Pacific Northwest 

Research Station

General Technical 

Report

PNW-GTR-889

January 2014

United States Department of Agriculture 

Forest Service

Storage and Flux of Carbon in 

Live Trees, Snags, and Logs 

in the Chugach and Tongass 

National Forests

T.M. Barrett
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Author

T.M. Barrett is a research forester, Forestry Sciences Laboratory, 1133 N Western 

Avenue, Wenatchee, WA 98801.

Cover photo by Jon Williams.
Abstract

Barrett, T.M. 2014. Storage and flux of carbon in live trees, snags, and logs in 

the Chugach and Tongass National Forests. Gen. Tech. Rep. PNW-GTR-889. 

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station. 44 p.

Carbon storage and flux estimates for the two national forests in Alaska are provided using inventory data from permanent plots established in 1995–2003 and 

remeasured in 2004–2010. Estimates of change are reported separately for growth, 

sapling recruitment, harvest, mortality, snag recruitment, salvage, snag falldown, 

and decay. Although overall aboveground carbon mass in live trees did not change 

in the Tongass National Forest, the Chugach National Forest showed a 4.5 percent 

increase. For the Tongass National Forest, results differed substantially for managed 

and unmanaged forest: managed lands had higher per-acre rates of sequestration 

through growth and recruitment, and carbon stores per acre that were higher for 

decomposing downed wood, and lower for live trees and snags. The species composition of carbon stores is changing on managed lands, with a carbon mass loss 

for yellow-cedar but increases for red alder and Sitka spruce. On unmanaged lands, 

the Chugach National forest had carbon mass increases in Sitka spruce and white 

spruce, and the Tongass National Forest had increases in western redcedar and red 

alder.

Keywords: Biomass, carbon cycle, carbon sequestration, phytomass, rain forest. 
Summary

Carbon accounting is becoming of increasing importance to forest managers, as 

markets develop for private forest landowners and public land managers incorporate 

carbon services into planning and management. In this report, inventory data from 

permanent plots established in 1995–2003 and remeasured in 2004–2010 are used 

to provide estimates of aboveground carbon storage and flux for the two national 

forests in Alaska. Estimates of change are reported separately for growth, sapling 

recruitment, harvest, mortality, snag recruitment, salvage, snag falldown, and 

decay.

For the Chugach National Forest, key findings are:

• The overall increase in live tree carbon mass was substantial, estimated 

as a 4.5 percent increase from 1999–2003 to 2004–2010, equivalent to an 

increase of

• 0.8 percent per year

• 165,000 tons of carbon mass (C) per year for the forest, and

• 552 lbs of C per forest acre per year

Although a recent increase in live tree biomass is not unusual for a national 

forest, the increase for the Chugach National Forest is not attributable to fire 

suppression or past harvest, unlike most other forests. We do not know whether 

the observed increase is caused by recovery from past disturbances (e.g., spruce 

beetle outbreaks) or is a result of warming temperatures in the region.

• Significant increases of live tree carbon mass occurred for the Sitka spruce 

and white spruce tree species. 

• Cottonwood, paper birch, western hemlock, and white spruce forest types 

all showed significant increases in live tree carbon mass. 

• No tree species or forest type showed a significant decrease in live tree

carbon mass.

For the Tongass National Forest, key findings from this report are:

• The Tongass National Forest stores massive amounts of forest carbon, more 

than any other national forest in the United States. The estimated aboveground average carbon density in the forest was 70 tons per acre in live 

trees, snags, and logs in 9.7 million ac of forest.
• Growth and recruitment of live trees removes from the atmosphere an 

estimated 760 lbs of carbon per acre per year, but net change in live carbon 

mass was not significantly different from zero, with mortality and harvest 

estimated at 670 lbs of carbon per acre per year. Turnover in the live tree 

and snag pool was estimated as 0.6 percent per year and 2.6 percent per 

year, respectively.

• On managed forest lands (estimated at 446,000 ac), there were significant 

increases in Sitka spruce and red alder live tree carbon mass, and a significant decrease in yellow-cedar carbon mass.

• On unmanaged forest (estimated at 6,294,000 ac with an additional 

2,974,000 ac of unsampled forest in wilderness), there was a large (6.6 

percent) increase in western redcedar carbon mass and also a significant 

increase in red alder carbon mass.

• Growth and recruitment was much higher in managed forest (1,608 lbs per 

acre per year) than in unmanaged forest (690 lbs per acre per year), and 

natural mortality was much lower (278 lbs per acre per year versus 619 lbs 

per acre per year). 

• Carbon density on unmanaged forest was estimated as 72 tons per acre, 

split as 7 percent logs, 13 percent snags, and 80 percent live trees. Carbon 

density on managed forest was estimated as 45 tons per acre, split as 38 

percent logs, 8 percent snags, and 54 percent live trees.

• Although management choices could potentially increase carbon sequestration in second-growth stands, e.g., by altering rotation lengths or utilization 

of harvested material, this report does not make any specific recommendations owing to the relatively small number of managed stands (58) that fell 

within the field plots.
Contents

1 Introduction

1 Methods

1 Data

11 Carbon Calculations

14 Chugach National Forest

23 Tongass National Forest

24 Changes Between Inventories

36 Discussion

39 Conclusion

40 Common and Scientific Names

40 Acknowledgments

41 Metric Equivalents

41 Literature Cited
1

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Introduction

Carbon dioxide (CO2) is thought to play a major role in global climate change, and 

as a result, efforts to measure the levels of carbon sequestration, storage, and flux in 

forests are of increasing interest to forest land managers. For national forests in the 

United States, this undertaking was reflected in several significant new developments that occurred in 2012:

1. Thirty years after publication of the original forest planning rule under the 

National Forest Management Act, a new forest planning rule was finalized. 

Among other requirements, new assessments for each national forest are to 

include a baseline assessment of carbon stocks, and forests are to monitor 

changes related to climate change and other stressors.

2. National forests began to use an annual “Climate Change Scorecard” 

assessment. Questions that forests now consider include progress toward a 

baseline assessment of carbon stocks, as well as an assessment of how disturbance and management activities are influencing carbon stocks, sequestration, and emissions.

This report is intended to help the two national forests in Alaska, the Chugach 

and the Tongass, make progress toward these new assessments by providing information on storage and flux of carbon in live and dead trees within the forests based 

on data collected by the USDA Forest Service Forest Inventory and Analysis (FIA) 

program. In addition, by providing estimates of temporal flux between carbon 

pools, the results reported here can improve understanding of some types of recent 

changes occurring in the national forests and their surrounding ecosystems. 

Methods

Data

The estimates in this report are derived from remeasured inventory plots installed 

by FIA. Only trees of at least 5 in diameter at breast height (d.b.h.) were used for 

analysis because a change in the plot layout resulted in no remeasurement information for smaller trees. The first inventories were installed from 1995 to 2000 in 

southeast Alaska (van Hees 2003) and from 1999 to 2003 in south-central Alaska 

(van Hees 2005). These combined inventories are referred to here as the “periodic” 

inventory. Many of these plots are being remeasured in the current “annual” FIA 

inventory system. This report combines those periodic (1995–2003) inventory plots 

with the remeasurement of those plots from 2004 to 2010; remeasurement intervals 

are shown for the Chugach National Forest in table 1 and for the Tongass National 

Forest in table 2. The period for remeasurement, which varied from 1 to 15 years, is 
2

general technical report pnw-gtr-889

a relatively short period to expect to see changes for such a large region. The varied 

interval of time for plot measurements complicates interpretation, as does the use 

of average annual values. For example, even if mortality rates were absolutely 

constant during the inventory period, an annual mortality rate calculated from plots 

remeasured after 1 year will be a little higher than the rate calculated from plots 

remeasured after a decade.

Detailed information on how measurements were taken can be found in the 

respective field manuals at http://www.fs.fed.us/pnw/fia/publications/fieldmanuals. 

Although the two national forests in Alaska are the focus of this report, the inventory crosses all ownerships (figs. 1 and 2). Plots were identified with each national 

forest using an administrative ownership variable in the FIA database. About 90.8 

Table 1—Number of remeasured forested plots by years of 

measurement, Chugach National Forest

Year of first measurement

Year of second measurement 1999 2001 2002 2003 All years

2004 7 1 2 1 11

2005 4 2 3 0 9

2006 8 3 1 0 12

2007 7 2 4 0 13

2008 9 1 3 0 13

2009 6 3 3 0 12

2010 8 0 5 0 13

 All years 49 12 21 1 83

Table 2—Number of remeasured forested plots by years of measurement, 

Tongass National Forest

Year of first measurement

Year of second measurement 1995 1996 1997 1998 2000 All years

2004 18 25 22 10 3 78

2005 21 15 22 22 2 82

2006 18 28 31 22 3 102

2007 24 24 26 13 0 87

2008 27 20 30 23 2 102

2009 23 20 33 11 2 89

2010 21 34 33 18 4 110

 All years 152 166 197 119 16 650
3

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

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Chugach National Forest wilderness study area

Chugach National Forest

Kenai National Wildlife Refuge

National Park Service

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Private

State 

State and Native

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0 50 100 200 Kilometers

ALASKA

Figure 1—Forest inventory plots and ownership in and surrounding the Chugach National Forest, southeast Alaska. Depicted plot

locations are approximate.
4

general technical report pnw-gtr-889

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Nonforest plots

Forest plots

Tongass National Forest wilderness

Tongass National Forest

National Park Service

Other federal

Private

State 

State and Native

^

0 50 100 200 Kilometers

ALASKA

Figure 2—Forest inventory plots and ownership in and surrounding the Tongass National Forest, southeast Alaska. Depicted plot

locations are approximate.

percent of the periodic inventory plots are being remeasured in the annual inventory, although plots that are inaccessible in either inventory reduce the number 

available for analysis. About 70 percent of the periodic plots (a random sample of 

the 90.8 percent) had been remeasured by the end of the 2010 field season.

