceanic temperate climates (Koeppen Dca, Dcb, and Do, and Cfb). 

There is a growing season of approximately 100 to 200 days, confined to late spring 

and summer when freezing temperatures are infrequent or absent. The 50 to 250 cm 

(20 to 100 inches) of precipitation are distributed evenly throughout the year. The nongrowing season is due to temperature-induced drought during the cold winters.

Soil/substrate/hydrology: Soils are sometimes referred to as “gray forest soils,” 

where silicate clay minerals accumulate in the B horizon. Some soils (Alfisols) have 

relatively high natural fertility; others are more leached, due to higher precipitation 

levels (Ultisols) and more common in the warmer parts of the region. Other orders in 

the U.S. system include Spodosols in the more northern regions and Inceptisols (Soil 

Survey Staff 1999) (see Brady and Weil 2002 for comparison of U.S. soil orders with 

Canadian and FAO systems).

Distribution

Geographic Range: This formation is most prominent in the Northern Hemisphere, 

where it occurs in four major, disjunct expressions in (1) western and central 

Europe, (2) eastern Asia, including Korea and Japan, (3) eastern North America, and 

(4) western North America. Cool temperate forests may occur as minor components 

of southern and montane New Zealand and in Australia, especially Tasmania. Cool 

temperate forests also occur in Chile.

Citations

Synonymy: 

> Cool Temperate Forest (Brown and others 1998) (Brown and others place the 

subalpine forests of the montane regions in their “Boreal and Subalpine Forest 

and Woodland” type.) 

< Taiga or Subarctic - Subalpine needle-leaved forests (biome type 6) (Whittaker 

1975) [Whittaker combines the subalpine forests of the temperate region with 

boreal forests.] 

> Temperate deciduous forests (biome type 4) (Whittaker 1975)

> Temperate evergreen (needle-leaved) forest (biome type 5) (Whittaker 1975) 

[Whittaker includes both temperate evergreen broadleaf and temperate evergreen needle-leaved forest in this biome type, but notes the distinction between 

the two in Plate 4.] 

> Temperate rain forests (biome-type 3) (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012) after R.H. Whittaker (1975)

Author of Description: D. Faber-Langendoen

Acknowledgments: Todd Keeler-Wolf, Ken Baldwin, Chris Lea

Version Date: 26 Aug 2014
66 USDA Forest Service RMRS-GTR-346. 2016.

1.B.3. Temperate Flooded & Swamp Forest (F026)

Overview

Database Code: 1.B.3 (F026)

Scientific Name: Temperate Flooded & Swamp Forest Formation

Common Name (Translated Scientific Name): Temperate Flooded & Swamp Forest 

Formation

Colloquial Name: Temperate Flooded & Swamp Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Temperate Flooded & Swamp Forest is a tree-dominated 

wetland influenced by minerotrophic groundwater, either on mineral or organic (peat) 

soil, found in mid latitudes of the globe.

Classification Comments: No distinction is made between warm versus cool 

temperate floodplain and swamp forests, because they do not have the same degree of 

change from broad-leaved evergreen to broad-leaved deciduous trees observed in uplands. Separation of temperate wetland from upland forests requires consideration of 

soils, vegetation and hydrology. At the wettest extremes, these forests are continuously 

flooded and aquatic vegetation growth forms may dominate the herb or field layer. 

Otherwise, these forests may be saturated and a peat layer may form. There are also 

practical user and ecological benefits to distinguishing wetland forests from upland 

forests at the formation level.

Similar NVC Types: 

1.B.1. Warm Temperate Forest & Woodland (F018): These typically contain welldrained soils, and lack any aquatic vegetation, peat or muck layer.

1.B.2. Cool Temperate Forest & Woodland (F008): These typically contain welldrained soils, and lack any aquatic vegetation, peat or muck layer.

1.B.5. Boreal Flooded & Swamp Forest (F036): Temperate Flooded & Swamp 

Forest (F026) less often contains a sphagnum peat layer and is more commonly 

dominated by hardwood species.

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013): 

Tall shrub swamps share many structural and habitat similarities to hardwood 

tree swamps, especially during the tree regeneration stage.

Diagnostic Characteristics: Temperate Flooded & Swamp Forest is defined as 

a tree-dominated wetland in a temperate climate that is influenced by minerotrophic 

groundwater, either on mineral or organic soils. The vegetation is dominated by broadleaved or needle-leaved trees, generally over 10 percent cover, and the substrate is 

either a wood-rich peat or a mineral soil on floodplains.

Vegetation

Physiognomy and Structure: Temperate Flooded & Swamp Forest is a forested 

wetland and peatland. These swamps are defined as tree-dominated wetlands that 
USDA Forest Service RMRS-GTR-346. 2016. 67

are influenced by minerotrophic groundwater. The vegetation is dominated by either 

broad-leaved or needle-leaved trees generally over 10 percent cover, and a wood-rich 

peat or a mineral soil on floodplains (National Wetlands Working Group 1997).

There are three general physiognomic variants of forested swamps: coniferous 

swamps, broad-leaved deciduous (hardwood) swamps, and broad-leaved evergreen 

(hardwood) swamps. Mixtures of the above can also be described. Shading of the 

understory tends to favor shade-tolerant species. In cool-temperate regions, hardwood 

swamps generally occur in somewhat richer conditions, giving way to shrub swamps 

and marshes in somewhat wetter locations. Coniferous swamps occur across a wider 

range of trophic levels from rich to poor (National Wetlands Working Group 1997).

Environment

Environmental Description: Soil/substrate/hydrology: In swamp forests, the water 

table is often below the major portion of the ground surface, and the dominant ground 

surface is at the hummock ground surface, that is; 20 cm or more above the average 

summer groundwater level. It is the aerated (or partly aerated) zone of substrates 

above the water that is available for root growth of trees. These temperate swamps 

are not as wet as marshes, fens and the open bogs. The drier treed swamps grade into 

upland forest on mineral soil, and the wettest treed swamps grade into scrubby treed 

fen, which is wetter with less tree canopy cover. Scrubby tree fens may grade into tall 

shrub swamps, but they are somewhat drier and have at least 10 percent tree canopy 

cover (National Wetlands Working Group 1997).

Flooded forests (sometimes called riverine or riparian swamps) have a more 

dynamic water table, with seasonal flooding inundating the vegetation for short 

(<7 days) to long (>1 month) periods. They are found along rivers, streams, and lakes. 

They are subject to dramatic water fluctuations, seasonal flooding, and an influx of 

sediment and mineral enrichment during high water periods. Peat accumulation is 

usually shallow, often less than 40 cm, but depths of 1 m can exist (National Wetlands 

Working Group 1997).

The temperate flooded and swamp forest occurs on mineral soils as well as on peat. 

In the cool temperate regions, the texture of underlying mineral soils is variable, ranging from clays to sands, and they frequently are Gleysols. On sands, iron-rich ortsteins 

or fragipans are often present, acting as impermeable layers that impede water drainage. Swamps on mineral soils tend to accumulate peat by paludification. When organic 

soils develop, they are Histosols (U.S. system) or Mesisols or Humisols (Canadian 

system) that are rich in woody peat, at least in the surface layers [see Brady and Weil 

(2002) for a comparison of U.S. soil orders with Canadian and FAO systems]. Swamps 

on peat have developed either by a basin-filling process or by paludification of previously drier mineral soils. In the basin-filling process, the previous ecosystem was a 

marsh or fen, whereas in paludification the swamp has developed over an older, dry 

upland forest on mineral soil (National Wetlands Working Group 1997).

The nutrient regime in swamps is highly variable, ranging from base-rich conditions 

with pH above 7.0, to base-poor conditions where pH can be in the range of 4.5 or 

lower. Temperate swamp forms may be recognized based on the base-rich/pH gradient, 

i.e., calcareous rich (eutrophic), intermediate (mesotrophic), and poor (oligotrophic) 

(National Wetlands Working Group 1997).
68 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: These forested wetlands are widely distributed throughout the 

mid-latitudes around the globe.

Citations

Synonymy: 

> Cold Temperate Swamp & Riparian Forest (Brown and others 1998) [Cool- and 

warm-temperate forested wetlands are distinguished, based on climate.] 

>< Swamp (National Wetlands Working Group 1997) [This type includes tree swamps 

with greater than 30 percent cover, boreal and temperate swamps, and both tree and 

tall-shrub (>1 m) swamps.] 

> Warm Temperate Swamp & Riparian Forest (Brown and others 1998) [Cool- and 

warm-temperate forested wetlands are distinguished, based on climate.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014

1.B.4. Boreal Forest & Woodland (F001)

Overview

Database Code: 1.B.4 (F001)

Scientific Name: Boreal Forest & Woodland Formation

Common Name (Translated Scientific Name): Boreal Forest & Woodland 

Formation

Colloquial Name: Boreal Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Boreal Forest & Woodland (or taiga) is dominated by 

needle-leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous hardwoods that cover the northern regions of North America and Eurasia, with 

extended cold winters and short mild summers.

Classification Comments: The Braun-Blanquet approach generally recognizes 

the Vaccinio-Piceetea class of vegetation as synonymous with Eurasian and North 

American boreal and sub-boreal coniferous forests, including both upland boreal 

forests and forested swamps (Peinado and others 1998; Spribille and Chytrý 2002; 

Kolbek and others 2003); however, Rivas-Martinez and others (1999b) separated the 

North American Boreal Forest & Woodland into a separate class, distinct from both 

European boreal forests and western temperate forests.
USDA Forest Service RMRS-GTR-346. 2016. 69

Various ecoregional treatments recognize the distinct vegetation and climate of the 

boreal region, compared to the temperate region. Brown and others (1998) separates 

arctic-boreal from both cool-temperate and warm-temperate vegetation. Walter (1985) 

recognizes the boreal biome “Zonobiome of the Cold-temperate Boreal Climate” 

(Zone VIII), distinct from the cool-temperate biome “Zonobiome of the TemperateNemoral Climate” (Zone VI) and two warm-temperate biomes, the “Zonobiome of 

the Winter-Rain Region with an Arid-Humid Climate and Sclerophyllic Woodlands” 

(Zone IV) and the “Zonobiome of the Warm-Temperate Humid Climate” (Zone V).

Some authors extend the North American Boreal Forest & Woodland southward 

into the southern Rocky Mountains and/or Appalachian Mountains (e.g., Brown and 

others 1998; Kuennecke 2008; Whittaker 1975), primarily because of the spruce-fir 

zones that occur in those ranges. But the more temperate climate, increasingly diverse 

conifer and hardwood growth forms, biogeographic patterns and distinctive species 

suggest that they can satisfactorily be placed in a temperate formation, where they 

extend up to the treeline in the subalpine regions (see also Rivas-Martinez and others 1999b). However, biogeographic comparisons across larger regions, including 

biome or formation scales, and which can be done at the genus level and above (e.g., 

McLaughlin 2007), suggest a greater similarity of high-elevation Engelmann sprucefir in the Rocky Mountains with that of the boreal. But similarities are less strong in 

the eastern deciduous region, where red spruce-fir forests share more species with the 

eastern temperate region. Chris Lea (pers. comm. 2012) notes that there are a number 

of subdominant species common to North American high montane/subalpine forests, 

North American boreal forests, and Eurasian boreal forests (a number of Vaccinium

spp., Linnaea borealis, Carex aquatilis, Carex utriculata, etc.), and at least one 

dominant tree species (Populus tremuloides) that is common to North American high 

montane/subalpine and North American boreal forests. Additionally, many fauna species (lynx, pine marten, pine grosbeak, golden-crowned kinglet, crossbills, etc.) show 

similar species distribution patterns. But many of these species also have considerable overlap in the temperate zone. We will continue to review this issue with North 

American and Eurasian colleagues.

Similar NVC Types: 

1.B.2. Cool Temperate Forest & Woodland (F008): 

1.B.5. Boreal Flooded & Swamp Forest (F036): 

7.A.2. Intensive Forestry Plantation & Agroforestry Crop (F043): Long-rotation 

plantations or woody restoration plantings of Boreal Forest & Woodland (F001) 

with an irregular structure and a largely spontaneous ground layer may initially 

be similar in their early stages of development, especially if planted in rows and 

the understory is strongly manipulated.

Diagnostic Characteristics: Boreal Forest & Woodland is dominated by needleleaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous 

hardwoods, with extended cold winters and short mild summers. Tree height rarely 

exceeds 15 m, and may be as low as 2 m in subarctic conditions. Lichens and mosses 

frequently dominate the ground layer.
70 USDA Forest Service RMRS-GTR-346. 2016.

Vegetation

Physiognomy and Structure: Boreal Forest & Woodland is dominated by needleleaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous 

hardwoods. Lichens and mosses often dominate the ground layer. The structure of 

Boreal Forest & Woodland varies from closed forest to lichen woodland and foresttundra. Closed forests dominate the southern boreal zone; lichen woodlands dominate 

the northern regions; and isolated forest-tundra patches occur in the tundra zone near 

or just above treeline (Elliott-Fisk 2000). Boreal forests are a disturbance-based forest, 

with fires and insect outbreaks as primary disturbances. Tree species diversity is very 

low. Evergreen spruce (Picea), fir (Abies), and deciduous larch (Larix) are common 

distinctive genera, as are broad-leaved deciduous aspen (Populus) and birch (Betula) 

(Whittaker 1975). 

Environment

Environmental Description: According to Brandt (2009), the boreal zone’s northern boundary in both North America and Eurasia is generally the southern limit of the 

tundra; its southern boundary generally coincides with the northern limit of temperate 

forests, or grasslands (steppes).

Climate: There are lengthy periods of freezing temperatures with the coldest 

month isotherm of 3 degrees C, and the growing season generally averaging less than 

100 days, occasionally interrupted by nights of below freezing temperatures. Snow 

may be present for extended periods (7 to 10 months) and soils are typically frozen in 

winter. Annual precipitation is 38 to 50 cm (15 to 20 inches). In North America, the 

northern boundary of the forest corresponds to the July isotherm of 13 degrees C, with 

departures due to montane or maritime influences (Elliott-Fisk 2000). The southern 

boundary in central and eastern Canada corresponds approximately with the 18 degree 

C July isotherm, but in the west the forest border shifts to slightly cooler regions with 

higher precipitation (Elliott-Fisk 2000). These broad-scale climatic factors are modified by local and regional topography, climates and soils.

Brandt (2009, and Table 2 therein) characterizes the limits of boreal forests based 

on their dominance by “cold-tolerant” trees species, i.e., tolerant of temperatures of 

minus 80 degrees C or lower (primarily within Abies, Larix, Picea, or Pinus but also 

Populus and Betula). Temperate forests are characterized by “cold-intolerant” species, 

i.e., they require temperatures above minus 45 degrees C to survive. A number of 

temperate species have “intermediate cold-tolerance,” common to the cool-temperate 

forest. Regions of the landscape where both species co-occur is sometimes referred 

to as the “hemiboreal subzone,” that is, the northern parts of the cool-temperate 

zone where cold-intolerant tree species, cold-tolerant tree species, and species with 

intermediate cold-tolerance co-occur, and with the cold-tolerant species contributing 

substantially to the forest cover. Brandt’s information provides the cold-tolerance 

limits of these species, but equally valuable in understanding the temperate versus 

boreal distinction would be the warm-tolerance limits. For example, in North America, 

Picea mariana appears to be less warm tolerant than Pinus banksiana, but both have 

the same cold tolerance.
USDA Forest Service RMRS-GTR-346. 2016. 71

Soil/substrate/hydrology: Most boreal soils were subject to extensive glaciations 

(excluding parts of the Yukon Territory, the Northwest Territories, and Alaska). Soils 

are somewhat poorly to excessively drained. They are the result of podzolization, 

which is a consequence of low temperatures and excess precipitation above that of 

evapotranspiration. Soils often contain a sandy ash-colored A horizon, with an accumulation of iron and aluminum with organic matter in the B horizon. Soils are 

generally of low fertility, as nutrients are also removed from the upper horizons. 

With the low temperatures, organic matter decomposes slowly, resulting in acidic soil 

conditions and low nitrogen and mineral levels (Elliott-Fisk 2000; Kuennecke 2008). 

Permafrost is absent or typically occurs less than 100 cm below the surface in the 

Boreal Forest & Woodlandzone. Spodosols are most common; Inceptisols, Histosols, 

and Entisols occasional (Soil Survey Staff 1999) (see Brady and Weil 2002 for a comparison of U.S. soil orders with Canadian and FAO systems).

Distribution

Geographic Range: Boreal Forest & Woodland is found in North America from 

Greenland to Newfoundland and across northern Canada into Alaska, and in Eurasia, 

throughout most of Scandinavia and Russia, and parts of China, Kazakhstan, and 

Mongolia (Brandt 2009). It is absent from the Southern Hemisphere.

Citations

Synonymy: 

 = Linnaeo americanae-Piceetea marianae (Rivas-Martínez and others 1999b) [The 

concept of Boreal Forest & Woodland as applied within North America closely 

corresponds to the concept here. The authors also appear to be the first in the BraunBlanquet tradition to recognize a distinct North American Boreal Forest & Woodland 

class.] 

< Vaccinio-Piceetea (Peinado and others 1998) [The authors discuss the full diagnostic floristic composition of boreal forests across the Northern Hemisphere, and then 

focus on North America. They extend the Boreal Forest & Woodland further south 

(into the temperate-montane and cool-temperate regions of western and eastern North 

America) than the concept provided here.] 

< Boreal Forest & Woodland Biome (Kuennecke 2008) [The author provides a general introduction to the entire boreal forest, but in North America extends the concept 

into the Southern Rockies and Appalachian Mountains.] 

= Taiga and Boreal Forest & Woodland (Elliott-Fisk 2000) [The treatment is restricted 

to North America.] 

< Taiga or Subarctic-Subalpine needle-leaved forests (biome-type 6) (Whittaker 1975) 

[Whittaker combines the subalpine forests of the temperate region with boreal forests.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments: Ken Baldwin, Chris Lea

Version Date: 26 Aug 2014
72 USDA Forest Service RMRS-GTR-346. 2016.

1.B.5. Boreal Flooded & Swamp Forest (F036)

Overview

Database Code: 1.B.5 (F036)

Scientific Name: Boreal Flooded & Swamp Forest Formation

Common Name (Translated Scientific Name): Boreal Flooded & Swamp Forest 

Formation

Colloquial Name: Boreal Flooded & Swamp Forest

Hierarchy Level: Formation

Placement in Hierarchy: 1.B. Temperate & Boreal Forest & Woodland (S15)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Boreal Flooded & Swamp Forest is a tree-dominated 

wetland influenced by minerotrophic groundwater (rarely ombrotrophic), either on 

mineral or organic (peat) soil, found in northern, high latitudes of North America and 

Eurasia, with extended cold winters and short mild summers.

Classification Comments: Subarctic and arctic (polar) flooded and swamp forests, 

including willow swamps (though these may not exceed 2 m), belong in this formation. Forested bogs and fens (>10 percent canopy) are also included here.

Similar NVC Types: 

1.B.3. Temperate Flooded & Swamp Forest (F026): These forests less often contain a sphagnum peat layer and are more commonly dominated by hardwood 

species.

1.B.4. Boreal Forest & Woodland (F001): These typically contain better drained 

soils, lack any aquatic vegetation or muck layer, and, if a peat layer is present, 

it is shallow (<40 cm).

2.C.2. Temperate to Polar Bog & Fen (F016): Boreal Flooded & Swamp Forest 

(F036) includes forested bogs with greater than 10 percent tree cover, along 

with poor swamps.

Diagnostic Characteristics: Boreal Flooded & Swamp Forest is defined as a 

tree-dominated wetland in a boreal climate that is influenced by minerotrophic 

groundwater, either on mineral or organic (peat) soils; less commonly, they occur in 

transitional floodplain habitats. The vegetation is dominated by over 10 percent cover 

from needle-leaved trees and the wood-rich (less commonly sphagnum-rich) peat that 

this vegetation lays down.

Vegetation

Physiognomy and Structure: These swamps are defined as tree-dominated wetlands that are influenced by minerotrophic groundwater, either on mineral or organic 

soils. The vegetation is dominated by over 10 percent cover by mostly needle-leaved 

trees and the wood-rich peat that this vegetation lays down; less commonly, they occur 

in transitional floodplain habitats (National Wetlands Working Group 1997).

There are two general physiognomic variants of boreal swamps: coniferous (needleleaved) swamps and hardwood (broad-leaved deciduous) swamps. Mixtures of the 
USDA Forest Service RMRS-GTR-346. 2016. 73

above can also be described. The understory contains shade-tolerant forest species. 

Generally in boreal regions, deciduous hardwoods occur in somewhat richer conditions and the deciduous swamps in drier wetland locations. Coniferous swamps occur 

across a wider range of trophic levels from rich to poor (National Wetlands Working 

Group 1997).

Environment

Environmental Description: Soil/substrate/hydrology: The water table is below 

most of the ground surface, and the dominant ground surface is at the hummock, that 

is, 20 cm or more above the average summer groundwater level. It is the aerated (or 

partly aerated) zone of substrates above the water that is available for root growth of 

trees and/or tall shrubs. Boreal swamps are not as wet as marshes, fens, and the open 

bogs. The drier treed swamps grade into upland forest on mineral soil, and the wettest 

treed swamps include tree fen, which is wetter with less tree canopy cover. Tree bogs 

can form on raised bogs, where the sphagnum mat may be relatively dry (National 

Wetlands Working Group 1997).

Boreal Flooded & Swamp Forest occurs on mineral soils as well as on peat. In the 

boreal region, the texture of underlying mineral soils is variable, ranging from clays 

to sands, and they frequently are Gleysols. On sands, iron-rich ortsteins or fragipans 

are often present, acting as impermeable layers that impede water drainage. Swamps 

on mineral soils tend to accumulate peat by the paludification process. When organic 

soils develop, they are Histosols (U.S. system) or Mesisols or Humisols (Canadian 

system) that are rich in woody peat, at least in the surface layers [see Brady and Weil 

2002 for comparison of U.S. soil orders with Canadian and FAO systems]. Swamps on 

peat have developed by a basin-filling process or by paludification of previously drier 

mineral soils. In the basin-filling process, the previous ecosystem was a marsh or open 

fen, whereas in paludification, the swamp has developed over an older, dry upland forest on mineral soil (National Wetlands Working Group 1997).

The nutrient regime in swamps is highly variable, ranging from base-rich conditions with pH above 7.0, to base-poor conditions where pH can be in the range of 4.5 

or lower. Swamp forms may be recognized based on the base-rich/pH gradient, i.e., 

calcareous-rich (eutrophic), intermediate (mesotrophic), and poor (oligotrophic to 

ombrotrophic) (National Wetlands Working Group 1997).

There are two general physiognomic variants of Boreal Swamp & Flooded Forest: 

coniferous (needle-leaved) swamps and hardwood (broad-leaved deciduous) swamps. 

Mixtures of the above can also be described. The understory contains shade-tolerant 

forest species. Generally in boreal regions, deciduous hardwood swamps occur in 

somewhat richer conditions, giving way to shrub swamps and marshes as conditions 

get wetter. Coniferous swamps occur across a wider range of trophic levels from rich 

to poor (National Wetlands Working Group 1997).

Distribution

Geographic Range: Boreal Flooded & Swamp Forest is found in North America, 

from Greenland to Newfoundland and across northern Canada into Alaska, and in 

Eurasia throughout most of Scandinavia and Russia, and parts of China, Kazakhstan, 

and Mongolia (Brandt 2009). It is absent from the Southern Hemisphere.
74 USDA Forest Service RMRS-GTR-346. 2016.

Citations

Synonymy: 

= Boreal Swamp and Riparian Forest (Brown and others 1998)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments: Ken Baldwin

Version Date: 26 Aug 2014

2. Shrub & Herb Vegetation (C02)

Overview

Database Code: 2 (C02)

Scientific Name: Mesomorphic Shrub & Herb Vegetation Class

Common Name (Translated Scientific Name): Mesomorphic Shrub & Herb 

Vegetation Class

Colloquial Name: Shrub & Herb Vegetation

Hierarchy Level: Class

Lower Level Hierarchy Units:

2.A. Tropical Grassland, Savanna & Shrubland (S01)

2.B. Temperate & Boreal Grassland & Shrubland (S18)

2.C. Shrub & Herb Wetland (S44)

Concept Summary

Type Concept Sentence: Grasslands, shrublands, open tree savannas, marshes, 

bogs and fens dominated by broadly mesomorphic (including scleromorphic) shrub 

and herb growth forms (including broad-leaved, needle-leaved, and sclerophyllous 

shrubs, and forb and graminoid herbs) with an irregular horizontal canopy structure, 

mesomorphic trees typically less than 10 percent cover (but tropical tree savannas 

typically less than 40 percent), tropical to boreal and subalpine climates, and wet to 

dry substrate conditions.

Classification Comments: This class includes both non-treed grasslands and 

shrublands, and open tree savannas, where tree canopy cover is typically less than 

10 percent. Non-tropical tree savannas, defined by a strong graminoid layer (>50 percent in UNESCO 1973) and some level of open tree cover (10 to 25 percent cover in 

UNESCO (1973), 10 to 30 percent cover in Nelson (2005), 10 to 50 percent cover 

in Curtis (1959)), often closely resemble open upland grasslands and shrublands, 

especially in grassland regions. Thus, in this particular realm of vegetation, the open 

tree canopy, in combination with the ground layer, helps define savanna vegetation, 

distinct from forests or woodlands (e.g., Nelson 2005). But in many other regions and 

vegetation types (e.g. forested swamps and bogs, longleaf pine woodlands (Peet 2006), 

California oak woodlands (Barbour and others 2007), subarctic woodlands), the role of 

canopy closure varies. Thus, in non-tropical regions, we place generally tree savannas 

where trees > 5 m have > 10 percent cover with woodland and forest. However, Dixon 

and others (2014) suggest that there may be good ecological reasons to treat upland 
USDA Forest Service RMRS-GTR-346. 2016. 75

tropical tree savannas with up to 40 percent tree cover, trees less than 8 m tall, and a 

substantial graminoid layer as part of 2. Shrub & Herb Vegetation (C02), and we allow 

for that option here.

Croplands with a spontaneous ground layer of “weeds,” where the annual rotation 

of crops prevents a persistent ground layer of herbs, are treated in 7. Agricultural & 

Developed Vegetation Class (CCL01). If agricultural practices are abandoned, these 

sites may succeed to more persistent “ruderal” grasslands and shrublands (and forests) 

and would be placed in this class.

Where grasses and shrubs overtop low trees (“brush prairie”), the stands are placed 

here in Shrub & Herb Vegetation. These situations may often occur in grassland 

or cool semi-desert regions (e.g., North American Great Plains or Great Basin). 

Also challenging are some scrub trees, such as juniper (Juniperus spp.) or mesquite 

(Prosopis spp.), which can form shrub-like stands, and are typically less than 5 m tall 

at maturity in parts of their range. Where forms are not easily defined, woody plants 

equal to or greater than 5 m at maturity are considered trees (FGDC 2008). In the 

United States, there are shrubby junipers (Juniperus communis, Juniperus pinchotii) 

that should be treated as shrubs. But pygmy conifers can potentially make 5 m and 

are treated as trees (Pinus edulis, Juniperus scopulorum, Juniperus monosperma, 

Juniperus occidentalis, Juniperus osteosperma).

There is a group of ephemerals that are generally mesomorphic, which can, under 

optimal rainfall conditions, grow on sand, including desert sands and pavement. They 

are adapted to deserts through their seed characteristics. Typically they do not occupy 

extensive deep shifting sands, only margins of sandsheets and more stable sands. 

They rely on seedbanks that may persist for decades in the sand and germinate under 

optimal winter or summer episodes of heavy rains. These are treated here as part of 

the mesomorphic shrub and herb class. Examples of psammophytic species include 

some sand verbenas (Abronia spp.) and several Asteraceae (e.g., Dicoria canescens, 

Palafoxia spp., etc.).

Similar NVC Types: 

3. Desert & Semi-Desert (C03): Desert grassland growth forms currently are not 

distinguished from temperate (mesomorphic) grasslands, and, where these 

grasslands lack xeromorphic shrubs, there may be no growth forms that provide 

xeromorphic criteria. In addition, the transition from dry temperate grassland 

to cool or warm semi-desert may be challenging, and rely more on floristics 

than growth forms. Desert grasslands lacking many xeromorphic associates in 

the sense of those in the southwestern United Staters (New Mexico, Texas, or 

Arizona) may be considered monsoonal and, could be considered mesomorphic 

grasslands. Further review is needed.

4. Polar & High Montane Scrub, Grassland & Barrens (C04): Distinguishing cryomorphic vegetation from mesomorphic can be a challenge in both arctic and 

alpine regions. Here we allow mesomorphic extensions into the cryomorphic 

climatic zone to be retained in the mesomorphic class (e.g., boreal mesomorphic tall willow shrublands along arctic drainageways are excluded from 

Cryomorphic Vegetation), whereas prostrate or dwarf willow species are treated 

as part of the cryomorphic class.
76 USDA Forest Service RMRS-GTR-346. 2016.

6. Open Rock Vegetation (C06): Sparsely vegetated sand dunes are similar to 

this class, but the vascular species present are typically mesomorphic, with 

adaptations to rooting in sand (psammophytic); crustose lichens and ferns are 

typically absent. Unstable scree may also contain scattered mesomorphic herbs 

and little to no nonvascular vegetation, but for now are retained in this class.

7. Agricultural & Developed Vegetation (CCL01): Agricultural grasslands in this 

class may be regularly mowed, hayed or grazed, and have an atypical “cut” 

structure periodically throughout the season, and may be dominated by exotic 

grasses. Developed grasslands in this class have a very regularly, often very 

low, cropped structure because of regular cutting or mowing (even weekly during the growing season).

Diagnostic Characteristics: Shrubs and herbs in non-tropical savanna regions 

are at least 10 percent cover, mesomorphic trees less than 10 percent cover, and the 

majority of cover is comprised of mesomorphic shrub (broad-leaved, needle-leaved, 

sclerophyllous, and rosette shrubs) and herb (forbs and graminoids) growth forms 

compared to xeromorphic or cryomorphic shrub and herb growth forms. The vegetation structure has irregular horizontal canopy spacing. In tropical upland savanna 

regions, trees typically have up to 40 percent cover, are less than 8 m tall, and the 

vegetation has a substantial graminoid layer.

Vegetation

Physiognomy and Structure: Growth Forms: Stands are dominated by any broadly mesomorphic (including scleromorphic) herb or shrub growth form, with or without 

a layer of nonvascular growth form (i.e., lichen, moss). Mesomorphic shrubs include 

broad-leaved, needle-leaved, sclerophyllous, and palm shrubs. Semi-shrubs are typically absent. Mesomorphic herbs include forbs (including flowering forbs, ferns, and

succulent forbs) and graminoids. These herbaceous growth forms are not exclusive to 

the mesomorphic class, and more work is needed to assess whether additional herbaceous growth form types should be recognized that may be distinctive for this class.

Structure: Stands have irregular shrub or herb horizontal stem spacing, typically 

with a moderately open to closed shrub or herb layer. There is less than10 percent mesomorphic tree cover (less than 40 percent in tropical tree savannas), and the majority 

of shrub and/or herb growth forms are mesomorphic, typically exceeding 10 percent 

cover (but may be as low as 1 to 10 percent cover). Nonvascular and dwarf-shrub 

growth forms may vary from 0 to 100 percent, and tree seedlings or saplings may be 

present at any level of cover if they are below the predominant heights of the shrubs 

and herbs. At maturity, dominant shrubs and herbs are typically greater than 0.3 m 

(sometimes over 5 to 10 m).

Environment

Environmental Description: Climate: Shrublands and grasslands occur in the 

following Trewartha Climatic zones:(Aw = Tropical wet-dry; Am = Tropical wet-dry 

(“monsoon”); BS = Semiarid [BSh, hot semiarid]; BW = Arid Specifically BWh (hot 

Subtropical High desert); BWn ( or Bn) ) Climates (cool coastal deserts) “n” for nebel 

= fog; Cs = Subtropical dry summer “Mediterranean”;Do = Oceanic “Marine West 

Coast”;BS = Semiarid (BSk, cool semiarid);Dc = Continental.
USDA Forest Service RMRS-GTR-346. 2016. 77

Soil/substrate/hydrology: Dry to moist soils. Sand dune, including psammophytic, 

vegetation is placed here in mesomorphic shrub and herb vegetation. Kudryashov 

(2010) describes the characteristics of “psammophyte” (i.e., plants that thrive in shifting sands, primarily in deserts, and that have a number of adaptations that enable them 

to exist on wind-blown sands).

Distribution

Geographic Range: In non-tropical regions, this type is most common in the 

Bailey (1989) Steppe Divisions of the Dry Domain, the Subarctic Divisions of the 

Polar Domain, and is less common in other divisions of Polar or Dry Domains. In the 

tropics, this type is uncommon in Humid Tropical and Humid Temperate Domains, but 

common in semi-humid Tropical Domains (savannas).

Citations

Synonymy: 

= Grassland Biomes (Woodward 2008) [Approximately equivalent. Although only 

grasslands are mentioned in the name, shrublands are considered as part of the 

concept.] 

> Range Land (Anderson and others 1976) [The authors exclude wet grasslands and 

shrublands, treating them as part of their “Wetlands” category.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 26 Aug 2014

2.A. Tropical Grassland, Savanna & Shrubland (S01)

Overview

Database Code: 2.A (S01)

Scientific Name: Tropical Grassland, Savanna & Shrubland Subclass

Common Name (Translated Scientific Name): Tropical Grassland, Savanna & 

Shrubland Subclass

Colloquial Name: Tropical Grassland, Savanna & Shrubland

Hierarchy Level: Subclass

Placement in Hierarchy: 2. Shrub & Herb Vegetation (C02)

Lower Level Hierarchy Units:

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019)

2.A.2. Tropical Montane Grassland & Shrubland (F017)

2.A.3. Tropical Scrub & Herb Coastal Vegetation (F024)

Concept Summary

Type Concept Sentence: Tropical Grassland, Savanna & Shrubland is dominated 

by mesomorphic grasses and shrubs, with or without scattered trees (but trees typically less than 40 percent cover), ranging from tropical coastal to inland lowland and 

montane grasslands and shrublands. Stands are found in warm tropical continental 
78 USDA Forest Service RMRS-GTR-346. 2016.

climates, typically from the equator to about 23 degrees N and S latitude, with low or 

pronounced rainfall seasonality, with either one or two short dry seasons, or one long 

dry season, but frost virtually absent.

Classification Comments: Dixon and others (2014) and others suggest that there 

may be good ecological reasons to treat upland tropical tree savannas, with up to 40 

percent tree cover, trees greater than 8 m tall, and a substantial graminoid layer, as part 

of 2. Shrub & Herb Vegetation (C02), and we allow for that option here. By contrast, 

in non-tropical regions, we place tree savannas with woodland and forest.

Similar NVC Types: 

1.A. Tropical Forest & Woodland (S17): Where tree cover exceeds 10 percent, 

stands are typically placed in Tropical Forest & Woodland (S17). However, in 

tropical upland savanna regions, stands more typically exceed 40 percent tree 

cover, trees are greater than 8 m tall, tree regeneration is abundant, and there is 

no substantial graminoid layer.

2.B. Temperate & Boreal Grassland & Shrubland (S18): Tropical Grassland, 

Savanna & Shrubland (S18) growth forms have a phenology driven by rain and 

drought, but not frost.

Diagnostic Characteristics: Tropical Grassland, Savanna & Shrubland is dominated by grasses and shrubs, with or without scattered trees (which may have up to 40 

percent cover). Some occur in climates too dry for forest; others depend on soil conditions or fire, or both, rather than climate, but frost is typically absent throughout the 

growing season. The structure is a single, major grass or shrub stratum, or a mix of the 

two, exceeding 10 percent cover, rarely with bare ground (Whittaker 1975).

Vegetation

Physiognomy and Structure: Tropical Grassland, Savanna & Shrubland is dominated by grasses and shrubs, with or without scattered trees (but tree cover less than 40 

percent). Some occur in climates too dry for forest; others depend on soil conditions 

or fire, or both, rather than climate. The structure is a single, major grass or shrub 

stratum, or a mix of the two, exceeding 10 percent cover, rarely with bare ground 

(Whittaker 1975). The range of variation in upland formations corresponds to Lowland 

versus Montane versus Coastal patterns of variation. 

Environment

Environmental Description: Stands are found in warm tropical continental climates, with low or pronounced rainfall seasonality, with either one or two short dry 

seasons, or one long dry season, but in all cases frost virtually absent.

Distribution

Geographic Range: This subclass is found widely throughout lowland and montane upland habitats of the tropical latitudes, from the equator to about 23 degrees N 

and S.

Citations

Synonymy: 

= Tropical Savanna Biome (Woodward 2008) [Woodward includes upland lowland 

and montane grassland.]
USDA Forest Service RMRS-GTR-346. 2016. 79

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

2.A.1. Tropical Lowland Grassland, Savanna & 

Shrubland (F019)

Overview

Database Code: 2.A.1 (F019)

Scientific Name: Tropical Lowland Grassland, Savanna & Shrubland Formation

Common Name (Translated Scientific Name): Tropical Lowland Grassland, 

Savanna & Shrubland Formation

Colloquial Name: Tropical Lowland Grassland, Savanna & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.A. Tropical Grassland, Savanna & Shrubland (S01)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Lowland Grassland, Savanna & Shrubland is 

characterized by a ground layer with a more-or-less continuous grass or graminoid 

layer, or mixed forb layer that may have up to 80 to 90 percent shrub cover and/or 

typically less than to 40 percent tree cover, and less than 8 m tall. Shrubs are predominantly broad-leaved evergreen and deciduous, but sclerophyllous growth forms are 

also included. Stands are found in warm tropical continental climates, with low or 

pronounced rainfall seasonality, with either one or two short dry seasons, or one long 

dry season.

Classification Comments: “Savanna” refers to a type of vegetation where grasses 

form a complete ground cover but there may also be an upperstory of scattered trees, 

shrubs, or palms. The word savanna comes from a Carib word for a treeless plain covered with grass (i.e., a grassland). The Spanish adopted the term when they colonized 

the West Indies, and they introduced it to other western languages. Today, among 

vegetation scientists, the meaning has changed somewhat: “savanna” refers to a type 

of vegetation where grasses form a complete ground cover; an upperstory of scattered 

trees, shrubs, or palms is usual (thus tropical grasslands, with or without scattered 

trees, are referred to as savannas). The term is mostly reserved to describe tropical 

vegetation, and the popular image of tropical savanna comes from the African part of 

the biome, where vast grasslands dotted with umbrella-shaped deciduous trees and 

thorny shrubs are inhabited by herds of large grazing animals. But it can also include 

low-statured woody vegetation with a strong graminoid layer, such as the Neotropical 

cerrado, or scrubby forms of African savanna. 

The term savanna has also been applied to vegetation of similar structure in temperate zones, but there the term grassland or prairie is used for non-treed grasslands, and 

savanna is only used when scattered trees are present (between 10 and 30 percent); 
80 USDA Forest Service RMRS-GTR-346. 2016.

these stands are placed in 1. Forest & Woodland Class (C01). Some scientists use the 

term savanna landscape to describe a group of interrelated grassland, gallery or riparian forest, swamps, and/or marsh vegetation.

Savannas in tropical Asia are most likely “derived” and not natural savannas. This 

means that they are the result of human activities such as logging, burning, and the 

grazing of livestock, any or all of which altered tropical dry (or deciduous) forests that 

once grew in the area. Since they are not considered natural, the tropical savannas of 

India and Southeast Asia are not described in this report (Woodward 2008).

The Caribbean pine savannas, like other treed savannas, should be placed according to the percent coverage of the tree layer. Where grasses and shrubs overtop low 

trees (“brush prairie”), the stands are placed here in Shrub & Herb Vegetation. In 

the tropics, the separation between the lowland shrubland and grassland and warm 

semi-desert thorn woodland/shrubland should be guided by the presence of succulents, 

small-leaved and thorny shrubs and trees, and other xeromorphic growth forms, characteristic of the latter.

Savannas that flood seasonally are common in the tropics, especially in South 

America (the Llanos, Beni, and Pantanal). The extensive hydrologic network combined with topographic complexities and precipitation gradients cause a complex 

spatial mosaic of upland and seasonally flooded types that might be challenging to 

classify, with waterlogged soils grading into drained soils within very short distances.

This type may extend to nearly treeline (3000 m elevation), covering the lower 

montane region. See description for 2.A.2. Tropical Montane Grassland & Shrubland 

Formation (F017).

Similar NVC Types: 

2.A.3. Tropical Scrub & Herb Coastal Vegetation (F024): Further review is needed 

to describe differences between Tropical Lowland Grassland, Savanna & 

Shrubland (F019), and Coastal Vegetation (F024).

4.A.1. Tropical High Montane Scrub & Grassland (F022): This type is often treated 

broadly to include both tropical montane and high montane vegetation, i.e., all 

vegetation near or above the tropical treeline (e.g., Quinn 2008).

7.B.2. Pasture & Hay Field Crop (CFO05): Tropical Lowland Grassland, Savanna 

& Shrubland (F019) may overlap in composition with pasture grasslands, 

particularly in grassland regions. And in regions where a pastoral tradition has 

existed from 100s to 1000s of years, recognition of native versus agricultural 

grasslands may be challenging.

Diagnostic Characteristics: Shrubs and herbs at least 10 percent cover, mesomorphic trees less than 40 percent cover, and less than 8 m tall, and the majority of cover 

is comprised of mesomorphic shrub (broad-leaved, sclerophyllous, and rosette shrubs) 

and herb (forbs and graminoids) growth forms compared to xeromorphic or cryomorphic shrub and herb growth forms. The vegetation structure has irregular horizontal 

canopy spacing.

