United States Department of Agriculture

DEPAR TMENT OF AGRICULT URE

Forest 

Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-967

June

2018

Forests of the Tanana Valley State 

Forest and Tetlin National Wildlife 

Refuge, Alaska: Results of the 

2014 Pilot Inventory
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Cover photo: Aerial image of boreal forest, bog, and pond areas in the Tanana River 

Valley taken coincident with the Goddard-LiDAR/Hyperspectral/Thermal LiDAR 

and multiband remote sensing sampling strips that will improve the accuracy of 

estimates of forest conditions across interior Alaska. Photo by Bruce Cook, NASAGoddard Space Flight Center.
Technical Coordinators 

Robert Pattison is a research ecologist, formerly with the U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research Station, 161 East 1st

Avenue, Door 8, Anchorage, AK 99501, currently with the U.S. Department of the 

Interior, Bureau of Land Management Oregon State Office; Hans-Erik Andersen 

is a research forester, U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Research Station, Pacific Wildland Fire Sciences Laboratory, 400 N 34th

Street, Suite 201, Seattle, WA 98103, and is an affiliate assistant professor, College 

of Forest Resources, University of Washington, Anderson Hall, Seattle, WA 98195; 

Andrew Gray is a research ecologist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 SW 

Jefferson Way, Corvallis, OR 97331; Bethany Schulz is a research ecologist, U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station, 

161 East 1st Avenue, Door 8, Anchorage, AK 99501; Robert J. Smith is a Ph.D. 

candidate, Department of Botany and Plant Pathology, Oregon State University, 

2082 Cordley Hall, Corvallis, OR 97331; Sarah Jovan is a research ecologist, U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station, 

Forestry Sciences Laboratory, 620 SW Main Street, Suite 400, Portland, OR 97205.

Contributing Authors 

Kristen Manies is an ecologist, U.S. Department of the Interior, Geological 

Survey, Menlo Park, CA 94025; Bruce McCune is a professor, Department of 

Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331; Chad Babcock is a Ph.D. candidate, School of Environmental and 

Forest Sciences, University of Washington, Anderson Hall, Seattle, WA 98195; 

Bruce Cook is an earth scientist and Doug Morton is physical scientist, National 

Aeronautics and Space Administration, Goddard Space Flight Center Biospheric 

Sciences Laboratory, Code 618, Greenbelt, MD 20771; Andrew Finley is an associate professor, Departments of Forestry and Geography, Michigan State University, 

126 Natural Resources Building, East Lansing, MI 48824. 

Abstract

Pattison, Robert; Andersen, Hans-Erik; Gray, Andrew; Schulz, Bethany; 

Smith, Robert J.; Jovan, Sarah, tech. coords. 2018. Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: results of the 2014 

pilot inventory. Gen. Tech. Rep. PNW-GTR-967. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacific Northwest Research Station. 80 p.

This report highlights key findings from a test (“pilot”) of an interior Alaska forest 

inventory design. The pilot inventoried the forests of the Tanana Valley State 

Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR) in the Tanana 

River Valley of interior Alaska, covering 2.5 million ac. The inventory consisted 

of a systematic grid of 98 field-measured plots integrated with NASA’s GoddardLiDAR/Hyperspectral/Thermal (G-LiHT) imaging system. We summarize and 

interpret basic resource information such as forest area, ownership, volume, carbon 

stocks in trees, ground layers, dead wood, and soils; and vegetation community 

structure and composition. The black spruce forest type covered 49 percent of the 

forested area. Most of the aboveground live tree biomass was found in Alaska birch 

and black spruce forest types, but white spruce forest types had the highest mean 

aboveground live tree biomass per acre. Standing dead tree biomass was 8 percent 

of the amount in the live tree pool, with the greatest amounts in the white spruce 

forest type. Soil carbon per acre in the measured layers was highest in black spruce 

forests and lowest in aspen forests. Biomass of ground layers (i.e., moss and lichen 

mats) was almost twice as high on black spruce forests than on other forest types. 

Shrub and grass cover were comparable among units, but forb cover was greater 

on TVSF than on TNWR. The design and protocols tested during this pilot were 

refined for the implementation of the large-scale inventory of forests of interior 

Alaska that started in 2016.

Keywords: Forest Inventory and Analysis, boreal forests, understory vegetation, 

down woody material, biomass, soil carbon, lichen, moss, carbon pools, LiDAR, 

remote sensing. 
Summary

The boreal forests of interior Alaska cover about 110 million ac and appear to be 

changing rapidly in response to warming temperatures. The status and trends of 

these forests are poorly understood owing, in part, to the lack of a comprehensive 

inventory. In 2014, the U.S. Forest Service’s Forest Inventory and Analysis (FIA) 

program in conjunction with the National Aeronautics and Space Administration’s 

(NASA) Goddard Space Flight Center carried out a test (“pilot”) of an interior 

Alaska inventory design. The pilot inventoried the forests of the Tanana Valley 

State Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR) in the Tanana 

River Valley of interior Alaska, covering 2.5 million ac. The inventory consisted 

of a systematic grid of 98 field-measured plots integrated with NASA’s GoddardLiDAR/Hyperspectral/Thermal (G-LiHT) imaging system. The design and protocols tested during this pilot were refined for the implementation of the large-scale 

inventory of forests of interior Alaska that started in 2016. 

Black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.) was the most 

common forest type, covering 49 ± 5 percent of the forested land area (total ± standard error). Most of the aboveground live tree biomass was found in Alaska birch 

(Betula neoalaskana Sarg.) (18.0 ± 4.4 million tons) and black spruce (13.9 ± 2.7 

million tons) forest types on the TVSF. However, white spruce (P. glauca Moench 

Voss) forest types had the highest mean aboveground live tree biomass per acre on 

both the TVSF (48.8 ± 11.6 tons per acre) and TNWR (46.2 ± 4.8 tons per acre). 

Black spruce forests on the TNWR had the lowest mean biomass per acre (8.8 ± 2.8 

tons per acre). Standing dead tree biomass was 8 percent of the amount in the live 

tree pool, with the greatest amounts in the white spruce forest type. Birch forests 

on the TVSF had 48 percent of the biomass of down woody materials (DWM) in 

the study area despite covering only 24 percent of the forested area. Birch (5.3 ±

1.6 tons per acre) and aspen (Populus spp. (5.8 ± 1.5 tons per acre) forests on the 

TVSF had the highest DWM biomass per acre, while black spruce forests (0.4 ± 0.1 

tons per acre) on TVSF lands had the lowest. The majority of the soil carbon (C) in 

the litter, organic, and the top 1 inch of mineral soil occurred on black spruce (36 

percent) and birch (23 percent) forest types across the two inventory units. Soil C 

per acre in the measured layers was highest in black spruce forests (28 ± 2.6 tons 

per acre) and lowest in aspen forests (14.9 ± 6.7 tons per acre). Frozen soils were 

encountered on 14 of the sampled plots, resulting in incomplete measurements and 

the potential for bias in the statistical estimates. Biomass of ground layers (i.e., 

moss and lichen mats) was greatest on black spruce forests on the TVSF (10.5 ±

1.3 tons per acre). These forests had almost twice the biomass per acre of any other 

forest type. Most of the nonvascular ground cover in the inventory unit was in the 
form of nitrogen-fixing feather mosses (57 ± 5 percent). Mean cover of tally tree 

species was greater on TVSF than TNWR (48 ± 2.4 vs. 38 ± 3.6 percent, respectively). Mean shrub and grass cover were comparable among units (overall means 

of 44 ± 2.5 and 10 ± 1.6 percent for shrubs and grasses, respectively), while forb 

cover was greater on TVSF than on TNWR (15 ± 2.4 vs. 7.0 ± 1.8, respectively. The 

most common vascular plant species recorded overall include (in descending order) 

lingonberry (Vaccinium vitis-idaea L.), black spruce, Alaska birch, bog Labrador 

tea (Ledum groenlandicum Oeder), white spruce, green alder (Alnus viridis (Chaix) 

DC.), bog blueberry (Vaccinium uliginosum L.), and prickly rose (Rosa acicularis 

Lindl.), all recorded on at least 35 percent of all plots. In terms of all estimated 

pools (aboveground live tree and standing dead tree, DWM, ground layer, and 

surface soil) C for the various forest types by inventory unit, soils were the largest 

pool (47 to 84 percent), live trees for 13 to 47 percent, standing dead trees for 1 to 

6 percent, DWMs accounted for 1 to 14 percent, and the ground layer for 0 to 7 

percent of the C in all estimated pools.

To increase the precision of the inventory estimates, the relatively sparse field 

plot sample was augmented with G-LiHT data collected in sample strips across 

the watershed. Initial analyses are described; work is ongoing to integrate the data 

into inventory estimation. G-LiHT is an airborne imaging system that simultaneously maps the composition, structure, and function of terrestrial ecosystems using 

LiDAR, imaging spectroscopy, and thermal imaging. G-LiHT provides highresolution (~3.28 ft [~1 m]) data that are well suited for studying tree-level ecosystem 

dynamics, including assessment of forest health and productivity of forest stands and 

individual trees. In addition, G-LiHT data support local-scale mapping and regionalscale sampling of plant biomass, photosynthesis, and disturbance.
Contents

1 Introduction

1 Inventory Design

7 Stratification and Analyses

9 Status of Forest Types and Tree Biomass on the TVSF and the TNWR

9 Methods

10 Results

14 Discussion

16 Characterizing Forest Vegetation of the Tanana Valley

16 Introduction

17 Methods

18 Results and Discussion

30 Patterns of DWM on the 2014 Tanana Pilot Inventory 

30 Introduction

30 Methods

31 Results

35 Discussion

37 Soil Carbon Content in the 2014 Tanana Pilot Inventory 

37 Introduction

37 Methods

39 Results

42 Discussion 

46 Carbon Storage and Other Functions of Moss and Lichen Mats in the 

Tanana River Valley of Alaska

46 Introduction

47 Methods

49 Results 

52 Discussion

55 Ecosystem C Pools in the Tanana Pilot 

59 A USFS-NASA Partnership to Leverage Advanced Remote Sensing Technologies for Forest Inventory

59 Introduction

60 Methods

64 Future Work 

64 Acknowledgments

64 Metric Equivalents

65 Literature Cited
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Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Introduction1

The Forest Inventory and Analysis (FIA) program of the U.S. Forest Service 

monitors the status and trends in the forests of the United States. One key region of 

the United States that has yet to be inventoried is Alaska’s interior boreal forests. 

Remoteness, a limited road network, and lack of infrastructure have prevented the 

FIA program from conducting an inventory in the region (Barrett and Gray 2011). 

In 2014, the Pacific Northwest Research Station’s FIA (PNW-FIA) program along 

with the National Aeronautics and Space Administration’s (NASA) Goddard Space 

Flight Center carried out a pilot inventory in the Tanana River Valley of interior 

Alaska. The inventory occurred on the state of Alaska’s Tanana Valley State Forest 

(TVSF) and the U.S. Fish and Wildlife Service’s Tetlin National Wildlife Refuge 

(TNWR). The inventory was a partnership among multiple agencies and organizations including the Alaska Division of Forestry, University of Alaska, U.S. Fish and 

Wildlife Service, U.S. Geological Survey, and Oregon State University. 

A pilot inventory in interior Alaska is timely because the boreal forests of the 

region contain an estimated 111 million ac of forested lands or roughly 15 percent 

of the forested land of the United States (Barrett and Gray 2011). Additionally, this 

region has seen some of the greatest increases in air temperature in North America 

(Hinzmann et al. 2013, Wolken et al. 2011). Climate change also appears to be 

driving increases in the frequency and severity of fires in the region (Kasischke 

and Turetsky 2006, Turetsky et al. 2011) as well as accelerated rates of permafrost 

degradation (Jorgenson et al. 2001, 2010). Studies suggest that spruce trees are 

experiencing declines in growth linked to increasing temperatures and longer growing seasons in some areas (Barber et al. 2000, Beck et al. 2011, Juday et al. 2015) 

while expanding in others (Roland et al. 2013). The region could be experiencing a 

biome shift toward ecosystems dominated by deciduous tree species, shrubs, and 

grasses (Beck et al. 2011, Johnstone et al. 2010). Other research indicates that the 

Alaska boreal forest represents a broad array of ecosystems that are likely to have 

unique responses to climate change (Chapin et al. 2010, Jorgenson et al. 2013). 

Inventory Design

The Tanana River Valley is drained by the Tanana River (fig. 1). In the southern part 

of the Tanana River Valley, the river is fed by streams from the Alaska Range, and, 

in the north, it is fed by streams from the Yukon-Tanana uplands. The valley bottom 

is typically a wide alluvial floodplain. The valley rises to 2,000 ft in its southern 

and eastern portions (Hanson 2013). Average summer temperatures in the valley are 

1 Authors: Robert Pattison, Hans-Erik Andersen, Andrew Gray, and Bethany Schulz.

The only place in the 

United States lacking 

a comprehensive 

forest inventory is the 

111 million acres of 

boreal forest in interior 

Alaska, which is 15 

percent of all forested 

land in the nation.
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GENERAL TECHNICAL REPORT PNW-GTR-967

63 °F, and average winter temperatures are -10 °F. The average annual precipitation 

in the valley is 10.5 inches (Hanson 2013). The TVSF and TNWR land management 

units are not contiguous, and their positions on the landscape reflect the differences 

in key management objectives (timber versus wildlife habitat). TVSF lands are most 

often situated on side hills and active floodplains where productive timber stands 

occur, with an average elevation of 1,340 ft above sea level (range 250 to 2,900 ft). 

TNWR, although south of the TVSF, is situated at higher elevations, with an average of 2,200 ft (range 1,770 to 2,860 ft), most commonly on poorly drained lands 

and lakes within the broad river drainage. 

The TVSF covers 1.82 million ac, and the TNWR covers 0.73 million ac. 

The inventory consisted of a field sample and a remotely sensed sample (fig. 2). 

Figure 1—Tanana River basin (in gray) and inventoried lands (in black) within the state of Alaska. The Yukon and Tanana Rivers are 

shown in blue.
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Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

A spatially balanced design was used to identify field sample points across all of 

interior Alaska following standard FIA procedures with a tessellation of hexagons 

and one sample plot selected per hexagon (Bechtold and Patterson 2005). The 

Tanana pilot inventory plot locations were identified at one-fourth the intensity (one 

plot per 24,000 ac) of the standard FIA sample of one plot per 6,000 ac. A total of 

104 plot locations were designated. In most cases, helicopters were required to get 

crews to the plots to take ground measurements (fig. 3). The remote sensing sample 

consisted of parallel strips of NASA’s Goddard-LiDAR/Hyperspectral/Thermal 

(G-LiHT) imaging system data flown by aircraft; strips were 5.8 mi apart and 800 

ft in width and included all preidentified field plot locations in the forested areas of 

the Tanana basin (mountainous nonforest areas were not flown). Figure 4 shows an 

example of an output from the G-LiHT data.

Field measurements were taken only at the 98 sample plots where lands qualifying as forest intersected all or part of the FIA plot footprint. Forest land is defined 

as an area at least 1 ac in size and >120 ft in width that currently has or recently had 

Figure 2—Pilot inventory plot design, showing the approximate location of the plot grid (green dots), the Goddard-LiDAR/Hyperspectral/Thermal imaging system sample strips, the Tetlin National Wildlife Refuge (orange), and the Tanana Valley State Forest (blue). 
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GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 3—Helicopter used to transport field crew to landing zone near a Forest Inventory and Analysis field plot. Mount Denali is in the 

background.

Forest Inventory and Analysis

Figure 4—Example of Goddard-LiDAR/Hyperspectral/Thermal imaging system airborne remote sensing data collected in the Tanana Valley.
5

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

at least 10 percent cover of tree species and is not being managed for a nonforest 

land use that would preclude forest succession. FIA-defined tree species are woody 

perennial plants that commonly have a single well-defined stem exceeding 15 ft 

in height at maturity over a substantial portion of their range. Forested plots were 

measured from June through August 2014. 

The nationally standardized “core” FIA plot footprint consists of a cluster of 

four points, with three points evenly spaced 120 ft from plot center (fig. 5). The core 

protocols consist of classifying land use, ownership, topography, and forest type on 

fixed 24-ft-radius subplots around each point; thus an individual plot may sample 

120 ft between 

subplot centers

24.0 ft subplot: trees ≥5 in d.b.h. + vegetation

6.8 ft radius microplot: trees <5 ft d.b.h.

Supplemental 6.8 ft radius microplot

Coarse wood transects: 2 × 24 ft per subplot

Fine wood transect 1 × 10 ft per subplot

Ground layer 20 × 50 cm microquads

Soil sample point

N

Figure 5—Design of the Forest Inventory and Analysis field plot used in the Tanana pilot study, showing the layout and location of the 

different measurements within the plot footprint. d.b.h. = diameter at breast height.
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GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 6—Field crew members measuring tree heights in a recently burned black spruce stand (cones 

and small branches appear clumped at the tops of the dead trees).