For analysis of change, only remeasurement plots and only portions of plots that 

were forested in both periods were used. That results in estimates that usually are 

smaller and less precise than when either the full periodic dataset or the full annual 

dataset is used (tables 3, 4, 5, and 6). In general, the periodic inventory used a more 

restrictive definition of forest land, by excluding Krummholz forest and by using a 

canopy cover definition that was less likely to define an area as forest than was the 

stocking definition used from 2004 to 2010. 
5

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 3—Effect of different estimation methods on forest type area, Chugach 

National Forest

Without wilderness study area With wilderness study areaa

Remeasurement 

plots onlyb 

All 2004–2010 

plotsc

All 2004–2010 

plotsc

Adjustment 

factord Forest type Total SE Total SE Total SE

Thousand acres

Yellow-cedar — — — — — — —

Black cottonwood 20 12 18 12 18 12 0.90

Black spruce 5 6 5 6 5 6 1.00

Lodgepole pine — — — — — — —

Mountain hemlock 287 45 351 45 784 158 2.73

Pacific silver fir — — — — — — —

Paper birch 25 16 20 13 20 13 0.80

Quaking aspen — — — — — — —

Sitka spruce 111 29 138 31 138 31 1.24

Western hemlock 127 32 140 33 140 33 1.10

Western redcedar — — — — — — —

White spruce 20 12 23 13 23 13 1.15

 All forest types 596 52 703 52 1135 160 1.90

a

 Includes wilderness study area plots measured in 2005. Because of the very small 

number of plots, this will not do well at representing forest in the wilderness study area.

b

 Does not include land that was defined as forest for only one of the inventories, or plots 

that were not included in both inventories; this method is what was used for estimates of 

change in this report and is labeled with “remeasurement plots only.”

c

 Estimates also adjust for nonsampled (access denied or hazardous) plots. These estimates 

should match what would be produced from the national database using the current inventory and are labeled with “all 2004–2010 plots.”

d

 For an approximate extrapolation of change estimates to all forest (including the wilderness study area), one could multiply carbon estimates for each forest type by this adjustment factor.

SE = Standard error of the estimate. The total plus or minus the standard error provides a 

68 percent confidence interval, and the total plus or minus two standard errors is about a 95 

percent confidence interval for the estimate.
6

general technical report pnw-gtr-889

Table 4—Effect of different estimation methods on carbon mass in live trees, 

Chugach National Forest

Without wilderness study area

With wilderness 

study areaa

Remeasurement 

plots onlyb

All 2004–2010 

plotsc

All 2004–2010 

plotsc

Species Total SE Total SE Total SE

Thousand tons

Black cottonwood 358 221 413 243 413 243

Black spruce — — 9 7 9 7

Mountain hemlock 7,755 1,492 9,382 1,510 20,839 6,488

Paper birch 147 75 158 77 158 77

Sitka spruce 5,553 1,177 8,309 1,792 10,292 2,409

Western hemlock 6,637 1,919 7,182 1,860 7,270 1,863

White spruce 358 138 497 180 497 180

 All species 20,809 2,707 25,951 3,117 39,478 7,822

a

 Includes wilderness study area plots measured in 2005. Because of the very small 

number of plots, this will not serve well at representing forest in the wilderness study 

area.

b

 Does not include land that was defined as forest for only one of the inventories, or plots 

that were not included in both inventories or any trees ≤5 in diameter at breast height; 

this method is what was used for change estimates in this report and is denoted with the 

note “remeasurement plots only.”

c

 Estimates also adjust for nonsampled (access denied or hazardous) plots. This method 

is denoted by the use of “all 2004–2010 plots.”

SE = Standard error.
7

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 5—Effect of different estimation methods on forest type area, Tongass National Forest

Without inaccessible wilderness area With inaccessible wilderness areaa

Remeasurement 

plots onlyb

All 2004–2010 

plotsc

All 2004–2010 

plotsc

Adjustment 

factord Forest type Total SE Total SE Total SE

Thousand acres

Yellow-cedar 1,261 99 1,433 101 2,199 221 1.74

Black cottonwood 36 18 36 17 98 59 2.72

Lodgepole pine 286 48 348 50 348 50 1.22

Mountain hemlock 820 78 1,229 90 2,013 214 2.45

Red alder 22 12 36 16 36 16 1.64

Sitka spruce 434 60 590 67 839 130 1.93

Subalpine fir — 4 4 4 4 na

Western hemlock 2,374 117 2,479 114 3,219 222 1.36

Western redcedar 575 66 587 63 960 148 1.67

 All forest types 5,808 105 6,741 101 9,715 233 1.67

a

 Includes wilderness area plots measured in 2005. 

b

 Does not include land that was defined as forest for only one of the inventories, or plots that were not 

included in both inventories; this method is what was used for estimates of change in this report and is 

labeled with “remeasurement plots only.”

c

 Estimates also adjust for nonsampled (access denied or hazardous) plots. These estimates should match 

what would be produced from the national database using the current inventory and are labeled with “all 

2004–2010 plots.”

d

 Calculated as the estimate from all plots divided by the estimate from remeasurement plots only. For 

an approximate extrapolation of change estimates to all forest (including the wilderness study area), one 

could multiply carbon estimates for each forest type by this adjustment factor.

SE = Standard error of the estimate. The total plus or minus the standard error provides a 68 percent 

confidence interval, and the total plus or minus two standard errors is about a 95-percent confidence 

interval for the estimate.
8

general technical report pnw-gtr-889

Table 6—Effect of different estimation methods on carbon mass in live trees, 

Tongass National Forest

Without wilderness study area

With wilderness 

study areaa

Remeasurement 

plots onlyb

All 2004–2010 

plotsc

All 2004–2010 

plotsc

Species Total SE Total SE Total SE

Thousand tons

Yellow-cedar 40,539 2,691 45,318 2,695 70,905 5,831

Black cottonwood 480 244 502 247 1,549 978

Lodgepole pine 4,563 485 4,840 488 6,923 1,093

Mountain hemlock 36,213 2,821 42,256 2,958 74,999 9,209

Oregon crab apple 1 1 1 1 1 1

Pacific silver fir 7 9 60 45 60 45

Red alder 717 194 1,824 390 2,092 437

Sitka spruce 65,426 5,916 81,481 6,252 116,012 11,883

Subalpine fir 144 102 127 83 127 83

Western hemlock 153,171 8,100 161,065 7,718 211,628 11,876

Western redcedar 20,174 2,209 21,566 2,144 45,051 8,571

 All species 321,436 10,811 359,040 10,391 529,347 19,558

a

 Includes wilderness study area plots measured in 2005. Because of the very small number of plots, this will not serve well at representing forest in the wilderness study area.

b

 Does not include land that was defined as forest for only one of the inventories, or plots 

that were not included in both inventories or any trees ≤5 in diameter at breast height; 

this method is what was used for change estimates in this report and is denoted with the 

note “remeasurement plots only.”

c

 Estimates also adjust for nonsampled (access denied or hazardous) plots. This method 

is denoted by the use of “all 2004–2010 plots.”

SE = Standard error.

Helicopter use is not allowed within much of the wilderness on the Tongass 

and the wilderness study area on the Chugach. Owing to this restriction, these 

areas were inaccessible during the periodic inventory. During the annual inventory, 

access was permitted in 2005, and 50 forested plots were measured in Tongass 

wilderness and 9 forested plots in the Chugach wilderness study area. However, 

after an environmental assessment, the areas were again removed from the inventory in 2006. Because none of the wilderness plots had remeasurement data, they 

are excluded from all estimates of change in carbon storage in this report but were 

included in comparisons of methods of estimations of forest type area (tables 3

and 5) and carbon mass (tables 4 and 6).
9

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

On the Chugach, of the 107 nonwilderness annual plots measured between 

2004 and 2010, just 83 were remeasured plots and only two of these had a record 

of past silvicultural activities, thus managed forest is not reported as a separate 

category for the Chugach National Forest. On the Tongass, there are 801 nonwilderness forested FIA plots that were measured between 2004 and 2010; of those, 650 

are remeasured plots that were initially established in the 1995–2000 inventory.

On the Tongass, 58 stands with remeasurement data had a record indicating 

some type of vegetation manipulation, usually clearcutting. (Note: stands are called 

“condition classes” by FIA, and denote an area of forest that is homogenous with 

respect to forest type, owner group, stand size, regeneration status, tree density, 

and reserved status. Although most plots intersect only a single stand, many plots 

intersect multiple stands.) Fifty-eight managed stands were sufficient to allow some 

separate analysis of managed and unmanaged forest, which was helpful because 

of the substantially different trajectories in carbon storage and flux. Classification 

as managed forest was based on a combination of time since clearcut harvest (a 

variable that was collected in the periodic inventory), records of trees harvested 

between the two inventory measurements, written plot descriptions, and the forest’s 

geographic information system layer for stand management. The managed category 

also includes some residual trees within harvest areas, and a few stands with selective or salvage logging, and thus the plots in the managed forest category include 

areas with complex structure and older trees in addition to areas of even-aged 

second growth. 