Vegetation

Physiognomy and Structure: Stands are dominated by any mesomorphic herb 

or shrub growth form, with or without a layer of nonvascular growth form (i.e., 

lichen, moss). Mesomorphic shrubs include broad-leaved, sclerophyllous, and palm. 
USDA Forest Service RMRS-GTR-346. 2016. 81

Semi-shrubs are typically absent. Mesomorphic herbs include forbs (including flowering forbs and ferns) and graminoids. “Savanna” refers to a type of vegetation where 

grasses form a complete ground cover; an upperstory of scattered trees, shrubs, or 

palms is usual. Stands vary widely from regular shrub or herb horizontal stem spacing 

to irregular, typically with a moderately open shrub layer. There is less than 40 percent 

mesomorphic tree cover, trees are less than 8 m tall, and the majority of shrub and/or 

herb growth forms is mesomorphic, typically exceeding 10 percent cover (but may be 

as low as 1 to 10 percent). Nonvascular and dwarf-shrub growth forms may vary from 

0 to 10 percent, and tree seedlings or saplings may be present at any level of cover, if 

they are below the predominant heights of the shrubs and herbs. At maturity, dominant 

shrubs and herbs are typically greater than 0.3 m (sometimes over 5 to 10 m).

The typical grasses are bunch grasses, some 2 to 4 m high. The blades are tough and 

contain many silica bodies. Savanna grasses use the C4 photosynthetic pathway. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. 

Trees of the savannas, with the exception of the huge Adansonia digitata (baobab), are 

rarely taller than 12 m. Most are only 2 to 6 m tall. A thick bark often defends savanna 

trees against fire. Many can sprout from their roots, another survival tactic in the face 

of frequent burning. In Africa, where grazing by large mammals is a major factor, 

many woody plants are armed with thorns. These same trees and shrubs are apt to have 

tiny leaves and very deep taproots. Other growth forms commonly found in tropical 

savannas include subshrubs and annual forbs and grasses, all well-adapted to strongly 

seasonal environments. The subshrub dies down at the end of one rainy season and 

produces new woody stems at the beginning of the next. Two flowering seasons are 

usual in the Tropical Savanna Biome. Some plants bloom at the very beginning of the 

rainy season even before their leaves have fully developed. Other species bloom in 

the middle of the rainy season or towards its end. Ecologists recognize different types 

of savanna according to the spacing and frequency of trees or other woody plants 

(Woodward 2008). The typical grasses are bunch grasses, some 2 to 4 m high. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. 

Many of the forbs are members of the pea or legume family (Woodward 2008). 

Environment

Environmental Description: Climate: This formation occurs typically within an 

annual precipitation range of 100 to 150 cm though lower and upper extremes are 

around 40 and 200 cm, respectively. The rainfall is seasonal, with either a short (1 to 

3 months) dry season or a long one (5 to 7 months). The wet season can be interrupted by a short period of drought that may last for 1 to 3 weeks. As distance from 

the equator increases, different types of savanna may form distinct zones, a pattern 

that results from the longer and longer dry seasons experienced, and the less and less 

total annual precipitation received the closer an area is to the permanent high pressure 

cells centered near 30 degrees latitude in both hemispheres (Woodward 2008). Mean 

annual temperature is about 22 to 25 degrees C, but can reach 6 degrees C in winter at 

the edges of the tropical distribution range (e.g., southern limit of Cerrado in Brazil, 

eastern southern Africa), with very occasional frosts.

Tropical savannas occur in areas with distinct annual rhythms based on alternating 

wet and dry seasons. Abundant precipitation during the rainy season makes this a 
82 USDA Forest Service RMRS-GTR-346. 2016.

type of tropical humid climate known as the Tropical Wet and Dry Climate (Aw in the 

Koeppen climate classification system), or often simply the Tropical Savanna Climate. 

The rains come during the high sun period, when the Intertropical Convergence Zone 

(ITCZ) is positioned nearby. The ITCZ is the place where the trade winds of the 

Northern and Southern hemispheres meet and force the air to rise and generate rainfall. 

Its position shifts during the year as the vertical rays of the sun migrate between the 

Tropic of Cancer and the Tropic of Capricorn. The low sun season, when the vertical 

rays strike in the opposite hemisphere, is the dry season. There may be 3 to 4 months 

when little or no precipitation falls. Total precipitation within the biome varies from 

100 to 150 cm (40 to 60 inches) to as little as 50 cm (20 inches) a year (Woodward 

2008). The tropical nature of the climate is apparent in the year-round warm temperatures, with frost being an unknown or extremely rare event. The temperature difference 

between the warmest month (usually at the end of the dry season) and the coolest 

month (during low sun) is only 2.8 to 5.5 degrees C (5 to 10 degrees F). The difference 

between daytime and nighttime temperatures is often greater (Woodward 2008). Even 

though a close correlation exists between tropical savannas and the Tropical Wet and 

Dry Climate, climate does not seem to be the main reason most savannas are found 

where they are. Repeated burning, low-nutrient soils, iron-rich hardpans close to the 

surface, and the impacts of large grazing and browsing mammals are also factors in 

the presence and maintenance of many of the world’s tropical grasslands (Woodward 

2008).

Soil/substrate/hydrology: Tropical savanna usually develops on nutrient-deficient, 

acidic soils with aluminum toxicity and pronounced alternation of wet and dry conditions (Woodward 2008).

Soils Comments: Soil formation: Soils in humid tropical climates are exposed 

to high rates of leaching, the dissolving and washing down into the soil column of 

any soluble compound. The typical soil-forming process is one of laterization. The 

amount of leaching that has occurred is related to the age of the land surface. The 

tropical savannas of Brazil and western Africa lie on very ancient surfaces (exposed 

continental shields) that for millions of years have been affected by high temperatures 

and relatively high amounts of rainfall. The bedrock has been deeply weathered, and 

most soluble compounds, including even silica compounds, have been removed. Since 

plant matter decays rapidly in constant warm, moist conditions, essentially no humus 

is available to help bind soluble bases (key plant nutrients) even temporarily. Left behind is a soft residue high in iron oxides and aluminum oxides and lacking most plant 

nutrients. The high amount of iron in the soils gives them a bright red or yellow color. 

Concentrations of aluminum can be high enough that the soil is mined as an ore (the 

ore of aluminum metal is called bauxite). In parts of the Brazilian Highlands, aluminum concentrations are so high as to be toxic to many plants. Native trees and shrubs 

have special adaptations to withstand these challenging conditions (Woodward 2008).

Soils developed on ancient surfaces that are composed of granitic rocks tend to be 

quite acidic (average pH = 4.9), further reducing the ability of the soil to hold nutrient 

bases. Another problem for plant life is the repeated wetting and drying of the ironrich soils that can turn them into a brick-hard layer known as laterite. This hardpan 

prevents root penetration and halts the percolation of water during the rainy season, 

creating waterlogged soils or even temporary pools of standing water. The existence 
USDA Forest Service RMRS-GTR-346. 2016. 83

of laterite can be one reason for the lack of trees in some tropical savanna areas 

(Woodward 2008).

In some parts of the tropics, weathering and leaching have been neither so prolonged nor extreme. In well-drained areas and regions where the crystalline bedrock 

is not as old or has been more recently exposed than described above, soil-forming 

processes more like those of temperate regions (podzolization) are able to take place. 

Over much of eastern and southern Africa, for example, the savanna soils are less 

acidic (pH = 6.2) and somewhat more fertile than on the more ancient shield surfaces 

(Woodward 2008). On base-rich bedrock such as basalt or limestone, soils develop 

that are high in essential plant nutrients such as calcium and magnesium (both are 

bases). They typically have a high clay content that makes them swell during the wet 

season and shrink and crack during the dry season. Such soils have relatively high 

natural fertility and tend to be associated with grass savannas (Woodward 2008).

Soil types: The typical, iron- and aluminum-rich, low-nutrient soils of the ancient 

plateaus of Africa and South America are classified in the U.S. Soil Taxonomy (Soil 

Survey Staff 1999) as Oxisols. “Oxi” refers to the oxides of those two elements that 

are so concentrated by tropical soil-forming processes. Similar soils are also found in 

the Tropical Rainforest Biome. In other classifications, they are known as Latosols or 

lateritic soils (Woodward 2008). Where drainage is better or younger crystalline rock 

forms the parent material of the soils, the soils are Ultisols according to the U.S. Soil 

Taxonomy. “Ulti” means ultimate or last: the last of the nutrients have been removed 

by leaching (Woodward 2008). The more fertile soils developed on basalt or limestone 

and still containing abundant plant nutrients are among the Vertisols of the U.S. Soil 

Taxonomy (Soil Survey Staff 1999). “Vert” means turn. The swelling and shrinking of 

the clay mixes or turns the soil so that no true horizons can form. In other soil classification systems, they are more vividly named “black cracking soils” (Woodward 2008).

Distribution

Geographic Range: This formation type is found in northern South America, western and southwestern Amazon Basin, Guiana Shield, Brazilian Shield, Western Africa 

(Guinea-Congolia/Sudania regional transition zone), sub-Sahel (Sudanian regional 

center of endemism), the Central African Plateau (Guinea-Congolia/Zambezia regional 

transition zone and the Zambezian regional center), and Eastern Africa (Somali-Masai 

regional center of endemism), northern Australia and Indomalaysia. They are typically 

located poleward of the Tropical Rainforest and Tropical Dry Forest biomes and form 

a transition between those forests and the deserts of the subtropics. The boundary 

between forest and savanna is often abrupt.

Citations

Synonymy:

= Tropical Savanna Biome (Woodward 2008)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012) after S. Woodward (2008)

Author of Description: C. Josse and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
84 USDA Forest Service RMRS-GTR-346. 2016.

2.A.2. Tropical Montane Grassland & Shrubland 

(F017)

Overview

Database Code: 2.A.2 (F017)

Scientific Name: Tropical Montane Grassland & Shrubland Formation

Common Name (Translated Scientific Name): Tropical Montane Grassland & 

Shrubland Formation

Colloquial Name: Tropical Montane Grassland & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.A. Tropical Grassland, Savanna & Shrubland (S01)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Montane Grassland & Shrubland is dominated 

by shrubs and herbs with mesomorphic growth forms (predominantly tussock grasses, 

large rosette plants, shrubs with evergreen coriaceous and sclerophyllous-ericoid

leaves, and cushion plants).

Classification Comments: In terms of overall physiognomy, this formation is 

closely related to 4.A.1 Tropical High Montane Scrub & Grassland Formation (F022) 

that has been placed within 4. Polar & High Montane Scrub, Grassland & Barrens 

Class (C04), and many authors would place all of the vegetation described here in that 

formation (e.g., Quinn 2008). The main reason for this split is that in the Tropics, the 

true cryomorphic vegetation, super-páramo and higher elevation puna, are treated in 

4.A. They grow above 4,300 m elevation up to the permanent snowline, with mean 

annual temperatures lesss than 3 degrees C, and soils have cryomorphic features (such 

as cryoturbation). Physiognomic distinctions are mostly based on the ground cover of 

the formation, which is continuous as compared to the low, semi-open coverage of the 

tropical cryomorphic formations.

Still, as defined here, 2.A.2 Tropical Montane Grassland & Shrubland Formation 

(F017) often is found at elevations above 3000 m, which means that 2.A.1. Tropical 

Lowland Grassland, Savanna & Shrubland Formation (F019) extends up to 3,000 m. 

This may be problematic with respect to the use of Montane versus Lowland as used, 

though usually there is a forest band between the two. This formation is near to sometimes above the treeline, but many will associate montane with a mid-elevation forest 

zone, including lower and upper montane forests.

Similar NVC Types: 

4.A.1. Tropical High Montane Scrub & Grassland (F022): Many authors would 

place what is described in Tropical Montane Shrubland, Grassland & Savanna with 

this formation (e.g., Quinn 2008).

Diagnostic Characteristics: Herbaceous perennials (forbs and grasses) and small 

woody shrubs are predominant, with small rosette and large caulirosulate plants with 

arborescent habit also present. The overall structure varies from semi-open to almost 

100 percent coverage. The vegetation structure has irregular horizontal canopy spacing, except for the vast expanses of grassland communities in some locations.
USDA Forest Service RMRS-GTR-346. 2016. 85

Vegetation

Physiognomy and Structure: Tropical Montane Grassland & Shrubland is dominated by shrubs and herbs with mesomorphic growth forms (predominantly tussock 

grasses, large rosette plants, shrubs with evergreen coriaceous and sclerophyllousericoid leaves, and cushion plants). Vegetation structure varies from grasslands, with 

few short woody growth forms, to a closed canopy of shrubs usually not taller than 

1 to 2 m high. Spatially patchy vegetation structure is typical due to both substrate 

heterogeneity and human influence characterized by periodic burning and grazing.

Environment

Environmental Description: Climate: The majority of the area covered by this 

vegetation corresponds to types that occur on tropical mountains above the limit of 

continuous, closed-canopy forest or forestline and below the sub-nival elevations, 

from 3000 to 4500 m (i.e., páramo and puna). The elevation range varies depending 

on the location, but it is the correlation between elevation and a decrease in temperature that, in natural conditions, generates the replacement of forested vegetation 

with grasslands and shrublands. There are other factors, such as the effect of recent 

glaciation periods, and anthropogenic disturbance as well. The variability in elevation 

range goes together with a great variation in climate among locations, but in general, 

the mean annual temperature for this type should be between 3 and 12 degrees C, with 

lower locations reaching a maximum of 14 degrees C average annual temperature, 

the greatest fluctuation in temperature occurring daily rather than seasonally. Due to 

the mountain setting, precipitation is highly variable as well, not only in the annual 

amount but its distribution, with some locales having a marked dry season and others 

more humid throughout the year.

Soil/substrate/hydrology: Given the volcanic origin of several tropical mountains, 

they have volcanic ash soils, with very high organic content and a high water-holding 

capacity. Other uplifts have formed metamorphic, sandstone or limestone ranges, with 

soils varying from shallow to deep, highly humic and forming clayish peat in locations 

with permanently high moisture.

Distribution

Geographic Range: Tropical Montane Grassland & Shrubland occurs in the tropical mountain regions of Central and South America, Africa, Malaysia, including New 

Guinea, Hawaii, lower ranges in the Caribbean, and Brazil.

Citations

Synonymy: 

< Tropical Alpine Biome (Quinn 2008) [Quinn includes both the tropical montane and 

tropical high montane scrub band grassland in her type.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: C. Josse

Acknowledgments:

Version Date: 26 Aug 2014
86 USDA Forest Service RMRS-GTR-346. 2016.

2.A.3. Tropical Scrub & Herb Coastal Vegetation 

(F024)

Overview

Database Code: 2.A.3 (F024)

Scientific Name: Tropical Scrub & Herb Coastal Vegetation Formation

Common Name (Translated Scientific Name): Tropical Scrub & Herb Coastal 

Vegetation Formation

Colloquial Name: Tropical Scrub & Herb Coastal Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 2.A. Tropical Grassland, Savanna & Shrubland (S01)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Scrub & Herb Coastal Vegetation is found in 

tropical coastal habitats, including beaches, bluffs and dunes, where wind and water 

are major drivers of the vegetation, from the equator to 23 degrees N and S latitude. It 

is dominated by prostrate perennials on the beach and foredune, and graminoids and 

scrub on backdunes and bluffs.

Classification Comments: This formation is only weakly defined by growth 

forms. It may be a more appropriate division-level distinction, but it does provide a 

convenient grouping of very similar divisions across the globe; thus it may be a formation, based on global scale coastal ecological processes and justified by a bottom-up 

perspective. See under 2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation 

Formation (F005).

There are windswept inland dunes that can appear similar to coastal environments. 

They may have established on more ancient coastal shorelines. Review is needed to 

determine whether the vegetation fits here or in 2.A.1. Tropical Lowland Grassland, 

Savanna & Shrubland Formation (F019).

In temperate coastal habitats, large perennial grasses are found, with a diversity of 

forbs and with higher wind and wave energy. A zone of ephemerals (such as Cakile, 

Atriplex, and Salsola) is perhaps more common (Barbour 1992).

Similar NVC Types: 

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019): Found in noncoastal habitats.

2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation (F005): The strength 

of the tropical versus temperate distinction may be weak in these coastal habits, but 

annual or ephemeral herbs may be more common in temperate beaches.

Diagnostic Characteristics: The vegetation often has morphological (psammophytic) adaptations to these habitats, including prostrate herbaceous perennial growth 

forms, with mesomorphic leaves, neither succulent nor sclerophyllous, less commonly 

with annual herbs, and increasingly with perennial grasses and shrubs on the stabilized 

backdunes. The backdune may have more typical mesomorphic or xeromorphic scrub 

and herb vegetation.
USDA Forest Service RMRS-GTR-346. 2016. 87

Vegetation

Physiognomy and Structure: The vegetation often has morphological (psammophytic) adaptations to the beach, dune, and bluff habitats, including prostrate 

herbaceous perennial growth forms with mesomorphic leaves, neither succulent nor 

sclerophyllous, less commonly with annual herbs, and increasingly with perennial 

grasses and shrubs on the stabilized backdunes. The tropical coastal vegetation tends 

to have prostrate or low perennial grasses on the beach and foredune and woody species (favored by the long growing season) on the backdunes. In drier tropical climates, 

there may be a shift to xeromorphic desert species (Barbour 1992).

Environment

Environmental Description: Tropical Scrub & Herb Coastal Vegetation includes 

upland habitats found along the coast, including beaches, bluffs and dunes, where 

wind, water, and salinity are major drivers of the vegetation. Beaches include the strip 

of sand or gravel that extends from the mean tideline to the top of the foredune (frontal 

foredune). The dune extends further inland wherever the sandy/gravelly site conditions 

restrict tree growth (less than 10 percent cover). Unconsolidated bluffs (but not marine 

rock cliffs) are more stable, relatively vertical habitats (Barbour 1992).

Beach sand is typically enriched with nutrients and organic matter from the sea or 

lake. The permeability of the sandy substrate permits drainage and leaching, with a 

tendency towards arid systems. Proximity to the sea or lake induces permanently high 

air humidity and reduces climatic extremes. Sea-level changes constantly rework the 

substrate (Seeliger 1992). Winds are a constant influence.

Distribution

Geographic Range: This formation is found in tropical coastal habitats, including 

beaches, bluffs and dunes, from the equator to 23 degrees N and S latitude.

The beach and foredune part of the concept is most distinctive. Backdune grasslands and shrublands may be structurally similar to inland grasslands and shrublands, 

and floristic information may be needed to determine their placement. 

Citations

Synonymy: 

> Coastal foredunes of southern Brazil (Seeliger 1992) [The author uses the 

vegetation type as a name for a chapter in a book on Latin American coastal plant 

communities. Beaches are not described.] 

= The Dune Plant Community (Seeliger 1992) [The author uses the vegetation type as 

a name for a section in a book on Latin American coastal plant communities. Beaches 

and dunes are included.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
88 USDA Forest Service RMRS-GTR-346. 2016.

2.B. Temperate & Boreal Grassland & Shrubland 

(S18)

Overview

Database Code: 2.B (S18)

Scientific Name: Temperate & Boreal Grassland & Shrubland Subclass

Common Name (Translated Scientific Name): Temperate & Boreal Grassland & 

Shrubland Subclass

Colloquial Name: Temperate & Boreal Grassland & Shrubland

Hierarchy Level: Subclass

Placement in Hierarchy: 2. Shrub & Herb Vegetation (C02)

Lower Level Hierarchy Units:

2.B.1. Mediterranean Scrub & Grassland (F038)

2.B.2. Temperate Grassland & Shrubland (F012)

2.B.3. Boreal Grassland & Shrubland (F028)

2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation (F005)

Concept Summary

Type Concept Sentence: Temperate & Boreal Grassland & Shrubland is dominated 

by mesomorphic grasses and shrubs, with or without scattered trees (and trees typically less than 10 percent cover), ranging from temperate coastal to inland lowland 

and montane grasslands and shrublands, with a strongly seasonal climate and at least 

some frost to extended cold seasons.

Classification Comments: Desert grasslands are treated in 3. Desert & SemiDesert Class (C03) based on the typical presence or abundance of xerophytic woody 

growth forms and, less commonly, the presence/abundance of ephemeral plants. 

Review of herbaceous growth forms is needed to determine if there are forms that 

more clearly distinguish desert grasslands from temperate grasslands. As Dixon et al. 

(2014) and others suggest, there may be good ecological reasons to treat upland 

tropical tree savannas, with up to 40% tree cover, trees <8 m tall, and a substantial 

graminoid layer, as part of 2. Shrub & Herb Vegetation Class (C02), and we allow 

for that option here. By contrast, in non-tropical regions, we place tree savannas with 

woodland and forest.

Similar NVC Types: 

1.B. Temperate & Boreal Forest & Woodland (S15): Temperate & Boreal Grassland 

& Shrubland (S18) tree cover is less than 10 percent.

2.A. Tropical Grassland, Savanna & Shrubland (S01).

3.B. Cool SemiDesert Scrub & Grassland (S11): Temperate & Boreal Grassland & 

Shrubland (S18) typically lacks the microphyllous leaved shrubs, more open 

and short grasses, and dry soils of cool semi-desert formation (S11), but dry 

grasslands, such as shortgrass prairies in North America, may have many similarities to cool semi-deserts.

6.B. Mediterranean, Temperate & Boreal Open Rock Vegetation (S04): Temperate 

& Boreal Grassland & Shrubland (S18) contains many rocky river and lake 

shoreline types.
USDA Forest Service RMRS-GTR-346. 2016. 89

Diagnostic Characteristics: Temperate & Boreal Grassland & Shrubland is 

dominated by mesomorphic grasses or grasses and shrubs, with or without scattered 

trees (and trees typically less than 10 percent cover), ranging from temperate to coastal 

and inland lowland and montane grasslands and shrublands, with a strongly seasonal 

climate, with at least some frost and with extended strong cold seasons.

Vegetation

Physiognomy and Structure: The vegetation varies from grasslands of open 

to dense bunch or sod grasses, often with scattered shrubs, to low (<2 m) open to 

dense shrublands and sclerophyllous or soft chaparral and drought-deciduous scrub. 

Xeromorphic growth forms are largely absent, and the surface layer contains a thin to 

thick litter and duff layer in contrast to desert grassland and scrub, where the surface 

layer may be bare or contain a biological crust. Structure is a single, major grass or 

shrub stratum, or a mix of the two, with mesomorphic tree cover typically less than 

10 percent, rarely with bare ground (Whittaker 1975). The range of variation in upland 

formations corresponds to Mediterranean, Temperate, Boreal, and Coastal climatic 

gradients. 

Environment

Environmental Description: The vegetation occurs in areas of moderately dry to 

wet, continental, coastal, and Mediterranean climates (moderately dry, warm temperate, maritime climates with little or no summer rain). A number of drivers can preclude 

establishment of forest vegetation in these climates, including climatic characteristics, 

water regime (droughty soils), and fire and flooding disturbances. 

Distribution

Geographic Range: This subclass occurs in the middle latitudes (between 25 and 

60 to 0 degrees N and S latitude) of both hemispheres, and is most abundant in North 

America, Eurasia (the steppes), South America, and parts of Southern Africa and 

Australia. Specific latitudes depend upon the continent on which they are located.

Citations

Synonymy:

 = Temperate Grassland Biome (Woodward 2008) 

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

2.B.1. Mediterranean Scrub & Grassland (F038)

Overview

Database Code: 2.B.1 (F038)

Scientific Name: Mediterranean Scrub & Grassland Formation

Common Name (Translated Scientific Name): Mediterranean Scrub & Grassland 

Formation

Colloquial Name: Mediterranean Scrub & Grassland
90 USDA Forest Service RMRS-GTR-346. 2016.

Hierarchy Level: Formation

Placement in Hierarchy: 2.B. Temperate & Boreal Grassland & Shrubland (S18)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Mediterranean Scrub & Grassland includes the sclerophyllous scrub that develops in Mediterranean climates found in the Mediterranean 

Basin, lowland California in the United States, west-central Chile, the western Cape 

Province of South Africa, and southwestern and southern Australia. It also includes 

Mediterranean grasslands, “wildflower fields,” and prairies from California.

Classification Comments: Each region of Mediterranean scrub has developed 

unique names for the type, including in California, chaparral and coastal scrub; in 

Chile, matorral and espinal; in Spain, tomillares; in France or French-speaking countries, maquis or garrigue; in Greece, phyrgana; in Israel, bath’a or goresh; in South 

Africa, fynbos and strandveld; and in Australia, kwongan and mallee (Kuennecke 

2008).

Mediterranean grassland and meadow are included in this formation. In California, 

they are separated from Mediterranean scrub at the division level (2.B.1.Na. California 

Grassland & Meadow Division (D021)), and the vegetation includes the Central 

Valley and foothill herbaceous vegetation with more pronounced summer drought. 

These drier Mediterranean California grasslands resemble desert grasslands. 

However, they have even less rain in the growing season than many desert grasslands. 

Although other Mediterranean regions of the world do have many annual species, 

California is the only region that has extensive annual-dominated herbaceous vegetation (T. Keeler-Wolf, pers. obs. 2011).

California “coastal prairies,” including diagnostics such as Festuca rubra, Festuca 

idahoensis, Danthonia californica, etc., are placed in 2.B.2 Temperate Grassland & 

Shrubland Formation (F012) and, within that formation, in the 2.B.2.Na Southern 

Vancouverian Lowland Grassland & Shrubland Macrogroup (M050).

Placement of montane (oro-) Mediterranean vegetation needs further review. 

In California, the growth forms of this vegetation are common to other, primarily 

cool-temperate vegetation, placed in the 2.B.2 Temperate Grassland & Shrubland 

Formation (F012). In Europe, “Oro-mediterranean grasslands and scrub” is treated 

as a separate formation from either “Temperate grasslands, heaths, and fringe vegetation” or “Mediterranean garrigue, maquis, mattoral, tomillar, and phrygna” vegetation 

(Rodwell and others 2002). Perhaps the “oroMediterranean” distinction in Europe includes a “warm temperate montane grassland and scrub” not found in other continents. 

Such a distinction could be made at the division level, if the flora of the montane 

Mediterranean vegetation was largely distinct from the lowland coastal Mediterranean 

vegetation.

Similar NVC Types: 

1.B.1. Warm Temperate Forest & Woodland (F018): The vegetation contains tree 

growth forms with greater than 10 percent cover. Combinations of dwarf scrubby trees less than 2 m with low shrubs may grade into Warm Temperate Forest.
USDA Forest Service RMRS-GTR-346. 2016. 91

2.B.2. Temperate Grassland & Shrubland (F012): The vegetation tends to produce 

highest biomass in the warm to hot summers and become dormant in the winter 

cool or cold periods. Above-ground portions of perennial grasses dry and 

wither, or annuals set seed and die by late fall.

Diagnostic Characteristics: Sclerophyll-leaved shrub growth forms prevail, but 

soft chaparral and drought-deciduous forms may also occur. Shrub growth forms range 

from arborescent (2 to 5 m tall) shrubs with a closed canopy, to less than 1 m and 

quite open. Mixed annual and perennial grasslands may also occur, with only scattered 

scrub. The vegetation tends to produce the most biomass in the cool rainy winter and 

becomes dormant in the summer drought. Above-ground portions of perennial grasses 

dry and wither, or annuals set seed and die by mid-spring to early summer. The type 

is restricted to the Mediterranean Basin, southwestern California in the United States, 

west-central Chile, the western Cape Province of South Africa, and southwestern and 

southern Australia.

Vegetation

Physiognomy and Structure: Shrubs have adaptations to drought, nutrient-poor 

soils and fire. Broad-leaved evergreen, sclerophyllous shrubs dominate the vegetation 

of areas with higher and more predictable winter rainfall, while facultatively deciduous shrubs, or perennial or annual herbs dominate where precipitation is lowest and 

less predictable. Depending on the interactions of rainfall, soil texture, and type and 

intensity of natural processes such as fire, browzing/grazing, and bioturbation, there is 

a complex variation of growth forms. This ranges from woody sclerophyll to woody 

drought-deciduous shrubs and from perennial bunch grasses to perennial geophytes 

(bulbs, corms, etc., especially common in South Africa) and to ephemeral annual 

herbs. Generally, sclerophylls occur where winter rain is adequate and predictable and 

soils are well drained. Facultatively deciduous scrub occurs in areas with drier or more 

unpredictable rainfall patterns and often on finer textured soils than sclerophyll scrub. 

Perennial herbaceous vegetation such as bunch grasses occur in areas with relatively 

high precipitation, while annual herbs (forbs) dominate episodically following favorable winter rainfall events, but may be largely stored as seedbanks in the soil in low 

rainfall years. The vegetation tends to produce highest biomass in the cool rainy winter 

and becomes dormant in the summer drought. Above-ground portions of perennial 

grasses dry and wither, or annuals set seed and die by mid-spring to early summer. 

Small numbers of summer annuals also occur (mostly Asteraceae tribe Madiae in 

California), which take advantage of lingering deep soil moisture by having evolved 

long taproots.

Environment

Environmental Description:

Climate: The Mediterranean climate is characterized by dry summers and mild, 

humid, sometimes rainy winters. Annual precipitation averages 25 to 100 cm. Freezing 

temperatures are relatively rare. Wherever mountains and predominant wind directions 

cause orographic effects (for example the rainfall increases on the windward side), 

annual precipitation at the higher elevations may be sufficient to support a change 

from scrub to woodland or forest [and these would be placed in 1.B.1 Warm Temperate 

Forest & Woodland Formation (F018)]. With increasing latitude, rainfall totals and 
92 USDA Forest Service RMRS-GTR-346. 2016.

length of the rainy season also increase, causing a comparable shift to woodland or 

forest (Kuennecke 2008). Many Mediterranean climate areas have been “invaded” by 

exotic annual grasses and other species that have tended to modify natural disturbance 

patterns such as fire (Keeley 2001).

Distribution

Geographic Range: This formation occurs in the Mediterranean Basin, and in 

the Mediterranean climate regions of southwestern California in the United States, 

west-central Chile, the western Cape Province of South Africa, and southwestern 

and southern Australia, at latitudes between 31 and 46 degrees N in the Northern 

Hemisphere and between 28 and 42 degrees S in the Southern Hemisphere. These 

areas form on the western or southern margins of continents where warm-season high 

pressure tends to settle offshore driving all precipitation to the north or south of the 

adjacent shore areas.

Citations

Synonymy:

> Chaparrallike Shrublands (Dallman 1998)

> Coastal Scrub (Dallman 1998)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: T. Keeler-Wolf

Acknowledgments:

Version Date: 26 Aug 2014

2.B.2. Temperate Grassland & Shrubland (F012)

Overview

Database Code: 2.B.2 (F012)

Scientific Name: Temperate Grassland & Shrubland Formation

Common Name (Translated Scientific Name): Temperate Grassland & Shrubland 

Formation

Colloquial Name: Temperate Grassland & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.B. Temperate & Boreal Grassland & Shrubland (S18)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Temperate Grassland & Shrubland is dominated by 

perennial grasses, forbs and shrubs typical of moderately dry to moist habitats, and is 

found in the mid-latitude regions of all continents (23 to 55 degrees N and S), varying from large open grassland landscapes to droughty hillside meadows in forested 

landscapes.

Type Concept: Temperate Grassland & Shrubland is dominated by mesomorphic 

perennial grasses and forbs and is found in the mid-latitude regions across the globe. 

It is associated with a moist to semi-arid climate and geographically occurs between 
USDA Forest Service RMRS-GTR-346. 2016. 93

temperate forests and deserts. The present plant assemblages were strongly affected by 

Pleistocene glaciations, though regions close to the equator may have retained vegetation back to the Tertiary.

Grasslands are a predominant type in this formation and each continent has its 

own popular name for its part of this formation. In North America, it is the prairie; 

in Eurasia, the steppe. South Americans usually refer to pampas and South Africans 

to the veld. The plants (and animals) of the North American and Eurasian sections of 

the biome are closely related, but have been impacted differently by Pleistocene and 

post-Pleistocene climate changes, human occupation and use, wildfires, and grazing 

pressures from both wild and domesticated large mammals. The origins of South 

America’s pampas and southern Africa’s veld are still poorly understood. Fire may be 

implicated, as it is a necessary management tool today in preventing the encroachment 

of woody plants.

In addition to the larger geographic areas of grasslands and associated shrublands, 

scattered grassland, shrub, and forb vegetation within temperate forest formations are 

included.

Although mesomorphic perennial grasses and shrubs are the most common growth 

forms in this formation, a large number of other herbaceous plants, primarily perennial 

forbs, are also found. Trees are not major components of the vegetation, except as a 

scattered layer (typically less than 10 percent cover).

Similar NVC Types: 

1.B.1. Warm Temperate Forest & Woodland (F018): Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10 percent cover or 

more, are placed here, but may have strong floristic similarities to grasslands.

1.B.2. Cool Temperate Forest & Woodland (F008): Open woodlands or tree savannas, with grassy or shrubby understories, and with trees 10 percent cover or 

more, are placed here, but may have strong floristic similarities to grasslands.

2.B.1. Mediterranean Scrub & Grassland (F038): The vegetation tends to produce 

highest biomass in the cool winters, and become dormant in the summer hot 

periods. Above-ground portions of perennial grasses dry and wither, or annuals 

set seed and die by late spring.

2.B.3. Boreal Grassland & Shrubland (F028): Temperate Grassland & Shrubland 

(F012) is currently separated based on geography and climate from boreal 

grassland (F028), but more specific vegetation criteria are needed.

2.B.4. Temperate to Polar Scrub & Herb Coastal Vegetation (F005): Temperate 

Grassland & Shrubland (F012) has similarities to coastal vegetation, especially 

between coastal and inland dunes in terms of growth forms and even winddriven processes.

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013): 

Temperate Grassland & Shrubland (F012) transition, such as wet-mesic or 

moist grasslands and prairies, may be very similar to freshwater marshes and 

wet meadows (F013).

3.B.1. Cool Semi-Desert Scrub & Grassland (F033): Typically with small leaved, 

xerophytic shrubs (e.g., sage) and more open bare ground, sometimes with 

biological crust.
94 USDA Forest Service RMRS-GTR-346. 2016.

7.B.2. Pasture & Hay Field Crop (CFO05): Temperate Grassland & Shrubland 

(F012) may overlap in composition with pasture grasslands (CFO05), particularly in grassland regions. And in regions where a pastoral tradition has existed 

from 100s to 1000s of years, recognition of native versus agricultural grasslands may be challenging.

Diagnostic Characteristics: Mesomorphic perennial grasses and shrubs are the 

most common growth forms in this formation, with a variable amount of perennial 

forbs. Trees are scattered to largely absent (typically less than 10 percent cover). 

Stands are found in the mid-latitude regions of all continents, typically associated 

with semi-arid climates or stressful sites in moist climates in the mid latitudes (23 to 

55 degrees N and S).

Vegetation

Physiognomy and Structure: Mesomorphic perennial grasses and shrubs are the 

most common growth forms in this formation, with a variable amount of perennial 

forbs. Trees are scattered to largely absent (typically less than 10 percent cover). 

Grasses and forbs grow to different heights at maturity. Furthermore, some grasses 

and most forbs are erect, while others are recumbent, creeping along the ground. Thus 

a distinct layering of plant foliage occurs in some temperate grasslands. Forbs and 

grasses may grow and bloom at different times during the growing season, so temperate grasslands may have recognizable color phases, or aspects, depending on what 

plants are blooming. This is especially evident in the east European steppes. Grasses 

and perennial forbs are well suited to withstand cold seasons and tolerate grazing and 

fire because of the position of their renewal buds near the ground surface. The plants 

are generally able to regenerate from these buds after seasonal die-downs, burns, or 

cropping by grazing animals (Woodward 2008). Among the grasses, both sod-forming 

and bunch grasses are prominent throughout, but bunch grasses become a much more 

frequent component of the vegetation in the drier short-grass regions.

Environment

Environmental Description: Gradation in precipitation amounts occurs in most 

regional expressions of the biome and is mirrored in the zonation pattern of the 

vegetation and animal life in each. In some instances, such as in North America, 

longitudinal zones dominate and replace each other in an east-west direction across the 

mid-continent. In other areas, latitudinal zonation is prominent and plant and animal 

communities change in a north-south direction. Still other natural grasslands are a 

consequence of rain shadows on the lee sides of major mountain ranges or of high 

elevation, as is the case in southern Africa (Woodward 2008).

Climate: Temperate grasslands have developed in regions having a semi-arid 

climate (mostly BSk in the Koeppen climate classification). Mid-latitude semi-arid 

climate regions receive 25 to 75 cm (10 to 20 inches) of precipitation a year. In 

some areas (most notably the mid-continental prairie of North America and the East 

European steppes of Eurasia), a significant amount falls as snow during the winter 

months, such that snowmelt contributes importantly to soil moisture in early spring. 

The interior position of grasslands on the large North American and Eurasian continents results in the wide annual range in temperatures, a temperature pattern that 

is considered typical for the biome. Winters see temperatures well below freezing, 
USDA Forest Service RMRS-GTR-346. 2016. 95

whereas summers can be scorchingly hot. Such a temperature pattern is described by 

climatologists as continental. Similar temperature conditions often occur in humid 

forested regions at the same latitudes (Woodward 2008).

North American and Eurasian grasslands owe their existence to their positions in 

the middle of large continents, where precipitation is reduced and temperature extremes are pronounced. The South American grasslands lie in the rain shadow east of 

the Andes Mountains. In Africa, elevation is a factor. According to latitude alone, these 

African grasslands are subtropical, but the elevated surface at the southern end of the 

African Plateau creates regional temperature patterns similar to middle latitude conditions (Woodward 2008).

In all regions of the formation, gradual changes in climate occur across great 

distances. In Eurasia, the variation occurs in a north-south direction. The wetter (subhumid) northern regions of the Temperate Grassland border the Cool Temperate Forest 

& Woodland and Boreal Forest & Woodland Formations, and the drier (arid) southern 

margins grade into the Desert formations. In the Americas, the gradation from subhumid to arid runs in an east-west direction, with progressively less precipitation the 

farther west one goes. In all areas a change in vegetation coincides with the change 

in total precipitation. Wetter areas contain taller grass species and usually a greater 

variety of plants and animals than do the shorter grass areas in the driest parts of the 

biome (Woodward 2008).

Soil/substrate/hydrology: The soils beneath prairies, steppes, pampas, and high 

veld are among the most fertile on Earth. Once the technology was available to break 

through the thick sod, many grasslands were converted to agriculture. Wheat and corn 

replaced native grasses, and the temperate grasslands became the breadbaskets of their 

respective countries (Woodward 2008).

Soils Comments:

Formation of Temperate Grassland soils: The underground portion of the grass 

plant is equally, if not more, important to the functioning of the ecosystem and formation of soil. Grasses develop a dense, intricate system of fine roots that not only acts to 

hold the plant in place but absorbs water and nutrients from the soil and stores some 

of the carbohydrates that the plant manufactures during photosynthesis for later use. 

In fact, more living plant matter (biomass) exists below ground in the temperate grasslands than above. Roots continually grow, die, and decay and thus contribute organic 

matter in the form of humus to the soil. The fine roots create a crumbly texture to the 

soil that allows water and air to penetrate to depths up to 3.5 m (12 feet) in the wetter 

parts of the biome, further enhancing the soil environment for plant growth. Those 

soluble compounds (e.g., calcium carbonate and magnesium carbonate) that might be 

leached to depth after rainstorms or snowmelt can be returned to the root zone during 

dry periods by capillary action along the tiny tunnels left by dead roots. The carbonates precipitate out near the top of the subsoil (B-horizon) when the soil moisture 

evaporates. The concentration of carbonates in this manner is the main feature of the 

soil-forming process known as calcification, which is characteristic of semi-arid and 

arid climate regions. The carbonate-rich layer forms closer to the surface the drier the 

climatic conditions (Woodward 2008).
96 USDA Forest Service RMRS-GTR-346. 2016.

Soil types: Grassland soils of temperate regions are classified in U.S. Soil 

Taxonomy as Mollisols. The prefix “moll” means soft and describes the friable or 

crumbly texture of these soils that persists even when the top layers dry out. Other 

parts of the world and the United Nations Food and Agriculture Organization use other 

names. In Canada they are called chernozemic soils; in Russia they are chernozems. 

Mollisols are brown in color due to the abundance of humus in both the topsoil and 

subsoil (A and B horizons). Color varies from dark brown and even black to chestnut 

brown and light brown as climate changes from subhumid to dry and grasses change 

from tall with deep roots to short with shallow roots. For the darkest of all, the truly 

black soils, the Russian name Chernozem (meaning black soil) is used, even in the 

United States. Chernozems have especially deep A and B horizons (each up to 1 m 

[3 feet] deep), both of which are dark with humus and humic acid stains. They have 

formed where semi-arid regions receive the most precipitation and where the parent 

material is a fine, windblown material known as loess. Loess originated as tiny particles on the newly exposed bare ground at the edge of continental glaciers when ice 

sheets retreated at the end of the Pleistocene ice age. Winds coming off the ice picked 

the dust-like material up and carried it to more humid, vegetated regions, where it accumulated. Thick deposits of loess occur in the Central Lowlands of North America, 

across much of semi-arid Eurasia, and in Uruguay and eastern parts of Argentina. 

Loess is often rich in carbonates. The soils developed on it are among the most fertile 

in the world, and today they produce much of the world’s wheat and corn (both of 

which are domesticated grasses) (Woodward 2008).

Distribution

Geographic Range: Temperate grasslands and shrublands occur in the middle latitudes (25 to 55 degrees latitude) of both hemispheres. Specific latitudes depend upon 

the continent on which they are located. The largest areas of this formation are found 

in the Northern Hemisphere on the North American and Eurasian continents. Smaller 

but still major segments of the formation are found in the Southern Hemisphere in 

South America and southern Africa (Woodward 2008).

Citations

Synonymy:

= Temperate Grassland (Woodward 2008) [Despite the name, shrublands found within 

the grassland regions are included in Woodward’s concept.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012) after S. Woodward (2008)

Author of Description: D. Faber-Langendoen and J. Messick

Acknowledgments:

Version Date: 26 Aug 2014

2.B.3. Boreal Grassland & Shrubland (F028)

Overview

Database Code: 2.B.3 (F028)

Scientific Name: Boreal Grassland & Shrubland Formation
USDA Forest Service RMRS-GTR-346. 2016. 97

Common Name (Translated Scientific Name): Boreal Grassland & Shrubland 

Formation

Colloquial Name: Boreal Grassland & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.B. Temperate & Boreal Grassland & Shrubland (S18)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Boreal Grassland & Shrubland is dominated by mesomorphic perennial grasses, forbs and shrubs, and is found in the northern mid-latitude 

(boreal) regions of North America and Eurasia, between 55 and 70 degrees N, with 

extended cold winters and short mild summers.

