United States Department of Agriculture

Assessing the Sustainability of 

Agricultural and Urban Forests 

in the United States

Forest Service FS-1067 June 2016
United States 

Department of 

Agriculture

Forest Service

FS-1067

June 2016

Assessing the 

Sustainability of 

Agricultural and 

Urban Forests in 

the United States
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Assessing the Sustainability of Agricultural and Urban Forests in the United States i

Assessing the Sustainability of Agricultural and Urban Forests in the United States

Abstract

The Forest Service, an agency of the U.S. Department of Agriculture (USDA), published the National Report on Sustainable 

Forests—2010 (USDA Forest Service 2011) (hereafter, National 

Report) several years ago and will be releasing a subsequent 

version of the report in 2017. Based on the Montréal Process 

Criteria and Indicators for Forest Sustainability, the National 

Report provides information on a comprehensive range of 

measures related to forest conditions and sustainability in the 

United States. Two important categories of forest resources—

agricultural and urban forests—are not treated directly in the 

National Report, however. 

The current report is designed to augment the National Report

by focusing on agricultural and urban forest resources within 

the context of national forest sustainability reporting. The report 

provides (1) a brief description of the benefits accruing from 

these resources; (2) displays and analyses of currently available 

data describing them, particularly at the national level; and 

(3) a discussion of potential strategies for developing consistent national datasets and ongoing reporting procedures. The 

ultimate aim is to lay the foundation for reporting information 

about agricultural and urban forests that is roughly comparable 

with the information presented for conventional forests in the 

National Report and that can be incorporated into the Forest 

Service’s ongoing forest sustainability reporting activities.

Editors:

Guy Robertson

Andy Mason

Contributing Authors:

Greg Liknes

Andy Lister

David Nowak

Charles Perry

Steve Rasmussen

Michele Schoeneberger 

Chris Woodall
ii Assessing the Sustainability of Agricultural and Urban Forests in the United States
Assessing the Sustainability of Agricultural and Urban Forests in the United States iii

Assessing the Sustainability of Agricultural and Urban Forests in the United States

Acknowledgments

Numerous individuals substantially contributed to the production of this report either through extensive review or the provision of important information.

Andy Mason and Richard Straight, both working at the U.S. 

Department of Agriculture (USDA), National Agroforestry 

Center in Lincoln, NE, at the time, deserve credit for coming 

up with the original idea for this report and its application of 

forest sustainability concepts to agricultural and urban forests.

Michele Schoeneberger of the National Agroforestry Center 

led the work on agricultural forests, with Andy Lister of the 

Forest Service and Steve Rasmussen of the Nebraska Forest 

Service contributing writeups on the Great Plains Tree and 

Forest Invasives Initiative, a forest inventory effort with 

which they are intimately familiar. David Nowak, an expert 

in urban forestry who works at the Forest Service, Northern 

Research Station, wrote the chapter on urban forests. Charles 

Perry, Greg Liknes, and Chris Woodall, research scientists 

affiliated with the Forest Service, Forest Inventory and Analysis program, provided the final chapter on potential forest 

inventory approaches.

The Forest Service’s Sonja Beavers and Louise Wilde provided 

essential help in editing, formatting, and publishing the final 

version of this report, and former Forest Service intern Yooni 

Choi produced many of the graphics used in chapter 2.

Numerous people provided comments and advice on the different chapters contained in this report. Of these individuals, Fred 

Cubbage of North Carolina State University deserves special 

thanks for his insightful comments on the initial chapters 

describing the application of sustainability measures and for his 

ongoing support of the Forest Service’s sustainability reporting 

efforts overall. Richard Pouyat and Beth Larry, Forest Service 

research scientists at the Washington Office, each commented 

on the entire document, and their perspectives on the report as a 

whole were invaluable.
iv Assessing the Sustainability of Agricultural and Urban Forests in the United States
Assessing the Sustainability of Agricultural and Urban Forests in the United States v

Assessing the Sustainability of Agricultural and Urban Forests in the United States

Executive Summary

Society is increasingly realizing the value of individual trees 

and forested areas found on urban, suburban, and agricultural 

lands. Termed agricultural and urban forests in this report, these 

resources directly enhance our lives and, if managed correctly, 

can increase the efficiency and productivity of agricultural 

and urban systems. A short list of benefits includes aesthetic 

amenities, water and soil retention, biodiversity conservation, 

recreational opportunities, and the sequestration of greenhouse 

gases, but many other values have also been identified. Moreover, research continues to reveal new and sometimes surprising 

ways in which trees in the places where we live and work 

provide tangible benefits for people.

Wise management is essential to sustain and enhance the values 

associated with agricultural and urban forests, and wise management, in turn, requires good information. The central purpose 

of this report is to assess the current state of information for 

agricultural and urban forests and lay the foundation for its improvement in the future. As scientists from the U.S. Department 

of Agriculture (USDA), Forest Service, we use the Montréal 

Process Criteria and Indicators (MP C&I) for Forest Sustainability, a comprehensive framework for forest assessment across 

the ecological, social, and economic dimensions of sustainability, 

as a starting point and frame of reference. Other scientists also 

used the MP C&I to assess the sustainability of the Nation’s 

conventional forest lands in the National Report on Sustainable 

Forests—2010 (USDA Forest Service 2011), a periodic Forest 

Service report with which the current report is closely associated. Ideally, our aim is to replicate the type of information 

base available for conventional forests for agricultural and 

urban forests. This information will enable us to better manage 

these resources, in their own right, and better integrate them 

with other land cover and land use types to facilitate policy 

formulation and landscape-scale management. Moreover, an 

agricultural and urban forest inventory will provide the data 

needed for comprehensive forest carbon estimates for inclusion 

in a national Greenhouse Gas Inventory. Owing primarily to 

the lack of a comprehensive inventory of agricultural and urban 

forest resources, however, we are a long way from this goal.

Key Findings

Agricultural and urban forests represent a vast topic area, and 

the information in this report only touches the surface. Nonetheless, we are able to glean a number of summary conclusions 

from the data and analysis presented here. 

Agricultural and urban forests are important. This point 

is obvious but deserves to be emphasized. The various and 

specific ways in which these resources benefit (and sometimes 

cost) human society are discussed in detail throughout this report.

Agricultural and urban forests represent a vast and varied 

resource. Urban lands in the United States total more than 60 

million acres (24 million hectares) (138 million acres [56 million 

hectares] if community lands are included). If current trends 

continue, this number will more than double by 2050. Croplands, 

grasslands, and rangelands total slightly more than 1 billion 

acres (400 million hectares). Tree cover on urban lands is currently estimated at 35 percent. Quantitative measures of forest 

cover on agricultural lands are not available, but the percent 

of forest cover on these lands is likely less than the tree cover 

on urban lands. Nevertheless, the sheer extent of agricultural 

lands ensures that the total amount of forests in this category is 

immense. These resources span the various ecoregions existing 

across the United States and play an essential role in all the 

landscapes in which they are found.

Data on agricultural and urban forests are relatively scarce. 

Forest inventory activities have long been applied coast to coast 

for conventional forests, and the resulting information forms 

the backbone of forest assessment and sustainability reporting 

in the United States. Similar inventory and reporting activities 

are sorely lacking for agricultural and urban forests at the 

national level. 

Data availability, however, is improving. Satellite imagery 

and related remote sensing techniques have allowed for forest 

cover estimates for urban forests; tools facilitating the digital 

collection and consolidation of urban forest data are being 

developed and used; and pilot inventory projects, including 

a wall-to-wall inventory in the upper Midwest, are building 

experience in inventorying agricultural and urban forests in an 

integrated fashion.
vi Assessing the Sustainability of Agricultural and Urban Forests in the United States

A national urban forest inventory under FIA is in its initial 

stages of implementation. The 2014 Farm Bill (formally the 

Agricultural Act of 2014, Public Law 113-79) directs the Forest 

Service’s Forest Inventory and Analysis (FIA) program to 

revise its strategic plan and describe the “organization, procedures, and funding needed” to implement an annualized urban 

forest inventory. This effort builds on years of preparatory 

work performed by FIA. Sampling protocols and related details 

for the program have been established and will further evolve 

as FIA and its collaborators gain more experience in inventorying urban trees and forests at the national scale.

A comprehensive inventory of agricultural and urban 

forests is feasible at a relatively modest cost. Based on lessons learned from the newly instituted urban forest inventory 

and using a combination of remote-sensing and plot-sampling 

strategies, a wall-to-wall inventory measuring the physical 

characteristics of trees and forests on agricultural and urban 

lands could be developed, likely at a fraction of the annual cost 

currently devoted to inventorying conventional forests. Building the institutional arrangements and devising a consistent 

sampling protocol spanning these different land use types, 

however, will require considerable effort.

Addressing the social and economic aspects of forest 

sustainability in agricultural and urban settings will still 

be problematic. A comprehensive physical inventory will go 

a long way in helping us understand the dimensions of this 

resource, but many important data gaps will remain, especially 

in regard to quantifying the benefits, uses, and values these 

forests supply to U.S. citizens.

Policy Recommendations

The principal policy recommendation of this report is that the 

Federal Government should seriously consider the development 

and implementation of a comprehensive inventory of trees and 

forests on both agricultural and urban lands, thus enabling a 

broader forest inventory covering all lands in the United States. 

Such an inventory should—

1. Incorporate an efficient combination of remote sensing and 

on-the-ground plot survey techniques.

2. Be consistent with the Forest Service FIA inventory program 

for conventional forests (and the newly instituted program 

for urban trees and forests) so that the resulting data can be 

consolidated and compared across different land use and 

land cover types.

3. Include explicit mechanisms for ongoing input from 

stakeholders across all levels of government and all sectors 

of society.

4. Be flexible and adaptive, while simultaneously maintaining 

consistency across space and time.

The Forest Service FIA program has already completed a number of pilot inventories and is instituting a national program 

in urban areas, and the USDA National Resources Inventory 

(NRI) program has experience inventorying forests on agricultural lands. These two programs—FIA and NRI—would 

likely lead the initial development of an agricultural inventory 

designed to complement FIA inventories for conventional and 

urban forests, and it is not too early to explicitly consider an 

expansion of urban FIA sampling activities into agricultural 

areas. Other Federal agencies, such as the U.S. Geological Survey 

and the National Aeronautics and Space Administration, should 

be involved at an early stage in the planning process. More 

important to the success of the project will be the cooperation 

from various municipalities and other local government entities 

and also from private-sector and nongovernmental organizations. Building these relationships will require time and effort, 

and the stakeholder engagement model, already established by 

FIA for conventional forests, provides a good starting point. 

The institutional foundation that results will be a valuable 

resource for improving the management of America’s forests 

wherever they are found.

The end result ideally will be a wall-to-wall inventory of forest 

resources spanning forest, agricultural, and urban lands—an 

inventory that draws on plot-sampling and remote-sensing data 

sources, meets the needs of the diverse user communities, and 

enables us to assess the sustainability of these resources. This 

report is designed to lay the foundation for the dialogue and 

decisions needed to achieve this goal.
Assessing the Sustainability of Agricultural and Urban Forests in the United States vii

Assessing the Sustainability of Agricultural and Urban Forests in the United States

Contents

Abstract....................................................................................................................................................................................................i

Acknowledgments..................................................................................................................................................................................iii

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

Chapter 1. Introduction ...........................................................................................................................................................................1

Guy Robertson

Chapter 2. Agricultural and Urban Forests and Their Relation to the Montréal Process Criteria and Indicators..................................5

Guy Robertson

Chapter 3. Agricultural Forests.............................................................................................................................................................21

Michele Schoeneberger, Andy Lister, and Steve Rasmussen

Chapter 4. Urban Forests ......................................................................................................................................................................37

David Nowak

Chapter 5. Developing a Monitoring Framework for Agricultural and Urban Forest Resources ........................................................53

Charles Perry, Greg Liknes, Guy Robertson, and Chris Woodall

List of Tables

Table 2.1. U.S. population by land category.........................................................................................................................................10

Table 3.1. The six categories of agroforestry practices commonly established in the United States...................................................22

Table 3.2. USDA 2008 Farm Bill programs supporting agroforestry practices...................................................................................23

Table 3.3. Issues in temperate and tropical regions that can be addressed by agroforestry technologies............................................25 

Table 3.4. A listing of the attribute data collected on the Great Plains Tree and Forest Invasives Initiative inventory plots..............26

Table 3.5. Estimated acres by rural function of trees for nonforest areas from the Great Plains Tree and Forest Invasives 

Initiative 2008-to-2009 inventories; 1,018 rural plots across Kansas, Nebraska, North Dakota, and South Dakota...........................27

Table 3.6. Number of trees by species for rural and urban nonforest areas from the Great Plains Tree and Forest Invasives 

Initiative 2008-to-2009 inventories; 1,018 rural plots across Kansas, Nebraska, North Dakota, and South Dakota...........................27

Table 3.7. Volume of wood material by species in Nebraska for rural and urban nonforest areas from the Great Plains Tree 

and Forest Invasives Initiative 2008-to-2009 inventories; 473 plots....................................................................................................28

Table 3.8. Estimated sequestration potential for selected U.S. land use practices...............................................................................30

List of Figures

Figure 2.1. Idealized depiction of forests in an urban-rural landscape...................................................................................................6

Figure 2.2. Land use in the United States, 2002 .....................................................................................................................................9

Figure 2.3. Forest Service and related data sampling activities for agricultural and urban forests...................................................... 11
viii Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 2.4. Montréal Process Criteria and Indicators for Forest Sustainability....................................................................................13

Figure 3.1. Agroforestry practices and their uses at the practice/site levels and their potential placement throughout the 

landscape...............................................................................................................................................................................................24

Figure 3.2. Establishment of a silvopasture system from opposite ends of the canopy closure spectrum ...........................................26

Figure 3.3. Acres of forested land at risk of mortality to insects and diseases.....................................................................................31

Figure 3.4. Current Fire Regime Condition Class in the contiguous United States.............................................................................32

Figure 3.5. Forest land and missing tree fractions derived from Forest Inventory and Analysis data .................................................33

Figure 4.1. Urban areas in the contiguous United States, 2000, based on the Census Bureau definition of urban land ......................38

Figure 4.2. Percent of U.S. counties classified as urban, 2000.............................................................................................................42

Figure 4.3. Percent of land classified as urban in 2000 (a) and projected percent of land classified as urban in 2050 (b), 

by county...............................................................................................................................................................................................43

Figure 4.4. Percent (a) and square kilometers (b) of nonurban forest subsumed by projected urban growth, 2000 through 

2050, by State........................................................................................................................................................................................44

Figure 4.5. Percent tree cover in urban areas, 2000, by county............................................................................................................45

Figure 5.1. Available LIDAR (Light Detection and Ranging) datasets as of August 2013, with potential application to 

tree inventory outlined in gray..............................................................................................................................................................62
Assessing the Sustainability of Agricultural and Urban Forests in the United States

Assessing the Sustainability of Agricultural and Urban Forests in the United States 1

Chapter 1 Guy Robertson

Introduction

Measurement is a prerequisite for effective management. This 

fact has long been recognized in the area of forest resources, 

as evidenced by the effort the U.S. Government has devoted 

to surveying the Nation’s forests for more than a century now. 

Charles Sargent produced one of the first inventories of U.S. 

forest resources in 1884 in conjunction with the 1880 census. 

Totaling more than 600 pages, the 1884 survey was close to a 

decade in the making and stands as a monument to the belief 

that quantitative information describing natural resources is 

important, even in an age when such information was extremely 

difficult to acquire (Sargent 1884). Since that time, the U.S. 

Department of Agriculture (USDA), Forest Service has undertaken increasingly frequent forest surveys, augmenting them 

with periodic assessments such as the Resources Planning Act 

(RPA) Assessment and, more recently, the National Report 

on Sustainable Forests—2010 (USDA Forest Service 2011), 

hereafter, the National Report.

1

The Forest Service, Forest Inventory and Analysis (FIA) program 

currently samples numerous measures describing forest resources 

on a rolling basis across all 50 States. The FIA program employs 

close to 600 scientists and technicians and is funded at more 

than $75 million per year (http://www.fia.fs.fed.us/ [August 

2015]). The FIA and related Forest Service assessment efforts, 

however, are directed primarily at measuring forest land as 

traditionally defined; these efforts largely omit the forest resources occurring on agricultural and developed urban lands. 

In a similar way, the National Resources Inventory (NRI), 

under­-taken by the USDA Natural Resources Conservation 

Service, or NRCS, provides information on forests using 

slightly different forest land definitions than FIA uses, but the 

NRI generally does not cover agricultural and urban forests 

either (USDA/NRCS 2009). These nonconventional forests are 

the topic of this report.

As our understanding of the complexity of forest ecosystems 

has grown and our relationship with them evolved, the scope 

and nature of our reporting efforts have changed. Whereas early 

surveys tended to focus on merchantable tree species, their stocking, and the productivity of underlying lands, current reporting 

efforts treat a much broader range of variables, covering ecological 

conditions and also social and economic factors that describe 

the human systems that rely on and affect forests. This tendency 

is epitomized by the recent growth of forest sustainability 

reporting efforts and their use of criteria and indicators (C&I) 

for information organization and display. At the national level, 

this trend is embodied in the National Report, the first edition 

of which was produced in 2003, with a subsequent version 

published in 2011. The next edition of the National Report is 

due for release in 2017.

These reports rely on a comprehensive set of measures for forest 

sustainability designed through an international collaboration 

known as the Montréal Process (http://www.montrealprocess.

org/ [August 2015]). The resulting Montréal Process Criteria 

and Indicators (MP C&I) for Forest Sustainability2 include 54 

indicators arranged under 7 major criteria spanning ecological, 

social, and economic dimensions. Many of the indicators in 

the MP C&I are pertinent to the description of agricultural and 

1

 The 1974 Forest and Rangeland Renewable Resources Planning Act mandates a periodic assessment of conditions and trends for the Nation’s renewable 

resources. The most recent assessment, Future of America’s Forest and Rangelands: Forest Service 2010 Resources Planning Act Assessment, was published 

in 2012 (USDA Forest Service 2012), and an interim update is slated for release in 2016. In contrast to the National Report on Sustainable Forests, the 

RPA Assessment provides information on a broader range of natural resources than just forests, and it does so in an integrated modeling framework with 

forward-looking (50-year) projections. The National Report treats a broader range of measures, each in a more concise fashion, but it does not provide future 

projections. Taken together, the RPA Assessment and the National Report, supported by FIA survey activities, comprise the backbone of Forest Service 

national assessment activities. A digital version of the RPA Assessment and related project information are available at http://www.fs.fed.us/research/rpa/ 

(August 2015). The National Report is further described in the following sections. See http://www.fs.fed.us/research/sustain/ (August 2015) for digital copies 

and related information.

2

 The full title is Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests.
2 Assessing the Sustainability of Agricultural and Urban Forests in the United States

urban forest resources, but the overwhelming focus of the effort 

at the international level and here in the United States has been 

on conventional forest lands; agricultural and urban forests are 

not explicitly addressed in the MP C&I.3

The consideration of agricultural and urban forests within the 

context of forest sustainability reporting is important for several 

reasons. First, we are increasingly recognizing the numerous 

public benefits provided by the trees in our cities, suburbs, and 

farms, many of which will be outlined further in this report. With 

this recognition have come myriad programs at local, regional, 

and national levels aimed at using trees and forestry to enhance 

the livability of our communities in general and to provide 

valuable services through their role as “green infrastructure” 

in particular. Second, we have come to see the challenge of 

sustaining natural and human environments as one of managing 

landscapes that span different ecosystem types, ownership 

classes, and land uses. Wildlands, agricultural lands, and developed areas are all seen as being integrated in a broader landscape 

in which changes in one category inevitably result in changes 

in the others. The status and management options for agricultural and urban forests are an essential component in this “all 

lands” approach to sustainable resource management. Finally, 

a more immediate and specific goal for developing statistics 

on agricultural and urban forest resources is that it will provide 

the data needed for a comprehensive estimate of forest carbon 

sequestration and thereby aid in the development of a national 

greenhouse gas inventory.

So developing an increased understanding of these resources is 

important; however, it also entails significant challenges. The 

study of conventional forests and their management has developed over a number of centuries, involving dedicated schools 

and institutions, professional designations (e.g., forester), and 

subdisciplines. Along with this professional development has 

come an established stream of data sampling and reporting 

activities (through programs such as the FIA) and also standardized industry and product designations for tracking the production 

and trade of wood products. Agricultural and urban forests have 

received no such longstanding attention. Certainly agroforestry 

and urban forestry have been increasingly recognized as important areas for research and development in their own right, but 

their knowledge base, statistical development, and institutional 

support are not yet commensurate with that of forestry proper.

Most importantly for the purposes of this report, neither agricultural nor urban forests enjoy anything like the same type of data 

coverage as has been established for conventional forests. The 

reasons for this lack of coverage are outlined in the following 

chapters, but, in general, they can be attributed, in part, to a 

lack of effort and, in large part, to the simple fact that agricultural and urban forest resources are difficult to define, delineate, 

and measure, occurring, as they do, interspersed with other land 

uses and across multiple ownerships and jurisdictions. The situation, however, is not hopeless. Urban forestry techniques and 

applications are being developed and refined by municipalities 

across the country, and the FIA program is embarking on a new 

effort to inventory urban forest resources, the details of which 

will be evolving during the coming years. In the realm of agroforestry, with the release of the USDA Agroforestry Strategic 

Framework, Fiscal Year 2011–2016 (USDA 2011), the Secretary 

of Agriculture has provided a first-of-its-kind roadmap for Federal agencies and other government bodies to use to advance 

the science, practice, and application of agroforestry as a means 

of enhancing America’s agricultural landscapes, watersheds, 

and rural communities.4

Along with an increased realization of the value of these nonconventional forest resources has come a willingness to direct 

attention and expend resources for their measurement. FIA, 

for example, has temporarily extended its sampling activities 

to a number of urban areas for the purposes of experiment (see 

figure 2.3 in chapter 2) and will be expanding this activity in 

the future. New technologies, notably those in the area of remote 

sensing and Geographic Information Systems, or GISs, are increasingly being harnessed to develop information about forest 

cover and extent in developed and rural areas. More collaborative 

and participatory forms of research, sampling, and information 

sharing promise to yield better data if we can successfully bring 

people together. One promising example of such an effort is 

in the Great Plains States, where four State forestry agencies 

partnered with FIA to develop and conduct a first-ever 2008to-2009 inventory of “nonforest” areas in Kansas, Nebraska, 

North Dakota, and South Dakota. Another, in the realm of 

urban forestry, is the expanding use of the “i-Tree Eco Model,” 

a tool that enables local citizens and professionals to inventory 

their local tree resources in a fashion that is flexible enough 

to meet their needs but can also produce information that is 

consistent across time and space so that it can be compared 

with inventories produced elsewhere.

Still, readers who are hoping that this report will provide comprehensive and accurate information about even basic forest 

inventory measures for agricultural and urban forests at the 

national level will be disappointed. Those data simply do not 

exist, and the information we do have is often the product of 

3

 Definitions and terminology associated with conventional forests and agricultural and urban forests are addressed more fully in chapter 2.

4

 In relation to the core focus of this report, the Agroforestry Strategic Framework specifically addresses the issue of resource monitoring and measurement 

in Objective 3.2 (“ASSESS PERFORMANCE: Account for and monitor agroforestry impacts and applications”) and in more detail in Strategy #2 (“Work 

within USDA to establish a comprehensive continuous national inventory of on-the-ground applications of agroforestry practices/systems or include in 

existing inventory structures [e.g., Forest Inventory and Analysis or the National Resources Inventory”]).
Assessing the Sustainability of Agricultural and Urban Forests in the United States 3

one-time studies limited in coverage to a specific place, time, or 

management question. It is essential for us to determine what 

we do know and explore ways to build a more complete base of 

knowledge and data for the future.

The purpose of this report is to lay the groundwork for better 

integrating agricultural and urban forest resources in nationallevel forest sustainability reporting efforts. Simply describing 

what we currently know about these resources will be a major 

part of the report, but we also want to consciously address questions about data and how they can be developed, organized, and 

reported now and in the future. Using the MP C&I as a starting 

point, we will assess the current availability of quantifiable 

data describing agricultural and urban forest resources at broad 

spatial scales and explore potential avenues for enhancing this 

information, either through expanded sampling and inventory 

efforts or through better use of already existing information 

sources.

The report is divided into five chapters. Following this introductory chapter, chapter 2 introduces key issues and concepts 

associated with agricultural and urban forest resources, and it 

provides a broad summary of the MP C&I as they potentially 

relate to reporting on these resources, particularly at the criterion level. The aim here is twofold: (1) explore ways in which 

agricultural and urban forests can be integrated with current 

sustainability reporting efforts applied to conventional forests; 

and (2) use the MP C&I and their comprehensive coverage of 

social, ecological, and economic aspects as a starting point for 

identifying the key information pieces we need to know about 

these resources.

Chapters 3 and 4 address agricultural and urban forests, respectively. Each chapter presents (1) a current description of the state 

of the resource to the extent that existing data allow, (2) a 

brief summary of the various ecosystem services and related 

benefits these forests provide, (3) a discussion of the ways in 

which these forests are affected through their close proximity to 

human systems, (4) an assessment of current data adequacy in 

describing these resources at national and regional scales, and 

(5) a discussion of potential strategies to enhance these data in 

the future. Chapter 5, the final chapter of the report, discusses 

potential approaches to enhancing data. The primary avenue 

considered here is expanded forest inventory and sampling 

techniques augmented with remote-sensing data. As a result, 

the primary focus in the chapter is on biophysical measures 

more than on social or economic measures, although the development of socioeconomic measures is considered when possible.

References

Sargent, C.S. 1884. Report on the forests of North America. 

Washington, DC: Government Printing Office. 612 p.

U.S. Department of Agriculture (USDA). 2011. USDA agroforestry strategic framework, fiscal year 2011–2016. Washington, 

DC: U.S. Department of Agriculture. 35 p. http://www.usda.

gov/documents/AFStratFrame_FINAL-lr_6-3-11.pdf. (August 

2015).

U.S. Department of Agriculture (USDA), Forest Service. 2011. 

National report on sustainable forests—2010. FS-979. Washington, DC: U.S. Department of Agriculture, Forest Service. 

212 p. http://www.fs.fed.us/research/sustain/. (August 2015).

U.S. Department of Agriculture (USDA), Forest Service. 2012. 

Future of America’s forest and rangelands: Forest Service 2010 

Resources Planning Act Assessment. Gen. Tech. Rep. WO-87. 