Estimates of carbon in down wood debris1 (DWD) are included based on 

transects that were installed in the periodic inventory (1995–2003). Although DWD 

was measured on a 1/16th subsample of plots from 2004 to 2010, the small number 

of these plots means it is not possible to measure change in DWD with sufficient 

precision for meaningful estimates. Down woody debris measurements were taken 

only on the first stand (condition class) of each plot, which causes more imprecision 

compared to live tree or snag estimates. Some plots with forest did not have DWD 

measurements taken, either because of snow or because only a small portion of the 

plot contained forest. Although this could create some bias in the estimates, less 

than 2.4 percent of the sampled forested area fell into this category, so the bias is 

likely to be minimal. 

Because of the many procedural differences between the 1995–2003 inventory 

and the 2004–2010 inventory, trying to estimate change by simple comparison of 

1

 The term “snag” is equivalent to the term “standing dead tree” used by FIA, and is 

defined as a dead tree that is at least 5 in d.b.h., has a bole with an unbroken length of at 

least 4.5 ft, and is less than a minimum number of degrees from vertical. Minimum lean 

angles used differed between the first and second inventories.
10

general technical report pnw-gtr-889

the two inventories would produce inaccurate estimates of carbon and biomass 

change for Alaska’s national forests. To be able to estimate change accurately, a 

number of edits to the dataset were required: 

(1) Building a stratification customized for remeasurement. 

(2) Reconciling every tree in the first inventory for its status at remeasurement (live, snag, harvested, or dead and down). 

(3) Reconciling the first inventory for (a) trees that would not meet the 

current definition for inclusion; (b) trees that had been missed; (c) species 

codes that were incorrect; and (d) incorrect tree status, most typically trees 

that had been recorded as dead but were found to have a few live branches 

in the second inventory.

(4) Adjusting for a definition of forest that changed from a cover-based to 

a stocking-based definition by including only portions of plots that were 

forested in both periods. Although this was the best choice available, it 

prevented the calculation of estimates of biomass/carbon change associated 

either with forest encroachment (such as increasing treeline) or permanent 

deforestation (such as when land is developed for housing or roads).

Statistical methods for calculating standard errors are the current standard 

methods used by FIA, as described in Bechtold and Patterson (2005). Some estimates report carbon mass per forest acre; these are produced using a combined ratio 

of means estimator (Cochran 1977). Where change estimates are called significant, 

it means that the 95 percent confidence interval (CI) does not contain zero; the 95-

percent CI is created by multiplying the estimated standard error by 1.96 and adding (or subtracting) it from the estimated mean. 

Standard FIA reports, including the most recent report for coastal Alaska 

(Barrett and Christensen 2011), drop nonsampled plots (hazardous or access denied) 

from the stratification process, so that estimates approximate population totals. The 

disadvantage of doing this is that it requires an assumption that nonsampled plots 

are no different from the strata mean estimated from remaining plots; as nonsampled plots tend to be on steeper ground (when hazardous) or at high elevation 

(where snow often prevents access), this assumption can be incorrect. In this report, 

the nonsampled plots were left in the stratification, with the result that estimated 

population totals will be smaller. Tables 3 through 6 show the difference that 

results from using these different methods. In addition, the area that was sampled 

for remeasurement is smaller than the area currently in the inventory, because the 

current inventory includes 1 year of data from national forest wilderness and the 

boundaries for that wilderness shifted between inventories. 
11

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

If extrapolation to the entire forest is desired, one might multiply per-acre values for specific forest types by the additional estimated land area. For example, in 

the Chugach National Forest, the area of Sitka spruce forest is estimated as 111,000 

ac using the remeasurement data, and 138,000 ac when the wilderness study area 

is included, or an increase of 24 percent (table 3), and the remeasurement data 

provides an estimate that carbon mass in Sitka spruce forest type increased at a rate 

of 56,000 tons per year. One could then make an educated guess that the increase 

including the wilderness study area was 56,000 × 1.24 = 69,400 tons. This is just 

a rough approximation, however, as there is no guarantee that Sitka spruce forest 

in the wilderness study area changed similarly to Sitka spruce forest outside of the 

wilderness study area.

Carbon Calculations

The aboveground carbon pools estimated in this report are those of (1) the live

tree pool; (2) the snag2 pool; and (3) the DWD (or log) pool (fig. 3). Carbon fluxes 

that are estimated in this report are (a) recruitment, (b) growth, and (c) mortality 

for the live tree pool and (d) snag recruitment, (e) decay, and (f) falldown for the 

snag pool (fig. 3). Net change in the live tree pool is measured as recruitment plus 

growth, minus mortality and harvest. Net change in the snag pool is equal to snag 

recruitment (part of live tree mortality) minus decay, falldown, and salvage. Within 

the forest ecosystem are a number of carbon pools that are not included here, such 

as carbon within non-tree vegetation, carbon within tree roots and stumps, and 

carbon in soil and litter. There are also a number of fluxes that are not estimated, 

including carbon moving from vegetation to soil or water, or decay of logs. Some 

current research projects are underway in the region to provide information about 

these processes.

Several different methods are available for calculating biomass and carbon for 

Alaska forests from individual tree measurements of diameter, species, and height. 

In this report, species-specific direct biomass estimators published in the research 

literature have been used, most of them developed for British Columbia (for rain 

forest species) or Alberta (for boreal species). A different method, which has typically been developed to address species without direct biomass equations, is called 

the “component ratio” method. In this method, tree volume equations are modified 

with estimated density to derive biomass estimates for the main part of the bole, 

and ratios are then applied to estimate biomass of components such as bark, top, 

2

 The data for down wood debris estimates is courtesy of Mikhail Yatskov, Ph.D. candidate, 

Oregon State University.
12

general technical report pnw-gtr-889

CO2

to salvage

Mortality

to harvest

to herbivory

Mortality

Falldown

Growth Decay

Decay

to water

to soil

Recruitment

1 2

3

Figure 3—Carbon flux between the (1) live, (2) snag, and (3) log pools of the forest.

branches, and foliage. This method has commonly been used in other states, but 

because of the low tree species diversity in Alaska, and resulting availability of 

species-specific biomass equations for all our major species, the component ratio 

method has not been used by FIA in Alaska. A third method, also not used in this 

report, has been used to produce many of the biomass variables in the database at 

the national FIA website (http://www.fia.fs.fed.us/tools-data/default.asp), and it 

is based on the component ratio method with adjustments based on Jenkins et al. 

(2003) and others (see Woudenberg et al. 2013, appendix J). 

Although attempts to develop a unified national method provides some consistency across regions, when used at a regional level these can produce estimates very 

different from estimates that use regional equations (e.g., Fried and Zhou 2008). 

The only way to compare accuracy of competing methods is to test them against 

independent datasets, which are very scarce because of the cost of drying and 

weighing trees. In general, because the regional equations are species specific, are 

based on both diameter and height, were derived from research specifically meant 

to estimate biomass, and are built from observations for trees typically sampled 

from ecosystems similar to where they are being applied, the local equations are 

probably preferable for any use other than national-level estimates. The regional 
13

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

variables are also available as part of the database on the national FIA website, and 

can be found in a separate tree table. In both this report and standard national FIA 

applications, carbon mass is assumed to be equal to 0.5 of dry biomass. Because of 

the simplicity of conversion, estimates are shown for carbon mass, and it is left to 

the reader to multiply by two if dry biomass estimates are desired.

The regional equation sets for Alaska trees come from the following published 

sources:

Tree type Biomass citation

Seedlings Alemdag (1984)

Paper birch Alemdag (1984)

Black spruce Manning et al. (1984)

Cottonwood Singh (1984)

Lodgepole pine3 Manning et al. (1984)

Mountain hemlock Shaw (1979)

Pacific silver fir Krumlik and Kimmins (1973)

Red alder Standish (1983)

Sitka spruce Standish (1983)

Tamarack Singh (1984)

Western hemlock Shaw (1979)

Western redcedar Shaw (1979)

White spruce Manning et al. (1984)

Yellow-cedar Standish (1983)

3

 Based on the location of plots, all sampled lodgepole trees are believed to be the shore 

pine subspecies (Pinus contorta Dougl. Ex Loudon subsp. contorta).

Currently, most regions of the country, including Alaska, do not have adjustments for portions of tree tops that are broken off (“missing tops”) in the national or 

regional biomass variables in the publicly available FIA database. However, missing 

tops are being increasingly accounted for in biomass or volume variables within 

some regional databases, thus biomass estimates for snags in this report have been 

adjusted to account for missing tops using simple conic geometry. No deductions 

were made for missing tops on live trees (which is much less common than missing 

tops on snags), because information for this had not been collected in the periodic 

southeast Alaska inventory.

Deductions for decay class have also typically not been available in national 

and regional databases. However, a Forest Service publication was recently developed to provide information on adjustments for decay in snags and logs (Harmon et 

al. 2011) and adjustments to the component-ratio variables in the national database 
14

general technical report pnw-gtr-889

are now being made. For this reason, wood decay deductions based on decay class 

estimated in the field (using Harmon et al. 2011, table 6) were made for both snags 

and logs in this report. These decay class deductions, along with missing top deductions, will produce some differences from values for snags published in Andersen 

(2011). Decay class for snags was set at the values measured during the periodic 

inventory because of a change in methodology, so estimates of carbon lost in snag 

decay represent reductions from fragmentation rather than progression to a higher 

decay class. 