Type Concept: Boreal Grassland & Shrubland is dominated by mesomorphic 

perennial grasses, forbs and shrubs, and is found in the northern mid-latitude (boreal) 

regions of North America and Eurasia. It is associated with cold semi-arid to moist climates, with extended cold winters and short mild summers, and geographically occurs 

mixed with boreal forests and wetlands. The climate generally favors establishment of 

forest vegetation; thus, the absence of forest vegetation is a result of local conditions 

related to water regime, soil parameters or disturbance regimes. The present assemblages of plants and animals date to after the Pleistocene, following glaciation, when 

modern climates were established. Wildfires and grazing also play a role in some of 

these grasslands.

Along with the mesomorphic perennial grasses, shrubs, and forbs, mosses and 

lichens can also play an important role. Boreal tree growth forms are not major components of the vegetation, except as a scattered layer (typically less than 10 percent). 

In disturbance situations, Boreal Grassland & Shrubland can grade to Boreal Forest & 

Woodland and may not be clearly separated from it floristically.

Classification Comments: Clarification of the growth forms, distribution and 

extent, and ecological processes that control boreal shrublands and grasslands is 

needed. Examples of vegetation from western boreal include: (1) Betula nana and/

or Salix glauca shrublands and Festuca altaica grasslands in cold air-influenced valleys and high-elevation areas below the alpine; (2) Elymus trachycaulus grassland or 

Amelanchier alnifolia / Leymus innovatus / Arctostaphylos uva-ursi scrub on warm 

aspects, often on coarse-textured materials; and (3) Post-fire disturbance vegetation 

that can be dominated by willows and may exclude tree regeneration.

Similar NVC Types: 

2.B.2. Temperate Grassland& Shrubland (F012): This type is currently separated 

based on geography and climate.

Diagnostic Characteristics: Mesomorphic perennial grasses and shrubs are the 

most common growth forms in this formation, with a variable amount of perennial 

forbs. Trees are scattered to minimally present (typically less than 10 percent cover) in 

the northern mid-latitude regions of North America and Eurasia, extending from cool 

temperate regions into the boreal region between 55 and 70 degrees N latitude.
98 USDA Forest Service RMRS-GTR-346. 2016.

Vegetation

Physiognomy and Structure: Boreal Grassland & Shrubland is dominated by 

mesomorphic perennial grasses, forbs and shrubs. Mosses and lichens can also play an 

important role. Boreal tree growth forms are not major components of the vegetation, 

except as a scattered layer (typically less than 10 percent). In disturbance situations, 

Boreal Grassland & Shrubland can grade to Boreal Forest & Woodland and may not 

be clearly separated from it floristically.

Environment

Environmental Description: Climate: This type is associated with cold semi-arid 

to moist climates, with extended cold winters and short mild summers, and geographically occurs mixed with boreal forests and wetlands. The climate generally favors 

establishment of forest vegetation; thus, the absence of forest vegetation is a result 

of local conditions related to water regime, soil parameters, or disturbance regimes. 

There are lengthy periods of freezing temperatures with the coldest month isotherm 

of 3 degrees C, and the growing season generally averaging less than 100 days, occasionally interrupted by nights of below-freezing temperatures. Snow may be present 

for extended periods (7 to 10 months) and soils are frozen in winter. Annual precipitation is 3,850 cm (1,520 inches). The northern and southern boundary of these boreal 

grasslands may be similar to that of boreal forest, but the reasons for the presence of 

grassland and shrubland rather than forest typically reflects water regime, soil characteristics, disturbance regime, and local climate that prevent tree growth.

Distribution

Geographic Range: This formation is found in the northern mid-latitude regions of 

North America and Eurasia, extending through much of the boreal region between 55 

and 70 degrees N latitude.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, S. Ponomarenko and D. Meidinger

Acknowledgments:

Version Date: 26 Aug 2014

2.B.4. Temperate to Polar Scrub & Herb Coastal 

Vegetation (F005)

Overview

Database Code: 2.B.4 (F005)

Scientific Name: Temperate to Polar Scrub & Herb Coastal Vegetation Formation

Common Name (Translated Scientific Name): Temperate to Polar Scrub & Herb 

Coastal Vegetation Formation

Colloquial Name: Temperate to Polar Scrub & Herb Coastal Vegetation

Hierarchy Level: Formation
USDA Forest Service RMRS-GTR-346. 2016. 99

Placement in Hierarchy: 2.B. Temperate & Boreal Grassland & Shrubland (S18)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Temperate to Polar Scrub & Herb Coastal Vegetation 

is found in temperate to polar coastal habitats, including beaches, bluffs and dunes, 

where wind and water are major drivers of the vegetation, across the mid to polar latitudes from 23 to 60 to 70 degrees N and S latitude, dominated by prostrate perennials 

on the beach and foredune, and graminoids and scrub on backdunes and bluffs.

Classification Comments: This formation is only weakly defined by growth 

forms. It may be a more appropriate division-level distinction, but it does provide a 

convenient grouping of very similar divisions across the globe; thus it may be a formation, based on global scale coastal ecological processes and justified by a bottom-up 

perspective. There are windswept inland dunes that can appear similar to coastal environments. They may have established on more ancient coastal shorelines. Review is 

needed to determine whether the vegetation fits here or in 2.B.2. Temperate Grassland 

& Shrubland Formation (F012). The tropical coastal vegetation tends to have prostrate 

or low perennial grasses on the beach and foredune and have woody species (favored 

by the long growing season) on the backdunes. In drier temperate climates, there may 

be a shift to xeromorphic cool desert species.

Similar NVC Types: 

2.A.3. Tropical Scrub & Herb Coastal Vegetation (F024): The strength of the 

tropical versus temperate distinction may be weak in these coastal habits, but 

perennial herbs may be more common in tropical beaches.

2.B.2. Temperate Grassland & Shrubland (F012): There are similarities between 

coastal and inland dunes in terms of growth forms and wind-driven processes.

Diagnostic Characteristics: The vegetation often has morphological (psammophytic) adaptations to these habitats, including prostrate herbaceous perennial growth 

forms, with mesomorphic leaves, neither succulent nor sclerophyllous, less commonly 

with annual herbs, and increasingly with perennial grasses and shrubs on the stabilized 

backdunes. The backdune may have more typical mesomorphic or xeromorphic scrub 

and herb vegetation.

Vegetation

Physiognomy and Structure: The vegetation often has morphological (psammophytic) adaptations to the beach, dune and bluff habitats, including prostrate herbaceous 

annual growth forms, with mesomorphic leaves, neither succulent nor sclerophyllous, 

less commonly with annual herbs, and increasingly with perennial grasses and shrubs 

on the stabilized backdunes. The temperate coastal vegetation tends to have prostrate 

or low perennial grasses on the beach and foredune and woody species (favored by 

the long growing season) on the backdunes. In drier climates, there may be a shift to 

xeromorphic cool desert species (Barbour 1992).
100 USDA Forest Service RMRS-GTR-346. 2016.

Environment

Environmental Description: This formation includes upland habitats found along 

the coast, including beaches, bluffs and dunes, where wind, water, and salinity are major drivers of the vegetation. Beaches include the strip of sand or gravel that extends 

from the mean tideline to the top of the foredune (frontal foredune). The dune extends 

further inland wherever the sandy/gravelly site conditions restrict tree growth (less 

than 10 percent cover). Unconsolidated bluffs (but not marine rock cliffs) are more 

stable, relatively vertical habitats (Barbour 1992).

Beach sand is typically enriched with nutrients and organic matter from the sea or 

lake. The permeability of the sandy substrate permits drainage and leaching, with a 

tendency towards arid systems. Proximity to the sea or lake induces permanently high 

air humidity and reduces climatic extremes. Sea-level changes constantly rework the 

substrate (Seeliger 1992). Winds are a constant influence. 

Distribution

Geographic Range: This formation is found in temperate coastal habitats, including beaches, bluffs and dunes, across the mid- to polar latitudes from 23 to 70 degrees 

N and S latitude.

Citations

Synonymy:

= The Dune Plant Community (Seeliger 1992) [The author uses the vegetation type as 

a name for a section in a book on Latin American coastal plant communities. Beaches 

and dunes are included.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

2.C. Shrub & Herb Wetland (S44)

Overview

Database Code: 2.C (S44)

Scientific Name: Shrub & Herb Wetland Subclass

Common Name (Translated Scientific Name): Shrub & Herb Wetland Subclass

Colloquial Name: Shrub & Herb Wetland

Hierarchy Level: Subclass

Placement in Hierarchy: 2. Shrub & Herb Vegetation (C02)

Lower Level Hierarchy Units:

2.C.1. Tropical Bog & Fen (F002)

2.C.2. Temperate to Polar Bog & Fen (F016)

2.C.3. Tropical Freshwater Marsh, Wet Meadow & Shrubland (F030)
USDA Forest Service RMRS-GTR-346. 2016. 101

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013)

2.C.5. Salt Marsh (F035)

Concept Summary

Type Concept Sentence: Shrub & Herb Wetland includes open bogs, fens, fresh 

and saltwater marshes, wet meadows and wet shrublands. The vegetation occurs from 

tropical to polar regions.

Classification Comments: These wetlands contain vegetation that is hydrophytic, 

but none-the-less, largely mesomorphic growth forms, not hydromorphic growth 

forms.

Similar NVC Types: 

1.A. Tropical Forest & Woodland (S17): This subclass contains flooded and swamp 

forests (which can transition to open bogs and marshes) and mangroves (which 

can be similar to salt marshes). Where tree cover exceeds 10 percent, stands are 

typically placed in Forest & Woodland subclasses.

5.B.1. Tropical Freshwater Aquatic Vegetation (F056)

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057)

Diagnostic Characteristics: Shrub & Herb Wetland is dominated by grasses and 

shrubs, with or without scattered trees (which may have up to 10 percent cover), sometimes with a wet moss layer (bogs and fens), halophytic growth forms (salt marsh), 

or a mix of emergent and hydromorphic growth forms, with seasonally to annually 

saturated or flooded soils, or standing water.

Vegetation

Physiognomy and Structure: This type is dominated by grasses and shrubs, with 

or without scattered trees (but tree cover typically less than 10 percent), sometimes 

with a strong moss (sphagnum or brown moss) component, or with hydromorphic 

growth forms. A summary of the range of variation for the various wetlands within the 

subclass is provided in Table 6.

Environment

Environmental Description: Stands are found in a variety of wetland settings, 

including seasonally to annually saturated or flooded soils, or standing water.

Distribution

Geographic Range: This subclass is found widely throughout the world in lowland 

and montane wetland habitats, from the tropics to the poles.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
102 USDA Forest Service RMRS-GTR-346. 2016.

2.C.1. Tropical Bog & Fen (F002)

Overview

Database Code: 2.C.1 (F002)

Scientific Name: Tropical Bog & Fen Formation

Common Name (Translated Scientific Name): Tropical Bog & Fen Formation

Colloquial Name: Tropical Bog & Fen

Hierarchy Level: Formation

Placement in Hierarchy: 2.C. Shrub & Herb Wetland (S44)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Bog & Fen is found where peat-accumulating 

conditions occur in the cold, wet mountain highlands and in various floodplains of the 

lowlands, where trees are excluded. They are dominated by sedges, heath, and moss 

peat.

Classification Comments: Tropical peat swamps, where tree cover exceeds 10 

percent, are treated under 1.A.4. Tropical Flooded & Swamp Forest Formation (F029).

Similar NVC Types: 

2.C.3. Tropical Freshwater Marsh, Wet Meadow & Shrubland (F030)

Diagnostic Characteristics: Tropical Bog & Fen is found where peat-accumulating 

conditions occur in the cold, wet mountain highlands and in various floodplains of the 

lowlands, where trees are excluded. They are dominated by sedges, heath, and moss 

peat.

Vegetation

Physiognomy and Structure: “True” tropical bogs and fens, with sedge or moss 

peat, are relatively rare. Tropical bogs are covered by a mixed vegetation of sedges 

and grasses, with scattered or clumped growth of dwarfed trees or shrubs. Given the 

lack of information on tropical bogs and fens worldwide, a summary is provided from 

Hawaii (Mueller-Dombois and Fosberg 1998).

The vegetation of most of the Hawaiian bogs may be a continuous or discontinuous 

dwarf-scrub interspersed with a matrix of hummocky sedges, usually with scattered 

emergent shrubs 1 or 2 m tall, or rarely, a bed of Sphagnum and grass with scattered 

shrubs and large ferns. Peatmoss (Sphagnum spp.) occurs in only a few Hawaiian 

bogs. Thus, peat is from sedges and grasses, with inclusions of woody peat. Most bogs 

are found as openings in rainforest, often next to cloud forests (Mueller-Dombois and 

Fosberg 1998).

Environment

Environmental Description: In tropical regions of the world, peat-accumulating 

conditions occur in the cold, wet highlands of the Andes and in the floodplains of 

the lowlands, where peatlands have a fluctuating water table, with groundwater and 

surface water movements being common, and trees are excluded. “True” tropical bogs 

and fens, however, with sedge or moss peat are relatively rare. Tropical bogs occur 

in high, rainy regions, on flat to gently sloping, water-soaked ground with nearly 
USDA Forest Service RMRS-GTR-346. 2016. 103

impervious clay beneath peat of depths varying from less than 0.1 to greater than 3 

m. Given the lack of information on tropical bogs and fens worldwide, a summary is 

provided from Hawaii (Mueller-Dombois and Fosberg 1998).

Most Hawaiian bogs are on relatively flat ground underlain by more-or-less impervious clay in areas of high rainfall, usually exceeding 250 cm per year. They range in 

size from less than 1,000 square m to over 5 ha. Organic overlays may vary from less 

than 10 cm (“protobogs” or “clay bogs”) to those with less than 40 cm (“semi-bogs”) 

to those with over 40 cm organic overlays (“true bogs”). The depth of the overlay is 

a function of age (some bogs originated over 11,000 years ago), temperature (with 

cooler locations having slower decomposition and greater peat depths) and anaerobic 

conditions (MuellerDombois and Fosberg 1998).

Two kinds of Hawaiian bogs can be distinguished: ombrogenous (fed by rainwater) 

and soligenous (fed by both rain- and groundwater). The first type can occur in areas 

of high rainfall, exceeding 12 m per year, so that the soil need not even be impervious 

for the bog to form. The second term, “soligenous bog” (or fen), is more appropriate 

for most Hawaiian bogs (Mueller-Dombois and Fosberg 1998).

Distribution

Geographic Range: Tropical Bog & Fen is found where peat-accumulating conditions occur in the cold, wet mountain highlands and in various floodplains of the 

lowlands, where trees are excluded. In the United States, the type is found in Hawaii.

Citations

Synonymy: 

> Peatlands (Mitsch and Gosselink 2000) [Bogs and fens are treated together, but 

tropical and temperate bogs are not separated. Forested bogs are included.] 

> Peatlands (Roth 2009) [Bogs and fens are treated together, but tropical and temperate bogs are not separated. Forested bogs are included.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and C. Josse

Acknowledgments:

Version Date: 26 Aug 2014

2.C.2. Temperate to Polar Bog & Fen (F016)

Overview

Database Code: 2.C.2 (F016)

Scientific Name: Temperate to Polar Bog & Fen Formation

Common Name (Translated Scientific Name): Temperate to Polar Bog & Fen 

Formation

Colloquial Name: Temperate to Polar Bog & Fen

Hierarchy Level: Formation

Placement in Hierarchy: 2.C. Shrub & Herb Wetland (S44)

Lower Level Hierarchy Units:

See examples in Appendix J
104 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Temperate to Polar Bog & Fen includes temperate 

bogs and fens dominated by Sphagnum or brown mosses with ericaceous shrubs, 

graminoids, and low scrub tree growth forms, across the mid-latitudes of the Northern 

Hemisphere from 23 to 70 degrees N, but is much less common in the southern 

mid-latitudes.

Classification Comments: Subarctic and arctic (polar) bogs and fens belong in this 

formation.

Similar NVC Types: 

1.B.5. Boreal Flooded & Swamp Forest (F036): This type includes forested bogs 

with greater than 10 percent cover along with poor swamps.

2.B.2. Temperate Grassland & Shrubland (F012): Upland transitions to wet-mesic 

or moist grasslands, such as wet-mesic prairies, can be hard to place.

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013): 

Fens and marshes can be similar, especially when fen peat mats are inundated 

(as with “shore fens”).

Diagnostic Characteristics: This peatland type is dominated by Sphagnum spp. 

or brown mosses, with ericaceous shrubs, graminoids, and low scrub tree growth 

forms (<5 m). The driest bogs, especially in permafrost terrain, may be covered in 

dwarf-shrubs and lichens. Bogs contain raised or level sphagnum peat surfaces that 

are ombrotrophic or weakly minerotrophic, whereas fens are groundwater-driven, and 

moderately to strongly minerotrophic.

Vegetation

Physiognomy and Structure: This peatland type is dominated by Sphagnum spp. 

or brown mosses, with ericaceous shrubs, graminoids, and low scrub tree growth 

forms (<5 m). The driest bogs, especially in permafrost terrain, may be covered in 

dwarf-shrubs and lichens. The vegetation on fens is closely related to the depth of the 

water table and the chemistry of the water present. The composition of vegetation may 

also reflect regional geographic variations. In general, graminoid vegetation and some 

bryophytes dominate wetter fens where the water table is above the surface. Shrubs 

are prominent in drier fens where the water table is lower. Trees appear on the driest 

fen sites where microtopographic features such as moss hummocks provide habitats as 

much as 20 cm above the water table. Sites in fens with waters extremely low in dissolved minerals are poor fens and have Sphagnum mosses and ericaceous shrubs. Poor 

fens are sometimes placed with bogs as “acid peatlands.” Fens with slightly higher 

concentrations of dissolved minerals are moderately rich fens and are dominated by 

sedges and brown mosses (such as Drepanocladus sp.). The moderate to extremely 

rich fens are sometimes collectively called “alkaline peatlands” or “rich peatlands” 

(National Wetlands Working Group 1997).

Environment

Environmental Description: The bog surface, which is raised or level with the 

surrounding terrain, is virtually unaffected by runoff waters or groundwater from the 
USDA Forest Service RMRS-GTR-346. 2016. 105

surrounding mineral soils. Generally the water table is at or slightly below the bog 

surface. As the bog surface is raised, so is the bog water table relative to the elevation 

of the water table at the edges of the bog. Precipitation, fog, and snowmelt are the 

primary water sources and, thus, all bogs are ombrogenous. Given that precipitation 

does not contain dissolved minerals and is mildly acidic, the surface bog waters are 

consequently low in dissolved minerals and acidic. Bog water acidity, usually between 

pH 4.0 and 4.8 (Gorham and Janssens 1992), is enhanced due to the organic acids that 

form during decomposition of the peat and the acids present within Sphagnum leaves 

(National Wetlands Working Group 1997). The soils are mainly Histosols in the US 

soil classification, and Fibrisols, Mesisols and Organic Cryosols (permafrost soils) in 

the Canadian soil classification system (National Wetlands Working Group 1997) [see 

Brady and Weil (2002) for comparison of Canadian soil orders with U.S. and FAO 

systems].

Fens are peatlands with a fluctuating water table. The waters in fens are rich in 

dissolved minerals and, therefore, are minerotrophic. Groundwater and surface water 

movement is a common characteristic of fens. Surface flow may be directed through 

channels, pools, and other open waterbodies that can form characteristic surface patterns. The dominant materials are moderately decomposed sedge and brown moss 

peats of variable thickness.

Distribution

Geographic Range: This formation is found across the mid-latitudes of the 

Northern Hemisphere from 23 to 70 degrees N, but is much less common in the southern mid-latitudes.

Citations

Synonymy: 

> = Bog Wetland Class (National Wetlands Working Group 1997) [The class may 

include perhaps poor fens,), but is otherwise synonymous with this formation.] 

> Fen Wetland Class (National Wetlands Working Group 1997) [The class is synonymous with the fen part of this formation. Trees are typically less than 10 percent 

cover.] 

> Peatlands (Mitsch and Gosselink 2000) [Bogs and fens are treated together, but 

tropical and temperate bogs are not separated. Forested bogs are included.] 

> Peatlands (Roth 2009) [Bogs and fens are treated together, but tropical and temperate bogs are not separated. Forested bogs are included.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014
106 USDA Forest Service RMRS-GTR-346. 2016.

2.C.3. Tropical Freshwater Marsh, Wet Meadow & 

Shrubland (F030)

Overview

Database Code: 2.C.3 (F030)

Scientific Name: Tropical Freshwater Marsh, Wet Meadow & Shrubland Formation

Common Name (Translated Scientific Name): Tropical Freshwater Marsh, Wet 

Meadow & Shrubland Formation

Colloquial Name: Tropical Freshwater Marsh, Wet Meadow & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.C. Shrub & Herb Wetland (S44)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Freshwater Marsh, Wet Meadow & Shrubland 

includes freshwater wet meadows, shallow and deep emergent marshes, with the 

upper limits of salinity at 0.5 ppt, above which it is considered saltwater. The vegetation comprises evergreen emergent aquatic macrophytes, chiefly graminoids such as 

rushes, reeds, grasses and sedges, and shrubs and other herbaceous species such as 

broad-leaved emergent macrophytes, floating-leaved and submergent species, and 

nonvascular plants such as brown mosses, liverworts, and macroscopic algae. It is 

found widely throughout wetland habitats of the tropical latitudes, from the equator to 

about 23 degrees N and S.

Classification Comments: Further review is needed of the similarities and differences between temperate and tropical freshwater marshes.

Similar NVC Types: 

2.C.1. Tropical Bog & Fen (F002): Tropical Freshwater Marsh, Wet Meadow & 

Shrubland (F030) more typically contains muck soils and lacks the heath and 

moss layers found in this bog and fen formation (F002).

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013)

Diagnostic Characteristics: The vegetation comprises evergreen emergent aquatic 

macrophytes, chiefly graminoids such as rushes, reeds, grasses and sedges, and 

shrubs and other herbaceous species such as broad-leaved emergent macrophytes, 

floating-leaved and submergent species, and nonvascular plants such as brown mosses, 

liverworts, and macroscopic algae, with tree cover less than 10 percent, with the upper 

limits of salinity at 0.5 ppt, above which it is considered saltwater, and where freezing 

temperatures are rare to absent.

Vegetation

Physiognomy and Structure: Tropical Freshwater Marsh, Wet Meadow & 

Shrubland vegetation predominantly comprises evergreen emergent aquatic macrophytes, chiefly graminoids such as rushes, reeds, grasses and sedges, and shrubs and 

other herbaceous species such as broad-leaved emergent macrophytes, floating-leaved 
USDA Forest Service RMRS-GTR-346. 2016. 107

and submergent species, and nonvascular plants such as brown mosses, liverworts, 

and macroscopic algae. There is a greater proportion of evergreen herbaceous plants in 

this tropic type, as compared to the temperate type. Vegetation is usually arranged in 

distinct zones of parallel or concentric patterns in response to gradients of water depth, 

frequency of drawdown, water chemistry or disturbance. Seasonal drawdowns may 

expose mudflats that are revegetated by pioneering herb and grass species.

Environment

Environmental Description: These wetlands have shallow water and levels that 

usually fluctuate daily, seasonally or annually due to tides (freshwater tidal), flooding, 

evapotranspiration, groundwater recharge, or seepage losses. Salinity is 0.5 ppt, above 

which it is considered saltwater. Seasonal drawdowns may occur.

The occurrence of large savanna extensions in flat land (Orinoco basin and Beni 

savannas), as well as of numerous lakes in the Amazon basin, create some unique 

tropical geomorphological settings that in the seasonal savannas are occupied by permanent marshes dominated by herbs such as Cyperus giganteus and Thalia geniculata, 

and seasonally inundated savannas that are dominated by grasses (Hymenachne amplexicaulis, Panicum mertensii, Paspalum fasciculatum). The vegetation surrounding 

the Amazonian lakes varies from flooded forest to dense aquatic vegetation formations, and the freshwater marshes belong to the more stable conditions in this gradient 

created by the river’s dynamics.

Distribution

Geographic Range: This formation is found widely throughout wetland habitats of 

the tropical latitudes, from the equator to about 23 degrees N and S.

Citations

Synonymy:

> Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate 

marshes are treated together, and inland saline marshes are included here too, and both 

emergent and aquatic vegetation.] 

> Nontidal Freshwater Marshes (Roth 2009) [It is not clear whether non-tidal salt 

marshes are included here. Both tropical and temperate marshes are treated together.] 

> Tidal Freshwater Marshes (Roth 2009) [Both tropical and temperate marshes are 

treated together.] 

> Tidal Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate marshes are treated together, and both emergent and aquatic vegetation.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: C. Josse and D. Faber-Langendoen, after National Wetlands 

Working Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014
108 USDA Forest Service RMRS-GTR-346. 2016.

2.C.4. Temperate to Polar Freshwater Marsh, Wet 

Meadow & Shrubland (F013)

Overview

Database Code: 2.C.4 (F013)

Scientific Name: Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland 

Formation

Common Name (Translated Scientific Name): Temperate to Polar Freshwater 

Marsh, Wet Meadow & Shrubland Formation

Colloquial Name: Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland

Hierarchy Level: Formation

Placement in Hierarchy: 2.C. Shrub & Herb Wetland (S44)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Temperate to Polar Freshwater Marsh, Wet Meadow & 

Shrubland includes wet riparian and swamp shrublands, wet meadows, wet prairies, 

and shallow and deep emergent marshes. The vegetation is comprised of seasonal 

green emergent, hydrophytic shrubs and herbs with at least 10 percent cover, on 

mucky, inundated or saturated soils across the mid-latitudes of the Northern and 

Southern hemispheres from 23 to 70 degrees.

Type Concept: Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland 

includes wet riparian and swamp shrublands, wet meadows, wet prairies, and shallow and deep emergent marshes on mucky, inundated or saturated soils across the 

mid-latitudes of the Northern and Southern hemispheres from 23 to 70 degrees. These 

wetlands have shallow water, with levels that usually fluctuate daily, seasonally or 

annually due to tides (freshwater tidal), flooding, evapotranspiration, groundwater 

recharge, or seepage losses. The vegetation is comprised of seasonal green emergent 

hydrophytic woody and herbaceous macrophytes with at least 10 percent cover, including graminoids such as rushes, reeds, grasses and sedges, other herbaceous species 

such as broad-leaved emergent forbs, and short to tall shrubs (primarily broad-leaved 

deciduous but some broad-leaved evergreen in warm-temperate regions). Associated 

with these plants are floating-leaved and submergent species, and nonvascular plants 

such as brown mosses, liverworts, and macroscopic algae. The vegetation is usually 

arranged in distinct zones of parallel or concentric patterns in response to gradients 

of water depth, frequency of drawdown, water chemistry or disturbance. Saline or 

brackish non-tidal marshes are excluded. Seasonal drawdowns may expose mudflats 

that are vegetated by pioneering herb and grass species. Plant communities of seasonal 

marshes are dynamic, shifting spatially with water levels and changing in composition 

over a short time. Communities of semi-permanent marshes usually are more stable, 

represented by stands of reeds, which may persist for many years in the absence of 

severe drought.
USDA Forest Service RMRS-GTR-346. 2016. 109

Classification Comments: Inland salt marshes are currently excluded here and 

placed with salt marsh. Freshwater tidal marshes are placed here. Further review is 

needed of the similarities and differences between temperate and tropical freshwater 

marshes. Subarctic and arctic (polar) marshes belong in this formation.

Similar NVC Types: 

1.B.3. Temperate Flooded & Swamp Forest (F026): Temperate to Polar Freshwater 

Marsh, Wet Meadow & Shrubland (F013) contains tall-shrub swamps that share 

many structural and habitat similarities to hardwood tree swamps (F026), especially during the tree regeneration stage.

2.C.3. Tropical Freshwater Marsh, Wet Meadow & Shrubland (F030): Temperate to 

Polar Freshwater Marsh, Wet Meadow & Shrubland (F013) is more strongly affected by cold climatic conditions, but vegetation criteria that distinguish these 

two formations need to be described.

2.C.2. Temperate to Polar Bog & Fen (F016): Fens and marshes can be similar, 

especially when fen peat mats are inundated (as with “shore fens”).

2.C.5. Salt Marsh (F035): Inland salt marshes are non-tidal, but saline (or haline) 

and may resemble some brackish freshwater marshes.

Diagnostic Characteristics: The vegetation is comprised of seasonal green emergent hydrophytic macrophytes, chiefly graminoids such as rushes, reeds, grasses and 

sedges, other herbaceous species such as broad-leaved emergent forbs, and short to 

tall, primarily broad-leaved deciduous shrubs (some broad-leaved evergreen shrubs 

in warm-temperate climates), across the mid-latitudes of the Northern and Southern 

hemispheres from 23 to 70 degrees.

Vegetation

Physiognomy and Structure: Temperate to Polar Freshwater Marsh, Wet 

Meadow & Shrubland vegetation predominantly comprises summer green emergent 

hydrophytic macrophytes, with at least 10 percent cover, including graminoids such 

as rushes, reeds, grasses and sedges, other herbaceous species such as broad-leaved 

emergent forbs, and short to tall shrubs (primarily broad-leaved deciduous, but some 

broad-leaved evergreen in warm-temperate regions). Associated with these plants are 

floating-leaved and submergent species, and nonvascular plants such as brown mosses, 

liverworts, and macroscopic algae. Vegetation is usually arranged in distinct zones of 

parallel or concentric patterns in response to gradients of water depth, frequency of 

drawdown, water chemistry or disturbance (National Wetlands Working Group 1997).

Environment

Environmental Description: A temperate freshwater marsh is a wetland that 

has shallow water and levels that usually fluctuate daily, seasonally or annually due 

to tides (freshwater tidal), flooding, evapotranspiration, groundwater recharge, or 

seepage losses. Marshes may experience water level drawdowns that will result in 

portions drying up and exposing the sediments. Marshes receive their water from the 

surrounding catchment as surface runoff, stream inflow, precipitation, storm surges, 

groundwater discharge, longshore currents and tidal action. Marshes dependent on 

surface runoff usually retain less permanent water than sites supplied by groundwater. 
110 USDA Forest Service RMRS-GTR-346. 2016.

The water table usually remains at or below the soil surface, but soil water remains 

within the rooting zone for most of the growing season, except in years of extreme 

drought. In semi-arid regions, some basin marshes may remain dry for several 

consecutive years, and consequently may assume some characteristics of terrestrial 

ecosystems until water levels are restored by above-average precipitation and runoff 

(National Wetlands Working Group 1997).

A marsh is a minerotrophic and usually eutrophic wetland. Nutrients are derived 

from the substrate through periodic aeration. High nutrient levels give rise to the 

characteristic high productivity of vascular plants and high decomposition rates of the 

plant material at the end of the growing season. Such high rates of decomposition give 

rise to marshes producing significant quantities of gases such as methane and carbon 

dioxide. Freshwater marshes are usually circumneutral to highly alkaline owing to the 

presence of dissolved minerals such as calcium, potassium carbonate, or potassium 

bicarbonate.

Soils and substrates encountered in marsh wetlands typically range from mineral 

soils such as Humic and Rego Gleysols to organic soils such as Humisols and 

Mesisols in the Canadian soil classification system (see Brady and Weil, 2002, for 

comparison of Canadian soil orders with U.S. and FAO systems). Normally, marsh 

sediment is a mixture of unconsolidated organic and inorganic material. Clumps, 

hummocks, or tussocks of live and dead herbaceous vegetation may exist in standing water. Those marshes that are seasonally dry or exposed to high energy currents 

usually accumulate little organic matter, in contrast to hydrologically more stable 

and permanently saturated marshes. In the latter case, such as in lakeshore or delta 

marshes, Humisols develop; this organic material can accumulate but seldom is more 

than 40 to 50 cm deep. Under persistent conditions of stable water, sedges and aquatic 

mosses create floating mats of vegetation. This is characteristic of marsh stages transitional to rich fens (National Wetlands Working Group 1997).

Marshes occur in many geomorphological settings which include low-lying areas 

adjacent to rivers, lakes, the sea, and any other position on the land surface where 

groundwater may discharge. In northern regions, marshes are common in nutrient-rich 

sites associated with rivers either in the floodplains or at their mouth on alluvial fans 

and deltas (National Wetlands Working Group 1997).

Distribution

Geographic Range: This formation is found on mucky, inundated or saturated 

soils across the mid-latitudes of the Northern and Southern hemispheres from 23 to 70 

degrees.

Citations

Synonymy:

< Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate 

marshes are treated together.] 

< Nontidal Freshwater Marshes (Roth 2009) [It is not clear whether nontidal salt 

marshes are included here. Both tropical and temperate marshes are treated together.] 

< Tidal Freshwater Marshes (Roth 2009) [Both tropical and temperate marshes are 

treated together.] 
USDA Forest Service RMRS-GTR-346. 2016. 111

< Tidal Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate marshes are treated together.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014

2.C.5. Salt Marsh (F035)

Overview

Database Code: 2.C.5 (F035)

Scientific Name: Salt Marsh Formation

Common Name (Translated Scientific Name): Salt Marsh Formation

Colloquial Name: Salt Marsh

Hierarchy Level: Formation

Placement in Hierarchy: 2.C. Shrub & Herb Wetland (S44)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Salt Marsh is a wetland that has shallow water and levels 

that usually fluctuate due primarily to tides along the coast or changes in water depth 

in depressions. Coastal salt marshes are primarily intertidal; that is, they are found 

in areas at least occasionally inundated by high tide but not flooded during low tide, 

including estuaries, lagoons, and the lee side of barrier islands. The vegetation is comprised of emergent shrubs and herbs with at least 10 percent cover, especially saline or 

halophytic species. They occur at all latitudes around the globe, but are concentrated 

in the temperate mid-latitudes (23 to 70 degrees N and S).

Classification Comments: Further review is needed of the similarities and differences between temperate and tropical salt marshes, as well as subarctic and arctic 

(polar) salt marshes, all of which are placed in this formation. From an overall 

physiognomic and ecological perspective, maintaining a single salt marsh formation 

is desirable. Although they represent a small fraction of the overall salt marsh area, 

there are extensive tropical salt marshes, often found in association with mangroves; 

the mangroves occupy the lower, regularly tidally inundated part of the intertidal zone 

and salt marsh the upper zone above the mangroves. Australia has more than one million hectares of salt marsh and sparsely vegetated high level tidal flats, with a large 

proportion of this being tropical. More information on potentially distinct floristics 

and growth forms of tropical salt marshes is needed.

Similar NVC Types: 

1.A.5. Mangrove (F006): Some mangrove formations may be mixed with salt 

marshes, but by and large they are physiognomically quite distinct.
112 USDA Forest Service RMRS-GTR-346. 2016.

2.C.4. Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland (F013): 

Salt Marsh (F035) contains inland salt marshes that are non-tidal and saline (or 

haline) and may resemble some brackish freshwater marshes (F013).

Diagnostic Characteristics: Salt Marsh is a wetland that has shallow water and 

levels that usually fluctuate due primarily to tides along the coast or changes in water 

depth in depressions. Coastal tidal salt marshes are found in areas at least occasionally 

inundated by high tide but not flooded during low tide. The vegetation is comprised 

of emergent aquatic macrophytes with at least 10 percent cover, especially saline or 

halophytic species, chiefly graminoids such as rushes, reeds, grasses and sedges, and 

shrubs and other herbaceous species such as broad-leaved emergent macrophytes. 

They occur at all latitudes around the globe, but are concentrated in the temperate midlatitudes (23 to 70 degrees N and S).

Vegetation

Physiognomy and Structure: Salt Marsh vegetation comprises primarily emergent 

aquatic macrophytes with at least 10 percent cover, especially saline or halophytic 

species, chiefly graminoids such as rushes, reeds, grasses and sedges, and shrubs and 

other herbaceous species such as broad-leaved emergent macrophytes. Floating-leaved 

and submergent species (aquatic vegetation) and macroscopic algae are present at 

varying levels of abundance.

In tidal salt marshes, the vegetation is usually arranged in distinct zones of parallel 

patterns in response to gradients of tidal flooding frequency and duration, water chemistry or disturbance. They are sometimes described simply as “high marsh” (limits of 

high tide) and “low marsh” (intertidal marsh). These salt marshes have gradients that 

include barren salt flats at the tidal edge, rushes, and then halophytic herbs and grasses 

at the outer edge. Daily drawdowns may expose mudflats that contain a sparse mix of 

pioneering herb and grass species.

Saline or brackish non-tidal marshes also have gradients but with fewer zones that 

include barren salt flats in the center of the marsh, rushes, and then halophytic herbs 

and grasses at the outer edge. Seasonal drawdowns may expose mudflats that are 

revegetated by pioneering herb and grass species.

Although the bulk of salt marshes are temperate to polar, there are tropical salt 

marshes, often found in association with mangroves; the mangroves occupy the lower, 

regularly tidally inundated part of the intertidal zone and salt marsh the upper zone 

above the mangroves. Australia has more than one million hectares of salt marsh and 

sparsely vegetated high level tidal flat, with the greater proportion of this being tropical. Tropical salt marshes are species-poor, and species richness increases with more 

temperate conditions; for example in Australia, the richest salt marsh floras are found 

in Tasmania and Victoria.

Environment

Environmental Description: A salt marsh is a wetland that has shallow water and 

levels that usually fluctuate due primarily to tides or drawdowns in seasonal saline 

basins. Coastal salt marshes are primarily intertidal; that is, they are found in areas at 

least occasionally inundated by high tide but not flooded during low tide, including 

estuaries, lagoons, and the lee side of barrier islands. Salt marshes form wherever 

the accumulation of sediments is equal to or exceeds the rate of land subsidence and 
USDA Forest Service RMRS-GTR-346. 2016. 113

where there is adequate protection from high energy waves and storms. Salt marshes 

are located in estuaries or lower stream reaches, and behind baymouth bars or other 

sheltered sites. Sediments can either be formed on marine-dominated coastlines from 

reworked marine sediments or formed in deltaic areas where the main source of mineral sediment is riverine.

Salt marsh chemistry is dominated by salinity. Salinity levels vary depending on a 

complex of factors, including frequency of inundation, rainfall, soil texture, freshwater 

influence, fossil salt deposits, and other factors. The lower limits of salinity are defined 

as at least 0.5 ppt, below which it is considered freshwater, though the oligohaline 

category (0.5 – 5 ppt) can be considered transitional freshwater (see Cowardin and 

others, 1979, for salinity scale). The concentration of most elements needed for plant 

growth also varies depending on these factors. A number of studies have shown that 

salt marshes are especially nitrogen limited. The water in non-tidal saline marshes 

is high in dissolved salts because water losses through evaporation concentrate 

sulphates and chlorides of sodium and magnesium. In highly saline non-tidal marshes, 

vegetation development is severely hampered because salt concentrations are so high 

as to become toxic to plants (National Wetlands Working Group 1997).

Distribution

Geographic Range: Salt marshes occur at all latitudes around the globe, but are 

concentrated in the temperate mid-latitudes (23 to 70 degrees N and S).

Citations

Synonymy:

= Salt Marshes (Woodward 2008)

> Tidal Salt Marshes (Mitsch and Gosselink 2000) [Non-tidal inland salt marshes are 

treated by them under their Freshwater Marsh type.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014

3. Desert & Semi-Desert (C03)

Overview

Database Code: 3 (C03)

Scientific Name: Xeromorphic Woodland, Scrub & Herb Vegetation Class

Common Name (Translated Scientific Name): Xeromorphic Woodland, Scrub & 

Herb Vegetation Class

Colloquial Name: Desert & Semi-Desert

Hierarchy Level: Class

Lower Level Hierarchy Units:

3.A. Warm Desert & Semi-Desert Woodland, Scrub & Grassland (S06)

3.B. Cool SemiDesert Scrub & Grassland (S11)
114 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Cool and warm semi-deserts dominated by xeromorphic 

growth forms, including succulent (e.g., cacti, euphorbias) and small-leaved shrubs

and trees, desert grasses and other xeromorphic growth forms, with an irregular horizontal canopy spacing that is often open to very sparse (1 percent) cover.

Classification Comments: In desert regions, the vegetation may be very sparse (at 

or below 1 percent). Some judgment is required to ensure how to sample and classify 

vegetation in stands where there is less than 1 percent vascular plant cover in parts, 

but not all, of the stand. That is, some deserts may have only patchy non-vegetated 

areas, whereas others may have extensive non-vegetated areas. More work is needed 

to define xeromorphic herbaceous growth forms, such as ephemerals, that may appear 

under rare high-precipitation years.

Semi-desert grasslands may be hard to identify in this class when woody plants are 

absent or uncommon, because there are no herbaceous growth forms currently recognized that are diagnostic for the xeromorphic class. Desert grasses may be xerophytic 

but not clearly xeromorphic. However, in many cases they will have strong floristic 

similarity to open desert shrublands and, if degraded, may be dominated by desert 

shrubs. More work is needed to determine if such growth forms can be specified (e.g., 

desert-blooming ephemerals).

Similar NVC Types: 

2. Shrub & Herb Vegetation (C02): Desert grasslands typically include xeromorphic 

shrubs and trees, which place them in the Xeromorphic class. Environmental 

drivers and stressors can cause desert grasslands to cross thresholds into desert 

scrub. They may also cause dry mesomorphic grasslands with small-leaved 

shrubs to appear similar to xeromorphic grasslands (e.g., shortgrass prairie in 

the North American Great Plains).

4. Polar & High Montane Scrub, Grassland & Barrens (C04): In montane deserts, 

there may be a transition from cool semi-desert to alpine that may be difficult 

to distinguish.

6. Open Rock Vegetation (C06): This class is restricted to open rock vegetation 

where nonvascular vegetation is at least 10 percent and where vascular plants, 

if present, are mesomorphic.

Diagnostic Characteristics: Xeromorphic tree (succulent tree, small-leaved tree) 

or shrub (succulent shrub, small-leaved shrub) growth forms have the majority of the 

cover compared to mesomorphic and cryomorphic shrub and herb growth forms, and 

mesomorphic trees have less than 10 percent cover. The vegetation has irregular horizontal canopy spacing, and may be as low as 1 percent cover.