Washington, DC: U.S. Department of Agriculture, Forest 

Service. 198 p. http://www.fs.fed.us/research/rpa/assessment/.

(August 2015).

U.S. Department of Agriculture (USDA), Natural Resources 

Conservation Service (NRCS). 2009. Summary report: 2007 

national resources inventory. Washington, DC: U.S. Department of Agriculture, Natural Resources Conservation Service; 

Ames, IA: Iowa State University, Center for Survey Statistics 

and Methodology. 123 p. http://www.nrcs.usda.gov/Internet/

FSE_DOCUMENTS/stelprdb1041379.pdf. (August 2015).
4 Assessing the Sustainability of Agricultural and Urban Forests in the United States
Assessing the Sustainability of Agricultural and Urban Forests in the United States

Assessing the Sustainability of Agricultural and Urban Forests in the United States 5

Chapter 2 Guy Robertson

Agricultural and Urban Forests and Their Relation 

to the Montréal Process Criteria and Indicators

In this chapter, we lay the groundwork for understanding 

agricultural and urban forest resources within the context of 

this report and the goal of better integrating these resources in 

forest sustainability reporting efforts. The chapter begins with 

a discussion of definitions and concepts related to agricultural 

and urban forests, followed by a brief description of the overall 

extent of these types of lands in the United States. The chapter 

concludes with a description of the Montréal Process Criteria 

and Indicators (MP C&I) for Forest Sustainability5 and their 

potential relation to the forests and trees that are found in our 

farms, suburbs, and cities.

Definitions

By agricultural and urban forests, we mean trees and woodlands 

that occur on or adjacent to farmland and developed areas and 

that would not normally be classified as forests under current 

forest inventory definitions. This grouping is essentially a subset 

of trees outside forests, or TOF, a term common in the scientific 

and governmental literature (see Long and Ramachandran 1999, 

for a listing of the various types of TOF found throughout the 

world). The agricultural and urban terminology used in this 

report, however, stresses the relationship of these trees to human 

occupation and land use patterns, an emphasis we want to 

maintain. The term forests emphasizes the broader ecosystem 

components and functions associated with agricultural and 

urban trees, including flora, fauna, and forest soils. This broad 

definition is used throughout the report.

What we have termed “conventional forests” refers to (relatively) 

large, contiguous tracts of natural or managed forests that contain 

(relatively) little human habitation or agricultural development 

within their boundaries. These forests are tallied in conventional 

forest inventory efforts. For example, the Forest Inventory and 

Analysis (FIA) inventory of the U.S. Department of Agriculture 

(USDA), Forest Service, defines forests as areas more than 120 

feet (37 meters) wide and more than 1 acre (.4 hectares) in total 

extent with at least 10 percent forest stocking. As they actually 

occur, however, the “forests” considered in this report span 

a continuum between developed lands and wildlands, where 

different types of land uses and natural vegetation cover tend 

to blend together in a mosaic that may be easily characterized 

at its extremes but that entails substantial gray areas when it 

involves mixtures of uses and cover types.

Precise definitions often appear to be somewhat arbitrary and, 

sometimes, even counterproductive. The challenge in applying 

definitions sometimes occurs when attempting to delineate 

“conventional forests,” and it is more common when trying to 

distinguish agricultural and urban forests, because they often 

occur at the interface of developed, agricultural, and natural 

landscapes. Definitions and distinctions are nonetheless essential 

for measurement and analysis and for the various programs, laws, 

and regulations with which we pursue sustainable resource management. We should remember, however, that these definitions 

divide what is essentially a unified landscape, and this division 

affects our statistics and the understandings that flow from them.

Characteristics and Underlying 

Concepts

To varying degrees, agricultural and urban forests share many 

of the attributes that characterize conventional forests, but they 

also differ in several fundamental ways from the types of forests 

covered in the National Report on Sustainable Forests—2010

(USDA Forest Service 2011a), hereafter the National Report; 

the RPA Assessment; or FIA periodic reporting documents. The 

main difference, of course, is that agricultural and urban forests 

each occur in developed landscapes in close proximity to human 

activities. As a result, the functions they serve and the benefits 

they provide to society are quite different from those that conventional forest provide, and the influences, positive and negative, 

5

 The full title is Montréal Process Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests.
6 Assessing the Sustainability of Agricultural and Urban Forests in the United States

they are subject to also differ. Next, their spatial configuration 

is different from that of conventional forests, being characterized 

by a higher degree of fragmentation, attenuation (i.e., occurring 

in lines or narrow lengths filling in the interstices between buildings, roads, and fields), and smaller areas with greater edge 

effects. Agricultural and urban forests are usually owned by a 

diverse set of individuals and entities whose primary concern 

is not forest management, whether it be for timber production, 

environmental conservation, or the provision of ecosystem 

services. This parcelization, or fragmentation of ownership, 

means that the management of these resources is considered 

amid other competing objectives, if it is considered at all.6

For clarity, these characteristics can be abbreviated as follows: 

(1) proximity to human activities, (2) spatial configuration and 

fragmentation, and (3) fragmented ownership and lack of forest 

management focus. In combination, these characteristics result 

in novel and often radically modified environments requiring 

different management strategies tailored to their specific situations. An example of how forest and trees can be integrated 

in an urban-rural continuum is provided in figure 2.1.7 Here, 

some of the potential functions (and benefits) of agricultural 

and urban forests are clear as are the various spatial forms these 

forests may take.

Figure 2.1. Idealized depiction of forests in an urban-rural landscape.

6

 The growing awareness and inclusion of forest management concerns in local planning efforts provide numerous exceptions to this observation, but, even 

for cases in which local forest management is active, forest management concerns must compete with a variety of other objectives for land use and planning. 

7

 Unfortunately, street trees and their functions are omitted from the diagram—a point noted by several of our reviewers.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 7

Proximity to Human Activities

Agricultural and urban forest resources generally occur in areas 

dominated by human activity—areas where we live, work, and 

produce most of the food that sustains us. Although we may not 

be aware of the role forests play in the landscape, seeing them 

as simply greenery by the roadside, trees and forests interact 

in numerous complex and subtle ways with people and their 

activities. In recent years, the benefits trees bring to us have 

increasingly been recognized, and the science underlying this 

recognition advanced. Trees in agricultural and urban settings 

certainly overlap in terms of the benefits they provide, but the 

benefits most commonly recognized on farms are that trees protect valuable top soil, livestock, crops, and wildlife (through, 

for example, windbreaks and shelterbelts) and improve local 

water quality (through, for example, riparian forest buffers). In 

urban areas, on the other hand, trees help abate pollution, mitigate temperatures, and provide healthier, more pleasing places 

to work and live. These benefits, however, comprise only a small 

sample of an ever-growing list of values and services we have 

come to associate with these resources. The following chapters 

will describe these benefits and services in greater detail for 

agricultural and urban settings, respectively. The purpose of 

this report, however, is not to analyze forest benefits in detail 

or use them as a reason to argue that trees are important; such 

an analysis could easily take up several books. The importance 

(although perhaps not the full extent) of these benefits is fully 

evidenced by the effort and expense individuals devote to planting and caring for trees in agricultural and urban environments. 

Rather, the crucial question for this report is to what extent 

these benefits can actually be measured.

The nature of the interaction between people and trees is not all 

positive. Trees can have negative impacts in various ways—by 

falling on houses or encroaching on fields, for example. The 

pollen of certain trees can be a serious allergy trigger, and leaves 

and other detritus are a nuisance and a source of considerable 

expense for residents and municipalities. Under certain conditions, the volatile gases emitted by some tree species can 

interact with ambient urban pollution to exacerbate smog 

(Benjamin and Winer 1998), although some studies indicate 

that these effects, in general, are less than the ameliorating 

effect of trees on ambient air pollution (Nowak et al. 2000). 

The negative interactions resulting from proximity, however, 

by and large, move in the opposite direction, with trees being 

negatively affected by human actions, including such factors as 

pollution, soil compaction, the introduction of invasive plants 

and animals, and, of course, fragmentation and destruction to 

make way for development. Again, the interactions are often 

complex and difficult to identify; positive effects on trees from 

carbon dioxide (CO2) and nitrogen (N) deposition (e.g., Lovett 

et al. 2000) and longer growing seasons (because urban environments are warmer, in general) have also been noted (Zhang 

et al. 2004). In an ideal situation, we would be able to measure 

the changing health of our agricultural and urban forests at 

multiple spatial scales, including the national level, where we 

could then discern the overall trend in forest health with respect 

to these resources. These types of comprehensive statistics, 

however, are not currently available, and a concerted effort to 

gather them is needed.

Spatial Configuration and 

Fragmentation

The spatial configuration of agricultural and urban forests differs 

from that of conventional forests, being characterized by a high 

degree of fragmentation and novel configurations, such as the 

“linear forests” found in windrows between fields or the green 

spaces separating housing developments. This characteristic 

is not always apparent when seen from the ground, but, when 

seen from the air, the fragmentation and attenuation of these 

forests are often strikingly obvious, particularly in agricultural 

areas. Conversely, the individual trees lining streets or planted 

in urban parks and gardens can comprise a substantial urban 

tree canopy (once again, this pattern is most evident when seen 

from the air), which, in general, is more sparse and varied than 

conventional forest canopies.

Common measures of forest area, such as those provided by the 

FIA and included in the National Report, are expressed in terms 

of extent of area, such as acres, square miles, or, in the interntional arena, hectares. These types of measures are difficult to 

apply to agricultural or urban configurations. Agricultural windbreaks, for example, occur in long narrow lines (hence the term 

linear forests), where the use of acres or similar measures can 

hardly capture the full extent or importance of the resource. At 

the extreme, individual trees on a street provide an example in 

which neither two-dimensional units (acres) nor one-dimensional 

units (miles or yards) suffice. In these cases, density measures 

such as trees per acre may be the best way to describe the resource. 

In any case, these different configurations entail significant 

challenges in sampling and reporting statistics to adequately 

describe the resource in question.

Forest fragmentation is also an important issue here. It includes 

the effects from proximity to the human activities identified previously but also involves a number of dynamics specific to forest 

ecosystems regardless of human influences. These dynamics 

include habitat connectivity, edge effects, and the ratio of core 

or interior forest to forest edge (Murcia 1995). The influence 

of these and associated factors will vary according to the forest 

type in question. Depending on their degree of fragmentation, 

forests may include a very different set of species and growth 

characteristics than outwardly similar and more intact forests 

occurring nearby. To adequately capture fragmentation and 

its trends over time, measures need to characterize the spatial 
8 Assessing the Sustainability of Agricultural and Urban Forests in the United States

configuration of the resource and not only its extent. This 

requirement is true for conventional forests as well, but the 

challenge is all the more pronounced in the case of agricultural 

and urban forest resources.

Fragmented Ownership and Lack of 

Forest Management Focus

A large proportion of conventional forests in the United States 

is composed of relatively large parcels managed by public and 

private landowners who view natural resource management 

as a core aspect of their ownership objectives. This ownership 

pattern is certainly evident for the vast public lands managed 

by the Forest Service and the U.S. Department of the Interior, 

Bureau of Land Management. In the private sector, despite the 

ongoing shift away from large holdings by forest management 

and wood products firms, most conventional forest land is still 

held in relatively large ownerships in which the character and 

potential value of the forest as a resource is recognized. The 

same cannot be said for agricultural and urban forests, where 

forest resources usually exist as a small portion of a broader 

land area dedicated to a variety of purposes with little or nothing to do with either traditional wood products production or 

forest-based ecosystem services. Moreover, resource ownership 

is seldom consolidated in the hands of an individual holder 

because of the mosaic of different ownerships that characterize 

agricultural and, especially, urban or suburban landscapes. 

In this setting, effective management demands significant 

collaboration among different owners and other stakeholders 

in the community. The dedication of urban foresters, municipal 

parks and recreation staff, and others notwithstanding, the 

management of forests and individual trees in these settings is 

often something of an afterthought or exists as a necessary but 

unwanted expense entailed in the production of intangible benefits that accrue to the community at large but that individual 

landowners cannot easily capture or profit from. 

At the same time, many of the trees and forests occurring 

in agricultural and urban settings require a higher degree of 

management than conventional forests need. As noted previously, these forests are often subject to higher levels of stress 

originating from a more diverse set of stressors. Because of 

their close proximity to human activity and habitation, their 

growth, health, and survival patterns will often directly and 

significantly affect people. Moreover, many of these trees were 

purposefully planted and have been nurtured throughout their 

lives. Hands-off management is often not a viable option and 

tree replacement through the process of natural regeneration 

cannot be assumed.

From the standpoint of gathering and reporting statistics to 

describe agricultural and urban forests, ownership fragmentation and lack of forest management focus present major 

challenges. To be specific, there is no national-level inventory 

activity for agricultural and urban forests that is comparable 

with the inventory the FIA provides for conventional forests. 

Many municipalities devote significant resources to planting 

and maintaining urban trees, and various programs promote 

tree planting and management on agricultural lands, but these 

activities often do not include inventory sampling, especially 

consistent sampling across time, space, and ownership or administrative boundaries. Agricultural and urban forest resource 

information consequently is disconnected, being composed of 

data from different counties and municipalities often produced 

in the course of one-time studies without regular updating and 

reporting functions. So, although we know these resources are 

important, we have little information on their status and extent 

at either the national or regional levels. As will be described 

later in the chapter on urban forests, this situation is improving 

through the use of satellite imagery.

Landscape-Scale Management and 

Conservation

Although we have aimed in this chapter to distinguish agricultural 

and urban forest resources from more conventional forests, it 

is important to emphasize the fact that, in actuality, landscapes 

exist on a continuum between developed and natural settings. 

This continuum involves not only the biophysical configuration 

of the landscape but also its social configuration, ranging from 

small and diverse ownerships focused on various goals to more 

homogenous ownerships focused on natural resource management. The breakpoints we have identified in this continuum 

help us to describe the resource, but we must remember that 

society’s objective should be to manage the continuum in its 

entirety. In recognition of this goal, the idea of landscape-scale 

conservation and management has been gaining increasing 

attention among public officials, natural resource managers, 

agriculturalists, urban planners, and interested members of the 

public. The focus on agricultural and urban forests in this report 

helps reinforce this concept, because we are taking what traditionally has been a subject for foresters and resource managers 

and extending it to the more complex mosaic of land uses that 

is found in the landscapes where most of us live and work. 

Although the distinctions we have drawn between conventional 

forests on the one hand and agricultural and urban forests on 

the other hand serve to aid in their measurement and analysis, 

understanding the underlying linkages between these resource 

categories is essential in their effective management.

The recognition of the need for integrated landscape-scale 

management is growing at all levels of government. At the 

national level, USDA Secretary Tom Vilsack has stressed the 

need for an all-lands approach to forest management that spans 

ecological and social boundaries (Vilsack 2009). The Forest 

Service has elaborated this approach in detail in a number of 

documents (e.g., USDA Forest Service 2009 and 2011b), as 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 9

has the National Association of State Foresters (NASF 2009). 

It is at the local and regional levels, however, where the types 

of innovative projects, programs, and activities that best exemplify landscape-scale conservation take place. Baltimore (MD) 

County’s Forest Sustainability Strategy is a notable example of 

this work, one that has received considerable attention at local 

and national levels (Baltimore County, MD 2005), but numerous other examples can be found throughout the country.

The growth of suburban and exurban development in forested 

areas has spawned a new term, the wildland-urban interface

(WUI), and a new area of research. Throughout the country, 

and particularly in regions prone to forest fires, the WUI and 

its management are driving innovative forms of collaboration 

among private citizens, municipalities, forest landowners, 

and public land management agencies, and they are providing 

a focus for multidisciplinary research combining social and 

ecological dimensions with the aim of modifying landscapes 

and landowner behavior.8

Landscapes managed under an all-lands approach involve social, 

economic, and political dimensions every bit as much as they 

involve the ecological aspects of a landscape. The MP C&I, 

with their comprehensive treatment of social, economic, and 

ecological elements of the forest, is well suited as a foundation 

for developing the information base needed for this style of 

management. Most of the focus of this report, however, is simply 

on measuring and reporting the biophysical dimensions of agricultural and urban forest resources; the type of information that 

can be developed using forest inventory and remote-sensing 

activities. At the same time, opportunities for developing a 

more robust social and economic database are considered to a 

limited degree.

Agricultural and Urban Land Area 

in the United States

To begin to understand the potential scope of agricultural and 

urban forest resources in the United States, figure 2.2 provides 

a summary display of major land uses at the national level. This 

information relies on specific definitions (Lubowski et al. 2005), 

and it is not precisely comparable with the similar statistics 

found in the various other reports and data streams covering 

land use in the United States. (For example, forest-use land 

referenced here excludes lands managed by the U.S. Department 

of Defense, wildlife refuges, and similar other areas, resulting 

in a somewhat smaller number than the 751 million acres [304 

Figure 2.2. Land use in the United States, 2002 (USDA 

Economic Research Service, http://www.ers.usda.gov/

publications/EIB14/eib14.pdf [August 2015]).

million hectares] of forest land reported in the 2010 National 

Report.) The chart, however, is sufficient to give us a general 

picture of the lay of the land without being distracted by the 

details of definition and precision, questions which will be addressed in greater depth in subsequent chapters of this report. 

Comprising 442 million acres (179 million hectares), cropland 

constitutes 19 percent of total land area, and the various windbreaks and shelter belts, riparian forest buffers, and woodlots 

found on lands in this category are most directly relevant in our 

consideration of agricultural forest resources. A considerable 

amount of pastureland is also forested, but a large proportion 

of this area is classified as forest land in the FIA inventories. 

Where forest canopy cover is not sufficient to meet FIA definitions for forest land, however, the trees on those lands, and the 

ecosystem services they provide, will not be accounted for in 

FIA inventories and would fall under the agricultural forest 

category considered in this report.

Urban areas were estimated to cover approximately 60 million 

acres (24 million hectares) in 2002, or 3 percent of total land 

area, but this number too is an artifact of definition, and the 

total area of land that is devoted to human habitation is much 

larger.9 More recent estimates place the total urban land area 

at 68 million acres (28 million hectares), and if community 

lands are included, the total more than doubles to 138 million 

acres (56 million hectares). This figure also underestimates the 

importance of urban and suburban forests because urban and 

suburban areas are where most people live (close to 85 percent 

of total U.S. population by current estimates—table 2.1) and 

the direct benefits to citizens are commensurately larger. These 

8

 The Forest Service’s “Forests on the Edge” project specifically targets the wildland-urban interface for the development of research and management tools. 

Relevant publications and project information are available at http://www.fs.fed.us/openspace/fote/ (August 2015).

9

 Theobald (2005), for example, estimated that 31 million acres (13 million hectares) of land existed in urban and suburban designations (less than 1.68 acres 

[.68 hectares] per housing unit) in 2000 but that an additional 226 million acres (91 million hectares) existed in the exurban category (1.68 to 39.98 acres per 

housing unit—the decimals are due to metric conversion).
10 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Table 2.1. U.S. population by land category (in millions).

1980 1990 2000 2008 Change 

1980–2008

Rural 46 45 49 50 4 (10%)

Urban 181 204 233 254 73 (40%)

Total 227 249 281 304 77 (34%)

Source: USDA Economic Research Service (http://www.ers.usda.gov/

StateFacts/US.htm [August 2015]).

areas and the exurban housing development that immediately 

surrounds them are expanding, with associated losses in other 

land use categories. 

The area statistics presented here help give us an idea of the 

potential scope of the resource. Their relative land areas, however, should not be used to gauge the relative value of agricultural

and urban forests to our society. Urban forests, for example, 

account for a very small share of total forest area in the United 

States, but their value is proportionately quite large. A 1994 study

estimated the total value of street trees alone to be in excess 

of $30 billion (Schoeneman and Ries 1994), and Nowak et al. 

(2002) estimated a total value for all urban trees of $2.4 trillion. 

Each estimate is based roughly on how much it would cost to 

replace these trees, and the linkage of these numbers to the actual

benefits derived from urban trees is loose, at best. Other studies 

(e.g., Donovan and Butry 2011) have analyzed real estate markets to show that urban trees have significant positive effects on 

real estate sale and rental values, demonstrating a direct linkage 

between urban trees and consumer willingness to pay.

Similar value estimates for agricultural forests were not available for this report, but, given the ecosystem services associated 

with these trees, the values are likely quite large. In any case, 

economic valuations of this type are, by necessity, quite imprecise. In practice, it is virtually impossible to develop a single 

measure that summarizes the contribution of these resources to 

society (note that the same can be said for forest resources in 

general).

Data Sources Specific to Forests 

in Agricultural and Urban Settings

A central focus throughout this report is the data sources available for understanding and measuring agricultural and urban 

forests. The FIA program and the National Resources Inventory, carried out by the USDA Natural Resources Conservation 

Service, constitute the backbone of national sampling of forest 

resources, but these inventories have not yet10 been consistently 

extended to the forests and trees considered in this report. What 

remains is a piecemeal collection of discreet studies and pilot 

projects, some of which are shown in figure 2.3. In the area of 

urban forestry, the FIA has extended forest sampling to urban 

areas on a pilot project basis in a number of States, in its Urban 

Pilot Plot projects and in the Pacific Rim Urban Inventory. On a 

more local level, a growing number of municipalities are using 

the Forest Service “i-Tree Eco” model to sample local urban 

forest resources in a consistent fashion, and, more generally, 

a growing number of municipalities, counties, and regional 

bodies are using remote-sensing and Geographic Information 

System, or GIS, technology to inventory and analyze their local 

forests and trees. These approaches are discussed further in the 

chapter 4, but the important point to remember is that these 

efforts are not integrated into a nationally consistent survey 

of urban forests. The Great Plains Tree and Forest Invasives 

Initiative (GPI), on the other hand, provides a consistent, wallto-wall survey of agricultural and urban forests for Kansas, Nebraska, North Dakota, and South Dakota. The GPI constitutes 

the best data source we have to date on agricultural forests, but 

it is (of course) limited to a specific region. The GPI is a central 

focus in chapter 3, which addresses agricultural forests.

In addition to the ground-sampling activities listed previously, 

satellite imagery and related remote-sensing applications provide a source of increasingly sophisticated information on forests 

that is uniformly consistent and available wall-to-wall for the 

entire Nation. For certain measures, notably forest cover, remote

sensing constitutes an extremely valuable source of information,

but it will never fully take the place of ground-based sampling 

for understanding many of the aspects of forests that are 

considered important.

The Long Term Ecological Research Network (LTER) maintains research sites in the contiguous United States, Puerto Rico,

Alaska, and Antarctica with the aim of tracking ecological 

change at specific locations over the span of decades or longer 

(see http://www.lternet.edu/ [August 2015] for project information and publications). Of particular interest for the purposes of 

this study, LTER sites in Baltimore County, MD, and Phoenix, 

AZ, focus on ecosystems in urban settings, and the Kellogg 

Biological Station LTER in Michigan focuses on agricultural 

environments. Given their site-specific nature, the LTERs 

are excellent for studying biological processes and exploring 

specific research questions in depth, but they do not deliver the 

type of broad-scale monitoring statistics that are the primary 

focus of this report.

10 A National Urban Forest Inventory under FIA is in its initial stages of implementation. This effort builds on years of preparatory work on the part of FIA. 

Sampling protocols and related details for the program have been established and will further evolve as FIA and its collaborators gain more experience in 

inventorying urban trees and forests at the national scale. Nationally consistent inventory data from this effort, however, will not be available for at least 

several years.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 11

Figure 2.3. Forest Service and related data sampling activities for agricultural and urban forests.

i-Tree Eco Assessments (1996–2012).

Pacific Rim Urban Forest Inventory (2010–2012); Urban Forest Inventory and Analysis Pilots (as of 2013);

Great Plains Tree and Forest Invasives Initiative Inventory (2008–2009).

i-Tree Eco

as of Jan. 2012

773 U.S. Projects

Pacific Rim Inventory

Urban Pilot Plots

Great Plains Initiative

1–10

11–25

26–50

51–69
12 Assessing the Sustainability of Agricultural and Urban Forests in the United States

The foregoing discussion shows that a large and growing set 

of information is available to help us understand forests in 

agricultural and urban settings, but this information is not well 

integrated at the national level. As a result, one the most important steps we can take in developing a national assessment 

of agricultural and urban forests, and the database to support 

this assessment, is to simply make better use of the data we are 

already collecting. This theme is central in chapter 5, which 

considers ways to improve our data collection and sustainability 

reporting efforts in regard to these forest resources.

The Montréal Process Criteria 

and Indicators and Agricultural 

and Urban Forests

A central tenant of forest sustainability reporting efforts is 

that decisions about how society manages its forests must be 

guided by accurate and sufficient information. This idea is not 

new, but the degree to which managers have recently tried 

to institutionalize and standardize the process is. To aid in 

this effort, analysts and managers have increasingly turned to 

criteria and indicators as fundamental tools to rationalize their 

reporting processes, explicitly identifying the specific pieces of 

information they will be tracking and refining over time.

The MP C&I are one such approach. Initiated in the mid-1990s 

and applied in the United States first in 2003 and more recently 

in 2010 (USDA Forest Service 2011a), the MP C&I codify a 

set of measures needed to manage temperate and boreal forests 

sustainably. Since it is the product of an international collaborative process involving 12 signatory countries, the content of 

the MP C&I represents, in effect, a broad compromise between 

widely different perspectives reflecting equally different conditions within their respective countries. It also reflects the individual perspectives of the many people who participated. Data 

availability was purposefully omitted as a requirement when 

choosing indicators for the MP C&I (Montréal Process 2007). 

The resulting C&I set should thus be seen as a comprehensive 

list that a broad range of individuals has chosen and further 

refined, which identifies factors that should be considered when 

attempting to ascertain the sustainability of forest ecosystems, 

whether or not all of those factors can readily be measured. 

The MP C&I are subject to periodic review and adjustment to 

incorporate the experiences of reporting countries.

The strengths of the MP C&I include their comprehensive 

coverage of ecological, social, and economic dimensions of 

forest sustainability and their flexible nature, in which many 

indicators are loosely defined and left to country analysts to 

address as they see fit. Weaknesses include a lack of systematic 

consistency across reporting countries, large information 

requirements, and the practical impossibility of adequately 

addressing certain indicators.