Chugach National Forest

Excluding its wilderness study area, tree biomass and carbon on the Chugach 

National Forest is fairly evenly split between three tree species: mountain hemlock, 

western hemlock, and Sitka spruce (table 7). White spruce, black cottonwood, and 

paper birch combined comprise only about 5 percent of total carbon mass, and 

other species such as black spruce or quaking aspen comprise less than 1 percent of 

carbon mass. Looking at the distribution by forest type instead of species provides 

similar results (table 8).

Compared to other species, white spruce has a higher proportion of carbon in 

snags (table 7; the white spruce proportion is 202/699 = 29 percent compared to

proportions of 2 to 9 percent for other species). This is likely the result of spruce 

beetle outbreaks in the 1990s, as is the slightly elevated proportion of dead Sitka 

spruce (9 percent) compared to the two hemlock species (4 percent for mountain 

hemlock and 5 percent for western hemlock).

Although the total carbon mass in mountain hemlock, western hemlock, and 

Sitka spruce forest types is similar within the Chugach National Forest, the density 

is much higher for the western hemlock and Sitka spruce forest types (table 9). 

Overall, there was a 4.5-percent increase in carbon mass in live trees in the 

Chugach National Forest from the first inventory (1999–2003) to the second inventory (2004–2010) (table 10). A recent increase in biomass is not unusual among 

national forests. Most U.S. national forests have been experiencing recent increases 

in carbon and biomass (Heath et al. 2010), with increases in recent decades generally attributed to temporal changes in harvesting or the long-term effect of fire 

suppression (Goodale et al. 2002). 

What makes the observed 4.5-percent increase interesting is that neither of 

these causes is a satisfactory explanation for the Chugach National Forest. With 

few roads, challenging topography, and high recreational and subsistence use, little 

harvest has occurred on the Chugach during the past half century. Forested areas 
15

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 7—Carbon mass in live trees and snags on the Chugach 

National Forest

Live trees Snags All trees

Species Total SE Total SE Total SE

Thousand tons

Black cottonwood 413 243 11 8 424 243

Black spruce 9 7 1 1 10 8

Mountain hemlock 9,382 1,510 418 96 9,800 1,545

Paper birch 158 77 4 5 162 77

Quaking aspen — — 4 4 4 4

Sitka spruce 8,309 1,792 860 281 9,169 1,928

Western hemlock 7,182 1,860 359 111 7,541 1,923

White spruce 497 180 202 124 699 269

 All species 25,951 3,117 1,859 345 27,810 3,271

Note: Estimates are created from all 2004–2010 plots but do not include the wilderness 

study area.

SE = Standard error.

Table 8—Carbon in live trees and snags by forest type within the Chugach 

National Forest

Live trees Snags All trees

Forest type Total SE Total SE Total SE

Thousand tons

Black cottonwood 632 419 33 32 665 425

Black spruce 5 6 6 8 11 14

Mountain hemlock 9,375 1,731 788 222 10,163 1,851

Paper birch 98 82 7 6 105 88

Sitka spruce 7,112 2,277 409 175 7,521 2,402

Western hemlock 8,483 2,373 602 241 9,085 2,494

White spruce 247 139 14 10 260 147

 All forest types 25,951 3,117 1,859 345 27,810 3,271

Note: Estimates are created from all 2004–2010 plots but do not include the wilderness study area.

SE = Standard error.
16

general technical report pnw-gtr-889

Table 9—Carbon mass per acre in trees by forest type in the Chugach 

National Forest

Live trees Snags All trees

Forest type Mean SE Mean SE Mean SE

Pounds per acre

Black cottonwood 48,962 30,191 2,589 2,133 51,551 30,052

Black spruce 2,023 410 2,504 507 4,527 917

Mountain hemlock 53,403 7,030 4,488 1,090 57,890 7,359

Paper birch 9,871 5,237 694 427 10,565 5,658

Sitka spruce 102,917 23,682 5,922 2,132 108,839 24,889

Western hemlock 121,024 16,960 8,591 2,727 129,616 16,729

White spruce 21,766 3,906 1,197 492 22,964 4,036

 All forest types 73,873 7,599 5,292 909 79,165 7,881

Note: Estimates are created from all 2004–2010 plots but do not include the 

wilderness study area.

SE = Standard error.

Table 10—Change in carbon mass in live trees by species from the first inventory (1999–2003) to the second 

inventory (2004–2010), Chugach National Forest

Carbon 

1999–2003 Mortality Growth Ingrowth Net change

Net change 

as percent of 

Species Total SE Total SE Total SE Total SE Total SE 1999–2003

- - - - - - - - - - - - - - - - - - - - - - Thousand tons - - - - - - - - - - - - - - - - - - - - - - Percent

Black cottonwood 358 221 17 13 55 39 1 2 40 41 11

Mountain hemlock 7,755 1,492 151 97 349 162 28 8 226 192 3

Paper birch 147 75 22 15 22 15 15

Sitka spruce 5,553 1,177 205 125 572 134 38 15 405 168 7

Western hemlock 6,637 1,919 125 59 269 175 25 9 168 177 3

White spruce 358 138 6 6 66 29 18 11 78 35 22

 All species 20,809 2,707 504 167 1,333 292 110 22 939 325 5

Note: Data are based on remeasurement plots only, which do not include trees < 5 in diameter at breast height.

SE = Standard error.

are within a comparably low fire frequency regime, owing to relatively low temperatures, high cloud cover, and ample precipitation in the summer months.

The last major spruce beetle outbreak in the region occurred in the 1990s, and 

the area most affected was not within the Chugach boundaries. Although recovery 

from the spruce beetle could be contributing to some biomass and carbon increase, 

one might expect the majority of effect to be delayed until regenerating trees 

approach the point of maximum mean annual increment, which would be quite a 

few years in the future. However, there was a previous large outbreak in the 1970s 

and 1980s (Berg et al. 2006), and there could be some ongoing recovery from that. 
17

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Likewise, there could have been other disturbances in the past (wind events, longago harvests, insect outbreaks) that are now contributing to the net increase of live 

tree biomass. 

Climate change or CO2 increase could also be contributing to the higher 

biomass storage. To put the observed changes into context, with the possible exception of a few small refugia, almost all of the Chugach was covered by ice during the 

last glacial maximum approximately 23,000 years BP (Reger et al. 2007). Pollen 

studies suggest that migration of coastal tree species back into the contemporary 

forest lands has been a long, slow process, with mountain hemlock and Sitka spruce 

moving into Prince William Sound only around 3,000 years BP (Ager 1999). Many 

of the Sitka spruce and hemlock trees in the Chugach were alive at the end of the 

Little Ice Age in the 1850s, and warming since then is thought to have facilitated 

the expansion of black spruce in the Kenai lowlands (Berg et al. 2009). In more 

recent times, trees included in these inventories would have been affected by the 

relatively warmer, drier phase of the Pacific Decadal Oscillation, which began in 

the mid-1970s (Whitfield et al. 2010). Weather station data in the region show that 

average growing season temperatures during the inventory period (1999–2010) 

were slightly warmer than the 30-year climate “normal” preceding the start of the 

inventory (1969–1998) (fig. 4). 

 (0.6)

 (0.4)

 (0.2)

 0.2

 0.4

 0.6

 0.8

 1.0

 1.2

 1.4

Apr May Jun Jul Aug Sep

Degrees Fahrenheit

Valdez

Anchorage

Homer

Kodiak

Figure 4—Average summer temperatures in the Chugach area were slightly warmer during the inventory 

period compared to the climate “normals” preceding the start of the inventory. Bars indicate average 

inventory summer temperature minus preceding 30-year averages.
18

general technical report pnw-gtr-889

Higher elevation treelines and afforestation resulting from lower water tables, 

although they have been observed in this region (Berg et al. 2009, Dial et al. 

2007), are not explanatory causes for the observed carbon mass increase because 

of the methods that were used, which analyzed only trends within existing forest. 

However, climate warming and CO2 increases could be affecting carbon storage 

and flux in a variety of ways. Growth rates will generally increase with increasing CO2 or with warmer temperatures, provided that soil water availability is not 

limiting. Maximum biomass density in forests tends to be relatively constant across 

a broad range of sites for any given tree species owing to self-thinning (Reineke 

1933, White 1981), so that the stand density index (in the absence of disturbance) 

can be expected to be less affected by climate change or CO2 increase than either 

mortality or growth rates. But there could be displacement of lower volume species 

(such as hardwoods or white spruce) by higher volume species (such as Sitka spruce 

and western hemlock). Increased stocking could occur in more marginal habitats 

as growing conditions improve (Vanclay and Sands 2009). More favorable growing conditions might even allow individual trees to reach a taller maximum height 

(Ryan and Yoder 1997). 

Teasing out the best explanations for the observed change is difficult because

of the relatively small number of plots. When looked at as an average annual rate, 

all the tree species show a nominal increase in live tree carbon mass. However,

only Sitka spruce and white spruce have increases that are more than 1.96 times

the standard error from zero (indicating statistically significant differences for a

95-percent CI), with estimated annual increases of 3.6 percent for white spruce and 

1 percent for Sitka spruce (tables 10 and 11). By forest type, the highest increase in 

per-acre carbon occurred in the cottonwood, western hemlock, and white spruce 

forest types (table 12).