Vegetation

Physiognomy and Structure: Growth Forms: Stands are dominated by xeromorphic growth forms (succulent tree, small-leaved tree, succulent shrub, small-leaved 

shrub, some types of rosette shrub) and various associated herb growth forms. 

Drought-deciduous, including facultatively drought-deciduous, trees may be present. 

Other characteristics include opportunistic leaf-flush (e.g., ocotillo), high incidence 

of energy allocation to protective structures such as spines, and allocation to heator moisture-loss structures. The various herb growth forms currently recognized in 
USDA Forest Service RMRS-GTR-346. 2016. 115

FGDC (2008) are not exclusive to the xeromorphic class, and more work is needed 

to assess whether additional herbaceous growth form types should be recognized that 

may be distinctive for this class. For example, Crassulacean Acid Metabolism (CAM) 

physiology is common in desert plants, especially among succulents.

In addition some desert vegetation has biological crust, comprised of soil particles, 

cyanobacteria, algae, microfungi, lichens, and bryophytes. The crusts do not develop 

under a closed canopy of vascular plants. They do occur in all climates following disturbance of that cover. However, the most conspicuous development of crusts occurs 

in hot, cool, and cold semi-arid and arid areas where plants are widely spaced.

Structure: Stands are very open and have irregular shrub or herb horizontal stem 

spacing, often with prominent non-vegetated surfaces. Xeromorphic trees are present, 

occasionally moderately dense (10 to 60 percent). There is less than 10 percent cover 

of mesomorphic trees, and xeromorphic tree, shrub and/or herb growth forms have 

the majority of cover compared to mesomorphic or cryomorphic shrubs or herbs. 

Tree cover varies from sparse to moderately closed (1 percent to 60 percent cover). 

Nonvascular and dwarf shrub growth forms may vary from 0 to 100 percent. At maturity, xeromorphic trees typically are greater than 2 m, tall shrubs typically greater than 

0.3 m, and herbs are of any height, but mostly greater than 0.3 m. A biological crust 

layer may also be present.

Environment

Environmental Description: Climate: In temperate climates, the growing season 

is typically very dry, and in tropical climates, droughts are persistent, and rain is 

minimal.

Soil/substrate/hydrology: Soils may be thin, rocky, saline/haline (salt pannes, playas). 

Distribution

Geographic Range: This type is found in the Desert divisions in Bailey’s (1989) 

Dry Domain.

Citations

Synonymy:

= Desert Biomes (Quinn 2009)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 17 Jul 2012

3.A. Warm Desert & Semi-Desert Woodland, 

Scrub & Grassland (S06)

Overview

Database Code: 3.A (S06)

Scientific Name: Warm Desert & Semi-Desert Woodland, Scrub & Grassland 

Subclass

Common Name (Translated Scientific Name): Warm Desert & Semi-Desert 
116 USDA Forest Service RMRS-GTR-346. 2016.

Woodland, Scrub & Grassland Subclass

Colloquial Name: Warm Desert & Semi-Desert Woodland, Scrub & Grassland

Hierarchy Level: Subclass

Placement in Hierarchy: 3. Desert & Semi-Desert (C03)

Lower Level Hierarchy Units:

3.A.1. Tropical Thorn Woodland (F039)

3.A.2. Warm Desert & Semi-Desert Scrub & Grassland (F015)

Concept Summary

Type Concept Sentence: Warm Desert & Semi-Desert Woodland, Scrub & 

Grassland occurs in dry warm-temperate, subtropical and tropical climates, uncommon 

near the equator to increasingly common between 15 and 35 degrees N and S latitude.

Classification Comments: This subclass includes the low desert-like tropical 

thornwoods, which can form a transition to 1.A.1. Tropical Dry Forest & Woodland 

Formation (F003). In the Neotropics, Brazilian caatinga includes both Tropical Dry 

Forest & Woodlands and extensive Tropical Thorn Woodland and scrub. This subclass 

also occurs in the Neotropics in the Guajira (Colombia, Venezuela), Gran Chaco 

(Bolivia, Argentina, Paraguay), Low Dry Inter-Andean Valleys (Bolivia, Argentina) 

and Pacific semi-deserts of west-southern Ecuador and northwestern Perú (Tumbes).

Similar NVC Types: 

1.A. Tropical Forest & Woodland (S17): Tropical Forest & Woodland (S17) in drier 

climates may have small-leaved sclerophyllous evergreen trees or deciduous 

trees that can be similar to trees found in thorn woodland in warm deserts. 

Thorn woodlands are sometimes included as part of Tropical Forest.

Diagnostic Characteristics: Vegetation is dominated by xeromorphic growth 

forms, and varies from open to closed woodlands, open shrub-scrub to complexes 

of succulents, thorn scrub, and microphyllous-leaved subshrubs, often less than 2 m 

tall, though scattered tall succulents may occur. Ephemeral (therophytic) herbaceous 

growth forms may also be present.

Vegetation

Physiognomy and Structure: Vegetation is dominated by xeromorphic growth 

forms, and varies from open to closed woodlands, open shrub-scrub to complexes 

of succulents, thorn scrub, and microphyllous-leaved subshrubs, often less than 2 m 

tall, though scattered tall succulents may occur. Ephemeral (therophytic) herbaceous 

growth forms may also be present within semi-desert woodlands. Desert grasslands 

often occur in transitional zones, typically containing a sparse layer of xeromorphic 

shrubs and open ground layer. Included are very open deserts where vegetation is very 

sparse, and where the ground layer is sandy, stony desert pavements, salt crust. Bare 

rock, often with nonvascular mats, is placed in open rock vegetation (Whittaker 1975).

Environment

Environmental Description:

Climate: Warm semi-desert woodlands, scrub and grasslands occur in dry warmtemperate, subtropical and tropical climates.
USDA Forest Service RMRS-GTR-346. 2016. 117

Distribution

Geographic Range: Warm Desert & Semi-Desert Woodland, Scrub & Grassland 

occurs in dry warm-temperate, subtropical and tropical climates, is uncommon near 

the equator to increasingly common between 15 and 35 degrees N and S latitude.

Citations

Synonymy:

> Warm Deserts (Quinn 2009) [The author does not include thorn woodlands.] 

= Warm semidesert scrub: biome-type 17 (Whittaker 1975) [The author does not 

include thorn woodlands.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and G. Navarro

Acknowledgments:

Version Date: 26 Aug 2014

3.A.1. Tropical Thorn Woodland (F039)

Overview

Database Code: 3.A.1 (F039)

Scientific Name: Tropical Thorn Woodland Formation

Common Name (Translated Scientific Name): Tropical Thorn Woodland Formation

Colloquial Name: Tropical Thorn Woodland

Hierarchy Level: Formation

Placement in Hierarchy: 3.A. Warm Desert & SemiDesert Woodland, Scrub & 

Grassland (S06)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Thorn Woodland includes warm semi-arid or 

arid deciduous woodlands and low forests with xeromorphic adaptations found in 

Tropical, Mediterranean and Temperate xeric and desertic bioclimates around the 

globe, uncommon near the equator to increasingly common between 15 and 35 degrees N and S latitude.

Classification Comments: Many authors include Tropical Thorn Woodland as part 

of a broadly defined “Tropical Dry Forest & Woodland” or “seasonally dry tropical 

forest” (SDTF). For example, Pennington and others (2006) use a wide interpretation 

of SDTF in the Neotropics, including formations as diverse as tall forest on moister 

sites to cactus scrub on the driest, but they exclude the Chaco of Argentina, Paraguay, 

and Bolivia because it receives frost. See also Oliveira-Filho and others (2006) who 

include caatinga and carrascos within their broad definition of SDTF, but exclude cerrados and chaco. Here, we create a separate formation for Tropical Thorn Woodlands 

in which we unite the xeromorphic parts of the caatinga, carrascos, cerrados, and 

chaco, separate from a more narrowly defined 1.A.1. Tropical Dry Forest & Woodland 

Formation (F003) that lacks xeromorphic growth forms.
118 USDA Forest Service RMRS-GTR-346. 2016.

Distribution of this type needs review. It may be most common in tropical climates, 

but may extend into warm-temperate regions, such as northern Mexico and southwestern United States. By our definition, a certain amount of frost can also occur.

Similar NVC Types: 

1.A.1. Tropical Dry Forest & Woodland (F003).

3.A.2. Warm Desert & Semi-Desert Scrub & Grassland (F015).

Diagnostic Characteristics: Tropical Thorn Woodland includes warm semi-arid or 

arid deciduous woodlands and low forests with several xeromorphic adaptations such 

as microphyllous and/or resinous leaves, thorns, brachyblasts, pachycaulal treelets and 

diverse shrubby and arborescent Cactaceae.

Vegetation

Physiognomy and Structure: The canopy is 8 to 15 m tall, open to dense, and 

dominated by low deciduous trees, arboreal cacti and high shrubs with xeromorphic 

adaptations. Very characteristic large colonies of thorny terrestrial clumping bromeliads, diverse thorn microphyllous scrubs and xeromorphic herbs and vines are 

frequently found in the understory.

Environment

Environmental Description: Climate: Tropical Thorn Woodland occurs in 

Tropical, Mediterranean and Temperate xeric and desertic bioclimate categories of 

the global bioclimatic classification of Rivas-Martínez and Rivas-Saenz (1996, 2009), 

with dry, semi-arid and arid ombrotypes.

Soil/substrate/hydrology: The soils are well to somewhat well drained, non-floodable and xeric, frequently on old alluvial plains and glacis.

Distribution

Geographic Range: The largest area of this formation in the Neotropics is the Gran 

Chaco ecoregion in southern Bolivia, northern Argentina, and northwestern Paraguay. 

Other important areas include the dry Inter-Andean Valley ecoregion of the southern 

Bolivian Andes and northwestern Argentina and the Caatinga ecoregion in Brazil and 

the Colombian-Venezuelan Guajira. Minor areas also occur in southwestern Pacific 

coastal Ecuador and adjacent northwestern Perú (Tumbesian ecoregion). In extratropical areas of South America, this formation occurs in semi-deserts and deserts of central 

Chile and in central-west Argentina (xeric Patagonia, Argentinian Monte). Elsewhere 

these woodlands may be expected in Africa and parts of the Indo-Malaysian tropics.

Citations

Synonymy:

= Tropical thorn scrub or thornwood: biome-type 9 (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: G. Navarro and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
USDA Forest Service RMRS-GTR-346. 2016. 119

3.A.2. Warm Desert & Semi-Desert Scrub & 

Grassland (F015)

Overview

Database Code: 3.A.2 (F015)

Scientific Name: Warm Desert & Semi-Desert Scrub & Grassland Formation

Common Name (Translated Scientific Name): Warm Desert & Semi-Desert Scrub 

& Grassland Formation

Colloquial Name: Warm Desert & Semi-Desert Scrub & Grassland

Hierarchy Level: Formation

Placement in Hierarchy: 3.A. Warm Desert & Semi-Desert Woodland, Scrub & 

Grassland (S06)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Warm Desert & Semi-Desert Scrub & Grassland occurs 

in dry warm-temperate, subtropical and tropical climates, is uncommon near the equator to increasingly common between 15 and 35 degrees N and S latitude.

Similar NVC Types: 

3.A.1. Tropical Thorn Woodland (F039).

Diagnostic Characteristics: Vegetation is dominated by xeromorphic growth 

forms, and varies from open shrub-scrub to complexes of succulents, thorn scrub, 

and microphyllous-leaved subshrubs, often less than 2 m tall, though scattered tall 

succulents may occur. Ephemeral (therophytic) herbaceous growth forms may also be 

present.

Vegetation

Physiognomy and Structure: Vegetation is dominated by xeromorphic growth 

forms, and varies from open shrub-scrub to complexes of succulents, thorn scrub, 

and microphyllous-leaved subshrubs, often less than 2 m tall, though scattered tall 

succulents may occur. Ephemeral (therophytic) herbaceous growth forms may also 

be present. Desert grasslands often occur in transitional zones, typically containing a 

sparse layer of xeromorphic shrubs and an open ground layer. Included are very open 

deserts where vegetation is very sparse, and where the ground layer is sandy, stony 

desert pavements, salt crust (bare rock, often with nonvascular mats is placed in lithomorphic vegetation). Australian semi-deserts, having evolved in long isolation, are 

most unlike other semi-deserts on other continents; succulents are lacking and spiny 

tussock grasses (spinifex, Triodia) are major plants (Whittaker 1975).

Environment

Environmental Description: Climate: Warm Desert & Semi-Desert Scrub & 

Grassland occurs in dry warm-temperate, subtropical and tropical climates. Mean 

summer temperatures are 29.5 to 35 degrees C, and mean winter temperatures 7 to 

15.5 degrees C. Annual precipitation is 0 to 25 cm as rain only (Quinn 2009). Soil/substrate/hydrology: Calcification, salinization, Aridisol, azonal, salt pans, rocky, sandy, 

with little humus (Quinn 2009).
120 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: Warm Desert & Semi-Desert Scrub & Grassland occurs in 

dry warm-temperate, subtropical and tropical climates, uncommon near the equator to increasingly common between 15 and 35 degrees N and S latitude. In North 

America, it is found in the Mojave, Sonoran, and Chihuahuan regions, and southward 

into México; in South America, from Argentina and Chile to Bolivia and Peru, then 

scattered parts of Venezuela and Colombia; great areas of the semi-desert surround the 

Sahara in northern Africa and extend through the Arabian Peninsula to Iran and the 

Thar Deseret of India. More limited areas with distinctive semi-desert occur in parts 

of the arid areas in East Africa (Somali-Chalbi) and Southwest Africa (Kalahari and 

Karoo). Australian semi-deserts are a quite distinctive form (Whittaker 1975).

Citations

Synonymy:

= Warm Deserts (Quinn 2009)

= Warm semi-desert scrub: biome-type 17 (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and G. Navarro

Acknowledgments:

Version Date: 26 Aug 2014

3.B. Cool Semi-Desert Scrub & Grassland (S11)

Overview

Database Code: 3.B (S11)

Scientific Name: Cool Semi-Desert Scrub & Grassland Subclass

Common Name (Translated Scientific Name): Cool Semi-Desert Scrub & Grassland 

Subclass

Colloquial Name: Cool Semi-Desert Scrub & Grassland

Hierarchy Level: Subclass

Placement in Hierarchy: 3. Desert & Semi-Desert (C03)

Lower Level Hierarchy Units:

3.B.1. Cool Semi-Desert Scrub & Grassland (F033)

Concept Summary

Type Concept Sentence: Cool Semi-Desert Scrub & Grassland occurs in dry, cooltemperate climates, at mid-latitudes (35 to 50 degrees N), typically in the interior of 

continents, and varies from low shrublands to very open grassland and shrub-steppe, 

including open rocky or sandy semi-desert vegetation. 

Classification Comments: The gradation in growth forms between 2.B Temperate 

& Boreal Grassland & Shrubland Subclass (S18) and 3.B Cool Semi-Desert Scrub & 

Grassland Subclass (S11) makes delimiting the concept a challenge. For example, in 

North America, microphyllous sagebrush shrubs may be common in parts of the western Great Plains, comparable to sagebrush types in the Great Basin.
USDA Forest Service RMRS-GTR-346. 2016. 121

Also montane cool semi-desert, in which the temperatures are more strongly hot/

cold, may resemble cryomorphic vegetation. For example, the Salar de Uyuni in 

southwestern Bolivia is the world’s largest salt flat at 10,582 square kilometers (4,086 

square miles), near the crest of the Andes, at 3,656 m (11,995 feet) elevation, and contains both xeromorphic and cryomorphic characteristics (C. Josse pers. comm. 2011).

Similar NVC Types: 

2.B. Temperate & Boreal Grassland & Shrubland (S18): Cool Semi-Desert Scrub & 

Grassland (S11) typically has small-leaved, xerophytic shrubs (e.g., sage) and 

more open bare ground, sometimes with biological crust.

Diagnostic Characteristics: Vegetation is dominated by microphyllous-leaved xeromorphic shrubs. Structure consists of typically low shrubs or graminoids and varies 

from very open grassland and shrub-steppe to shrubland.

Vegetation

Physiognomy and Structure: The vegetation is dominated by microphyllousleaved xeromorphic shrubs. Structure consists of typically low shrubs or graminoids 

and varies from very open grassland and shrub-steppe to shrubland. Vegetation is not 

as much limited by substrates as by drought and fires (Whittaker 1975). Open rocky or 

sandy cool semi-desert vegetation is also placed here. 

Environment

Environmental Description: Climate: Cool Semi-Desert Scrub & Grassland 

occurs in dry, cool-temperate climates, typically in the interior of continents (Quinn 

2009). 

Distribution

Geographic Range: This type occupies extensive landscapes of the Great Basin of 

the western United States, central Asia and Iran, in South America (Patagonia and the 

Andes) and parts of Australia (Whittaker 1975).

Citations

Synonymy:

= Cold Deserts (Quinn 2009)

= Cool-temperate semi-desert scrub: biome-type 18 (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

3.B.1. Cool Semi-Desert Scrub & Grassland (F033)

Overview

Database Code: 3.B.1 (F033)

Scientific Name: Cool Semi-Desert Scrub & Grassland Formation

Common Name (Translated Scientific Name): Cool Semi-Desert Scrub & Grassland 

Formation
122 USDA Forest Service RMRS-GTR-346. 2016.

Colloquial Name: Cool Semi-Desert Scrub & Grassland

Hierarchy Level: Formation

Placement in Hierarchy: 3.B. Cool Semi-Desert Scrub & Grassland (S11)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Cool Semi-Desert Scrub & Grassland occurs in dry, cooltemperate climates, at mid-latitudes (35 to 50 degrees N), typically in the interior of 

continents.

Classification Comments: The gradation in growth forms between 2.B Temperate 

& Boreal Grassland & Shrubland Subclass (S18) and 3.B Cool Semi-Desert Scrub & 

Grassland Subclass (S11) makes delimiting the concept a challenge. For example, in 

North America, microphyllous sagebrush shrubs may be common in parts of the western Great Plains, comparable to sagebrush types in the Great Basin.

Also montane cool semi-desert, in which the temperatures are more strongly hot/

cold, may resemble cryomorphic vegetation. For example, the Salar de Uyuni in 

southwestern Bolivia is the world’s largest salt flat at 10,582 square kilometers (4,086 

square miles), near the crest of the Andes, at 3,656 m (11,995 feet) elevation, and contains both xeromorphic and cryomorphic characteristics (C. Josse pers. comm. 2011).

Similar NVC Types: 

2.B.2. Temperate Grassland & Shrubland (F012): Cool Semi-Desert Scrub & 

Grassland (F033) typically has small-leaved, xerophytic shrubs (e.g., sage) and 

more open bare ground, sometimes with biological crust.

4.A.1. Tropical High Montane Scrub & Grassland (F022): Cool Semi-Desert Scrub 

& Grassland (F033) at high altitudes in the tropics, may be cool or rather hot/

cold deserts that share some characteristics of cryomorphic vegetation of the 

tropical high montane grasslands (F022) because of the freezing temperatures.

Diagnostic Characteristics: Vegetation is dominated by microphyllous-leaved xeromorphic shrubs. Structure consists of typically low shrubs or graminoids and varies 

from open grassland and shrub-steppe to shrubland.

Vegetation

Physiognomy and Structure: The vegetation is dominated by microphyllousleaved xeromorphic shrubs and grasses. Structure consists of typically low shrubs or 

graminoids and varies from open grassland and shrub-steppe to shrubland. Vegetation 

not as much limited by substrates as by drought and fires (Whittaker 1975).

Environment

Environmental Description: Climate: This type occurs in dry, cool-temperate 

climates, typically in the interior of continents (Quinn 2009).

Distribution

Geographic Range: This formation occupies extensive landscapes of the Great 

Basin of the western United States, central Asia and Iran, in South America (Patagonia 

and the Andes) and parts of Australia (Whittaker 1975).
USDA Forest Service RMRS-GTR-346. 2016. 123

Citations

Synonymy:

= Cold Deserts (Quinn 2009)

= Cool-temperate semi-desert scrub: biome-type 18 (Whittaker 1975)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

4. Polar & High Montane Scrub, Grassland & 

Barrens (C04)

Overview

Database Code: 4 (C04)

Scientific Name: Cryomorphic Scrub, Herb & Cryptogam Vegetation Class

Common Name (Translated Scientific Name): Cryomorphic Scrub, Herb & 

Cryptogam Vegetation Class

Colloquial Name: Polar & High Montane Scrub, Grassland & Barrens

Hierarchy Level: Class

Lower Level Hierarchy Units:

4.A. Tropical High Montane Scrub & Grassland (S16)

4.B. Temperate to Polar Alpine & Tundra Vegetation (S12)

Concept Summary

Type Concept Sentence: Tundra, alpine and tropical high montane habitats dominated by cryomorphic growth forms (including dwarf shrubs, krummholz, associated 

herbs, lichens and mosses), with low height and open to closed canopy.

Classification Comments: Our criteria would place a stand with 1 percent or more 

cover of cryomorphic shrubs and herbs, and 99 percent cover of nonvascular lichen 

and moss in this class, if stands lack mesomorphic vegetation (e.g., lichen tundra, typically foliose and fruticose lichens) (Viereck and others 1992). Review is needed on the 

placement of páramo and puna in South America. Currently only super-páramo and 

higher elevation puna are placed here, as this class is restricted to the more strongly 

cryomorphic high montane forms of puna and páramos (e.g., in Venezuela there are 

stands dominated by cryomorphic growth forms but lack the typical grass cover). This 

is because lower elevation páramo and moist puna have mesomorphic grasses covering the ground (often exceeding 80 percent cover), whereas cryomorphic shrubs and 

herbs, although present and conspicuous, may be less than 20 percent cover. These 

lower elevation stands also lack any cryoturbation. Using these criteria, we would 

place these lower elevation stands in the mesomorphic “Tropical Montane Grassland 

& Shrubland” formation. On the other hand, we don’t yet have a working set of “cryomorphic herbs” versus “mesomorphic herb” growth forms so it is hard to know how 

to weigh the presence of these mesomorphic herbs against the cryomorphic shrubs. 

Consistent placement of the subalpine and alpine zones across tropical, temperate and 

boreal regions is needed.
124 USDA Forest Service RMRS-GTR-346. 2016.

Similar NVC Types: 

2. Shrub & Herb Vegetation (C02): Distinguishing cryomorphic vegetation from 

mesomorphic vegetation can be a challenge in both arctic and alpine regions. 

Here we allow mesomorphic extensions into the cryomorphic climatic zone 

to be retained in the mesomorphic class (e.g., boreal mesomorphic tall willow 

shrublands along arctic drainages, or the tropics, lower elevation expressions of 

high montane páramo and puna in South America).

3. Desert & Semi-Desert (C03): In high montane deserts, the xeromorphic desert 

growth forms will transition to cryomorphic growth forms. Review is needed to 

see where issues may arise between temperate alpine and dry deserts or tropical 

high montane puna and high deserts.

6. Open Rock Vegetation (C06): This class is restricted to cryptogam dominated 

sites associated with mesomorphic vegetation, as found in tropical, temperate 

and boreal vegetation regions.

Diagnostic Characteristics: Cryomorphic shrub, krummholz, herb, and nonvascular growth forms (including dwarf shrubs, paramoid or associated herbs, lichens, 

mosses) have the majority of cover compared to mesomorphic or xeromorphic shrub 

and herb growth forms, and mesomorphic trees less than 10 percent cover. The vegetation structure is irregular horizontally, and of low height, often much less than 1 m tall.

Vegetation

Physiognomy and Structure: Growth Forms: Stands are dominated by cryomorphic growth forms, such as dwarf shrub, caulirrosulate (páramo) and various 

associated herb growth forms (forb, graminoid), along with nonvascular lichen and 

moss growth forms. The various herb growth forms are not exclusive to the cryomorphic class, and more work is needed to assess whether additional herbaceous growth 

form types should be recognized that may be distinctive for this class (e.g., creeping or 

matted herb growth forms). In addition, lichens in this class may more commonly be 

foliose or fruticose (e.g., reindeer lichens), at least in Arctic tundra (Billings 2000).

Structure: Stands have open to closed irregular shrub or herb stem spacing; often a 

single low complex stratum, sometimes with prominent non-vegetated surfaces. There 

is less than 10 percent mesomorphic tree cover, and typically greater than 10 percent 

shrub or herb cover (but sparse open cover between 1 percent and 10 percent may 

occur), and with a majority of that cover being cryomorphic shrub and/or herb 

growth form, as compared to mesomorphic or xeromorphic shrub and/or herb cover. 

Nonvascular growth forms may vary from 0 to 100 percent. At maturity, shrubs are 

typically less than 0.3 m, but occasionally as tall as 1 m, and herbs are typically less 

than 0.5 m.

Environment

Environmental Description: Climate: Growing season is either very short, with 

snow cover persisting for most of the year, or growth is greatly restricted by freezing 

to near-freezing temperatures, such as the EDf climate zone of Koeppen (cold continental climate without dry season).
USDA Forest Service RMRS-GTR-346. 2016. 125

Distribution

Geographic Range: This type occurs in the Bailey (1989) Polar Domain, especially Tundra divisions, but also in the alpine elevations in other domains.

Citations

Synonymy:

= Arctic and Alpine Biomes (Quinn 2008)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 17 Jul 2012

4.A. Tropical High Montane Scrub & Grassland (S16)

Overview

Database Code: 4.A (S16)

Scientific Name: Tropical High Montane Scrub & Grassland Subclass

Common Name (Translated Scientific Name): Tropical High Montane Scrub & 

Grassland Subclass

Colloquial Name: Tropical High Montane Scrub & Grassland

Hierarchy Level: Subclass

Placement in Hierarchy: 4. Polar & High Montane Scrub, Grassland & Barrens 

(C04)

Lower Level Hierarchy Units:

4.A.1. Tropical High Montane Scrub & Grassland (F022)

Concept Summary

Type Concept Sentence: Tropical High Montane Scrub & Grassland is dominated 

by herbaceous perennials and small-leaved low woody shrubs or small sub-woody 

species in high tropical mountains, where freezing and cryogenic processes occur. 

It occurs in all tropical high mountains worldwide, where it occupies the sub-nival 

elevations.

Classification Comments: The páramo and the dry and moist puna are not included 

in this subclass, because they have primarily mesomorphic adaptations, and because 

the soils are not subject to cryogenic processes. These vegetation types are treated 

with 2.A.2 Tropical Montane Grassland & Shrubland Formation (F017). Nonetheless, 

although the páramo and the dry and moist puna are not subject to cryogenic soil processes, they are subject to varying levels of freezing. Perhaps the term “cryomorphic” 

places too great a restriction on the concept of “tropical alpine” vegetation.

Also challenging to place consistently in this class is the South American xerophytic vegetation of the Altiplano region of central and-southern Bolivia, northern 

Argentina, and Chile, because the cryomorphic definition is very similar to xeromorphic; that is to say, they share ecological processes and have similar structures (growth 

forms) to each other. The vegetation is not Cool Semi-Desert, but is a hot/cold semidesert, while at the same time is hardly affected by edaphic processes of cryoturbation 
126 USDA Forest Service RMRS-GTR-346. 2016.

and geliturbation expected of the cryomorphic class. We find again the diurnal rhythm 

of ice/thaw of the tropical mountains, but it is marked in these high dry southern areas 

with very high daily solar temperatures and very low nocturnal temperatures. For example, in the Great Salt Flats of Uyuni (Salar de Uyuni) at 3,800 m of altitude, during 

the day temperatures can rise to 20 degrees C and at night to –20 degrees C. This is an 

extreme case related to the immense salt flats, but the lands that surround them repeat 

almost the same features listed above, although with smaller thermal amplitudes (C. 

Josse pers. comm. 2011). So high elevation semi-deserts share some characteristics 

with the tropical high montane vegetation.

Diagnostic Characteristics: Herbaceous perennials and small woody, small-leaved 

prostrate sub-shrubs, with a predominance of tap roots and creeping or densely caespitose root systems.

Vegetation

Physiognomy and Structure: Tropical High Montane Scrub & Grassland is dominated by herbaceous perennials and woody shrubs or small-leaved low sub-woody 

species in high tropical mountains, where freezing and cryogenic processes occur. The 

predominant growth forms are rosulate plants with deep taproots and several plants 

with densely cespitose root systems and or creeping prostrate habit. The canopy cover 

varies from very low to open or semi-open. It occurs in all tropical high mountains 

worldwide, where it occupies the sub-nival altitudinal belt. Species have, in general, 

adapted to sliding or movement of the substrate due to the diurnal alternation of freezing and melting, which is a typical phenomenon of the high tropical mountains.

Environment

Environmental Description: Climate: Diurnal and non-seasonal energy pattern, 

with seasonal moisture regime consisting of a rainy summer and a dry winter that is a 

typical pattern of high tropical mountains, in contrast to non-tropical high mountains 

(temperate, boreal, Mediterranean) where there is a seasonal energy regime and where 

the rainfall has not matched up with the warmest time of year. In the Andes, this formation is generally above 4,500 m altitude.

Soil/substrate/hydrology: Soils have alterations in structure and texture due to 

deformation caused by freezing processes (contraction and dilatation) with diurnal periodicity of freezing and thawing. The substrates are mostly fine to medium textured, 

stony on the surface (loose stony pavement), with a muddy matrix that is saturated 

with meltwater and freezes daily. In tropical mountains, surface layers that freeze may 

overlie unfrozen subsurface layers. An important effect of frost heaving is the upward 

movement of stones in soils and unconsolidated deposits that is more rapid and pervasive in wetter soils with a sparse vegetation cover. The process associated with frost 

can also cause upward or downward displacement of soil material in mass that can 

result in slope cryoplanation terraces at several scales. These soils are located in the 

highest areas of tropical mountains above 4,500 m altitude.

Distribution

Geographic Range: This subclass occurs in tropical high montane regions of South 

America, eastern Africa, and New Guinea. Further review is needed to determine 

whether it occurs in Central America, Malaysia, and tropical oceanic islands. In the 
USDA Forest Service RMRS-GTR-346. 2016. 127

Neotropics, this type occupies the highest elevations of the tropical Andes, above 

4,500 m altitude, from Venezuela to Argentina, and is well represented in the central 

Andes of Bolivia and Perú.

Citations

Synonymy:

< Alpine semi-desert: biome-type 19 (Whittaker 1975) [Whittakerdoes not separate 

out tropical from temperate.] 

< Tropical Alpine Biome (Quinn 2008) [Quinn includes both the tropical montane and 

tropical high montane scrub band grassland in her type.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: G. Navarro and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

4.A.1. Tropical High Montane Scrub & Grassland 

(F022)

Overview

Database Code: 4.A.1 (F022)

Scientific Name: Tropical High Montane Scrub & Grassland Formation

Common Name (Translated Scientific Name): Tropical High Montane Scrub & 

Grassland Formation

Colloquial Name: Tropical High Montane Scrub & Grassland

Hierarchy Level: Formation

Placement in Hierarchy: 4.A. Tropical High Montane Scrub & Grassland (S16)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical High Montane Scrub & Grassland is dominated 

by herbaceous perennials and small-leaved low woody shrubs or small sub-woody 

species in high tropical mountains, where freezing and cryogenic processes occur. 

They occur in all tropical high mountains, where they occupy the sub-nival altitudinal 

belt, generally above 4,500 m altitude in the Andes.

Classification Comments: The páramo and the dry and moist puna are not in this 

formation, because they have primarily mesomorphic adaptations, and because the 

soils are not subject to cryogenic processes. These vegetation types are treated with 

2.A.2 Tropical Montane Grassland & Shrubland Formation (F017). Nonetheless, 

although the páramo and the dry and moist puna are not subject to cryogenic soil processes, they are subject to varying levels of freezing. Perhaps the term “cryomorphic” 

places too great a restriction on the concept of “tropical alpine” vegetation.

Also challenging to place consistently in this class is the South American xerophytic vegetation and the Altiplano of central and southern Bolivia, Argentina, and 

Chile, because the cryomorphic definition is very similar to xeromorphic; that is to 
128 USDA Forest Service RMRS-GTR-346. 2016.

say, they share ecological processes and have similar structures (growth forms) to each 

other. The vegetation is not Cool Semi-Desert, but is a hot/cold semi-desert, while at 

the same time is hardly affected by edaphic processes of cryoturbation and geliturbation expected of the cryomorphic class. We find again the diurnal rhythm of ice/thaw 

of the tropical mountains, but it is marked in these high dry southern areas with very 

high daily solar temperatures and very low nocturnal temperatures. For example, in 

the Great Salt Flats of Uyuni (Salar de Uyuni) to 3,800 m of altitude, during the day 

temperatures can rise to 20 degrees C and at night to –20 degrees C. This is an extreme 

case related to the immense salt flats, but the lands that surround them repeat almost 

the same features listed above, although with smaller thermal amplitudes (C. Josse 

pers. comm. 2011). So high-elevation semi-deserts share some characteristics with the 

tropical high montane vegetation.

Similar NVC Types: 

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019).

2.A.2. Tropical Montane Grassland & Shrubland (F017): This formation contains 

high montane vegetation that is at or near treeline in the tropics, but is not 

subject to regular freezing or affected by cryogenic soil processes. In the 

Neotropics we place páramo and puna in this formation because they predominantly do not have cryogenic soils or experience frost.

3.B.1. Cool Semi-Desert Scrub & Grassland (F033): At high altitudes in the tropics, 

these cool or rather hot/cold deserts share some characteristics of cryomorphic 

vegetation because of the freezing temperatures.

4.B.1. Temperate & Boreal Alpine Vegetation (F037): This formation lacks constant 

freezing temperature and cryomorphic soils.

Diagnostic Characteristics: Herbaceous perennials and small woody, small-leaved 

prostrate sub-shrubs, with a predominance of taproots and creeping or densely caespitose root systems.

Vegetation

Physiognomy and Structure: Tropical High Montane Scrub & Grassland is dominated by herbaceous perennials and woody shrubs or small-leaved low sub-woody 

species in high tropical mountains, where freezing and cryogenic processes occur. The 

predominant growth forms are rosulate plants with deep taproots and several plants 

with densely cespitose root systems and or creeping prostrate habit. The canopy cover 

varies from very low to open or semi-open. It occurs in all tropical high mountains 

worldwide, where it occupies the sub-nival altitudinal belt. Species have, in general, 

adapted to sliding or movement of the substrate due to the diurnal alternation of freezing and melting, which is a typical phenomenon of the high tropical mountains.

Environment

Environmental Description: Climate: Diurnal and nonseasonal energy pattern, 

with seasonal moisture regime consisting of a rainy summer and a dry winter that is a 

typical pattern of high tropical mountains, in contrast to non-tropical high mountains 

(temperate, boreal, Mediterranean) where there is a seasonal energy regime and where 

the rainfall has not matched up with the warmest time of year. In the Andes, this formation is generally above 4,500 m altitude.
USDA Forest Service RMRS-GTR-346. 2016. 129

Soil/substrate/hydrology: Soils have alterations in structure and texture due to 

deformation caused by freezing processes (contraction and dilatation) with diurnal 

periodicity of freezing and thawing. The substrates are mostly fine to medium 

textured, stony on the surface (loose stony pavement), with a muddy matrix that is 

saturated with meltwater and freezes daily. In tropical mountains, surface layers that 

freeze may overlie unfrozen subsurface layers. An important effect of frost heaving is 

the upward movement of stones in soils and unconsolidated deposits that is more rapid 

and pervasive in wetter soils with a sparse vegetation cover. The process associated 

with frost can also cause upward or downward displacement of soil material in mass 

that can result in slope cryoplanation terraces at several scales. These soils are located 

in the highest areas of tropical mountains above 4,500 m altitude.

Distribution

Geographic Range: Tropical High Montane Scrub & Grassland is dominated by 

herbaceous perennials and small-leaved low woody shrubs or small sub-woody species 

in high tropical mountains, where freezing and cryogenic processes occur. It occurs in 

all tropical high mountains worldwide, where it occupies the sub-nival altitudinal belt.

Citations

Synonymy:

< Alpine semi-desert: biome-type 19 (Whittaker 1975) [The author does not separate 

out tropical from temperate.] 

< Tropical Alpine Biome (Quinn 2008) [Quinn includes both the tropical montane and 

tropical high montane scrub band grassland in her type.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: G. Navarro, C. Josse and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

4.B. Temperate to Polar Alpine & Tundra Vegetation 

(S12)

Overview

Database Code: 4.B (S12)

Scientific Name: Temperate to Polar Alpine & Tundra Vegetation Subclass

Common Name (Translated Scientific Name): Temperate to Polar Alpine & Tundra 

Vegetation Subclass

Colloquial Name: Temperate to Polar Alpine & Tundra Vegetation

Hierarchy Level: Subclass

Placement in Hierarchy: 4. Polar & High Montane Scrub, Grassland & Barrens 

(C04)

Lower Level Hierarchy Units:

4.B.1. Temperate & Boreal Alpine Vegetation (F037)

4.B.2. Polar Tundra & Barrens (F031)
130 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Alpine dwarf shrublands, krummholz, forb meadows, 

grasslands, and cryptogam barrens occurring above treeline in temperate and boreal 

regions around the globe, predominantly in North America and Eurasia, with more 

isolated occurrences in the Southern Hemisphere. Polar tundra is dominated by dwarf 

shrubs, cushion shrubs, sedges and grasses, mosses and lichens, and is found in the 

high latitudes north of 60 degrees N in the Arctic region and south of 50 degrees S in 

the Antarctic region, in permafrost soils that range from dry to seasonally saturated.

Classification Comments: This type excludes very sparse alpine semi-desert vegetation, where the alpine regions grade into high-elevation deserts. Soils show cryogenic 

features. Alpine tundra, scree, and talus, along with fellfields and barrens, are placed here 

because they contain cryomorphic vegetation similar to other vegetation in this class. 

Snowbank vegetation, which can be seasonally saturated, with wetland-like conditions, is 

tentatively included here.

Placement of alpine vegetation in arctic and subarctic regions is under review. In 

those regions, the vegetation is beyond the latitudinal limits of trees. If alpine vegetation exists in those regions, then the subclass should include Arctic or Subarctic in the 

name. Alpine tundra of most Eurasian and North American mountains is similar to that 

of the Arctic tundra but with a richer flora (Quinn 2008).

The High Arctic is often bare not because it is “rock” but because of the climate 

(cold and wind) and cryomorphic processes, hence it fits here. In true polar deserts, 

even cryptogams are sparse, and total cover is 0 to 3 percent (Quinn 2008).

We include “wet tundra” (tundra on saturated, somewhat peaty soils) with dry to 

mesic tundra. Arctic wet meadows and marshes are treated with temperate and boreal 

wet meadows and marshes under 2.C.4 Temperate to Polar Freshwater Marsh, Wet 

Meadow & Shrubland Formation (F013).

Diagnostic Characteristics: Alpine dwarf shrublands, forb meadows and 

grasslands occurring above treeline in temperate and boreal regions. Vegetation is 

dominated by graminoids, low creeping or matted dwarf shrubs, and perennial forbs, 

often in cushion or rosette form, as well as cryptogams. Polar tundra growth forms 

are varied, often with complex patterns of dominance by dwarf shrubs, sedges and 

grasses, mosses and lichens. In many tundra areas, the deep layers of the soil are permanently frozen, and only the surface layer is thawed and becomes biologically active 

during the summer.

Vegetation

Physiognomy and Structure: Alpine vegetation includes creeping and matted 

dwarf shrubs, and occasional trees along with alpine grasses and forbs, including cushion forms of dwarf shrubs and forbs. The ground layer varies from densely vegetated 

to open, rocky, rubbly or frost-sorted habitats (Whittaker 1975; Quinn 2008). Polar 

tundra exists on the treeless arctic plains; the vegetation growth forms are varied and 

often with complex patterns of dominance by dwarf shrubs, sedges and grasses, mosses and lichens (Whittaker 1975). The Low Arctic region typically contains continuous 

vegetation cover (80 to 100 percent), except in rocky places, and contains the typical 

mix of dwarf shrubs, sedges and grasses, mosses and lichens. Tundra also occurs in 

the High Arctic, and plants are primarily lichens and mosses with scattered herbs. 
USDA Forest Service RMRS-GTR-346. 2016. 131

It includes polar desert or barrens on rock substrates, where even cryptogams are 

sparse, and total cover is 1 to 3 percent (Quinn 2008). Alpine tundra of most Eurasian 

and North American mountains is similar to that of the Arctic but with a richer flora 

(Quinn 2008). 

Environment

Environmental Description: Alpine vegetation occurs above the treeline. Treeline 

varies depending on latitude and the “mountain mass” (i.e., large mountain masses 

retain more heat and tend to have higher treeline elevations, whereas smaller and more 

isolated mountain masses tend to have lower treeline elevations). In addition to elevation, exposure to wind is a key factor in the type of vegetation; in snowy regions, it 

impacts on the depth and duration of snow cover and, hence, protection of the vegetation, length of growing season, and soil moisture conditions.

Climate: For alpine vegetation, the “tundra” climate of high altitudes does not 

necessarily correspond to that of high latitudes (i.e., Arctic tundra). Although both 

regions have low mean annual temperature and short growing seasons, and experience a seasonal change in sun angle (high in the summer, low in the winter), the light 

regimes are quite different. Alpine regions never experience 24 hours of day or night; 

day length varies with latitude. And although permafrost occurs on high mountains, it 

does not produce the kinds of landforms found in the Arctic because few flat sites are 

available. Conversely, avalanches and rockslides are common in alpine regions, but do 

not occur in the Arctic (Quinn 2008). Some alpine regions can have very deep snow 

(several meters), whereas the Arctic generally has low snow cover.

Temperatures in the Arctic and Antarctic vary with the season, which has periods 

of 24-hour light (summer) and dark (winter). The number of days with those extremes 

varies with latitude, ranging from 1 day at the Arctic and Antarctic circles (661⁄2 degrees N and S latitude) to 6 months at the poles. Temperatures vary both with latitude 

and degree of continentality. Mean temperatures of the warmest summer months vary 

considerably but generally average between 4.5 and 13 degrees C. In the winter, they 

average from 20 to 30 degrees C. Annual precipitation, which often falls as snow, is 

typically less than 25 cm, but some localities may have as much as 50 cm.