With 54 different indicators arranged under 7 criteria spanning 

ecological, social, and economic dimensions, the types of variables, their degree of accuracy and specificity, and the availability of information to treat them differ greatly between the 

indicators and their respective criteria.11 Although certain indicators are easily addressed with available datasets, many others 

involve considerable information gathering and analysis, and 

still others can be reported only in an anecdotal or qualitative 

fashion, if at all. When applied to agricultural and urban forest 

resources, the data gaps and associated challenges become even 

more apparent, but these problems are as much the result of our 

lack of baseline data and analysis tools as they are the result of 

an inherent deficiency in the MP C&I or potential mismatch 

between conventional forest resources and the resources that 

are the subject of this report. More to the point, the MP C&I 

provides an excellent starting point (but only a starting point) 

for determining the current status of and potential future needs 

for information in assessing the sustainability of agricultural 

and urban forests, the challenges and data gaps inherent in the 

system notwithstanding.

The Seven Criteria in Relation to Agricultural and Urban Forest Resources

The basic structure of the MP C&I is displayed in figure 2.4. 

The figure shows the seven criteria along with the general areas 

they cover. The remainder of this chapter will be devoted to 

addressing these criteria one by one as they relate to agricultural and urban forest resources. In this fashion, we hope to 

use the MP C&I to highlight the various aspects of agricultural 

and urban forests as they relate to the general concerns of 

sustainability and the specific challenges of measurement and 

reporting. Although we have omitted a discussion of each of 

the individual indicators, we do reference certain key indicators 

if they are particularly important. A more detailed mapping of 

the MP C&I into specific indicators, tailored to agricultural and 

urban forests, is provided on a provisional basis in chapter 5.

11 The number of indicators was reduced to 54 in 2009 (too late for inclusion in the 2010 National Report). A current listing of the criteria and indicators 

comprising the MP C&I is available in the Montréal Process Booklet, 4th edition (Montréal Process 2009). http://www.montrealprocess.org/documents/

publications/general/2009/2009p_4.pdf (August 2015). 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 13

Figure 2.4. Montréal Process Criteria and Indicators for Forest Sustainability.*

MP C&I = Montréal Process Criteria and Indicators.

*The full title is Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests.

Note: The criteria titles and descriptive information are abbreviations.

Criterion 1: Conservation of Biological Diversity. The nine 

indicators in Criterion 1 provide information on the extent and 

character of forests as they relate to ecosystem, species, and 

genetic diversity. These indicators comprise the core variables 

of a biophysical inventory and include the amount of forests of 

different types (as measured in acres), the number and status of 

different species of flora and fauna contained within them, and 

the genetic resources they represent. Measuring the extent of 

agricultural and urban forest resources is a central concern in 

this report, and, in an ideal world, we would be able to replicate 

the simple area measures for these resources that are already 

available for conventional forests in the first two indicators 

displayed for this criteria in the National Report. The primary 

FIA data used for conventional forests, however, are not available for agricultural and urban forest resources, and, owing to 

the fragmentation of these resources, the type of area measures 

may not always be appropriate (as was discussed previously). 

Much of the rest of this report is devoted to issues involved in 

developing this type of baseline inventory data.
14 Assessing the Sustainability of Agricultural and Urban Forests in the United States

To the extent that agricultural and urban forests serve as an 

important reservoir for biodiversity, the species and genetic 

diversity measures found in Criterion 1 will also be important, 

particularly if these resources harbor species not found on 

conventional forest lands. Moreover, recent studies have found 

that scattered trees, a configuration common to urban and some 

agricultural landscapes, have a disproportionately large positive 

effect on animal diversity, at least for birds and bats (Fischer 

et al. 2010, Manning et al. 2006). Add to this effect the high 

number of introduced species (intentionally and accidentally), 

and it is not surprising that agricultural and, especially, urban 

landscapes can exhibit a high degree of biological diversity, 

although this diversity should not be seen as a substitute for 

intact natural ecosystems (Kowarik 2011). By extending FIA 

sampling activities to agricultural and urban forests, some of 

this information may be developed using the sampling process, 

but the Criterion 1 biodiversity indicators in the main National 

Report also rely on a number of data sources that will likely not 

be easily replicated in agricultural and urban settings. This data 

challenge is even more pronounced for genetic diversity, an 

area that presented challenges for the National Report as well.

Criterion 2: Maintenance of Productive Capacity of Forest 

Ecosystems. Criterion 2 contains five indicators providing 

information on growth, harvests, and inventory of valued forest 

outputs. These outputs include conventional wood products, 

such as lumber or wood fiber for paper or other uses, and “nonwood” forest products, a category covering an array of other 

outputs ranging from mushrooms and herbs to Christmas trees. 

Owing to their status as a major industry with long-established 

accounting and tracking procedures, the wood products indicators in Criterion 2 enjoy fairly good coverage through the FIA 

program and regular reporting of harvest activity. The nonwood 

forest products category, on the other hand, includes a large 

number of products for which little or no information is readily 

available. Regarding agricultural and urban forests, a central 

question will be the degree to which these types of outputs, either 

wood or nonwood, are important. These forests most likely are 

not the source of substantial volumes of wood products, and 

the same type of growth and yield measures that are applied to 

conventional forests would not be useful. Urban forests generate significant amounts of woody biomass in the form of yard 

wastes and debris, a small proportion of which is recovered 

through mulching, recycling, and other uses (including a growing amount of bioenergy generation). In addition, substantial 

amounts of nonwood products may be harvested from agricultural and urban forests, although these products may not always 

enter the cash economy through sale or exchange (Poe et al. 2013). 

Agroforestry, for example, purposefully integrates nonwood 

forest products (and wood products in some cases) with agricultural production (see Gold et. al. 2000 for an overview of 

agroforestry in the United States). In addition, if energy from 

woody-biomass becomes more common in the future, trees in 

urban, and, particularly, in agricultural settings, may come to 

constitute an important source of energy (Ruark et al. 2006). 

How trees grown expressly for energy production will be 

classified—as forests or as crops—remains an open question, 

however. In any case, the data streams available to cover these 

outputs are not well established, and initial reporting efforts 

will be incomplete if undertaken at all.

Although the commodity outputs flowing from agricultural and 

urban forests may at present be relatively insubstantial, the ecosystem services associated with these resources are generally 

well recognized—they are the reason these trees were established 

or preserved in the first place. The actual definition of what constitutes an ecosystem service can include a variety of beneficial 

aspects, some of which have been enumerated in the previous 

chapter, but, in general, these services are not directly associated 

with easily quantified measures (although our capacity in this 

area is increasing). 

The MP C&I do not explicitly treat ecosystem services in 

Criterion 2,12 reserving that topic for Indicator 28 in Criterion 6 

(“payments for ecosystem services”),13 but given the importance 

of ecosystem services as a primary output and justification for 

agricultural and urban forest resources, the services associated 

with these resources should perhaps be specifically considered 

within Criterion 2. This inclusion would entail first identifying 

key services on which we wish to concentrate and then working 

to devise, where possible, quantitative measures of the capacity 

of forest resources to actually supply them. 

Criterion 3: Maintenance of Forest Ecosystem Health and 

Vitality. Criterion 3 contains two indicators, focused on biotic 

disturbances (insects, diseases, and invasive species) and abiotic 

disturbances (fire, drought, storms, pollution, and development). 

Although biotic and abiotic disturbances are treated separately, 

they are often closely related. Drought-stricken forests, for 

example, are more susceptible to insect infestation and then, 

in turn, to fire. Numerous similar associations between biotic 

and abiotic disturbance agents can be found in the various paths 

through which forest ecosystems evolve over time. The Forest 

Service, Forest Health Protection, or FHP, program supplied 

the major data sources used to populate this indicator in the 

2010 National Report.

12 Criterion 4, which addresses soil and water conservation is closely linked to the concept of ecosystem services, particularly those related to the provision 

and flow regulation of water. Carbon sequestration, addressed in Criterion 5, also constitutes an important ecosystem service, and several other indicators are 

closely associated with ecosystem services, but none treat them explicitly.

13 Note that “payments for ecosystem services” is not the same as a physical measurement of outputs nor is it a measure of the total value to society provided 

by these services.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 15

As evidenced by the progression of Dutch elm disease through 

the tree lined streets of our towns and cities in the past century 

and by the wildfires that have afflicted our western towns in 

more recent years, forest health and disturbance are crucial 

considerations for agricultural and urban forests. The adverse 

effects of disturbance are often obvious and direct because 

these resources are interspersed with human settlement and 

activity, ranging from the loss of benefits trees provide to, in 

the case of fire, loss of property and even lives. 

Owing to their different spatial configuration and proximity to 

human disturbance agents (such as pollution and ignition sources), 

and to their often artificial species distribution, agricultural and 

urban forests may be more susceptible to certain disturbance 

events. The tendency to rely on a limited set of species in urban 

forestry, for example, has led to concerns about enhanced 

vulnerability to species-specific pathogens (Lacan and McBride 

2008). The species selected for agricultural lands too have been 

limited in regions, as evidenced by predominance of ash trees 

found in the Great Plains, trees which are now at considerable 

risk to emerald ash borer (Agrilus planipennis; EAB) infestation 

(Rasmussen 2009). All these factors point to the importance 

of understanding and monitoring the health of agricultural and 

urban forests, but, as is true with the provision of basic inventory data, no mechanisms are in place to develop these data for 

agricultural and urban forests in a consistent fashion, at either 

the national or regional level.

The 2010 edition of the National Report identified rising levels 

of forest disturbance, particularly that associated with insects, 

as one of its keys findings and a leading indicator of potential 

threats to the sustainability of conventional forests in the near 

future, particularly in relation to impending climate change. 

This same issue likely applies in the case of agricultural and 

urban forests (indeed, the GPI inventory, discussed in the next 

chapter, was largely motivated by concern for potential damage 

from the EAB).

Criterion 4: Conservation and Maintenance of Soil and 

Water Resources. The five indicators in Criterion 4 are designed 

to measure the current status of water and soil resources in 

forested ecosystems and our efforts to conserve them. The data 

sources used to populate these indicators range from information 

on protective land use designations to State-level data on water 

quality impairment and FIA sampling of soil conditions.

Soils are a foundational element for forested ecosystems, and 

water quality enhancement and flow retention are recognized 

as essential outputs associated with these ecosystems. Soils and 

water are likewise important in the case of agricultural and urban forests. Soil conservation was the prime motivation behind 

the establishment of the windbreaks and shelterbelts and related 

forested areas that comprise a large proportion of our agricultural 

forest resources.14 In a similar way, the importance of forests 

in the provision of water for urban populations has long been 

recognized, resulting in explicit management prescriptions to 

enhance and conserve water resources in forested watersheds 

serving municipal entities (e.g., the Bull Run Watershed serving 

Portland, OR), and, more recently, innovative policies that 

incentivize and motivate private landowners to preserve forest 

cover and water quality (the New York City (NYC) Long-Term 

Watershed Protection Program,15 for example). Another recent 

example is the Executive Order16 signed on May 12, 2009, by 

President Obama that is aimed at protecting and restoring the 

Chesapeake Bay Watershed, which has led to the establishment 

of a goal to establish 14,400 miles of riparian forest buffers by 

2025. Moreover, by providing permeable surfaces and water 

retention, forested green spaces within municipal boundaries are 

now being increasingly proposed as an alternative to physical 

water control infrastructure (i.e., drainage pipes) in urban areas 

(Booth et al. 2002). 

Although soil and water conservation are recognized as a key 

aspect of agricultural and urban forests, their measurement 

within the context of Criterion 4 will likely remain challenging. 

Soil sampling through an expanded FIA program or similar 

activity could provide some data on soils at least, but developing 

information on water quality would be hampered by the unique 

spatial configurations and lack of management focus associated 

with agricultural and urban forests identified in the previous 

section. Most of the data will depend on reporting by State or 

local agencies, and the data streams associated with these reporting mechanisms are often inconsistent or otherwise difficult to 

aggregate and compare—a problem that hampered reporting 

for Criterion 4 for conventional forests in the National Report

as well. 

Criterion 5: Maintenance of Forest Contribution to Global 

Carbon Cycles. The role of forest ecosystems (including forest 

soils) in absorbing, storing, and emitting carbon is the key focus 

14 The most visible example of this effort is the creation of the Soil Conservation Service and the Prairie States Forestry Project by the Roosevelt 

administration to combat loss of topsoil in the Dust Bowl States during the Great Depression. See Munns and Stoeckeler (1946) for a description of the 

project and its relative success.

15 The NYC Long-Term Watershed Protection Program has received a great deal of attention during the past decade for providing an innovative solution 

to the complex problem of supplying clean drinking water to one of the world’s largest cities and for its explicit recognition of the value of forest-based 

ecosystem services. See Pires (2004) for a description of the project. Program information is available on the project’s Web site. http://www.nyc.gov/html/

dep/html/watershed_protection/index.shtml. (August 2015).

16 http://www.executiveorder.chesapeakebay.net/default.aspx. (August 2015).
16 Assessing the Sustainability of Agricultural and Urban Forests in the United States

of Criterion 5. In addition to forest ecosystem carbon accounts, 

Criterion 5 indicators track the amount of carbon stored in longlived forest products, and fossil fuel carbon emissions avoided 

through the use of wood to generate energy. In the National 

Report, the indicators in Criterion 5 are populated using forest 

inventory data or information tracking wood products and 

energy production that is then converted to carbon equivalents 

using conversion factors. These conversion factors, which estimate such aspects as the tons of carbon per acre of a given type 

of forest with a given stocking level or the amount of carbon 

in different wood products along with their rate of decay, are 

subject to substantial error bounds, but they are getting more 

accurate at a rapid pace as researchers gain more knowledge 

in this relatively new research area. The overarching goal of 

Criterion 5 is, of course, to better understand the influence of 

forests and forestry on global climate change via their contribution to atmospheric carbon balances.

Developing comparable information on carbon for agricultural 

and urban forest resources will involve two steps. First, baseline 

inventory and production data must be obtained. Basic inventory 

data could be developed by expanding FIA or similar sampling 

activities, but sampling would have to include information sufficient to develop estimates of forest volume (which FIA certainly 

does at present for conventional forest ecosystems) and not just 

forest cover. Forest soils also constitute significant carbon sinks 

(Pouyat et al. 2006), and soil carbon estimates specific to agricultural and urban forest soil types will need to be developed. 

Measuring forest outputs from agricultural and urban forests 

in the form of wood products and energy would likely be more 

difficult, owing to reasons noted in the previous discussion of 

Criterion 2, and a first step would be to ascertain whether these 

outputs are sufficiently large to justify a major data-gathering 

effort in the first place. The second challenge will be to develop 

appropriate carbon conversion factors to transform inventory 

and output measures into carbon equivalents. For forest carbon, 

conversions may simply entail using factors already in use for 

forested ecosystems, but agricultural and urban forests will 

often differ considerably in terms of spatial configuration and 

species composition, and we cannot simply assume that the 

conversion factors currently in use will be appropriate in this 

new setting. Nonetheless, substantial progress has already been 

made in estimating carbon volumes, at least for urban forests 

(Nowak et al. 2002). Assuming that the base data for wood 

products and energy outputs are available, conversion factors 

will probably be quite similar to those used to estimate carbon 

for these outputs in the case of conventional forests, but whether 

the amounts of carbon involved actually justify the effort needed 

to estimate them remains a question.

In the case of agricultural forests, and agroforestry systems 

in particular, payments for carbon sequestration may present 

a growing opportunity (Schoeneberger 2008) as could the 

production of woody biomass for energy production. Once 

again, however, the question remains as to whether the resulting 

plantings would be classified as forests or crops. In any case, 

the possible advent of these kinds of activities bears watching. 

The activities would be directly related to the indicators in 

Criterion 5 and to other indicators covering the production 

of forest products and ecosystem services, and the economic 

activities that accompany them.

Criterion 6: Maintenance and Enhancement of Socioeconomic 

Benefits. Containing 20 of the 54 indicators that comprise the 

MP C&I in total, Criterion 6 addresses a range of socioeconomic 

dimensions associated with forests and the goods and services 

they provide. This criterion is further divided into five subcriteria: 

(1) production and consumption; (2) investment in the forest 

sector; (3) employment and community needs; (4) recreation 

and tourism; and (5) cultural, social, and spiritual needs and 

values. Each subcriterion and its respective indicators obviously 

will relate to agricultural and urban forest resources in different 

ways, and many will likely not be appropriate or feasible in 

this context at all. Moreover, the primary focus of the current 

report is to explore options for developing baseline inventory 

information, and many of the indicators in Criterion 6 fall out­side this objective and are perhaps best viewed as candidates 

for future development as opposed to targets for the work 

considered here.

That being said, a number of indicators in Criterion 6 still have a 

direct bearing on agricultural and urban forests and on the benefits they provide to society. Although it appears that the types 

of tangible forest products measured in the first subcriterion 

(production and consumption) are generally lacking in the case 

of the trees and forests considered in this report, this assumption should be viewed merely as a working hypothesis—it is 

quite possible that deeper investigation will reveal significant 

outputs of tangible products, particularly in the nonwood 

category or in terms of fuel wood and feedstock for energy 

production. Moreover, this subcriterion contains an indicator 

measuring payments for forest-based ecosystem services, services that we have identified as a primary aspect of agricultural 

and urban forests, although, whether we can develop measures 

of money transfers for these services, and relate them directly 

to forests and trees, is another question.

Investments in the forest sector, the second subcriterion, can be 

directly translated into a call for information on investments in 

agricultural and urban forestry, although once again, the data 

available to address this question may be sketchy, relying as 

they do on disparate reporting activities from local and regional 

entities across the Nation. The third subcriterion, which addresses 

the needs of forest-dependent industries and communities, is 

probably the least applicable of the five, because the direct 

dependence on forests for economic livelihood applies in the 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 17

case of conventional forestry but not in the case of agricultural 

and urban forests (with the possible exception of agroforestry 

systems, but, even in this case, the dependence will be only 

partial). At the same time, however, the role of trees and forests 

in providing community amenities must be recognized even 

though this role cannot be measured in terms of jobs or income 

generated. Moreover, recreation, the focus of the fourth subcriterion, is often closely related to urban and suburban green 

spaces, many of which are forested, and it would not be that 

much of a stretch to claim that the aesthetic contribution of trees 

to urban and rural landscapes results in a significant, although 

difficult to define, contribution to tourism activity.

To the extent that forests and trees add to the beauty of developed landscapes and the wellbeing of their inhabitants, the fifth 

and final subcriterion, will apply to agricultural and urban forests 

every bit as much as it does to conventional forests. Indicator 44, 

“The Importance of Forests to People,” is of particular note 

here and has a direct connection to feelings residents have for 

the forest and trees that occupy their neighborhoods and surrounding lands. 

Criterion 7: Legal, Institutional, and Economic Framework 

for Forest Conservation and Sustainable Management. The 

indicators in Criterion 7 are used to characterize the policies 

and institutions countries use to sustainably manage their forest 

resources. Although the topics addressed in Criterion 7 are 

central to our efforts to ensure sustainability, they are extremely 

resistant to quantification and standardized reporting. The 

National Report first addressed the topics in a narrative fashion 

in 2003, and, more recently in the 2010 edition, using a matrix 

approach to summarize qualitative judgments. In either case, 

the result could provide only a framework and descriptive summary of laws and institutions and not a consistent, permanent 

metric, such as is possible with forest areas and volumes, water 

quality, etc. The Montréal Process Working Group recently 

reduced and revised the Criterion 7 indicators, partly in recognition of the practical challenges they present (see Montréal 

Process 2009 for revised list), but this revision does not alter 

the fact that developing concise and consistent measures to 

describe policies and institutions is a very difficult task. These 

same challenges will also exist in the case of agricultural and 

urban forests, and perhaps more so because the institutional 

arrangements for managing these resources are nowhere near 

as developed at the national level as they are for conventional 

forests. A likely approach to treating agricultural and urban forest resources in regard to Criterion 7 could involve a narrative 

description of the various policies and institutions addressing 

these resources without recourse to the specific indicators 

found in the MP C&I.

The Relation of the MP C&I as a 

Whole to Agricultural and Urban 

Forest Resources

The foregoing discussion demonstrates a considerable overlap 

between the MP C&I and the types of issues we need to address 

to understand agricultural and urban forest resources in the 

United States. At the same time, the fit is not always exact or 

comfortable. Some of the indicators are directly applicable in 

this different context, some will call for considerable adjustment, and others simply make no sense when applied to trees 

on agricultural or urban lands. The MP C&I help us identify 

and organize our information needs and assess our ability to 

fill them when viewed at the criterion level. This function is 

exactly what the MP C&I are designed to accomplish regarding 

conventional forests, and so the use of this tool in relation to 

agricultural and urban forests is broadly comparable with the 

approach applied in the National Report, although it would be 

unrealistic to expect or enforce a one-to-one correspondence 

between the MP C&I and any candidate system for agricultural 

and urban forests. Rather, the MP C&I should be viewed as 

a guide and source of ideas for identifying indicators specific 

to these resources, with the ultimate aim of enabling us to 

characterize and integrate them with our understanding of conventional forest resources and their sustainable management. 

This approach is exemplified in the mapping of MP indicators 

into provisional measures for agricultural and urban forests 

provided in chapter 5 of this report.

This report views the MP C&I as a static list through which 

we can organize information about agricultural and urban 

forest resources, but, to remain relevant, the MP C&I (or any 

other C&I framework) must adapt to changing circumstances 

and societal demands. In fact, identifying the various ways 

in which agricultural and urban forests affect human welfare 

(through public health, real estate values, livability, etc.) may 

help us recast portions of the MP C&I in the future. Likewise, 

investigating the novel ecosystems that these forest resources 

represent can help shed light on basic ecosystem processes and 

point to new measures that are useful in considering conventional forests as well.

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20 Assessing the Sustainability of Agricultural and Urban Forests in the United States
Assessing the Sustainability of Agricultural and Urban Forests in the United States

Assessing the Sustainability of Agricultural and Urban Forests in the United States 21

Chapter 3 Michele Schoeneberger, Andy Lister, 

and Steve Rasmussen

Agricultural Forests

The role of trees in supporting agricultural production and the 

health and vitality of rural landscapes has long been recognized. 

Of the two types of forest resources (agricultural and urban) 

analyzed in this report, however, agricultural forests are perhaps 

less well understood. Whereas urban forestry has specific educational programs, dedicated activities, and departments in many 

municipalities, agricultural forestry, when considered at all, is 

often subsumed under the general heading of farm management. 

Of course agroforestry, in which trees are integrated with other 

forms of crop production, is a well-developed area of study and 

application, but this field encompasses only part of the resources 

treated here. In any case, the available data for understanding 

these resources at the national level are very sparse.

Most of this chapter is devoted to establishing definitions and 

describing important characteristics of agricultural forests. The 

data we do have rely on several different sources. In 1982, 1987, 

and 1992, the U.S. Department of Agriculture (USDA), Natural 

Resources Conservation Service (NRCS) National Resources 

Inventory (NRI) assessed the extent of windbreaks nationally. 

The NRCS also tracks the application of new agroforestry practices undertaken through the USDA’s technical and financial 

assistance programs. Neither of these data collection activities 

represents a wall-to-wall inventory of agricultural forest resources, 

however. The Great Plains Tree and Forest Invasives Initiative 

(GPI) recently completed a more comprehensive inventory of 

windbreaks and other agroforestry plantings, but the scope is 

geographically limited to only States in the northern Midwest. 

The 2008-to-2009 GPI inventory was a cooperative effort 

among the four Great Plains States forestry agencies (Kansas, 

Nebraska, North Dakota, and South Dakota), made possible 

with USDA Forest Service funding, and scientifically guided 

by the agency’s National Inventory and Monitoring Applications Center. A modified Forest Service Forest Inventory and 

Analysis (FIA) protocol was used in the GPI inventory, which 

lacks some of the data collected on standard FIA plots (Lister 

et al. 2009b). We use the GPI as a model for understanding the 

kind of data development efforts that could be applied at the 

national level.

This chapter begins with a discussion of definitions and 

characteristics of agricultural forests, followed by a description 

of available data (primarily from the GPI). Next we describe 

the various benefits associated with these forests, the risks 

they face, and the opportunities they present through expanded 

planting activity. The chapter concludes with an assessment of 

the adequacy of currently available information and suggested 

strategies for improving the data, in general and relative to the 

Montréal Process Criteria and Indicators (MP C&I) for Forest 

Sustainability. This same overall framework is applied to 

urban forests in the next chapter. When appropriate, we make 

reference to specific indicators in the National Report on Sustainable Forests—2010—hereafter, referred to as the National 

Report (USDA Forest Service 2011).

Definitions and Characteristics of 

Agricultural Forests

Agricultural forest resources consist of deciduous and coniferous 

manufactured tree plantings and natural woodlands that generally do not meet conventional definitions of “forest” because of 

their size and width. Manufactured plantings within agricultural 

lands (hereafter, referred to as working trees or agroforestry) 

are those that have been intentionally established in specific 

locations, with specific species, and in specific arrangements to 

achieve specific functions and that are closely associated with 

agricultural or forage production (USDA NRCS 1996). Naturally 

occurring woodlands within the agricultural matrix, in contrast, 

are unintentionally established through wind, water, or animal 

seed dispersal and root sproutings; they commonly occur as 

isolated patches of various dimensions, such as upland woods, 

woody draws, and riparian forests.

Working trees are established through the application of five 

categories of agroforestry practices, which include (1) field, 

farmstead, and livestock windbreaks; (2) riparian forest buffers 

along waterways; (3) silvopasture systems with trees, livestock, 

and forages growing together; (4) alley cropping that integrates 
22 Assessing the Sustainability of Agricultural and Urban Forests in the United States

annual crops with high-value tree and shrubs; and (5) forest 

farming, in which food, herbal (botanical), and decorative products are grown under the protection of a managed forest canopy. 

Special applications of these five practices can be designed to 

accomplish a wide range of other economic, environmental, 

and social objectives, including odor mitigation, organic food 

production, improved pollinator habitat, snow retention, or biomass feedstock production. A brief description of the practices 

and their uses is presented in table 3.1. Additional information 

for each of these practices is available at the USDA National 

Agroforestry Center Web site (http://nac.unl.edu [August 2015]). 

Christmas tree plantations and nut and fruit orchards generally 

are excluded from the working tree category (Perry et al. 2009), 

although both types have the potential to become important 

components within agroforestry practices: for example, the use 

of Christmas trees in an alley cropping system or bioterraces 

and the planting of nut and fruit trees in a windbreak design to 

alter microclimate for adjacent practices and to enhance dispersal of natural enemies of crop pests. As they commonly occur, 

however, Christmas tree plantations and nut and fruit orchards 

are not included in the definition of agricultural forest resources 

considered in this report.