Although the Chugach’s 165,000 tons per year net accumulation in live tree 

carbon may seem small compared to the live tree carbon pool of 26 million tons, it 

is a significant local carbon sink. The equivalent CO2 sequestration rate would be 

605,000 tons per year, given the equivalency rate of 3.67 tons of CO2.

However, the net increase of live tree carbon on the Chugach is just one 

component of carbon dynamics within the larger regional landscape. During the 

same period, there was a decrease in live tree carbon mass on private lands in the 

southeast/south-central region comparable in magnitude to the increase observed 

on the Chugach. In addition, we do not know if the increase in live tree carbon on 

the Chugach is being augmented or counterbalanced by changes in the DWD and 

belowground carbon pools. 
19

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 11—Annual change in live tree carbon 

mass by species for the Chugach National 

Forest

Species Total SE

Thousand tons per year

Black cottonwood 5 4 

Mountain hemlock 65 55 

Paper birch 3 2 

Sitka spruce 56 23 

Western hemlock 22 22 

White spruce 13 6 

All species 165 67 

Note: Data are based on remeasurement plots only, which 

do not include trees < 5 in diameter at breast height.

SE = Standard error.

Table 12—Per-acre annual change in live tree 

carbon mass by forest type, Chugach National 

Forest

Forest type Mean SE

Pounds per acre per year

Black cottonwood 964 448

Black spruce 23 —

Mountain hemlock 493 406

Paper birch 377 142

Sitka spruce 383 426

Western hemlock 787 354

White spruce 773 297

 All forest types 552 225

Note: Data are based on remeasurement plots only, which 

do not include trees < 5 in diameter at breast height.

SE = Standard error.
20

general technical report pnw-gtr-889

There was an estimated 1.6-percent decrease in carbon stored in snags, which 

was not significantly different from zero (table 13). When this is shown as per-acre 

annual change, all the forest types except Sitka spruce had a nominal decrease in 

snags but none was statistically significant at the 95 percent CI except paper birch 

(table 14). Estimates for snag carbon mass typically have higher sampling error than 

live trees. In addition, there is some additional uncertainty for the estimates of snag 

loss, owing to data collection procedures (see discussion of snag estimates for the 

Tongass National Forest).

When the DWD transects from the periodic inventory were used, there was an 

estimated 10 (±2) Mg per ha of carbon mass in down logs in forest lands within the 

Chugach National Forest, or 4.6 (±0.8) tons per acre. There are not enough plots 

to precisely estimate DWD carbon mass by forest type within the Chugach, so in 

table 15, values for these forest types within the larger inventory region are shown. 

Although down wood carbon mass in the white spruce, mountain hemlock, and 

western hemlock forest within the Chugach is similar to the regional values, the 

carbon mass in logs in Sitka spruce forest is about half within the Chugach compared to the region. 

For the landscape analysis, using the full 2004–2010 dataset and excluding the 

wilderness study area, there were 26 forested plots in the Copper River landscape, 

35 forested plots in the Kenai Peninsula landscape, and 46 forested plots in the 

Table 13—Annual carbon mass change in snags by species, Chugach National Forest

Time 1 

carbon

Snag 

recruitment

Snag 

fragmentation Snag falldown Net change

Species Total SE Total SE Total SE Total SE Total SE

Thousand tons

Black cottonwood 32 31 1 1 0 0 4 4 -3 4

Black spruce 1 1 — — — — — — — —

Mountain hemlock 478 111 14 10 1 2 19 7 -6 13

Paper birch 4 5 — — 0 0 — — 0 0

Quaking aspen 18 14 — — 0 0 1 1 -2 1

Sitka spruce 439 175 24 17 6 4 3 3 15 17

Western hemlock 425 144 5 3 7 3 10 5 -12 6

White spruce 342 210 1 1 10 9 13 7 -22 15

 All species 1,738 337 46 19 23 11 50 12 -28 27

Note: Data are based on remeasurement plots only, which do not include trees < 5 in diameter at breast height.

SE = Standard error.
21

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 14—Per-acre annual change in carbon mass of snags 

by forest type, Chugach National Forest

Forest type Mean SE

Pounds per acre

Black cottonwood -431 398

Black spruce -343 —

Mountain hemlock -107 141

Paper birch -203 98

Sitka spruce 195 279

Western hemlock -182 78

White spruce -424 354

 All forest types -95 91

Note: Data are based on remeasured plots only, which do not include 

trees < 5 in diameter at breast height.

SE = Standard error.

Table 15—Carbon mass in downed logs by forest type

Chugach National 

Forest

All of inventory 

region

Forest type Mean SE Mean SE

Pounds per acre

Black cottonwood 15,446 8,036 5,268 1,295

Black spruce 580 2,500 580

Mountain hemlock 4,241 1,116 4,152 491

Paper birch 11,205 3,661 5,536 670

Quaking aspen 4,643 1,920

Sitka spruce 9,241 4,196 17,768 3,839

Western hemlock 19,554 5,848 18,973 982

White spruce 7,143 2,857 7,009 2,054

 All forest types 9,152 1,607 11,518 670

Note: Estimates use data from the 1995–2003 inventory.
22

general technical report pnw-gtr-889

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Landscape

Copper River

Kenai Peninsula

Prince William Sound

Nonforest plots

Forest plots

Chugach National Forest

Chugach National Forest wilderness study area

0 50 100 200 Kilometers

Figure 5—The three landscape areas (Copper River, Kenai Peninsula, and Prince William Sound) within the Chugach National Forest.

Prince William Sound landscape. For the remeasured dataset, there were 23 forested plots in the Copper River landscape, 25 plots in the Kenai landscape, and 35 

plots in the Prince William Sound landscape (fig. 5). Although the relatively small 

number of plots in each landscape makes estimates imprecise, the nominal carbon 

mass density decreases as one moves westward from the Copper River landscape, 

across the Prince William Sound landscape, and into the Kenai landscape (table 16); 

a decrease in density could be explained by climate limiting the growth of Sitka 

spruce and western hemlock and becoming more favorable for smaller boreal species (white spruce and hardwoods) as one moves westward across the forest. 

For the forest overall, the mean storage of 69,800 lbs per acre (= 78.2 Mg/ha) in 

live tree carbon density is less than the 94.2 Mg/ha estimated for Chugach National 

Forest by Heath et al. (2011). The 84,800 lbs per acre (= 95.0 Mg/ha) in aboveground 

tree carbon is split as 82 percent live trees, 7 percent in snags, and 11 percent in 

logs (table 16). The carbon in unmeasured pools (forest floor, understory vegetation, 

soil organic carbon, and roots) could exceed the aboveground tree carbon.
23

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 16—Carbon pools and flux for three Chugach landscapes

Landscape

Copper River

Prince 

William Sound Kenai Peninsula

Chugach 

National Forest

Mean SE Mean SE Mean SE Mean SE

Pool: Pounds per acre

Live treesa 76,398 16,659 76,973 12,715 52,834 11,255 69,816 7,692 

Snagsa 4,476 1,530 5,435 933 7,587 2,779 5,832 1,011 

Logsb 14,701 5,348 7,000 1,786 7,897 1,888 9,138 1,625 

 Total 95,575 89,408 68,318 84,786

Flux—live trees: Pounds per acre per year

Growth 1,362 803 398 170 761 125 733 210 

Recruitment 75 26 27 7 75 17 52 9

Mortality (144) 66 (337) 152 (139) 94 (233) 79 

Flux—snags: Pounds per acre per year

Snag recruitment 65 29 233 129 95 74 153 65 

Snag fragmentation (46) 23 (70) 32 (120) 103 (79) 35 

Snag falldown (134) 79 (131) 45 (258) 75 (169) 37 

Note: Does not include trees ≤ 5 in diameter at breast height.

a

 Based on data from remeasurement plots only.

b

 Based on data collected from 1999 to 2003.

SE = Standard error.

Tongass National Forest

Including its wilderness area, aboveground live and snag carbon on the Tongass 

National Forest is estimated to be 601 (± 21) million tons on an estimated 9.715 million ac of forest. Some 233 million tons (39 percent) of this carbon is on land that is 

legally excluded from timber harvesting, such as formally designated wilderness. 

Using the remeasurement database, an estimated 448,000 ac of forest fell into the 

“managed” category (i.e., had some previous silvicultural activity). 

Excluding inaccessible wilderness, the estimated amount of carbon stored in 

western hemlock trees is more than double that of any other species (table 17). 

Other species accounting for substantial amounts of carbon are Sitka spruce, 

yellow-cedar, mountain hemlock, and western redcedar. Sitka spruce and cottonwood forest types have a relatively small amount of tree carbon in snags, only 6 

percent of total tree carbon mass, while western redcedar, lodgepole (shore) pine, 

and yellow-cedar forest types have a relatively large proportion of carbon in snags, 
24

general technical report pnw-gtr-889

Table 17—Carbon mass in live trees and snags by species on the Tongass 

National Forest

Live trees Snags All trees

Species Total SE Total SE Total SE

Thousand tons

Yellow-cedar 45,318 2,695 10,793 975 56,111 3,120

Black cottonwood 502 247 78 54 580 289

Lodgepole pine 4,840 488 1,065 146 5,905 567

Mountain hemlock 42,256 2,958 4,378 490 46,634 3,195

Oregon crab apple 1 1 4 5 5 5

Pacific silver fir 60 45 — — 60 45

Red alder 1,824 390 51 25 1,874 395

Sitka spruce 81,481 6,252 7,321 1,103 88,802 6,486

Subalpine fir 127 83 40 34 167 93

Western hemlock 161,065 7,718 24,019 1,521 185,084 8,483

Western redcedar 21,566 2,144 3,242 457 24,808 2,454

 All species 359,040 10,391 50,991 2,248 410,030 11,119

Note: Data are from all 2004–2010 plots; inaccessible wilderness areas are not included.