Soil/substrate/hydrology: Most alpine soils are regularly disturbed by freezing, erosion and downslope slides, and contain a mix of rocks and fine particles (Quinn 2008). 

Three major types of soils occur in the alpine regions. (1) Poorly developed rocky or 

stony soils (or Entisols) are sometimes called Lithosols when formed on bare rock 

of slopes and ridges and Regosols when formed on unconsolidated rock-like talus, 

scree, or rubble (soil orders from Soil Survey Staff (1999)) (see Brady and Weil 2002 

for comparison of U.S. soil orders with Canadian and FAO systems). (2) Alpine turf 

and meadow soils (or Inceptisols) are up to 75 cm deep and exhibit distinct horizons; 

and (3) bog soils (Histosols) are found in depressions or where seepage saturates the 

ground to a depth of 1 m or more (Quinn 2008). 

In many polar tundra areas, the deep layers of the soil are permanently frozen 

(permafrost), and only the surface layer is thawed and becomes biologically active 

during the summer (Whittaker 1975). Soils may be dry to seasonally saturated. 
132 USDA Forest Service RMRS-GTR-346. 2016.

Permafrost is ground that is permanently frozen, and is widespread in the Arctic, 

covering large parts of Canada and Russia. It is discontinuous in the Boreal Forest & 

Woodland region to the south. It can extend down more than 600 m, depending on 

mean annual temperature, type of soil and rock, proximity to the ocean and topography. In the summer, only the soil surface may thaw, up to 20 to 60 cm. On slopes, the 

thawed soil may begin to move, a process called solifluction (Quinn 2008). Permafrost 

also creates specific landscape features collectively called patterned ground, forming 

circles, polygons, nets, hummocks, steps or stripes (Quinn 2008).

Distribution

Geographic Range: Temperate to Polar Alpine & Tundra Vegetation occurs above 

treeline in temperate and boreal regions around the globe, predominantly in North America 

and Eurasia, with more isolated occurrences in the Southern Hemisphere. Polar tundra is 

dominated by complex patterns of dominance by dwarf-shrubs, sedges and grasses, mosses 

and lichens, and is found in the high latitudes north of 60 degrees N in the Arctic region 

and south of 50 degrees S in the Antarctic region, where climatic conditions exclude 

tree and tall-shrub growth forms.

Citations

Synonymy:

>< Alpine grassland: biome-type 15 (Whittaker 1975)

>< Alpine shrubland: biome-type 14 (Whittaker 1975)

< Arctic and Antarctic Tundra (Quinn 2008) [The author includes both lithomorphic or 

open rock and cryomorphic vegetation in the Polar High Arctic semi-desert description 

as well as wet tundras.] 

= Low Arctic Tundra (Bliss 2000) [Bliss includes both dry and wet tundra in his 

description.] 

= Mid-latitude Alpine Tundra (Quinn 2008) [Approximately equivalent. Quinn includes alpine scree and talus in her concept.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments: Chris Lea

Version Date: 26 Aug 2014

4.B.1. Temperate & Boreal Alpine Vegetation (F037)

Overview

Database Code: 4.B.1 (F037)

Scientific Name: Temperate & Boreal Alpine Vegetation Formation

Common Name (Translated Scientific Name): Temperate & Boreal Alpine 

Vegetation Formation

Colloquial Name: Temperate & Boreal Alpine Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 4.B. Temperate to Polar Alpine & Tundra Vegetation (S12)

Lower Level Hierarchy Units:

See examples in Appendix J
USDA Forest Service RMRS-GTR-346. 2016. 133

Concept Summary

Type Concept Sentence: Alpine dwarf shrublands, forb meadows and grasslands 

occurring above the continuous forest line in temperate and boreal regions around the 

globe, predominantly in North America and Eurasia, with more isolated occurrences in 

the Southern Hemisphere.

Classification Comments: Excludes very sparse alpine semi-desert vegetation, 

where the alpine regions grade into high elevation deserts. Soils show cryogenic 

features. Krummholz is placed here. Scree and talus are also placed here. Fellfields, 

which are placed here, have a mix of nonvascular and vascular plants that may overlap 

with 6.D.2.

Placement of alpine vegetation in arctic and subarctic regions is under review. In 

those regions, the vegetation is beyond the latitudinal limits of trees. If alpine vegetation exists in those regions, then the subclass should include Arctic or Subarctic in the 

name. Alpine tundra of most Eurasian and North American mountains is similar to that 

of the Arctic but with richer flora (Quinn 2008).The growth form distinctions between 

alpine vegetation and polar tundra need further review.

Alpine tundra of most Eurasian and North American mountains is similar to that of 

the Arctic but with richer flora (Quinn 2008).

Similar NVC Types: 

4.A.1. Tropical High Montane Scrub & Grassland (F022).

4.B.2. Polar Tundra & Barrens (F031): Occurs latitudinally beyond the treeline, 

though may extend southward into mountains of the subarctic (subpolar) woodland regions.

Diagnostic Characteristics: Alpine dwarf shrublands, forb meadows and grasslands occurring above the continuous forest line in temperate and boreal regions. 

Vegetation is dominated by graminoids, low creeping or matted dwarf shrubs, and 

perennial forbs, often in cushion or rosette form. Krummholz and alpine vegetation on 

scree or talus are also placed here.

Vegetation

Physiognomy and Structure: Creeping and matted dwarf shrubs and occasional 

trees may occur, along with alpine grasses and forbs, including cushion forms of dwarf 

shrubs and forbs. Krummholz growth forms may also occur. The ground layer varies 

from densely vegetated to open, rocky, rubbly or frost sorted habitats (Whittaker 1975; 

Billings 2000; Quinn 2008). An extended list of alpine growth forms is provided by 

Billings (2000, Table 14.3).

Environment

Environmental Description: Treeline varies depending on latitude and the 

“mountain mass” (i.e., large mountain masses retain more heat and tend to have higher 

treeline elevations, whereas smaller and more isolated mountain masses tend to have 

lower treeline elevations). In addition to elevation, exposure to wind is a key factor 

in the type of vegetation; in snowy regions, it impacts the depth and duration of snow 

cover and, hence, protection of the vegetation, length of growing season, and soil 

moisture conditions.

Climate: The “tundra” climate of high altitudes does not necessarily correspond to 

that of high latitudes (i.e., Arctic tundra). Although both regions have low mean annual 
134 USDA Forest Service RMRS-GTR-346. 2016.

temperature and short growing seasons, and experience a seasonal change in sun angle 

(high in the summer, low in the winter), the light regimes are quite different. Alpine 

regions never experience 24 hours of day or night; day length varies with latitude. And 

although permafrost occurs on high mountains, it does not produce the kinds of landforms found in the Arctic because few flat sites are available. Conversely, avalanches 

and rockslides are common in alpine regions, but do not occur in the Arctic (Billings 

2000; Quinn 2008). Some alpine regions can have very deep snow (several meters), 

whereas the Arctic generally has low snow cover.

Soil/substrate/hydrology: Most alpine soils are regularly disturbed by freezing, erosion and downslope slides, and contain a mix of rocks and fine particles (Quinn 2008). 

Three major types of soils occur in the alpine regions. (1) Poorly developed rocky or 

stony soils (or Entisols) are sometimes called Lithosols when formed on bare rock 

of slopes and ridges and Regosols when formed on unconsolidated rock-like talus, 

scree, or rubble (soil orders from Soil Survey Staff 1999) (see Brady and Weil 2002, 

for comparison of U.S. soil orders with Canadian and FAO systems). (2) Alpine turf 

and meadow soils (or Inceptisols) are up to 75 cm deep and exhibit distinct horizons; 

and (3) bog soils (Histosols) are found in depressions or where seepage saturates the 

ground to a depth of 1 m or more (Billings 2000; Quinn 2008).

Distribution

Geographic Range: Temperate & Boreal Alpine Vegetation occurs above treeline 

in temperate and boreal regions around the globe, predominantly in North America 

and Eurasia, with more isolated occurrences in the Southern Hemisphere.

Citations

Synonymy:

>< Alpine grassland: biome-type 15 (Whittaker 1975)

>< Alpine shrubland: biome-type 14 (Whittaker 1975)

= Mid-latitude Alpine Tundra (Quinn 2008) [Approximately equivalent. Quinn includes alpine scree and talus in her concept.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments: Chris Lea

Version Date: 26 Aug 2014

4.B.2. Polar Tundra & Barrens (F031)

Overview

Database Code: 4.B.2 (F031)

Scientific Name: Polar Tundra & Barrens Formation

Common Name (Translated Scientific Name): Polar Tundra & Barrens Formation

Colloquial Name: Polar Tundra & Barrens

Hierarchy Level: Formation
USDA Forest Service RMRS-GTR-346. 2016. 135

Placement in Hierarchy: 4.B. Temperate to Polar Alpine & Tundra Vegetation (S12)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Upland or dry polar tundra is dominated by dwarf-shrubs, 

sedges and grasses, mosses and lichens, and is found in the high latitudes north of 60 

degrees N in the Arctic region and south of 50 degrees S in the Antarctic region, in 

permafrost soils that range from dry to seasonally saturated.

Classification Comments: Plants are primarily lichens and mosses with scattered 

herbs (Quinn 2008). We include “wet tundra” (tundra on saturated, somewhat peaty 

soils) with dry to mesic tundra. Arctic wet meadows and marshes are treated with 

temperate and boreal wet meadows and marshes under 2.C.4 Temperate to Polar 

Freshwater Marsh, Wet Meadow & Shrubland Formation (F013). The concept of this 

formation includes the vegetation types of barrens, graminoid tundras, prostrate-shrub 

tundras and erect-shrub tundras of the Arctic (CAVM 2003).

Similar NVC Types: 

4.B.1. Temperate & Boreal Alpine Vegetation (F037): Polar vegetation may extend 

southward into the subarctic mountain regions.

Diagnostic Characteristics: The vegetation growth forms are varied and often with 

complex patterns of dominance by dwarf-shrubs, low sedges and grasses, mosses and 

lichens, and creeping or matted herbs. Soil conditions are dry to seasonally saturated, 

with deep layers of the soil permanently frozen, with only the surface layer thawing in 

summer and becoming biologically active.

Vegetation

Physiognomy and Structure: The vegetation growth forms are varied and often 

form complex patterns of dominance by dwarf-shrubs, sedges and grasses, mosses and 

lichens. The Low Arctic region typically contains continuous vegetation cover (80 to 

100 percent), except in rocky places, and contains the typical mix of dwarf-shrubs, 

sedges and grasses, mosses and lichens. Plants in the High Arctic tundra are primarily 

lichens and mosses with scattered herbs. The High Arctic has fine soil material, and 

can be wet and strongly influenced by cryoturbation, with more sparse vegetation. 

Wetter tundra includes low sedge- and moss-dominated types. It is called “graminoidmoss tundra” by Bliss (2000), who describes it as containing species of Carex and 

Eriophorum, along with an abundance of bryophytes, but few lichens.

Environment

Environmental Description: Climate: Temperatures in the Arctic and Antarctic 

vary with the season, which has periods of 24-hour light (summer) and dark (winter). 

The number of days with those extremes varies with latitude, ranging from 1 day 

at the Arctic and Antarctic circles (661⁄2 degrees N and S latitude) to 6 months at 

the poles. Temperatures vary both with latitude and degree of continentality. Mean 

temperatures of the warmest summer months vary considerably but generally average 
136 USDA Forest Service RMRS-GTR-346. 2016.

between 4.5 and 13 degrees C. In the winter, they average from –20 to –30 degrees C. 

Precipitation, which often falls as snow, is typically less than 25 cm, but some localities may have as much as 50 cm.

Soil/substrate/hydrology: In many tundra areas, the deep layers of the soil are 

permanently frozen (permafrost), and only the surface layer is thawed and becomes 

biologically active during the summer (Whittaker 1975). Soils may be dry to seasonally saturated. Permafrost is ground that is permanently frozen, and is widespread 

in the Arctic, covering large parts of Canada and Russia. It is discontinuous in the 

Boreal Forest & Woodland region to the south. It can extend down more than 600 m, 

depending on mean annual temperature, type of soil and rock, proximity to the ocean, 

and topography. In the summer, only the soil surface may thaw, up to 20 to 60 cm. 

On slopes, the thawed soil may begin to move, a process called solifluction (Quinn 

2008). Permafrost also creates specific landscape features collectively called patterned 

ground, forming circles, polygons, nets, hummocks, steps or stripes (Quinn 2008). 

Distribution

Geographic Range: Upland or dry polar tundra is found in the high latitudes north 

of 60 degrees N in the Arctic region and south of 50 degrees S in the Antarctic region.

Citations

Synonymy:

< Arctic and Antarctic Tundra (Quinn 2008) [Polar (High Arctic) deserts are included in the authors concept.] 

< Low Arctic Tundra (Bliss 2000) [Bliss includes dry and wet tundra in his overall 

concept, but the tall shrub tundra, low shrub tundra, dwarf shrub heath tundra, 

and cottongrass-dwarf-shrub heath tundra are all dry tundra and fit here.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and S. Ponomarenko

Acknowledgments:

Version Date: 26 Aug 2014

5. Aquatic Vegetation (C05)

Overview

Database Code: 5 (C05)

Scientific Name: Hydromorphic Vegetation Class

Common Name (Translated Scientific Name): Hydromorphic Vegetation Class

Colloquial Name: Aquatic Vegetation

Hierarchy Level: Class

Lower Level Hierarchy Units:

5.A. Saltwater Aquatic Vegetation (S09)

5.B. Freshwater Aquatic Vegetation (S13)

Concept Summary

Type Concept Sentence: Open freshwater and saltwater wetlands dominated by 

aquatic vegetation, either rooted with leaves rising up to or near the surface, or floating 
USDA Forest Service RMRS-GTR-346. 2016. 137

freely on the water surface. Stands typically have surface water, generally up to 2 m 

in depth, along ocean, lake, pond, and river margins in non-tidal, tidal and intertidal 

habitats.

Classification Comments: Open-water submerged and floating aquatic herb and 

alga wetland vegetation is included here if found in shallow aquatic habitats, usually 

less than 2 m in depth (e.g., along lakeshores and rivershores) and less than 8 ha in 

size (i.e., ponds), where active wave-forming or bedrock shoreline features are lacking (following the U.S. wetland classification criteria of Cowardin and others 1979). 

Other deeper or larger aquatic habitats, such as lakes, rivers, estuaries and oceans, are 

included in the non-vegetated aquatic class, where the vegetation layer is no longer a 

controlling layer in the system. Submerged tidal aquatic vegetation has been mapped 

where cover is less than 10 percent (Orth and others 2010).

Similar NVC Types: Non-vegetated category: lakes and rivers may overlap with 

this class, but typically are >2 m deep and larger than 8 ha, and lakeshores are shaped 

by wave-forming processes.

7. Agricultural & Developed Vegetation (CCL01): These cultural wetlands may 

have a vegetation structure that is regularly managed (e.g., rice paddies), the 

water levels may be regularly manipulated, or the shores of the wetland may be 

highly modified by concrete, berms, etc.

Diagnostic Characteristics: Hydromorphic growth forms dominate, including 

rooting and floating aquatic herbs and alga. Emergent growth forms have less than 

10 percent cover, and hydromorphic vegetation is at least 1 percent cover. Vegetation 

structure has irregular horizontal canopy spacing, and shoreline edges are shaped by 

natural processes.

Vegetation

Physiognomy and Structure: Growth Forms: Stands have hydromorphic growth 

forms, including rooted and floating aquatic herbs and alga, with various other growth 

forms.

Structure: Stands typically have surface water, up to 2 m in depth, and have aquatic 

herbs either rooted with leaves rising up to or near the surface or floating freely on 

the water surface, or alga. The vegetation cover varies from very open to closed, with 

irregular horizontal canopy spacing. Emergent growth forms have less than 10 percent 

cover, and hydromorphic vegetation is at least 1 percent cover. The height of the vegetation is a function of the water depth along the ocean, lake, river, or in the pond, but 

practically, only vegetation within 2 m of the water surface is included in this type.

Environment

Environmental Description: Climate: Found in any climate where water regimes 

are sufficient to support rooted or floating vegetation.

Soil/substrate/hydrology: This type includes shallow aquatic habitats, typically less 

than 2 m in depth (e.g., along ocean, lake and river shores) and less than 8 ha in size 

(i.e., ponds), where active wave-forming or bedrock shoreline features are lacking 

(Cowardin 1985). Other deeper or larger aquatic habitats, such as lakes, rivers, estuaries and oceans, are included in the non-vegetated Aquatic class, where the vegetation 

layer is no longer a controlling layer in the system.
138 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: This type is found around the globe wherever open freshwater 

lakes, rivers and ponds are found.

Citations

Synonymy:

< Coastal Mudflats and Brackish Waters (Rodwell and others 2002)

< Freshwater Aquatic Vegetation (Rodwell and others 2002)

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 26 Aug 2014

5.A. Saltwater Aquatic Vegetation (S09)

Overview

Database Code: 5.A (S09)

Scientific Name: Saltwater Aquatic Vegetation Subclass

Common Name (Translated Scientific Name): Saltwater Aquatic Vegetation 

Subclass

Colloquial Name: Saltwater Aquatic Vegetation

Hierarchy Level: Subclass

Placement in Hierarchy: 5. Aquatic Vegetation (C05)

Lower Level Hierarchy Units:

5.A.1. Floating & Suspended Macroalgae Saltwater Vegetation (F052)

5.A.2. Benthic Macroalgae Saltwater Vegetation (F053)

5.A.3. Benthic Vascular Saltwater Vegetation (F054)

5.A.4. Benthic Lichen Saltwater Vegetation (F055)

Concept Summary

Type Concept Sentence: Saltwater Aquatic Vegetation occurs in shallow to deep 

saline habitats where emergent vegetation is less than 10 percent cover, and submerged or floating-aquatic plants have greater than 1 percent cover, occurring around 

the globe from the equator to the polar regions.

Similar NVC Types: 

5.B. Freshwater Aquatic Vegetation (S13).

Diagnostic Characteristics: Saltwater Aquatic Vegetation occurs in shallow to 

deep water habitats where emergent vegetation is less than10 percent cover, and 

submerged or floating-aquatic plants have greater than 1 percent cover, with the lower 

limits of salinity set at 0.5 ppt, below which it is considered freshwater. Water levels 

are seasonally stable, permanently flooded, or intermittently exposed during droughts, 

low flows, or intertidal periods. This vegetation occurs around the globe from the 

equator to polar regions in saltwater habitats.
USDA Forest Service RMRS-GTR-346. 2016. 139

Vegetation

Physiognomy and Structure: Submerged or floating aquatic plants and/or macroalgae usually dominate the vegetation, with less than 10 percent of the surface water 

area occluded by standing emergent or woody plants. Macroalga may be common. 

Open surface water at a range of depths is present for all or most of the year.

Environment

Environmental Description: Saltwater Aquatic Vegetation occurs in deeper waters 

of wetlands or in shallow open-water habitats that are transitional along the coast 

between the intertidal salt marshes or other intertidal areas, and permanent, deep-water 

oceans. Water levels may be influenced by intertidal periods. More rarely, they occur 

as floating vegetation in shallow zones of deep oceans or in inland saline habitats 

with permanent water. The lower limits of salinity for this formation are set at 0.5 ppt, 

below which aquatic vegetation is considered freshwater.

Distribution

Geographic Range: Saltwater Aquatic Vegetation occurs in both shallow to moderately deep saltwater benthic habitats and in floating habitats around the globe from the 

equator to the polar regions.

Citations

Synonymy:

>< Shallow Water Wetland Class (National Wetlands Working Group 1997) [The 

authors include both saltwater aquatic and freshwater aquatic vegetation in their 

concept and restrict the type to wetland aquatic vegetation, whereas the concept 

used here could extend to deeper water habitats.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, C. Lea, K. Goodin

Acknowledgments:

Version Date: 26 Aug 2014

5.A.1. Floating & Suspended Macroalgae Saltwater 

Vegetation (F052)

Overview

Database Code: 5.A.1 (F052)

Scientific Name: Floating & Suspended Macroalgae Saltwater Vegetation Formation

Common Name (Translated Scientific Name): Floating & Suspended Macroalgae 

Saltwater Vegetation Formation

Colloquial Name: Floating & Suspended Macroalgae Saltwater Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.A. Saltwater Aquatic Vegetation (S09)

Lower Level Hierarchy Units:

See examples in Appendix J
140 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Floating & Suspended Macroalgae Saltwater Vegetation 

includes areas dominated by macroalgae that are floating on the surface or are suspended freely in the water column, i.e., macroalgae that are not rooted or attached 

to the bottom. Examples include Gracilaria Rafts, Kelp Rafts, Rockweed Rafts, 

Sargassum Rafts, and Ulva Rafts.

Classification Comments: There are no known marine, floating, or suspended 

vascular plant species. Vascular vegetation that floats on the surface, but is rooted in 

the substrate is included in 5.A.3 Benthic Vascular Saltwater Vegetation Formation 

(F054).

Diagnostic Characteristics: Includes areas dominated by macroalgae that are 

floating on the surface or are suspended freely in the water column, i.e., macroalgae 

that are not rooted or attached to the bottom. 

Vegetation

Physiognomy and Structure: The vegetation includes areas dominated by macroalgae that are floating on the surface or are suspended freely in the water column, 

i.e., macroalgae that are not rooted or attached to the bottom. Examples include 

Gracilaria Rafts, Kelp Rafts, Rockweed Rafts, Sargassum Rafts, and Ulva Rafts.

Environment

Environmental Description: The macroalgae are floating on the surface or are suspended freely in the water column.

Distribution

Geographic Range: This type is found throughout the world’s oceans.

Citations

Synonymy:

= Biotic Subclass: Floating/Suspended Macroalgae (FGDC 2012)

Primary Concept Source: Federal Geographic Data Committee (2012)

Author of Description: K. Goodin and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

5.A.2. Benthic Macroalgae Saltwater Vegetation 

(F053)

Overview

Database Code: 5.A.2 (F053)

Scientific Name: Benthic Macroalgae Saltwater Vegetation Formation

Common Name (Translated Scientific Name): Benthic Macroalgae Saltwater 

Vegetation Formation

Colloquial Name: Benthic Macroalgae Saltwater Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.A. Saltwater Aquatic Vegetation (S09)

Lower Level Hierarchy Units:

See examples in Appendix J
USDA Forest Service RMRS-GTR-346. 2016. 141

Concept Summary

Type Concept Sentence: The vegetation includes subtidal or intertidal bottoms and 

other areas dominated by attached macroalgae, including kelp, intertidal fucoids, and 

calcareous algae, which are usually submersed within or extend to the surface of the 

water column, though they may be exposed during low tides.

Type Concept: Benthic Macroalgae Saltwater Vegetation includes subtidal or 

intertidal bottoms and any other areas characterized by a dominant cover of attached 

macroalgae, which are usually submersed within or extend to the surface of the water 

column. They may be exposed during low tides. The aquatic beds dominated by macroalgae include kelp, intertidal fucoids, and calcareous algae. Macroalgal communities 

can exist at all depths within the photic zone, on diverse substrates, and across a range 

of energy and water chemistry regimes. Many macroalgal types and communities have 

low temporal persistence and can bloom and die back within short periods. This aspect 

of macroalgae can be reflected with a temporal persistence modifier.

Classification Comments: Free-floating macroalgae are included under 5.A.1 

Floating & Suspended Macroalgae Saltwater Vegetation Formation (F052). 

Macroalgal communities (typically coralline/crustose algae) that build substrate in a 

reef setting are categorized separately as Reef Biota and not included here.

Similar NVC Types: 

5.A.3. Benthic Vascular Saltwater Vegetation (F054).

5.A.4. Benthic Lichen Saltwater Vegetation (F055).

Vegetation

Physiognomy and Structure: The vegetation includes subtidal or intertidal bottoms and any other areas characterized by a dominant cover of attached macroalgae, 

which are usually submersed within or extend to the surface of the water column. They 

may be exposed during low tides. The aquatic beds dominated by macroalgae include 

kelp, intertidal fucoids, and calcareous algae. Many macroalgal types and communities 

have low temporal persistence and can bloom and die back within short periods. This 

aspect of macroalgae can be reflected with a temporal persistence modifier.

While many researchers organize macroalgae based on their pigmentation, the 

Coastal and Marine Ecological Classification Standard (CMECS) (FGDC 2012) 

takes a growth morphology approach to defining benthic algal biotic groups. This 

decision was driven by the fact that macroalgal assemblages often include a variety 

of co-existing algal species, making delineations of individual species difficult. This 

approach also captures the influence that the algal growth structure has in shaping the 

local environment, by providing shelter, shade, and detrital material to an area, which 

is important to associated fauna. Thus CMECS distinguishes sheet group, filamentous 

group, coarsely branched group, thick leathery group, jointed calcareous group, and 

crustose group

Environment

Environmental Description: This type can exist at all depths within the photic 

zone, on diverse substrates, and across a range of energy and water chemistry regimes. 
142 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: This type is found throughout the world’s oceans.

Citations

Synonymy:

= Biotic Subclass: Benthic Macroalgae (FGDC 2012)

Primary Concept Source: Federal Geographic Data Committee (2012)

Author of Description: K. Goodin and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

5.A.3. Benthic Vascular Saltwater Vegetation (F054)

Overview

Database Code: 5.A.3 (F054)

Scientific Name: Benthic Vascular Saltwater Vegetation Formation

Common Name (Translated Scientific Name): Benthic Vascular Saltwater 

Vegetation Formation

Colloquial Name: Benthic Vascular Saltwater Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.A. Saltwater Aquatic Vegetation (S09)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: The vegetation includes subtidal or intertidal bottoms of 

rooted vascular vegetation beds commonly dominated by any number of seagrass or 

eelgrass species, including species of Cymodocea, Halodule, Thalassia, Halophila, 

Vallisneria, Ruppia, Phyllospadix, and Zostera, and which are usually submersed in 

the water column or floating on the surface, or exposed during low tides.

Classification Comments: Non-rooted floating vascular plants are not known to 

occur in marine environments, and free floating macroalgae are included under 5.A.1 

Floating & Suspended Macroalgae Saltwater Vegetation Formation (F052).

Similar NVC Types: 

5.A.2. Benthic Macroalgae Saltwater Vegetation (F053). 

5.A.4. Benthic Lichen Saltwater Vegetation (F055). 

5.B.1. Tropical Freshwater Aquatic Vegetation (F056). 

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057). 

Diagnostic Characteristics:

Vegetation

Physiognomy and Structure: The vegetation includes subtidal or intertidal bottoms and any other areas characterized by a dominant cover of rooted vascular plants 

that are usually submersed in the water column or floating on the surface. They may 

be exposed during low tides. The vascular vegetation beds are commonly dominated 

by any number of seagrass or eelgrass species, including Cymodocea, Halodule, 

Thalassia, Halophila, Vallisneria, Ruppia, Phyllospadix, and Zostera..
USDA Forest Service RMRS-GTR-346. 2016. 143

Environment

Environmental Description: Seagrass beds may occur in true marine salinities, 

and they may extend into the lower salinity zones of estuaries. Seagrass beds are complex structural habitats that provide refuge and foraging opportunities for abundant 

and diverse faunal communities in shallow waters. Seagrass beds require a specific set 

of ecological conditions for success, and they are generally perceived as areas of high 

environmental quality.

Distribution

Geographic Range: This type is found throughout the world’s oceans.

Citations

Synonymy:

= Biotic Subclass: Aquatic Vascular Vegetation (FGDC 2012)

Primary Concept Source: Federal Geographic Data Committee (2012)

Author of Description: K. Goodin and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

5.A.4. Benthic Lichen Saltwater Vegetation (F055)

Overview

Database Code: 5.A.4 (F055)

Scientific Name: Benthic Lichen Saltwater Vegetation Formation

Common Name (Translated Scientific Name): Benthic Lichen Saltwater Vegetation 

Formation

Colloquial Name: Benthic Lichen Saltwater Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.A. Saltwater Aquatic Vegetation (S09)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Saltwater tidal areas dominated by submerged or 

emergent lichens on the surface of the substrate, occurring in two major zones: the 

intertidal (or Littoral) Lichen Zone, and the Supratidal (or Supralittoral) Lichen Zone.

Classification Comments: Fletcher (1973) describes Marine Lichen types. Lichen 

zones are described by Fletcher (1973), Gilbert and Giavarini (1997), and Hawksworth 

(2000). Although some mosses have been reported in tidal salt marshes, they have not 

been reported as dominant (Garbary and others 2008). Thus, at this time, benthic communities dominated by mosses are only recognized in freshwater tidal situations.

Similar NVC Types: 

5.A.2. Benthic Macroalgae Saltwater Vegetation (F053).

5.A.3. Benthic Vascular Saltwater Vegetation (F054).
144 USDA Forest Service RMRS-GTR-346. 2016.

Vegetation

Physiognomy and Structure: Benthic saltwater tidal areas dominated by submerged or emergent lichens may form patches or visible patterns on the surface of the 

substrate. Lichens are generally recognized as a symbiotic association with a fungus 

and an alga (or cyanobacterium) living together and forming patches or a visible pattern on the surface of the substrate. 

Environment

Environmental Description: Benthic saltwater lichens occur in relatively 

recognizable zones based on, among other factors, the extent to which they are submerged or flooded. The two major zones are the Intertidal (or Littoral) Lichen Zone, 

dominated by patches of lichens that are regularly submerged by marine tides, and 

the Supratidal (or Supralittoral) Lichen Zone, which are rarely submerged, but are 

regularly wetted by splash and sea spray, often in rocky habitats.

Distribution

Geographic Range: This type distribution is not well known.

Citations

Synonymy:

= Biotic Subclass: Marine Lichens (FGDC 2012)

Primary Concept Source: Federal Geographic Data Committee (2012)

Author of Description: K. Goodin and D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

5.B. Freshwater Aquatic Vegetation (S13)

Overview

Database Code: 5.B (S13)

Scientific Name: Freshwater Aquatic Vegetation Subclass

Common Name (Translated Scientific Name): Freshwater Aquatic Vegetation 

Subclass

Colloquial Name: Freshwater Aquatic Vegetation

Hierarchy Level: Subclass

Placement in Hierarchy: 5. Aquatic Vegetation (C05)

Lower Level Hierarchy Units:

5.B.1. Tropical Freshwater Aquatic Vegetation (F056)

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057)

Concept Summary

Type Concept Sentence: Freshwater Aquatic Vegetation occurs in shallow to deep 

freshwater habitats where emergent vegetation is less than10 percent cover, and submerged or floating-aquatic plants have greater than 1 percent cover, occurring around 

the globe from the equator to the polar regions.

Classification Comments: The concept of this subclass extends to deeper water 

habitats (i.e., deeper than 2 m in lakes) and to riverine bottoms, but in practice, 
USDA Forest Service RMRS-GTR-346. 2016. 145

freshwater aquatic classifications may supersede this one from a user standpoint [see 

Formation Class]. That is, it may be desirable to first assign a lake or river type to the 

aquatic system, and secondarily note the NVC vegetation type present. Vegetation 

found in many urban and agricultural ponds may be very similar to natural freshwater 

aquatic vegetation, because agricultural and urban ponds typically manipulate the 

physical setting, not the vegetation itself. There are distinct cultural aquatic vegetation types, but these should be limited to situations in which the vegetation itself 

is manipulated for horticultural (e.g., aquatic gardens) or agricultural (e.g., water 

chestnuts grown in impoundments, rice paddies) that are parallel with terrestrial cultural vegetation. However, many agricultural ponds may actively prevent vegetation 

from forming. For practical applications of classification and mapping of freshwater 

aquatic vegetation, the agricultural and urban ponds may be initially placed within the 

7. Agricultural & Developed Vegetation Class (CCL01), and, where evidence is gathered to show they have a natural composition, they may be reclassified.

Similar NVC Types: 

5.A. Saltwater Aquatic Vegetation (S09).

7.C. Herbaceous & Woody Developed Vegetation (CSC03).

7.D. Agricultural & Developed Aquatic Vegetation (CSC04).

Diagnostic Characteristics: Freshwater Aquatic Vegetation occurs in shallow 

to deep water habitats where emergent vegetation is less than10 percent cover, and 

submerged or floating aquatic plants have greater than 1 percent cover, with the upper 

limits of salinity set at 0.5 ppt, above which it is considered saltwater. Water levels 

are seasonally stable, permanently flooded, or intermittently exposed during droughts, 

low flows or intertidal periods. Freshwater Aquatic Vegetation occurs around the globe 

from the equator to the polar regions in freshwater habitats.

Vegetation

Physiognomy and Structure: Submerged or floating aquatic plants usually 

dominate the vegetation, with less than 10 percent of the surface water area covered 

by standing emergent or woody plants. Open surface water up to 2 m or more deep is 

present for all or most of the year (National Wetlands Working Group 1997).

Environment

Environmental Description: Freshwater Aquatic Vegetation is subject to aquatic 

processes typical of upper limnetic or infralittoral lake zones, such as nutrient and gas 

exchange, oxidation and decomposition. Ionic composition of waters varies widely. 

The upper limits of salinity for Freshwater Aquatic Vegetation are set at 0.5 ppt, above 

which the vegetation is considered 5.A Saltwater Aquatic Vegetation Subclass (S09). 

Dissolved minerals, acid base balances, and nutrient levels are influenced by the 

hydrology, underlying geological materials, nutrient fluxes, and plant communities. 

Freshwater Aquatic Vegetation is usually situated on substrates of limnic peat, mixed 

limnic organic mineral material, and marl in stable water regimes. Little sediment 

accumulation occurs in high energy shallow waters such as tidal regimes, rivers or 

large lakes. In semi arid regions, shallow waters dry up intermittently, often leaving 

evaporite alkaline salt deposits. Except in highly saline or acidic waters, these deposits 

provide a substrate for rooted submerged and floating macrophytes, algae and aquatic 

mosses (National Wetlands Working Group 1997).
146 USDA Forest Service RMRS-GTR-346. 2016.

Freshwater Aquatic Vegetation is found in shallow water that usually has standing or flowing water less than 2 m deep in mid-summer. Water levels are seasonally 

stable, permanently flooded, or intermittently exposed during droughts or low flows. 

Shallow-water vegetation may also occupy bays and margins of profundal zones of 

lakes (National Wetlands Working Group 1997).

Freshwater Aquatic Vegetation occurs in ponds, pools, shallow lakes, oxbows, 

sloughs, natural and artificial impoundments, or channels. Boundaries are determined 

by water-eroded shorelines, beaches or landward margins of mudflats, recent limnic 

deposits, floating mats, emergents or hydrophytic trees or shrubs. Bordering mats of 

rooted emergent vegetation, including inundated trees, may occupy up to 10 percent of 

the shallow-water area. Shallow waters are found in all hydrogeomorphic settings, but 

are usually associated with lacustrine, fluvial, stream, river, and permafrost systems 

(National Wetlands Working Group 1997).

Distribution

Geographic Range: Freshwater Aquatic Vegetation occurs in shallow to deep 

freshwater habitats around the globe from the equator to the polar regions.

Citations

Synonymy:

>< Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate 

marshes are treated together, and inland saline marshes are included here too, as are 

emergent and aquatic vegetation.] 

>< Shallow Water Wetland Class (National Wetlands Working Group 1997) [The 

authors include both saltwater aquatic and freshwater aquatic vegetation in their concept and restrict the type to wetland aquatic vegetation, whereas the concept used here 

could extend to deeper water habitats.] 

>< Tidal Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate marshes are treated together, as are emergent and aquatic vegetation.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997)

Acknowledgments:

Version Date: 26 Aug 2014

5.B.1. Tropical Freshwater Aquatic Vegetation (F056)

Overview

Database Code: 5.B.1 (F056)

Scientific Name: Tropical Freshwater Aquatic Vegetation Formation

Common Name (Translated Scientific Name): Tropical Freshwater Aquatic 

Vegetation Formation

Colloquial Name: Tropical Freshwater Aquatic Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.B. Freshwater Aquatic Vegetation (S13)
USDA Forest Service RMRS-GTR-346. 2016. 147

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical Freshwater Aquatic Vegetation occurs in shallow 

to deep freshwater habitats where emergent vegetation is less than10 percent cover, 

and submerged or floating-aquatic plants have greater than 1 percent cover, occurring 

around the globe within the tropical regions (roughly, between 30 degrees N and 30 

degrees S in latitude).

Classification Comments: The concept of this formation extends to deeper water 

habitats (i.e., deeper than 2 m in lakes) and to riverine bottoms, but in practice, 

freshwater aquatic classifications may supersede this one from a user standpoint [see 

Formation Class and Subclass Classification Comments]. 

Similar NVC Types: 

5.A.3. Benthic Vascular Saltwater Vegetation (F054).

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057).

7.D.1. Agricultural Aquatic Vegetation (CFO12): Although in some cases there 

may be difficulty distinguishing natural ponds (F056) from agricultural ponds 

(CFO12), in the large majority of cases, they are distinct in ecological setting, 

edges, and in composition.

7.D.2. Developed Aquatic Vegetation (CFO13): Although in some cases there may 

be difficulty distinguishing natural (F056) from urban ponds (CFO13), in the 

large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

Diagnostic Characteristics: Tropical Freshwater Aquatic Vegetation occurs in 

shallow to deep water habitats where emergent vegetation is less than10 percent cover, 

and submerged or floating-aquatic plants have more than1 percent cover, with the upper limits of salinity set at 0.5 ppt, above which it is considered saltwater. Water levels 

are seasonally stable, permanently flooded, or intermittently exposed during droughts, 

low flows or intertidal periods. Tropical Freshwater Aquatic Vegetation occurs around 

the globe within the tropical regions (roughly, between 30 degrees North and 30 

degrees South in latitude). Vegetation is more typically present throughout the year, or 

fluctuates in response to factors other than temperature.

Vegetation

Physiognomy and Structure: Submerged or floating aquatic plants usually 

dominate the vegetation, with less than 10 percent of the surface water area covered 

by standing emergent or woody plants. Above-sediment or floating biomass remains 

relatively constant in abundance throughout the year, or fluctuates in response to factors other than temperature change (e.g., water levels or suspended sediment). Open 

surface water up to 2 m or more deep is present for all or most of the year (National 

Wetlands Working Group 1997).

Environment

Environmental Description: Tropical Freshwater Aquatic Vegetation is subject to 

aquatic processes typical of upper limnetic or infralittoral lake zones, such as nutrient 

and gaseous exchange, oxidation and decomposition. Ionic composition of waters 
148 USDA Forest Service RMRS-GTR-346. 2016.

varies widely. The upper limits of salinity for Tropical Freshwater Aquatic Vegetation 

are set at 0.5 ppt. Dissolved minerals, acid-base balances, and nutrient levels are 

influenced by hydrology, underlying geological materials, nutrient fluxes and plant 

communities. Tropical Freshwater Aquatic Vegetation usually is situated on substrates 

of limnic organic or mineral material, or marl in stable-water regimes. Little sediment 

accumulation occurs in high-energy shallow waters such as tidal regimes, rivers or 

large lakes. In semi-arid regions, shallow waters dry up intermittently, often leaving 

evaporite alkaline salt deposits. Except in highly saline or acidic waters, these deposits 

provide a substrate for rooted submerged and floating macrophytes, algae and aquatic 

mosses (National Wetlands Working Group 1997).

Tropical Freshwater Aquatic Vegetation is found in shallow water that usually 

has standing or flowing water less than 2 m deep in mid-summer. Water levels are 

seasonally stable, permanently flooded, or intermittently exposed during droughts or 

low flows. Shallow-water vegetation may also occupy bays and margins of profundal 

zones of lakes (National Wetlands Working Group 1997).

Tropical Freshwater Aquatic Vegetation occurs in ponds, pools, shallow lakes, 

oxbows, sloughs, natural and artificial impoundments, canals, or stream and river 

channels, including freshwater portions of estuaries. Boundaries are determined by 

water-eroded shorelines, beaches or landward margins of mudflats, recent limnic 

deposits, floating mats, emergents or hydrophytic trees or shrubs. Bordering mats of 

rooted emergent vegetation, including inundated trees, may occupy up to 10 percent 

of the shallow water area. Shallow waters are found in all hydrogeomorphic settings, 

but are usually associated with lacustrine, fluvial, stream, river and permafrost systems 

(National Wetlands Working Group 1997).

Distribution

Geographic Range: Tropical Freshwater Aquatic Vegetation occurs in shallow 

to deep freshwater habitats around the globe within the tropical regions (roughly, 

between 30 degrees N and 30 degrees S latitude).

Citations

Synonymy:

>< Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate 

marshes are treated together, and inland saline marshes are included here too, as are 

emergent and aquatic vegetation.] 

>< Shallow Water Wetland Class (National Wetlands Working Group 1997) [The 

authors include both saltwater aquatic and freshwater aquatic vegetation in their concept and restrict the type to wetland aquatic vegetation, whereas the concept used here 

could extend to deeper water habitats.] 

>< Tidal Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate marshes are treated together, as are emergent and aquatic vegetation.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997), modified C. Lea

Acknowledgments:

Version Date: 26 Aug 2014
USDA Forest Service RMRS-GTR-346. 2016. 149

5.B.2. Temperate to Polar Freshwater Aquatic 

Vegetation (F057)

Overview

Database Code: 5.B.2 (F057)

Scientific Name: Temperate to Polar Freshwater Aquatic Vegetation Formation

Common Name (Translated Scientific Name): Temperate to Polar Freshwater 

Aquatic Vegetation Formation

Colloquial Name: Temperate to Polar Freshwater Aquatic Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 5.B. Freshwater Aquatic Vegetation (S13)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Temperate to Polar Freshwater Aquatic Vegetation occurs 

in shallow to deep freshwater habitats (e.g., lakes, ponds, canals, streams, rivers, and 

freshwater portions of estuaries) where emergent vegetation is less than10 percent 

cover, and submerged or floating-aquatic plants have greater than 1 percent cover, occurring around the globe in both hemispheres, from the tropics north and south to the 

polar regions.

Classification Comments: The concept of this formation extends to deeper water 

habitats (i.e., deeper than 2 m in lakes) and to riverine bottoms, but in practice, 

freshwater aquatic classifications may supersede this one from a user standpoint [see 

Formation Class and Subclass Classification Comments].

Similar NVC Types: 

5.A.3. Benthic Vascular Saltwater Vegetation (F054).