Support for Agroforestry Practices

A wide range of USDA conservation programs support the 

application of agroforestry practices by providing various forms 

of financial assistance, including conservation practice payments 

and rental payments, to establish and manage agroforestry plantings (table 3.2). The Food, Conservation, and Energy Act of 

2008 (2008 Farm Bill) actually increased financial assistance to 

landowners for forestry-related conservation activities, including 

agroforestry and woodland practices. The recently signed 2014 

Farm Bill contains modest budget cuts, but, in general, the conservation title still provides technical and financial assistance in 

this area for private landowners.

The 2008 and 2014 Farm Bills carry on a long tradition of 

conservation support for agroforestry practices, beginning with 

the windbreaks planted after the Dust Bowl in the 1930s. From 

1935 to 1942, the Forest Service, working with the Works Progress Administration and Civilian Conservation Corps, planted 

windbreaks throughout the Great Plains. The Prairie States 

Forestry Project planted more than 217 million trees on nearly 

18,641 miles (30,000 kilometers) of shelterbelts in six Great 

Plains States from North Dakota to Texas (Sauer et al. 2010). 

After World War II, the Soil Conservation Service (now the 

NRCS) was given a leadership role to assist landowners with 

planning and planting windbreaks throughout the United States. 

Table 3.1. The six categories of agroforestry practices commonly established in the United States.

Agroforestry practice Description Primary use*

Riparian forest buffer A combination of trees and other vegetative types established on the 

banks of streams, rivers, wetlands, and lakes.

• Reduce nonpoint source pollution from adjacent land uses

• Reinforce streambank stability

• Protect aquatic and terrestrial habitats

• Provide economic diversification either through plant 

production or recreational fees

Windbreak (also referred 

to as shelterbelt)

Linear plantings of trees and shrubs to form barriers to reduce 

wind speed. Depending on the primary use, the windbreak may be 

specifically referred to as crop or field windbreak, livestock windbreak, 

living snow fence, or farmstead windbreak.

• Control wind erosion

• Protect wind-sensitive crops

• Enhance crop yields 

• Reduce animal stress and mortality

• Serve as a barrier to dust, odor, and pesticide drift

• Modify climate around farmsteads

• Manage snow dispersal

Alley cropping Rows of trees planted at wide spacing intervals while growing annual 

crops in the alleyways.

• Diversify crops in time and space

• Diversify income

• Protect soil quality 

Silvopasture Trees combined with pasture and livestock production. • Diversify crops in time and space

• Diversify income

Forest farming (a form of 

multistory cropping)

Natural stands whose canopies have been manipulated to grow highvalue crops in the understory, such as mushrooms, decorative florals, 

and medicinal herbs (e.g., ginseng).

• Diversify crop production

Special applications 

(e.g., tree planting)

Use of agroforestry technologies to help solve special concerns 

such as disposal of animal wastes, filtering irrigation tail water while 

producing a short- or long-rotation woody crop.

• Provide treatment of municipal and agricultural wastes

• Provide treatment of stormwater 

• Center pivot corner plantings

• Produce biofeed stock

*In addition to the targeted benefits listed in the table column, agroforestry plantings can also be simultaneously managed to provide enhanced wildlife provisions for 

game and nongame species and greenhouse gas mitigation through carbon sequestration and reduction in fuel emissions.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 23

Table 3.2. USDA 2008 Farm Bill programs supporting agroforestry practices.*

Programs1 Riparian forest 

buffer 

Windbreak 

(also referred to 

as shelterbelt)

Alley cropping Silvopasture Forest farming

(a form of multistory cropping)

Special applications 

(e.g., tree planting)

AMA2 C C C

AWEP3 C C

BCAP C/I/R

CBWI4 C 

CCPI5 C C C C C C

CCRP C/I/R C/I/R C/I/R C/I/R

CREP C/I/R C/I/R 

CRP C/I/R

CSP U U U U U

EQIP C C C C C C

MRBI6 C C

SARE PG PG PG PG PG PG

WHIP C C C C C C

WRP C/E C/E C/E C/E

C = cost-share payment. E = easement payment. I = incentive payment. PG = producer grant. R = rental payment. U = land use payment. 

* Not all combinations, practices, or programs will be available in all States and territories.

1

 Programs: AMA = Agricultural Management Assistance Program; AWEP = Agricultural Watershed Enhancement Program; BCAP = Biomass Crop Assistance 

Program; CBWI = Chesapeake Bay Watershed Initiative; CCPI = Cooperative Conservation Partnership Initiative; CCRP = Continuous Conservation Reserve Program; 

CREP = Conservation Reserve Enhancement Program; CRP = Conservation Reserve Program; CSP = Conservation Stewardship Program; EQIP = Environmental 

Quality Incentives Program; MRBI = Mississippi River Basin Healthy Watersheds Initiative; SARE = Sustainable Agriculture Research and Education; WHIP = Wildlife 

Habitat Incentives Program; WRP = Wetlands Reserve Program.

2

 AMA is available in 16 States: Connecticut, Delaware, Hawaii, Maine, Maryland, Massachusetts, Nevada, New Hampshire, New Jersey, New York, Pennsylvania, 

Rhode Island, Utah, Vermont, West Virginia, and Wyoming.

3

 AWEP will vary by State and the types of partnership agreements that are funded each year.

4

 CBWI is available in the six Chesapeake Bay States: Delaware, Maryland, New York, Pennsylvania, Virginia, and West Virginia.

5

 CPPI will vary by State and type of partnership agreements that are funded each year.

6

 MRBI is available in 12 participating States (selected watersheds): Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, 

Tennessee, and Wisconsin.

For many years, financial assistance was provided through the 

Agricultural Conservation Program administered by the Farm 

Service Agency with technical assistance from NRCS. The 1985 

Farm Bill initiated the Conservation Reserve Program that also 

included agroforestry practices.

Gold and Garrett (2009) note that agroforestry practice and 

systems are used interchangeably by many people in the field, 

but it is in the deliberate design, placement, and integration of 

practices within agricultural operations that systems are created—

systems that are capable of addressing a number of issues at 

multiple scales of concern (fig. 3.1; table 3.3). Water and riparian 

zone management is an area of particular focus for efforts that 

integrate intentional tree planting with agricultural and ecological 

objectives. For example, the 2008 Farm Bill and a number of 

related water-quality initiatives17 have supported the widespread 

establishment of riparian buffers. Between 2008 and 2010, about 

13,000 buffers covering about 123,000 acres (50,000 hectares) 

were applied on the ground. The practice is most commonly 

used in Mississippi River Basin States; however, some buffers 

were installed in a total of 47 States.

In addition, numerous regional and local efforts are being 

made along these lines. The 2008 Farm Bill and Range-Wide 

Conservation Plan for Longleaf Pine (America’s Longleaf 

2009), an effort to frame and coordinate longleaf restoration 

throughout the Southeastern United States, will also likely 

further promote agroforestry plantings in the Southern United 

States, with longleaf pine (Pinus palustris) trees integrated into 

either silvopasture or alley cropping systems. Each practice 

provides a means for reestablishing longleaf pine while giving 

landowners the opportunity to generate annual income in several 

ways: (1) through the intensive management of the understory 

(forage), alley (crops), and livestock components; (2) through 

a longer term, higher value income from the pine component 

(e.g., from sawtimber); and (3) potentially from hunting fees, 

carbon sequestration credits, and other environmental services 

markets.

Agricultural forest resources also include “naturally established 

trees.” Although not intentionally established, these trees also 

provide many of the ecosystem services (e.g., carbon sequestration, wildlife habitat, recreational opportunities, and protection 

of water and soil resources) that landowners and society at large 

desire. Although they often occur as small, isolated patches, 

these naturally occurring woodlands, like working tree systems, 

serve as critical islands for supporting a diversity of floral 

and faunal species within agricultural settings, and, thus, they 

have a greater positive impact on biodiversity conservation 

17 These initiatives include the Chesapeake Bay Watershed Initiative, the Mississippi River Basin Healthy Watersheds Initiative, the Upper Mississippi 

Forestry Partnership, the White Water to Blue Water initiative, and Green Lands to Blue Water initiative.
24 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 3.1. Agroforestry practices and their uses at the practice/site levels and their potential placement throughout 

the landscape (Schoeneberger et al. 2001; artwork by G. Bentrup, USDA National Agroforestry Center, Lincoln, NE). 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 25

Table 3.3. Issues in temperate and tropical regions that 

can be addressed by agroforestry technologies.

North America—temperate Tropical regions

• Income diversification

 Market driven 

• Environmental protection

 Water quality

 Soil erosion

• Wildlife habitat restoration

 Biodiversity conservation

• Aesthetics, quality of life

• Renewable energy production

• Climate change

 Carbon sequestration, markets

• Food and energy security

 Tree fodder

 Fuel wood

 Security of land and tree tenure

• Poverty alleviation

 Market-driven income generation

• Building human and institutional 

capacity

 Advancement of women

• Health and nutrition

 Medicinal plants

• Biodiversity conservation

• Protection of watershed services

 Water quality

 Soil erosion

• Climate change mitigation

 Carbon markets

 Desertification

Sources: Gold and Garrett (2009), Garrity (2004).

than implied by the relatively small area of land they occupy 

(Guertin et al. 1997). Numerous naturally occurring strips of 

trees grow along rivers and streams in sections that may be too 

narrow to be considered forest in standard inventory definitions, 

but they exist as remnants of bottomland forests that have been 

partially cleared. Although not specifically planted as a riparian 

forest buffer, these remnants provide the same functions as intentionally planted riparian forest buffers. Also, in agricultural 

areas that still have fencerows, birds perched on the fences often 

plant volunteer trees. Many landowners have removed these 

naturally occurring trees, but, if left in place, either managed or 

unmanaged, these areas serve as wildlife corridors and can also 

function as windbreaks. 

Relationship to Forest Inventory 

Activities

Most working and naturally established trees on agricultural 

lands are not explicitly inventoried by either of the two primary 

natural resource inventories of the United States: the FIA pro­gram of the Forest Service and the NRI of the USDA NRCS 

(Perry et al. 2005). Both programs have slightly differing definitions used for including forest lands in their respective inventories and assign different classifications for those forests that are 

included. Although some agricultural forest areas are included in 

the FIA inventory, the shape of these forests is often too narrow 

and too limited in size (e.g., windbreaks, shelterbelts, and riparian forest buffers) to meet FIA’s definition of forested land.

FIA defines “forest” as land at least 120 feet (37 meters) wide, 

1 acre (.4 hectares) in size, with at least 10 percent cover (or 

equivalent stocking) by live trees of any size, including land 

that formerly had such tree cover and that will be naturally or 

artificially regenerated. Forest land includes transition zones, 

such as areas between forest and nonforest lands that have at 

least 10 percent cover (or equivalent stocking) of live trees and 

forest areas that are adjacent to urban and built-up lands. Roadside, streamside, and shelterbelt strips of trees must have a crown 

width of at least 120 feet (37 meters) and continuous length of at 

least 363 feet (111 meters) to qualify as forest land. Unimproved 

roads, trails, streams, and clearings in forest areas are classified 

as forest if they are less than 120 feet (37 meters) wide or an acre 

in size. Tree-covered areas in agricultural production settings, 

such as fruit orchards, or tree-covered areas in urban settings, 

such as city parks, are not considered forest land (USDA Forest 

Service 2007). 

NRCS defines “forest land” as a land cover/use category that is 

at least 10 percent stocked by single-stemmed woody species 

of any size that will be at least 13 feet (4 meters) tall at maturity. 

Also included is land bearing evidence of natural regeneration 

of tree cover (cutover forest or abandoned farmland) that is 

not currently developed for nonforest use. When viewed from 

above, 10 percent stocking equates to an aerial-canopy cover 

of leaves and branches of 25 percent or greater. The minimum 

area for classification as forest land is 1 acre (.4 hectares), and 

the area must be at least 100 feet (30 meters) wide (USDA 2009). 

This definition of forest land is slightly different from FIA, but 

it similarly excludes many agricultural forest resources.

Getting a complete accounting of all agricultural forest resources, 

in relation to these inventories, is made even more difficult by 

the fact that these plantings exist along a tree-density spectrum 

ranging from many to a few trees, depending on type or practice 

(e.g., a single-row windbreak, to forest farming for agroforestry 

practices or savannah-like isolated trees, to wooded draws for 

naturally occurring trees) and on stage of development (e.g., 

a practice with newly established seedlings to one with fully 

mature trees). This continuum can exist even within a single 

practice, making it more challenging to easily and consistently 

incorporate the continuum into an inventory scheme. A good 

example of this continuum is evident with silvopasture, where 

a site may be established by planting seedlings within a pasture 

or by thinning an existing stand (fig. 3.2). Although the functions of both approaches will ultimately be similar, they will 

probably look quite different, even when fully established.

Because many agricultural and urban forest resources do not 

meet these definitions, current FIA and NRI estimates for forest 

land do not accurately reflect the area and percent of land cover 

these forests occupy, not to mention their productivity, species 

composition, successional stage, age class, and ownership type, 

or the presence and effects that result from biotic and abiotic 

agents (e.g., insects, disease, invasive species, weather events, 

and climate change). The lack of an accurate dataset for agricultural forest resources hinders our ability to estimate and project 

the magnitude of the ecosystem services they can provide. This 
26 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 3.2. Establishment of a silvopasture system from opposite ends of the canopy closure spectrum.

challenge is particularly true for the highly fragmented and linear 

working tree or agroforestry plantings, such as windbreaks and 

riparian forest buffers, which make up most agroforestry plantings currently installed throughout the agricultural and urban 

continuum, and which have been shown to provide significant 

benefits to landowners and society.

Currently Available Data

Because agricultural forest resources are often not fully included 

in national-level forest inventories, such as FIA and NRI, no 

consistent data-reporting stream describes their status over 

time or for all regions of the United States. In 1982, 1987, and 

1992, the NRCS NRI assessed the extent of windbreaks at the 

national scale, but additional rounds of data collection have not 

been completed since 1992, and the dataset that was produced 

is limited only to windbreaks. The 1982-through-1992 trend 

indicated the quantity of windbreaks nationwide decreased by 

about 5 percent.

Other data that exist are limited to one-off studies and simply 

represent a snapshot in time and are applied to limited areas. 

Perhaps the best and largest example of this type of effort is 

the GPI, a collaborative effort between State forestry agencies 

in Kansas, Nebraska, North Dakota, and South Dakota and the 

Forest Service National Inventory and Monitoring Applications 

Center. The GPI provides important information about agricultural forests in the Great Plains States, and, more importantly 

for the purposes of this report, it serves as a model for similar 

activities that could be extended to develop a national inventory 

of forest resources on all agricultural lands.

The attributes of interest for agricultural forest resources are 

much the same as for forest land and urban forests, with a few 

differences. A useful example is the list of attributes chosen for 

the 2008-to-2009 inventories of nonforest areas used in the GPI 

(table 3.4). The goal of the GPI is to “characterize the tree resource 

using methods compatible with those of FIA so a holistic understanding of the resource can be obtained by integrating the two 

surveys.” (Lister 2009: pg. 1). Additional data, however, such as 

Function of Trees (e.g., farmstead, field or livestock windbreak, 

living snowfence), provide an additional level of information 

needed in directing management decisions specific to agricultural forests at the regional and State levels. The GPI inventory 

includes trees and forests in agricultural and urban settings 

(classified as rural land [R] or urban land [U], respectively). In 

this sense, the GPI mirrors the overall purpose of this report, 

which seeks to understand agricultural and urban forests in 

unison and explore the possibility of developing enhanced data 

within the context of current forest inventory activities.

Table 3.4. A listing of the attribute data collected on the 

Great Plains Tree and Forest Invasives Initiative inventory 

plots.

Data type Attribute Plot type1

Plot GPS coordinates U, R

Plot Rural or urban plot U, R

Condition Primary land use2 U, R

Condition Windbreak width (3-m increments) R

Condition Windbreak condition3 R

Condition Windbreak age R

Condition Planted versus natural U, R

Condition Function of trees4 R

Condition NFT land use present/absent R

Condition Canopy cover class U

Condition Owner group (private or Federal/State/local) U, R

Tree Species or genus grouping U, R

Tree Diameter (2.54-cm increments) U, R

Tree Height to location of diameter measurement U, R

Tree Height to base of the live crown (1.5-m increments) U

Tree Height to top of tree (1.5-m increments) U, R

Tree Crown dimensions—perpendicular axis lengths 

(1.5-m increments)

U

Tree Foliage present or absent U

Tree Crown light exposure class U

Tree Crown dieback class U, R

Tree Distance and azimuth to three nearest buildings U, R

FIA = Forest Inventory and Analysis program. GPS = Global Positioning System. 

NFT = nonforest tree.

1

 Plot types are urban (U) and rural (R).

2

 This attribute consists of 17 anthropic and natural classes and includes inaccessible and denied-access areas.

3

 Good, fair, or poor, based on criteria including percent of live trees, windbreak 

completeness, density of trees, presence of invasive species, evidence of diseases, presence of regeneration, and expected longevity.

4

 Tree-planting functions include farmstead, field or livestock windbreak, living 

snowfence, home acreage planting, wildlife habitat planting, abandoned farmstead, 

planted riparian buffer, natural riparian forest buffer, or narrow wooded strip.

Notes: On each plot, different types of data were collected. Plot data characterize the entire plot area. Condition data characterize contiguous areas that are 

formed using land use delineation rules. Tree data are those collected on trees 

not found in conditions that would be classified by FIA as forest.

Source: Lister et al. (2009a).
Assessing the Sustainability of Agricultural and Urban Forests in the United States 27

Using data collected from lands classified as nonforest with trees, 

GPI cooperators were able to develop estimates for (1) acres by 

rural function of the trees (table 3.5), (2) the number of live trees 

by species and genus (table 3.6), and (3) cubic foot volume by 

tree species and genus (table 3.7). Because data were collected 

on working trees (conservation tree plantings) and naturally 

established trees (natural wooded nonplanted strips and isolated 

trees) on the nonforest lands with tree acres, the 2008-to-2009 

GPI inventory estimates show naturally established tree acreage 

outnumbering planted and managed tree acreage that provide 

a specific function or benefit (covering about 5.8 million acres 

[2.3 million hectares] and 1.4 million acres [.6 million hectares], 

respectively, as shown in table 3.5) by a factor of nearly four. 

These findings are counter to what many would generally think 

of occurring in the “tree-less” Great Plains, and they beg the 

question as to the ratio of natural to planted stands that may 

prevail in regions where natural tree cover is considered a 

normal component of undisturbed landscapes.

Table 3.5. Estimated acres by rural function of trees for nonforest areas from the Great Plains Tree and Forest Invasives 

Initiative 2008-to-2009 inventories; 1,018 rural plots across Kansas, Nebraska, North Dakota, and South Dakota.

Function of trees/groupings Four-State total Sampling error (%)

Total acres of rural nonforest areas with trees (1 + 2 + 3) 7,192,847 3.28

1. Isolated trees (no windbreak effect) 5,236,720 4.47

2. All planted and managed tree groupings that provide agroforestry/conservation benefits 1,430,332 6.21

2a. Farmstead/rural acreage windbreak 380,493 12.42

2b.Field windbreak 567,601 10.29

2c. Livestock windbreak 370,918 11.31

2d.Other (living snowfence, wildlife habitat, planted riparian buffer) 111,320 30.55

3. All natural wooded nonplanted or managed tree groupings that provide agroforestry/conservation benefits 525,795 17.32

3a. Natural riparian forest buffer 311,757 20.69

3b.Narrow wooded strip 214,038 30.98

Source: Rasmussen (2009).

Table 3.6. Number of trees by species for rural and urban nonforest areas from the Great Plains Tree and Forest Invasives Initiative 2008-to-2009 inventories; 1,018 rural plots across Kansas, Nebraska, North Dakota, and South Dakota.

Number of trees on nonforest areas Sample error (%)

Urban or 

rural land

Rural land

(1,018 plots)

Urban land

(900 plots)

Urban or 

rural land Rural land Urban land

All species 457,727,233 405,681,452 52,045,780 4.95 5.39 11.57

Redcedar/juniper spp. 61,150,584 57,395,932 3,754,651 12.04 12.73 23.71

Spruce spp. 2,070,409 1,188,709 881,700 23.3 37.44 21.13

Pine spp. 1,189,481 638,846 550,635 55.92 89.82 61.09

Ponderosa pine 4,697,723 3,371,058 1,326,665 26.82 30.05 56.44

Scotch pine 1,224,399 568,599 655,800 25.52 35.5 36.38

Unknown conifer 161,690 — 161,690 48.03 — 48.03

Maple spp. 4,343,304 1,698,884 2,644,419 39.34 67.49 47.9

Boxelder 16,133,318 15,126,390 1,006,928 18.64 19.76 33.63

Silver maple 1,952,524 1,220,336 732,188 28.59 37.4 43.91

Birch spp. 1,553,839 23,201 1,530,639 70.26 100.43 71.31

Hackberry spp. 42,973,682 37,599,777 5,373,905 12.4 13.75 24.12

Ash spp. 84,948,214 80,851,554 4,096,660 14.18 14.88 16.7

Honeylocust spp. 11,386,682 10,146,011 1,240,671 21.41 23.73 30.92

Walnut spp. 3,498,105 1,212,821 2,285,284 24.85 31.17 34.26

Osage-orange 35,163,159 33,430,768 1,732,391 22.4 23.49 34.92

Apple spp. 1,514,003 491,961 1,022,043 21.01 44.32 22.66

Mulberry spp. 18,452,877 15,653,023 2,799,854 13.38 14.62 33.09

Cottonwood and poplar spp. 23,761,322 22,606,254 1,155,068 17.13 17.89 39.84

Cherry and plum spp. 5,164,658 4,387,627 777,031 26.36 30.79 22.09

White oak 8,990,369 7,075,181 1,915,189 30.25 37.12 36.91

Northern red oak 1,454,589 347,465 1,107,124 23.23 50.32 26.11

Willow spp. 19,369,938 18,397,647 972,291 19.8 20.61 58.83

Mountain-ash spp. 113,522 95,177 18,345 61.33 70.57 100

Basswood spp. 299,437 130,853 168,584 35.2 73.84 24.99

Elm spp. 37,997,665 31,785,504 6,212,161 11.75 12.92 28.27

Siberian elm 48,828,792 45,373,796 3,454,995 15.4 16.45 26.71

Saltcedar 95,883 95,883 — 61.31 61.31 —

Russian-olive 6,851,894 6,775,025 76,869 55.27 55.89 50.73

Unknown hardwood 12,385,171 7,993,169 4,392,002 21.25 30.77 21.31

Source: Rasmussen (2009).
28 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Table 3.7. Volume of wood material by species in Nebraska for rural and urban nonforest areas from the Great Plains 

Tree and Forest Invasives Initiative 2008-to-2009 inventories; 473 plots.

Cubic feet (volume) Sample error (%)

Urban or 

rural land

Rural land

(273 plots)

Urban land

(200 plots)

Urban or 

rural land Rural land Urban land

All species 1,197,851,451 1,029,114,765 168,736,686 9.31 10.61 13.41

Redcedar/juniper spp. 104,679,072 99,922,733 4,756,338 15.89 16.52 42.56

Spruce spp. 6,826,779 134,636 6,692,143 59.82 56.94 61.01

Pine spp. 1,149,376 2,832 1,146,544 53.73 71.25 53.86

Ponderosa pine 16,355,515 15,676,071 679,444 94.17 98.2 75.05

Scotch pine 13,484,649 8,662,964 4,821,685 29.19 40.02 38.65

Unknown conifer 899,170 — 899,170 79.51 — 79.51

Maple spp. 2,490,979 37,874 2,453,105 63.28 77.58 64.24

Boxelder 19,681,365 18,815,638 865,727 49.6 51.78 69.67

Silver maple 36,515,083 14,144,474 22,370,608 28.82 54.24 32.21

Birch spp. 691,002 — 691,002 73.34 — 73.34

Hackberry spp. 78,128,686 55,767,826 22,360,859 28.06 37.7 27.8

Ash spp. 134,401,630 122,485,896 11,915,734 31.72 34.64 35.12

Honeylocust spp. 30,976,600 24,681,327 6,295,273 37.71 45.7 48.27

Walnut spp. 3,649,265 1,124,073 2,525,193 44.17 42.09 61.01

Osage-orange 16,453,870 16,052,126 401,743 32.51 33.23 100

Apple spp. 2,735,117 252,735 2,482,382 47.18 55.43 51.67

Mulberry spp. 44,514,022 37,340,146 7,173,876 17.75 19.96 36.67

Cottonwood and poplar spp. 348,073,545 331,651,606 16,421,939 25.18 26.31 50.14

Cherry and plum spp. 15,308,859 14,615,034 693,825 89.69 93.93 35.02

White oak 39,428,806 26,116,997 13,311,809 54.91 77.59 57.25

Northern red oak 4,266,768 183,663 4,083,105 32.05 100.43 33.19

Willow spp. 56,101,791 55,166,341 935,451 47.29 48.08 75.23

Basswood spp. 6,646,095 727,083 5,919,012 50.85 99.79 55.77

Elm spp. 53,406,451 45,634,354 7,772,097 21.54 24.33 38.92

Siberian elm 136,747,213 120,601,811 16,145,402 18.83 20.85 34.2

Russian-olive 8,631,554 8,551,995 79,559 92.94 93.8 100

Unknown hardwood 15,608,188 10,764,529 4,843,659 40.77 57.22 33.08

Source: Rasmussen (2009).

Inventory data of this type provide the initial basis for developing 

assessments of potential economic and ecological effects of agricultural forests and their relation to emerging issues. In the case 

of the Great Plains, a high-priority concern is the destruction of 

the ash (Fraxinus spp.) resource by the emerald ash borer (Agrilus 

planipennis; EAB). The data in table 3.6, which lists the number 

of trees by species across all four States, and table 3.7, which lists 

the volume of wood material by tree species in Nebraska, demonstrate the dominance of ash, and thus emphasizes its relevance 

to regional- and State-level management directions. Individual 

State-level information is particularly important, because this 

level is where practical management decisions commonly occur. 

This example also illustrates the importance of including data on 

forest health and disturbance processes in inventory activities. In 

general, the GPI inventory results strongly support the need for 

accounting for all tree resources in rural and agricultural landscapes, and not only those established with agroforestry practices 

and using Farm Bill Program support.

The GPI inventory provides an initial model for future inventory 

work. The recently completed GPI inventory in Kansas, Nebraska, 

North Dakota, and South Dakota offers one potential way to 

efficiently inventory—using consistent protocols—agricultural 

and urban forest resources nationwide. The GPI State forestry 

agencies cooperated with the Forest Service National Inventory 

and Monitoring Applications Center to develop and use a modified 

FIA protocol that lacks some of the data collected on a standard 

FIA plot (Lister et al. 2009b). It appears, however, that sufficient 

data exist to report on several of the most fundamental measures 

(e.g., area and percent of forest, by age class; effects, by biotic 

and abiotic agents).