SE = Standard error.

at 20, 17, and 17 percent, respectively (table 18). On a per-acre basis, the western 

hemlock and Sitka spruce forest types have the highest amount of carbon (table 19).

Changes Between Inventories

Change in live tree carbon by species— 

There was no significant change in live tree carbon mass overall between the two 

inventories (table 20), and there was no significant change when looked at separately as unmanaged land (table 21) or managed land (table 22). There was a significant 

increase of red alder live tree carbon mass on both managed and unmanaged lands. 

On unmanaged lands, western redcedar live tree carbon mass had a significant 

increase, estimated as a 6.6-percent increase from the first inventory. On managed 

lands, there was also a marginally significant increase in Sitka spruce live tree 

carbon mass (table 22) and a significant decrease in yellow-cedar live tree carbon 

mass. Annual rates of change are shown in table 23.

Change in live tree carbon by forest type— 

Carbon flux attributable to growth and recruitment of live trees is 690 lbs per acre 

per year on managed lands and 1,608 lbs per acre per year on unmanaged lands. 

In general, in unmanaged forest, forest types with high carbon flux in growth and 
25

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 18—Carbon mass in live trees and snags by forest type within the 

Tongass National Forest

Live trees Snags All trees

Forest type Total SE Total SE Total SE

Thousand tons

Yellow-cedar 46,734 4,268 9,372 969 56,105 5,049

Black cottonwood 954 830 65 55 1,019 866

Lodgepole pine 3,428 666 693 160 4,121 794

Mountain hemlock 39,716 4,234 4,265 695 43,981 4,707

Red alder 1,185 646 138 95 1,323 734

Sitka spruce 45,381 6,867 2,721 540 48,102 7,215

Western hemlock 192,176 10,965 26,253 2,138 218,429 12,099

Western redcedar 29,465 3,560 7,485 1,012 36,950 4,389

 All forest 359,040 10,391 50,991 2,248 410,030 11,119

Note: Data are from all 2004–2010 plots; inaccessible wilderness areas are not included.

SE = Standard error.

Table 19—Carbon mass per acre in trees by forest type in the Tongass 

National Forest

Live trees Snags All trees

Forest type Mean SE Mean SE Mean SE

Pounds per acre

Yellow-cedar 65,209 3,769 13,076 978 78,285 4,346

Black cottonwood 53,517 37,213 3,662 2,634 57,179 38,518 

Lodgepole pine 19,726 2,297 3,988 673 23,714 2,689

Mountain hemlock 64,624 4,926 6,939 1,005 71,563 5,493

Red alder 66,058 17,871 7,689 3,484 73,747 20,752 

Sitka spruce 153,936 15,538 9,228 1,516 163,165 16,156 

Western hemlock 155,057 5,410 21,182 1,441 176,239 5,666

Western redcedar 100,441 5,829 25,515 2,119 125,957 6,724

 All forest types 106,531 2,949 15,130 659 121,661 3,142

Note: Data are from all 2004–2010 plots; inaccessible wilderness areas not included.
26

general technical report pnw-gtr-889 Table 20—Change in carbon mass (million tons) in live trees by species from the first inventory (1995–2000) to the second inventory (2004–2010), Tongass National Forest Time 1 carbon Time 2 carbon Mortality Harvest Growth Ingrowth Net change

Species Total SE Total SE Total SE Total SE Total SE Total SE Total SE

Million tons

Yellow-cedar 40,539 2,691 40,435 2,680 -1,929 446 -631 284 2,307 265 148 18 -104 533Black cottonwood 480 244 529 263 -6 6 55 30 49 30Lodgepole pine 4,563 485 4,430 477 -334 83 167 46 34 7 -133 91Mountain hemlock 36,213 2,821 36,103 2,866 -1,686 286 -103 115 1,496 201 183 30 -110 339

Oregon crab apple 1 1 1 1 0 0 0 0 0

Pacific silver fir 7 9 8 10 1 1 1 1 1Red aldera 717 194 1,075 269 -72 34 274 74 155 53 358 110

Sitka spruce 65,426 5,916 66,864 5,934 -3,629 1,282 -283 274 4,688 1,348 662 146 1,438 1,903

Subalpine fir 144 102 130 99 -14 14 0 2 -14 14

Western hemlock 153,171 8,100 153,520 8,108 -10,000 1,405 -1,031 436 10,385 837 995 130 349 1,630

Western redcedar 20,174 2,209 20,952 2,267 -334 165 -600 449 1,600 223 112 49 778 536

All species 321,436 10,811 324,047 10,725 -18,003 2,017 -2,646 1,127 20,972 1,699 2,289 275 2,611 2,883

Note: Based on remeasured plots only; does not include trees < 4.5 in diameter at breast height.a Indicates that net change is significantly different using a 95-percent confidence interval.

SE = Standard error.
27

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 21—Change in carbon mass (million tons) in live trees by species on unmanaged lands from the first inventory (1995–2000) to the second inventory (2004–2010), Tongass National Forest

Time 1 carbon Time 2 carbon Mortality Growth Ingrowth Net change

Species Total SE Total SE Total SE Total SE Total SE Total SE

Million tons

Yellow-cedar 39,239 2,644 39,677 2,660 -1,889 445 2,186 250 142 18 439 475Black cottonwood 480 244 529 263 -6 6 55 30 — — 49 30

Lodgepole pine 4,563 485 4,429 477 -334 83 167 46 33 7 -134 91

Mountain hemlock 35,942 2,821 35,886 2,862 -1,686 286 1,457 198 174 30 -56 316

Oregon crab apple 1 1 1 1 — — 0 0 — — 0 0Pacific silver fir 7 9 8 10 — — 1 1 — — 1 1Red aldera 500 157 676 203 -67 34 163 50 79 36 175 80

Sitka spruce 62,607 5,821 62,814 5,810 -3,348 1,265 3,445 1,301 111 25 208 1,800Subalpine fir 144 102 130 99 -14 14 0 2 — — -14 14Western hemlock 147,704 8,057 147,789 8,057 -9,731 1,403 9,315 788 501 47 85 1,521Western redcedara 19,519 2,168 20,811 2,267 -317 164 1,562 221 47 9 1,292 254

All species 310,706 10,870 312,750 10,788 -17,392 2,009 18,350 1,593 1,086 76 2,044 2,503

Note: Based on remeasured plots only and includes only trees > 5 in diameter at breast height; unmanaged land indicates no recorded silvicultural activity.a Indicates that net change is significantly different from zero using a 95-percent confidence interval.
28

general technical report pnw-gtr-889 Table 22—Change in carbon mass (million tons) in live trees by species on managed lands from the first inventory (1995–2000) to the second inventory (2004–2010), Tongass National Forest Time 1 carbon Time 2 carbon Mortality Harvest Growth Ingrowth Net change

Species Total SE Total SE Total SE Total SE Total SE Total SE Total SE

Million tons

Yellow-cedara 1,301 698 758 509 -40 29 -631 284 121 98 7 3 -543 234

Black cottonwood — — — — — — — — — — — — — —Lodgepole pine — — 1 1 — — — — — — 1 1 1 1Mountain hemlock 271 177 217 160 — — -103 115 39 35 9 5 -54 119Oregon crab apple — — — — — — — — — — — — — —Pacific silver fir — — — — — — — — — — — — — —Red aldera 217 118 399 179 -5 4 — — 111 54 76 40 183 76

Sitka sprucea 2,820 1,190 4,050 1,346 -280 204 -283 274 1,243 366 550 145 1,230 622

Subalpine fir — — — — — — — — — — — — — —Western hemlock 5,466 1,618 5,731 1,588 -269 111 -1,031 436 1,070 303 494 123 264 611Western redcedar 655 466 142 69 -17 17 -600 449 38 28 65 48 -514 469

All species 10,729 2,742 11,297 2,581 -611 245 -2,646 1,127 2,622 661 1,203 269 567 1,463

Note: Data are based on remeasured plots only and include only trees ≥ 5 in diameter at breast height; managed land indicates recorded silvicultural activity.a Indicates that net change is significantly different from zero using a 95-percent confidence interval.

SE = Standard error.
29

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 23—Annual live tree carbon mass change by species and management 

class, Tongass National Forest, Alaska

Managed Unmanaged All forest

Species Total SE Total SE Total SE

Thousand tons per year

Yellow-cedar -39 18 55 40 16 44

Black cottonwood — — 8 5 8 5

Lodgepole pine 0 0 -12 9 -12 9

Mountain hemlock -10 14 -7 32 -17 35

Oregon crab apple — — 0 0 0 0

Pacific silver fir — — 0 0 0 0

Red alder 16 7 17 8 33 11

Sitka spruce 115 62 38 179 152 189

Subalpine fir — — -2 2 -2 2

Western hemlock 34 52 -28 162 6 170

Western redcedar -41 38 122 24 81 46

 All species 75 129 190 252 265 281

Note: Data are based on remeasurement plots only and do not include trees < 5 in diameter at 

breast height.