5.B.1. Tropical Freshwater Aquatic Vegetation (F056).

7.D.1. Agricultural Aquatic Vegetation (CFO12): Although in some cases there may 

be difficulty distinguishing natural (F057) from agricultural ponds (CFO12), in 

the large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

7.D.2. Developed Aquatic Vegetation (CFO13): Although in some cases there may 

be difficulty distinguishing natural (F057) from urban ponds (CFO13), in the 

large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

Diagnostic Characteristics: Temperate to Polar Freshwater Aquatic Vegetation 

occurs in shallow to deep water habitats (e.g., lakes, ponds, canals, streams, rivers, 

and freshwater portions of estuaries) where emergent vegetation is less than10 percent 

cover, and submerged or floating-aquatic plants have greater than 1 percent cover, 

with the upper limits of salinity set at 0.5 ppt, above which it is considered saltwater. 

Water levels are seasonally stable, permanently flooded, or intermittently exposed during droughts, low flows or intertidal periods. Temperate to Polar Freshwater Aquatic 

Vegetation occurs around the globe in both hemispheres, from the tropics north and 

south to the polar regions. Vegetation may only be seasonally present, and is absent 

during colder months.
150 USDA Forest Service RMRS-GTR-346. 2016.

Vegetation

Physiognomy and Structure: Submerged or floating aquatic plants usually 

dominate the vegetation, with less than 10 percent of the surface water area covered 

by standing emergent or woody plants. In cold seasons, rooted vegetation (submerged 

and floating-leaved) usually dies back to sediment, and floating plants may largely 

disappear. Biomass may persist longer or throughout the year in warmer parts of the 

range. Open surface water up to 2 m or more deep is present for all or most of the year 

(National Wetlands Working Group 1997).

Environment

Environmental Description: Temperate to Polar Freshwater Aquatic Vegetation 

is subject to aquatic processes typical of upper limnetic or infra-littoral lake zones, 

such as nutrient and gas exchange, oxidation and decomposition. Ionic composition of 

waters varies widely. The upper limits of salinity for Temperate to Polar Freshwater 

Aquatic Vegetation are set at 0.5 ppt. Dissolved minerals, acid-base balances, and nutrient levels are influenced by the hydrology, underlying geological materials, nutrient 

fluxes, and plant communities. Temperate to Polar Freshwater Aquatic Vegetation is 

usually situated on substrates of limnic organic or mineral material, or on marl in stable-water regimes. Little sediment accumulation occurs in high-energy shallow waters 

such as tidal regimes, rivers, or large lakes. In semi-arid regions, shallow waters dry 

up intermittently, often leaving evaporite alkaline salt deposits. Except in highly saline 

or acidic waters, these deposits provide a substrate for rooted submerged and floating 

macrophytes, algae, and aquatic mosses (National Wetlands Working Group 1997).

Temperate to Polar Freshwater Aquatic Vegetation is found in shallow water that 

usually has standing or flowing water less than 2 m deep in mid-summer. Water levels 

are seasonally stable, permanently flooded, or intermittently exposed during droughts 

or low flows. Shallow water vegetation may also occupy bays and margins of profundal zones of lakes (National Wetlands Working Group 1997).

Temperate to Polar Freshwater Aquatic Vegetation occurs in ponds, pools, shallow 

lakes, oxbows, sloughs, natural and artificial impoundments, canals, or stream and 

river channels, including freshwater portions of estuaries. Boundaries are determined 

by water-eroded shorelines, beaches or landward margins of mudflats, recent limnic 

deposits, floating mats, emergents or hydrophytic trees or shrubs. Bordering mats of 

rooted emergent vegetation, including inundated trees, may occupy up to 10 percent of 

the shallow water area. Shallow waters are found in all hydrogeomorphic settings, but 

are usually associated with lacustrine, fluvial, stream, river, and permafrost systems 

(National Wetlands Working Group 1997).

Distribution

Geographic Range: Temperate to Polar Freshwater Aquatic Vegetation occurs in 

shallow to deep freshwater habitats around the globe in both hemispheres, from the 

tropics north and south to the polar regions.

Citations

Synonymy:

>< Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate 

marshes are treated together, and inland saline marshes are included here too, as are 

emergent and aquatic vegetation.] 
USDA Forest Service RMRS-GTR-346. 2016. 151

>< Shallow Water Wetland Class (National Wetlands Working Group 1997) [The 

authors include both saltwater aquatic and freshwater aquatic vegetation in their concept and restrict the type to wetland aquatic vegetation, whereas the concept used here 

could extend to deeper water habitats.] 

>< Tidal Freshwater Marshes (Mitsch and Gosselink 2000) [Both tropical and temperate marshes are treated together, as are emergent and aquatic vegetation.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, after National Wetlands Working 

Group (1997), modified C. Lea

Acknowledgments:

Version Date: 26 Aug 2014

6. Open Rock Vegetation (C06)

Overview

Database Code: 6 (C06)

Scientific Name: Cryptogam - Open Mesomorphic Vegetation Class

Common Name (Translated Scientific Name): Cryptogam - Open Mesomorphic 

Vegetation Class

Colloquial Name: Open Rock Vegetation

Hierarchy Level: Class

Lower Level Hierarchy Units:

6.A. Tropical Open Rock Vegetation (S02)

6.B. Temperate & Boreal Open Rock Vegetation (S04)

Concept Summary

Type Concept Sentence: Tropical, temperate, and boreal habitats are characterized 

or dominated by plant growth forms, such as lichen, bryophyte, alga, or fern, that 

have structural adaptations for living on stable rock surfaces or on unstable rocky substrates, such as cliffs, talus, scree, pavement, cobble, lava or boulderfields, and with 

associated mesomorphic grass, shrub and tree growth forms.

Classification Comments: This class is defined by primarily nonvascular, often 

crustose lichen, ferns or very sparse other vascular vegetation that is controlled by the 

rocky substrate. The substrate can be classed as either stable (large boulders, outcrops, 

monoliths, etc.) or unstable (colluvium such as scree, talus or dense, alluvial cobble). 

Stable substrates prevent vascular plant roots from penetrating. Species adapted to 

such substrates have no roots and occupy the surface of the substrates, such as nonvasculars (lichens, mosses, liverworts), or are largely prevented from growing on the 

substrate, except in localized fissures or cracks. Whenever the vegetation is able to establish sufficient cover on the rocky surface (typically greater than 10 percent cover), 

the growth forms of the vegetation determine the class. Vascular spore-bearing plants 

(ferns and others) are included in this class. Spikemoss (Selaginella) regularly adheres 

to cliff and outcrops, as do many species of ferns such as Polypodium, Cheilanthes, 

Pellaea, etc.
152 USDA Forest Service RMRS-GTR-346. 2016.

Lithology may be consolidated or unconsolidated, but the conditions of the substrate preclude development of soil and either strongly impede the penetration of roots 

or require specialized adaptations of roots to support the plant species. Lithomorphic 

or open rock vegetation may be similar to desert or polar types where climate per se

limits the overall plant growth, and substrate limitations are secondary.

Open sand dunes are excluded from this class in general as open sand dunes are an 

extreme condition of other classes (i.e., mesomorphic, xeromorphic), where the constant movement of sand (ablation, deposition, etc.) is at too extreme a pace for even 

the typical adaptations of psammophytic plants, such as creeping stolons, rhizomes, 

etc., to keep up.

Larson and others (2000) characterize cliffs as having a “high, steep, or overhanging face of rock,” whereas rock outcrop is a “portion of bedrock protruding through 

the soil.” Lava flows and colluvial deposits would lay over the soil. They include both 

consolidated and unconsolidated cliffs in their definition, including sand, gravel or 

loess, as well as rock cliffs. Here we restrict it to rock (or at least very rocklike) materials. Apart from stating that a cliff need only be “high enough that falling off will kill 

you,” they suggest that even 3 m of height is sufficient to create suitable cliff habitat.

Defining this class to include sparse vascular vegetation stands that are limited in 

their cover because of substrate is an issue. For example, scree vegetation could be 

considered very similar to psammophytic (dune and other sandy) vegetation and be 

treated as an extreme form of mesomorphic vegetation [mostly or all in 2. Shrub & 

Herb Vegetation Class (C02)]. Scree is usually dominated by sparse vascular plants, 

has considerable soil development for vascular plant establishment, but has unstable 

substrate on which nonvascular vegetation cannot become well established (C. Lea 

pers. comm. 2012). However, whereas dunes can have vegetation that greatly exceeds 

10 percent cover, this is less common on scree; by-and-large, the vascular vegetation 

remains sparse, and nonvascular vegetation is typical. Talus is generally stable enough 

that it has significant nonvascular vegetation, whereas scree may be unstable and less 

commonly contains a strong nonvascular component; further review of this distinction 

is needed. Thus talus fits in this Open Rock Vegetation Class based on the nonvascular 

vegetation criteria, and scree fits in this class because of the sparse vascular vegetation, perhaps in combination with nonvascular vegetation.

Further review may suggest that this class can be improved by distinguishing 

(probably at the subclass level), the less “rocklike” vegetation (including vegetation 

on scree, badlands, pavement) from the true solid open rock vegetation (C. Lea pers. 

comm. 2012). Scree and other loose rocky substrates (volcanic cinders) typically have 

enough soil development to support a dominant layer of disturbance-adapted, facultative mesomorphic shrubs and/or herbs (e.g., in the United States, Ribes spp., Prunus 

virginiana, and other forest, woodland, or shrubland shrubs in the central Rockies), 

and true lithomorphs (saxicolous lichens) are quite sparse, if present at all. Although 

the surface may be “rocky,” the driving ecological factor is the availability of soil in 

quantity under the relatively shallow rock armoring and the absence of large, stable 

substrates for true lithomorphs (saxicolous lichens) to establish. Cobbles along rivers and streams may also not typically support lithomorphic growth forms, and may 

best be treated as sometimes sparse flooded types within mesomorphic formations. 

Badlands (hard clays) and desert pavements also tend to support facultative vascular 
USDA Forest Service RMRS-GTR-346. 2016. 153

species, as opposed to lithomorphs or lithophiles, and could be considered for the xeromorphic class. Given this narrower definition of open rock vegetation, a requirement 

for less than10 percent vascular cover and nonvascular cover greater than vascular 

cover may be more appropriate, to separate them from sparse or occasionally sparse 

types (scree, volcanic cinders) in which vascular layers are clearly dominant and nonvascular is insignificant (C. Lea pers. comm. 2012).

Similar NVC Types: 

2. Shrub & Herb Vegetation (C02): In moist climates, cliff, talus, scree, and rock 

outcrops can contain inclusions of mesomorphic vegetation, but the lithomorphic or rock substrate limits their cover. Where mesomorphic cover is greater 

than 10 percent of total vascular vegetation (excluding ferns and allies), the 

vegetation is placed in this class.

3. Desert & Semi-Desert (C03): Dry habitats with sparse vegetation on rocky 

surfaces. When xeromorphic plants have greater than 10 percent cover on rocky 

substrates, or, if less than 10 percent, are the dominant growth present, stands 

are classified as xeromorphic vegetation.

4. Polar & High Montane Scrub, Grassland & Barrens (C04): In either extreme 

alpine habitats or in polar deserts, the vegetation will be limited to growing on 

rocks and become so sparse as to qualify as lithomorphic or open rock vegetation. But where the vegetation typically has less than 10 percent cover of total 

vascular vegetation (excluding ferns and allies), and is dominated by cryomorphic growth forms, it belongs in this class. This class also includes stands in 

polar regions where the vascular vegetation has extensive moss or fruticose or 

foliose lichen (but not crustose lichen) and is on mineral soil (i.e., lichen tundra 

vegetation).

Diagnostic Characteristics: Lithomorphic or open rock growth forms dominate, 

including lichen (especially foliose and crustose lichens), bryophyte, alga, ferns (nonwoody, including clubmosses, etc.), and crevice-dwelling (rupicolous) vascular plants. 

Vascular vegetation is less than 10 percent cover, and is comprised of mesomorphic 

vegetation. Vegetation structure may be patchy across the rocky surfaces.

Vegetation

Physiognomy and Structure: Growth Forms: Stands have varying levels of 

nonvascular growth forms (including bryophyte, lichen, alga), and vascular ferns, 

and vascular flowering vegetation is typically sparse to absent. Foliose and crustose 

(saxicolous) lichens may be particularly diagnostic. Vascular plants may have a variety 

of adaptations that allow them to thrive in these rocky habitats (sometimes referred to 

as rupicolous species). 

Structure: The structure is very open to closed, with irregular spacing of nonvascular and fern vegetation, which can vary from absent (but vascular plants are at least 

sparsely present up to 10 percent) to continuous. Vascular plant cover is patchy, confined to crevices in the substrate, and is comprised of mesomorphic vegetation. Height 

of the nonvascular or fern species is typically less than 0.3 m; other growth forms are 

highly variable in height, as they may include creeping or matted to tall erect herbs, 

shrubs, and trees.
154 USDA Forest Service RMRS-GTR-346. 2016.

Environment

Environmental Description: Climate: Found on bare rock and in rock crevices of 

cliffs, scree, talus, lava, pavement, other rock outcrops, and cobble-gravel habitat, with 

soils typically absent. Most often in non-desert or non-polar climates where substrate 

features limit establishment of mesomorphic vegetation. Habitat with flat bedrock, but 

with thin soil layers, typically excluded.

Soil/substrate/hydrology: Organic soil component usually lacking, substrate either 

consolidated rock, or cobble, gravel, or stone with or without regular movement.

Distribution

Geographic Range: Azonal areas found in regions from tropical to polar zones. 

Citations

Synonymy:

= Cliff, Bluffs and Rock Outcrops (Wardle 1991) [Wardle’s concept is applied to New 

Zealand.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: Hierarchy Revisions Working Group

Acknowledgments:

Version Date: 26 Aug 2014

6.A. Tropical Open Rock Vegetation (S02)

Overview

Database Code: 6.A (S02)

Scientific Name: Tropical Open Rock Vegetation Subclass

Common Name (Translated Scientific Name): Tropical Open Rock Vegetation 

Subclass

Colloquial Name: Tropical Open Rock Vegetation

Hierarchy Level: Subclass

Placement in Hierarchy: 6. Open Rock Vegetation (C06)

Lower Level Hierarchy Units: 

6.A.1. Tropical Cliff, Scree & Other Rock Vegetation (F011)

Concept Summary

Type Concept Sentence: Tropical rock habitats (such as cliffs, talus, scree, pavement, cobbles, lava, or boulderfields) at low elevations from approximately 23 degrees 

N to 23 degrees S latitude (typically frost free) from the equator characterized by 

nonvascular plant growth forms that have structural adaptations for living on stable 

rock surfaces or in unstable rocky substrates. A sparse cover of various mesomorphic 

vascular growth forms, including woody plants, may be present.

Classification Comments: There is little information that has been comprehensively evaluated across the globe, making it difficult to describe the type concept. 

We suggest that cliff and slope sites with hardpacked sedimentary rocks and clays be 

included in this class. More work is needed to clarify the distinctions between Open 

Rock Vegetation and other sparsely vegetated habitats where rocky substrates are 
USDA Forest Service RMRS-GTR-346. 2016. 155

dominant and lichen vegetation is absent. For example, many rocky river and lake 

shoreline types may be placed in 2.A.3. Tropical Scrub & Herb Coastal Vegetation 

Formation (F024) where vegetation is patchy but may exceed 10 percent.

Currently all vascular plant cover is treated together. But cover of ferns (nonwoody, including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) 

vascular plants may need to be considered separately from other vascular cover when 

deciding on cover thresholds for this class.

Further review may suggest that this subclass can be improved by distinguishing 

the less “rocklike” vegetation (including vegetation on scree, badlands, and pavement) 

from the true lithomorphic (solid rock) vegetation (C. Lea pers. comm. 2012).

Similar NVC Types: 

6.B. Temperate & Boreal Open Rock Vegetation (S04): Warm-temperate cliffs contain subtropical-like cliff features.

Diagnostic Characteristics: Rocky or rocklike substrates dominated by lithomorphic or open rock growth forms, including lichen (especially foliose and crustose 

lichens), bryophyte, and alga, with cover greater than 1 percent; vascular vegetation 

(including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) vascular 

plants is typically less than 10 percent cover. Vascular cover may include either 

evergreen broad-leaved or drought-deciduous trees and shrubs or evergreen herbs. 

Vegetation structure may be patchy across the rocky surfaces.

Vegetation

Physiognomy and Structure: Stands typically contain a covering of crustose lichens and/or sparse covering of vascular plants. Vascular and nonvascular plant cover, 

especially bryophytes, lichens, algae, or ferns, is greater than 1 percent; vascular plant 

cover, including bromeliad growth forms, is largely determined by the rock fissures 

and is typically less than 10 percent, with irregular horizontal spacing. Vascular woody 

growth forms of either evergreen broad-leaved or drought-deciduous woody plants, 

including lianas, may be present.

Environment

Environmental Description: Stable rock surfaces (e.g., outcrops) prevent vascular 

plant roots from penetrating, and their presence is largely determined by the rock 

fissures. On unstable rocky surfaces (e.g., talus), the presence of vascular plants 

is largely determined by a degree of permanence. Tropical climates, where daily 

temperate changes are greater than the seasonal changes, are various and often less determinative than presence of open rock surfaces. Substrates are typically dry to moist, 

but occasionally wet, and typically lack soil development of any kind.

Distribution

Geographic Range: Tropical Open Rock Vegetation is found in localized areas 

throughout the tropical latitudes, where frost is essentially absent, approximately from 

23 degrees N to S around the equator.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)
156 USDA Forest Service RMRS-GTR-346. 2016.

Author of Description: D. Faber-Langendoen and J. Sawyer

Acknowledgments:

Version Date: 26 Aug 2014

6.A.1. Tropical Cliff, Scree & Other Rock Vegetation 

(F011)

Overview

Database Code: 6.A.1 (F011)

Scientific Name: Tropical Cliff, Scree & Other Rock Vegetation Formation

Common Name (Translated Scientific Name): Tropical Cliff, Scree & Other Rock 

Vegetation Formation

Colloquial Name: Tropical Cliff, Scree & Other Rock Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 6.A. Tropical Open Rock Vegetation (S02)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Tropical rock habitats (such as cliffs, talus, scree, pavement, cobbles, lava, or boulderfields) at low elevations from approximately 23 degrees 

N to 23 degrees S latitude (typically frost free) from the equator characterized by 

nonvascular plant growth forms that have structural adaptations for living on stable 

rock surfaces or in unstable rocky substrates. A sparse cover of various mesomorphic 

vascular growth forms, including woody plants, may be present.

Classification Comments: There is little information that has been comprehensively evaluated across the globe, making it difficult to describe the type concept. 

We suggest that cliff and slope sites with hardpacked sedimentary rocks and clays be 

included in this class. More work is needed to clarify the distinctions between Open 

Rock Vegetation and other sparsely vegetated habitats where rocky substrates are 

dominant and lichen vegetation is absent. For example, many rocky river and lake 

shoreline types may be placed in 2.A.3. Tropical Scrub & Herb Coastal Vegetation 

Formation (F024) where vegetation is patchy but may exceed 10 percent.

Currently all vascular plant cover is treated together. But cover of ferns (nonwoody, including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) 

vascular plants may need to be considered separately from other vascular cover when 

deciding on cover thresholds for this class.

Similar NVC Types: 

6.B.1. Temperate & Boreal Cliff, Scree & Other Rock Vegetation (F034): Warmtemperate cliffs contain subtropical-like cliff features.

Diagnostic Characteristics: Rocky or rocklike substrates dominated by cryptogam 

growth forms, including lichen (especially foliose and crustose lichens), bryophyte, 

and alga, with cover greater than 1 percent; vascular vegetation (including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) vascular plants is typically less 

than 10 percent cover. Vascular cover may include either evergreen broad-leaved or 
USDA Forest Service RMRS-GTR-346. 2016. 157

drought-deciduous trees and shrubs or evergreen herbs. Vegetation structure may be 

patchy across the rocky surfaces.

Vegetation

Physiognomy and Structure: Stands typically contain a covering of crustose lichens and/or sparse covering of vascular plants. Vascular and nonvascular plant cover, 

especially bryophytes, lichens, algae, or ferns, is greater than 1 percent; vascular plant 

cover, including bromeliad growth forms, largely determined by the rock fissures 

is typically less than 10 percent, with irregular horizontal spacing. Vascular woody 

growth forms of either evergreen broad-leaved or drought-deciduous woody plants, 

including lianas, may be present.

Environment

Environmental Description: Stable rock surfaces (e.g., outcrops) prevent vascular 

plant roots from penetrating, and their presence is largely determined by the rock 

fissures. On unstable rocky surfaces (e.g., talus), the presence of vascular plants 

is largely determined by a degree of permanence. Tropical climates, where daily 

temperate changes are greater than the seasonal changes, are various and often less determinative than presence of open rock surfaces. Substrates are typically dry to moist, 

but occasionally wet and typically lack soil development of any kind.

Distribution

Geographic Range: Tropical Cliff, Scree & Other Rock Vegetation is found in 

localized areas throughout the tropical latitudes from 23 degrees N to S around the 

equator.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and J. Sawyer

Acknowledgments:

Version Date: 26 Aug 2014

6.B. Temperate & Boreal Open Rock Vegetation 

(S04)

Overview

Database Code: 6.B (S04)

Scientific Name: Temperate & Boreal Open Rock Vegetation Subclass

Common Name (Translated Scientific Name): Temperate & Boreal Open Rock 

Vegetation Subclass

Colloquial Name: Temperate & Boreal Open Rock Vegetation

Hierarchy Level: Subclass

Placement in Hierarchy: 6. Open Rock Vegetation (C06)

Lower Level Hierarchy Units:

6.B.1. Temperate & Boreal Cliff, Scree & Other Rock Vegetation (F034)
158 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Rocky habitats (such as cliffs, talus, scree, pavement, 

cobbles, recent lava flows, or large rock outcrops) characterized by temperate, including Mediterranean, and boreal cryptogam and lithophilic growth forms, including 

saxicolous lichens, bryophytes, algae, and/or ferns and other pteridophytes. Tree 

growth forms typically have less than 10 percent cover, are very sparse; woody growth 

forms, when present, include cold-deciduous broad-leaved and needle-leaved trees and 

shrubs.

Classification Comments: There is little information that has been comprehensively evaluated across the globe, making it difficult to describe the type concept. We 

tentatively include cliff and slope sites with hardpacked sedimentary rocks and clays 

(badlands) within this class. More work is needed to clarify the distinctions between 

rock vegetation and other sparsely vegetated habitats where rocky substrates are dominant and lichen vegetation is absent, such as scree or volcanic cinders. For example, 

many rocky river and lake shoreline types may be placed in 2.B.4 Temperate to Polar 

Scrub & Herb Coastal Vegetation Formation (F005) where vegetation is patchy but 

may exceed 10 percent.

Further review may suggest that this subclass can be improved by distinguishing 

the less “rocklike” vegetation (including vegetation on scree, badlands, pavement) 

from the true open consolidated rock vegetation (C. Lea pers. comm. 2012). Scree 

and other loose rocky substrates (volcanic cinders), where the median particle size is 

greater than 10 cm in diameter, typically have enough soil development to support a 

dominant layer of disturbance-adapted, facultative mesomorphic shrubs and/or herbs 

(e.g., in the United States, Ribes spp., Prunus virginiana, and other forest, woodland, 

or shrubland shrubs in the central Rockies), and true lithomorphs (saxicolous lichens) 

are quite sparse, if present at all. Although the surface may be “rocky,” the driving 

ecological factor is the availability of soil in quantity under the relatively shallow 

rock armoring and the absence of large, stable substrates for lithomorphs (saxicolous 

lichens) to establish. Cobbles along rivers and streams may also not typically support 

lithomorphic or open rock growth forms, and may best be treated as sometimes sparse 

flooded types within mesomorphic formations. Badlands (hard clays) and desert pavements also tend to support facultative vascular species, as opposed to cryptogams, and 

could be considered for the xeromorphic class. Given this narrower definition of lithomorphic or open rock vegetation, a requirement for less than 10 percent vascular cover 

and nonvascular cover greater than vascular cover would be more appropriate for 

distinguishing the “true” lithomorphic types, and separate out sparse or occasionally 

sparse types (scree, volcanic cinders) in which vascular layers are clearly dominant 

and lithomorphic nonvascular is insignificant (C. Lea pers. comm. 2012).

Similar NVC Types: 

2.B. Temperate & Boreal Grassland & Shrubland (S18): Many rocky river and lake 

shoreline types are placed in 2.B.4 Temperate to Polar Scrub & Herb Coastal 

Vegetation Formation (F005) where vegetation may be patchy but can exceed 

10 percent.

6.A. Tropical Open Rock Vegetation (S02): Subtropical cliffs may resemble warmtemperate cliffs.
USDA Forest Service RMRS-GTR-346. 2016. 159

Diagnostic Characteristics: Rocky or rocklike substrates dominated by cryptogam 

species, including lichens (especially foliose and crustose lichens), bryophytes, algae, 

and rupicolous mesomorphic vascular plants, often with a strong component of ferns 

and other pteridophytes. Vascular vegetation is typically less than 10 percent cover, 

and may include either evergreen needle-leaved or cold-deciduous broad-leaved trees 

or shrubs. Vegetation structure may be patchy across the rocky surfaces.

Vegetation

Physiognomy and Structure: Stands typically contain a covering of saxicolous 

foliose and/or crustose lichens growing directly on rock surfaces and/or sparse covering of vascular plants growing in soil pockets. Vascular and nonvascular plant cover 

is greater than 1 percent; vascular plant cover is typically less than 10 percent, with irregular horizontal spacing, and is typically exceeded by nonvascular cover, especially 

lichens, bryophytes, and/or algae. A sparse cover of vascular mesomorphic growth 

forms, including evergreen needle-leaved or cold-deciduous broad-leaved woody 

plants, may be present. Herbs are often seasonally green.

Environment

Environmental Description: This vegetation occurs on large relatively stable 

rocky habitats, such as cliffs, talus, recent lava flows, or rock outcrops, at low to 

moderate elevations. On stable rock surfaces (e.g., outcrops), vascular plant roots 

are prevented from penetrating most of the substrate, and their presence is largely 

determined by the rock fissures, where minimal soil development and more moisture 

occurs. On less stable rocky surfaces (e.g., talus), the presence of vascular plants is 

largely determined by a degree of permanence and depth to soil under the boulders. 

Low-elevation temperate and boreal climates are various, often less determinative 

than presence of open rock surfaces. Substrates are typically very dry to moist, but 

occasionally wet and typically lack soil development of any kind. The climate is cool 

and warm temperate, Mediterranean, and to boreal, and even subarctic, where frosts 

occur regularly (except in part of the Mediterranean region), snow is not permanent, 

and there are strong daily and seasonal temperature changes. The median particle size 

is greater than 10 cm in diameter. 

Distribution

Geographic Range: Temperate & Boreal Open Rock Vegetation is found in localized areas throughout the mid-latitudes from 23 to 70 degrees N or S around the globe.

Citations

Synonymy:

= Cliff, bluffs and rock outcrops (Wardle 1991) [Wardle’s concept is applied to New 

Zealand.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen 2012)

Author of Description: D. Faber-Langendoen and J. Sawyer

Acknowledgments:

Version Date: 26 Aug 2014
160 USDA Forest Service RMRS-GTR-346. 2016.

6.B.1. Temperate & Boreal Cliff, Scree & Other Rock 

Vegetation (F034)

Overview

Database Code: 6.B.1 (F034)

Scientific Name: Temperate & Boreal Cliff, Scree & Other Rock Vegetation 

Formation

Common Name (Translated Scientific Name): Temperate & Boreal Cliff, Scree & 

Other Rock Vegetation Formation

Colloquial Name: Temperate & Boreal Cliff, Scree & Other Rock Vegetation

Hierarchy Level: Formation

Placement in Hierarchy: 6.B. Temperate & Boreal Open Rock Vegetation (S04)

Lower Level Hierarchy Units:

See examples in Appendix J

Concept Summary

Type Concept Sentence: Vegetation in temperate and boreal habitats found 

in rocky or rocklike habitats (such as cliffs, talus, scree, pavement, cobbles, lava, 

boulderfields, or badlands) at low elevations at mid latitudes around the globe characterized by nonvascular plant growth forms that have structural adaptations for living 

on stable rock surfaces or in unstable rocky substrates. A sparse cover of vascular 

mesomorphic growth forms, including needle-leaved and cold deciduous broad-leaved 

woody plants, may be present.

Classification Comments: Mediterranean rock vegetation is included here with 

temperate rock vegetation. We suggest that cliff and slope sites with hardpacked sedimentary rocks and clays (badlands) be included in this class. More work is needed to 

clarify the distinctions between rock vegetation and other sparsely vegetated habitats 

where rocky substrates are dominant and lichen vegetation is absent. For example, 

many rocky river and lake shoreline types may be placed in 2.B.4 Temperate to Polar 

Scrub & Herb Coastal Vegetation Formation (F005) where vegetation is patchy but 

may exceed 10 percent.

The term scree is used broadly to include talus. Talus may be the preferred term for 

lower elevation habitats, where a variety of geological factors are at work, whereas 

scree may be the preferred term for high elevation or polar habitats where frost action 

is the driving factor in producing the rocky habitat. Colloquially, in the western United 

States, and as used here, scree generally refers to smaller particle, looser, rock debris, 

and is often mixed with soil, whereas talus generally refers to larger, more stable particles, with little surface soil. Scree may be somewhat more abundant in high montane 

settings (perhaps because of more pronounced freeze-thaw cycles and weathering of 

rock), but both can be found at all elevations and latitudes.

Currently, vascular plant cover includes ferns (non-woody, including clubmosses, 

etc.) and crevice-dwelling (rupicolous) vascular plants. Consideration could be given 

to excluding these from the vascular species cover estimates.
USDA Forest Service RMRS-GTR-346. 2016. 161

More work is needed to separate rock vegetation from very sparsely vegetated 

habitats dominated by rocky substrates where lichen vegetation is absent. Placement 

of rocky river and lake shoreline types needs review. Similar NVC Types: 

6.A.1. Tropical Cliff, Scree & Other Rock Vegetation (F011): Warm temperate cliffs 

within the temperate & boreal cliff formation (F034) contain subtropical-like 

cliff features similar to tropical cliffs (F011).

Diagnostic Characteristics: Rocky or rocklike substrates dominated by cryptogam 

growth forms, including lichen (especially foliose and crustose lichens), bryophyte, 

and alga, and lithophilic or rupicolous vascular plants, often with a strong component 

of ferns and other pteridophytes. Vascular vegetation is typically <10 percent cover, 

and may include mesomorphic vegetation, such as evergreen needle-leaved or colddeciduous broad-leaved trees or shrubs. Vegetation structure may be patchy.

Vegetation

Physiognomy and Structure: Stands typically contain a covering of saxicolous 

foliose and/or crustose lichens growing directly on rock surfaces, and/or sparse covering of vascular plants growing in soil pockets. Vascular and nonvascular plant cover 

is greater than 1 percent; vascular plant cover is typically less than 10 percent, with irregular horizontal spacing, and is typically exceeded by nonvascular cover, especially 

lichens, bryophytes, and/or algae. The vascular woody growth forms are a mix of 

evergreen needle-leaved or cold-deciduous broad-leaved trees and shrubs.

Environment

Environmental Description: Stable rock surfaces (e.g., outcrops) prevent vascular plant roots from penetrating most of the substrate, and their presence is largely 

determined by the rock fissures, where minimal soil development and more moisture 

occurs. On less stable rocky surfaces (e.g., talus), the presence of vascular plants is 

largely determined by a degree of permanence, and depth to soil under the boulders. 

The low-elevation climates are temperate or boreal (excluding Mediterranean ones), 

where there are strong daily temperate changes and even greater seasonal variations. 

These climates, though, are often less determinative than presence of open rock surfaces. Substrates are typically very dry to moist, but occasionally wet, and typically 

lack soil development of any kind.

Distribution

Geographic Range: Temperate & Boreal Cliff, Scree & Other Rock Vegetation is 

found in localized low elevations throughout the temperate and boreal region (including the Mediterranean region) of the mid-latitudes from 23 or 70 degrees N or S.

Citations

Synonymy:

< Cliff, bluffs and rock outcrops (Wardle 1991) [Wardle’s concept is applied through 

New Zealand, including both alpine and temperate regions.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen and J. Sawyer

Acknowledgments:

Version Date: 26 Aug 2014
162 USDA Forest Service RMRS-GTR-346. 2016.

7. Agricultural & Developed Vegetation (CCL01)

Overview

Database Code: 7 (CCL01)

Scientific Name: Anthromorphic Vegetation Class

Common Name (Translated Scientific Name): Anthromorphic Vegetation Class

Colloquial Name: Agricultural & Developed Vegetation

Hierarchy Level: Cultural Class

Lower Level Hierarchy Units:

7.A. Woody Agricultural Vegetation (CSC01)

7.B. Herbaceous Agricultural Vegetation (CSC02)

7.C. Herbaceous & Woody Developed Vegetation (CSC03)

7.D. Agricultural & Developed Aquatic Vegetation (CSC04)

Concept Summary

Type Concept Sentence: Vegetation of agricultural lands, including row crops, intensive pastures, orchards, vineyards, plowed or harvested fallow fields, rice paddies, and 

farm ponds, and vegetation of developed lands, including urban, suburban and rural cities 

and villages, typically lawns, parks, horticultural gardens, golf courses, and urban ponds.

Classification Comments: Although this is a somewhat “bulky” class in terms 

of structural variation (including tree, shrub and herbaceous stands), they largely 

intergrade based on human manipulation, and the subclasses jointly cross ecological 

gradients. Thus, ecologically, it appears most helpful to group them initially into a 

single class. It is important to conceptually separate this class of planted and cultivated 

vegetation (such as intensive short-rotation pine plantations) from natural/semi-natural 

vegetation (such as successional and natural pine communities, or restoration pine 

plantings or long-rotation pine plantations where the understory is largely controlled 

by natural processes) because of the distinctive growth forms, species, ecology, biogeographic patterns (or lack thereof) and degree of human manipulation; this is best 

done by explicitly accounting for this distinctive vegetation in this class. 

If mesomorphic tree growth forms are greater than 10 percent in canopy and at 

least of minor importance in the regeneration layer, stands may better fit 1. Forest & 

Woodland Class (C01), whereas, if the forests may have an irregular tree canopy but a 

highly regular or mowed understory, such as in urban parks and lawns, they better fit 

with developed vegetation.

Agricultural orchards have a very regularly spaced tree canopy (often pruned or 

trained), with a plowed, mowed, or hayed ground layer.

Urban and agricultural ponds typically have a highly managed growth form composition, regulated water levels, and hardened, human-created shorelines.

Separation of agricultural and developed vegetation based on anthropogenic processes from vegetation formed under natural processes is parallel to that proposed in 

soil taxonomy, where the need for separation of soils altered by humans over centuries 

has been proposed (Bryant and Galbraith 2003). Several national soil systems, such 

as that for China (Zitong and others 2003), and international systems, such as the 

FAO (1988, in Di Gregorio 2005), already recognize a new soil order, Anthrosols, and 

Bryant and Galbraith (2003) suggest that the U.S. system should do the same.
USDA Forest Service RMRS-GTR-346. 2016. 163

Similar NVC Types: 

1. Forest & Woodland (C01): Where mesomorphic tree growth forms are greater 

than 10 percent in canopy, and are irregular in structure in the understory (i.e., 

natural processes occur for tree saplings, seedlings, herbs and shrubs), stands 

may better fit here (e.g., tree plantations where the ground layer is not managed 

or eliminated).

2. Shrub & Herb Vegetation (C02): Where mesomorphic shrub and herb growth 

forms are irregular in structure (i.e., natural processes occur for tree seedlings, 

herbs and shrubs), stands may better fit here (e.g., pastures where non-intensive 

grazing of livestock on native or introduced grasslands).

5. Aquatic Vegetation (C05): Farm and urban ponds that are not regularly managed 

may contain a native set of growth forms and species that place them in this 

class.

Diagnostic Characteristics: Agricultural vegetation often has a very regularly 

horizontally spaced tree, shrub or herb canopy, with the ground layer subject to annual 

plowing, planting, pruning, haying, sometimes coupled with flooding (e.g., rice paddies). Developed vegetation may have a regular or irregularly spaced canopy layer, but 

always has a highly regular ground layer, typically caused by annual, often frequent, 

mowing or clipping, or essentially absent and replaced by pavement.

Vegetation

Physiognomy and Structure: Growth Forms: Agricultural stands are dominated 

by tree, shrub, and herb growth forms, sometimes with distinctive cultural forms 

(vineyards, orchard trees, rice paddies). No growth forms per se have been described 

that are specific to agricultural vegetation. Developed stands are dominated by a wide 

variety of growth forms, but herb and shrub growth forms are often most characteristic, used to create lawns and gardens, with annuals, bulbs, or perennial rooted plants. 

FGDC (2008) does not provide guidance on cultural growth forms.

Structure: Agricultural vegetation structure is very open to closed, typically with 

very regular horizontal spacing and regularly manipulated heights; with some or all of 

the plant parts being harvested, often on an annual or more frequent basis. A tree sapling or seedling layer is typically absent under the canopy (e.g., vineyards, orchards). 

Vegetation typically has greater than 10 percent cover, but completely bare or flooded 

surfaces are possible for short durations (e.g., plowed fields, rice paddies). Developed 

vegetation is typically closed, with regular or irregular horizontal spacing and height, 

often closely mown on a regular basis (resulting in uniform, short heights (<0.1 m), 

or the vegetation pattern is irregular, but highly regulated (e.g., flower gardens). 

Vegetation cover typically is greater than 10 percent, but completely bare surfaces are 

possible for short durations.

Environment

Environmental Description: Climate: Found in all climatic domains, most common in non-arid climates.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.
164 USDA Forest Service RMRS-GTR-346. 2016.

Citations

Synonymy:

< Agricultural Land (Anderson and others 1976)

>< Cultivated Aquatic or Regularly Flooded Areas (Di Gregorio 2005) [This type is 

restricted to only wetland vegetation, but includes both agricultural and developed 

vegetation.] 

>< Cultivated and Managed Terrestrial Areas (Di Gregorio 2005) [This type is 

restricted to only upland vegetation, but includes both agricultural and developed 

vegetation.] 

>< Urban or Builtup Land (17. Other Urban or Build Up Land) (Anderson and others 

1976) [Anderson includes both non-vegetated and vegetated urban lands in this class, 

but subclass 17 covers the more extensive developed vegetation types.]

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen, G. Fults, and T. Keeler-Wolf

Acknowledgments:

Version Date: 26 Aug 2014

7.A. Woody Agricultural Vegetation (CSC01)

Overview

Database Code: 7.A (CSC01)

Scientific Name: Woody Agricultural Vegetation Subclass

Common Name (Translated Scientific Name): Woody Agricultural Vegetation 

Subclass

Colloquial Name: Woody Agricultural Vegetation

Hierarchy Level: Cultural Subclass

Placement in Hierarchy: 7. Agricultural & Developed Vegetation (CCL01)

Lower Level Hierarchy Units:

7.A.1. Woody Horticultural Crop (CFO01)

7.A.2. Forest Plantation & Agroforestry (CFO02)

7.A.3. Woody Wetland Horticultural Crop (CFO03)

Concept Summary

Type Concept Sentence: Agricultural crops dominated by shrub and tree vegetation, including orchards, vineyards, woody berry crops, intensive (often short-rotation) 

forest plantations, various agroforestry woody crops, and woody wetland crops, such 

as cranberries.

Similar NVC Types: 

1.A. Tropical Forest & Woodland (S17): Long-rotation plantations or woody restoration plantings with an irregular structure and a largely spontaneous ground 

layer may initially be similar in their early stages of development, especially if 

planted in rows and the understory is strongly manipulated.
USDA Forest Service RMRS-GTR-346. 2016. 165

1.B. Temperate & Boreal Forest & Woodland (S15): Long-rotation plantations or 

woody restoration plantings with an irregular structure and a largely spontaneous ground layer may initially be similar in their early stages of development, 

especially if planted in rows and the understory is strongly manipulated.

7.B. Herbaceous Agricultural Vegetation (CSC02).

7.C. Herbaceous & Woody Developed Vegetation (CSC03).

7.D. Agricultural & Developed Aquatic Vegetation (CSC04): Some urban ponds 

with woody vegetation may be similar to 7.A.

Vegetation

Physiognomy and Structure: Agricultural crops dominated by shrub and tree 

vegetation, including orchards, vineyards, woody berry crops, intensive (often shortrotation) forest plantations, various agroforestry woody crops, and woody wetland 

crops, such as cranberries.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.A.1. Woody Horticultural Crop (CFO01)

Overview

Database Code: 7.A.1 (CFO01)

Scientific Name: Woody Horticultural Crop Formation

Common Name (Translated Scientific Name): Woody Horticultural Crop Formation

Colloquial Name: Woody Horticultural Crop

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.A. Woody Agricultural Vegetation (CSC01)

Concept Summary

Type Concept Sentence: Agricultural crops dominated by shrub and tree vegetation, including orchards, vineyards, and woody berry crops.

Similar NVC Types: 

7.A.2. Forest Plantation & Agroforestry (CFO02).

Diagnostic Characteristics: Typically found as row crops, often in monocultures.

Vegetation

Physiognomy and Structure: Agricultural crops dominated by shrub and tree 

vegetation, including orchards, vineyards, and woody berry crops.
166 USDA Forest Service RMRS-GTR-346. 2016.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.A.2. Forest Plantation & Agroforestry (CFO02)

Overview

Database Code: 7.A.2 (CFO02)

Scientific Name: Forest Plantation & Agroforestry Formation

Common Name (Translated Scientific Name): Forest Plantation & Agroforestry 

Formation

Colloquial Name: Forest Plantation & Agroforestry

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.A. Woody Agricultural Vegetation (CSC01)

Concept Summary

Type Concept Sentence: Agricultural crops dominated by intensive (often shortrotation) forest plantations and various agroforestry woody crops.