Anecdotal reports from State forestry personnel indicate the 

cost of the GPI inventory was much less than for a traditional 

FIA inventory on forest lands. A cost comparison that includes 

all the direct and indirect costs of the GPI inventory (e.g., support 

from Forest Service FIA personnel), however, would be needed 

before broader conclusions can be made. The use of a modification of the Forest Service FIA protocol for the GPI enabled 

State personnel to leverage the infrastructure and institutional 

knowledge contained in the FIA program, and the combination 

of estimates from both surveys produced a more holistic understanding of the tree resources in these States. Furthermore, using 

proven FIA techniques (including data recorder software and 

reporting tools) helped to contain costs compared with creating 

a completely new inventory infrastructure. The GPI is the best 

example of an inventory spanning agricultural and urban forest 

resources that we have to date; it serves as a possible model 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 29

for sustained reporting activities in this area. Any such efforts, 

however, will likely be modified considerably. Further details 

of possible strategies to accomplish this goal are addressed in 

in chapter 5.

Benefits Associated With 

Agricultural Forests

The benefits and services that have been identified to date from 

working trees and forests in agricultural settings are wide ranging and are limited as much by our current understanding of 

landscape systems as by the actual role these resources play. A 

short list of benefits includes (1) maintaining air, water, and soil 

quality; (2) mitigating climate change and increasing adaptability 

to its effects; (3) enhancing crop productivity and protecting 

livestock; (4) conserving energy; and (5) diversifying income. 

(See relevant chapters in Garrett [2009]; additional information 

is also available at http://www.unl.edu/nac/workingtrees.htm

[August 2015]). In addition to providing these relatively tangible 

benefits, trees provide an aesthetic contribution to rural landscapes, and serve a role in preserving biodiversity as a practical 

benefit to mankind and as a value in its own right. As noted 

previously, many of these benefits and services are also derived 

from naturally established trees in agricultural settings.

Agroforestry provides numerous opportunities to enhance the 

benefits flowing from agricultural forests by applying innovative techniques and time-tested practices. In chapter 1 of North 

American Agroforestry: An Integrated Science and Practice 

(Garrett 2009), the authors state that “agroforestry in the United 

States and Canada is driven by sustainable development and 

growth in the ‘green’ marketplace, which will help mitigate 

rural decline and harmful environmental impacts of agriculture” 

(Gold and Garrett 2009: pg. 46). They add that “global awareness of tropical agroforestry has positively affected the development of agroforestry in the United States and Canada, and 

many of the practices are adopted from the tropics” (Lassoie 

et al. 2009: pg. 46). They also note that North American agroforestry “is in an active phase of development and has emerged 

during the past decade as a science and a defined set of practices, 

shaped and tailored to address urgent land use sustainability 

issues” (Lassoie et al. 2009: pg. 46).

Although agroforestry practices can be used to pursue a broad 

range of objectives in sustainable landscape management, two 

areas in particular are currently receiving focused attention in 

policy and management discussions. These practices are (1) the 

expanded use of agroforestry techniques to enhance ecosystem 

services and take advantage of the nascent market opportunities 

associated with them and (2) the potential renewable energy 

production from agroforestry applications.

Increased Tree Planting for Carbon 

Sequestration and Other Environmental 

Service Markets

The 2008 Farm Bill (Section 1245—Environmental Services 

Markets) and the American Clean Energy and Security Act of 

2009 (House Resolution 2454) each provide an initial framework for facilitating participation in carbon offset credit trading 

and other ecosystem services markets through tree plantings 

and related forest management on agricultural lands. Should 

carbon offset markets become widespread, particularly at the 

national level, they could provide an additional income source to 

agricultural landowners and, thus, motivate an increased interest in mixing trees with other agricultural production activities. 

Moreover, considerable development of market mechanisms at 

the regional level is aimed at preserving and enhancing water 

quality, biodiversity, and other ecosystem services. Biofuels 

may represent another growing opportunity to enhance farm 

incomes using trees.

Agroforestry is an appealing option for sequestering carbon on 

agricultural lands because it can sequester significant amounts 

of carbon while leaving the bulk of the land in agricultural 

production. The cash earnings potentially gained from carbon 

sequestration can help diversify farm incomes, an important 

consideration given the unpredictability of crop prices. This 

sequestration can all be achieved while providing many of the 

other services associated with agricultural forests (Schoeneberger 2008). The Intergovernmental Panel on Climate Change’s 

Technical Paper V (Gitay et al. 2002), which was developed in 

response to a request made by the United Nations Convention 

on Biodiversity, identifies agroforestry as a carbon-sequestering 

activity that can create more biologically diverse systems than 

conventional agricultural lands, having beneficial effects on 

aboveground and belowground biodiversity. Again, the benefit 

of agroforestry lies in its ability to meet multiple purposes and 

contribute to the creation of multifunctional landscapes, thereby 

meeting multiple objectives.

The Congressional Research Service further supports the carbon 

sequestering potential of agricultural forests in its report, U.S. 

Tree Planting for Carbon Sequestration (Gorte 2009: pg. 1), 

which states that “tree planting has greater carbon sequestration 

potential than other land use practices” and that “afforestation of 

crop or pasture land is estimated to have the potential to sequester 

between 2.2 and 9.5 metric tons of CO2 [carbon dioxide] per 

acre per year” (table 3.8). The report notes that “these estimates 

have a very wide range of possibilities because tree growth and 

forest soil carbon accumulation varies widely among species 

and locations” (Gorte 2009: pg. 1. See also Smith et al. 2006). 

Of course, tree planting for carbon sequestration would have 

to be balanced against food production and related activities, 

and the effect of afforestation would have to take into account 
30 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Table 3.8. Estimated sequestration potential for selected 

U.S. land use practices.

Activity

(in metric tons of CO2

per acre per year)

EPA (2005) USDA (2004)

Afforestation (previously cropland/pasture) 2.2–9.5 2.7–7.7

Reforestation 1.1–7.7 —

Riparian or conservation buffers (nonforest) 0.4–1.0 0.5–0.9

Reduced/conservation tillage 0.6–1.1 0.3–0.7

Grazing management 0.1–1.9 1.1–4.8

EPA = U.S. Environmental Protection Agency. USDA = U.S. Department of 

Agriculture. CO2 = carbon dioxide.

Sources: Adapted from Gorte (2009). EPA: EPA Office of Atmospheric Programs 

(2005: table 2-1). USDA: Lewandrowski et al. (2004: table 2.2).

potential changes in land use elsewhere. Afforestation and agroforestry applications, however, when appropriate, can provide an 

effective way to secure carbon sequestration while potentially 

enhancing other ecosystem services and augmenting farm 

incomes.

One potential role for an inventory of agricultural forest resources would be to provide a data foundation for better carbon 

accounting. This database would have to be married to some form 

of carbon modeling to translate inventory data into estimates of 

carbon storage and flux. The National Report provides exactly 

such an estimate for conventional forests under Criterion 5. 

Although we are not able to estimate current national levels of 

carbon sequestration from tree-based plantings on agricultural 

lands, tools, such as NRCS’s COMET 2.0 (http://www.comet2.

colostate.edu/) have been developed to assess tree-contributed 

carbon at the individual entity (farm/ranch) level. The latest 

version of COMET (COMET-Farm, released in June of 2013 

and available at http://www.cometfarm.nrel.colostate.edu/

[August 2015]) does not currently have this capability but 

will include an improved component for estimating carbon for 

agroforestry and other woody perennial plantings on farms and 

ranches by 2016. Carbon estimates from these plantings can 

also be made from data collected using FIA inventory protocols 

(as was used, for example, in the GPI inventory) and potentially 

with two other Forest Service tools: i-Tree (discussed in the 

context of urban forests in chapter 4) and the Forest Vegetation 

Simulator (Dixon 2002). In any case, an inventory of agricultural forests will need to consider exactly what kind of information is needed to render reliable estimates of aboveground and 

belowground carbon sequestration. In particular, the ability to 

accurately estimate woody biomass in agroforestry plantings is 

critical to a full accounting of the current carbon pool and the 

future potential for carbon sequestration on agricultural lands. 

Another aspect will be the measurement of revenues generated 

from the provision of environmental services (Indicator 27 in the 

National Report), which is carbon sequestration in this instance, 

although coverage certainly can (and should) be extended to 

other services when revenues do exist. 

Renewable Energy Feedstock From 

Agroforestry

Plant material, such as wood and grass, potentially represents a 

substantial source of domestic renewable energy feedstock that 

is considered carbon neutral in the human time scale (because 

plants grow back). Various methods exist that enable these renewable feedstocks to be produced, harvested, and converted to 

products; making bioenergy and coproduct production promising 

options. Although the cost of biomass feedstock is still high 

relative to its inherent energy content, researchers and investors 

continue to find new, cost-effective solutions to bring bioenergy 

and coproducts to the marketplace. Awareness and interest are 

growing in using agroforestry plantings as a means to augment 

cellulosic feedstock production here in the United States. Many 

of the practices, particularly windbreaks, alley cropping, and 

riparian forest buffers, readily lend themselves to expanded 

designs and management options that would enable coproduction of feedstock from these plantings with the other services 

being targeted by landowners and society.

The potential increases in tree planting due to expanding carbon 

offset markets (as discussed in the previous section) are also 

likely to result in a greater supply of cellulosic feedstock for 

energy production from agricultural forests. The definition of 

“renewable biomass” in HR 2454 is very broad (i.e., any organic 

matter that is available on a renewable basis from non-Federal 

land...) and includes woody biomass from agricultural forests 

and other feedstocks that could potentially be mixed with it, including crop residue and waste from animals, construction, food, 

yards, etc. The opportunities for using agroforestry applications 

to produce energy in conjunction with other feedstock streams 

and with the provision of other environmental services could 

prove to be fertile ground for developing innovative techniques 

and diversified income streams. A direct measure of this activity 

would be the application to agricultural forests of the Montréal 

Process (MP) indicator measuring the use of forest biomass for 

energy generation (Indicator 24 in the National Report). The 

advent of any major use of agroforestry in energy production 

would also lead to major changes in the role and extent that 

forests and trees have on agricultural lands as a whole, however, 

and any inventory will need to be flexible enough to register 

these changes should they occur.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 31

Major Threats and Influences 

That Affect Agricultural Forest 

Resources

Agricultural forest resources are threatened by many of the 

same native and invasive insects, diseases, invasive plants, 

and abiotic agents (e.g., wind, drought, flooding, fire, climate 

change) as conventional and urban forests. For conventional 

forests, these disturbance agents and their effects are covered 

under the two indicators in Criterion 3 in the National Report. 

Elevated levels of forest disturbance and mortality, especially 

those associated with insect infestations, were identified as 

perhaps the most troubling overall finding of the 2010 edition 

of National Report. In a related 2006 study, the Forest Service 

completed a strategic assessment for risk of tree morality 

because of major insects and diseases, and estimated that a 

total of 58 million acres (23 million hectares) in the contiguous 

United States (including about 27 million acres [11 million 

hectares] of private, county, and State lands) are at risk18 from 

insects and diseases (USDA Forest Service 2006; fig. 3.3). 

Most of this risk can be attributed to 42 risk agents, including 

13 nonnative (exotic) forest pest species already established 

in the contiguous United States and Alaska. Although only 

FIA data from forest land were used in this risk assessment, it 

should be assumed that risks for tree species on forest land are 

mostly the same as in agricultural settings where these species 

also are found.

The ash (Fraxinus spp.) species is an example of a tree that is 

threatened on all lands on which it occurs, and the continuing 

health of this species is the focus of considerable management 

activity. The primary goal of the GPI, for example, is to prepare for the arrival of invasive pests, such as the EAB, which 

the GPI cooperators describe as a “highly invasive, exotic 

insect that attacks and kills all species of North American ash 

trees” (Rasmussen 2009: pg. 1). The GPI cooperators note that 

after its introduction into the United States from China in the 

1990s, the EAB has killed more than 50 million ash trees in 

the Northeastern and North Central United States and in the 

provinces of Ontario and Quebec in Canada. As of July 2012, 

the EAB has not been detected west of Iowa, Minnesota, and 

Missouri, but the threat to the Great Plains States is very real, 

owing to the large number of ash trees that are found in this 

region—an estimated 85 million ash trees exist on acres classified as “nonforest-with-trees” in the four Great Plains States 

Figure 3.3. Acres of forested land at risk of mortality to insects and diseases (USDA Forest Service 2006).

18 The threshold for mapping risk in the assessment was the expectation that, without remediation, 25 percent or more of the standing live basal area on trees 

more than 1 inch in diameter will die during the next 15 years because of insects and diseases.
32 Assessing the Sustainability of Agricultural and Urban Forests in the United States

(table 3.6). Resource managers need to know the total area and 

relative locations of these at-risk species to make informed 

management decisions and formulate policies and programs 

supporting management actions.

Wildland fire poses a significant threat to forest land and to 

some forest resources in agricultural settings, as suggested 

by the map of departure from reference condition vegetation, 

fuels, and disturbance regimes in many landscapes in the 

contiguous United States (fig. 3.4). The large number of wildfires encompassing more than 250 acres (101 hectares) also 

illustrates the fire threat to agricultural forests in many parts 

of the United States. Management of agricultural forests and 

immediately adjacent land is needed to reduce fuel loads but 

is often not done. With greater use of silvopasture systems, 

however, potential wildfires in southern and western landscapes 

could be reduced, because a well-managed silvopasture system 

maintains low fuel levels.

Data Adequacy and Major Data 

Gaps

As discussed previously, data for agricultural forest resources 

are inadequate because many working trees and naturally 

established trees are not explicitly inventoried by either FIA or 

NRI, the two primary natural resource inventories of the United 

States. The incomplete nature of the data is illustrated by the 

estimated 458 million trees on rural and urban “nonforest-withtree” acres estimated by the GPI inventory in Kansas, Nebraska, 

North Dakota, and South Dakota (table 3.6). The 7.2 million 

acres (2.9 million hectares) estimated by the GPI cooperators 

(table 3.5) is significantly more than the 4.1 million acres (1.7 

million hectares) of private forest reported for the four Great 

Plains States in Forest Resources of the United States, 2007 

(Smith et al. 2009), which includes only lands that meet the 

FIA definition for forested land use. The conclusion in this 

Figure 3.4. Current Fire Regime Condition Class in the contiguous United States (http://www.frcc.gov [August 2015]).

Notes: Fire Regime Condition Class (FRCC) is an interagency, standardized tool for determining the degree of departure from reference condition vegetation, fuels, and 

disturbance regimes. Assessing FRCC can help guide management objectives and set priorities for treatments. FRCC assessments determine how similar a landscape’s 

fire regime is to its natural or historical state. FRCCs are divided into three categories: FRCC I landscapes contain vegetation, fuels, and disturbances characteristic of 

the natural regime; FRCC II landscapes are moderately departed from the natural regime; and FRCC III landscapes reflect vegetation, fuels, and disturbances that are 

uncharacteristic of the natural regime. So, essentially, a landscape in FRCC I has key ecosystem components intact, such as large old trees and soil characteristics that 

would naturally be found on that site. An FRCC II landscape has land that is not very similar to its natural regime in terms of vegetation, disturbance, or both. An FRCC 

III landscape has lost key ecosystem components (e.g., the loss of characteristic large trees due to uncharacteristic wildfires that occurred in uncharacteristic fuels).

Source: LANDFIRE: Fire Regime Groups, U.S. Department of Agriculture and U.S. Department of the Interior. Accessed 24 November 2015 at http://www.landfire.gov/

geoareasmaps/2012/CONUS_EVT_c12.jpg.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 33

report is that the amount of nonforest land with trees (not 

covered by existing inventories) is significantly larger than 

the amount of forest land in the four Great Plains States that is 

currently inventoried. The extent to which this finding extends 

to other regions with a high proportion of agricultural lands 

is very much an open question, one that cannot be answered 

without adequate inventories of agricultural forests.

Perry et al. (2009) reported large data gaps owing to the exclusion of certain trees and forests from existing inventories for 

the Great Plains States and smaller gaps for Illinois, Indiana, 

Iowa, Michigan, Minnesota, Missouri, and Wisconsin. By 

comparing estimates of land area with tree cover between the 

Vegetation Continuous Field (VCF—a global dataset derived 

from MODIS [MODerate Resolution Imaging Spectrometer] 

satellite imagery) and FIA, they found significant differences in 

those estimates in Kansas, Missouri, Nebraska, North Dakota, 

and South Dakota. They also reported large areas of missing 

trees that generally increased while moving westward across 

the 11-State region (fig. 3.5). Moreover, Zomer et al. (2009), 

in their report on the global extent and patterns of agroforestry, 

noted that moderate levels of between 10 and 30 percent tree 

canopy cover describe most agricultural land in Midwestern 

North America. These tree-cover estimates were made from 

MODIS VCF remote-sensing data. The fact that significant differences exist between estimates of forest canopy from FIA and 

VCF estimates indicates that in nonforest areas the information 

gap is probably even greater.

Figure 3.5. Forest land and missing tree fractions 

derived from Forest Inventory and Analysis data 

(from Perry et al. 2009).

Note: Missing tree fraction is determined by comparing FIA (Forest Inventory and 

Analysis) forest land area estimates with MODIS (MODerate Resolution Imaging 

Spectrometer) VCF (Vegetation Continuous Field) estimates of tree canopy cover.

The overall conclusion is that the extent of agricultural forests 

is considerable, in absolute terms and, in some regions at least, 

relative to the area of conventional forests. With the exception 

of those States covered by the GPI, however, we have little to 

no idea as to the actual size of this resource. Satellite imagery 

and other remotes sensing techniques may provide a relatively 

cost-effective way to get at this most basic question of total 

area, but the crucial questions of species composition, stand 

structure and age, or forest health conditions cannot be answered 

with a reasonable degree of accuracy through this approach. 

For this type of information, on-the-ground sampling—similar 

to that undertaken by the FIA—will be needed.

The foregoing discussion on data gaps focuses on the information 

needed to produce a biophysical inventory. The MP C&I, however, 

seek to be comprehensive in their coverage of the information 

important to understanding forest sustainability, and it includes 

a number of economic and social indicators that fall outside the 

scope of standard inventories and are not included in the GPI 

or similar efforts. Nonetheless, a biophysical inventory is a core 

requirement of any broader sustainability assessment.

Given the lack of national inventory data, a national-level 

report on agricultural forests based on the MP C&I would have 

little or no substance. Using the GPI as a model, however, we 

can anticipate how a national inventory of agricultural forest 

resources could meet the general requirements of the MP C&I 

and similar forest sustainability reporting efforts. Although a 

number of the 54 MP indicators will not really be applicable to 

agricultural forests (see discussion in previous chapter), many 

others, particularly those addressing the biophysical characteristics of forests, can readily be applied to agroforestry plantings 

and natural forests on agricultural lands. Many of the measures 

in the GPI (table 3.4) can help derive estimates of such variables 

as areal extent, stocking volumes, forest health and disturbance 

incidence, and species composition. These measures are the 

building blocks of any inventory, and they also fit some basic 

requirements of the MP C&I.

The MP C&I can be used to suggest additional variables to be 

sampled in a GPI-type inventory for agricultural (and urban) 

lands. For example, Criterion 4, with its emphasis on soil and 

water resources, would suggest the inclusion of some form 

of soil descriptor, in terms of type or condition, and perhaps 

a spatial measure, such as distance to nearest body of water. 

The indicators addressing nontimber forest products (NTFPs) 

in Criteria 2 and 6 suggest measures that would indicate the 

presence or absence of regionally important NTFPs. The MP 

C&I also suggest a number of variables that could be modeled 

or otherwise derived from the inventory data. In this regard, 

the GPI attribute of “function” could be used to address several 

of the socioeconomic indicators in Criterion 6, particularly in 

relation to environmental services, although the categories used 
34 Assessing the Sustainability of Agricultural and Urban Forests in the United States

for this attribute (note 3 in table 3.4) would likely have to be 

expanded to accomplish this task. Likewise, the GPI measure 

of “Primary Land Use” (note 1 in table 3.4) could provide important information about ownership type and protected status 

needed to address indicators in Criterion 1.

Other MP indicators would need to be developed largely 

outside of the inventory-reporting stream. Initial ideas on how 

to develop these variables are included in the indicator-byindicator development presented in chapter 5. In any case, the 

aim is not to fully replicate the MP C&I for agricultural and 

urban forests, as much as it is to use it as a reference and guide 

in designing a comprehensive data framework for understanding the sustainability of these forest resources.

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36 Assessing the Sustainability of Agricultural and Urban Forests in the United States
Assessing the Sustainability of Agricultural and Urban Forests in the United States

Assessing the Sustainability of Agricultural and Urban Forests in the United States 37

Chapter 4 David Nowak

Urban Forests

Urban forests (and trees) constitute the second forest resource 

considered in this report. We specifically emphasize the fact 

that agricultural and urban forests exist on a continuum defined 

by their relationship (and interrelationship) with a given landscape. These two forest types generally serve different purposes, 

however. Whereas agricultural forests are considered primarily 

in terms of their contribution to biodiversity conservation or, 

as in the case of agroforestry, to agricultural production, urban 

forests are assessed primarily in terms of the range of environmental services and values they provide to urban and suburban 

residents. The potential list of services is extensive and will 

vary according to different individuals, organizations, and locations, with many services being difficult to precisely quantify. 

Trees affect numerous environmental processes, such as water 

cycling; sound propagation; and pollution formation, dispersion, 

and removal. Trees also directly affect human populations by 

altering the social, economic, health, and aesthetic aspects of 

urban environments. These effects exist in all treed landscapes 

but are more prominent in urban areas because of the higher 

concentration of people.

As in the previous chapter, this chapter begins with a general 

description of the resource, including formal definitions. This 

first section also includes a brief listing of environmental 

services associated with urban forests and the specific threats 

they face. The second section presents currently available data 

for understanding urban forests at the national scale. These data 

rely heavily on satellite imagery and are focused on describing 

the extent of forest cover in urban areas. The chapter concludes 

with a discussion of the adequacy of the current information 

base and strategies for improving it.

Definitions and Characteristics 

of Urban Forest Ecosystems

Urban forests are defined by their proximity to human populations and include numerous physical elements that constitute 

urban development. The characteristics of these forests are 

determined by both their natural components and the anthropogenic elements in the landscapes in which they occur.

Definitions

For purposes of this report, urban forests are composed of all 

the trees within our urban lands. The definition conceptually 

extends to include the various ecosystem components that 

accompany these trees (e.g., soils or understory flora), although 

we do not explicitly identify all these components. Urban forests 

can contain forested stands, like in rural areas, but they also 

contain trees found along streets, in residential lots, in parks, 

and in other land uses. The forests are a mix of planted and 

naturally regenerated trees. For data gathering and reporting 

purposes, the key to defining urban forests lies in the definition 

of what precisely constitutes urban land. Using the Census 

Bureau’s definition, urban land consists of all territory, population, and housing units located within either urbanized areas or 

urban clusters (Census Bureau 2014).

Urbanized areas consist of densely settled territories that contain 

50,000 or more people; urban clusters consist of densely settled 

territories that have at least 2,500 people but fewer than 50,000 

people (fig. 4.1). Urbanized area and urban cluster boundaries 

encompass densely settled territories and are defined by—

 A cluster of one or more block groups or census blocks with 

a population density of at least 1,000 people per square mile.

 Surrounding block groups and census blocks with a population density of 500 people per square mile.

 Less densely settled blocks that form enclaves or indentations 

or that are used to connect discontinuous areas (Census 

Bureau 2014). 

This definition of urban lands is based solely on census blocks 

and their population density. Census blocks, in turn, are determined in part by physical features on the land, both constructed, 

such as roads and rail lines, and natural, such as rivers and 
38 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 4.1. Urban areas in the contiguous United States, 2000, based on the Census Bureau definition of urban land 

(Nowak and Dwyer 2007).

ridgelines. (Additional information is available at the Census 

Bureau’s Web site—http://www.census.gov/ [August 2015].) 

The resulting definitions of urban lands will not always match 

the jurisdictional boundaries of cities and towns. Urban forests, 

however, are most commonly managed at the municipal level. 

A uniform definition that can consistently span different jurisdictional boundaries is essential for developing consistent national 

and regional inventories, especially if the inventories are to 

be combined with inventories from other land use classes, but 

jurisdictional boundaries will often be crucial in determining 

how, and if, forest resources will be managed. Assessments 

conducted within jurisdictional boundaries (community forests) 

and urban boundaries (urban forests) can be found within State 

reports at http://www.nrs.fs.fed.us/data/urban (August 2015). 

Information about wildland-urban interfaces, or WUIs, is available

at http://www.nrs.fs.fed.us/disturbance/fire/wui/ (August 2015).

Characteristics of Urban Forests 

Urban forest ecosystems have many special characteristics that, 

in combination, distinguish them from other forest types. These 

characteristics include (1) close proximity to large or dense 

human populations, (2) relatively high diversity of species and 

forest patch structures, (3) multiple public and private ownership types, and (4) management often geared toward sustaining 

tree health and ecosystem services. More than 80 percent of the 

U.S. population lives in urban areas; thus, urban forests greatly 

influence the day-to-day lives of most Americans.

These influences include positive and negative experiences (see 

Associated Benefits and Costs in the following section). Often, 

the only “nature” some urbanites experience in their lives is 

from contact with urban forests. These trees and forests provide 

an array of species and structural diversity that is not typically 

found in other forests. Species richness and diversity in urban 

forests are typically greater than what is found in surrounding 

native stands, with urban forests containing varying proportions 

of nonnative tree species (Nowak 2010). Not only are species 

diverse, but the tree configurations in urban areas also can be 

diverse, crossing many land use types and including single tree 

specimens, linear rows of street trees or trees along fence rows, 

and large patches of intact forest stands. The diversity of trees 

is often dwarfed by the diversity of landowners in urban areas. 

The ownership of trees ranges from numerous small parcels of 

family homes, to private commercial tracts, to varying-sized 

public properties with varying densities of trees. Urban trees 

include a mix of planted and naturally regenerated species 

(Nowak 2012) and often are managed to sustain tree health and 

benefits and to minimize risk to or conflict with human populations. They typically are not managed as a crop to be harvested; 

rather, they are a landscape element to be enhanced or sustained.

Urban Forest Sustainability

One main objective of urban forest management is to provide 

for optimal and sustainable benefits from trees for current and 

future generations. To promote optimum sustainability, managers

need to understand the current resource and how it is changing 

so they can properly guide the resource to a desired future state. 