SE = Standard error.

recruitment also had high carbon flux out of the live tree carbon pool into snag and 

log pools. In both management classes, the Sitka spruce forest type has the highest rate of growth and recruitment, estimated at about 1,909 lbs of carbon mass per 

acre per year overall, followed by the western hemlock forest type, with growth and 

recruitment at about 993 lbs of carbon mass per acre per year (table 24). Across all 

lands, annual per-acre flux out of the live tree carbon pools is 88.5 percent mortality 

and 11.5 percent harvest. On managed lands, carbon flux out of the live tree pool is 

21.8 percent mortality and 78.2 percent harvest.

On managed lands in the Tongass National Forest, there was a significant 

decrease of live tree carbon mass for the yellow-cedar forest type, and a significant 

increase for the red alder forest type (table 25). On unmanaged lands (table 25), 

there were significant increases of live tree carbon within the cottonwood and 

western redcedar forest types. Overall on the Tongass, live tree carbon increased in 

the cottonwood, red alder, and western redcedar forest types, and no forest type had 

a significant decrease. 

Change in carbon in the snag pool— 

Overall, the turnover in the snag carbon pool on the Tongass National Forest is 

about 2 percent per year, with no significant difference between inputs into the 
30

general technical report pnw-gtr-889

Table 24—Average annual rates of flux in the live tree carbon pool by forest type and 

management class, Tongass National Forest

Growth Recruitment Mortality Harvest

Forest type Mean SE Mean SE Mean SE Mean SE

Pounds per acre per year

Unmanaged:

Yellow-cedar 304 37 36 4 323 59 — —

Black cottonwood 959 378 11 13 — — — —

Lodgepole pine 113 31 16 3 101 35 — —

Mountain hemlock 344 56 34 7 353 92 — —

Red alder 266 104 615 306 268 196 — —

Sitka spruce 1,711 386 36 11 1,245 541 — —

Western hemlock 909 131 39 4 933 158 — —

Western redcedar 618 64 41 5 461 90 — —

 All unmanaged 652 59 38 2 619 74 — —

Managed:

Yellow-cedar 741 361 20 16 732 514 5,831 1,999

Lodgepole pine — — — — — — — —

Mountain hemlock — — — — — — — —

Red alder 458 548 436 151 — — — —

Sitka spruce 1,661 475 565 182 335 254 691 499

Western hemlock 895 245 477 91 229 112 809 539

Western redcedar 248 — 1,089 — — — 18 0

 All managed 1,107 231 501 83 278 110 997 395

All forest:

Yellow-cedar 313 38 36 4 331 59 112 77

Black cottonwood 959 378 11 13 — — — —

Lodgepole pine 113 31 16 3 101 35 — —

Mountain hemlock 344 56 34 7 353 92 — —

Red alder 358 251 529 173 139 127 — —

Sitka spruce 1,694 302 215 73 938 371 233 176

Western hemlock 908 120 85 13 859 143 85 59

Western redcedar 608 63 68 23 449 88 — —

 All forest 687 58 73 8 593 69 77 32

Note: Data for this table are from remeasured plots only and do not include trees < 5 in diameter at breast 

height.

SE = Standard error.
31

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 25—Per-acre net annual live tree carbon change by forest type, 

Tongass National Forest

Managed forest

Unmanaged 

forest All forest

Forest type Mean SE Mean SE Mean SE

Pounds per acre per year

Yellow-cedar -5,802 2,235 18 60 -94 98

Black cottonwood — — 970 390 970 390

Lodgepole pine — — 28 41 28 41

Mountain hemlock — — 25 84 25 84

Red alder 894 396 612 606 748 358

Sitka spruce 1,200 998 502 708 738 578

Western hemlock 334 712 16 207 50 199

Western redcedar 1,319 — 197 95 227 96

 All forest types 333 578 71 94 91 97

Note: Where the standard error is zero, it indicates that only one plot had a stand that fell into 

this category. Boldface type indicates a change that was significantly different from zero 

using a 95-percent confidence interval.

Note: Estimates are calculated from remeasured plots only and include only trees ≥ 5 in 

diameter at breast height.

SE = Standard error.

snag carbon pool (snag recruitment) and outputs from the snag carbon pool (fragmentation, falldown, and salvage). The decay-resistant species of yellow-cedar and 

western redcedar have lower turnover rates, of roughly 1 percent per year, than do 

other species (table 26). Salvage of snags is generally incidental to clearcutting, and 

accounts for only a small proportion (about 2 percent) of flux out of the snag carbon pool. About half of the carbon stored in snags is western hemlock, which had 

a small (less than 1 percent) but significant decrease (table 26). Lodgepole (shore) 

pine had a small (1.6 percent) but significant increase of carbon in the snag pool 

(table 26).

Estimates of flux into and out of the snag pool differed widely among the different forest types (table 27). On a per-acre basis, unmanaged forest had influx into 

the snag pool that was roughly three times larger than that of managed forest, and 

outflux from the snag pool was roughly the same. Loss of snags on managed lands 

was estimated to be about three times snag recruitment, for a net decrease in the 

snag pool estimated as 239 (± 149) lbs per acre per year.

The reliability of estimates for changes in the snag pool was affected by two 

data issues. The second inventory used a less inclusive definition for snags, by 

changing the lean angle used to define snags from 15 to 45 degrees from horizontal. 
32

general technical report pnw-gtr-889 Table 26—Annual rates of change in snag carbon by species, 1995–2000 to 2004–2012, Tongass National Forest Initial carbon (1995–2000) Snag recruitment Snag fragmentationa Snag falldown Salvage Net change

Species Total SE Total SE Total SE Total SE Total SE Total SE

 Thousand tons - - - - - - - - - - - - - - - - - - - - Thousand tons per year - - - - - - - - - - - - - - - - - - - - - - -

Yellow-cedar 10,996 1,000 93 23 38 9 49 10 13 15 -6 31Black cottonwood 117 86 1 1 1 1 8 7 — — -8 6

Lodgepole pineb 928 153 26 6 5 1 5 2 — — 15 7

Mountain hemlock 3,920 573 120 21 58 14 21 5 2 3 39 25Oregon crab apple — — — — — — — — — — — —Pacific silver fir — — — — — — — — — — — —Red alder 33 21 3 2 1 1 1 0 — — 2 2Sitka spruce 5,974 978 241 88 101 29 28 12 1 1 111 94Subalpine fir 19 19 3 3 0 0 — — — — 3 3Western hemlockb 24,976 1,771 463 58 397 47 243 35 7 5 -185 81

Western redcedar 3,258 501 24 14 14 12 23 9 — — -13 17

All species 50,221 2,326 973 109 616 58 377 42 23 18 -43 130

Note: Data are based on remeasurement plots only and do not include trees < 5 in diameter at breast height.a Snag fragmentation includes the loss of mass from shrinkage (smaller diameter and heights) but not the loss of mass from a change in decay class.b Indicates that net change is significantly different using a 95-percent confidence interval.
33

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 27—Annual per-acre change in snag carbon by forest type and management class, Tongass 

National Forest

Snag 

recruitment

Snag 

fragmentationa Snag falldown Salvage Net change

Forest type Mean SE Mean SE Mean SE Mean SE Mean SE

Pounds per acre per year

Unmanaged forest:

Yellow-cedar 201 29 128 17 118 27 — — -46 46

Black cottonwood — — 58 60 249 245 — — -307 304

Lodgepole pine 95 32 30 11 36 16 — — 29 37

Mountain hemlock 259 81 114 35 29 9 — — 116 88

Red alder — — 149 109 177 129 — — -326 239

Sitka spruce 494 163 314 139 131 62 — — 49 196

Western hemlock 505 90 341 43 188 29 — — -24 103

Western redcedar 354 81 207 54 99 20 — — 48 94

 All unmanaged 354 40 223 21 128 14 — — 4 47

Managed forest:

Yellow-cedar 224 76 -12 44 211 76 303 371 -278 349

Red alder — — 7 8 — — — — -7 8

Sitka spruce 123 71 16 12 62 52 197 221 -153 224

Western hemlock 97 85 145 86 221 140 41 37 -310 226

 All managed 106 54 86 50 156 81 104 79 -239 149

All forest:

Yellow-cedar 201 28 125 17 120 26 6 8 -50 46

Black cottonwood — — 58 60 249 245 — — -307 304

Lodgepole pine 95 32 30 11 36 16 — — 29 37

Mountain hemlock 259 81 114 35 29 9 — — 116 88

Red alder — — 81 71 92 84 — — -172 155

Sitka spruce 369 112 214 94 108 45 67 76 -19 151

Western hemlock 462 81 320 40 192 30 4 4 -54 95

Western redcedar 345 79 202 53 97 19 — — 46 92

 All forest 335 38 212 20 130 14 8 6 -15 45

Note: Data are based on remeasurement plots only, 1995–2000 and 2004–2010.

a Snag fragmentation includes the loss of mass from shrinkage (smaller diameter and heights) but not the loss of mass from 

a change in decay class.

SE = Standard error.
34

general technical report pnw-gtr-889

Although these instances should have been coded as procedural changes, which 

were corrected during analysis, it is possible that some instances were coded 

identically as snag falldown, leading to overestimates of falldown. The other data 

issue was that a procedural change for estimating decay class made it impossible 

to include the decrease in density that occurs as snags age, which would lead to 

underestimate of snag decay. The missing decay component can be even greater 

than the volume loss from snag fragmentation for some species and decay classes 

(Harmon et al. 2000). Although estimates for snag losses are presented here despite 

these uncertainties, because the estimates are still the best available information, 

caution should be exercised in use of either the two components of snag carbon loss 

shown, or the resulting net change in snag carbon. 