Forest Inventory and Analysis

multiple forest or nonforest conditions (Bechtold and Patterson 2005). Trees ≥5 

inches diameter at breast height (d.b.h.) are measured on each subplot, and trees 1 to 

4.9 inches d.b.h. are measured, and seedlings ≥1-ft tall and <1 inch d.b.h. counted, 

on 6.8-ft radius microplots offset from each point (fig. 6). Core-optional protocols 

implemented in the Western States and also in this pilot included measurement 

of understory vegetation on the subplots and down woody materials (DWM) on 
7

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

transects crossing each subplot. The PNW-FIA program worked with partners 

and scientists in the region to identify key variables of interest to understand the 

current state of these boreal ecosystems. In addition to the core and core-optional 

FIA field protocols, PNW-FIA incorporated additional field protocols based on 

responses from and interactions with scientists and stakeholders through a series of 

workshops. Specific changes to the field protocols included the addition of a second 

microplot on each FIA subplot (USDA FS 2016) to allow for improved sampling 

of small-diameter trees such as those found in many lowland black spruce (Picea 

mariana (Mill.) Britton, Sterns and Poggenb.) forests common throughout interior 

Alaska (Van Cleve et al. 1983). Previous work by PNW-FIA in 2007 in interior 

Alaska identified the need for increased sampling of small-diameter trees (Andersen et al. 2011). As soils in boreal forests can contain up to 85 percent of the total 

ecosystem carbon (C) (DeLuca and Biosvenue 2012, Malhi et al. 1999, Tarnocai et 

al. 2009), the PNW-FIA program modified the optional “Phase 3” FIA soil protocol 

(O’Neill et al. 2005) to improve the sampling of boreal forest soils. Ground layer 

cover of nonvascular plants can be an important component of ecosystem function 

and structure in boreal ecosystems (Hollingsworth et al. 2008). PNW-FIA implemented a ground layer protocol to improve the sampling of nonvascular ground 

cover on field plots using methods that had been tested in the region (Smith et al. 

2015). Nonforest conditions on plots that were field visited with measured forest 

land (e.g., meadows next to forest) were also measured to provide information on 

transition zones and surrounding vegetation. In addition, collaborators with the U.S. 

Fish and Wildlife Service measured a full vascular plant census on subplot 1 and 

sampled insects on the plots in the TNWR.

Stratification and Analyses

Incorporation of remotely sensed data can improve the ability to provide statistically sound insights with a reduced intensity of field plots for some variables of 

interest (Andersen et al. 2011, Barrett et al. 2009). Population estimates, means, and 

variances were calculated using standard procedures for poststratification, using 

remotely sensed information to improve the accuracy of the plot-based estimates 

(Cochran 1977, Scott et al. 2005). Because the G-LiHT data were not yet fully 

processed and available for this initial pilot compilation, we used the Landsat-based 

National Land Classifcation Database (NLCD) to develop our stratification (Homer 

et al. 2007). Poststratification layers are independent of field data and improve the 

precision of inventory estimates based on the ability of stratification classes to reflect 

variation in field attributes; when available, the G-LiHT stratification should markedly improve the precision of inventory estimates. NLCD pixels that intersected 
8

GENERAL TECHNICAL REPORT PNW-GTR-967

the ownership layers for TVSF and TNWR defined the area of the population, and 

NLCD classes were grouped into strata by ownership and potential forest/nonforest 

classes. The ratios of the number of pixels within each strata to the known area of 

sampled lands determined the stratum weights for plots in each class and were used 

to calculate population means and variances. Ratio estimates (e.g., tons/acre), and 

their variances were calculated using the ratio of means estimator (Scott et al. 2005).

This initial analysis of the interior pilot data focused on biomass and C attributes and compiled plot data into estimates by landowner (TVSF and TNWR) and 

forest type. The FIA program defines forest types as “a classification of forest land 

based upon, and named for, the tree species that forms the plurality of live-tree 

stocking” (USDA FS 2016). Variance estimates are reported as standard errors (SE) 

and are shown in the text as ± SE.

Subsequent inventory implementation—

Since conducting the measurements and initial analyses for this pilot study, FIA 

was funded by Congress to implement a forest inventory for interior Alaska. In 

partnership with the Alaska Department of Natural Resources, University of 

Alaska Fairbanks and Anchorage, and local landowners, field work in the Tanana 

River basin was initiated in 2016 and is planned for completion in 2018. Based on 

the results of the pilot, as well as logistical and cost considerations, the following 

changes were made to procedures as envisioned in the pilot:

• Plot density was reduced to one-fifth the national density from one-fourth 

as implemented in the pilot (to one plot per 30,000 ac)

• The boundaries of the river-basin inventory units were adjusted to avoid 

splitting large national parks into separate units sampled many years apart. 

The Tanana unit was adjusted to encompass Denali National Park (originally in three units), while the Copper-Susitna unit was adjusted to encompass Wrangell-St. Elias National Park (originally in two units).

• The second microplot for measuring seedlings and saplings was dropped. 

Instead, saplings are being measured in a larger area around the core microplot equal to the area of two microplots (radius 9.6 ft). These trees will be 

readily distinguishable from the national core.

• Soil cores are being collected at three locations on the plot instead of one 

to improve the precision of estimates of this large C pool, and greater 

effort will be made to collect mineral soil to a depth of at least 4 inches 

whenever possible.
9

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Status of Forest Types and Tree Biomass on the TVSF 

and the TNWR2

Interior Alaska is experiencing some of the greatest increases in temperature in 

North America (Stafford et al. 2000). These changes appear to be contributing to 

increases in the frequency and severity of fires (Kasischke and Turetsky 2006), 

declines in growth of white spruce (Picea glauca Moench Voss) (Beck et al. 2011), 

changes in hydrology as permafrost degrades (Jorgenson et al. 2013), and greater 

occurrence of insect outbreaks (Hansen et al. 2016, Sherriff et al. 2011). The 

changes occurring in the region highlight the importance of providing a baseline 

assessment of the current status of the forests in the region. Knowledge of the current status of forests in the region is also important to gain insights into the capacity 

to use forest resources for timber and energy production (Fresco and Chapin 2009). 

Methods

The footprint of 98 plots intersected with lands that met the FIA definition of forest 

(fig. 7). The FIA plots were used to provide estimates of the area of the forest types 

and the aboveground biomass of live and standing dead trees in the TVSF and the 

TNWR. Trees ≥5 inches d.b.h. were measured on each 24-ft-radius subplot, and trees 

1 to 4.9 inches d.b.h. were measured on two 6.8-ft-radius microplots per subplot. Tree 

measurements included d.b.h., height (and height to broken top), species, crown ratio, 

crown class, and damages. In addition, seedlings (conifers ≥0.5 ft tall or hardwoods 

≥1 ft tall, and <1 inch d.b.h.) were counted by species in each microplot. (Smaller trees 

in many ecosystems are often ephemeral; these size limits are used by FIA nationally 

to balance field effort with the likelihood of a tree being established and likely to survive in favorable conditions.) The area of each sample size per plot defined the treesper-acre area expansion for each tree. Aboveground “bone-dry” (oven-dry; 0 percent 

moisture content) tree biomass was calculated for trees ≥1 inch d.b.h. using equations 

in Manning et al. (1984) for black spruce, white spruce, and quaking aspen (Populus 

tremuloides Michx.); Singh (1984) for tamarack (Larix laricina (Du Roi) K. Koch); 

Alemdag (1984) for Alaska birch (Betula neoalaskana Sarg.); and Standish (1983) for 

balsam poplar (P. balsamifera L. var. angustifolia (James) S. Watson ). A taper model 

was used to adjust estimates for broken-top snags and snag decay class used to assign 

decay-reduction factors from Woodall et al. (2011). Merchantable volume of live trees 

(cubic foot, for trees ≥5 inches d.b.h., and international board-foot rule, for conifers ≥9 

inches d.b.h. and hardwoods ≥11 inches d.b.h.) were calculated with equations from 

Larson and Winterberger (1988).

2 Authors: Robert Pattison, Andrew Gray, and Hans-Erik Andersen.
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GENERAL TECHNICAL REPORT PNW-GTR-967

Results

The majority (89 percent) of the total land area of both inventory units (TVSF and 

TNWR) was forested (table 1). Twenty percent of the land area in TNWR was 

nonforest, whereas 3 percent of the land area in TVSF was nonforest. 

Black spruce (48 percent) and birch (29 percent) forests were the most common 

forest types across both inventory units (table 2). On the TVSF, black spruce and 

birch forests represented 42 and 32 percent of the area, respectively, while on the 

TNWR they represented 69 and 20 percent of the area, respectively (table 2). 

There were 3,861 live trees and 271 standing dead trees measured on the 98 

forested plots across the TVSF and TNWR. Six tree species were measured; white 

spruce had the most aboveground live tree biomass, followed by black spruce and 

Alaska birch (table 3).

There were an estimated 55.604 (± 5.38) million tons of aboveground live tree 

biomass on the two inventory units (table 4). The majority (86 percent) of this was 

found on forests of the TVSF (47.6 ± 5.0 million tons). An estimated 4.3 (± 1.0) 

million tons of standing dead tree biomass were found on the two inventory units, 

or 7.7 percent of the live tree biomass. Proportions of dead to live were lowest in 

the black spruce forest type (2.8 ± 0.6 percent) and substantially higher in the white 

spruce forest type (11.5 ± 6.1 percent).

Figure 7—Aerial photo of mosaic of forest and wetlands in the Tanana River Valley. 

Forest Inventory and Analysis

Black spruce (48 

percent) and birch (29 

percent) forests were 

the most common 

forest types across 

both inventory units. 
11

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Table 1—Estimated area of land cover categories in the Tanana Valley State 

Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR), derived from the 

Forest Inventory and Analysis field plot weightsa

Land type TVSF SE TNWR SE Total SE

Acres

Forest 1,740,617 34,026 537,052 44,517 2,277,669 56,032

Nonforest 58,872 29,047 145,688 46,727 204,560 55,019

Noncensus water 0 0 0 0 0 0

Census water 0 0 52,833 28,064 52,833 28,064

Total area 1,823,599 44,738 727,043 64,538 2,560,642 78,528

Note: Census water includes bodies of water ≥4.5 ac in size and rivers ≥200 ft wide. SE = standard error.

a Estimated area is based on the plot sample and may differ from mapped classifications.

Table 2—Estimates of the area of forest types in the Tanana Valley State Forest 

(TVSF) and Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Acres

Black spruce 732,460 103,208 373,017 58,304 1,105,478 118,537

White spruce 240,778 71,419 56,148 31,017 296,926 77,864

Aspen 82,319 46,142 0 0 82,319 46,142

Birch 555,832 97,770 107,887 46,882 663,718 108,429

Poplar 94,000 48,112 — — 94,000 48,112

Nonstocked 35,227 30,491 — — 35,227 30,491

Total area 1,740,617 34,026 537,052 44,517 2,277,669 56,032

Note: Totals may be off because of rounding; data subject to sampling error. SE = standard error. — = estimated 

at less than 500 ac. 

Table 3—Estimated aboveground live tree biomass by species in the Tanana 

study area, showing totals and per-acre means

Species Total SE Mean SE

- - - -Thousand tons- - - - - - - -Tons per acre- - - -

Tamarack 13 10 0.01 0

White spruce 18,350 4,444 8.06 1.95

Black spruce 16,897 2,500 7.42 1.09

Alaska birch 16,605 3,669 7.29 1.61

Quaking aspen 1,764 1,419 0.77 0.62

Balsam poplar 1,974 999 0.87 0.44

All species 55,604 5,378 24.4 2.3

SE = standard error.
12

GENERAL TECHNICAL REPORT PNW-GTR-967

The forests of the TVSF had higher live tree biomass per acre (27.3 ± 2.8 tons 

per acre) than those of the TNWR (14.9 ± 3.7), primarily owing to the greater 

proportions of white spruce forest area on TVSF (fig. 8). On both the TVSF and the 

TNWR, the greatest tree biomass per acre occurred in white spruce forest types, and 

the lowest occurred in black spruce forests. White spruce forests had similar biomass 

per acre for both the TVSF (48.8 ± 11.6 tons per acre) and the TNWR (46.2 ± 4.8 

tons per acre), whereas black spruce forests on the TVSF had twice the biomass per 

acre as TNWR. Nonstocked forest was found on one recently disturbed plot and had 

the highest standing dead tree biomass per acre (7.3 ± 0 tons per acre). Black spruce 

forests had the lowest standing dead tree biomass per acre (0.4 ± 0.1 tons per acre). 

Similar to the biomass results, merchantable net volume of live trees was 

substantially higher on TVSF than on TNWR (table 5). Merchantable volumes per 

acre were much higher in white spruce forests than the other forest types, and were 

lowest in black spruce for cubic-foot volume. Although cubic-foot volume of black 

spruce was lower on TNWR than TVSF, the reverse was true for board-foot volume, reflecting a greater density of large trees on that forest type in TNWR than in 

Table 4—Estimates of total aboveground tree biomass (thousands of tons) for 

live and standing dead trees in forests on the Tanana Valley State Forest (TVSF) 

and the Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Thousand tons

Live trees:

Black spruce 13,891 2,652 3,279 1,136 17,170 2,885

White spruce 11,752 4,433 2,592 1,486 14,344 4,676

Aspen 1,811 1,822 — — 1,811 1,822

Birch 18,009 4,403 2,139 1,339 20,148 4,602

Poplar 2,132 1,097 — — 2,132 1,097

Nonstocked — — — — — —

Total live 47,594 5,009 8,010 1,957 55,604 5,378

Standing dead trees:

Black spruce 367 99 115 42 481 107

White spruce 1,559 867 95 78 1,654 871

Aspen 188 174 — — 188 174

Birch 1,350 358 41 32 1,391 359

Poplar 331 287 — — 331 287

Nonstocked 256 222 — — 256 222

Total dead 4,052 948 251 90 4,303 952

SE = standard error. — = no samples fell in this combination of classes.
13

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

0

10

20

30

40

50

60

70

Black

spruce

White

spruce

Aspen Birch Poplar Nonstocked All types

Biomass density (tons/acre)

Forest type

Forest type

Live trees

Standing dead trees

TVSF

TNWR

Total

Black Nonstocked

spruce

White

spruce

Aspen Birch Poplar All types

0

2

4

6

8

10

1

3

5

7

9

Biomass density (tons/acre)

TVSF

TNWR

Total

Figure 8—Estimates of aboveground live and standing dead tree biomass per acre (tons per acre) in forest types on the Tanana Valley State Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR). 
14

GENERAL TECHNICAL REPORT PNW-GTR-967

TVSF. Hanson (2013) estimated 963 ft3/ac and 1,885 board feet per acre net volume 

on state lands in the Tanana Valley, of which 63 percent was TVSF. The lower 

volume estimates from the FIA inventory may be due to the different land base, or 

to using different equations in our current compilation system. Older FIA documentation had some of the same equations Hanson (2013) identified for interior Alaska, 

which we will evaluate before completing the basinwide inventory.

Discussion

There was almost twice the tree biomass per acre on forests of the TVSF as on the 

TNWR forests. Within the TNWR, white spruce forests had more than five times 

the biomass per acre as black spruce forests (table 4). These results highlight the 

variability in forests within the region. Forest composition and structure in interior 

Alaska are strongly determined by physiographic characteristics that influence solar 

radiation, and soil temperature and moisture (Viereck et al. 1983). Sites with colder 

soils (e.g., lowlands and north-facing slopes) are commonly dominated by black 

spruce forests with lower tree biomass, whereas sites with warmer soils (e.g., southfacing uplands) are often dominated by white spruce or deciduous forests (Viereck et 

al. 1983). The TVSF is characterized primarily by sites supporting more productive 

forests that are important for their timber resources (Hanson 2013). The TNWR is 

Table 5—Estimates of live tree merchantable net volume (cubic and board foot) 

in forests on the Tanana Valley State Forest (TVSF) and the Tetlin National 

Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Cubic feet per acre

Black spruce 183 40 115 61 160 34

White spruce 1,988 518 1,616 277 1,918 424

Aspen 955 845 — — 955 845

Birch 984 213 146 97 848 188

Poplar 591 68 — — 591 68

All forest types 743 127 279 105 634 101

Board feet per acre (international rule)

Black spruce 148 72 352 332 217 122

White spruce 6,950 2,215 5,831 967 6,738 1,805

Aspen 198 176 — — 198 176

Birch 2,007 698 178 191 1,709 599

Poplar 1,011 442 — — 1,011 442

All forest types 1,728 459 890 435 1,531 366

SE = standard error. — = no samples fell in this combination of classes.

There was almost twice 

the tree biomass per 

acre on forests of the 

TVSF as on the TNWR 

forests.
15

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

primarily composed of less productive lowland forests, as indicated by aboveground 

live tree biomass per acre in black spruce forests at half the amounts found in TVSF. 

However, areas of more productive forests occur within the TNWR as evidenced by 

the presence of white spruce forests with high tree biomass per acre (fig. 9). Although 

black spruce forests had relatively low tree biomass per acre, the collective acreage of 

these forests highlights their importance to total tree biomass in the region. 

Although the values for tree biomass per acre within forest types were generally consistent with the values found in Viereck et al. (1983) (table 6), the values 

for birch forests in this study were lower. One potential reason for the discrepancy 

might be that the FIA field sample was a probabilistic sample, whereas Viereck et 

al. (1983) subjectively sampled forests, which may have resulted in a sample of more 

productive forests present in the primary study area that was being used. 