Tree cover in urban areas has been declining in recent years 

(Nowak and Greenfield 2012b) and tree cover is constantly 

changing due to various natural and anthropogenic forces. 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 39

Natural forces for change include natural regeneration, tree 

growth and tree mortality from insects and diseases, storms, 

fire, old age, etc. Anthropogenic factors that influence tree 

cover include tree planting and tree mortality or removal from 

either direct or indirect human actions such as development and 

pollution. The combination of these factors through time determines existing and future forest structure, species composition,

and tree-cover levels.

Sustaining desired levels of services or benefits is most easily 

related to sustaining a certain level and distribution of tree cover. 

Sustaining a desired level of canopy cover requires ensuring 

an adequate establishment of new trees (via planting or natural 

regeneration) to offset loss in tree canopy due to tree mortality. 

Determining the exact tree establishment rate is difficult because

trees grow (increasing canopy through time), trees are different 

sizes (canopy loss from the removal of one large tree cannot be 

replaced by planting one small tree), and the system is constantly

changing due to human (e.g., development) and natural (e.g., 

storms) factors that can create drastic cover changes in a short 

period of time. Although sustaining canopy cover is important, 

it is different from optimizing canopy cover, which requires 

additional information on species and locations to ensure the 

optimal distribution of benefits at minimal cost over time.

Monitoring urban forests is critical to ensure sustainable, optimal, and healthy urban forests. Monitoring data can be used to 

detect changes and determine if management plans are meeting 

their desired goals. By monitoring, managers can better understand how the resource is changing and management plans 

can be adjusted to ensure healthy urban forests that meet the 

desired goals of the local residents and sustain forest benefits 

for future generations.

Benefits and Costs Associated With 

Urban Forests

Urban trees provide innumerable annual ecosystem services 

that affect the local physical environment (such as air and water 

quality) and the social environment (such as individual and 

community well-being). These services can positively influence 

urban quality of life but also have various costs (Nowak and 

Dwyer 2007). Urban forest services (benefits) and disservices 

(costs) include, but are not limited to, the following.

Energy conservation and carbon dioxide sequestration. Trees 

reduce energy needs for heating or cooling buildings by shading buildings in the summer, reducing summer air temperatures 

(primarily through transpirational cooling), and by blocking 

winter winds. Trees also can increase heating needs, however, 

by shading buildings in the winter if planted in improper locations close to structures. The energy effects of trees vary with 

regional climate and their location around the building (Heisler 

1986).

Urban trees reduce carbon dioxide (CO2), a major greenhouse 

gas, by directly removing it from the atmosphere and storing 

(“sequestering”) the carbon in the trees as biomass. By reducing building energy use, trees can also reduce the emission 

of CO2 from power plants. Tree-maintenance activities often 

require the use of fossil fuels that emit CO2, however, and 

improperly located trees around buildings can increase energy 

demands and consequent emissions of CO2 (e.g., Nowak 2000; 

Nowak et al. 2002b).

Air quality. Trees influence air quality in a number of ways. 

Trees remove pollution from the air by intercepting airborne 

particles on their leaves and branches, and absorbing gaseous 

pollutants into their leaves via stomata. Pollution removal by 

trees within a city can be on the order of thousands of tons 

annually, with air-quality improvement typically less than 1 

percent (Nowak et al. 2006a). Trees also emit various volatile 

organic compounds that can contribute to the formation of 

ozone (O3). By lowering air temperatures via transpirational 

cooling and shading, however, trees lower the emission of 

volatile organic compounds from vegetation and numerous 

anthropogenic sources (e.g., gasoline), thus reducing the potential for ozone formation. In addition, trees can produce pollen 

that can exacerbate allergies. Finally, by reducing building energy requirements, trees reduce pollutant emissions from power 

plants, thereby improving air quality (Nowak 1994; Nowak et 

al. 2006a; Nowak and Dwyer 2007).

Urban hydrology. By intercepting and retaining or slowing 

the flow of precipitation reaching the ground, urban forests can 

play an important role in urban hydrologic processes. They 

can reduce the rate and volume of stormwater runoff, flooding 

damage, and stormwater treatment costs, and they can enhance 

water quality. Estimates of runoff for an intense storm in 

Dayton, OH, for example, showed that the existing tree canopy 

reduced potential runoff by 7 percent; a modest increase in 

the canopy would have reduced runoff by nearly 12 percent 

(Sanders 1986). The greatest percent of rainfall interception 

occurs during the more common small storm events. During 

large rain events, the percent of rainfall interception can drop 

to a very small percent as most of the rain reaches the ground. 

During these large storm events, trees exert a relatively small 

effect from rainfall interception. To better manage storm 

runoff, a number of U.S. cities are moving forward with the use 

of enhanced tree plantings in combination with other “green 

infrastructure” in lieu of expanded pipe and culvert networks, 

or “grey infrastructure” (Philadelphia’s Green Infrastructure 

Plan is a notable example).

Noise reduction. Properly designed plantings of trees and 

shrubs can significantly reduce noise levels (Anderson et al. 

1984). Wide belts (approximately 100 feet [30 meters]) of tall 

dense trees combined with soft ground surfaces can reduce 
40 Assessing the Sustainability of Agricultural and Urban Forests in the United States

apparent loudness by 50 percent or more (6 to 10 decibels) 

(Cook 1978). Although noise reduction from plantings along 

roadsides in urbanized areas often is limited due to narrow 

roadside planting space (less than 10 feet [3 meters] in width), 

reductions in noise of 3 to 5 decibels can be achieved with narrow dense vegetation belts with one row of shrubs roadside and 

one row of trees behind (Reethof and McDaniel 1978).

Quality of life. The presence of urban trees can make the 

urban environment a more aesthetic, pleasant, and emotionally 

satisfying place in which to live, work, and spend leisure time 

(Dwyer et al. 1991; Taylor et al. 2001a, 2001b; Ulrich 1984). 

Studies of urbanites’ preferences and behavior have confirmed 

the strong contribution of trees and forests to the quality of life 

in urban areas. Urban forests also provide significant outdoor 

leisure and recreation opportunities for urbanites (e.g., Dwyer 

1991, Dwyer et al. 1989).

Urban forest environments provide aesthetically pleasing surroundings, increased enjoyment of everyday life, and a greater 

sense of connection between people and the natural environment. Trees are among the most important features that contribute to the aesthetic quality of residential streets and community 

parks (Schroeder 1989). Perceptions, such as aesthetic quality 

and personal safety, are highly sensitive to features of the urban 

forest such as number of trees per acre and viewing distance 

(Schroeder and Anderson 1984).

Community well-being. Urban forests make important contributions to the vitality and character of a city, neighborhood, 

or subdivision. Furthermore, the act of planting and caring for 

trees, when undertaken by residents, yields important social 

benefits and a stronger sense of community. In addition, empowerment to improve neighborhood conditions in inner cities 

has been attributed to involvement in urban forestry efforts 

(Kuo and Sullivan 2001a, 2001b; Sommer et al. 1994a, 1994b; 

Westphal 1999, 2003).

Physical and mental health. Reduced stress and improved 

physical health for urban residents have been associated with 

the presence of urban trees and forests. Landscapes with trees 

and other vegetation have produced more relaxed physiological 

states in humans than landscapes without these natural features. 

Hospital patients with window views of trees recovered significantly faster and with fewer complications than comparable 

patients without such views (Ulrich 1984).

Local economic development. Urban forest resources contribute to the economic vitality of a city, neighborhood, or 

subdivision. By improving the environment, trees contribute to 

increased property values, sales by businesses, and employment 

(e.g., Anderson and Cordell 1988; Corrill et al. 1978; Donovan 

and Butry 2008; Dwyer et al. 1992; Wolf 2003, 2004). Urban 

forest maintenance and management activities also create jobs 

to help the local economy, and wood from removed trees and 

limbs can be used to produce various wood products or fuels 

(e.g., fire wood or ethanol) that can be used by residents, while 

creating additional jobs in the process.

Management costs. Although natural regeneration is a powerful 

force in shaping the urban forest (Nowak 2012), tree planting 

and various maintenance activities (e.g., watering, raking, 

pruning, tree removals) incur economic costs while helping 

to provide for safe and healthy urban forests. Enhancing tree 

cover in environments that tend to be precipitation limited 

involves additional economic and environmental costs. Planting 

trees in these environments can produce substantial benefits 

for the urban population, but such plantings often require 

water or economic resources that may be scarce. In addition to 

management costs, various risks associated with urban forests 

related to falling trees and limbs may pose additional costs 

through personal injury, property damage, and power outages. 

Proper management and maintenance can minimize risks and 

costs, while enhancing numerous benefits for current and future 

generations. Disposal of leaves and other detritus can incur 

significant cost but also represents a potentially valuable supply 

of wood or organic matter (e.g., for mulch, wood products or 

bioenergy applications).

Major Threats and Influences Affecting 

the Urban Forest

Numerous potential threats can significantly alter urban forests 

and their associated benefits. These threats (Nowak et al. 2010) 

include the following.

Insects and diseases. Urban forests can be, and are, severely 

affected by numerous insects and diseases, many of them introduced from other geographic regions into urban centers. Some 

insects and diseases—such as the gypsy moth, Asian longhorned 

beetle, emerald ash borer, and Dutch elm disease—have caused 

significant tree mortality that has virtually eliminated dominant 

tree species in some places (e.g., Dozier 2012, Liebhold et al. 

1995).

Wildfire. Uncontrolled fires can cause significant damage to 

trees and forests and dramatically alter the urban landscape, 

especially in urban areas adjacent to wildlands (Nowak 1993, 

Spyratos et al. 2007). High population growth and urban expansion in California, for example, have led to a substantial increase 

in fire ignitions in wildland-urban interface areas (Syphard et 

al. 2007). In addition, the intermingling of trees with manufactured structures in these areas significantly complicates and 

limits the options available for fire suppression activities and 

vegetation management practices used to reduce fire risk.

Storms. Urban forests can be altered and have been significantly 

damaged by wind, ice, and snow storms that result in broken 

branches and toppled trees (e.g., Greenberg and McNab 1998, 

Irland 2000, Proulx and Greene 2001, Valinger and Fridman 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 41

1997). As in the case of fire, the proximity of trees to buildings, 

roads, and power lines complicates forest management in this 

regard, while elevating the potential damage that can result.

Invasive plants. Invasive plants such as kudzu (Pueraria 

lobata), English ivy (Hederal helix), European buckthorn 

(Rhamnus cathartica), and Norway maple (Acer plantanoides) 

can degrade or alter urban forests by removing and replacing 

native plants and altering ecosystem structure. English ivy and 

kudzu have been known to cover acres of canopy trees (Dozier 

2012, Webb et al. 2001). The introduction of nonnative species 

in gardens and parks enhances this risk.

Development. Land development significantly alters the urban 

landscape, affecting plant and wildlife populations and forest 

biodiversity and health (Nowak et al. 2005). Development can 

lead to rapid reductions in tree populations (clearing of forest 

stands), can alter species composition (e.g., tree planting after 

development), can increase tree populations (e.g., tree planting 

in formerly cleared areas), and can alter the urban environment 

(e.g., increase or decrease in air temperatures). Development 

associated with urban expansion into rural areas can also significantly alter the regional landscape, particularly in forested 

regions where forest area is reduced, fragmented, or parcelized 

(i.e., forest stands remain intact but have multiple landowners). 

In timber-producing regions, when development alters the rural 

forest landscape, it will likewise affect the available timber 

supply and forest management practices (Zhang et al. 2005).

Pollution. Air and water pollution can affect tree health in 

urban areas if pollutant concentrations reach damaging levels. 

Forests have been shown to be affected by air pollution, 

especially from regional deposition of ozone, nitrogen, sulfur, 

and hydrogen (Stolte 1996). Ozone has been documented to 

reduce tree growth (Pye 1988), reduce resistance to bark beetle, 

and increase susceptibility to drought (Stolte 1996). Air pollution can also enhance tree growth through increased levels of 

carbon dioxide or by providing essential plant nutrients such as 

sulfur and nitrogen (e.g., NAPAP 1991).

Climate change. Climate change is expected to produce 

warmer air temperatures, altered precipitation patterns, and 

more extreme temperature and precipitation events (EPA 2009, 

IPCC 2007). These climate changes can cause changes in 

urban forest composition (Iverson and Prasad 2001, Johnston 

2004) and have the potential to exacerbate other urban forest 

threats (e.g., invasive species and pests). Climate change has 

the potential to alter urban forests, not only through species 

changes, but also through direct effects from storms, floods, 

etc., that may kill large portions of the forest in relative short 

time periods. Urban forest managers will need to understand 

and adapt to potential species shifts and changes to the environment to produce sustainable and healthy urban forests under 

future climatic conditions.

Improper management. Because numerous people directly 

manage most of the urban forest, the decisions and actions of 

the managers significantly affect urban forest composition and 

health. Improper decisions related to species selection, tree 

locations, and maintenance can lead to conflicts with the urban 

population and infrastructure, tree damage, and poor tree health 

that can lead to premature tree mortality. Actions or inactions 

taken by the multitude of urban landowners can pose a threat 

to urban forests, but they can also help bolster urban forest 

health and sustainability if proper tree care and management 

are conducted.

Currently Available Data on U.S. 

Urban Forests

Although far from complete for national assessment needs, the 

data describing urban forests in the United States is improving. 

Remote-sensing techniques are being used to construct urban 

forest cover estimates at the local and regional level across the 

country. In addition, new urban forest field data are continually 

being collected by local groups and cities, and through the Forest 

Inventory and Analysis (FIA) program of the U.S. Department 

of Agriculture, Forest Service in select metropolitan areas. 

Tools are being designed and improved to help municipalities 

inventory their forests in a consistent fashion while fostering 

the participation of interested citizens.

Extent of Urban Land in the United 

States

The importance of urban forests and their benefits in the United 

States is increasing because of the expansion of urban land. The 

percent of the coterminous United States classified as urban 

increased from 2.5 percent in 1990 to 3.1 percent in 2000, an 

area about the size of Vermont and New Hampshire combined. 

The States with the highest percent urban land are New Jersey 

(36.2 percent), Rhode Island (35.9 percent), Connecticut (35.5 

percent), and Massachusetts (34.2 percent), and 7 of the top 10 

most urbanized States are located in the Northeastern United 

States (fig. 4.2). Urban land in the coterminous United States in 

2010 increased to 3.6 percent (U.S. Census 2014). Most of the 

1990-to-2000 urban expansion occurred in previously forested 

areas (33.4 percent of the expansion) or agricultural lands 

(32.7 percent). The dominant type of land uses or cover classes 

occurring in a given State largely determines the type of land 

being converted to development. States where more than 60 

percent of urban land expansion occurred in forests were Rhode 

Island (64.8 percent of urban expansion), Connecticut (64.1 

percent), Georgia (64.0 percent), Massachusetts (62.9 percent), 

West Virginia (62.2 percent), and New Hampshire (61.3 percent). 

States where more than 60 percent of urban land expansion 
42 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 4.2. Percent of U.S. counties classified as urban, 2000 (Nowak et al. 2010).

occurred in agricultural lands were Nebraska (68.9 percent), 

Indiana (66.8 percent), Illinois (64.8 percent), and Wisconsin 

(62.0 percent) (Nowak et al. 2005). These estimates of urban 

land and urban land expansion within land cover types are based 

on Census Bureau maps of urban land and National Land Cover 

Database (NLCD) maps of land cover types. Although these 

maps may have some inaccuracies, the urban land maps are 

fairly accurate because they are based on extensive census data.

The most urbanized regions of the United States are the Northeast (9.7 percent of total land area) and Southeast (7.5 percent), 

with these regions also exhibiting the greatest increase in 

percent urban land between 1990 and 2000 (1.5 and 1.8 percent, respectively). States with the greatest increase in percent 

urban land between 1990 and 2000 were Rhode Island (5.7 

percent), New Jersey (5.1 percent), Connecticut (5.0 percent), 

Massachusetts (5.0 percent), Delaware (4.1 percent), Maryland 

(3.0 percent), and Florida (2.5 percent). States with the greatest 

absolute increase in urban land are Florida (925,000 acres; 

374,000 hectares), Texas (871,000 acres; 352,000 hectares) and 

California (737,000 acres; 298,000 hectares) (Nowak et al. 2005).

Given the urban growth patterns of the 1990s, urban land is 

projected to expand from 3.1 percent of conterminous United 

States in 2000, to 8.1 percent in 2050, an increase in area 

greater than the size of Montana (fig. 4.3). The total projected 

amount of U.S. forest land projected to be subsumed by urbanization between 2000 and 2050 is about 29.2 million acres (11.8 

million hectares), an area approximately the size of Pennsylvania (Nowak and Walton 2005) (fig. 4.4).
Assessing the Sustainability of Agricultural and Urban Forests in the United States 43

Figure 4.3. Percent of land classified as urban in 2000 (a) and projected percent of land classified as urban in 2050 

(b), by county (Nowak and Walton 2005).

(a)

(b)
44 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Figure 4.4. Percent (a) and square kilometers (b) of nonurban forest subsumed by projected urban growth, 2000 

through 2050, by State (Nowak and Walton 2005).

(a)

(b)
Assessing the Sustainability of Agricultural and Urban Forests in the United States 45

Urban Tree-Cover Estimates

Tree cover in urban lands in the United States (circa [ca.] 2005) 

is currently estimated at 35.0 percent (Nowak and Greenfield 

2012a). Urban tree cover has declined slightly in recent years 

(ca. 2002 to 2009) with a loss of about 4 million urban trees per 

year (Nowak and Greenfield 2012b). These estimates are based 

on photo interpretation of tree cover nationally. Urban tree cover varies across the United States, with urban tree cover tending 

to be highest in forested regions, followed by grasslands and 

deserts (Nowak et al. 2001). In addition to photo-interpretation 

estimates, tree-cover maps for the United States have been 

produced based on 30-meter resolution satellite data (ca. 2001) 

as part of the NLCD (USGS 2008) (fig. 4.5). These tree-cover 

maps underestimate tree cover on average by 9.7 percent, with 

underestimation varying across the conterminous United States 

(Greenfield et al. 2009, Nowak and Greenfield 2010).

Based on field data sampled from several cities combined with 

national urban tree-cover estimates, an estimated 3.8 billion 

urban trees are growing in the conterminous United States (the 

actual range of the national estimate is between 2.4 and 5.7 billion 

trees, based on minimum and maximum city tree-cover density 

estimates) (Nowak et al. 2001). These trees have an estimated 

structural asset value of $2.4 trillion (Nowak et al. 2002a). The 

structural value averages about $600 per tree and is based on 

a formula from the Council of Tree and Landscape Appraisers 

that estimates the replacement or compensatory (if a tree is too 

large to be directly replaced) value of a tree. Structural values 

vary by location, tree size, species, and condition of the tree. The 

urban forest nationally stores about 709 million tons (643 million 

metric tons) of carbon (Nowak et al. 2013), which is valued at 

$94.3 billion, or $146.7 per metric ton of carbon (Interagency 

Working Group 2015, U.S. EPA 2015). Soils in urban areas 

also store about 2.1 billion tons of carbon in the United States 

(Pouyat et al. 2006). These values are current asset values that 

would be lost through the loss of existing urban forests nationally.

In addition to these structural values, urban forests annually 

provide substantial functional values or benefits based on the 

ecosystem services they provide. Some of these functional benefits accrue in the tree (e.g., carbon storage) and can be partially 

or completely lost when the trees die (e.g., tree decomposition 

can release carbon back to the atmosphere). Other functional 

values do not accrue within a tree, however, and thus are continuously gained as long as the forest is healthy and functioning 

and will not be lost when the forest dies (e.g., accrued energy 

savings from temperature moderation and shade during a tree’s 

lifetime are not lost when the tree dies). 

Urban trees in the conterminous United States remove approximately 651,000 metric tons (717,000 tons) of air pollution 

annually, with a value of $4.7 billion (Nowak et al. 2014). 

These trees also annually sequester about 25.6 million metric 

tons of carbon (28.2 million tons of carbon) (Nowak et al. 

2013), or $3.8 billion per year based on 2015 estimates of the 

total cost of a unit of carbon emissions to a society (Interagency 

Working Group 2015, U.S. EPA 2015). In addition, the total 

annual contribution of trees in urban parks and recreation areas 

to the value of recreation experiences provided in the United 

States could exceed $2 billion (Dwyer 1991).

Figure 4.5. Percent tree cover in urban areas, 2000, by county (Nowak et al. 2010).
46 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Local Inventory Activities and Related 

Tools

The foregoing text has stressed information available at the 

national scale, relying primarily on remote-sensing data of 

urban tree cover combined with various one-time analyses of 

city tree populations to derive estimates of national urban tree 

totals and economic values. Urban forests, however, are managed at the local level and, in recent years, local citizens and 

interest groups have become increasingly engaged in assessing 

urban forest resources and improving their condition through 

management. New tools have emerged to facilitate this activity. 

The i-Tree Eco model is one example, in which local residents 

are encouraged to use standard sampling protocols in their local 

area to ensure the collection of consistent data that measure 

important aspects of urban forests (Nowak et al. 2008).19 Since 

i-Tree’s introduction in 2006, there have been more than 60,000 

users in more than 120 countries, with user downloads increasing at a rate of about 25 percent per year. This growth reflects 

the desire by citizens and managers to better understand the ecosystem services that urban forests provide. The i-Tree provides 

a foundation for a growing database on local forest conditions, 

but it does not constitute a consistent national survey of urban 

forest resources in the United States.

Building a National Inventory

In an effort to better understand the urban forest resource at the 

national scale, urban forest inventory methods were pilot-tested 

in five States (Colorado, Indiana, New Jersey, Tennessee, and 

Wisconsin; Cumming et al. 2008). Statewide urban forest 

inventories have also been conducted more recently in Alaska, 

California, Hawaii, Oregon, and Washington. Data from these 

State assessments are run through the i-Tree model to provide 

estimates of ecosystem services and values. This activity is the 

foundation for the full implementation of a national urban forest 

inventory and monitoring program of major metropolitan areas 

that started in 2014 with the FIA program staff measuring field 

plots in Baltimore, MD, and Austin, TX.

Assessing Data Adequacy and 

Identifying Major Data Gaps

Although i-Tree Eco assessments and urban forest assessments 

by FIA are increasing, major gaps still exist in basic urban forest field data. Local city assessments provide urban forest data 

that are useful at the local scale, but local-scale assessments, in 

general, are piecemeal in nature and are not always consistent 

with efforts undertaken elsewhere. Alone, these local inventories cannot be readily used as building blocks for a national 

assessment. The State urban forest assessments are geared to 

providing consistent urban forest data at the State scale, but 

they are currently of limited usefulness at the national scale due 

to the small number of State assessments so far completed.

The planned implementation of an FIA urban forest inventory 

and monitoring program at the national level will fill a major 

information gap in the effort to improve urban natural resource 

stewardship (Cumming et al. 2008). The starting of FIA measurement and monitoring in Baltimore, Austin, and other cities 

will facilitate better linking and consistency among FIA urban 

and conventional forest inventories and also inclusion within 

i-Tree. This new national FIA urban program is expanding to 

other cities and will provide more useful data at the local scale 

due to increased sample sizes within the cities. These data will 

provide critical baseline information and monitoring data from 

local to regional scales. These local-scale analyses will provide 

limited information, however, for a national assessment. Until 

all metropolitan areas are assessed, development of a national 

urban forest assessment will be challenging.

Local-scale urban forest information can be, and is being, ana­lyzed using i-Tree, but these data are collected by various groups 

with varying degrees of quality control and are not an adequate 

substitute for field data gathered through a national inventory in 

a consistent fashion across space and time. This critical information gap needs to be filled to fully assess and understand our 

Nation’s urban forest resources. Information from a national 

survey can be used to better understand the magnitude of this 

resource, and how it is changing through time, so that better 

management plans and policies can be developed to sustain 

and enhance urban forest benefits for future generations. This 

understanding, in turn, will enable us to disseminate improved 

best practices, identify emergent threats, and devise national 

and regional policies and partnerships aimed at improving 

stewardship of these valuable resources. If integrated with conventional forest inventory activity through the FIA program, 

along with similar surveys of agricultural forests resources, a 

national urban forest inventory would constitute an essential 

piece of the information base needed to successfully engage 

in landscape-scale resource conservation that bridges jurisdictional boundaries, ownership classes, and land use types.

Efforts to assess current urban forests at the national scale have 

several limitations due to the gaps in urban forest data. To 

produce national or regional estimates of urban forests and their 

19 The i-Tree Eco model is a new iteration of the UFORE (Urban Forest Effects) model and is one of several urban forest tools found within the i-Tree 

modeling suite. i-Tree is developed, maintained, and supported by a consortium of partners, including the Forest Service, Davey Tree, National Arbor Day 

Foundation, Society of Municipal Arborists, International Society of Arboriculture, and Casey Trees. Information on the model and other i-Tree applications 

is available at http://www.itreetools.org.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 47

effects, national or regional tree-cover data are combined with 

averages from various local urban forest assessments, and these 

localities may not truly represent the overall region of analysis. 

National and regional averages, from limited amounts and limited 

spatial distribution of urban forest field samples, present challenges in providing truly accurate regional or national estimates.

Another challenge faced by national and regional urban forest 

estimates is the accuracy of the tree-cover data at these scales. 

Tree-cover maps based on 30-meter resolution images from the 

early 2000s are limited in their ability to accurately estimate tree 

cover, particularly in urban areas. Recent photo-interpretations 

of tree cover nationally demonstrate that these tree-cover 

maps underestimate tree cover, on average, by 9.7 percent 

with underestimation varying across the conterminous United 

States (Greenfield et al. 2009; Nowak and Greenfield 2010). 

Improved tree-cover estimates will provide a basis for better 

estimates of urban forest structure, functions, and values from 

local to broader scales, but these estimates will still be limited 

by the absence of information from field data assessments (e.g., 

number of trees, species composition, diameter distribution, 

tree health). This field derived information on urban forests is 

lacking for most cities and regions of the United States. Most 

data from field assessments are derived from individual efforts 

on the part of municipalities or regional collaborations. As a 

result, although the quantity and quality of urban forest data are 

increasing, these data are not sufficient to adequately monitor 

or assess urban forests at the regional or national scale.