Classification Comments: Long-rotation plantations or woody restoration plantings with an irregular structure and a largely spontaneous ground layer are placed in 

1.A Tropical Forest & Woodland Subclass (S17) or 1.B. Temperate & Boreal Forest & 

Woodland Subclass (S15) as the vegetation structure and composition may be largely 

native or naturalized. But in their early stages of development, especially if planted in 

rows and the understory is strongly manipulated, they may better fit within this class.

Similar NVC Types: 

1.A.1. Tropical Dry Forest & Woodland (F003): Long-rotation plantations or 

woody restoration plantings with an irregular structure and a largely spontaneous ground layer may initially be similar in their early stages of development, 

especially if planted in rows and the understory is strongly manipulated.

1.B.2. Cool Temperate Forest & Woodland (F008): Long-rotation plantations or 

woody restoration plantings with an irregular structure and a largely spontaneous ground layer may initially be similar in their early stages of development, 

especially if planted in rows and the understory is strongly manipulated.

1.B.4. Boreal Forest & Woodland (F001): Long-rotation plantations or woody restoration plantings with an irregular structure and a largely spontaneous ground 

layer may initially be similar in their early stages of development, especially if 

planted in rows and the understory is strongly manipulated.

7.A.1. Woody Horticultural Crop (CFO01).
USDA Forest Service RMRS-GTR-346. 2016. 167

Vegetation

Physiognomy and Structure: Agricultural crops dominated by intensive (often 

short-rotation) forest plantations and various agroforestry woody crops.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.A.3. Woody Wetland Horticultural Crop (CFO03)

Overview

Database Code: 7.A.3 (CFO03)

Scientific Name: Woody Wetland Horticultural Crop Formation

Common Name (Translated Scientific Name): Woody Wetland Horticultural Crop 

Formation

Colloquial Name: Woody Wetland Horticultural Crop

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.A. Woody Agricultural Vegetation (CCL01)

Concept Summary

Type Concept Sentence: Agricultural crops dominated by woody wetland crops, 

such as cranberries.

Classification Comments: There may be planted wetland tree crops that may also 

be placed here, though if they are intensive tree plantations, they may preferably be 

placed in 7.A.2 Intensive Forestry Plantation & Agroforestry Crop Formation (F043).

Vegetation

Physiognomy and Structure: Agricultural crops dominated by woody wetland 

crops, such as cranberries.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
168 USDA Forest Service RMRS-GTR-346. 2016.

7.B. Herbaceous Agricultural Vegetation (CSC02)

Overview

Database Code: 7.B (CSC02)

Scientific Name: Herbaceous Agricultural Vegetation Subclass

Common Name (Translated Scientific Name): Herbaceous Agricultural Vegetation 

Subclass

Colloquial Name: Herbaceous Agricultural Vegetation

Hierarchy Level: Cultural Subclass

Placement in Hierarchy: 7. Agricultural & Developed Vegetation (CCL01)

Lower Level Hierarchy Units:

7.B.1. Row & Close Grain Crop (CFO04)

7.B.2. Pasture & Hay Field Crop (CFO05)

7.B.3. Herbaceous Horticultural Crop (CFO06)

7.B.4. Fallow Field & Weed Vegetation (CFO07)

7.B.5. Herbaceous Wetland Crop (CFO08)

Concept Summary

Type Concept Sentence: Agricultural vegetation, including row crops, planted 

grain crops, pastures, hayfields, horticultural crops (such as commercial flower operations), fallow fields and early successional weed fields, and wetland rice and taro crop 

fields.

Similar NVC Types: 

7.A. Woody Agricultural Vegetation (CCL01).

7.C. Herbaceous & Woody Developed Vegetation (CSC03): Residential vegetable 

gardens overlap with 7.B.

Vegetation

Physiognomy and Structure: Agricultural vegetation, including row crops, planted 

grain crops, pastures, hayfields, horticultural crops (such as commercial flower operations), fallow fields and early successional weed fields, and wetland rice and taro crop 

fields.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal 

Geographic Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
USDA Forest Service RMRS-GTR-346. 2016. 169

7.B.1. Row & Close Grain Crop (CFO04)

Overview

Database Code: 7.B.1 (CFO04)

Scientific Name: Row & Close Grain Crop Formation

Common Name (Translated Scientific Name): Row & Close Grain Crop Formation

Colloquial Name: Row & Close Grain Crop

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.B. Herbaceous Agricultural Vegetation (CSC02)

Concept Summary

Type Concept Sentence: Agricultural vegetation, including row crops, such as 

corn, soybeans, cotton, tobacco, sunflowers, a wide variety of vegetables, and some 

planted grain crops (annual rye, wheat).

Classification Comments: Some planted grain crops, such as annual rye or wheat 

are more akin to row crops than to hay or pasture and so they are placed here, rather 

than in 7.B.2 Pasture & Hay Field Crop Formation (CFO05).

Vegetation

Physiognomy and Structure: Agricultural vegetation, including row crops, such 

as corn, soybeans, cotton, tobacco, sunflowers, a wide variety of vegetables, and some 

planted grain crops (annual rye, wheat).

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.B.2. Pasture &Hay Field Crop (CFO05)

Overview

Database Code: 7.B.2 (CFO05)

Scientific Name: Pasture & Hay Field Crop Formation

Common Name (Translated Scientific Name): Pasture & Hay Field Crop Formation

Colloquial Name: Pasture & Hay Field

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.B. Herbaceous Agricultural Vegetation (CSC02)

Concept Summary

Type Concept Sentence: Agricultural vegetation, including pastures and hayfields, 

often regularly mowed, fertilized, intensively grazed, and/or manipulated to maintain a 

particular desirable structure and composition.
170 USDA Forest Service RMRS-GTR-346. 2016.

Classification Comments: Agricultural pastures and hayfields differ from native 

or naturalized grasslands in the degree to which both structure and composition are 

manipulated through regular mowing, fertilization, intensive grazing, and other practices. These modifications to structure and composition provide distinctive vegetation 

characteristics as compared to native or natural grasslands. If agricultural practices are 

discontinued, native and exotic species from the surrounding landscape may establish 

and the field will become more “semi-natural.” Where this occurs, the vegetation is reclassified as a native or naturalized “old-field” [see 2.A Tropical Grassland, Savanna 

& Shrubland Subclass (S01) or 2.B Temperate & Boreal Grassland & Shrubland 

Subclass (S18].

Some planted grain crops, such as annual rye or wheat, are more akin to row 

crops than to hay or pasture and so they are placed in 7.B.1 Row & Close Grain Crop 

Formation (CFO04).

Similar NVC Types: 

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland (F019): Pastures may 

overlap in composition with native grasslands, particularly in grassland regions. 

In regions where a pastoral tradition has existed from hundreds to thousands of 

years, recognition of native versus agricultural grasslands may be challenging.

2.B.2. Temperate Grassland & Shrubland (F012): Pastures may overlap in composition with native grasslands, particularly in grassland regions. In regions where 

a pastoral tradition has existed from hundreds to thousands of years, recognition of native versus agricultural grasslands may be challenging.

Vegetation

Physiognomy and Structure: Agricultural vegetation, including pastures and 

hayfields, often regularly mowed, fertilized, intensively grazed, and/or manipulated to 

maintain a particular desirable structure and composition.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.B.3. Herbaceous Horticultural Crop (CFO06)

Overview

Database Code: 7.B.3 (CFO06)

Scientific Name: Herbaceous Horticultural Crop Formation

Common Name (Translated Scientific Name): Herbaceous Horticultural Crop 

Formation
USDA Forest Service RMRS-GTR-346. 2016. 171

Colloquial Name: Herbaceous Horticultural Crop

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.B. Herbaceous Agricultural Vegetation (CSC02)

Concept Summary

Type Concept Sentence: Agricultural vegetation, including horticultural crops 

(such as commercial flower operations).

Vegetation

Physiognomy and Structure: Agricultural vegetation, including horticultural crops 

(such as commercial flower operations).

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.B.4. Fallow Field & Weed Vegetation (CFO07)

Overview

Database Code: 7.B.4 (CFO07)

Scientific Name: Fallow Field & Weed Vegetation Formation

Common Name (Translated Scientific Name): Fallow Field & Weed Vegetation 

Formation

Colloquial Name: Fallow Field & Weed Vegetation

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.B. Herbaceous Agricultural Vegetation (CSC02)

Concept Summary

Type Concept Sentence: Agricultural vegetation, fallow fields and early successional weed fields.

Vegetation

Physiognomy and Structure: Agricultural vegetation, fallow fields and early successional weed fields.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)
172 USDA Forest Service RMRS-GTR-346. 2016.

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.B.5. Herbaceous Wetland Crop (CFO08)

Overview

Database Code: 7.B.5 (CFO08)

Scientific Name: Herbaceous Wetland Crop Formation

Common Name (Translated Scientific Name): Herbaceous Wetland Crop Formation

Colloquial Name: Herbaceous Wetland Crop

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.B. Herbaceous Agricultural Vegetation (CSC02)

Concept Summary

Type Concept Sentence: Agricultural wetland vegetation, such as wetland rice and 

taro crop fields.

Vegetation

Physiognomy and Structure: Agricultural wetland vegetation, such as wetland 

rice and taro crop fields.

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.C. Herbaceous & Woody Developed Vegetation 

(CSC03)

Overview

Database Code: 7.C (CSC03)

Scientific Name: Herbaceous & Woody Developed Vegetation Subclass

Common Name (Translated Scientific Name): Herbaceous & Woody Developed 

Vegetation Subclass

Colloquial Name: Herbaceous & Woody Developed Vegetation

Hierarchy Level: Cultural Subclass

Placement in Hierarchy: 7. Agricultural & Developed Vegetation (CCL01)

Lower Level Hierarchy Units:
USDA Forest Service RMRS-GTR-346. 2016. 173

7.C.1. Lawn & Recreational Vegetation (CFO09)

7.C.2. Horticultural Garden Vegetation (F041)

7.C.3. Open Developed Vegetation (CFO10)

7.C.4. Developed Wetland Vegetation (CFO11)

Concept Summary

Type Concept Sentence: Vegetation includes closely cropped vegetation such as 

lawns, gardens, sports fields, and golf courses, as well as vegetation growing in urban 

materials, such as pavement, from dry lands to emergent wetlands. Tree canopy varies 

from 0 to 100 percent (e.g., open to shaded lawns and gardens).

Similar NVC Types: 

5.B. Freshwater Aquatic Vegetation (S13).

7.A. Woody Agricultural Vegetation (CCL01). 

7.B. Herbaceous Agricultural Vegetation (CSC02): Herbaceous & Woody 

Developed Vegetation (CSC03) contains residential vegetable gardens that 

overlap with Herbaceous Agricultural Vegetation (CSC02).

Vegetation

Physiognomy and Structure: Vegetation includes closely cropped vegetation such 

as lawns, gardens, sports fields, and golf courses, as well as vegetation growing in 

urban materials, such as pavement, from dry lands to emergent wetlands. Tree canopy 

varies from 0 to 100 percent (e.g., open to shaded lawns and gardens).

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.C.1. Lawn, Garden & Recreational Vegetation 

(CFO09)

Overview

Database Code: 7.C.1 (CFO09)

Scientific Name: Lawn & Recreational Vegetation Formation

Common Name (Translated Scientific Name): Lawn & Recreational Vegetation 

Formation

Colloquial Name: Lawn & Recreational Vegetation

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.C. Herbaceous & Woody Developed Vegetation (CSC03)
174 USDA Forest Service RMRS-GTR-346. 2016.

Concept Summary

Type Concept Sentence: Vegetation includes closely cropped vegetation such as 

lawns, gardens, sports fields, and golf courses, as well as gardens. Tree canopy varies 

from 0 to 100 percent (e.g., open to shaded lawns and gardens). 

Vegetation

Physiognomy and Structure: Vegetation includes closely cropped vegetation such 

as lawns, gardens, sports fields, and golf courses, as well as gardens. Tree canopy varies from 0 to 100 percent (e.g., open to shaded lawns and gardens). 

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.C.2. Other Developed Vegetation (CFO10)

Overview

Database Code: 7.C.2 (CFO10)

Scientific Name: Other Developed Vegetation Formation

Common Name (Translated Scientific Name): Other Developed Vegetation 

Formation

Colloquial Name: Other Developed Vegetation

Hierarchy Level: Cultural Formation

Concept Summary

Type Concept Sentence: Other Developed vegetation includes vegetation growing 

in urban materials, such as pavement. Tree canopy varies from 0 to 100 percent (e.g., 

open to shaded weed vegetation in pavement cracks).

Vegetation

Physiognomy and Structure: Other Developed vegetation includes vegetation 

growing in urban materials, such as pavement. Tree canopy varies from 0 to 100 percent (e.g., open to shaded weed vegetation in pavement cracks).

Distribution

Geographic Range: Widely distributed across the globe, except in very dry or very 

cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)
USDA Forest Service RMRS-GTR-346. 2016. 175

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.C.3. Developed Wetland Vegetation (CFO11)

Overview

Database Code: 7.C.3 (CFO11)

Scientific Name: Developed Wetland Vegetation Formation

Common Name (Translated Scientific Name): Developed Wetland Vegetation 

Formation

Colloquial Name: Developed Wetland Vegetation

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.C. Herbaceous & Woody Developed Vegetation (CSC03)

Concept Summary

Type Concept Sentence: Very uncommon vegetation that includes urban, suburban 

and rural planted and managed emergent and woody wetlands, such as small urban 

ponds with emergent vegetation. Tree canopy can vary from 0 to 100 percent (e.g., 

open to shaded planted wetlands).

Classification Comments: Type is very uncommon and concept needs review. 

Emergent and woody wetlands are typically natural to semi-natural.

Vegetation

Physiognomy and Structure: Vegetation includes urban, suburban and rural 

planted and managed emergent and woody wetlands, such as small urban ponds with 

emergent vegetation. Tree canopy can vary from 0 to 100 percent (e.g., open to shaded 

planted wetlands).

Distribution

Geographic Range: Localized across the globe, except in very dry or very cold 

regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.D. Agricultural & Developed Aquatic Vegetation 

(CSC04)

Overview

Database Code: 7.D (CSC04)

Scientific Name: Agricultural & Developed Aquatic Vegetation Subclass

Common Name (Translated Scientific Name): Agricultural & Developed Aquatic 
176 USDA Forest Service RMRS-GTR-346. 2016.

Vegetation Subclass

Colloquial Name: Agricultural & Developed Aquatic Vegetation

Hierarchy Level: Cultural Subclass

Placement in Hierarchy: 7. Agricultural & Developed Vegetation (CCL01)

Lower Level Hierarchy Units:

7.D.1. Agricultural Aquatic Vegetation (CFO12)

7.D.2. Developed Aquatic Vegetation (CFO13)

Concept Summary

Type Concept Sentence: Floating and submerged vegetation found in managed agricultural and developed sites, such as farm ponds, urban ponds, and other open water 

sites in urban, suburban, and rural settings.

Classification Comments: Agricultural and developed aquatic vegetation that is 

not regularly managed may contain a native or naturalized set of growth forms and 

species that places it in 5.B Freshwater Aquatic Vegetation Subclass (S13).

Similar NVC Types: 

5.B. Freshwater Aquatic Vegetation (S13).

7.A. Woody Agricultural Vegetation (CCL01): Agricultural & Developed Aquatic 

Vegetation (CFO12) contains urban ponds with woody vegetation that may be 

similar to Woody Agricultural Vegetation (CCL01).

Vegetation

Physiognomy and Structure: Floating and submerged vegetation found in managed agricultural and developed sites, such as farm ponds, urban ponds, and other 

open water sites in urban, suburban, and rural settings.

Environment

Environmental Description: Typical habitats include farm ponds, urban ponds, 

and other open water sites in urban, suburban, and rural settings. 

Distribution

Geographic Range: Patchily distributed across the globe, except in very dry or 

very cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014

7.D.1. Agricultural Aquatic Vegetation (CFO12)

Overview

Database Code: 7.D.1 (CFO12)

Scientific Name: Agricultural Aquatic Vegetation Formation

Common Name (Translated Scientific Name): Agricultural Aquatic Vegetation 

Formation
USDA Forest Service RMRS-GTR-346. 2016. 177

Colloquial Name: Agricultural Aquatic Vegetation

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.D. Agricultural & Developed Aquatic Vegetation (CSC04)

Concept Summary

Type Concept Sentence: Floating and submerged vegetation found in managed 

agricultural sites, such as farm ponds.

Classification Comments: Agricultural aquatic vegetation that is not regularly 

managed may contain a native or naturalized set of growth forms and species that 

places it in 5.B Freshwater Aquatic Vegetation Subclass (S13).

Similar NVC Types: 

5.B.1. Tropical Freshwater Aquatic Vegetation (F056): Although in some cases 

there may be difficulty distinguishing natural from agricultural ponds, in the 

large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057): Although in some 

cases there may be difficulty distinguishing natural from agricultural ponds, in 

the large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

7.D.2. Developed Aquatic Vegetation (CFO13).

Diagnostic Characteristics: Agricultural aquatic vegetation typically has a highly 

managed growth form composition, regulated water levels, and hardened, humancreated shorelines.

Vegetation

Physiognomy and Structure: Floating and submerged vegetation found in managed agricultural sites, such as farm ponds.

Environment

Environmental Description: Commonly found in agricultural aquatic sites, such 

as farm ponds.

Distribution

Geographic Range: Patchily distributed across the globe, except in very dry or 

very cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012Faber-Langendoen and others 

2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
178 USDA Forest Service RMRS-GTR-346. 2016.

7.D.2. Developed Aquatic Vegetation (CFO13)

Overview

Database Code: 7.D.2 (CFO13)

Scientific Name: Developed Aquatic Vegetation Formation

Common Name (Translated Scientific Name): Developed Aquatic Vegetation 

Formation

Colloquial Name: Developed Aquatic Vegetation

Hierarchy Level: Cultural Formation

Placement in Hierarchy: 7.D. Agricultural & Developed Aquatic Vegetation (CSC04)

Concept Summary

Type Concept Sentence: Floating and submerged vegetation found in managed 

developed sites, such as urban ponds.

Classification Comments: Developed aquatic vegetation sites that are not regularly managed may contain a native or naturalized set of growth forms and species in 

which case the vegetation is placed in 5.B Freshwater Aquatic Vegetation Subclass 

(S13).

Similar NVC Types: 

5.B.1. Tropical Freshwater Aquatic Vegetation (F056): Although in some cases 

there may be difficulty distinguishing natural from urban ponds, in the 

large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

5.B.2. Temperate to Polar Freshwater Aquatic Vegetation (F057): Although in some 

cases there may be difficulty distinguishing natural from urban ponds, in the 

large majority of cases, they are distinct in ecological setting, edges, and in 

composition.

7.D.1. Agricultural Aquatic Vegetation (CFO12).

Vegetation

Physiognomy and Structure: Floating and submerged vegetation found in managed developed sites.

Environment

Environmental Description: The vegetation can be found in urban ponds, and 

other open water sites in urban, suburban and rural settings. 

Distribution

Geographic Range: Patchily distributed across the globe, except in very dry or 

very cold regions.

Citations

Synonymy:

Primary Concept Source: Hierarchy Revisions Working Group, Federal Geographic 

Data Committee (Faber-Langendoen and others 2012)

Author of Description: D. Faber-Langendoen

Acknowledgments:

Version Date: 26 Aug 2014
USDA Forest Service RMRS-GTR-346. 2016. 179

References

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964. U.S. Department of the Interior, Geological Survey, Washington, DC. 26 pp. 

Bailey, R. G. 1989. Explanatory supplement to ecoregions map of the continents. 

Environmental Conservation 16: 307–309. 

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190 USDA Forest Service RMRS-GTR-346. 2016.

Appendix A. Hierarchy Revisions Working Group 

2010–2012

Canada 

Del Meidinger British Columbia Ministry of Forests, now consultant

Serguei Ponomarenko NatureServe-Canada

Jean-Pierre Saucier Ministère des Ressources naturelles, Québec

United States

Don Faber-Langendoen NatureServe (chair)

Gene Fults Natural Resources Conservation Service

Andy Gray U.S. Forest Service

Eileen Helmer U.S. Forest Service, Puerto Rico

Bruce Hoagland University of Oklahoma

Todd Keeler-Wolf California Department of Fish and Game

David Tart U.S. Forest Service

Alan Weakley North Carolina Botanic Garden, University of North Carolina

Latin America

Carmen Josse NatureServe, Chile

Gonzalo Navarro Bolivia & Universidad Complutense de Madrid
USDA Forest Service RMRS-GTR-346. 2016. 191

Level 1– Formation Class 

Level 2 – Formation 

Subclass

Level 3 – Formation Wetland and 

aquatic formations marked with *

 1. Forest & Woodland [Mesomorphic Tree Vegetation]1.A. Tropical Forest & 

Woodland

1.A.1. Tropical Dry Forest & Woodland

1.A.2. Tropical Lowland Humid Forest 

1.A.3. Tropical Montane Humid Forest

1.A.4. Tropical Flooded & Swamp 

Forest *

1.A.5. Mangrove*

1.B. Temperate & Boreal 

Forest & Woodland

1.B.1. Warm Temperate Forest & 

Woodland

1.B.2. Cool Temperate Forest & 

Woodland

1.B.3. Temperate Flooded & Swamp 

Forest *

1.B.4. Boreal Forest & Woodland

1.B.5. Boreal Flooded & Swamp 

Forest *

2. Shrub & Herb Vegetation 

[Mesomorphic Shrub & Herb 

Vegetation] 

2.A. Tropical Grassland, 

Savanna & Shrubland

2.A.1. Tropical Lowland Grassland, 

Savanna & Shrubland 

2.A.2. Tropical Montane Grassland & 

Shrubland 

2.A.3. Tropical Scrub & Herb Coastal 

Vegetation

2.B. Temperate & Boreal 

Grassland & Shrubland

2.B.1. Mediterranean Scrub & Grassland

2.B.2. Temperate Grassland & Shrubland

2.B.3. Boreal Grassland & Shrubland

2.B.4. Temperate to Polar Scrub & 

Herb Coastal Vegetation 

2.C. Shrub & Herb Wetland 2.C.1. Tropical Bog & Fen *

2.C.2. Temperate to Polar Bog & Fen*

2.C.3. Tropical Freshwater Marsh, 

Wet Meadow & Shrubland*

2.C.4. Temperate to Polar Freshwater 

Marsh, Wet Meadow & Shrubland*

2.C.5. Salt Marsh*

3. Desert & Semi-Desert [Xeromorphic Woodland, Scrub & 

Herb Vegetation]

3.A. Warm Desert & SemiDesert Woodland, Scrub 

& Grassland

3.A.1. Tropical Thorn Woodland

3.A.2. Warm Desert & Semi-Desert 

Scrub & Grassland

Appendix B. Formation level units, Level 1 to Level 3.
192 USDA Forest Service RMRS-GTR-346. 2016.

3.B. Cool Semi-Desert 

Scrub & Grassland

3.B.1. Cool Semi-Desert Scrub & 

Grassland

4. Polar & High Montane Scrub, 

Grassland & Barrens [Cryomorphic Scrub, Herb & Cryptogam Vegetation] 4.A. Tropical High Montane Scrub & Grassland4.A.1. Tropical High Montane Scrub & 

Grassland

4.B. Temperate to Polar 

Alpine & Tundra Vegetation

4.B.1. Temperate & Boreal Alpine 

Dwarf-shrub & Grassland

4.B.2. Polar Tundra & Barrens

5. Aquatic Vegetation [Hydromorphic Vegetation]5.A. Saltwater Aquatic 

Vegetation

5.A.1. Floating & Suspended Macroalgae Saltwater Vegetation* 

5.A.2. Benthic Macroalgae Saltwater 

Vegetation*

5.A.3. Benthic Vascular Saltwater 

Vegetation* 

5.A.4. Benthic Lichen Saltwater Vegetation*

5.B. Freshwater Aquatic 

Vegetation

5.B.1. Tropical Freshwater Aquatic 

Vegetation*

5.B.2. Temperate to Polar Freshwater 

Aquatic Vegetation*

6. Open Rock Vegetation 

[Cryptogam - Open Mesomorphic Vegetation] 

6.A. Tropical Open Rock 

Vegetation

6.A.1. Tropical Cliff, Scree & Other 

Rock Vegetation

6.B. Temperate & Boreal 

Open Rock Vegetation

6.B.1. Temperate & Boreal Cliff, Scree 

& Other Rock Vegetation

7. Agricultural & Developed 

Vegetation [Anthromorphic 

Vegetation] 

7.A. Woody Agricultural 

Vegetation 7.A.1. Woody Horticultural Crop

7.A.2. Forest Plantation & Agroforestry

7.A.3. Woody Wetland Horticultural 

Crop*

7.B. Herbaceous Agricultural Vegetation 7.B.1. Row & Close Grain Crop

7.B.2. Pasture & Hay Field Crop

7.B.3. Herbaceous Horticultural Crop

7.B.4. Fallow Field & Weed Vegetation

7.B.5. Herbaceous Wetland Crop*

7.C Herbaceous & Woody 

Developed Vegetation

7.C.1. Lawn, Garden & Recreational 

Vegetation

7.C.2. Other Developed Vegetation

7.C.3. Developed Wetland Vegetation*

7.D. Agricultural & Developed Aquatic Vegetation7.D.1. Agricultural Aquatic Vegetation*

7.D.2. Urban & Recreational Aquatic 

Vegetation*
USDA Forest Service RMRS-GTR-346. 2016. 193

6 natural classes 13 natural subclasses 37 natural formations

1 cultural subclass 4 cultural subclasses 13 cultural formations

Non-vegetated Classes (non - NVC)8. Natural Open Fresh Water Lake

River

Subterranean Freshwater

9. Natural Open Salt Water Estuary and Ocean

10. Cultural Open Water Reservoir and Canal (etc.)

11. Perennial Snow/Ice Perennial Snowfield

Ice Sheet

Glacier

12. Natural Surface Bare Area Consolidated Bare Area 

(Rock, etc)

Unconsolidated Bare Area 

(Sand, Gravel, etc)

13. Natural Subterranean Cave (etc).

14. Cultural Surface Bare Area Developed, Low Intensity

Developed, Medium Intensity

Developed, High Intensity

15. Cultural Subterranean Mine Shaft (etc.)
194 USDA Forest Service RMRS-GTR-346. 2016.

Appendix C. Glossary of Terms

The following set of terms are selected from the FGDC (2008) standard. 

Agricultural vegetation — A vegetation type that exhibits (a) rapid turnover in 

structure, typically at least on an annual basis, either through comprehensive 

manipulation of physiognomy and floristics by harvesting and/or planting, 

or by continual removal of above ground structure (e.g., cutting, haying), or 

(b) showing strong linear (planted) features. The herbaceous layer may be 

bare at various times of the year. 

Abiotic — Pertaining to the nonliving parts of an ecosystem, such as soil particles, 

bedrock, air, and water (Helms 1998).

Abundance — The total number of individuals of a taxon or taxa in an area, volume, 

population, or community; often measured as cover in plants (Lincoln and 

others 1998).

Basal area — The cross-sectional area of all stems of a species or all stems in a stand 

measured at breast height (4.5 feet or 1.37 meters above the ground) and 

expressed per unit of land area (Helms 1998).

Biome — Major type of natural vegetation that occurs wherever a particular mix of 

climatic and edaphic conditions is encountered; also considered as a major 

ecosystem type. (Ladle and Whittaker 2011).

Canopy cover — The percentage of ground covered by the vertical projection of the 

outermost perimeter of the natural spread of foliage of plants. Small openings 

in the canopy are included (SRM 1989; USDA NRCS 1997). cf. foliar cover.

Class — See formation class.

Classification — The grouping of similar types (in this case, vegetation types) according to criteria (in this case, physiognomic and floristic). The rules for 

classification shall be clarified prior to delineation of the types within the 

classification standard. Classification methods should be clear, precise, and 

based on objective criteria so that the outcome is theoretically independent of 

who applies the classification (UNEP/FAO 1995; FGDC 1997).

Classification plot records — Plot records that contain the data necessary to inform 

the development or revision of the floristic units within the NVC. Such plots 

typically contain high quality data on floristic composition and structure, 

and conform to the standard articulated in Section 3.1.1 (Jennings and others 

2006).

Close grown crops — Crops that are generally drill-seeded or broadcast, such as 

wheat, oats, rice, barley, and flax, resulting in very narrow regularly spaced, 

structure (adapted from NRI 2003).

Cover — See canopy cover, foliar cover.

Cropland — See agricultural vegetation.

Cross-walk — To describe and document the relationships between members of one 

set or series and members of another set or series. These relationships may be 

one-to-one, one-to-many, or many-to-many.

Cryomorphic — Pertaining to plants having structural or functional adaptations to 

survive cold temperatures and resist frost damage (e.g., alpine creeping dwarfshrubs, krummholz).
USDA Forest Service RMRS-GTR-346. 2016. 195

Cryptogam — A plant that produces by spores or gametes rather than seed, i.e. an 

alga, bryophyte or pteridophyte (fern). For vegetation purposes, often extended to include lichen, which are comprised of a fungus and an alga.

Cultural vegetation — Vegetation with a distinctive structure, composition, and 

development determined by regular human activity (Küchler 1969).

Developed vegetation — A vegetation type that typically contains an almost continuous herbaceous (typically grass) layer, with a closely cropped physiognomy, 

typically through continual removal of above ground structure (e.g. cutting, 

mowing), and where tree cover is highly variable, or other highly manipulated 

planted gardens. 

Diagnostic growth form — Any growth form or group of growth forms whose relative constancy or abundance differentiates one vegetation type from another.

Diagnostic growth forms include dominant growth form and indicator growth 

form.

Division — The fourth level in the natural vegetation hierarchy, in which each 

vegetation unit is defined by a group of plant communities in a given continental or other broad geographic area exhibiting a common set of dominant 

growth forms and many diagnostic plant taxa (including character taxa of the 

dominant growth forms) corresponding to broad climatic and environmental 

characteristics. (Westhoff and van der Maarel 1973, p 664-665; Whittaker 

1975). 

Dominance — The extent to which a given taxon or growth form has a strong influence in a community because of its size, abundance, or cover. (Lincoln and 

others 1998). 

Dominant growth form — Growth form with the highest percent of cover, usually in 

the uppermost dominant layer (in other contexts dominant growth forms can 

be defined in terms of biomass, density, height, coverage, etc).

Epiphyte — A vascular or nonvascular plant that grows by germinating and rooting 

on other plants or other perched structures, and does not root in the ground 

(adapted from FGDC 1997).

Existing vegetation — Vegetation found at a given location at the time of observation 

(Jennings and others 2006). cf. potential natural vegetation.

Field stratum — The layer of vegetation consisting of herbs, regardless of height, as 

well as woody plants less than 0.5 m in height (Jennings and others 2006).

Floating aquatic stratum — The layer of vegetation consisting of rooted or drifting 

plants that float on the water surface; e.g. duckweed, water-lily (Jennings and 

others 2006).

Foliar cover — The percentage of ground covered by the vertical projection of the 

aerial portion of plants. Small openings in the canopy and intraspecific overlap are excluded (SRM 1989). cf. canopy cover.

Forb — A non-aquatic, non-graminoid herb with relatively broad leaves and/or showy 

flowers. Includes both flowering and spore-bearing, non-graminoid herbs.

Formation — The third level in the natural vegetation hierarchy, in which each 

vegetation unit is defined by geographically widespread (global) plant communities of similar physiognomy and dominant growth forms, typically 

related to major topographic and edaphic conditions occurring within major 
196 USDA Forest Service RMRS-GTR-346. 2016.

climatic conditions (Whittaker 1975; Lincoln and others 1998). The formation 

largely corresponds to a (cf.) “biome.” 

Formation class — The first (highest) level in the natural vegetation hierarchy, in 

which each vegetation unit is defined by a characteristic combination of 

dominant growth forms adapted to a very basic set of moisture/temperature 

regimes.

Formation subclass — The second level in the natural vegetation hierarchy, in which 

each vegetation unit is defined by geographically widespread (global) plant 

communities of similar physiognomy and dominant growth forms, typically 

related to major climatic conditions (Whittaker 1975; Lincoln and others 

1998).

Graminoid — A non-aquatic, flowering herb with relatively long, narrow leaves and 

inconspicuous flowers with parts reduced to bracts. Includes grasses, sedges, 

rushes, and arrowgrasses.

Ground stratum — see nonvascular stratum.

Growth form — The shape or appearance of a plant reflecting growing conditions 

and genetics. Growth form is usually consistent within a species, but may 

vary under extremes of environment (Mueller-Dombois and Ellenberg 1974). 

Growth forms determine the visible structure or physiognomy of plant communities (Whittaker 1973a).

Habitat — A general term referring to the locality, site and particular type of local 

environment occupied by an organism or community (adapted from Lincoln 

and others 1998). 

Herb — A vascular plant without perennial aboveground woody stems, with perennating buds borne at or below the ground surface (Whittaker 1975; FGDC 1997). 

Includes forbs (both flowering forbs and spore-bearing ferns), graminoids, 

and herbaceous vines.

Herb stratum — See field stratum.

Hydromorphic — Pertaining to plants having structural or functional adaptations for 

living in water-dominated or aquatic habitats (adapted from FGDC 1997 and 

Lincoln and others 1998).

Indicator growth form — A growth form whose presence, abundance, or vigor is 

considered to indicate certain site conditions. 

Land cover — The observed (bio) physical cover of the Earth’s surface (Di Gregorio 

2005).

Land use — The arrangements, activities, and inputs people undertake in a certain 

land cover type to produce, change, or maintain it (Di Gregorio 2005).

Layer (vegetation) — A structural component of a community consisting of plants 

of approximately the same height and growth form (e.g., tree overstory, tree 

regeneration). cf. stratum.

Liana — A woody, climbing plant that begins life as terrestrial seedlings but relies 

on external structural support for height growth during some part of its life 

(Gerwing 2004), typically exceeding 5 m in height or length at maturity.

Life form — Plant type defined by the characteristic structural features and method of 

perennation, generally as defined by Raunkiaer (1934; see Beard 1973). 
USDA Forest Service RMRS-GTR-346. 2016. 197

Lithomorphic — Pertaining to plants, especially cryptogams, having structural or 

functional adaptations for living on rock surfaces or in rocky substrates 

(i.e. particle sizes larger than 2 mm diameter) or very hard surfaces, such as 

dense clay badlands (adapted from Lincoln and others 1998). 

Macroclimate — The climate of a major geographical region primarily reflecting 

latitude and continental position, excluding the effects of landform and vegetation (adapted from Bailey 1988, 1996; Lincoln and others 1998; Forman 

and Godron 1986).

Mesoclimate — The climate of a geographic area resulting from modification of the 

macroclimate by the influences of landforms, altitude, aspect, and slope gradient (Bailey 1988, 1996).

Mesomorphic — Pertaining to plants requiring environmental conditions of moderate 

moisture and temperature or which are only partially protected against desiccation (adapted from Lincoln and others 1998).

Microclimate — The climate of the immediate surroundings or habitat resulting 

from modification of the mesoclimate by the influences of local topography, 

vegetation, and soil (adapted from Lincoln and others 1998; and Bailey 1988, 

1996).

Moss stratum — See ground stratum.

Natural vegetation — Vegetation where ecological processes primarily determine 

species and site characteristics, that is, vegetation comprised of a largely 

spontaneously growing set of plant species that are shaped by both site and 

biotic processes (Kuchler 1969; Westhoff and Van der Maarel 1973).

Nonvascular — A plant or plant-like organism without specialized water or fluid conductive tissue (xylem and phloem). Includes mosses, liverworts, hornworts, 

lichens, and algae (adapted from FGDC 1997).

Nonvascular stratum — The layer of vegetation consisting of non-vascular plants 

growing on soil or rock surfaces. This includes mosses, liverworts, hornworts, 

lichens, and algae (Jennings and others 2006). Sometimes called the ground 

stratum.

Non-vegetated — A category used to classify lands with limited capacity to support 

life and typically having less than 1 percent vegetative cover. Vegetation, if 

present, is widely spaced. Typically, the surface of barren land is sand, rock, 

exposed subsoil, or salt-affected soils. Subcategories include salt flats; sand 

dunes; mud flats; beaches; bare exposed rock; quarries, strip mines, gravel 

pits, and borrow pits; river wash; oil wasteland; mixed barren lands; and other 

barren land (adapted from NRI 2003). Exceptions include vegetation that 

exhibits a distinct composition under very sparse conditions (e.g., sea rocket 

coastal shore vegetation, or amaranth coastal vegetation). These types rarely 

have greater than 1 percent cover.

Physiognomy — The visible structure or outward appearance of a plant community 

as expressed by the dominant growth forms, such as their leaf appearance or 

deciduousness (Fosberg 1961, Jennings and others 2006). cf. structure.

Planted/cultivated — See cultural vegetation. 
198 USDA Forest Service RMRS-GTR-346. 2016.

Plot — In the context of vegetation classification, an area of defined size and shape 

that is intended for characterizing a homogenous occurrence of vegetation. 

cf. relevé.

Potential natural vegetation — The vegetation that would become established 

if successional sequences were completed without interference by man 

or natural disturbance under the present climatic and edaphic conditions 

(Tüxen 1956). cf. existing vegetation. 

Range of variation — The values of an attribute, such as species composition or 

environmental parameters, that fall within the upper and lower bounds determined for that attribute. The range of variation in the floristic composition of 

a vegetation type may, for example, be expressed in terms of its beta diversity 

(cf. Wilson and Shmida 1984; McCune and others 2002), either along an 

environmental gradient or as the amount of compositional change among a 

group of plots.

Relevé — A record of vegetation intended for characterizing a stand of vegetation 

having uniform habitat and relatively homogeneous plant cover, and which 

is large enough in area to contain a large proportion of the species typically 

occurring in the plant community (Mueller-Dombois and Ellenberg 1974) 

cf. plot. 

Reserved — A section of the FGDC standard that will be addressed or developed in 

subsequent versions.

Ruderal — Vegetation found on human-disturbed sites, with no apparent recent 

historical natural analogs, and whose current composition and structure (1) is 

not a function of continuous cultivation by humans and (2) includes a broadly 

distinctive characteristic species combination, whether tree, shrub or herb 

dominated. The vegetation is often comprised of invasive species, whether 

exotic or native, that have expanded in extent and abundance due to the human 

disturbances” (Curtis 1959; Ellenberg 1988; Lincoln and others 1998). 

Sampling strategy — The means and criteria used to select the locations for plots 

(based on Tart and others 2005b; Mueller-Dombois and Ellenberg 1974; and 

Gauch 1982). 

Seral — A vegetation type (or component species) that is nonclimax; a species or 

community demonstrably susceptible to replacement by another species or 

community (Daubenmire 1968).

Semi-natural vegetation — Vegetation in which past or present human activities significantly influence composition or structure, but do not eliminate or 

dominate spontaneous ecological processes (Westhoff and Van der Maarel 

1973). cf. ruderal.

Shrub — A woody plant that generally has several erect, spreading, or prostrate stems 

that give it a bushy appearance. In instances where growth form cannot be determined, woody plants less than 5 m in height at maturity shall be considered 

shrubs. Includes dwarf-shrubs, krummholz, and low or short woody vines 

(adapted from FGDC 1997; and Box 1981).
USDA Forest Service RMRS-GTR-346. 2016. 199

Shrub stratum — The layer of vegetation consisting of woody plants more than 

0.5 m tall but less than 5 m in height, such as shrubs, tree seedling and 

saplings, and lianas. Epiphytes may also be included in this stratum. Rooted 

herbs are excluded even if they are over 0.5 m in height (adapted from 

Jennings and others 2006).

Stand — A spatially continuous unit of vegetation with uniform composition, 

structure, and environmental conditions. This term is often used to indicate a 

particular example of a plant community (Jennings and others 2006).

Stratum — A structural component of a community consisting of plants of approximately the same height, e.g., tree, shrub, or herb strata (Jennings and others 

2006). 

Structure (vegetation) — (1) The spatial pattern of growth forms in a plant community, especially with regard to their height, abundance, or coverage within 

the individual layers (Gabriel and Talbot 1984). (2) The spatial arrangement 

of the components of vegetation resulting from plant size and height, vertical 

stratification into layers, and horizontal spacing of plants (Lincoln and others 

1998; Mueller-Dombois and Ellenberg 1974). cf. physiognomy. 

Subclass — See Formation subclass.

Submerged aquatic stratum — The layer of vegetation consisting of rooted or drifting plants that by-and-large remain submerged in the water column or on the 

aquatic bottom, e.g. sea grass (Jennings and others 2006).

Tree — A woody plant that generally has a single main stem and a more or less 

definite crown. In instances where growth form cannot be determined, woody 

plants equal to or greater than 5 m in height at maturity shall be considered 

trees (adapted from FGDC 1997). Includes dwarf trees (Tart and others 

2005b) or “treelets” (Box 1981).

Tree stratum — The layer of vegetation consisting of woody plants more than 5 m 

in height, including mature trees, shrubs over 5 m tall, and lianas. Epiphytes 

growing on these woody plants are also included in this stratum (Jennings and 

others 2006).

Type — See vegetation type.

Vegetation — The collective plant cover of an area (FGDC 1997).

Vegetation type — A named category of plant community or vegetation defined on 

the basis of shared floristic and/or physiognomic characteristics that distinguish it from other kinds of plant communities or vegetation (Tart and others 

2005a). This term can refer to units in any level of the NVC hierarchy.

Xeromorphic — Pertaining to plants having structural or functional adaptations to 

prevent water loss by evaporation (Lincoln and others 1998).
200 USDA Forest Service RMRS-GTR-346. 2016.

 Table D.1—General Growth Forms 

Growth Form 

Code Name and Definition

T

Tree - A woody plant that generally has a single main stem and a more or less definite crown. In 

instances where growth form cannot be readily determined, woody plants equal to or greater 

than 5 m in height at maturity are to be considered trees (adapted from FGDC 1997). Excludes 

krummholz (wind-stunted trees), but includes small trees or “treelets” (Box 1981). Tall multistemmed woody plants with strong canopy structure and that will exceed 5 m would be included 

here (e.g. mature, multi-stemmed Quercus ellipsoidalis in the United States or some Australian 

mallee eucalypts). 

S

Shrub - A woody plant that generally has several erect, spreading, or prostrate stems that give 

it a bushy appearance. In instances where growth form cannot be readily determined, woody 

plants less than 5 m in height at maturity are to be considered shrubs (adapted from FGDC 1997). 