The FIA forest type classification is a simple grouping based on dominant species and obscures the reality that many forests have multiple dominant tree species, 

and that many with the same species are significantly different in stature, function, 

and composition of other species. This topic is explored in more detail later in this 

report. With additional work and some subjective assessment, it might be possible 

to group plots to level IV or V classes of Viereck et al. (1992) or other classifications 

that users might find useful.

Figure 9—Dense ground layer of forage lichens and mosses in patchy mosaic of a mixed black and 

white spruce forest.

Forest Inventory and Analysis
16

GENERAL TECHNICAL REPORT PNW-GTR-967

Although this study represents a preliminary estimate for a subset of the landscape, it demonstrates the variation present in forest composition and density and 

the effect that can have on landscape- and regional-level estimates of live and dead 

tree biomass. We expect the mean biomass densities for forest land to change as we 

complete the Tanana River basin and move on to other areas of interior Alaska. Live 

tree growth is being estimated from increment cores and will be reported in future 

publications. Mortality rates will be difficult to estimate with much precision until 

these plots are up for remeasurement, hopefully in 10 to 12 years.

Characterizing Forest Vegetation of the Tanana Valley3

Introduction

Knowledge of the existing distribution and abundance of plant species and how 

they are organized into plant community types is important for monitoring the 

successional changes of natural ecosystems in response to both discrete and 

chronic disturbances. Many recent studies in Alaska have documented large-scale 

changes in vegetation cover linked to changes in climatic conditions. Shrubs are 

expanding into both arctic (e.g., Berner et al. 2015, Tape et al. 2006) and alpine 

tundra (Dial et al. 2007, 2016), hardwoods replace spruce in some areas (Johnstone et al. 2010), and white spruce forests are expanding in others (Roland et al. 

2013). Our understanding of successional pathways is evolving as increasing fire 

frequency and permafrost degradation re-order community structure (Johnstone 

et al. 2008, Jorgenson et al. 2013). At the same time, new pest outbreaks are being 

observed that could further influence shifts in vegetation composition (Nossov 

et al. 2011, USDA FS 2015). These changes can affect biomass accumulation and 

3 Author: Bethany Schulz.

Table 6—Tree biomass for different forest types near Fairbanks, Alaska

Forest type

Number of 

stands Range Mean SE

Tons per acre

Black spruce 4 7.07 49.00 22.72 9.40

White spruce 4 27.44 109.64 77.81 19.09

Aspen 2 20.76 78.02 49.39 28.63

Birch 3 41.00 65.63 49.77 7.95

Poplar 3 18.14 80.42 53.96 18.58

SE = standard error.

Source: Viereck et al. 1983.
17

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

greenhouse gas emissions (Rupp 2011), which are commonly used to assess rates of 

climate change. In the past, national assessments of greenhouse gas emissions have 

excluded most of Alaska outside of southeast coastal forests owing to lack of data 

and the minimal amount of managed forested lands, and the long-held idea that the 

boreal region was a C sink.

Forest vegetation in interior Alaska is less species-rich in vascular plants than 

in other biomes, with a limited number of overstory tree species and fewer FIA 

forest types. However, plant species organize into many unique assemblages, 

depending on site characteristics. Characterizing forest plant communities beyond 

forest types determined by tree stocking can sharpen our focus/understanding of 

the consequences of the changes we may detect in future measurements, potentially 

influenced by changes in climate and disturbance regimes.

Vegetation data collected on the ground are relatively scarce in Alaska 

and are usually collected within a limited spatial extent owing to the logistical 

challenges of travel in interior Alaska. For example, sampling strategies are 

often limited to a land management unit (Roland et al. 2013) or along the limited 

road system (Hollingsworth et al. 2006, Malone et al. 2009). The FIA 2014 pilot 

project in interior Alaska provides a systematic sample of 71 plots within the 

TVSF and 27 plots on the TNWR. This relatively small sample size allows us 

to begin to explore the current structure and species distributions. Given rapid 

changes occurring and expected to occur in interior Alaska, documenting vegetation conditions now is essential for monitoring vegetation change over time. 

Using data generated from FIA’s Vegetation Profile (VEG profile) protocol along 

with standard inventory data, the vegetation in the different forest communities 

sampled are characterized. 

Methods

Standard national FIA core data elements, as described in the introduction, were 

collected on 98 plots and distributed systematically across the TVSF and the 

TNWR in interior Alaska. In addition, the FIA Core-Optional VEG Profile level 

of detail 3 protocol was implemented on all plots (USDA FS 2014c). Both forest 

and nonforest conditions were sampled if accessible. Data were collected on 

each subplot. 

Structure was measured as canopy cover of growth habits by height layer (see 

the tabulation below). Growth habits include graminoids (grass-like plants), forbs, 

shrubs, tally species trees, and nontally tree species. Tally tree species are those that 

are tracked and measured with core FIA tree measurements. The tally list is short 
18

GENERAL TECHNICAL REPORT PNW-GTR-967

for Alaska, and only six species are found in interior Alaska: black spruce, white 

spruce, Alaska birch, balsam poplar, trembling aspen, and tamarack. Other species 

encountered as trees are recorded as nontally trees. 

Layer number Range

1 Ground level (0 to 2 ft)

2 Greater than 2 to 6 ft

3 Greater than 6 to 16 ft

4 Greater than 16 ft

Species information was collected for the four most abundant vascular plant 

species per growth habit, if the species was present with at least 3 percent canopy 

cover on a subplot. Abundance was recorded as a percentage of the area of a subplot 

with canopy cover. The growth habits for species data are as described for structure, except for trees, which are recorded as small trees (distinct main stem but less 

than 5 inches d.b.h.) or large trees (at least 5 inches d.b.h.), regardless of tally tree 

status. These data were summarized by averaging subplot cover measurements by 

plot (and condition for those plots with more than one condition class), and determining the percentage of plots where species were recorded for various domains. 

Estimates of forest structure and species cover were produced following standard 

FIA compilations (Bechtold and Patterson 2005). 

In addition, a full census of all vascular plants on subplot 1 was implemented 

on the plots within the TNWR by the U.S. Fish and Wildlife Service (which also 

conducted insect surveys). Here, all species were recorded with an ocular estimate 

of percentage canopy cover, with no minimum cover limitation. 

Results and Discussion

Standard FIA forest types are based on the existing tree species stocking. Forest 

type is one of several variables that define a forested “condition;” other biologically 

defined variables include stand size class and tree density. Although the official 

definition refers to the “plurality” of tree species, all FIA forest types in Alaska 

refer to one tree species only. Because plot centers are systematically selected, there 

are many plots where several conditions or forest types occur on a single plot. For 

the interior Alaska pilot, nonforest conditions on forested plots were included in 

measurements; 15 of 26 subplots with nonforest conditions have VEG Profile data.

Of the 98 sampled plots, 73 were intact (fully forested in a single condition), 11 

were fully forested but with multiple conditions, and 14 plots included some nonforest land cover class (table 1). The black spruce forest type was the most common, 

with 38 intact plots, and occurred on 7 plots with multiple conditions and 8 plots 

with some nonforest conditions. Alaska birch was the second most common with 20 
19

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

intact plots; white spruce was third with 8 intact plots. All the nonforest land cover 

classes sampled were natural vegetation types, with shrubland being most common. 

Full descriptions of forested conditions sampled and distribution between the two 

land managers are included in table 7.

Structure—

Average cover by growth habit and layer varied by forest type and land manager 

(fig. 10). Note that all aspen and balsam poplar stands are within the TVSF, and that 

the white spruce forests on TNWR are represented by mixed-condition plots and 

some plots with nonforest conditions. Tree cover in black spruce stands on TVSF 

was greatest in layer 3, while tree cover in TNWR was greatest in layer 2. White 

spruce stands had similar profiles for both management areas, but with grass and 

forbs providing more cover in TVSF. The tally tree species cover tends to be highest 

in birch and balsam poplar stands. Aspen and balsam poplar stands occurred only 

in TVSF. Balsam poplar had the highest average cover of tally trees in layer 4 of all 

forest types, but these estimates are based on very small sample sizes. Nontally tree 

cover was minimal and is not shown to simplify the figures. 

Shrubs were common in all types but varied by height. Low shrubs in layer 

1 dominate in most forest types, with average canopy cover from greater than 25 

to over 40 percent. In some stands, these low shrubs provide continuous ground 

fuels that play an important role in fire behavior. Tall shrubs (layers 3 and 4) are 

prominent in birch, white spruce, and balsam poplar forest stands. Tall shrubs often 

provide browse for wildlife species and contribute more to total biomass than other 

components of understory vegetation. Grass can compete with trees in regeneration harvest units; it was present in all types, with the highest values found in birch 

forest types on TVSF. Forbs were most abundant in balsam poplar stands.

Vascular plant species—

Two methods were used to collect species records: (1) the core FIA VEG Profile 

and (2) a full census on subplot 1 conducted by TNWR. In total, 79 genera, 145 

species, 11 subspecies, and seven varieties were recorded; 47 genera, 94 species, 

and 7 subspecies were recorded with the VEG Profile; and 68 genera, 115 species, 

10 subspecies, and 7 varieties from the full census. There were 32 genera, 45 

species, 3 subspecies, and 7 varieties recorded unique to the full census. Over the 

same TNWR plots where the full census was conducted, only 34 genera, 54 species, and 6 subspecies were recorded over the 105 subplots with the VEG Profile 

method. Scientific and common names, recorded growth habits, wetland indicator 

status, and with constancy (percentage of plots where recorded) by owner and 

survey method are shown in appendix 1. Note that the genus Carex is represented 

Tall shrubs (layers 3 

and 4) are prominent 

in birch, white spruce, 

and balsam poplar 

forest stands.
20

GENERAL TECHNICAL REPORT PNW-GTR-967 Table 7—Number of plots by forested condition and percentage of plots with records of large (LT) and small (SD) trees by species Tree species Plot count Black spruce Alaska birch White spruce Quaking aspen Balsam poplar Tamarack Condition and forest type description Total TVSF TNWR LT SD LT SD LT SD LT SD LT SD SD - - - - Number - - - - - - - - - - - - - - - - - - - - - - - - - Percentage of plots where recorded - - - - - - - - - - - - - - - - - - - - - Single condition: Black spruce 38 25 13 47 100 21 50 21 0 8 8 0 0 8 Alaska birch 20 17 3 20 45 80 90 55 60 5 25 5 5 0 White spruce 8 8 0 0 0 75 50 100 88 25 25 13 0 0 Aspen 3 3 0 0 33 33 67 67 67 67 67 0 0 0 Balsam poplar 3 3 0 0 0 0 0 33 67 0 0 100 100 0

Nonstocked 1 1 0 0 0 0 0 0 0 0 0 0 0 0

Multiple condition:

Black spruce/Alaska birch 4 4 0 75 100 100 100 50 100 0 0 0 0 0Black spruce/multiage 3 0 3 33 100 0 100 67 100 0 0 0 0 0

White spruce/multiage 2 1 1 0 0 0 0 100 100 0 0 50 0 0

Alaska birch/multiage 1 1 0 0 0 100 100 100 100 0 0 0 0 0White spruce/Alaska birch 1 0 1 0 100 100 100 100 100 0 0 0 0 0

Some nonforest:

Black spruce/shrubland 3 2 1 33 100 0 33 0 0 0 0 0 0 33

Black spruce/mixed vegetation 2 1 1 50 100 50 0 50 100 0 50 0 0 0

White spruce/shrubland 2 2 0 0 0 100 50 100 50 0 0 0 0 0Black spruce/shrubland/mixed 

vegetation

1 1 0 100 100 100 0 100 100 0 0 0 0 0

Black spruce/nonvascular 1 0 1 100 100 0 100 0 0 0 0 0 0 0White spruce/mixed vegetation 1 1 0 100 100 0 100 100 100 0 0 0 0 0Alaska birch/shrubland 1 1 0 0 0 0 0 0 0 0 0 0 0 0Alaska birch/nonvascular 1 0 1 0 100 0 100 0 0 0 0 0 0 0Alaska birch/mixed vegetation 1 1 0 100 100 0 100 100 0 0 0 0 0 0White spruce/nonvascular 1 0 1 100 0 0 0 0 100 0 0 0 0 0
21

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

0 10 20 30 40 50 60

<2

2-6

6-16

>16

Canopy cover (percent)

Layer height (ft)

TVSF black spruce

Tally tree Shrub Grass-like Forbs

Canopy cover (percent)

0 10 20 30 40 50

<2

2-6

6-16

>16

Layer height (ft)

TNWR black spruce

Tally tree Shrub Grass-like Forbs

0 20 40 60

<2

2-6

6-16

>16

Layer height (ft)

TVSF birch

Canopy cover (percent)

Tally tree Shrub Grass-like Forbs

0 10 20 30 40 50 60 70

<2

2-6

6-16

>16

Layer height (ft)

TNWR birch

Canopy cover (percent)

Tally tree Shrub Grass-like Forbs

0 10 20 30 40 50 60 70

<2

2-6

6-16

>16

Layer height (ft)

TVSF aspen

Canopy cover (percent)

Tally tree Shrub Grass-like Forbs

0 10 20 30 40 50 60 70

<2

2-6

6-16

>16

Leyer height (ft)

TVSF balsam poplar

Canopy cover (percent)

Tally tree Shrub Grass-like Forbs

Canopy cover (percent)

0 10 20 30 40 50 60 70

<2

2-6

6-16

>16

Layer height (ft)

TVSF white spruce

Tally tree Shrub Grass-like Forbs

Canopy cover (percent)

0 10 20 30 40 50 60 70

<2

2-6

6-16

>16

Layer height (ft)

TNWR white spruce

Tally tree Shrub Grass-like Forbs

Figure 10—Average cover by growth habit by layer for five predominant forest types in the Tanana Valley State Forest (TVSF) and the 

Tetlin National Wildlife Refuge (TNWR).
22

GENERAL TECHNICAL REPORT PNW-GTR-967

by 20 species. There are also 17 species of Salix (8 of which can attain small tree 

size), and 6 species of Equisetum. No introduced or invasive species were recorded 

in either effort. There is one record of the common dandelion (Taraxacum officinale ssp. ceratophorum (Ledeb.) Schinz ex Thell.), but this subspecies is native to 

Alaska. 

Combining both methods of species surveys, in total 26 obligate wetland 

species (those species almost always occurring in wetlands) were recorded on 

20 plots. Fourteen obligate wetland species were recorded on 11 plots using the 

Veg Profile method, and another 12 obligate species were recorded using the full 

census method plots. On TVSF, five plots had obligate wetland species; three were 

single-condition black spruce, one was black spruce with shrubland, and another 

was black spruce with shrubland and mixed vegetation. On TNWR, 12 plots were 

single-condition black spruce, 1 was black spruce with nonvascular vegetation, and 

2 were white spruce—one with shrublands and another with nonvascular vegetation. Finding obligate wetland species within black spruce vegetation types is not 

unusual, considering that black spruce can be found in a variety of landscape positions. Wetland species occurring within a white spruce forest type is a bit unusual, 

as it is generally understood that white spruce is found on drier, more productive 

sites. This could indicate the presence of thermokarst formation—areas where ice 

wedges have melted out, often producing small ponds of standing water surrounded 

by slightly elevated lands now draining and drying out (Jorgenson et al. 2001). As 

we continue work in interior Alaska, it would be beneficial to note potential signs of 

thermokarst formation.

Most abundant species—

Tree and shrub species dominated the most commonly recorded abundant species 

for each forest type using the core FIA VEG Profile (table 8), and most forest types 

had several top species in common. The hardwood types with only a few sample 

plots had a few unique species that are included in table 8, but most species are 

ubiquitous across most forest types. The most abundant species plus any fruitbearing species by land manager are shown in tables 9 and 10.

Tree species distributions are displayed by size across forest conditions in table 

1. The VEG Profile data allow for a different perspective of regeneration than the 

sapling and seeding counts on microplots; abundance is recorded as canopy cover 

over the entire subplot area. Large trees were 5 inches or greater in diameter, and 

small trees were less than 5 inches in diameter (USDA FS 2014b). Black spruce 

and birch forest types are tied for number of other tree species found on singlecondition plots, but white spruce and birch trees are found on more forest types 

and condition combinations than black spruce trees (table 7). Fifty percent of black 
23

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

spruce plots had small Alaska birch trees present with at least 3 percent cover. Cooccurrence of spruce and birch on many plots reflects how FIA forest types do not 

identify mixed stands. 

Nontally tree species were recorded as either large or small trees on seven plots 

and included green alder (Alnus viridis (Chaix) DC.), Bebb willow (Salix bebbiana 

Sarg.), and Scouler’s willow (S. scouleriana Barratt ex Hook.). The seven plots 

included three white spruce, three birch, and one black spruce forest type. 