Data adequacy relative to the Montréal Process Criteria 

and Indicators (MP C&I) for Forest Sustainability. As 

described previously, the information we currently have about 

urban forest resources at the national level is largely restricted 

to urban forest cover estimates derived from the analyses of 

satellite images or photo-interpretation, along with some estimates of tree counts and economic values modeled or otherwise 

derived from the cover estimates and various field data assessments. This information is much less than the database that 

was assembled to address the 54 MP indicators covered in the 

National Report on Sustainable Forests—2010, hereafter the 

National Report (USDA Forest Service 2011). Nonetheless, the 

data on urban forests that we currently do have will go a long 

way in addressing some of the key indicators on forest extent 

found in MP Criterion 1, and these data constitute an important 

foundation for developing a more comprehensive inventory. 

Knowledge of local or regional tree species distributions can 

be cross-referenced with cover data to develop estimates of 

total regional or national species counts and thereby potential 

susceptibility to pest epidemics and other pathogens. This 

example is only one illustration of how the forest cover data 

can be used in conjunction with other data to address MP indicators or other concerns at different spatial scales. Numerous 

other possibilities exist. The MP indicators on carbon balances 

in Criterion 5 can likewise be addressed in this fashion and 

could be improved with the addition of soil sampling and soils 

information. Most of this type of information, however, will 

be the result of one-time analyses, which may provide useful 

information but will not result in the consistency across time 

and space that is the ultimate goal of the MP C&I and similar 

reporting efforts. For that, a more comprehensive data gathering and reporting effort combining remote-sensing capabilities 

with on-the-ground inventory sampling will be needed.

As it currently stands, the nationally consistent data we have on 

urban forests enable us to partially address the following MP 

criteria:

Criterion 1: Conservation of biological diversity. Treecover data only, giving us an idea of the extent of forests but 

not their species structure or diversity. Fragmentation may 

be measured and described using available data, but analysis 

techniques will have to be developed. Tree counts can be 

extrapolated from existing data (although these counts are 

not considered in the MP C&I).

Criterion 2: Maintenance of productive capacity. Rough 

estimates of standing volume and volume growth can be 

derived from forest cover information, but on-the-ground 

sampling is needed for greater precision. MP indicators on 

timber and wood fiber production are not very applicable 

in this context, but other output measures specific to urban 

forests may be devised.

Criterion 5: Maintenance of forest contribution to global 

carbon cycles. Carbon stocks and net sequestration on urban 

forests can be estimated using forest cover and volume 

stocking estimates developed for Criteria 1 and 2. On-theground sampling is needed for greater precision, and overall 

carbon estimates for urban areas could be improved with the 

addition of soil sampling.

The other MP criteria and many of the indicators in the three 

criteria listed above currently cannot be adequately addressed 

at the national level with available data. Although a number of 

these indicators are not very applicable in the realm of urban 

forestry, others, such as those covering forest health, are essential to understanding and managing urban forests.

Strategies for Improving Urban 

Forest Data

Improvement in urban forest data gathering and reporting 

activities can be accomplished by (1) synthesizing existing data 

and standardizing data collection and formatting and (2) gathering more data from local to national scales.
48 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Standardizing and Synthesizing 

Available Data

As increasing amounts of urban tree and forest data become 

available, the ability to synthesize and report these data in a 

fashion useful to managers, planners, or policymakers working 

at local, regional, and national scales becomes paramount. Data 

collection efforts are currently not systematic, but rather opportunistic, being based on local managers’ desires and efforts 

to collect and analyze urban forest data. A key challenge of this 

effort is developing ways by which these local efforts can contribute to, and benefit from, data collection efforts elsewhere. 

This integration can best be accomplished by developing 

consistent data collection protocols that can be used in different 

settings and then by providing consistent data reporting and 

analysis tools so that information can be easily shared. The 

i-Tree model, discussed previously, is an example of how this 

type of consolidation can be achieved on a voluntary basis. By 

providing local practitioners with tools that make their jobs 

easier, i-Tree facilitates consistent data generation and reporting, 

allowing for comparability and (to a limited extent) aggregation 

across space and time. Local reports are produced (e.g., Nowak 

et al. 2006b) and data can be combined with aerial cover analyses 

to estimate regional- to national-scale characteristics of urban 

forests. Although this activity does not take the place of an 

integrated national inventory, it does provide a wealth of data 

for understanding local conditions and for developing studies 

at broader scales. It can also provide an important source of 

information for validating and augmenting broader inventory 

efforts. Regarding data standardization, efforts are also currently 

underway to develop international urban forest data-collection 

standards.

In addition to the information developed by i-Tree, a great deal 

of disparate information is available from a wide variety of 

sources, ranging from municipal reports to academic studies 

and broader natural resource sampling efforts, such as the yearly 

North American Breeding Bird Survey. With these various 

sources of data, the challenge becomes how to combine information to better understand urban forests in a broader spatial and 

social context. In most cases, this kind of work takes the form 

of one-time analyses that can contribute background information 

supporting the type of consistent and repeated data-reporting 

efforts that are called for by the MP C&I. For those cases in 

which data collection efforts are ongoing, it may be possible 

to institute analysis protocols to develop measures that can 

be reported consistently across space and time. This type of 

analysis, combining available data in an opportunistic fashion 

from multiple sources, is, in fact, a key strategy in addressing 

a number of the MP indicators on conventional forests in the 

National Report, but it requires a sustained effort and an explicit 

commitment to consistency, which is not easy. Nonetheless, 

until a national urban forest inventory is fully implemented, 

this approach is the most likely strategy for addressing the data 

needs of the MP C&I. Moreover, even with a fully implemented 

inventory, this kind of synthetic approach will be essential 

for addressing many of the social, economic, and institutional 

indicators that are found in Criteria 6 and 7 of the MP C&I.

New Data Gathering Opportunities 

and Challenges

The most obvious means for attaining long-term and consistent 

data for urban forest analysis from the regional to national 

scale is to integrate urban tree data collection within existing 

forest inventory work under the FIA program, which currently 

collects data for conventional forests across the entire United 

States. In preparation for a national urban inventory, pilot 

testing of FIA plots and data collection techniques in urban 

areas (Cumming et al. 2008) has been conducted in Indiana 

(Nowak et al. 2007), Wisconsin (Cumming et al. 2007), New 

Jersey, Tennessee (Nowak et al. 2012), Alaska, California, 

Colorado, Hawaii, Oregon, and Washington. A more recent 

action, the 2014 Farm Bill (formally the Agricultural Act of 

2014, Public Law 113-79), laid the legislative foundation for a 

national urban inventory by directing FIA to revise its strategic 

plan and describe the “organization, procedures, and funding 

needed” to implement an annualized urban forest inventory. 

To this end, FIA has implemented a monitoring program that 

focuses on metropolitan regions and began data collection 

in the Baltimore, MD, and Austin, TX, metropolitan areas in 

2014 and additional areas in 2015 (i.e., Houston, TX; Madison, 

WI; Milwaukee, WI; Providence, RI; St. Louis, MO, and Des 

Moines, IA). FIA intends to sample and monitor more metropolitan areas in the coming years. Through the inclusion of 

additional metropolitan areas, a better national picture of urban 

areas can be obtained over time.

A central question in institutionalizing a national inventory of 

urban forests is exactly what variables to measure. The i-Tree 

Eco urban variables have been developed and tested within the 

State urban pilot projects (Cumming et al. 2008) and provide a 

starting point for considering this question (see box 1). i-Tree 

Eco is designed to be consistent with many standard FIA 

variables while simultaneously being responsive to the needs of 

urban foresters, and both professionals and volunteers can use 

it. A nationally instituted inventory of urban forests would differ somewhat from a typical i-Tree Eco local analysis in terms 

of variables and protocols for measurement, but the general 

analyses involving plot-level, tree-level, and environmental 

variables would be consistent. The new urban FIA monitoring 

program is integrating data collection with i-Tree variables so 

that both i-Tree and FIA analysis programs can analyze the 

data. Should this inventory be expanded to agricultural forests, 

the degree to which these protocols would be adjusted to allow 

for consistency across agricultural and urban forests will need 
Assessing the Sustainability of Agricultural and Urban Forests in the United States 49

Box 1. i-Tree Eco Sampling Variables*

Plot-Level Information

Tree cover: The amount of the plot covered by tree canopy (in 

percent)

Shrub cover: The amount of the plot covered by shrub canopy 

(in percent)

Plantable space: Estimate of the amount of the plot area that 

is plantable for trees (in percent)

Land Use

Actual land use(s): Required (e.g., residential, golf course, 

park, commercial)

Percent of area in each land use

Ground Cover

Ground cover types present (e.g., bare soil, cement, grass)

Percent of area under each ground cover type

Shrub Information

Shrub species: Identify the shrub species

Shrub height

Percent of total shrubs area

Percent of the shrub mass that is missing

Tree Information (for individual tree measurements)

Land use (specific to tree)

Species

Status (records presence or removal of tree relative to past 

inventory)

Tree Characteristics

Total tree height

Height to live top

Height to crown base

Crown width

Percent canopy missing

Crown dieback

Crown light exposure

Percent impervious surface under the tree

Percent shrub cover under the tree

DBH (diameter at breast height)

Direction to building

Shortest distance to building

*Abbreviated version. For more detail on included variables and sampling protocols see: www.itreetools.org.

to be addressed, as will be the potential inclusion of additional 

variables (e.g., soils) targeted at specific MP indicators or 

related information needs.

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Assessing the Sustainability of Agricultural and Urban Forests in the United States

Assessing the Sustainability of Agricultural and Urban Forests in the United States 53

Chapter 5 Charles Perry, Greg Liknes, 

Guy Robertson, and Chris Woodall

Developing a Monitoring Framework for 

Agricultural and Urban Forest Resources

An explicit aim of this report is to lay the groundwork for a 

consistent and durable national inventory of agricultural and 

urban forest resources20 in the United States. The benefits these 

resources convey are numerous and the values the public holds 

for them well established (Louman et al. 2009). Moreover, the 

growing focus on all-lands management and landscape-scale 

conservation highlights the need for information that spans 

different land use categories and ecosystem types. The effort 

to develop a comprehensive estimate of forest-based carbon 

sequestration for the U.S. Greenhouse Gas Inventory is just 

one example of this need. Although currently available data 

enable us to draw some inferences about the general condition 

and extent of agricultural and urban forests, the level of our 

knowledge is relatively low, and we lack even the most basic 

measures of forest condition for most of the country’s agricultural lands. Through the use of satellite images to develop forest 

cover estimates for urban areas, the situation for urban forests 

is somewhat better. For urban forests, however, we have only 

incomplete or inconsistent information on forest health, species 

composition, and a host of other indicators deemed important.

To rectify this problem, a national inventory of agricultural and 

urban forest resources should be designed and implemented. 

The purpose of this chapter is to help lay the technical groundwork for such an inventory. In brief, we propose combining 

on-the-ground survey activities with remote-sensing analysis 

as a cost-effective means of obtaining the core data needed for 

a national inventory of agricultural and urban forest resources 

that is compatible with existing forest land inventory and 

reporting systems (see Oswalt et al. 2014). Precedents for 

this work have already been well established in (1) the U.S. 

Department of Agriculture (USDA), Forest Service Forest 

Inventory and Analysis (FIA) inventory of conventional forests 

and the pilot tests it has undertaken for agricultural and urban 

forests in the Great Plains Tree and Forest Invasives Initiative 

(GPI) inventory work cited in chapter 3 and (2) satellite-derived 

forest cover estimates presented for urban areas in chapter 4. 

Moreover, the pending implementation of an urban FIA inventory will yield valuable information about urban forests and 

experience that can be applied in agricultural settings. In the 

final section of this chapter, we discuss the national forest sustainability reporting process and the Montréal Process Criteria 

and Indicators (MP C&I) for Forest Sustainability21 as important 

reference points for developing an agricultural- and urbanfocused inventory. What is needed, however, is the consolidation 

of these disparate pieces to form an integrated data collection 

and reporting activity that is consistent across space and sustained over time.

This work will entail a substantial amount of technical development in terms of exactly what variables will be included, how 

they will be measured, and how they will be reported. It will 

also require institutional development to coordinate activities 

on a national scale and ensure they are maintained in the future. 

Most of this chapter is devoted to the first concern, stipulating 

the technical aspects of a national inventory of agricultural and 

urban forests. Although we do not recommend explicit institutional arrangements or identify specific tasks for specific agencies, a number of agencies have relevant skills and experience 

for this work, and interagency collaboration will be essential, 

particularly at the beginning. Likewise, collaboration with State 

and local government entities and with stakeholders outside of 

government will be very important in ensuring public support 

and in making sure the outputs from any inventory work that is 

undertaken provide value to the public at large. In this regard, 

many of the technical recommendations made in this chapter 

should be viewed as provisional; they will need to be subject 

to broader interagency and public review, and many will likely 

20 As a matter of definition, forest resources referenced in this chapter specifically include and focus on those trees growing on land outside the formal 

definition of forest land used by the Forest Inventory and Analysis program of the Forest Service. (See chapter 2 for an expanded discussion of definitions 

used in this report.)

21 The full title is Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests.
54 Assessing the Sustainability of Agricultural and Urban Forests in the United States

need to be revised in an adaptive fashion as we learn from 

experience and as new information needs emerge. That being 

said, considerable agreement is likely on the core biophysical 

indicators that could be included in an initial inventory. When 

such agreement exists, implementation can proceed without 

undue discussion and debate.

Current State of Information on 

Agricultural and Urban Forest 

Resources

No national baseline data currently exist that describe the condition of agricultural or urban tree resources. An inventory of 

urban trees has been piloted in a number of cities, (e.g., Cumming 

et al. 2008, Nowak et al. 2011), and forest cover estimates derived 

from satellite imagery have been generated for urban areas for 

all regions of the country (see Nowak et al. 2008 and “Regional 

Reports” at http://www.nrs.fs.fed.us/data/urban/ [August 2015]). 

In addition, agricultural and urban tree resource inventories 

have been piloted in some of the Great Plains States, where 

these resources represent a large fraction of the total forest 

cover (Lister et al. 2012). Taken together, this work constitutes 

the foundation for the displays of currently available information 

on agricultural and urban forests presented in chapters 3 and 4,

respectively. In addition to these regional inventories and 

tree-cover estimates, a great deal of location-specific data exist 

on urban tree cover, forest structure, and ecological functions 

and values. This data collection is the result of the efforts of 

researchers and of numerous municipalities to understand their 

local forest and tree resources. For urban forests, the opportunity to compare and consolidate this information is enhanced 

by the growing use of the i-Tree Eco model (see chapter 4 and 

http://www.itreetools.org/eco/). Comprehensive assessments 

of urban forest structure, however—number of trees, species 

composition, diameter distribution, tree health, etc.—are still 

lacking for most cities and regions of the United States. So, even 

as the quantity of urban forest data is increasing, these data are 

not sufficient to adequately monitor or assess urban forests at 

the regional or national scale. This situation should be greatly 

improved through the implementation of an urban FIA inventory, although the resulting data will not be available for at least 

several years. With the exception of those areas inventoried 

in the GPI described in chapter 3, the state of knowledge for 

agricultural forest resources is considerably less developed.

The urban pilot inventories and the GPI inventory, discussed 

previously, were designed and implemented in collaboration 

with the Forest Service FIA, and the developers were very cognizant of FIA methods and definitions (for details, see http://

www.fia.fs.fed.us/library/field-guides-methods-proc/ [August 

2015]). It is possible to integrate these pilot studies with the 

national FIA plot network and resultant analyses, but the actual 

mechanisms for doing so are not yet fully developed. So, although 

these inventory efforts represent one-time studies tailored to 

the specific questions that motivated them, they represent an 

initial effort at a consistent inventory and can help guide us in 

determining what a national inventory would look like.

Desired State of Agricultural 

and Urban Forest Resources 

Monitoring

A national monitoring system for agricultural and urban forest 

resources ideally will meet the following overarching criteria.

The sampling design will be statistically valid and national 

in scope, and it will be designed in a manner that facilitates 

comparisons over space and time.

Sampling and reporting protocols will be explicitly adopted 

and published.

These protocols will include an orderly process for suggesting, adopting, and implementing changes to the indicator set 

and measurement protocols.

The definition of land uses will be comprehensive and 

include sufficient detail to facilitate the seamless integration 

of data from all land use categories into a whole without 

confusion, doublecounting, or undercounting among similar 

land uses.

All data collected by each inventory will be entered into 

a database that is easily accessible to the public and accompanied by full and transparent documentation. Common 

elements across inventories could be compiled into one 

database to meet reporting needs.

The content and format of these databases will facilitate 

data extraction and use with forecasting models and other 

analysis techniques (e.g., Urban Forest Effects, or UFORE, 

and Forest Vegetation Simulator, or FVS).

Periodic reports and data summaries will be published according to an explicit schedule.

Data gaps will be explicitly identified across social, economic, and ecological dimensions, and efforts will be made 

to address these gaps where possible.

A permanent steering committee or similar governing body 

will be established to work in collaboration with relevant 

user communities to review project outputs and revise 

procedures and measures as needed.

Permanent institutional and budgetary arrangements will be 

made to ensure project durability.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 55

Suggested Criteria and Indicator 

Framework as a Starting Point 

for Variable Development

Criteria and indicator frameworks involve a hierarchical organization of specific indicators arranged under more general, thematic 

criteria. A major advantage in using this type of framework 

is that it provides an explicit and deliberate way to organize, 

display, assess, and revise diverse collections of information on 

topics that are widely accepted as relevant to forest sustainability 

and management. The MP C&I (Montréal Process Working 

Group 2009) represent one such approach designed to provide 

a comprehensive view of conventional forests and their sustainability. Although the 54 distinct MP indicators are not all 

applicable to agricultural and urban forests, the 7 MP criteria 

(i.e., overarching themes that encompass multiple indicators) 

provide a good starting point to begin to organize and assess 

the particular pieces of information needed to better understand 

agricultural and urban forests and their sustainability. This 

approach has the added benefit of enabling us to better integrate 

the information we develop for agricultural and urban lands 

with that reported periodically for conventional forests in the 

National Reports on Sustainable Forests; the most recent 

version is the National Report on Sustainable Forests—2010, 

hereafter, the National Report (USDA Forest Service 2011). 

Those reports adhere to the MP C&I framework that 11 other 

nations also follow.

In the following framework, we explicitly use the MP criteria 

to organize a list of suggested indicators for monitoring agricultural and urban forests. A number of these indicators are 

already included in the inventory activities noted previously 

and in chapters 3 and 4. Others are suggested by certain MP 

indicators that make sense in the context of agricultural and 

urban forests but are not included in current pilot inventories, 

and still others are added as a potential means of augmenting 

the information for a given criterion, even if a close analog 

does not exist in either existing inventory activities or the MP 

indicator set. As a result, the indicators listed here range from 

existing field-tested measures that would likely be included as 

core variables without substantial modification in any future 

inventory, to measures that are feasible but may require some 

modification, to measures that would need substantial revision 

or new development before implementation. In light of the different status and feasibility associated with each indicator, we 

have included a priority recommendation (“core,” “suggested 

for consideration,” and “possible for consideration”), and 

we have listed possible data sources for each. The following 

indicator list does not represent an attempt to replicate the full 

range of MP C&I for agricultural and urban forests; it is merely 

a starting point.

MP Criterion 1: Conservation of 

Biological Diversity

Criterion 1 describes biological characteristics of forest ecosystems, the distribution and diversity of forest species, and efforts 

to preserve them. Measures of forest extent and cover, tree 

species distribution, and the diversity of forest flora and fauna 

are considered under Criterion 1.

1.1 Ecosystem diversity

1.1a Area and percent of tree cover in agricultural and 

urban settings. The spatial configuration of these 

resources will present challenges in devising consistent 

measures. A potential strategy here would be to report 

acres by well-defined cover classes (e.g., scattered trees, 

natural woodlands, agroforestry plantings) as was provided in the GPI inventory. Additional descriptors such 

as species grouping (e.g., coniferous, broadleaved), age 

class, diameter class, or vigor may be included. Total 

percent forest cover estimated using remote-sensing 

techniques would be a complimentary measure.

Status: Core indicator in any inventory. Included in the 

GPI inventory (e.g., Lister et al. 2012), Urban Inventory 

Pilots (e.g., Nowak et al. 2011), and satellite-derived 

urban forest cover estimates.

Data sources: Plot-based inventory sampling; satellite 

and related remote-sensing imagery.

1.1b Area and percent of forest by ownership and protection status (e.g., parks, conservation easements). Fieldlevel sampling or Geographic Information System, or 

GIS, mapping combining forest cover information (developed in Indicator 1.1) with landowner and land use 

designations. It is often difficult to achieve consistency 

in these determinations, so the challenges associated 

with this task should not be overlooked.

Status: Core indicator. Generally addressed in the GPI 

inventory (“Primary Land Use” condition attribute; 

Lister et al. 2012), Urban Inventory Pilots (e.g., Nowak 

et al. 2011), and i-Tree Eco model (through observed 

land use; see http://www.itreetools.org/eco/ [August 

2015]).

Data sources: Plot-based inventory sampling in combination with publicly available land ownership information, including the Protected Areas Database, or PAD 

(see http://www.protectedlands.net [August 2015]) 

and the National Conservation Easement Database, or 

NCED (see http://www.nced.conservationregistry.org

[August 2015]).
56 Assessing the Sustainability of Agricultural and Urban Forests in the United States

1.1c Fragmentation of tree cover. Average patch size or 

other fragmentation metric.

Status: Suggested for consideration. Developing 

meaningful metrics will be a challenge. 

Data sources: Forest cover information developed in 

Indicator 1.1a combined with spatial analysis techniques 

such as FRAGSTATS (see http://www.umass.edu/

landeco/research/fragstats/fragstats.html [August 2015]).

1.2 Species diversity

1.2.a Number of tree species. Tree species is a common 

attribute collected for individual trees in plot-sampling 

protocols. The ability to collate and present species counts 

in summary statistics will require further development. 

Candidate measures include the relative proportion of 

native to nonnative species, indexes describing overall 

tree species diversity, and counts for species of specific 

interest (e.g., ash [Fraxinus spp.] in the GPI inventory. 

To the extent possible, trees should be identified as 

cultivated or naturalized.

Status: Core indicator, although level of reporting 

detail will need to be considered.

Data sources: This information ideally would be collected through tree-level sampling in plot-based inventory. It may be more cost effective to integrate existing 

street tree inventories, but these inventories would have 

to meet a common standard.

Note: The MP C&I here includes an indicator for the number 

of forest associated species for fauna and flora, which 

includes animal and nontree plant species. Certain fauna 

(notably bird species through the U.S. Geological Survey 

North American Breeding Bird Survey) are currently 

tallied by ecoregion. Information on shrub cover is 

included in the i-Tree Eco urban tree sampling methodology, but a tally of shrub species is not incorporated 

in any of the current inventory activities. As a result, 

we are not suggesting measurement of fauna and shrub 

species at this time.

1.2.b Presence of species at risk. This indicator would register the presence of threatened or endangered (as defined 

by law) flora and fauna species in agricultural and urban 

forests.

Status: Suggested for consideration. Measurement and 

reporting protocols would require development.

Data sources: Mapping of threatened and endangered 

species sightings and known ranges into forest cover 

and land use data developed in Indicator 1.1a.

Note: The MP C&I include indicators on forest-related genetic 

diversity. At this time, we are not suggesting coverage 

of genetic diversity associated with agricultural and 

urban forest resources, although it should be noted that 

genetic diversity (or the lack thereof) is an important 

factor affecting agricultural and urban forests, especially 

those that are planted.

MP Criterion 2: Maintenance of 

Productive Capacity of Forest 

Ecosystems

Criterion 2 measures the balance between the capacity of 

forests to produce valued outputs for society and current rates 

of extraction of those products. The relationship between tree 

growth rates, timber stocking volumes, and timber harvest 

levels is a central focus, although this focus has been extended 

in the MP C&I to nonwood forest products as well. It is not 

clear how this focus could be directly applied to agricultural 

and urban forests, where numerous forest-related benefits are 

produced in combination and most often are not measured or 

traded. At the same time, the qualitative value of specific ecosystem services from these resources is increasingly recognized 

by society, and future measures relating the flows of specific 

services to the capacity of agricultural and urban forests to 

produce them could be incorporated here. Several examples are 

suggested in the following section.

2.1 Area and percent of agricultural and urban forests 

explicitly devoted to goods production. This indicator 

would include natural and planted forests managed for 

bioenergy production, agroforestry production systems, 

the production of foodstuffs and other products, and 

timber or wood fiber production. Volume and area 

measures of agroforestry plantings would be the most 

likely focus.

Status: possible for consideration. Substantial development required.

Data sources: plot-based inventory sampling, USDA 

Census of Agriculture.

2.2 Presence of nonwood forest products and harvest 

of same. This indicator would register the presence of 

important nonwood forest products at a given location 

and indicate whether harvest activity is currently occurring.

Status: Possible for consideration. Substantial development required.

Data sources: Plot-based inventory sampling and 

USDA Census of Agriculture augmented with local 

user surveys.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 57

MP Criterion 3: Maintenance of 

Forest Ecosystem Health and Vitality 

(Disturbance)

Criterion 3 measures the occurrence of forest disturbance processes resulting in tree mortality or loss of vigor. The MP C&I 

divide disturbance processes into two main categories: (1) biotic 

(insects, disease, and nonnative invasive species) and (2) abiotic 

(fire, weather, pollution, and land clearing for development).22

As is true with the conventional forests addressed in the National 

Report, the indicators in Criterion 3 have direct relevance for 

understanding the sustainability of our agricultural and urban 

forests and managing them accordingly.

3.1 Incidence of tree mortality or damage by disturbance 

type. This indicator would register tree mortality and 

evidence of damage by general disturbance category 

(when possible).

Status: Core indicator. Current inventories contain 

various measures for tree vigor and presence of damage. 

Developing meaningful metrics will be a challenge, as 

will identifying specific disturbance agents in many cases.

Data sources: Ideally these data would be collected 

through tree-level sampling in plot-based inventories. It 

may be more cost effective to integrated existing street 

tree inventories, but these would have to meet a common 

standard.

3.2 Incidence of wildfire in agricultural and urban areas.

This indicator measures incidence and extent of wildfires in agricultural and urban areas. Number of structures 

destroyed could also be tracked.

Status: Suggested for consideration.

Data sources: Tally of major incidences from relevant 

sources such as the Monitoring Trends in Burn Severity 

database.23

3.3 Forest cover lost to development. Agricultural and 

urban forests are particularly prone to conversion to 

other land uses through the process of development. 

This indicator would measure the area of forests lost to 

this particular disturbance factor.

Status: Core indicator. Change analysis associated with 

Indicator 1.1.a, although additional analysis to identify 

developed areas is needed.

Data sources: Plot-based sampling and remote-sensing 

techniques used for Indicator 1.1a. 