Includes krummholz (wind-stunted trees), but excludes small trees, (Box 1981). Includes dwarfshrubs (less than 30 cm), low or short woody vines, and arborescents (woody plants that branch 

at or near ground-level but grow to low tree heights). (Box 1981). Some multi-stemmed, bushy 

woody species (“scrub”) that reach up to 10 m may be included here, such as Australian mallee 

comprised of Eucalyptus viridis and Eucalyptus dumosa). 

H

Herb - A vascular, non-woody plant without perennial aboveground woody stems, with perennating buds borne at or below the ground surface. (Whittaker 1975; FGDC 1997). Includes forbs (both 

flowering forbs and spore-bearing vascular plants), graminoids, and herbaceous vines.

N

Nonvascular - A plant or plant-like organism without specialized water or fluid conductive tissue 

(xylem and phloem). Includes mosses, liverworts, hornworts, lichens, and algae (adapted from 

FGDC 1997). Also called thallophytes or “nonvascular cryptogams,” (that is, excluding the vascular 

cryptogams; see Herb) (Box 1981).

E Epiphyte - A vascular or nonvascular plant that grows by germinating and rooting on other plants 

or other perched structures, and does not root in the ground (adapted from FGDC 1997). 

L

Liana - A woody, climbing plant that begins life as terrestrial seedlings but relies on external structural support for height growth during some part of its life (Gerwing 2004), typically exceeding 5 

m in height or length at maturity. Non-woody climbers are treated as “Herb.”

Appendix D. Growth Form Names, Codes, and 

Definitions

Names, definitions and codes for general and specific growth forms for use in collecting vegetation plot data (from Table E.1 of FGDC 2008) (see also Whittaker 1975:359; Tart and others 

2005b; Box and Fujiwara 2005). 
USDA Forest Service RMRS-GTR-346. 2016. 201

General 

Growth 

Form Code

Table D.2—Specific Growth Forms

Specific 

Growth 

Form Code Name and Definition

T

TBD

Broad-leaved deciduous tree - A tree with a branching crown, leaves that have 

well-defined leaf blades that are generally of at least microphyll size (>225 

mm2, or 0.35 in2)

 a and that seasonally loses all of its leaves and becomes 

temporarily bare-stemmed (adapted from FGDC 1997; Box 1981). Includes 

monopodial and sympodial growth forms.

TBE

Broad-leaved evergreen tree - A tree with a branching crown, leaves that 

have well-defined leaf blades that are generally of at least microphyll sized 

(>225 mm2 or 0.35 in2) and that has green leaves all year round. (FGDC 1997, 

Box 1981). Includes monopodial and sympodial growth forms, and woody-like 

bananas (Musa spp.).

 TBES

Sclerophyllous tree - A type of broad-leaved evergreen tree with leaves that 

are stiff and firm, and retain their stiffness even when wilted. The leaves are 

typically relatively small (microphyll to small mesophyll in size) and sometimes 

rather linear, (FGDC 1997; Whittaker 1975; Box 1981). 

TN

Needle-leaved tree - A tree with slender, often cylindrical, elongated leaves or 

with small overlapping leaves. Includes scale-leaved and needle-leaved trees, 

deciduous and evergreen, needle-leaved trees, such as Abies, Larix, Picea, 

Pinus, Thuja (FGDC 1997; Box 1981). 

TU

Succulent tree – A tree or arborescent plant with fleshy stems or leaves with 

specialized tissue for the conservation of water (FGDC 1997). Includes Cactaceae, Yucca brevifolia (Joshua trees), euphorbias, and others over 5 meters in 

height at maturity. An “arborescent stem-succulent” (Box 1981). Some Dracaenaceae may fit here. 

TM

Small-leaved tree - A tree with very small leaves (<225 mm2, or 0.35 in2)*, or 

even leafless, sometimes armed with spines. Includes both evergreen and deciduous small-leaved trees, such as Acacia greggii, Mimosa spp. (adapted from 

“thorn tree” by Whittaker 1975) .

TP

Palm tree - An evergreen, broad-leaved, flowering, non-sporing, tree, typically 

with a simple, unbranched stem and terminal, rosulate crown of large, pinnate 

or fan-shaped leaves. A type of rosette tree. Palms are the primary taxa (but 

see Dracaenaceae, some Pandanaceae, etc.; Box 1981). Hyphaene thebaica is 

an example of a branched palm tree.

TF

Tree fern - An evergreen, broad-leaved, spore-bearing tree (or arborescent 

fern) with a simple, unbranched stem and terminal, rosulate crown of large 

fronds. A type of rosette tree, including taxa from Cyatheaceae (Box 1981). 

TG

Bamboo tree- A woody-stemmed, arborescent grass that is equal to or greater 

than 5 m in height at maturity. Only applies to woody-stemmed bamboos. 

Includes the “Arborescent grasses” (Box 1981). Other more typically woody 

grasses, such as Arundo, Saccharum, currently excluded, and treated as Herbgraminoid.
202 USDA Forest Service RMRS-GTR-346. 2016.

S

SD

Dwarf-shrub – A mature caespitose, creeping, matted, or cushion-forming 

shrub that is generally small-leaved and is typically less than 30 cm tall at maturity due to genetic and/or environmental constraints (adapted from MuellerDombois and Ellenberg 1974). 

 SBD

Broad-leaved deciduous shrub - A shrub that is typically more than 30 cm tall 

at maturity with leaves that have well-defined leaf blades that are generally of 

at least microphyll size (>225 mm2, or 0.35 in2* and seasonally loses all of its 

leaves and becomes temporarily bare-stemmed (FGDC 1997).

 SBE

Broad-leaved evergreen shrub - A shrub that is typically more than 30 cm tall 

at maturity with leaves that are generally of at least microphyll sized (>225 

mm2, or 0.35 in2 )* and has green leaves all year round (adapted from FGDC 

1997; Box 1981).

 SBES

Sclerophyllous shrub - A type of broad-leaved evergreen shrub, typically with 

relatively small, leaves that are stiff and firm, and retain their stiffness even 

when wilted (FGDC 1997; Whittaker 1975).

SN

Needle-leaved shrub - A shrub that is typically more than 30 cm tall at maturity with slender, elongated leaves or with small overlapping leaves that usually 

lie flat on the stem (FGDC 1997). Includes scale-leaved as well as needle-leaved 

shrubs, and deciduous as well as evergreen.

SU

Succulent shrub – A fleshy shrub that is typically more than 30 cm tall at maturity with specialized tissue for the conservation of water (adapted from FGDC 

1997 and the Thorn shrub of Whittaker 1975). Includes cacti less than 5 meters 

in height at maturity. Includes both the “Typical Stem succulents” and “Bush 

succulents” (Box 1981). Includes Aloe, Agave.

SM

Small-leaved shrub - A shrub that is typically more than 30 cm tall at maturity 

with very small leaves (<225 mm2, or 0.35 in2)*, or even leafless, sometimes 

armed with spines, usually having compound, deciduous leaves that are often 

reduced in size. Includes Larrea tridentata, Prosopis glandulosa, Acacia neovernicosa, Senna, Calliandra (Jennings and others 2006; Whittaker 1975).

Bamboo shrub- A woody-stemmed, shrubby grass that is less than 5 m in 

height at maturity. Only applies to woody-stemmed bamboos. Includes 

Arundo, Saccharum, Sinarundinaria spp (=Yushania spp.). 

SP

Palm shrub - An evergreen, broad-leaved, typically unbranched shrub that is 

typically more than 30 cm tall at maturity with a simple stem and terminal, 

rosulate crown of large, pinnate or fan-shaped leaves. Includes palms and 

palm-like plants, such as espeletia. 

H

HA

Aquatic herb - A flowering or non-flowering herb structurally adapted to live 

floating or submerged in an aquatic environment. Does not include emergent 

plants such as cattails and sedges. (FGDC 1997; Jennings and others 2006). 

Includes flowering and non-flowering, and forb and graminoid aquatic herbs. 

Further subdivision may be warranted if ecologically meaningful.

HF Forb - A non-aquatic, flowering or spore-bearing, non-graminoid herb.

 HFF Flowering forb - A forb with relatively broad leaves and showy flowers. Does 

not include graminoids, ferns, or fern-allies.

 HFE Spore-bearing forb - A non-flowering, spore-bearing forb. Includes nonaquatic, non-woody ferns, clubmosses, spikemosses, horsetails, and quillworts.

 HFS

Succulent forb - A flowering forb with a fleshy stem and often with reduced 

leaves. Includes Salicornia and others.

HG

Graminoid - A non-aquatic, flowering herb with relatively long, narrow leaves 

and inconspicuous, reduced flowers. Includes grasses, sedges, rushes, and 

arrow-grasses. Aquatic graminoids are treated with aquatic herbs. 
USDA Forest Service RMRS-GTR-346. 2016. 203

N

NB

Bryophyte - A nonvascular, non-flowering, photosynthetic plant that bears 

leaf-like appendages or lobes and attaches to substrates by rhizoids. Includes 

mosses, liverworts, and hornworts (Abercrombie and others 1966).

NA

Alga - A nonvascular, photosynthetic plant with a simple form ranging from 

single- or multi-celled to a filamentous or ribbon-like thallus with relatively 

complex internal organization (Abercrombie and others 1966).

NL

Lichen - An organism generally recognized as a single plant that consists of a 

fungus and an alga or cyanobacterium living in symbiotic association (FGDC 

1997). Technically, lichen is not a plant, but is often treated together with moss 

as a type of nonvascular growth form.

E E

Epiphyte - A vascular or nonvascular plant that grows by germinating and 

rooting on other plants or other perched structures, and does not root in the 

ground (adapted from FGDC 1997). This growth form may be used as a modifier of other growth forms, e.g., HFF(Flowering forb). 

L L

Liana - A woody, climbing plant that begins life as terrestrial seedlings but 

relies on external structural support for height growth during some part of its 

life (Gerwing 2004), typically exceeding 5 m in height or length at maturity. 

Non-woody climbers are treated as a type of “Herb.”

 acf. Gillison (2013, Table 12.3), who defines microphylls as 225-2025 mm2, and nanophylls as 25-225 mm2.
204 USDA Forest Service RMRS-GTR-346. 2016.

Appendix E. Growth Forms from Box and Fujiwara 

(2005)

Main Terrestrial Plant Life Forms. This classification from Box and Fujiwara 

(2005, Table 4.2) represents an expanded version of the original model of 90 plant 

‘ecophysiognomic’ types and their worldwide climatic envelopes (Box 1981). 

Physiognomic groupings are shown on the left, numbers of types and short descriptions of the 114 actual types are shown on the right. Box and Fujiwara (2013) provide 

a revised and expanded set of types.

Growth Forms

# of 

Types Descriptions

Trees

 Evergreen (broad-leaved) Laurophyll 4 tropical, tropical-montane, subtropical/warm-temperate, 

cool-maritime

Gymnosperm 1 (sub)tropical broad/linear-leaved

Microphyll 1 (sub)tropical coriaceous

Sclerophyll 4 (sub)tropical, warm-temp., mediterranean, tall-temperate

 Deciduous (broad-leaved) Raingreen 3 monsoon-mesomorphic, montane, xero-microphyll

Bottle Trees 1 tropical (raingreen)

Summergreen 2 nemoral, short-summer

 Needle-leaved (evergreen) 6 tropical-xeric, heliophilic long‐needled, submediterranean, 

temperate, cool-laurophyll, boreal/montane

Small Trees

 Evergreen Laurophyll 4 tropical, cloud-forest, subtropical/warm-temperate, coolmaritime

Sclerophyll 1 tropical macro-sclerophyll

 Deciduous 2 raingreen, summergreen

Needle-leaved 1 dwarf-needle/scale-leaved

Tuft-Trees and Treelets 3 palm trees, bottle palms, palm treelets

Arborescents

 Evergreen Laurophyll 2 tropical, extra-tropical

Sclerophyll 1 tropical/subtropical

 Deciduous 2 raingreen, summergreen

 Stemgreen 2 mesic-microphyll, xeric/leafless

Tuft-Arborescents 4 tree-ferns, tropical-alpine, coriaceous, sclerophyll/

succulent

Krummholz (needleleaved)2 evergreen, summergreen

Shrubs

 Evergreen Laurophyll 2 tropical, subtropical/warm-temperate
USDA Forest Service RMRS-GTR-346. 2016. 205

Sclerophyll 2 mediterranean, hot‐desert

Succulent 1

Needle-Leaved 1

Semi-evergreen xeric 1 temperate

 Summergreen 2 nemoral-mesomorphic, xeromorphic

Dwarf-Shrubs

 Evergreen 4 mediterranean, temperate, maritime-heath, boreal/tundra

 Summergreen 1 boreal/tundra

 Xeromorphic 1 leptophyll/leafless

 Cushion-form 2 mesic-evergreen, xeromorphic

Rosette-Shrubs 2 trunkless palms, xeric leaf-succulent

Stem-Succulents 5 columnar, branched-arborescent, typical, frutescent, cryptic

Semi-Shrubs 3 mesomorphic, xeromorphic, xylopodial-xeromorphic

Graminoids

 Broad-leaved (bamboos) 2 arborescent, dwarf

 Tall 3 cane‐graminoids, typical-tall, tall-tussock

 Short 5 spreading, bunch, short-tussock, sclerophyll, desert-grasses

Forbs

 Evergreen 3 tropical-arborescent, tropical, temperate

 Deciduous Raingreen 2 typical, cold-desert

Summergreen 3 tall, typical, spring‐ephemeral

 Xeromorphic 2 succulent, cushion-form

 Ephemeral 2 desert-ephemeral, cold‐desert

Ferns 3 evergreen, raingreen, summergreen

Vines Lianas 1 tropical-evergreen

Vines 3 evergreen, raingreen, summergreen

Epiphytic 1

Epiphytes Rosette 2 large-tropical, stenophyll

Stem‐Succulent 1

Shrublet 1 wintergreen-shrublet

Herbs 3 tropical-forb, fern, small-fern

Cryptogams 2 mat-forming, xeromorphic

Growth Forms

# of 

Types Descriptions
206 USDA Forest Service RMRS-GTR-346. 2016.

Appendix F. Comparisons to Other Formation-Level 

Classifications

F.1. Main World Terrestrial Biome Types (Box and Fujiwara 2005)a

(These biomes types are recognized by most modern treatments of 

world vegetation).

Tropical rain forest (including montane and cloud forests)

Tropical deciduous forest, woodland, and thorn scrub

Tropical savanna (i.e. grassland)

Deserts

Warm deserts (subtropical)

Cold-winter deserts (continental)

Mediterranean forest, scrub, and shrublands

Temperate forests

Deciduous broad-leaved forest

Evergreen broad-leaved forest (incl. laurel forest, warm-temperate 

mixed forest)

Temperate rain forest

Conifer forests

Boreal (including deciduous)

Montane conifer forest (temperate montane and subalpine)

Grasslands (temperate)

Tundra and alpine vegetation

Polar and temperate-alpine tundra

Tropical alpine vegetation

Terrestrial wetlands (swamp, marsh, bog, fen)

aBox, E.O. and K. Fujiwara. 2005. Vegetation types and their broad-scale distribution. Page 

106–128 in: van der Maarel, E. Vegetation ecology. Blackwell Publishing. Malden, MA. 
USDA Forest Service RMRS-GTR-346. 2016. 207

F.2. World Wildlife Fund Major Habitat Types (Olson 2001) a

Tropical & Subtropical Moist Broadleaf Forests

Tropical & Subtropical Dry Broadleaf Forests

Tropical & Subtropical Coniferous Forests

Temperate Broadleaf & Mixed Forests

Temperate Coniferous Forests

Boreal Forests/Taiga 

Tropical & Subtropical Grasslands, Savannas, & Shrublands

Temperate Grasslands, Savannas, & Shrublands

Flooded Grassland & Savannas [temperate and tropical]

Montane Grassland & Savannas [temperate and tropical]

Polar 

Mediterranean Forests, Woodlands, & Shrub

Deserts & Xeric Shrublands

Mangroves

Lake

Rock & Ice

aDavid M. Olson, Eric Dinerstein, Eric D. Wikramanayake, and others 2001. Terrestrial ecoregions 

of the world: A new map of life on earth. BioScience 51(11): 933-938. 
208 USDA Forest Service RMRS-GTR-346. 2016.

F.3. Formations (Biomes) - (Whittaker 1975)

Forests and Woodlands

1. Tropical rain forest

2. Tropical seasonal forest

3. Temperate rain forest

4. Temperate deciduous forest

5a. Temperate evergreen forest — broadleaf

5b. Temperate evergreen forest — needleleaf

5c. Temperate evergreen forest — sclerophyll [Mediterranean]

6. Taiga & subarctic-subalpine needle-leaved forest

7. Elfin woodland 

8. Tropical broadleaf woodland

9a. Thornwood— woodland

9b. Thornwood--scrub

10a. Temperate woodland — needleleaf

10b. Temperate woodland — sclerophyll

10c. Temperate woodland — deciduous broadleaf

Shrublands

11a. Temperate shrubland — deciduous

11b. Temperate shrubland — heath

11c. Temperate shrubland — sclerophyll [Mediterranean]

11d. Temperate shrubland — subalpine, needleleaf

11e. Temperate shrubland — subalpine, broadleaf

Grasslands and Alpine Vegetation

12. Savanna [tropical grassland]

13. Temperate grassland

14. Alpine shrubland

15. Alpine grassland

Cold and Warm Deserts and Tundra

16. Tundra

17. Warm semidesert scrub

18a. Cool semidesert — open scrub

18b. Cool semidesert — dry grassland

19. Arctic-alpine semidesert

20. True desert 

21. Arctic-alpine desert

Swamps, Marshes and Bogs

22. Cool temperate bog

23. Tropical freshwater swamp forest

24. Temperate freshwater swamp forest

25. Mangrove swamp

25. Saltmarsh

Marine and Aquatic

[26-29 are aquatic]

29. Marine rocky shores

30. Marine sandy beaches

31. Marine mudflats

Whittaker, R.H. 1975. Communities and ecosystems. 2nd edition. MacMillan, New York. 

(pp. 135-161).
USDA Forest Service RMRS-GTR-346. 2016. 209

Formations of Australia (Specht and Specht 2001) a,b 

Australian types

Closed forests (rainforests) - tropical north-eastern Australia

Closed forests (rainforests) —subtropical eastern Australia

Closed forests (rainforests) —temperate south-eastern Australia

Semi-deciduous closed forests —monsoonal northern Australia

Semi-deciduous closed forests —subtropical eastern Australia

Eucalypt open forests and woodlands —monsoonal northern Australia

Eucalypt open forests and woodlands —subtropical eastern Australia

Eucalypt open forests and woodlands —temperate south-eastern Australia

Eucalypt open forests and woodlands —montane south-eastern Australia

Eucalypt open forests and woodlands —temperate south-western Australia

Eucalypt open forests and woodlands —Australia wetland forests

Mallee eucalypt open-scrubs —monsoonal northern Australia

Mallee eucalypt open-scrubs —subtropical eastern Australia

Mallee eucalypt open-scrubs —temperate south-eastern Australia

Mallee eucalypt open-scrubs —temperate south-western Australia

Heathlands and related shrublands —monsoonal northern Australia

Heathlands and related shrublands —subtropical eastern Australia

Heathlands and related shrublands —temperate south-eastern Australia

Heathlands and related shrublands —montane south-eastern Australia

Heathlands and related shrublands —temperate south-western Australia

Tussock grasslands

Acacia vegetation —subhumid, subtropical eastern Australia

Acacia vegetation —Ausralian Arid Zone

Hummock grasslands —Australian Arid Zone

Chenopod low shrublands —southern Australia Arid Zone

Aquatic vegetation —tropical and subtropical northern Australia

Aquatic vegetation —temperate southern Australia

Coastal dune vegetation

Coastal wetland vegetation (mangroves, salt marshes, and brackish wetlands)

a Specht, R.L. and A. Specht. 2001. Australia, ecosystems of.pages 307–324, in: S.A. Levin, ed. 

Encyclopedia of Biodiversity, Vol. 1. Academic Press, New York. 

b Floristic groups are also provided for each formation.
210 USDA Forest Service RMRS-GTR-346. 2016.

F.5. Australian Native Vegetation (NWLRA 2001)

Vegetation profile fact sheets were developed for each type listed below, as 

provided by the NWLRA (National Land and Water Resources Audit Advisory 

Council). 2001. Australian native vegetation assessment 2001. National Land 

and Water Resources Audit. Canberra, Australia. 

•	 Rain forest and vine thickets 

•	 Eucalypt and tall open forests 

•	 Eucalypt open forests 

•	 Eucalypt low open forests 

•	 Eucalypt woodlands 

•	 Acacia forests and woodlands 

•	 Callitris forests and woodlands 

•	 Casuarina forests and woodlands 

•	 Melaleuca forests and woodlands 

•	 Other forests and woodlands 

•	 Eucalypt open woodlands 

•	 Tropical Eucalypt woodlands/grasslands 

•	 Acacia open woodlands 

•	 Mallee woodlands and shrublands 

•	 Low closed forests and closed shrublands 

•	 Acacia shrublands 

•	 Other shrublands 

•	 Heath 

•	 Tussock grasslands 

•	 Hummock grasslands 

•	 Other grasslands, herblands, sedgelands and rushlands 

•	 Chenopod shrublands, samphire shrubs and forblands 

•	 Mangroves, tidal mudflats, samphires, claypans, sand, rock, salt 

lakes, lagoons and freshwater lakes 
USDA Forest Service RMRS-GTR-346. 2016. 211

F.6. European Vegetation Survey (2002)a

A. Coastal mud-flats and brackish waters

B. Saltmarsh, sand-dune and sea-cliff vegetation

C. Rock crevice, scree and boulderfield vegetation

D. Freshwater aquatic vegetation

E. Springs, shoreline, and swamp [marsh] vegetation

F. Bogs and fens

G. Temperate grasslands, heaths, and fringe vegetation

H. Dry grasslands and semi-deserts

I. Oromediterranean grasslands and scrub

J. Montane tall-herb, grassland, fell-field and snowbed vegetation

K. Mediterranean garrigue, maquis, mattoral, tomillar and phyrygna

L. Temperate broadleaved forests and scrub

M. Montane heaths and coniferous forests

N. Weed communities

a Rodwell, J.S., J.H.J. Schamineé, L. Mucian, S. Pignatti, J. Dring and D. Moss. 2002. The 

diversity of European vegetation. An overview of phytosociological alliances and their 

relationships to EUNIS habitats. ECLNV. Report ECLNV nr. 2002/054. National Reference 

Centre for Agriculture, Nature and Fisheries, Wageningen, NL. 168 p.
212 USDA Forest Service RMRS-GTR-346. 2016.

Appendix G. Examples of Descriptive Methods for 

Describing Physiognomy — Structure

Küchler’s method for structural description of vegetation

Küchler’s (1967), method is a good example of the Descriptive-Mapping 

Physiognomic Approach (I). See also below for variations based on Dansereau (1951) 

and Beard (1981). These methods do not represent classifications, as such; rather, classifications are produced by combining the categories, sometimes a priori (e.g., Specht 

1974), but more often, a posteriori, based on the process of mapping (e.g., Beard 

1981). 

Life-Form Categories

Basic Life Forms Special Life Forms

Woody Plants Climbers (lianas) C

Broadleaf evergreen B Stem succulents K

Broadleaf deciduous D Tuft plants T

Needleleaf evergreen E Bamboos V

Needleleaf deciduous N Epiphytes X

Aphyllous O

Semi-deciduous (B+D) S Leaf Characteristics

Mixed (D+E) M hard (sclerophyll) h

Herbaceous Plants soft w

Graminoids G succulent k

Forbs H large (>400 cm2) l

Lichens, mosses L small (<4 cm 2) s

Structural Categories

Height (Stratification) Coverage

> 35 m 8 continous (>75 percent) c

20–35 m 7 interrupted (50–75 percent) i

10–20 m 6 parklike, in patches (25–50 percent) p

5–10 m 5 rare (6–25 percent) r

2–5 m 4 barely present, sporadical (1–5 percent b

0.5–2 3 almost absent, extremely scarce(<1 percent) a

0.1–0.5 2

<0.1 1
USDA Forest Service RMRS-GTR-346. 2016. 213

Other Examples

Dansereau (1951) has six categories, instead of four. Basic Life Forms is separated 

into two parts: Basic Life-forms (trees, shrubs, herbs, bryophytes, epiphytes, lianas) 

and Function (deciduous, semi-deciduous, evergreen, evergreen-succulent or leafless); 

Leaf Characteristics is separated into Leaf Shape and Size (needle, graminoid, small, 

large-broad, compound, thalloid) and Leaf Texture (filmy, membranous, sclerophyll, 

succulent-fungoid). Height and Coverage categories are similar to Küchler.

Beard (1981) provides an example amended specifically for Australia that consists 

of three categories: (1) Physiognomy of Dominant Stratum (Tall Trees >25 m tall, 

Medium Trees 10–25 m tall, Low Trees <10 m tall, Shrubs >1 m tall, Dwarf shrubs 

<1 m tall, Bunch Grasses, Hummock grass, Forbs, Lichens&Mosses, Succulents); 

(2) Floristics (Eucalyptus, Acacia, Triodea, Heterogenous); and (3) Density (Dense 

canopy, Mid-dense canopy, Incomplete Canopy, Rare but Conspicuous, Barrenvegetation largely absent, Scattered).

Beard, J.S. 1981. Classification in relation to vegetation mapping. Pages 97–106 in: 

A.N. Gillison and D.J. Anderson. Vegetation classification in Australia. CSIRO and 

Australian National University Press, Canberra, Australia 229 pp.
214 USDA Forest Service RMRS-GTR-346. 2016.

Appendix H. Key to bioclimatic maps of the world—

Rivas Martinez & Rivas-Saenz

In territories with a northern latitude of >72 or a southern latitude 

of > 56°. In territories outside this latitude and with an altitude of 

less than 200 m (1): annual positive temperature Tp < 380

Polar

In territories with an altitude of less than 200 m (1): annual 

positive temperature TP > 380.

2

2 In territories with an altitude of less than 200 m (1). 

continentality index lc < 11, positive temperature of the summer 

quarter Tps > 320, mean annual temperature < 6°, annual 

positive temperature 320–720

Boreal

Does not meet the conditions 3

3 In territories with an altitude of less than 200 m (1), depending 

on the continentality index lc, the values of the mean annual 

temperature T and the annual positive temperature Tp must be 

as follows: for lc < 21: T < 5.3° and Tp < 720; for lc = 21 – 28: T 

< 4.8° and Tp < 740; for lc > 28: T < 3.8° and Tp < 800

Boreal

Does not meet the conditions 4

4 Summer with no water deficit; ombrothermic index of the hottest 

two months in the summer quarter los2 > 2 or the summer 

ombrothermic index resulting from the compensation losc4 > 2

Temperate

Does not meet the conditions Mediterranean 

If the location is situated at an altitude of over 200 m, the temperature values 

need to be calculated theoretically, increasing T by 0.6°, M by 0.5°, and lt or 

ltc by 13 units for every 100 m over that altitude; if it is situated to the north of 

parallel 48° N or to the south of parallel 51° S, the values of the mean annual 

temperature and the annual positive temperature Tp must also be calculated 

by increasing T by 0.4° and Tp by 12 units for every 100 m over this altitude. 

When lc ≥ 21 (continental) or when lt or ltc < 120 the thermotype is calculated 

based on the annual positive temperature, and the theoretical values of Tp at 

200 m, increasing 55 units every 100 m over this altitude.

Abbreviations: See Rivas Martinez and others (1999)

Tp = Yearly positive temperature. In tenths of degrees C, sum of the monthly 

average temperature of those months whose average temperate is above 0 

oC.

Tps = Summer positive temperature. Positive temperature of the summer 

quarter. 

Ic = Continentality Index (year thermic interval). Ic = Tmax – Tmin. In degrees 

C, the number expresses the range between the average temperatures of the 

warmest month (Tmax) and the coldest (Tmin) months of the year. (Hyperoceanic Ic = 0-11, Oceanic = 11-21, Continental = 21=65).

Iosc = Summer compensated ombrothermic Index. 
USDA Forest Service RMRS-GTR-346. 2016. 215

Appendix I. Key to Formation Class (Level 1)

The user should be aware of the following features of the classification, as it 

relates to the key: 

•	 Classifies existing vegetation, regardless of its relation to site potential 

or land use. 

•	 Includes all existing vegetation—natural (forests, grasslands, etc) and 

cultural (lawns, orchards, etc).

•	 Applies to all vegetated areas, vascular and nonvascular, where cover 

is greater than 1 percent. 

•	 Typically defines high level types using a “combination of growthforms” approach to classify vegetation, rather than simply structure 

•	 A number of thresholds are appearing with some regularity in the 

definition of classes, and it is worth noting them here to assess their 

merits and their role in the key

o >10 percent tree cover (mesomorphic forest types, xeromorphic woodland types)

o <10 percent vascular plant cover (lithomorphic or cryptogamic 

vegetation types)

o <10 percent emergent plant cover (aquatic vegetation types)

o +50 percent (or simple majority) when two or more co-equivalent growth forms are present.

•	 Wetlands are not a class because wetlands often lack distinctive 

growth forms at the highest level; but all major wetland types are recognized at level 3. For some users a separate key focused on wetland 

may be desirable. 

Within the shrub and herb vegetation class, shrublands are distinguished from 

grasslands when shrubs have >25 percent cover, or if both shrubs and herbs 

are <25 percent, then shrubs exceed herb cover. 

Finally, this key should always be used in conjunction with the description of 

the types. As Rodwell (1991) stated, “With something as complex and variable 

as vegetation, no key can pretend to offer an infallible shortcut to diagnosis...

[Keys] should therefore be seen as simply a crude guide to identifying the 

types of woodland and scrub in the scheme and must always be used in conjunction with the data tables and community descriptions.”
216 USDA Forest Service RMRS-GTR-346. 2016.

Selecting the Area to Key

For general survey work, where a sampling design is not being used, simply 

select a uniform and representative area in the site, which may be as small 

as a plot (typically 20 x 20 m (0.04) or larger, such as 0.5 ha (1 acre) or more. 

When the goal is to assign the vegetation type of a large area (e.g., 0.5 ha or 

more), several plots or assessments can be done, and the most typical type 

present may be assigned to the plot, patch, or polygon. Occasionally, very distinct vegetation and ecological patches may occur at smaller scales, such as a 

localized seep, or sloping fen, and if such patches are to be noted, the area to 

be keyed should be restricted to that patch.

This key provides ecological guidance on identification of vegetation 

types. It is not meant to determine policy. 

After keying out a class, read brief description on the next page (Brief Descriptions of Formation Classes) to verify the placement. Fuller descriptions 

are available at usnvc.org and natureserve.org/explorer/classeco.htm. Terms 

used in the key are defined in Appendix C (Glossary) and Appendix D (Growth 

forms).

Areas with less than 1 percent total vascular plant cover are not considered in 

the key. Areas in deep water, although theoretically classifiable with this key, 

will also be classified in coordination with lake, river and ocean classifications1. 

1. Vegetation structure and/or composition determined by a spontaneously growing 

set of plant species shaped by ecological processes............................................... 2

1. One or more layers of the vegetation’s structure and/or composition determined 

by regular human activity such as planting, tilling, cropping, mowing, and/or irrigating (see C7)......................................Agricultural & Developed Vegetation (C7)

2. Mesomorphic tree height equal to or taller than other growth forms and mesomorphic tree cover >10 percent2 ............................................. Forest & Woodland (C1)

1 The USNVC will coordinate classification of freshwater aquatic vegetation with the U.S. wetland and deep water classification standard (Cowardin 1979) and the draft Coastal and Marine

Ecological Classification Standard (CMECS). For example, water bodies that are deeper than

2 m and >8 ha in size are treated as lakes, and aquatic vegetation may be treated as part of a lake 

type.

2 Dixon et al. (2014) suggest that in temperate zones, trees typically have less than 10 

percent canopy cover, are less than 5 m tall and single-layered, or in tropical regions, 

trees typically have less than 40 percent canopy cover, are less than 8 m tall, and 

single layered. 
USDA Forest Service RMRS-GTR-346. 2016. 217

2. Mesomorphic tree height shorter than other growth forms (any percentage), or 

mesomorphic tree cover <10 percent2.................................................................... 3

3. Habitats having flooded conditions; hydromorphic plant cover >1 percent, emergent plant cover <10 percent ............................................Aquatic Vegetation3 (C5)

3. Habitats various, temporary surface water may be present; hydromorphic plant 

cover variable or absent, emergent plant cover >10 percent.................................. 4

4. Vegetation on rocky substrates (bedrock, cliff, talus, scree) and with cryptogams 

(including lichens, mosses, algae, ferns) >1 percent and vascular plant cover predominantly mesomorphic growth forms, but <10 percent. .......................................

...................................................................................... Open Rock Vegetation (C6)

4. Vegetation on rocky substrates and with cryptogams >1 percent, and vascular plant 

cover predominantly cryomorphic or xeromorphic growth forms and <10 percent, 

OR vegetation on other substrates and cryomorphic, mesomorphic4 (except tree 

cover), xeromorphic (including nonvascular) plant cover >1 percent; .................... 5

5. Cryomorphic shrub and herb plant cover is the plurality of cover, cold temperature 

conditions limiting; height 0.3 m in polar and temperate alpine regions, various in 

tropical high mountain regions...... Polar & High Mountain Scrub & Grassland (C4)

5. Xeromorphic or mesomorphic plant cover is the majority of the cover; cold temperature conditions not limiting; height >0.3 m...................................................... 6

6. Xeromorphic tree, shrub, and herb plant cover (e.g., succulents) is the majority of 

cover; water strongly limiting......................................... Desert & Semi-Desert (C3)

6. Mesomorphic shrub and herb plant cover is the majority of the cover, water less 

limiting.......................................................................Shrub & Herb Vegetation (C2)

3 See footnote 1.
218 USDA Forest Service RMRS-GTR-346. 2016.

Brief Definitions of Formation Classes 

Forest & Woodland [Mesomorphic Tree Vegetation] (C01)

Tropical, temperate and boreal forests and woodlands, and open tree savannas*, 

characterized by mesomorphic tree growth forms (including broad-leaved, needleleaved, sclerophyllous, krummholz, palm, bamboo trees, and tree ferns), typically with 

at least 10 percent cover, irregular horizontal spacing and canopy structure; and spanning climatic and moisture conditions from humid, to seasonally dry, and wet to dry, 

respectively. Includes native forests as well as managed and some plantation forests 

where human management is infrequent. 

*Tropical savanna thresholds may differ from temperate savannas.

Shrub & Herb Vegetation [Mesomorphic Shrub & Herb 

Vegetation] (C02)

Grasslands, shrublands, marshes, bogs and fens characterized by mesomorphic 

shrub and herbaceous plant growth forms (including broad-leaved, needle-leaved, 

sclerophyllous, and rosette shrubs, forbs and graminoids) with mesomorphic trees 

typically less than 10 percent cover, irregular horizontal spacing, and a varied canopy 

structure, typically >0.3 m tall; climatic and moisture conditions vary from humid to 

seasonally dry, and wet to dry, respectively.

Desert & Semi-Desert [Xeromorphic Scrub & Herb Vegetation] 

(C03)

Cool and warm deserts and semi-deserts characterized by xeromorphic growth 

forms (including succulent [e.g., cacti, euphorbias], small-leaved shrubs and trees, 

forbs and graminoids) with sparse, irregular horizontal spacing and an open to sparse 

and varied canopy structure, typically >0.3 m tall; climatic and moisture conditions 

vary from dry to very dry. Includes open rocky habitats (barrens, polar desert) of polar 

tundra.

Polar & High Mountain Scrub and Grassland [Cryomorphic 

Scrub, Herb & Cryptogam Vegetation] (C04)

Polar, alpine and tropical high montane habitats characterized by cryomorphic 

growth forms (including dwarf-shrubs, forbs, graminoids, lichens and bryophytes) 

with sparse to dense horizontal spacing and a short, open to closed canopy structure, 

typically <0.3 m tall; climatic and moisture conditions vary from dry to very dry. 

Includes open rocky habitats of alpine vegetation.

Aquatic Vegetation [Hydromorphic Vegetation] (C05)

Open freshwater and saltwater wetlands characterized by aquatic growth forms, 

either rooted with leaves rising up to or near the surface, or floating freely on or below 

the water surface; emergent cover <10 percent. Stands typically have surface water, 

generally up to 2 m in depth, along ocean, lake, pond, and river margins in freshwater, 

tidal, or intertidal habitats.
USDA Forest Service RMRS-GTR-346. 2016. 219

Open Rock Vegetation [Cryptogam — Open Mesomorphic 

Vegetation] (C06)

Open rocky habitats (such as cliffs, talus, scree, pavement, cobbles, lava, or boulder 

fields) characterized by cryptogam and open mesomorphic growth forms (including 

lichens, bryophytes, algae or ferns), and mesomorphic, herb, shrub, and tree growth 

forms less than 10 percent cover, with very sparse horizontal spacing and a very open 

canopy structure. Typically found in tropical, temperate, and boreal regions. Excludes 

rocky habitats of polar, alpine, and cool and warm desert and semi-desert vegetation.

Agricultural & Developed Vegetation [Anthromorphic Vegetation] 

(CCL01)

Agricultural lands (including row crops, intensive pastures, orchards, vineyards, 

plowed or harvested fallow fields, rice paddies, and farm ponds) and Developed lands 

(vegetation of urban, suburban, and rural cities and villages; typically lawns, parks, 

gardens, golf courses, and urban ponds). 
220 USDA Forest Service RMRS-GTR-346. 2016.

Appendix J. Examples of Divisions

1.B.2. Cool Temperate Forest & Woodland Divisions

Figure J.1—Distribution of the Cool Temperate Forest formation, based on 

ecoregions where Cool Temperate Forest is or was the dominant vegetation. 

Map is based on Olson and others (2001), and modified from a map by M. 

Jennings.

DIVISIONS 

North America

•	 Eastern North American Forest & Woodland

•	 Western North American Cool Temperate Woodland & Scrub

•	 Rocky Mountain Cool Temperate Forest & Woodland

•	 Vancouverian Cool Temperate Forest

South America

•	 1.B.2.Ee Valdivian Cool Temperate Forest

•	 1.B.2.Ef Magellanian Cool Temperate Forest

Eurasia

•	 Western Eurasian Cool Temperate Forest & Woodland

•	 Central Eurasian Cool Temperate Forest & Woodland

•	 Eastern Asian Cool Temperate Forest & Woodland

Australian-New Zealand

•	 Southern New Zealand-Tasmanian Cool Temperate Forest & 

Woodland?

•	 Southeast Australian Cool Temperate Forest & Woodland
USDA Forest Service RMRS-GTR-346. 2016. 221

2.A.1. Tropical Lowland Grassland, Savanna & Shrubland Divisions

Grassland and Shrubland divisions taken from Dixon et al. (2014). See also FaberLangendoen and Josse (2010)

2.A.1.Ea Caribbeo-Mesoamerican Lowland Shrubland, Grassland & Savanna

2.A.1.Eb Amazonian Shrubland & Savanna

2.A.1.Ed Brazilian-Parana Lowland Shrubland, Grassland & Savanna

2.A.1.Er Colombian-Venezuelan Lowland Shrubland, Grassland & Savanna

2.A.1.Es Guianan Lowland & Upland Grassland, Savanna & Shrubland

2.A.1.Ff West-Central African Mesic Woodland & Savanna

2.A.1.Fg Eastern & Southern African Dry Savanna & Woodland

2.A.1.Fh Mopane Savanna

2.A.1.Fi Sudano-Sahelian Dry Savanna

2.A.1.Fn Miombo & Associated Broadleaf Savanna

2.A.1.Fo Eastern African Moist Woodland & Savanna

2.A.1.Fp Malagasy Dry Forest & Scrubland

2.A.1.Fq Malagasy Subhumid Woodland & Savanna

2.A.1.Ij Indo-Malayan Mesic Savanna & Grassland

2.A.1.Lk Australian Tropical Savanna

2.A.1.Ol Polynesian Lowland Shrubland, Grassland & Savanna

2.A.1.Om Eastern Melanesian Lowland Shrubland, Grassland & Savanna

2.B.1. Mediterranean Scrub & Grassland Divisions

Grassland and Shrubland divisions taken from Dixon et al (2014. See also FaberLangendoen and Josse (2010)

2.B.1.Ei Chilean Mediterranean Scrub, Grassland & Forb Meadow 

2.B.1.Ej Chaco-Espinal Scrub & Grassland 

2.B.1.Fh South African Cape Mediterranean Scrub 

2.B.1.Le Australian Mediterranean Scrub 

2.B.1.Na Californian Scrub 

2.B.1.Nb Californian Grassland & Meadow 

2.B.1.Pc Mediterranean Basin Scrub 

2.B.1.Pd Mediterranean Basin Montane Grassland & Scrub 

2.B.1.Pg Mediterranean Basin Dry Grassland 

2.B.1.Pk Northern African Mediterranean Scrub 

2.B.1.Pl Mediterranean Alpine Grassland & Scrub 
222 USDA Forest Service RMRS-GTR-346. 2016.

2.B.2. Temperate Grassland & Shrubland Divisions

Grassland and Shrubland divisions taken from Dixon et al. (2014). See also FaberLangendoen and Josse (2010).

2.B.2.Ek Pampean Grassland & Shrubland

2.B.2.En Madrean Grassland & Shrubland

2.B.2.Eo Patagonian Grassland & Shrubland

2.B.2.Fm Southern African Montane Grassland

2.B.2.Li Australian Grassland & Shrubland

2.B.2.Lj New Zealand Grassland & Shrubland

2.B.2.Na Western North American Grassland & Shrubland

2.B.2.Nb Great Plains Grassland & Shrubland

2.B.2.Nc Eastern North American Grassland & Shrubland

2.B.2.Nd Western North American Interior Sclerophyllous Chaparral

2.B.2.Ne Southeastern North American Grassland & Shrubland

2.B.2.Pf European Grassland & Heath

2.B.2.Pg Western Eurasian Grassland & Shrubland

2.B.2.Ph Eastern Eurasian Grassland & Shrubland

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