Other alder and willow species were commonly recorded as shrubs and 

provided cover in the mid layers of most other conditions sampled. An alder species was recorded on 58 of 98 plots, and on 30 of those plots, the average subplot 

cover was greater than 15 percent. Green alder was the most commonly recorded 

species. Alder species are important pioneer species on many sites. They provide 

nitrogen fixation via symbiotic bacterial nodules, and litter production leads to 

higher C incorporation into soil, producing sites suitable for other plant species. 

Soils beneath alders are known to be higher in C and nitrogen than adjacent 

spruce or mixed-forest stands (Mitchell 1968). Thin-leaf alder Alnus incana (L.) 

Table 8—Most common abundant species and percentage of plots where recorded overall and by forest type

Forest type

Species common name

All plots

(n = 98)

Black 

spruce

(n = 38)

Alaska 

birch

(n = 20)

White 

spruce

(n = 8)

Balsam 

poplar

(n = 3)

Aspen

(n = 3)

Other

(n = 25)

Percentage of plots where recorded

Lingonberry 72 1 84 3 65 4 38 0 33 88

Black spruce 68 2 100 1 45 0 0 33 76

Alaska birch 67 3 53 4 100 1 88 2 0 67 2 68

Bog Labrador tea 62 4 87 2 55 5 0 0 33 64

White spruce 58 5 34 70 3 100 1 67 2 67 2 72

Green alder 53 6 40 75 2 63 3 0 67 2 60

Bog blueberry 38 7 53 4 25 0 0 33 44

Prickly rose 36 8 8 70 3 88 2 67 2 33 32

Bluejoint 28 9 13 40 38 67 2 67 2 28

Dwarf birch 24 10 42 5 5 0 0 0 24

Field horsetail 16 11 20 63 3 67 2 33 16

Quaking aspen 16 11 30 25 0 100 1 4

Fireweed 12 3 25 13 33 67 2 8

Thinleaf alder 8 0 5 38 100 1 0 4

Balsam poplar 6 0 5 13 100 1 0 4

Redosier dogwood 2 0 0 0 67 2 0 0

Note: Superscripts indicate the rank of the five most common species within each forest type; n = number of plots.
24

GENERAL TECHNICAL REPORT PNW-GTR-967

Table 9—Most commonly recorded species, plus fruit-bearing species in Tanana 

Valley State Forest (TVSF), with constancy and average cover where present

Common name Constancy Average cover SE

Percent

Alaska birch 69 22 3.1

Lingonberry 67.6 13 2.2

White spruce 63.4 17 2.8

Black spruce 59.2 39 3.5

Bog Labrador tea 57.7 21 3.5

Prickly rose 42.3 15 3.8

Bluejoint reed grass 35.2 16 3.7

Mountain alder 26.8 12 2.4

Bog blueberry 25.4 10 2.4

Field horsetail 23.9 27 6.6

Cloudberry 14.1 4 1.2

High bush cranberry 12.7 11 6.4

Black crowberry 11.3 6 1.6

American red raspberry 4.2 2 0.4

Red currant 2.8 2 0.5

SE = standard error.

Table 10—Most commonly recorded species, plus fruit-bearing species in Tetlin 

National Wildlife Refuge (TNWR), with constancy and average cover where present

Common name Constancy Average cover SE

Percent

Black spruce 92.6 24 3

Lingonberry 85.2 8 1.1

Bog Labrador tea 77.8 24 3.4

Bog blueberry 70.4 8 1.3

Alaska birch 63 19 6.7

Grayleaf willow 51.9 4 0.9

Dwarf birch 44.4 11 2.5

White spruce 44.4 15 5.1

Mountain alder 40.7 16 4.3

Black crowberry 33.3 8 2.2

Prickly rose 22.2 4 2.1

Cloudberry 7.4 2 0.8

SE = standard error.
25

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Moench ssp. tenuifolia (Nutt.) Breitung has been 

subject to die-back in recent years, especially in 

dense stands that form along riverbanks (Nossov 

et al. 2011, USDA FS 2015).

There were 54 plots with one to three species of 

willow, and 32 plots with one of the seven willow 

species that may be encountered either as shrubs 

or trees (app. 1) (USDA NRCS 2015, Viereck and 

Little 2007). Grayleaf willow was recorded most 

often. Willows are important browse species, with 

feltleaf (Salix alaxensis (Andersonn) Coville, Bebb 

(S. bebbiana Sarg.), and grayleaf all being important for moose browse. Bebb willow is the most 

common species forming “diamond willow:” stems 

with diamond-shaped patterns along their trunks 

that can be carved into walking sticks or furniture 

(fig. 11). Formations are formed by several species 

of fungi that attack branches at the junction with 

the main stem (Viereck and Little 2007) 

Tall alder and willow shrubs represent an 

underaccounted source of biomass; allometric 

equations based on cover and height alone do not 

exist. Although common in lands classified as 

forests, they also cover vast landscapes as the tall 

shrub vegetation cover. Tall shrubland cover type 

represent a measureable portion of the landscape: 6 

percent of interior/Cook inlet—19,065,193 ac (tall 

shrub) and an additional 316,209 ac (low or tall 

shrub) (Boggs et al. 2014).

Common low shrubs include the important berry species valued as traditional 

food sources, lingonberry, (Vaccinium vitis-idaea L.), and bog blueberry, (V. 

uliginosum L.) (Hupp et al. 2015) as well as species that create continuous fuels 

for wildfire such as bog Labrador tea (Ledum groenlandicum Nutt.) and dwarf 

birch, (Betula nana L.) (fig. 12). Bog Labrador tea and lingonberry make up the 

majority of shrub cover in layer 1 in black spruce forest types (mean canopy cover 

21.4 (SE 3.0) and 10.8 (SE 2.1), respectively). Prickly rose (Rosa acicularis Lindl.) 

produce rose hips, important for human use and forage for bird species (Viereck 

and Little 2007).

Figure 11—Carved Bebb’s willow stems displaying “diamond willow” 

scar formations.

Matthew O’Driscoll

Common low shrubs 

include the important 

berry species valued 

as traditional food 

sources, lingonberry, 

(Vaccinium vitis-idaea

L.), and bog blueberry.
26

GENERAL TECHNICAL REPORT PNW-GTR-967

Only a few herbaceous species appear in tables 8 through 10; bluejoint grass 

(Calamagrostis canadensis (Michx.) P. Beauv.) and field horsetail (Equisetum 

arvense L.). Both can indicate rich, wet soils. Although many forb and grass species 

were recorded (65 forb species and 34 grass-like species), they may be more commonly present with percentage canopy cover lower than 3 percent. 

Overall, TVSF is more diverse, with a wider range of elevations, forest types, 

and lower constancies for most common species recorded. Although berry species 

may be more dispersed on TVSF, one might find bigger patches there. If you are 

looking for new berry picking spots, you may have better success on the TNWR. 

Figure 12—Detail of vegetation on a boreal forest floor showing forage lichen and lingonberry. 

Sarah Ellison
27

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Crosswalk to the Alaska Vegetation Classification—

The Alaska Vegetation Classification (Viereck et al. 1992) is widely referenced by 

land managers and resource specialists and is often used to interpret vegetation mapping efforts in Alaska (Boggs et al. 2001, 2014; Cella et al. 2008). This classification 

is broadly hierarchical. Level I describes the major vegetation cover: forest, scrub, 

and herbaceous. At Level II, forests are defined as needle-leaved, broadleaved, and 

mixed. Needle-leaved and broadleaved designations indicate that conifer or deciduous tree species make up 75 percent or more of the tree cover. In mixed forests, 

there is no clear dominance of either needle-leaved or broadleaved species. Level 

III is defined by canopy closure; closed forests have canopy cover of 60 percent or 

more, open forests have between 25 and 60 percent canopy closure, and woodlands 

have less than 25, but at least 10 percent cover. Scrub vegetation classes (dominated 

by shrubs) include dwarf tree scrub, tall scrub, low scrub, and dwarf scrub. The 

dwarf tree scrub class is defined as vegetation having 10 percent or more cover of 

a tree species that will not exceed the height of 10 ft at maturity, and tall scrub is 

vegetation at least 5 ft tall, with 25 percent or more cover in tall shrubs. Herbaceous 

vegetation types are dominated by nonwoody vegetation and are divided into graminoid, forbs, bryoid (mosses and lichens), and aquatic vegetation. These are further 

divided by moisture classes; dry, mesic, and wet. Level IV of the Alaska Vegetation 

Classification begins to specify the dominant vegetation species, which can be difficult to distinguish from remotely sensed data over large geographic areas. 

Using VEG Profile data together with tree data collected, each subplot or condition can be classified to at least Level III, and often beyond. I examined the Veg 

Profile subplot species records and classified each to Level III of the Alaska Vegetation Classification, often referring to Veg Profile Structure, Plot, Condition and Tree 

data to verify or adjust the Level III class. For each subplot or condition assessed, 

the FIA forest type assigned was noted. Hardwood stands less than 20 years old 

and conifer stands less than 30 years old were not included to avoid misplacement 

into Level I scrub types (10 complete and 2 partial plots). Table 11 demonstrates the 

wide variety of structure and composition that each of the five FIA forest types can 

represent, with both the FIA black spruce and birch forest types each keying out to 

nine different Alaska Vegetation Classification Level III classes. Summarizing the 

results of inventory by FIA forest types can lose sight of the complex relationships 

among site qualities, past and ongoing disturbances, and species composition and 

structure. As forest inventory continues in interior Alaska, there may be reason to 

further define the FIA forest types in this region.
28

GENERAL TECHNICAL REPORT PNW-GTR-967

Summary—

Vegetation data collected on the ground are relatively scarce in Alaska, but is essential to aid the interpretation of the remotely sensed data that managers have come 

to depend on with increasing frequency. One goal of vegetation data analysis is to 

understand how existing vegetation communities may change in the future. Shifts 

in species composition can be a signal of changes in moisture availability or drainage that are not evident at the soil surface. Changes in vegetation structure often 

Table 11—Number of plots of each Forest Inventory and Analysis (FIA) forest 

type where at least one subplot or condition represents a Level III type of the 

Alaska Vegetation Classification

Level III

Level I Level II FIA forest type Closed (1) Open (2) Woodland (3)

I (forest) Number of plots

A (needle-leaf) Black spruce 9 33 14

White spruce 4 9 4

Birch 2 2 0

Balsam poplar 0 1 0

B (broadleaf) Birch 12 7 1

Aspen 1 0 0

Balsam poplar 1 3 0

C (mixed) Black spruce 0 8 4

White spruce 2 4 1

Birch 6 10 0

Balsam poplar 1 0 0

II (scrub)

A (dwarf tree) Black spruce 2 9 6

Nonstocked 0 0 2

B (tall scrub) White spruce 0 1 0

Nonstocked 1 0 0

C (low scrub) Black spruce 0 1 0

White spruce 0 1 0

Birch 0 1 0

Nonstocked 1 2 0

III (herbaceous) Dry (1) Mesic (2) Wet (3)

A (graminoid) Nonstocked 0 0 2

B (forb) Nonstocked 0 0 1
29

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

trigger further change to communities by altering waterflow, nutrient cycling, and 

capture of solar radiation (Jorgenson et al. 2013, Sturm et al. 2001). Although the 

interior Alaska pilot was a first-time visit, some novel plant communities sampled 

could indicate sites undergoing transitions. 

The VEG Profile provides important information about the arrangement of 

vascular plants in the forest stands sampled. Structure characterization is important 

for fire behavior modeling and wildlife habitat assessments. Data on the distribution of large and small trees reveal the presence of multiple other tree species on 

most plots assigned to a single-species forest type, suggesting that alternative 

successional pathways are possible under particular disturbance regimes, including climate change (Johnstone et al. 2010, Mann et al. 2012, Rupp 2011). Although 

VEG Profile captures the presence of large shrubs and nontally trees with cover and 

height layer, the only allometric equations for calculating biomass of large shrubs 

are based on stem diameters (Chojnacky and Milton 2008). Stem diameter measures 

for large woody shrubs and nontally tree species should be considered in the future 

for inclusion into biomass estimations (e.g., Bond-Lamberty et al. 2002, Mack et 

al. 2008). In addition, adding a full census of vascular plant species on at least one 

subplot per plot would capture important rare or indicator species that can occur 

with minimal abundance and provide a measure of species richness across the vast 

landscapes of interior Alaska. 

Although vegetation data allow us to describe forested areas with more detail 

and inference than tree data alone, we can go further by fully integrating the full 

suite of data variables collected. Standard plot and condition information collected 

on FIA plots, along with the special interior Alaska protocols (ground layer and 

soils), go a long way toward elucidating the types of changes that may be occurring. 

Combining tree, Veg Profile, soils, and ground layers provides the means to classify 

vegetation types further, incorporating landscape and topographic positions, which 

is helpful when overall species diversity is limited.
30

GENERAL TECHNICAL REPORT PNW-GTR-967

Patterns of DWM on the 2014 Tanana Pilot Inventory4

Introduction

Down woody materials are an important component of forest ecosystem structure 

and function. Down woody materials influence nutrient cycling, contribute to wildlife habitat and forest fires, and can contain a substantial proportion of terrestrial 

ecosystem biomass (Harmon et al. 1986, Woodall 2010). Relative to other forests 

types, the role of DWM in boreal forests is poorly understood (Pan et al. 2011, 

Pedlar et al. 2002). Recent natural disturbances in boreal forests of Siberia and 

Canada have led to an estimated 27 percent increase in the total deadwood (standing dead and DWM) in these forests (Pan et al. 2011). As boreal forest ecosystems 

of interior Alaska are experiencing some of the greatest increases in temperature 

globally (Arctic Climate Impact Assessment 2005) with associated declines in 

spruce productivity (Beck et al. 2011) and increases in fire frequency and severity 

(Kasischke and Turetsky 2006, Turetsky et al. 2011), it is important to understand 

the current status of these systems both to provide insights into the role of fire and 

to serve as a baseline for monitoring trends. 

Methods

As part of the 2014 Tanana pilot inventory, we carried out standard DWM 

sampling protocols (USDA FS 2014a). Down woody materials were sampled 

on accessible forest conditions on all field plots (i.e., portions of plots that were 

forested and where access was not hazardous). Sampling occurred by using the 

line-intercept method along transects located through the center of each of the 

subplots (fig. 5). Each transect is segmented to tally coarse woody debris (CWD) 

and fine woody debris (FWD). Coarse woody debris includes downed, dead 

tree and shrub boles, large limbs, and other woody pieces that are >3 inches 

diameter, >6 inches in length, and severed from their original source of growth. 

Coarse woody debris also consists of dead tally tree species or single-stemmed 

woodland species trees that are leaning more than 45° from vertical. Fine woody 

debris consists of downed, dead branches, twigs, and small tree or shrub boles 

<3 inches in diameter that are not attached to a living or standing dead source. 

Fine woody debris is tallied on 6- to 10-ft transects depending on the size of 

pieces. These FWD transects occur along the 24-ft CWD transects (fig. 5). 

The attributes collected on each piece intersecting the transect differ based on 

whether the pieces are CWD or FWD. For each CWD piece, transect diameter, 

4 Authors: Robert Pattison, Andrew Gray, and Hans-Erik Andersen.
31

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

species, and decay class were recorded. Decay class is a classification of the level 

of decay based on shape, presence of bark or branches, and wood density. Decay 

class 1 refers to pieces with little decay, while decay class 5 refers to pieces that 

have advanced decay.

Field data were compiled into estimates of DWM biomass using estimators 

based on transect diameter, transect length, and species detailed in Woodall and 

Monleon (2008). These estimators generate a volume for CWD pieces and convert 

these volumes into per-unit-area estimates. Volume estimates are then converted to 

biomass by accounting for species-specific wood density and decay class (Woodall 

and Monleon 2008). The estimates of the DWM content by forest type and owner 

for the Tanana pilot inventory unit were derived using the poststratified plot weights 

described in the “Introduction” (“Stratification and Analyses” section). 

Results

Birch forests on the TVSF had an estimated 4,122 (± 1,080) thousand tons of biomass in DWM or 48 percent of the total DWM biomass in the two inventory units 

(fig. 13). About 72 percent of that biomass was in CWD. The next highest DWM 

biomass values occurred on white spruce forests on TVSF, which had an estimated 

1,244 (± 453) thousand tons of biomass or 14 percent of the total DWM biomass 

in the two inventory units. For these forests, CWD made up 79 percent of the total 

DWM biomass. Within each forest type and landowner category, the percentage 

of DWM in CWD and fine woody materials (FWM) varied. Black spruce forests 

on TVSF and birch forests on TNWR had the lowest proportion of total DWM in 

CWD (33 to 39 percent). The remaining forest types had 50 to 79 percent of the 

total DWM in CWM (fig. 13). Birch forests on TVSF had the most CWD and FWD 

stocks (tables 12 and 13). 

Aspen forest types had the highest DWM biomass per acre, while black spruce 

forest types had the lowest (fig. 14). Birch forest DWM biomass per acre showed 

high variability between TVSF and TNWR with birch forests on TVSF having 2.8 

times more DWM biomass per acre than on TNWR. The CWD consisted of a range 

of decay classes (fig. 15) for each forest type. 