MP Criterion 4: Conservation and 

Maintenance of Soil and Water 

Resources

Criterion 4 measures soil and water conditions within forests 

and describes management activity aimed at protecting and 

enhancing these conditions. Reporting for conventional forests 

in the National Report is limited by the absence of consistent 

data on resource conditions and on management prescriptions 

and compliance. It is also hampered by the fact that forest management and conservation is most often directed at sustaining 

multiple benefits, with soil and water resources not identified 

explicitly as the primary management objective, although 

it should be noted that water conservation and management 

are increasingly being identified as specific goals for urban 

forest management. These same obstacles apply in the case of 

agricultural and urban forests. 

4.1 Soil

4.1a Area and percent of tree cover for which the landmanagement focus is the protection of soil resources.

Measures tree area explicitly managed for soil conservation and enhancement. May be more relevant in 

agricultural settings.

Status: Possible for consideration; NRCS data may 

address some of these issues. Stronger linkages required.

Data sources: Tree-cover information developed in 1.1a 

combined with land use and protective status mapping.

4.1b Area and percent of forest land with degraded 

soils. This indicator measures extent of forest land in 

agricultural and urban areas exhibiting significant soil 

degradation.

Status: Suggested for consideration.

Data sources: Plot-based inventory sampling. It may be 

possible to intersect tree cover on agricultural and urban 

land with USDA Natural Resources Conservation Service maps of highly erodible soils. (Note: FIA sampling 

for conventional forests now includes sampling of soil 

conditions on a subset of plots. Similar measures may 

be feasible for agricultural and urban forests.)

4.2 Water

4.2.a Area and percent of tree cover for which the land 

management focus is the protection of water resources.

This indicator measures agricultural and urban forest 

22 Climate change is also listed as an abiotic disturbance agent in the National Report, although its potential impact is complex and will encompass many of 

the other biotic and abiotic disturbance factors.

23 The Monitoring Trends in Burn Severity project is a multiagency effort to map the burn severity and fire perimeters across all lands of the United States. 

See Eidenshink et al. (2007) for an overview and http://www.mtbs.gov/ (August 2015) for the project Web site.
58 Assessing the Sustainability of Agricultural and Urban Forests in the United States

area explicitly managed for water conservation and 

enhancement. In urban settings, consideration could 

extend beyond urban boundaries to include upland 

forests and riparian areas in water catchment areas. One 

strategy would be simply to measure the area of forest 

land occurring in officially designated municipal watershed areas (e.g., Portland, Oregon’s Bull Run Watershed 

Management Unit or Boston’s Quabbin reservoir). Note, 

however, that the resulting area measures will include 

conventional forest lands as currently inventoried by FIA.

Status: Possible for consideration. Substantial development required.

Data sources: Plot-based inventory sampling and land 

use designations.

4.2b Area and percent of degraded water bodies, or stream 

length in the vicinity of agricultural and urban tree 

cover. This indicator measures extent of forest-associated 

water bodies exhibiting significant degradation in 

agricultural and urban areas. The separation of “forestassociated water bodies” from other water bodies may 

not make sense in agricultural and urban contexts, and 

this indicator may be redundant in the context of more 

general surveys of water conditions in these areas.

Status: Possible for consideration. Significant development required. 

Data sources: Water condition surveys combined with 

forest cover information developed in Indicator 1.1a.

4.2c Area and percent of impermeable surfaces underlying 

agricultural and urban tree resources. This indicator 

measures the extent of impermeable surfaces (e.g., asphalt, 

concrete) underlying agricultural and urban forests and 

trees. Most applicable in urban settings. Indicator may 

be redundant with general measures of impermeable 

surface in developed areas.

Status: suggested for consideration. Already a component of i-Tree Eco model. Development of summary 

measures required.

Data sources: plot-based inventory sampling.

MP Criterion 5: Maintenance of Forest 

Contributions to Global Carbon Cycles 

Criterion 5 addresses the relationship between forests and atmospheric carbon. It relies on three principal measures: (1) carbon 

stocks and fluxes in forested ecosystems, (2) carbon stocks 

and fluxes in durable forest products, and (3) avoided carbon 

emissions from the use of wood for energy. The first of these 

measures will be most relevant for the monitoring of agricultural and urban forests proposed in this report. Carbon pools in 

forest products and avoided emissions may also be relevant for 

agricultural and urban forests in general, but these measures 

are already incorporated into the MP indicators covered in the 

National Report.

24

5.1 Total and unit-area agricultural and urban forest 

ecosystem carbon stocks and fluxes. Measures carbon 

stocks and net carbon sequestration for forest resources 

on agricultural and urban lands.

Status: Core indicator. Preliminary estimates already 

developed for urban areas based on tree-cover estimates. 

Models for calculating carbon balance already fully 

developed for conventional forests.

Data sources: Forest inventory data developed in 

Criterion 1 in combination with forest carbon modeling 

techniques.

5.2 Effects of agricultural and urban forests on energy 

consumption. Measures the influence of agricultural 

and urban forests on energy consumption. Likely most 

applicable to urban areas where trees may serve to 

mitigate temperature extremes through shading or wind 

protection (note that windbreaks around rural buildings 

will serve the same purpose but low population density 

will limit total contribution). Other factors may also be 

applicable.

Status: Possible for consideration. i-Tree eco is an 

important foundation (http://www.itreetools.org/eco/

index.php [August 2015]).

Data sources: Forest inventory and tree-cover estimates 

developed in Indicator 1.1a in combination with modeling and analysis techniques (preliminary estimation is 

likely feasible, but precision will be an issue).

MP Criterion 6: Maintenance 

and Enhancement of Long-Term 

Socioeconomic Benefits

Criterion 6 measures a broad array of socioeconomic benefits 

and functions related to forested ecosystems. In the MP C&I, 

Criterion 6 contains 20 indicators with focus areas in (1) production and consumption (of forest products and services); (2) investment in the forest sector; (3) employment and community needs; 

24 The data used to calculate these numbers in the National Report are derived from tallies of final production of wood products and wood-based energy 

from all sources and would include those produced from agricultural and urban forest resources. The estimates for forest ecosystem carbon pools and fluxes 

presented in the National Report, on the other hand, are derived from FIA survey data of conventional forests and do not include agricultural and urban areas.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 59

(4) recreation and tourism; and (5) cultural, social, and spiritual 

needs and values. All these indicators are broadly applicable 

to agricultural and urban forests, but they present a number 

of challenges in regard to devising and implementing specific 

measures. First, there is the lack of management focus noted in 

chapter 2, in which agricultural and urban forests are seldom 

managed specifically for forest outputs but rather for their broader 

contribution to landscape functions and in combination with 

other land cover and use classes. Second, many of the indicators 

in Criterion 6 rely on disparate datastreams and sampling activities. Whereas many of the indicators in Criteria 1 through 5 

can be addressed using data on tree cover, species, size, and 

health generated through remote-sensing or inventory-sampling 

activities (note how many of the indicators suggested previously 

are derived from information developed in Indicator 1.1a), 

indicators in Criterion 6 often require data-gathering efforts 

tailored to a single indicator. As a result of these challenges, the 

indicator list we present for Criterion 6 is less fully developed 

than those presented for the previous five criteria, and the 

specific indicators are more provisional in nature.

This lack of development should not be taken as an indication 

of the relative importance of Criterion 6 so much as the difficulty 

in addressing it with the data and resources currently at hand. 

Criterion 6 would be a likely place to focus future efforts to 

further develop and refine indicators and the data-gathering 

efforts needed to support them. The following section is merely 

a starting point for this process.

6.1 Production and consumption

6.1a Production and consumption of tangible products 

from agricultural and urban forests. Measures volume 

and value of tangible products derived from agricultural 

and urban forests. Tangible products include wood and

nonwood forest products that can be bought and sold 

or otherwise gathered and consumed. Agroforestry 

would likely be the main focus, but outputs from other 

forest and tree resources should not be ignored. Initial 

efforts could concentrate on identifying major product 

categories for future data-gathering and compilation 

efforts (e.g., biomass for bioenergy applications).

Status: Suggested for consideration. Substantial development required. Universal coverage likely not feasible.

Data sources: To be determined.

6.1b Production of ecosystem services from agricultural 

and urban forests. Measures volume (in appropriate 

units) of ecosystem services derived from agricultural 

and urban forests. The potential range of these services 

is outlined in the previous chapters but could include, 

for example, water quality and flow regulation, wildlife 

habitat, or carbon sequestration. Comprehensive, quantitative measures are likely not feasible, but indicative 

information from analysis of inventory data and review 

of current literature can help describe the dimensions 

of the various ecosystem services associated with these 

resources.

Status: Suggested for consideration. Substantial development required.

Data sources: Inventory information developed in 

Criterion 1 combined with estimation techniques equating forest area or tree counts with supply of ecosystem 

services.

6.1c Revenue from forest-based ecosystem services on 

agricultural and urban lands. Measures actual payments for ecosystem services derived from agricultural 

and urban forest resources. This measure would track 

market activity and not actual value (the value of these 

resources will usually be much higher). A comprehensive 

survey is probably not feasible, but major categories of 

payment and their magnitudes can be identified. In many 

cases, however, these revenues will not be specific to 

forests or trees (e.g., conservation easements for mixed 

forest and field lands).

Status: Possible for consideration. Substantial development required.

Data sources: Reports documenting program budgets, 

payments for conservation easements, and related 

payments.

6.2 Investments in agricultural and urban 

forestry

6.2a Investment in agricultural and urban forest resource 

management. Measures money invested in creating 

and managing agricultural and urban forests, including 

municipal budgets devoted to urban forestry, government 

payments to support forest management and conservation 

on agricultural lands, and investments in agroforestry 

plantings. Comprehensive measurement will be challenging given the number and variety of data sources 

that must be aggregated.

Status: Suggested for consideration. Substantial development required.

Data sources: Municipal budgets, State and Federal 

program budgets, and others.

6.2b Investment in research and education related to 

agricultural and urban forest resource management.

Measures money invested in research and education 

directed to urban forestry and agroforestry. Would include financial support for accredited university programs 

and research institutions. Students enrolled or degrees 

granted could be used as an alternate measure.
60 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Status: Suggested for consideration.

Data sources: Institutional budgets, scholarship programs, 

and related support.

6.3 Employment and community needs

6.3a Employment related to agricultural and urban forestry. Measures number of employees engaged in the 

management of agricultural and urban forest resources. 

Could include municipal employees working in urban 

forestry, arboriculturalists, and workers engaged in agro­forestry. Comprehensive measurement will be challenging.

Status: Possible for consideration. Substantial development required.

Data sources: Municipal reports, U.S. Bureau of Labor 

Statistics.

6.3b Distribution of benefits from agricultural and urban 

forest resources. Measures percent of tree cover or 

other relevant descriptors, including contextual elements 

like tree location and health, in relation to population 

by income class or minority status. Primarily directed 

to urban forestry and designed to explore issues of 

environmental justice.

Status: Possible for consideration.

Data sources: Inventory and forest cover estimates 

developed in Criterion 1 in combination with Census 

Bureau and similar demographic data sources.

6.4 Recreation and tourism. Although agricultural and 

urban forests positively affect recreation and tourism 

values through the amenities they provide (indeed the 

amenity benefits of these forests may be their most important value), delineating them from the more general 

category of green space or related recreational lands/

facilities is impossible in this context. No indicators are 

suggested for this subcriterion at this time.

6.5 Cultural, social, and spiritual values associated with 

agricultural and urban forests. The same limitations 

as noted for recreation and tourism previously apply.

The values associated with these resources are a 

fundamental concern for this report, but their concise 

measurement remains elusive. This subcriterion could 

be the focus of indicator development in the future.

MP Criterion 7: Legal, Institutional, 

and Economic Framework for the 

Sustainable Management of Agricultural and Urban Forest Resources

Criterion 7 addresses a core issue in sustainable resource management. At the same time, the institutions, laws, and economic 

arrangements it seeks to assess are extremely difficult to measure in a concise, quantitative fashion. This difficulty resulted 

in a more flexible and qualitative approach being applied to 

conventional forests in the National Report, and a similar 

degree of flexibility will be required in the case of agricultural 

and urban forests.

7.1 Legal framework

7.1a National laws and regulations relating to urban 

forest resources. Lists current Federal laws and regulations that are relevant to urban forestry and forest 

resources. Case studies of relevant State, county, and/or 

local laws and regulations may be included for context.

Status: Suggested for consideration.

Data sources: Congressional legislation and agency 

regulations. 

7.1b National laws and regulations relating to agricultural forests. Lists current Federal laws and regulations 

that are relevant to agroforestry and agricultural forest 

resources. Case studies of relevant State, county, and 

local laws and regulations may be included for context.

Status: Suggested for consideration.

Data sources: Congressional legislation and agency 

regulations.

(Note: 7.1a and 7.1b could be combined.)

7.2 Institutional framework

7.2a National institutions with a primary focus in urban 

forestry. Lists national institutions that are relevant to 

urban forestry and forest resources. International and 

prominent regional institutions may also be listed.

Status: Suggested for consideration.

Data sources: Miscellaneous.

7.2b National institutions with a primary focus in agroforestry and agricultural forest resources. Lists 

national institutions that are relevant to agroforestry 

and agricultural forest resources. International and 

prominent regional institutions may also be listed.

Status: Suggested for consideration.

Data sources: Miscellaneous.

(Note: 7.2a and 7.2b could be combined.)

7.3 Economic framework

7.3a Economic instruments available to promote sustainable management of agricultural and urban forest 

resources. Identifies principal economic instruments 

and strategies that can be used to promote sustainable 

forest management in agricultural and urban settings.
Assessing the Sustainability of Agricultural and Urban Forests in the United States 61

Status: Possible for consideration.

Data sources: Literature review, case studies, digital 

maps of conservation easements and land trusts, and 

others.

Instituting a National Agricultural 

and Urban Tree Resource 

Monitoring Program

A major first step in developing a national monitoring system 

for agricultural and urban forests resources will be to consolidate 

existing data and extend the coverage to other regions and localities to develop nationwide coverage. This expansion will rely 

heavily on existing inventory activities (GPI, i-Tree Eco, and 

FIA urban pilots) as a starting point for developing variables 

and measurement protocols. The national urban forest inventory 

being developed by FIA will likewise serve as a foundation, especially if it can be extended to agricultural lands sometime in 

the future. However the activity proceeds, the resulting inventory 

data must be as consistent as possible with that developed by 

FIA for conventional forests. In fact, application of the current 

FIA sampling grid and remote-sensing stratification approaches 

with expanded definitions that appropriately encompass agricultural and urban tree resources may be the most straightforward 

way to develop a nationally consistent inventory.

At the same time, opportunities for further refining current measures and including new ones should be considered on an ongoing basis. This process needs to be flexible and draw from ideas 

from various quarters ranging from stakeholder consultations 

to broader sustainability frameworks such as the MP C&I, and 

it will involve numerous compromises balancing information 

needs with the practical feasibility of data acquisition and reporting. Although developing a set of information covering all the 

criteria in the MP C&I (or similar comprehensive framework) 

is our ideal goal, initial efforts should be focused on developing 

a nationally consistent database of inventory data as stipulated 

in MP Criterion 1 (see framework in previous section).

User groups need to be involved at the beginning in the development of the fundamental questions to be addressed by the 

inventory and of the techniques needed to answer those questions. 

It is critical to achieve agreement between the user community 

and the agencies conducting the inventory. A diverse and vibrant 

user community (e.g., States, counties, local communities, 

private businesses, and relevant nongovernmental organizations) provides context for criteria and indicator assessments, 

and it is crucial for providing support for monitoring efforts 

over the long run. User communities need to be engaged at 

scoping sessions (e.g., through the Roundtable on Sustainable 

Forests) for criteria and indicator development and alignment 

with corresponding information needs. The criteria and indicator framework outlined previously can serve as a starting point 

for these discussions. In addition, it will be important to partner 

and align with FIA’s inventory of forested landscapes. Other 

relevant criteria and indicator schemes should be reviewed at 

the criterion level, with the acknowledgment that many indicators will not cross over to agricultural and urban tree resources 

on a one-to-one basis. Official definitions of populations and 

attributes of interest to satisfy criteria and indicator reporting 

need to be developed: urban (e.g., near homes for cooling) and 

agricultural (e.g., near fields for windbreaks or near streams 

for sediment control). The importance of explicit definitions of 

indicators and measures to be sampled cannot be overstated.

Possible Monitoring Directions

The core strategy suggested in this report for developing an inventory of agricultural and urban forests involves the combination 

of remote-sensing data with plot-based, on-the-ground sampling 

activities. The techniques for implementing this strategy are 

largely in place, having been developed for conventional forests 

by FIA, though the novel configurations of agricultural and urban 

forests may present new technical issues in terms of measurement 

and reporting. The greatest challenges associated with developing 

this inventory, however, are more organizational than technical, 

because it will require the coordination of numerous actors over 

a sustained period of time. In addition, the biophysical inventory 

envisioned here will not, by itself, address many aspects of forest 

sustainability, particularly in regard to its social and economic 

dimensions—further development in these areas will be required.

Remote sensing provides context. Aerial photography historically has been used in a variety of forest resource monitoring 

applications. In recent decades, satellite remote sensing along 

with digital aerial imagery have become popular data sources 

for augmenting on-the-ground field data collection. Agricultural 

and urban trees present a special challenge regarding remote 

sensing because their spatial extent is frequently smaller than 

can be discerned by medium-resolution sensors, such as Landsat 

(30-meter) and MODIS (250-meter) sensors; a host of sensors 

on satellites have a much finer spatial resolution (e.g., Quickbird, 

IKONOS). The major trade-offs with finer spatial resolution are 

typically narrower coverage (less spatial extent) and increased 

processing time and storage requirements. Improvements in 

computing resources are quickly overcoming these trade-offs, 

and a host of methods are being developed to map tree cover 

across large areas using high-resolution imagery. The National 

Agriculture Imagery Program (NAIP) of the USDA is currently 

delivering 1-meter resolution imagery for most of the United 

States with an approximate 3-year return interval. The NAIP 

data are delivered to some States as color imagery, although, in 

some cases, extra funding has been acquired to supply colorinfrared imagery.
62 Assessing the Sustainability of Agricultural and Urban Forests in the United States

Yet another source of remote-sensing data that could help in 

monitoring agricultural and urban tree resources is LIDAR 

(Light Detection and Ranging). Although LIDAR has been 

shown to provide valuable information about structure and 

diversity of tree cover (see, for example, Lefsky, Cohen et al. 

1999; Lefsky, Harding et al. 1999; and Wulder 1998), it is not 

yet widely available. For example, the U.S. Geological Survey 

aggregates LIDAR datasets at a Web portal (http://lidar.cr.usgs.

gov [August 2015]), and coverage as of November 2012 is far 

from nationwide (fig. 5.1).

Whether to produce wall-to-wall maps and geospatial datasets 

of agricultural and urban tree resources, or to augment in situ 

sampling efforts via stratified estimation or other techniques, 

NAIP and LIDAR data are promising sources of information. 

A successful agricultural and urban tree-monitoring program 

would benefit from ongoing support of the NAIP (or NAIP-like) 

program, especially with the addition of color-infrared information in all States. LIDAR is rapidly becoming available in many 

areas, but most of the acquisition is driven by local, regional, 

or statewide efforts. To leverage these data in combination with 

plot-based sampling, the effort would have to procure funding 

to acquire LIDAR in a consistent, nationwide manner, which is 

the goal of the 3D Elevation Program (Snyder 2012). Also, the 

schedule in which images are made available will have to be 

integrated with on-the-ground-sampling activities and periodic 

data development and reporting to ensure temporal and spatial 

consistency.

Plot-based sampling enriches remote-sensing estimates.

Although remote-sensing techniques and the data they yield are 

continually improving, they cannot take the place of on-theground sampling when it comes to developing information of 

important forest attributes such as species distribution, forest 

health, and tree size or age. Plot-based sampling will be a key 

element in any nationwide monitoring program for agricultural 

and urban areas. Through FIA sampling of conventional forest 

lands and the use of similar techniques for agricultural and urban 

forests in the programs outlined in chapters 3 and 4, we now 

have ample experience in sampling forests and trees on agricultural and urban lands. The challenge in extending this activity 

to a national scale lies in harmonizing current activities, fixing 

national standards for measurement, and developing a statistically sound sampling frame so that data can be aggregated over 

space and time. One promising approach would be to build on 

the FIA national grid to establish a sampling frame that encompasses all landowners and uses, with neither gaps nor overlaps. 

This approach would facilitate scaling from site-specific 

Figure 5.1. Available LIDAR (Light Detection and Ranging) datasets as of August 2013, with potential application to 

tree inventory outlined in gray (U.S. Interagency Elevation Inventory, http://coast.noaa.gov/inventory/ [August 2015]).
Assessing the Sustainability of Agricultural and Urban Forests in the United States 63

observations to the State, regional, and national scales, and, 

from a statistical standpoint, the approach would be quite similar 

to FIA’s current work. The scientific foundation for this type 

of activity is well established. Establishing a national sampling 

frame, however, will still require substantial statistical analysis 

up front to establish consistency and validity, coordination 

between different regions and actors, and focused attention 

over time.

Possible Program Solutions

We have proposed a national monitoring system for agricultural 

and urban trees and forests that combines plot-based sampling 

activities with remote-sensing techniques. This solution would 

go a long way in addressing the core biophysical indicators 

identified previously in relation to the MP Criterion 1 and many 

other indicators that are keyed off of these data. The specific 

institutional arrangements for this work are beyond the scope 

of this report. The Forest Service FIA program obviously has 

a role to play, especially given its pending expansion into 

regular sampling in urban areas. Other agencies within the 

USDA (notably the Natural Resources Conservation Service 

and the National Agricultural Statistics Service) constitute likely 

contributors, as does the U.S. Geological Survey in the U.S. 

Department of the Interior, and the National Aeronautics and 

Space Administration. At this stage, however, it is important 

to be open to new ideas and potential collaborators beyond the 

agencies traditionally charged with monitoring and managing 

public lands. An associated opportunity and challenge will be 

engaging and integrating the various State and local governments and private-sector entities that can contribute to the 

project or otherwise have a stake in its outcome.

The involvement of other agencies, stakeholders, and interested 

parties could suggest a number of new attributes that can be 

measured. On urban forest land, for example, it is important 

to know the distance to buildings or distance to streams; in 

agricultural landscapes, it is useful to know the length of tree 

resources, distance to streams, orientation to prevailing winds, 

any associated agricultural practices and uses, associated land 

use, distance to buildings, and soil volume and chemistry. One 

strength of a criteria and indicator framework such as MP C&I 

is that it provides an orderly process for adjusting and augmenting 

the types of information to be gathered, and similar arrangements 

should be specified for any monitoring program for agricultural 

and urban forest resources.

Cost estimates for an inventory could be derived from past 

experiences or pilot studies (i.e., the GPI inventory and urban 

pilots), but it is important to consider how relevant these costs 

might be to a different sampling design. For example, the cost 

of establishing a national urban forest inventory using existing 

FIA plot densities and annualized panel system has been estimated to be approximately $2.5 million per year, but whether 

similar costs would be associated with agricultural lands or 

the resulting data for agricultural and urban areas sufficient to 

meet user needs remains an open question. Likewise, although 

explicit cost information is not available for the GPI inventory, 

anecdotal reports from State forestry personnel indicate the cost 

was much less than for a traditional FIA inventory on forest 

land. In each of these cases, the indications are that a national 

inventory of agricultural and urban forest resources could be 

had for a relatively modest cost—less than $10 million per 

year, but additional work will be needed to verify this cost.

Temporal consistency is as important as spatial consistency; 

sustained attention and energy are paramount to develop any 

nationwide monitoring program, or the program could become 

another one-off national study. Regarding implementation, 

the data-gathering cycle (e.g., 1 to 10 years) and the reporting 

cycle (couched in the context of user-group desired outputs) 

need to be determined. Arrangements and support for ongoing 

sampling activity will be necessary as will a schedule for 

expected reports and related data outputs to be produced on a 

rolling basis.

Conclusions

Adequate information is a prerequisite for sustainable forest 

resource management. This assumption is the foundation for 

forest inventory activities under the FIA and for comprehensive 

forest sustainability reporting under the Montréal Process. The 

extension of these activities in some form to agricultural and 

urban forests is an obvious step in our efforts to better understand and manage these resources and the landscapes in which 

they occur. Developing a national inventory for agricultural 

and urban forests, however, will not be an easy task. In the first 

place, it will demand a dedicated funding stream. On a yearly 

basis, the amount may not be all that large, perhaps on the order 

of $10 million (as opposed to approximately $60 million for 

FIA inventory of forest lands), but the expenditure will have 

to be sustained. A bigger challenge will likely be achieving 

the agreement and coordination needed to institute a national 

inventory that is consistent over space and time. This effort 

will require the integration of different activities undertaken 

by multiple agencies and individuals across the Nation and a 

sustained dedication to compiling and publishing the resulting 

information. On the whole, a considerable amount of data is 

available, as is expertise at all levels of our society, but coordination and consolidation of these resources remain an issue.

The development and implementation of a national urban 

forest inventory by FIA will go a long way in establishing the 

technical and institutional capacity for a broader forest inventory covering all lands in the United States. The extension of 

FIA-type sampling to agricultural lands, however, will entail 

various adjustments, exactly as the extension of conventional 
64 Assessing the Sustainability of Agricultural and Urban Forests in the United States

FIA sampling to urban lands has required. It is not too early to 

explicitly consider exactly what would be involved in an FIAtype inventory of agricultural forests.

The first step in this process will be to engage the potential user 

community—understanding their perspectives and meeting their 

needs are critical for developing an effective inventory. Most of 

the information presented in this report is designed to aid in this 

engagement by identifying important dimensions and issues 

associated with agricultural and urban forest resources and 

providing ideas about how they might be measured. Another 

priority from the onset will be to fully use existing information 

sources and applicable technologies; we have focused throughout this report on identifying available tools and data and how 

they might be used in the context of a national inventory. At the 

same time, it is important that we do not limit ourselves simply 

to the data that are currently available or the immediate issues 

that are foremost in the minds of stakeholders; the comprehensive framework of the MP C&I helps remind us of the broader 

range of issues that need to be considered, even if quantitative 

measurement for many is likely not attainable. The end result 

ideally will be (1) a wall-to-wall inventory of forest resources 

spanning forest, agricultural, and urban lands and (2) an inventory that draws on plot-sampling and remote-sensing data 

sources, meets the needs of the diverse user communities, and 

enables us to assess the sustainability of these resources. This 

report has been designed to lay the foundation for the dialogue 

and decisions needed to achieve this goal.

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