On a per-acre basis, aspen and birch forest types had the highest CWD biomass, 

while black spruce had more than an order of magnitude less (table 14). Interestingly, birch forest types on TNWR lands had five times less CWD than on TVSF 

lands, but this trend was not apparent for FWD (table 15). Deciduous forest types 

had the highest FWD on a per-area basis (table 15). 

On a per-acre basis, 

aspen and birch forest 

types had the highest 

CWD biomass, while 

black spruce had 

more than an order of 

magnitude less.
32

GENERAL TECHNICAL REPORT PNW-GTR-967

White spruce TNWR

0

1,000

2,000

3,000

4,000

5,000

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

CWD and FWD biomass (thousand tons)

Black spruce TNWR

FWD

CWD

Birch TNWR

Figure 13—Downed woody material biomass on an area basis for each of the forest types in the 

Tanana Valley State Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR). Error bars 

represent the standard error of the estimates. Estimates are for coarse woody debris (CWD) and fine 

woody debris (FWD). 

Table 12—Estimated total coarse woody debris (CWD) biomass stocks in forest types on the Tanana Valley 

State Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR)

TVSF TNWR Total

Forest type CWD biomass SE CWD biomass SE CWD biomass SE

Thousand tons

Black spruce 298.4 100.5 344.6 141.4 643.0 173.5

White spruce 981.7 440.9 194.9 131.1 1,176.5 460.0

Aspen 480.2 297.0 — — 480.2 297.0

Birch 2,950.3 1,030.2 94.7 58.5 3,045.1 1,031.8

Poplar 278.7 220.0 — — 278.7 220.0

Nonstocked 7.4 6.4 — — 7.4 6.4

Total biomass 4,996.7 1,074.2 634.2 181.5 5,630.9 1,089.4

SE = standard error. — = no samples fell in this combination of classes.
33

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Table 13—Estimated total fine woody debris (FWD) biomass stocks in forest types on the Tanana Valley State 

Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR)

TVSF TNWR Total

Forest type FWD biomass SE FWD biomass SE FWD biomass SE

Thousand tons

Black spruce 460.9 116.8 276.0 95.0 736.8 150.5

White spruce 261.9 104.5 104.8 57.5 366.7 119.3

Aspen 196.3 114.8 — — 196.3 114.8

Birch 1,171.3 326.4 185.9 93.6 1,357.2 339.6

Poplar 280.5 145.8 — — 280.5 145.8

Nonstocked 54.1 46.8 — — 54.1 46.8

Total biomass 2,425.0 303.4 566.6 123.5 2,991.6 327.6

SE = standard error. — = no samples fell in this combination of classes.

White spruce TNWR

0

2

4

6

8

10

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

CWD and FWD biomass (tons/acre)

Black spruce TNWR

FWD

CWD

Birch TNWR

Figure 14—Estimated density (tons/acre) of biomass in down woody material (DWM) for each of the 

forest types in the Tanana Valley State Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR). 

Error bars represent + 1 standard error of the estimated totals for coarse woody debris (CWD) and 

fine woody debris (FWD) in each category. 
34

GENERAL TECHNICAL REPORT PNW-GTR-967

White spruce TNWR

0

2

4

6

8

10

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

CWD and FWD biomass (tons/acre)

Black spruce TNWR

Decay 1

Decay 2

Birch TNWR

Decay 3

Decay 4

Decay 5

Figure 15—Composition of coarse woody debris (CWD) and fine woody debris (FWD) biomass by 

decay class for each of the forest types in the Tanana Valley State Forest (TVSF) and Tetlin National 

Wildlife Refuge (TNWR). Decay class 1 refers to the least decayed, and decay class 5 refers to the 

most advanced decayed pieces. 

Table 14—Estimated coarse woody debris (CWD) biomass (tons per acre) in forest types on the Tanana Valley 

State Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR)

TVSF TNWR Total

Forest type CWD biomass SE CWD biomass SE CWD biomass SE

Tons per acre

Black spruce 0.4 0.1 0.9 0.3 0.6 0.1

White spruce 4.1 1.3 3.5 1.3 4.0 1.1

Aspen 5.8 1.5 — — 5.8 1.5

Birch 5.3 1.6 0.9 0.4 4.6 1.3

Poplar 3.0 1.8 — — 3.0 1.8

Nonstocked 0.2 0.0 — — 0.2 0.0

All forest 2.9 0.6 1.2 0.3 2.5 0.5

SE = standard error. — = no samples fell in this combination of classes.
35

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Discussion

There was an eightfold variation in DWM per unit area across the various forest 

types and ownerships. With the exception of birch forests on the TNWR, the highest values occurred on deciduous forests. Birch forests on the TVSF had 48 percent 

of the DWM of the total in the two inventory units with 71 percent of that DWM 

on these forests consisting of CWD. The 2.8-fold difference in birch DWM on state 

and TNWR lands indicates key functional differences may occur within forest 

types. These differences may be attributable in part to differences in tree biomass 

as birch forests on TVSF lands (32.4 tons per acre) had 1.6 times more tree biomass 

than birch forest on TNWR lands (20.0 tons per acre) (fig. 16). Differences among 

forest types may also be attributed to tree longevity and inherent mortality rates, 

where aspen and birch forests tend to be the least long lived of the interior species 

(fig. 17). Greater DWM biomass per acre in black spruce forests on TNWR lands 

compared to TVSF, despite the lower live-tree biomass, may reflect slower wood 

decomposition on wetter sites owing to anaerobic conditions in water-logged wood 

when temperatures are conducive to microbial activity. The greater amounts of fine 

wood could result in more extreme fire behavior in hardwood stands than conifer 

stands, but height to tree crown base and abundance of understory vegetation is also 

important to predicting fire behavior.

The values of DWM biomass in this study are similar to other studies of boreal 

forest with similar forest types. For example, DeLuca and Biosvenue (2012 and 

references therein) found CWD values ranging from 2.6 to 8.0 (tons of biomass 

acre-1). These values are similar to those found in this study (fig. 14).

Table 15—Estimated fine woody debris (FWD) biomass in forest types on the Tanana Valley State Forest 

(TVSF) and the Tetlin National Wildlife Refuge (TNWR)

TVSF TNWR Total

Forest type FWD biomass SE FWD biomass SE FWD biomass SE

Tons per acre

Black spruce 0.6 0.1 0.7 0.2 0.7 0.1

White spruce 1.1 0.3 1.9 0.3 1.2 0.3

Aspen 2.4 0.4 — — 2.4 0.4

Birch 2.1 0.4 1.7 0.5 2.0 0.4

Poplar 3.0 0.3 — — 3.0 0.3

Nonstocked 1.5 0.0 — — 1.5 0.0

All forest 1.4 0.2 1.1 0.2 1.3 0.1

SE = standard error. — = no samples fell in this combination of classes.

Differences among 

forest types in the 

amount of down wood 

material were related to 

aboveground biomass 

as well as species' 

inherent mortality 

rates.
36

GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 17—Field crew member laying out a Forest Inventory and Analysis plot in an aspen forest. 

Sarah Ellison

0

0 10 20 30 40 50 60

2

4

6

8

10

Tree biomass (tons/acre)

DWM biomass (tons/acre)

Aspen TVSF

Birch TVSF

Poplar TVSF White spruce TNWR

White spruce TVSF

Birch TNWR

Black spruce TNWR

Black spruce TVSF

Figure 16—Relationship between aboveground live tree biomass and down woody material (DWM) 

biomass on the forest types and ownerships on the Tanana pilot inventory. Categories include black 

spruce, white spruce, birch, aspen, and poplar in the Tanana Valley State Forest (TVSF) and Tetlin 

National Wildlife Refuge (TNWR). 
37

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Soil Carbon Content in the 2014 Tanana Pilot Inventory5

Introduction

Boreal ecosystems account for about 50 percent of the world’s forest ecosystem 

C stocks (Malhi et al. 1999). The majority of the C in these ecosystems often 

occurs in soils (DeLuca and Biosvenue 2012, Malhi et al. 1999, Tarnocai et al. 

2009). In addition to their C storage capacity, boreal forest soils are important 

components of ecosystem productivity owing to their role in nutrient cycling and 

the limitations frozen soils place on tree growth. As boreal forests are experiencing some of the greatest increases in temperature globally (Arctic Climate 

Impact Assessment 2005, Trenberth et al. 2007) with concurrent increases in fire 

severity and frequency that can consume soil C (Kasischke and Turetsky 2006, 

Turetsky et al. 2011), it is important that inventory and monitoring efforts in the 

boreal regions sample soils. 

Methods

The FIA program measured soils in the early 2000s on a 1/16th sample of the 

standard field plots (i.e., one plot per 96,000 ac). The soil sampling protocol for 

the 2014 Tanana pilot inventory occurred on all plots and was based on standard 

FIA soils sampling protocols (O’Neill et al. 2005) but also integrated additional 

boreal forest-specific sampling methods developed by scientists from the U.S. 

Geological Survey (USGS) (USDA FS 2014b). One of the key differences 

between standard FIA protocols and those used in the Tanana pilot inventory 

was the use of an electric drill and a metal corer (Nadler and Wein 1998) that 

improved the ability to sample the thicker organic layers common in many 

boreal forest soils (fig. 18). Also, because of the thickness of organic soil layers 

in boreal Alaska, the target depth for mineral soil samples was 4 inches instead 

of 8 inches.

The soil sampling methods are outlined in the Tanana pilot inventory manual 

(USDA FS 2014b). Some details of these methods include the following: sampling 

soils at a location 30 ft south of subplot 2; use of a 12-inch circular frame to sample 

litter and live moss; and measuring depth of the active (unfrozen) soil layer at the 

time of sampling. Fourteen percent of forested plots were sampled in June, 60 

percent in July, and 26 percent in August.

Soil cores were separated into five layers and their thicknesses measured: 

dead moss (recognizable plant matter with few roots), root-dominated duff 

(mainly fine and very fine roots with old plant matter), upper humified duff 

5 Authors: Robert Pattison, Andrew Gray, Hans-Erik Andersen, and Kristen Manies.
38

GENERAL TECHNICAL REPORT PNW-GTR-967

(dark amorphous material with unrecognizable plant parts), lower humified duff 

(when present, a sticky amorphous layer without distinct plant fibers), and mineral soil (grittier and denser than organic layers, with no distinct plant parts). 

Samples were analyzed for oven-dried weights and C content among other 

properties. Sample bulk density was calculated based on oven-dried weight and 

sample volume as determined from the sample’s length and the diameter of the 

corer. These values were then converted into C in pounds per acre. Mineral 

soil samples varied between 1 and 4 inches in thickness. To provide a standardized measure of C content of mineral soil, the C concentration of the mineral 

soil was calculated for a 1-inch depth. Total soil C for a plot was determined 

as the sum of the litter and live moss, dead moss, root-dominated duff, upper 

and lower humified duff layers, and 1-inch of mineral soil. In addition to total 

soil C, separate analyses were generated for each of the five layers. Estimates 

of soil C by forest type and ownership were generated using the poststratified 

plot weights described in the introduction and the double-sampling equations 

described in Scott et al. (2005). 

Figure 18—Soil core after extraction showing the live moss layer on the right and mineral soil on the left.

Forest Inventory and Analysis
39

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Results

There were an estimated 56,728 (± 4,224) thousand tons of soil C on the TVSF and 

TNWR (table 16). The majority (75 percent) of this was found on the forests of the 

TVSF (42,310 ± 4,065 thousand tons) (fig. 19). 

Total measured soil C per acre was relatively similar across forest types for 

both inventory units (table 17). Deciduous forest types tended to have lower soil C 

per acre than evergreen forest types (table 17). 

The organic layer contained the greatest proportion (65 to 81 percent) of 

measured soil C across all forest types on both TVSF and TNWR lands (figs. 

19 and 20). Birch forests on TNWR had the lowest (65 percent) proportion of 

measured soil C in the organic layer, while white spruce on TNWR and poplar on 

TVSF had the highest (81 percent). Mineral soil (1 inch) contained between 8 and 

Table 16— Estimated soil carbon stocks for all soil layers in forest types on the Tanana Valley State Forest 

(TVSF) and the Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Thousand tons

Black spruce 20,455 2,810 10,502 1,044 30,969 2,863

White spruce 5,894 2,019 1,671 250 7,474 2,177

Aspen 1,224 548 — — 1,224 548

Birch 13,232 1,436 2,445 293 15,662 1,440

Poplar 2,069 730 — — 2,069 730

Nonstocked 433 — — — 433 —

Total carbon 42,310 4,065 14,432 1,125 56,728 4,224

SE = standard error. — = no samples fell in this combination of classes.

Table 17—Estimated total soil carbon (litter, live moss, organic layer and 1 inch of mineral soil) per acre on 

forest types in the Tanana Valley State Forest (TVSF) and the Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Tons per acre

Black spruce 27.9 3.8 28.2 2.8 28.0 2.6

White spruce 24.5 8.4 29.8 4.4 25.2 7.3

Aspen 14.9 6.7 — — 14.9 6.7

Birch 23.8 2.6 22.7 2.7 23.6 2.2

Poplar 22.0 7.8 — — 22.0 7.8

Nonstocked 12.3 0 — — 12.3 0

All forest 24.3 2.3 26.9 2.1 24.9 1.9

SE = standard error. — = no samples fell in this combination of classes.

Soil carbon (C) per acre 

was relatively similar 

across forest types for 

both inventory units. 

Deciduous forest types 

tended to have lower 

soil C per acre than 

evergreen forest types.
40

GENERAL TECHNICAL REPORT PNW-GTR-967

26 percent of measured soil C, with the lowest percentages occurring in balsam 

poplar forests and the highest occurring in birch forests on TNWR. Litter and live 

moss accounted for 4 to 11 percent of the measured soil C for all the forest types 

on both inventory units. 

There was a large variation in the contribution of the various layers within 

the organic layer to the total organic layer content (figs. 21 and 22). Dead moss 

accounted for 0 to 21 percent of the organic layer. Birch forests on the TNWR and 

balsam poplar forests on the TVSF had no dead moss, while black spruce forests on 

the TVSF had 21 percent of the organic layer C made up of dead moss. 

Root-dominated duff was found on all forest types and accounted for 9 percent of the aspen forest organic layer and 100 percent of the balsam poplar forest 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Soil carbon (thousand tons)

Black spruce TNWR

Mineral

Organic layer

Birch TNWR

Litter and live moss

0

5,000

10,000

15,000

20,000

Figure 19—Soil carbon (litter and live moss, organic layer, and 1 inch of mineral soil) for the different 

forest types in the Tanana Valley State Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR). 
41

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

organic layer on the TVSF. The upper humified duff layer was not present on 

balsam poplar forests but accounted for 17 to 35 percent of the other forest types 

on the TVSF and TNWR. The lower humified duff layer was not present on white 

spruce and birch forests on the TNWR, nor balsam poplar forests of the TVSF. 

However, this layer accounted for 50 percent of the organic layer of the aspen 

forests on the TVSF. 

Thaw depths were deepest in the balsam poplar and aspen forest types and shallowest in black spruce forests (fig. 23). Within a forest type, there did not appear to 

be differences in thaw depths between the TVSF and TNWR. 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Soil carbon (tons/acre)

Black spruce TNWR

Mineral

Organic layer

Birch TNWR

Litter and live moss

0

5,000

10,000

15,000

20,000

Figure 20—Distribution of soil carbon between litter and live moss, organic and mineral (1 inch) 

soil layers on a per-acre basis for forest types in the Tanana Valley State Forest (TVSF) and Tetlin 

National Wildlife Refuge (TNWR). 
42

GENERAL TECHNICAL REPORT PNW-GTR-967

Discussion 

Across the Tanana pilot inventory unit, most of the total soil C occurred in black 

spruce and birch forests on TVSF lands (table 16). The total soil C per acre was 

relatively similar between forest types and ownerships (table 17). White spruce 

forests on the TNWR had the highest total soil C per acre, and aspen forests on 

TVSF had the lowest values (table 17). The majority of C in the soils estimated 

in this study was found in the organic layer (figs. 19 and 20). However, it is likely 

that substantial amounts of mineral soil C were present at depths greater than 

the 1 inch estimated here. For soils in the Bonanza Creek Experimental Forest, 

the C in the upper 1 inch represents 4 to 18 percent of the C down to 39 inches 

(1 m) in floodplain forests, and 12 percent to 19 percent in upland forests.6

 Those 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Organic layer carbon (tons/acre)

Black spruce TNWR

Birch TNWR

0

15

10

5

20

25

30

Lower humified duff

Upper humified duff

Root-dominated duff

Dead moss

Figure 21—Distribution of soil carbon within the organic layer per acre for forest types in the Tanana 

Valley State Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR). The layers within the 

organic layer include dead moss, root-dominated duff, upper humified duff, and lower humified duff. 

6 Yarie, J. 2017. Personal communication. Soil scientist, University of Alaska Fairbanks. 

Fairbanks, AK 99775.
43

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

estimates do not include any black spruce stands, which likely have an even lower 

proportion of C in the top 1 inch. Using 15 percent as a rough guide with the FIA 

sample would suggest that mineral soils down to 39 inches (1 m) have as much or 

up to twice as much C as the organic layer. Although there was a high amount of 

variability as to which of the organic layers contributed the most to organic layer 

C content, in general, the root-dominated duff layer tended to contain most of the 

C in the organic layer C content. 

The values in this study are similar to those in other studies in the region (Hollingsworth et al. 2008, Kane and Vogel 2009, Ping et al. 2010). Hollingsworth et al. 

(2008) found that the C content of the organic layer of black spruce forests ranged 

from 15 to 24 tons per acre, while Kane and Vogel (2009) found values that ranged 

from 17 to 33 tons per acre. In an inventory of 52 sites in interior Alaska dominated by black spruce across a range of topographic positions from well drained 

to poorly drained, Ping et al. (2010) found that organic layer contained 24 to 1,156 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Organic layer carbon (thousand tons)

Black spruce TNWR

Birch TNWR

0

15,000

10,000

5,000

20,000

Lower humified duff

Upper humified duff

Root-dominated duff

Dead moss

Figure 22—Estimates of organic layer carbon (dead moss, root-dominated duff, upper humified 

duff, and lower humified duff) content for the different forest types in the Tanana Valley State Forest 

(TVSF) and Tetlin National Wildlife Refuge (TNWR). 
44

GENERAL TECHNICAL REPORT PNW-GTR-967

tons per acre. Their work sampled soils down to 39 inches, and found that organic 

layer had 13 to 100 percent of the total C within the top 39 inches of soils in this 

wide range of sites. 

The total soil C was weakly but positively related to stand age for the black 

spruce forest types (r2 = 0.14, P = 0.0303) but not for other forest types in this 

study. Kane and Vogel (2009) found a similar trend for black spruce forests in 

the Tanana Valley region. As mentioned above, TVSF lands are considered to 

be more productive upland ecosystems, whereas TNWR is characterized as less 

productive, low-lying ecosystems. In spite of these general differences, we did 

not find clear differences in soil C characteristics between these two landowner 

groups. When examined on a per-acre basis, black and white spruce and birch 

forest types had similar soil C content on both ownerships. One potential reason 

might be that a simple characterization of forest types based on the predominant 

tree canopy species may fail to recognize the diversity of conditions where black 

spruce can be abundant (Viereck and Johnston 1990). Consequently, additional 

effort should be made to refine black spruce forest types based on additional 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Thaw depth (inches)

Black spruce TNWR

Birch TNWR

0

35

20

5

40

25

10

30

15

45

Figure 23—Box and whisker plots of thaw depth for the forest types in the Tanana Valley State 

Forest (TVSF) and Tetlin National Wildlife Refuge (TNWR). Each box shows the upper and lower 

quartile, the central bar shows the median, the whiskers show the minimum and maximum values. 

Depths were measured to a maximum value of 40 inches. 
45

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

features (Hollingsworth et al. 2008). Incorporating vegetative and ground cover 

data could help in this regard (see “Characterizing Forest Vegetation of the 

Tanana Valley” section) and may lead to more refined insights into understanding soil C as it relates to aboveground composition. 

Thaw depths were greatest in the balsam poplar and aspen forest types (fig. 23). 

This finding was consistent with previous work suggesting that these forest types 

typically occur on sites where soils thaw more rapidly in the early growing season 

and where there is little to no permafrost (Jorgenson et al. 2010). 

Soils in boreal regions are typically sampled later in the season than our field 

season—e.g., September and October (Hollingsworth et al. 2008)—to capture the 

maximum thaw depth of soils and limit the occurrence of frozen layers. However, 

visiting all plots within a short window late in the season is logistically unfeasible 

for a broad-scale multiresource inventory. One of the primary concerns in undertaking the Tanana pilot inventory was that soils in some low-lying poorly drained 

forests such as those dominated by black spruce might be frozen above the mineral 

layer as the soil corer is unable to sample frozen soils. This concern was warranted 

for some forest types. For example, 14 of the 95 plots where soils were collected had 

frozen layers above mineral soil. Of these plots, 13 occurred on black spruce forest 

types (TNWR n = 2, TVSF n = 11), and one occurred on birch forest types (TVSF). 

Two of the 14 plots had soils frozen very near the surface (dead moss layer). Overall, 38 percent of the black spruce forests plots on the TVSF did not have the entire 

organic layer sampled. Our inventory procedures assume that nonsampled information is “missing at random”; i.e., that the mean of the values that were measured is 

the same as the mean of the nonsampled areas and the population as a whole. The 

presence of frozen soils therefore leads to lower precision of total soil C estimates 

for black spruce forest types on TVSF in particular, where frozen soils were most 

frequently encountered. Soils frozen above the mineral layer were encountered on 

plots sampled throughout the growing season (fig. 24). Most of these plots had thaw 

depths of less than 15 inches at the time of measurement. This result is consistent 

with Ping et al. (2010), who found that organic layer thickness for a range of black 

spruce forests was relatively shallow, ranging from 1 to 15 inches for 51 of their 

52 field sites. The remaining site had the entirety of the 39-inches-depth sample 

consisting of organic layer. As mentioned above, Ping et al. (2010) found that the 

organic layer contained between 13 and 95 percent of the total soil C down to 39 

inches for the 51 plots (mean = 51 percent, SE = 19 percent). Collectively, these 

results suggest that organic layers are relatively shallow and contain a substantial 

proportion of the soil C.
46

GENERAL TECHNICAL REPORT PNW-GTR-967

Carbon Storage and Other Functions of Moss and 

Lichen Mats in the Tanana River Valley of Alaska7

Introduction

How much C is stored in the ground layer of boreal forests? In northern areas, 

moss and lichen mats are key players in C cycling because they are often the main 

interface between soils and the atmosphere (fig. 25). Moss mats in boreal forests 

account for 20 percent of understory net C uptake and the majority of understory 

nitrogen fixation (Hasselquist et al. 2016, Lindo et al. 2013). The C storage capacity of ground layers is potentially huge: moss-dominated peatlands currently store 

roughly 33 percent of the world’s terrestrial C (Yu 2012). 

Despite this massive potential, ground layer nutrient cycling is now shifting in 

response to global changes. Specific challenges include increasing area in fires and 

the expansion of tall shrub vegetation, both of which reduce ground layers. Ground 

layer carbon losses are rising as arctic and boreal wildfires combust more material 

than at any point in the last several thousand years (Hu et al. 2015, Kelly et al. 2013, 

Turetsky et al. 2015). Of particular concern are declines of forage lichens on which 

caribou and other wildlife depend, and whose decline will have socioeconomic 

impacts on hunting, tourism, and subsistence practices (Joly et al. 2009). Knowing how these changes might interact with carbon cycling at the soil-atmosphere 

interface (fig. 25) requires us to understand carbon pool status and trends using 

emerging forest inventory methods. Thaw depth (inches)

0

35

20

5

40

25

10

30

15

45

16-May 5-Jun 25-Jun 15-Jul 4-Aug 24-Aug 13-Sep

Sample date 2014

Figure 24—Relationship between thaw depth and sample date for plots. Thaw depth is the average of 

four measurements at the soil sample site. Light grey symbols (n = 14) represent plots where mineral 

soil was not reached owing to the presence of frozen soil.

7 Authors: Robert J. Smith, Sarah Jovan, Andrew Gray, and Bruce McCune.
47

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Methods

Carbon and nitrogen pools in boreal ground layers—

We evaluated ground layer attributes at 96 sites in the study area using the FIA 

Ground Layer Indicator (Smith et al. 2015). This indicator converts field-measured 

depth and cover of ground-dwelling mosses and lichens into a plot-level estimate of 

biomass, carbon, and nitrogen for each functional group (fig. 26). Moss and lichen 

species were grouped into functional groups that were relatively easy to identify 

after a few hours’ training and that corresponded with important nutrient and 

habitat functions (fig. 27). A further benefit of this method is the ability to assess 

ecosystem functions of ground layers (e.g., wildlife forage, biological nitrogen-fixation, many others). The Ground Layer Indicator is rapid (about 1 to 2 hours survey 

time) and complements existing FIA protocols.

Figure 25—Conceptual carbon (C) balance in moss and lichen mats at the soil-atmosphere interface. 

In addition to regulating C, ground layers have many other functions (see table 18).

CC License
48

GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 26—Four of the 13 functional groups used in the Ground Layer Indicator (see table 18 for all 

groups). The indicator measures depth and cover of all 13 functional groups to estimate biomass, 

carbon, and nitrogen (N).

CC License

Figure 27—A microquad used to measure cover of lichen and moss functional groups in the 

ground layer.

Forest Inventory and Analysis
49

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Environmental influences and validation—

To identify the best environmental and stand-level factors explaining ground layer 

attributes, we used nonparametric multiplicative regression (NPMR) (McCune 2006, 

McCune and Mefford 2011), which estimates mean responses as a smoothed function 

of all possible interactions of an optimized predictor subset. To validate measurements, we used a separate, multiobserver dataset to evaluate whether observers might 

estimate plot-level biomass differently: in August 2015, six observers used the Ground 

Layer Indicator (Smith et al. 2015) at premarked sampling units in two plots in north 

central Minnesota (one upland forest and one peat moss wetland). From a separatemeans linear mixed model, a finding of no significant difference among observers’ 

biomass estimates would lend credibility to Ground Layer Indicator measurements 

from both Minnesota and Alaska.

Results 

Carbon and nitrogen pools in boreal ground layers—

Functional group abundances differed across the study area (table 18). Most frequent 

and abundant were nitrogen-fixing feather mosses, often forming extensive, thick carpets. Sphagnum peat mosses were less frequent but often achieved highest within-plot 

biomass. Forage lichens were moderate in frequency but also had considerable biomass 

where encountered (table 18). On average, there were 6.6 functional groups per plot. 

Moss and lichen functional groups reflected the capacity to fix nitrogen, provide wildlife 

forage, indicate disturbance, alter hydrology, or signal nutrient-enriched conditions 

(among other functions; table 18). 

Across the study area, there was an estimated total of 12,588 (± 1,356) thousand tons 

of ground layer biomass (tables 19 and 21). Of this, there was an estimated 5,586 (± 601) 

thousand tons of carbon and 138 (± 15) thousand tons of nitrogen in ground layers (table 

19). Ground layer biomass per acre across the inventory unit was 5.53 (± 0.60) tons per 

acre (table 20). There was 2.46 (± 0.26) tons per acre of C, and 122 (± 13) pounds per acre 

of nitrogen (table 20). 

Forest types—

Black spruce forest types had by far the greatest total (table 19) and per-acre mean (table 

20) ground layer biomass across the study area. Total biomass and nutrient stores in black 

spruce forest types were roughly seven times that in white spruce and Alaska birch forest 

types (table 19). As a per-plot average, mean biomass and mean nutrient content in black 

spruce forest types were roughly double that of white spruce forest types, and nearly four 

times that of most hardwood forest types (table 20). Within the TVSF and the TNWR, 

most (75 percent) of the ground layer biomass was found in black spruce forest types 

(table 21). Black spruce forest types on both the TVSF and the TNWR also had the highest estimates of ground layer biomass on a per-acre basis (table 22). Black spruce forest 

types on the TVSF tended to have greater ground layer biomass per acre than TNWR. 
50

GENERAL TECHNICAL REPORT PNW-GTR-967

Table 18—Estimates by functional group for forested lands, based on the ground layer measurements at 96 

plots in the study areaa

Mass Carbon Nitrogen (N) Cover

Functional group Functions Mean SE Mean SE Mean SE Mean SE

 - - - - - - - - - - Pounds per acre- - - - - - - - - - - -Percent- -

Biotic soil crust Soil trapping, soil water influx, 

disturbance indicator

3 1 1 0 <0.1 <0.1 <0.1 <0.1

Orange lichens Indicate nutrient overenrichment 0 0 0 0 <0.1 <0.1 <0.1 <0.1

Forage lichens Wildlife forage (caribou, etc.) 394 93 175 41 2 1 6 1

Other foliose lichens Invertebrate habitat, bare site 

colonization

9 2 4 1 <0.1 <0.1 <0.1 <0.1

Other fruticose lichens Invertebrate habitat, bare site 

colonization

70 16 31 7 1 <0.1 2 <0.1

N-fixing foliose lichens N-fixation, nutrient cycling 148 28 66 13 4 1 4 1

N-fixing fruticose 

lichens

N-fixation, increases albedo 32 22 14 10 1 1 1 <0.1

Other feather mosses Rainfall interception, soil cooling 645 184 286 82 8 2 7 2

N-fixing feather mosses Broad-area N-fixation, soil cooling 6,818 802 3,026 356 78 9 57 5

Sphagnum peat moss Carbon storage (peat), water 

regulation, soil cooling

1,853 619 823 275 17 6 10 3

Turf (acrocarp) mosses Soil accrual, bare site colonization 1,050 147 466 65 11 1 18 2

Flat (thalloid) 

liverworts

Soil/detritus binding, water 

infiltration

29 20 13 9 0 0 1 <0.1

Stem-and-leaf 

liverworts

Soil/detritus binding, water 

infiltration

16 7 7 3 0 0 0 0

Note: The units for mass, carbon, and N are in pounds per acre. SE = standard error.

a Each of the mutually exclusive groups integrates growth forms, potential indicator status, and ecosystem effects.

Table 19—Estimates of ground layer biomass, carbon, and nitrogen stocks by 

forest type for forested lands in the study area

Mass Carbon Nitrogen

Forest type Total SE Total SE Total SE

Thousand tons

Black spruce 9,551 1,472 4,238 653 104 16

White spruce 1276 439 566 195 15 5

Aspen 199 133 89 59 2 1

Alaska birch 1,508 340 669 150 17 4

Balsam poplar 11 7 5 2 0 0

Nonstocked 43 39 18 17 0 0

Total 12,588 1356 5,586 601 138 15

SE = standard error.
51

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Table 20—Estimates of ground layer biomass, carbon, and nitrogen per unit acre by forest type for forested 

lands in the two inventory units in the study area

Mass Carbon Nitrogen

Forest type Mean SE Mean SE Mean SE

- - - - - - - - - - - - - - - Tons per acre - - - - - - - - - - - - - - - - - - Pounds per acre - - - -

White spruce 4.18 0.95 1.85 0.42 95 21

Black spruce 8.58 0.92 3.81 0.41 187 19

Aspen 2.36 0.85 1.05 0.38 52 19

Alaska birch 2.35 0.38 1.04 0.17 52 9

Balsam poplar 0.11 0.04 0.05 0.02 3 1

Nonstocked 1.22 1.22 0.54 0.54 25 25

Total 5.53 0.60 2.46 0.26 122 13

Note: The units for nitrogen are pounds per acre. SE = standard error.

Table 22—Estimated ground layer biomass per acre in forest types on the Tanana Valley State Forest (TVSF) 

and the Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Tons per acre

Black spruce 10.5 1.3 4.8 0.7 8.6 0.9

White spruce 3.9 1.1 5.4 1.5 4.2 0.9

Aspen 2.4 0.8 — — 2.4 0.8

Birch 2.3 0.4 2.7 0.7 2.4 0.4

Poplar 0.1 0.04 — — 0.1 0.04

Nonstocked 1.22 0 — — 1.2 0

Total biomass 5.9 0.7 4.5 0.5 5.5 0.6

SE = standard error. — = no samples fell in this combination of classes.

Table 21—Estimated ground layer biomass stocks in forest types on the Tanana Valley State Forest (TVSF) 

and the Tetlin National Wildlife Refuge (TNWR)

Forest type TVSF SE TNWR SE Total SE

Thousand tons

Black spruce 7,748 1,432 1,803 341 9,551 1,472

White spruce 968 397 308 187 1,276 439

Aspen 199 133 — — 199 133

Birch 1,214 305 294 149 1,508 340

Poplar 11 7 — — 11 7

Nonstocked 43 39 — — 43 39

Total 10,183 1,322 2,405 304 12,588 1,356

SE = standard error. — = no samples fell in this combination of classes.
52

GENERAL TECHNICAL REPORT PNW-GTR-967

Environmental influences and validation—

From the NPMR models, the best predictors of ground layer attributes were related 

to solar radiation and vegetation attributes like forb cover and stand age. Specifically, ground layer carbon and nitrogen were greatest in older stands and lowest 

in plots with high forb cover and high solar radiation. From the comparison of 

estimates based on multiple observers in Minnesota, mean biomass did not differ 

among observers after accounting for site differences (F = 0.77, p = 0.57) (fig. 28), 

suggesting good repeatability of the measurement method. 

Discussion

Carbon and nitrogen pools in boreal ground layers—

Ground layers are a substantial C pool in boreal forests of interior Alaska, while at 

the same time enhancing a variety of ecosystem functions (table 18). Our finding of 

around 4,500 to 17,000 pounds per acre of biomass is within the range of variability 

Observer

Log10 microplot mass (g)

-3

A B C D E F

Site

Wetland

Upland

2

1

0

-1

-2

3

Figure 28—Mean biomass did not differ between six observers in Minnesota after accounting for 

differences between sites (F = 0.77, p = 0.57 from F-test). Agreement between observers suggests 

good repeatability of the Ground Layer Indicator. Boxes indicate the interquartile range of observations, lines within boxes are the median, whiskers extend to the 1.5 times the interquartile range, and 

dots are outlier observations.
53

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

observed in other moss and lichen mats of the Tanana River area (Barney and 

Van Cleve 1973, Mack et al. 2008), which gives a sense of the C storage capacity 

of boreal forest ground layers in interior Alaska. That multiple observers did not 

statistically differ indicates that estimates are realistic and repeatable. The high 

abundance of nitrogen-fixing feather mosses suggests large landscape nutrient 

effects: cyanobacteria in nitrogen-fixing feather mosses contribute the majority of 

biologically available nitrogen in boreal forest understories, an amount that can be 

nearly equal to the total amount of nitrogen entering from rainfall (Lagerström et 

al. 2007). Nitrogen input from feather mosses has ultimate consequences for nutrient ratios, plant growth, and ecosystem productivity (Lindo et al. 2013). Together, 

these findings imply that moss and lichen mats in the Tanana River region contribute substantially to forest nitrogen and organic carbon stores. 

Environmental influences—

It is unclear whether observed patterns will hold as environmental conditions 

change in interior Alaska. We found that biomass, C and nitrogen were sensitive to a topographic proxy of solar radiation, suggesting that mass accumulation in ground layers is tied to sheltered thermal situations (and probably moist 

topographic positions as well). Carbon emissions from ground layers and peat 

will become an increasing possibility as droughts, climate warming, and melting permafrost cause dropping water tables (Fenner and Freeman 2011, Gorham 

1991) and increasing fire risks (Kasischke and Stocks 2012). Future efforts to map 

landscape C could benefit from using topographic proxies of important hydrologic 

and thermal attributes. 

We documented more biomass and carbon in old stands relative to younger 

stands, consistent with evidence that moss and lichen mats are C “sinks” in old, 

undisturbed boreal forests, but can be net C “sources” in recently burned stands 

and for several years after fires (Harden et al. 2000). This emphasizes the dual 

challenges that wildfires pose to C storage, not only from acute combustive 

losses (fig. 29), but also from legacy effects that can hinder growth and C uptake 

for decades. Carbon emissions from burned ground layers, as well as subsequent regrowth of fire-promoting vascular vegetation, could potentially amplify 

climate warming (Chapin et al. 2010, Kasischke and Stocks 2012, Turetsky et al. 

2015). Anticipating these changes will require continued monitoring of vascular 

and nonvascular vegetation, as well as novel predictive approaches for mapping 

C pools.
54

GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 29—An increasingly common sight: large wildfires in Alaska’s boreal forests and tundra are 

releasing more carbon from moss and lichen mats than at any point in the last several thousand years. 

National Park Service and Alaska Division of Forestry
55

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Future extensions: carbon distribution mapping—

Mapping forest floor C has been a valuable product of FIA inventories (Woodall 

2012). As inventories move forward, it will be critical to include ground layer 

mosses and lichens, as well as the deep organic peat layers (>8 inches deep) that 

frequently lie beneath them if we are to avoid grossly underestimating carbon 

(Bona et al. 2013, Chimner et al. 2014). 

Carbon estimation in ground layers could also be linked with remote sensing 

approaches, which have previously been used to map forage lichen cover for caribou 

habitat, fire effects on moss mats, peatland drought status, ecosystem productivity 

of moss mats, and forest floor organic C (Harris and Bryant 2009; Kushida et al. 

2004; Lewis et al. 2011; Nelson et al. 2013; Pastick et al. 2014, respectively). Recent 

LiDAR, hyperspectral and thermal imaging (G-LiHT) (see Andersen et al., this 

publication) could be calibrated with our ground layer biomass estimates to improve 

stratification of plot measurements and infer regional patterns. The wealth of potential information and tools at our disposal will provide opportunities for ground layer 

carbon estimation in Alaska, a part of our Nation that is at the forefront of ongoing 

global changes.

Ecosystem C Pools in the Tanana Pilot8

Boreal ecosystems account for about 50 percent of global forest ecosystem C stocks 

(Malhi et al. 1999). Unlike other forested ecosystems where trees contain a large 

proportion of ecosystem C, the majority of the C in these ecosystems often occurs 

in soils (DeLuca and Biosvenue 2012, Malhi et al. 1999, Tarnocai et al. 2009). The 

results of this pilot inventory found that soil organic layers plus mineral soil to a 

1-inch depth had 47 to 84 percent of total ecosystem C (live tree, standing dead 

tree, DWM and soil), depending on forest type and location (figs. 30 and 31). White 

spruce forests on TVSF lands had the lowest proportion (45 percent) of ecosystem 

C contained in soils. Black spruce forests on TNWR lands had the highest (84 

percent) proportion of total ecosystem C contained in soils. Aboveground live tree 

C accounted for 13 to 45 percent of total ecosystem C with black spruce forests on 

TNWR lands having the lowest (13 percent) percentage and white spruce forests on 

TVSF having the highest (45 percent) percentage (fig. 32). The standing dead tree 

(“snag”) pool was the smallest overall (2.2 percent of total C) and ranged from 0.5 

percent in black spruce forests on the TNWR to 5.9 percent in white spruce forests 

on the TVSF. When converted to C (biomass × 0.5) (Harmon et al. 2008), DWM 

contributed a relatively small proportion of the total (live tree, snag, DWM, and 

8 Author: Robert Pattison.

Soil organic layers 

plus mineral soil to a 

1-inch depth had 47 

to 84 percent of total 

ecosystem carbon.
56

GENERAL TECHNICAL REPORT PNW-GTR-967

soil) C. Black spruce forests on TVSF had the lowest proportion (1.4 percent) of 

total C in DWM, while aspen forest types on TVSF had the highest (14 percent) (fig. 

30). These results are consistent with other studies (DeLuca and Biosvenue 2012) 

which have found that coarse woody debris (CWD) accounted for 8 to 11 percent of 

total ecosystem (tree, CWD, soil) C. Ground layer as a distinct pool accounted for 

0 to 7 percent of total ecosystem (live tree, snag DWM, and soil) C (fig. 33). Poplar 

forests had the lowest ground layer content, and white spruce forests had the highest 

C in the ground layer (fig. 33). 

The results of this study highlight the variability both in the amount of total 

ecosystem C found across forests and in how that C is distributed within forest 

ecosystems. There was close to a twofold variation in total ecosystem C across the 

forests in this study. There was also close to a twofold variation in the portion C 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Total forest carbon (thousand tons)

Black spruce TNWR

Live tree

Snag

Birch TNWR

DWM

Soil

0

5,000

15,000

10,000

25,000

20,000

35,000

30,000

Figure 30—Estimated carbon in trees, down woody material (DWM) and soils in thousands of tons 

as a total for each of the forest in the Tanana Valley State Forest (TVSF) and Tetlin National Wildlife 

Refuge (TNWR). Error bars represent + 1 standard error of the estimated totals for trees, DWM, and 

soils in each category.
57

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

that was found in soils and more than a threefold variation in the percentage of C 

found in trees (fig. 31). The percentage of total ecosystem C found in soils in this 

study (45 to 84 percent) is consistent with that found in other boreal forests (De 

Luca and Boisvenue 2012); however, differences in methodology confound direct 

comparisons. In this study, black spruce forest soils contained up to 84 percent of 

the total ecosystem C, elsewhere black spruce forest soils contained 87 percent of 

ecosystem C (De Luca and Biosvenue 2012). 

The inability to sample frozen soils particularly those in low-lying and poorly 

drained sites such as those dominated by black spruce suggests that soil C was 

underestimated in these forests. Ping et al. (2010) found that soil organic C in black 

spruce forests tended to increase as water drainage decreased. These sites are also 

the most likely to have frozen soils that limit sampling. These authors suggest that 

White spruce TNWR

White spruce TVSF

Black spruce TVSF

Aspen TVSF

Birch TVSF

Poplar TVSF

Forest type and owner

Total forest carbon (tons/acre)

Black spruce TNWR

Live tree

Snag

Birch TNWR

DWM

Soil

0

10

30

20

50

40

60

Figure 31—Estimated carbon in live tree, standing dead trees (“snag”) down woody material (DWM) 

and soil in tons per acre as a total for each of the forest types in the Tanana Valley State Forest 

(TVSF) and Tetlin National Wildlife Refuge (TNWR). Error bars represent + 1 standard error of the 

estimated totals for trees, DWM, and soils in each category.
58

GENERAL TECHNICAL REPORT PNW-GTR-967

Figure 32—Field crew member measuring tree distance from a subplot center in a white spruce forest. 

Forest Inventory and Analysis

Forest type and owner

White

spruce

Aspen Poplar

Carbon (tons/acre)

Black

spruce

Live tree

Dead tree

Birch

DWM

Ground layer

Soil

0

5

15

10

25

20

30

Figure 33—Amount of carbon in various pools by forest types. DWM = down woody material.
59

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

sampling at depths less than 40 inches can underestimate soil organic C by as much 

as 68 percent in black spruce forests. In spite of these limitations, the soil data from 

this inventory represent an important contribution to understanding soil C dynamics in a region that has limited sampling (Ping et al. 2010) and is vulnerable to 

climate change (Hinzmann et al. 2013). 

Live trees represented another substantial C pool in these forests. The portion of 

ecosystem C found trees in this study (13 to 45 percent) is similar to that seen in other 

boreal forests (11 to 64 percent) (DeLuca and Biosvenue 2012). Within black spruce 

forests, those on the TNWR had the lowest portion (13 percent) of total ecosystem C 

in trees; this appeared to be the result of lower tree C in these forests (fig. 31).

While the ground layer did not represent a substantial contribution to total ecosystem C (fig. 33), understanding the composition of this layer can provide insights 

into ecosystem productivity and into soil C properties (Hollingsworth et al. 2008). 

This study did not attempt to quantify the C content of understory vegetation. 

Other studies suggest that understory vegetation typically contains less than 1 

percent of the total ecosystem C of boreal forests (DeLuca and Biosvenue 2012). 

Changes in vegetation composition, including but not limited to shrub encroachment (Johnstone et al. 2010), may alter the contribution of understory vegetation to 

total ecosystem C in boreal forests. 

A USFS-NASA Partnership to Leverage Advanced 

Remote Sensing Technologies for Forest Inventory9

Introduction

To increase the precision of the inventory estimates, the relatively sparse FIA field 

plot sample collected in TVSF and TNWR was augmented with sampled airborne 

remotely sensed data acquired with the G-LiHT system to increase the precision 

of inventory parameter estimates. G-LiHT is a portable, airborne imaging system, 

developed at the NASA-Goddard Space Flight Center, which simultaneously maps 

the composition, structure, and function of terrestrial ecosystems using LiDAR, 

imaging spectroscopy, and thermal imaging. G-LiHT provides high-resolution 

~3.3 ft (~1 m) data that are well suited for studying tree-level ecosystem dynamics, 

including assessment of forest health and productivity of forest stands and individual trees. In addition, G-LiHT data support local-scale mapping and regionalscale sampling of plant biomass, photosynthesis, and disturbance. The data are 

accurately georeferenced and can be matched very precisely with field plot data that 

are georeferenced using high-accuracy (dual-frequency, GLONASS-enabled) global 

positioning system. 

9 Authors: Hans-Erik Andersen, Chad Babcock, Robert Pattison, Bruce Cook, Doug 

Morton, and Andrew Finley.

G-LiHT is a portable, 

airborne imaging 

system that 

simultaneously maps 

the composition, 

structure, and 

function of terrestrial 

ecosystems using 

LiDAR, imaging 

spectroscopy, and 

thermal imaging.
60

GENERAL TECHNICAL REPORT PNW-GTR-967

Methods

G-LiHT collection—

G-LiHT airborne remote sensing data was acquired in July–August 2014 along 

single swaths 273 yd wide (250 m wide) spaced 5.78 mi (9.3 km) apart over the 

entire Tanana inventory unit of 52.1 mi2 (135 000 km2) (fig. 2). G-LiHT flight lines 

were aligned so as to (1) ensure coverage over every FIA plot established for the 

2014 pilot and (2) capture as much variability in aboveground biomass as possible 

within each flight line. 

G-LiHT remote sensing measurements—

LiDAR—Detailed specifications for the G-LiHT instrument are provided in Cook 

et al. (2013). The airborne LiDAR data collected in the project provides detailed 

information on the terrain surface morphology and forest structure within each data 

swath (fig. 34A and 34B). 

Figure 34—Examples of Goddard-LiDAR/Hyperspectral/Thermal measurements for an area within Bonanza Creek Experimental 

Forest: (a) LiDAR-derived terrain model, (b) LiDAR-derived canopy height model, (c) normal-color image derived from hyperspectral 

sensor data (continuous spectral profiles for various features (soil (left), forest (right)) are shown in insets), and (d) color-infrared image 

derived from hyperspectral sensor data.
61

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

The detailed LiDAR terrain model (fig. 34A) can be subtracted from a LiDARbased canopy surface model to generate a high-resolution (e.g., 3.3-ft [1-m]) canopy 

height model (fig. 34B). High-resolution LiDAR-derived canopy height and cover 

information can then be used to characterize important structural conditions such 

as forest stand size class and canopy cover (Andersen 2009). 

In addition, detailed terrain measurements could potentially be used to detect 

and characterize geomorphological features associated with permafrost distribution 

and change (fig. 35). 

Hyperspectral imaging—G-LiHT’s hyperspectral imaging sensor provides detailed 

information on the spectral reflectance properties of surface features that is highly 

complementary to the 3-D canopy structural information provided by LiDAR. At 

every image pixel, the hyperspectral sensor captures a spectrum of reflectance values ranging from the violet (420 nm) to the near-infrared (950 nm) with a spectral 

resolution of less than 5 nm and a spatial resolution of 3.3 ft (1 m). Spectral profiles 

associated with common surface types such as soil and forest are shown in figure 

35. Products such as normal color (fig. 34C) and color-infrared (fig. 34D) high-resolution images can then be generated from hyperspectral image, and can provide 

useful information related to forest type and condition. 

Figure 35—Example of small-scale geomorphological features (patterned ground [polygons] in permafrost soils) captured in GoddardLiDAR/Hyperspectral/Thermal high-resolution LiDAR terrain model. 
62

GENERAL TECHNICAL REPORT PNW-GTR-967

The full range of reflectance values can be used in a supervised classification 

algorithm to generate maps of forest or species type. For example, figure 36 shows 

the result of applying a Spectral Angle Mapper supervised classification method to 

G-LiHT hyperspectral data in a forest near Fairbanks, Alaska. Although hyperspectral 

image processing and analysis is highly complex and sensitive to a number of factors, 

including surface moisture, solar illumination conditions, etc., preliminary results 

show the potential of this data for characterizing composition (species class), condition 

(insect damage, drought stress), and mortality of vegetation within the scene. 

High-resolution digital camera—A Nikon D7100 digital single lens reflex (DSLR) 

camera with 20mm f/2.8D lens was mounted next to the G-LiHT sensor to acquire ultra-high resolution normal color frame imagery to supplement the G-LiHT 

measurements (fig. 37). Because the DSLR imagery was collected as an experiment 

in this project, there were limitations to the data; for example, approximately 50 

percent of the field-of-view was blocked by the G-LiHT instrument and frame rate 

was too low to enable stereo collection. That being said, it is evident that the DSLR 

camera provided highly detailed information on many scene components, including 

CWD, ground cover (lichens, mosses), tree mortality, and hydrology. 

LiDAR-based biomass prediction—

Detailed LiDAR-derived metrics obtained from G-LiHT (e.g., height percentiles, 

canopy cover by height stratum, etc.) can be used to quantify 3-D canopy structure 

over an area at the scale of an FIA plot or subplot, thereby enabling prediction of 

inventory attributes (e.g., aboveground biomass) via linear regression analysis. For 

Figure 36—Forest type mapping using Spectral Angle Mapper (SAM) classification algorithm applied to Goddard-LiDAR/Hyperspectral/Thermal hyperspectral measurements. White circles depict Forest Inventory and Analysis subplots. 
63

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

example, figure 38 shows the results of a regression analysis at FIA plots within 

TVSF and TNWR established in the 2014 Tanana pilot. Interestingly, the results 

indicate that the strength of the regression relationship between LiDAR-based predictor variables and field-measured AGB is increased by including a larger sample of 

small-diameter trees provided by the second microplot on each FIA subplot. 

Figure 37—High-resolution image from digital single lens reflex camera collected concurrently with Goddard-LiDAR/

Hyperspectral/Thermal. Predicted AGB (tons/ac)

Actual AGB (tons/acre)

1 microplot, R2 = 0.82,

RMSE = 9.20 tons/ac

2 microplots, R2 = 0.89,

RMSE = 8.67 tons/ac

0

40

20

80

60

100

0 4020 8060 100

Predicted AGB (tons/ac)

Actual AGB (tons/acre)

0

40

20

80

60

100

0 4020 8060 100

Figure 38—LiDAR-based predicted aboveground biomass (AGB) vs. actual (field-based) AGB for Forest Inventory and Analysis (FIA) 

plots with one microplot (left) and FIA plots with two microplots (right). RMSE = root mean squared error.
64

GENERAL TECHNICAL REPORT PNW-GTR-967

Future Work 

Standard (design-unbiased, plot-based) FIA estimation approaches will be compared with model-assisted (i.e., approximately design-unbiased) and model-based 

approaches which utilize auxiliary information provided by G-LiHT-derived 

structural and spectral metrics (Bechtold and Patterson 2005, Gregoire et al. 2011, 

McRoberts et al. 2014, Särndal et al. 2003). Previous studies have indicated that the 

precision of aboveground carbon/biomass estimates—and the cost-efficiency of the 

inventory–can be increased through the combined use of airborne LiDAR data and 

field data in a two-phase, model-assisted sampling framework (Barrett et al. 2009, 

Ene et al. 2013). The accuracy and bias of the different approaches to estimation 

and inference will be evaluated using simulation (e.g., Ene et al. 2012). 

Acknowledgments

Thanks to the office staff at the Anchorage Forestry Sciences Laboratory and coordinators and data collection crews from the Forest Service and Bonanza Creek Long Term 

Ecological Research at the University of Alaska Fairbanks for collecting and managing the data that went into this report. For the ground layer protocol, Doug Daoust 

and Allison Nelson provided project support; Bethany Schulz and Robert Pattison 

advised on the field method; soil samples were analyzed by Dr. Amacher at the Rocky 

Mountain Research Station. Ken Winterberger contributed to field work; and Courtney 

Kerns, Bobby Henderson, Peter Nelson, and Elisa DiMeglio assisted with the multiobserver comparison. Thanks to Doug Hanson, John Yarie, and Teresa Hollingsworth 

for reviews of the original manuscript. Kurt Hellman helped edit the final manuscript. 

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 2.54 Centimeters

Feet (ft) 305 Meters

Acres (ac) .405 Hectares

Miles (mi) 1.609 Kilometers

Cubic feet (ft3

) .0283 Cubic meters

Pounds (lb) 454 Grams

Pounds (lb) .454 Kilograms

Tons (ton) 907 Kilograms

Tons (ton) 0.907 Tonnes or megagrams

Pounds per acre (lb/ac) 1.12 Kilograms per hectare

Pounds per acre .00112 Tonnes per hectare

Tons per acre 2.24 Tonnes or megagrams per hectare

Cubic feet per acre (ft3/ac) .07 Cubic meters per hectare

Degrees Fahrenheit .56(°F – 32) Degrees Celsius
65

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

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Appendix

Table 23—Scientific and common names of vascular plant species recorded, their growth habits as 

recorded, wetland status, and constancy on plots by inventory method and owner (continued)

Method/owner

VEG Profile Full census

Scientific name Common name

Growth 

habit(s)a

Wetland 

statusb TVSF TNWR TNWR

Percentage of plots

Alnus incana ssp. tenuifolia Thinleaf alder SH, tr 11.3 0 3.8

Alnus viridis Green alder SH FAC 22.5 0 0

Alnus viridis ssp. crispa Mountain alder SH, SD 26.8 40.7 34.6

Alnus viridis ssp. sinuata Sitka alder SH 7 7.4 3.8

Amerorchis rotundifolia Roundleaf orchid FB 0 0 3.8

Andromeda polifolia Bog rosemary SH FACW 0 0 11.5

Anemone parviflora Smallflowered anemone FB FACU 0 0 3.8

Arctagrostis latifolia Wideleaf polargrass GR FACW 0 3.7 7.7

Arctagrostis latifolia ssp.

arundinacea

Wideleaf polargrass GR 0 3.7 19.2

Arctagrostis latifolia ssp. 

latifolia

Wideleaf polargrass GR 0 0 19.2

Arctostaphylos alpina Alpine bearberry SH 1.4 0 0

Arctostaphylos rubra Red fruit bearberry SH 5.6 11.1 61.5

Arctostaphylos uva-ursi Kinnikinnick SH UPL 2.8 0 0

Betula glandulosa Resin birch SH FAC 8.5 25.9 19.2

Betula nana Dwarf birch SH FAC 15.5 44.4 42.3

Betula neoalaskana Alaska birch TT, SD FACU 69 63 57.7

Calamagrostis canadensis Bluejoint GR FAC 35.2 7.4 30.8

Calamagrostis purpurascens Purple reedgrass GR 1.4 0 0

Callitriche palustris Vernal water-starwort FB OBL 0 3.7 0

Carex aquatilis Water sedge GR OBL 4.2 7.4 7.7

Carex bigelowii Bigelow’s sedge GR FAC 0 0 3.8

Carex canescens Silvery sedge GR FACW 1.4 0 0

Carex capitata Capitate sedge GR FAC 0 0 7.7

Carex chordorrhiza Creeping sedge GR OBL 1.4 0 0

Carex concinna Low northern sedge GR FAC 0 3.7 11.5

Carex disperma Softleaf sedge GR FACW 0 0 3.8

Carex echinata Star sedge GR OBL 0 3.7 0

Carex gynocrates Northern bog sedge GR OBL 0 0 7.7

Carex lasiocarpa Woollyfruit sedge GR OBL 0 0 3.8

Carex lenticularis Lakeshore sedge GR OBL 1.4 0 0

Carex leptalea Bristlystalked sedge GR OBL 0 0 3.8

Carex limosa Mud sedge GR OBL 0 0 3.8
77

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Table 23—Scientific and common names of vascular plant species recorded, their growth habits as 

recorded, wetland status, and constancy on plots by inventory method and owner (continued)

Method/owner

VEG Profile Full census

Scientific name Common name

Growth 

habit(s)a

Wetland 

statusb TVSF TNWR TNWR

Percentage of plots

Carex magellanica Boreal bog sedge GR OBL 1.4 0 15.4

Carex membranacea Fragile sedge GR FACW 1.4 0 0

Carex microchaeta Smallawned sedge GR FAC 2.8 3.7 11.5

Carex saxatilis Rock sedge GR FACW 0 3.7 11.5

Carex stylosa Variegated sedge GR FACW 1.4 0 0

Carex utriculata Northwest territory sedge GR OBL 0 7.4 0

Carex vaginata Sheathed sedge GR OBL 0 0 3.8

Ceratophyllum demersum Coon’s tail FB OBL 0 3.7 3.8

Chamaedaphne calyculata Leatherleaf SH FACW 2.8 3.7 23.1

Chamerion angustifolium ssp. 

angustifolium

Fireweed FB 15.5 7.4 23.1

Cicuta virosa Mackenzie’s water 

hemlock

FB OBL 0 0 3.8

Circaea alpina Small enchanter’s 

nightshade

FB FACW 1.4 0 0

Comarum palustre Purple marshlocks FB OBL 1.4 0 7.7

Cornus canadensis Bunchberry dogwood FB FACU 18.3 0 0

Cornus sericea ssp. sericea Redosier dogwood SH 2.8 0 0

Cornus suecica Lapland cornel SH FAC 1.4 0 0

Cystopteris fragilis Brittle bladderfern FB FACU 0 0 3.8

Dasiphora fruticosa ssp.

floribunda

Shrubby cinquefoil SH 1.4 11.1 30.8

Delphinium glaucum Sierra larkspur SH FACW 0 0 3.8

Drosera rotundifolia Roundleaf sundew FB OBL 0 0 3.8

Dryas integrifolia Entireleaf mountain-avens FB FACU 0 0 3.8

Empetrum nigrum Black crowberry SH FAC 11.3 33.3 53.8

Epilobium palustre Marsh willowherb FB OBL 0 0 3.8

Equisetum arvense Field horsetail FB FAC 23.9 11.1 46.2

Equisetum fluviatile Water horsetail FB OBL 4.2 3.7 0

Equisetum palustre Marsh horsetail FB FACW 2.8 3.7 0

Equisetum pratense Meadow horsetail FB FACW 1.4 7.4 11.5

Equisetum scirpoides Dwarf scouringrush FB FACU 1.4 7.4 46.2

Equisetum sylvaticum Woodland horsetail FB FAC 18.3 25.9 23.1

Erigeron acris Bitter fleabane FB FAC 0 0 3.8

Erigeron elatus Swamp boreal-daisy FB 0 0 3.8

Erigeron lonchophyllus Shortray fleabane FB FACW 0 0 3.8
78

GENERAL TECHNICAL REPORT PNW-GTR-967

Table 23—Scientific and common names of vascular plant species recorded, their growth habits as 

recorded, wetland status, and constancy on plots by inventory method and owner (continued)

Method/owner

VEG Profile Full census

Scientific name Common name

Growth 

habit(s)a

Wetland 

statusb TVSF TNWR TNWR

Percentage of plots

Eriophorum Cottongrass GR 0 3.7 3.8

Eriophorum brachyantherum Northland cottonsedge GR OBL 0 11.1 19.2

Eriophorum vaginatum Tussock cottongrass GR FACW 7 25.9 26.9

Festuca altaica Altai fescue GR FAC 2.8 0 7.7

Festuca rubra Red fescue GR FAC 0 0 7.7

Fragaria virginiana Virginia strawberry FB UPL 1.4 0 0

Geocaulon lividum False toadflax FB FACU 22.5 25.9 42.3

Glyceria grandis var. grandis American mannagrass GR 0 0 3.8

Goodyera repens Lesser rattlesnake 

plantain

FB FAC 0 0 3.8

Hedysarum alpinum Alpine sweetvetch FB FACU 0 3.7 7.7

Huperzia selago var. selago Fir clubmoss SH 0 0 3.8

Iris Iris FB 0 0 3.8

Iris setosa Beachhead iris FB FAC 1.4 0 3.8

Larix laricina Tamarack SD FACW 7 0 0

Ledum groenlandicum Bog labrador tea SH 57.7 77.8 96.2

Ledum palustre ssp. decumbens Marsh labrador tea SH 8.5 25.9 34.6

Lemna minor Common duckweed FB OBL 0 3.7 0

Linnaea borealis Twinflower FB FACU 9.9 3.7 11.5

Lupinus Lupine FB 0 3.7 3.8

Lupinus arcticus Arctic lupine FB FACU 1.4 0 7.7

Lycopodium annotinum Stiff clubmoss SH 4.2 3.7 15.4

Lycopodium complanatum Groundcedar SH 4.2 0 0

Lycopodium lagopus One-cone clubmoss SH FACU 0 0 3.8

Lycopodium obscurum Rare clubmoss SH 1.4 0 0

Menyanthes trifoliata Buckbean FB OBL 1.4 0 3.8

Mertensia paniculata Tall bluebells FB FACU 8.5 7.4 26.9

Moehringia lateriflora Bluntleaf sandwort FB FACU 1.4 0 0

Moneses uniflora Single delight FB FACU 0 0 26.9

Orthilia secunda Sidebells wintergreen FB FACU 0 3.7 30.8

Oxytropis deflexa Nodding locoweed FB FACU 0 0 3.8

Oxytropis deflexa var. foliolosa Nodding locoweed FB 0 0 3.8

Parnassia palustris var. tenuis Marsh grass of parnassus FB 0 0 7.7

Parrya nudicaulis Nakedstem wallflower FB 0 0 3.8

Pedicularis Lousewort FB 0 0 3.8
79

Forests of the Tanana Valley State Forest and Tetlin National Wildlife Refuge, Alaska: Results of the 2014 Pilot Inventory

Table 23—Scientific and common names of vascular plant species recorded, their growth habits as 

recorded, wetland status, and constancy on plots by inventory method and owner (continued)

Method/owner

VEG Profile Full census

Scientific name Common name

Growth 

habit(s)a

Wetland 

statusb TVSF TNWR TNWR

Percentage of plots

Pedicularis labradorica Labrador lousewort FB FACW 0 0 7.7

Pedicularis parviflora Smallflower lousewort FB FACW 0 0 3.8

Petasites frigidus Arctic sweet coltsfoot FB FACW 1.4 14.8 19.2

Petasites frigidus var. frigidus Arctic sweet coltsfoot FB 0 0 7.7

Picea glauca White spruce TT, SD FACU 63.4 44.4 46.2

Picea mariana Black spruce TT, SD FACW 59.2 92.6 92.3

Poa arctica ssp. lanata Arctic bluegrass GR 0 0 3.8

Polygonum alpinum Alaska wild rhubarb FB 5.6 0 3.8

Polygonum viviparum Alpine bistort FB 0 0 3.8

Populus balsamifera Balsam poplar TT, SD FACU 7 3.7 3.8

Populus tremuloides Quaking aspen TT, SD FACU 18.3 11.1 15.4

Pyrola Wintergreen FB 0 0 7.7

Pyrola asarifolia Liverleaf wintergreen FB FACU 0 3.7 19.2

Pyrola chlorantha Greenflowered 

wintergreen

FB FACU 0 0 7.7

Pyrola grandiflora Largeflowered 

wintergreen

FB FAC 0 0 3.8

Ranunculus Buttercup FB 0 0 3.8

Ranunculus lapponicus Lapland buttercup FB 0 0 7.7

Ribes hudsonianum Northern black currant SH FAC 1.4 0 0

Ribes triste Red currant SH FAC 2.8 0 11.5

Rosa Rose SH 0 3.7 0

Rosa acicularis Prickly rose SH FACU 42.3 18.5 46.2

Rubus arcticus Arctic raspberry SH FAC 0 0 3.8

Rubus chamaemorus Cloudberry FB, SH FACW 14.1 7.4 42.3

Rubus idaeus American red raspberry SH FACU 4.2 0 0

Rumex aquaticus var.

fenestratus

Western dock FB 0 0 11.5

Salix Willow SH 4.2 0 0

Salix alaxensis Feltleaf willow SH, tr FAC 5.6 3.7 19.2

Salix arbusculoides Littletree willow SH, tr FACW 1.4 11.1 34.6

Salix barclayi Barclay’s willow SH, tr FAC 1.4 3.7 3.8

Salix barrattiana Barratt’s willow SH FACW 1.4 0 0

Salix bebbiana Bebb willow SH, SD FAC 16.9 3.7 3.8

Salix boothii Booth’s willow SH, tr OBL 0 0 3.8

Salix commutata Undergreen willow SH FAC 0 0 3.8
80

GENERAL TECHNICAL REPORT PNW-GTR-967

Table 23—Scientific and common names of vascular plant species recorded, their growth habits as 

recorded, wetland status, and constancy on plots by inventory method and owner (continued)

Method/owner

VEG Profile Full census

Scientific name Common name

Growth 

habit(s)a

Wetland 

statusb TVSF TNWR TNWR

Percentage of plots

Salix glauca Grayleaf willow SH, tr FAC 5.6 51.9 84.6

Salix hastata Halberd willow SH FAC 4.2 0 7.7

Salix interior Sandbar willow SH FACW 7 0 15.4

Salix monticola Park willow SH 1.4 0 15.4

Salix myrtillifolia Blueberry willow SH FACW 7 14.8 26.9

Salix planifolia Diamondleaf willow SH FACW 1.4 0 11.5

Salix pseudomonticola False mountain willow SH FAC 1.4 3.7 3.8

Salix pulchra Tealeaf willow SH FACW 8.5 0 7.7

Salix richardsonii Richardson’s willow SH FACW 0 3.7 0

Salix scouleriana Scouler’s willow SH, SD FAC 1.4 3.7 3.8

Saussurea angustifolia Narrowleaf saw-wort FB FAC 0 0 30.8

Saussurea angustifolia var.

yukonensis

Narrowleaf saw-wort FB 0 0 3.8

Senecio congestus Marsh fleabane FB 0 0 3.8

Shepherdia canadensis Russet buffaloberry SH FACU 1.4 3.7 7.7

Sorbus scopulina Greene’s mountain ash SH FACU 1.4 0 0

Spiraea Spirea SH 1.4 0 0

Spiraea stevenii Beauverd spirea SH FACU 5.6 0 3.8

Spiranthes romanzoffiana Hooded lady’s tresses FB OBL 0 0 3.8

Stellaria longifolia Longleaf starwort FB FAC 0 0 3.8

Taraxacum officinale ssp.

ceratophorum

Common dandelion 

(native)

FB 0 0 3.8

Tofieldia pusilla Scotch false asphodel FB FAC 0 0 7.7

Triantha glutinosa Sticky tofieldia FB FACW 0 0 3.8

Trichophorum cespitosum Tufted bulrush GR 0 0 3.8

Triglochin maritima Seaside arrowgrass GR OBL 0 0 3.8

Typha latifolia Broadleaf cattail FB OBL 0 3.7 0

Vaccinium Blueberry SH 1.4 0 0

Vaccinium oxycoccos Small cranberry SH OBL 0 0 19.2

Vaccinium uliginosum Bog blueberry SH FAC 25.4 70.4 92.3

Vaccinium vitis-idaea Lingonberry SH FAC 67.6 85.2 100

Valeriana capitata Captiate valerian FB FAC 0 0 11.5

Viburnum edule High bush cranberry SH FACU 12.7 0 0

a Growth habits: FB = forb; GR = grass-like; SH = shrub or subshrub; tr = potential for tree form; TT = tally tree. 

b Wetland status: FAC = facultative (occur in wetlands and non-wetlands); FACW = facultative wetland (usually occur in wetlands); FACU = facultative 

upland (usually occur in non-wetlands); OBL = obligate wetland (almost always occur in wetlands); UPL = obligate upland (almost never occur in wetlands).


Pacific Northwest Research Station

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U.S. Department of Agriculture

Pacific Northwest Research Station

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Portland, OR 97208–3890

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