Change in carbon in the log pool— 

Roughly 7 percent of aboveground carbon in unmanaged stands of the Tongass 

National Forest is stored in the log (DWD) pool. On managed forest, about 37 percent of carbon is in the log pool. The higher volume of carbon in logs is found in 

the western hemlock, Sitka spruce, and western redcedar forest types, and lower 

volume in the yellow-cedar, cottonwood, lodgepole (shore) pine, and mountain hemlock forest types (table 28). The red alder forest type also had a high carbon density 

in the log pool (table 28); this corresponds well with the role of red alder as a pioneering species that establishes after disturbance.

No remeasurement data is available for the log pool. We can make a rough 

estimate of influx into the log pool on unmanaged lands as:

(mortality – snag recruitment) + snag falldown [low estimate]

which is (619 – 354) + 128 = 393 lbs per acre per year. This will be an underestimate, as some of the input into the log pool comes from breakage of live trees (an 

unknown rate), and some input into the log pool comes from snag fragmentation. 

A higher estimate would be to assume that all of snag falldown and fragmentation 

goes into the log pool:

(mortality – snag recruitment) + snag falldown + snag fragmentation

[high estimate]

which is (619 – 354) + 128 + 223 = 616 lbs per acre per year. This range (393–616 

lbs per acre per year) would give us a rough estimate of annual inputs into the log 

pool of 3.8 to 6.0 percent per year, which would provide turnover rates if the log 

pool were in equilibrium. Decomposition rates of spruce on the Kenai Peninsula of 
35

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Table 28—Carbon mass in downed logs by forest type and management 

class, Tongass National Forest

Managed Unmanaged All

Forest type Mean SE Mean SE Mean SE

Pounds per acre

Yellow-cedar — — 6,250 893 6,250 893 

Black cottonwood — — 3,571 1,786 3,571 1,786 

Lodgepole pine — — 1,339 446 1,339 446 

Mountain hemlock 65,625 1,339 2,679 446 3,571 446 

Red alder 15,179 8,929 21,875 10,714 16,518 8,036 

Sitka spruce 33,036 4,464 11,607 2,232 15,179 2,232 

Western hemlock 33,482 4,018 16,071 893 17,857 893 

Western redcedar 57,143 10,268 12,500 1,786 12,946 1,786 

 All forest types 33,482 3,125 10,268 446 11,607 446 

Note: Uses plot measurements from 1995 to 2003.

SE = Standard error.

about 1.9 percent per year (Harmon et al. 2005) suggest that the log pool on unmanaged lands might be increasing; better monitoring information for logs would 

improve the ability to track forest carbon over time. The log pool on managed lands 

is unlikely to be in equilibrium, given the temporal variation in harvesting. 

Combined live tree, snag, and log pools— 

Overall, gross flux (growth + recruitment) from the atmosphere to live trees in the 

Tongass National Forest is estimated at about 760 lbs per acre per year (table 29). 

Growth is mostly balanced by mortality and harvest, so that net flux (based on 

increases in the live tree pool) from the atmosphere to the forest is estimated at 91 

(standard error = 97) lbs per acre per year, reduced by an estimated slight decrease 

in the snag pool of 15 (standard error = 45) lbs per acre per year. This estimated net 

sequestration rate is not significantly different from zero, and also does not include 

any changes in the log pool. There may be some additional sequestration occurring 

because the combined harvest and salvage (85 lbs per acre per year) would have 

some portion that became durable wood products. 

Aboveground tree carbon on the Tongass National Forest is 79.3 percent in

the live tree pool, 12.4 percent in the snag pool, and 8.3 percent in the log pool 

(table 29). Turnover in the live tree carbon pool is about 0.6 percent per year, turnover of the snag carbon pool is about 2.9 percent per year, and the approximated 

turnover in the log pool, assuming equilibrium, is 3.8 to 6.0 percent per year.
36

general technical report pnw-gtr-889

Table 29—Carbon pools and flux for aboveground trees in the Tongass 

National Forest

Management class

Managed Unmanaged

Tongass 

National Forest

Mean SE Mean SE Mean SE

Pool: Pounds per acre

Live treesa 48,102 10,199 115,896 3,731 110,689 3,515

Snagsa 7,524 2,249 18,107 818 17,294 778

Logs 33,482 3,125 10,268 446 11,607 446

 Total 89,108 144,271 139,590

Flux—live tree pool: Pounds per acre per year

Growth 1,107 231 652 59 687 58

Recruitment 501 83 38 2 73 8

Mortality 278 110 619 74 593 69

Harvest 997 395 — — 77 32

Flux—snag pool: Pounds per acre per year

Snag recruitment 106 54 354 40 335 38

Snag fragmentationb 86 50 223 21 212 20

Snag falldown 156 81 128 14 130 14

Snag salvage 104 79 — — 8 6

a Uses remeasurement plots and initial (1995–2003) data. To keep flux and pools in correct proportions, does not include trees < 5 in diameter at breast height.

b Snag fragmentation includes the loss of mass from shrinkage (smaller diameter and 

heights) but not the loss of mass from a change in decay class.

SE = Standard error.

Discussion

A number of carbon pools and fluxes were not included in this report: (1) carbon in 

nonforested lands, which includes alpine environments, wetlands, grasslands, and 

shrublands; (2) below-ground carbon, including roots, soils, and organic materials; 

(3) carbon in nontree vegetation and litter within forest; (4) carbon in a few pools 

currently not measured by FIA, which includes stumps below 4.5 feet and dead 

saplings; and (5) (with the exception of tables 4 and 6) carbon in forest lands in 

inaccessible wilderness. The missing carbon in the belowground pools could be as 

large as the aboveground stores. 

The overall carbon mass stored in just aboveground trees, snags, and logs in 

the Tongass National Forest is huge. Using the per-acre values by forest types, 

and extrapolating to include the uninventoried wilderness areas, provides a rough 
37

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

estimate of about 650 million tons in aboveground tree carbon, equivalent to 2.4 

billion tons of CO2. 

Carbon storage and flux are very different between managed and unmanaged 

forests. Harvesting on the Tongass was very low before 1955, peaked in the early 

1970s at more than 500 million board feet (MMBF) per year, and then dropped 

over time to current rates at less than 100 MMBF per year (Brackley 2009). On 

managed lands, this results in an age class structure with a large cohort of stands 

30 to 50 years old, very few stands older than 60 years, and relatively few stands 

under 20 years of age. The cohort of stands 30 to 50 years old are contributing to a 

nominal (not statistically significant) net increase of carbon in live trees, but they 

probably have several decades to go before reaching a point of maximum mean 

annual increment. For instance, Taylor (1934) estimated that the maximum mean 

annual increment occurs at around 70 years. In contrast to what is happening on the 

Tongass, privately owned managed forest in southeast Alaska is showing a statistically significant decrease in carbon mass in live trees, a consequence of harvesting 

that peaked in the 1990s (resulting in a relatively younger stand distribution for 

second-growth) and current harvesting levels that are above that of the Tongass. 

Some species shifts occurred when old-growth forest was converted to second 

growth; the data reflects this by the observed net decrease in yellow-cedar and net 

increase in Sitka spruce on managed lands, as well as by the higher proportion of 

carbon mass in Sitka spruce observed on managed lands (35 percent) relative to 

unmanaged lands (20 percent). Managed lands had almost triple the density of carbon mass in logs compared to unmanaged lands, but less than half the snag density 

and live tree density. Carbon flux among pools is also substantially different, with 

much higher growth and recruitment and lower mortality in managed stands.

The Tongass National Forest is unique within the National Forest System in 

the large amount of old growth outside of wilderness, and unique in the proportion 

of harvesting that has occurred in old growth rather than second growth during 

recent decades. Harvesting of old growth creates an initial net release of CO2

 into 

the atmosphere relative to leaving stands unmanaged, which can continue for years 

as logs and snags left after harvest decompose (Harmon et al. 1990). Some of the 

carbon from harvest is stored in wood products, with transmission back into the 

atmosphere over time. Because harvest levels peaked in the 1970s, and much of the 

resulting wood products would now be in landfills, wood products from the Alaska 

region are now believed to be a net emitter of carbon (Loeffler et al. 2012). Theoretically, at some point in the future, the managed second-growth stands that follow 

harvest could result in a greater net sequestration of carbon than leaving stands 

unmanaged, but the relatively low growth rates of most stands in the Tongass and 
38

general technical report pnw-gtr-889

the relatively high amount of dead wood left after harvest would reduce this potential. Although there is a substantial amount of recent literature about the effects of 

forest management on carbon stores, different authors have reached widely different 

conclusions about net sequestration because of different assumptions about the 

timeframe of interest, initial volume, postharvest residuals, decay rates, the amount 

of energy expended in harvest and transport, utilization rates, lifespan of wood 

products, future growth rates of second-growth stands, temporal discounting, and 

substitution effects. 

Including consideration of carbon sequestration into management of existing 

second growth is likely to be less controversial. Possible management actions to 

increase carbon sequestration for these situations could include altering rotation age 

(for even-age stands) or structural composition (for uneven-age stands) or increasing 

utilization of woody material from harvest sites. Although the carbon estimates 

made in this report provide information about overall carbon storage and flux in 

the Tongass National Forest, providing specific management recommendations for 

second growth would benefit from additional inventory in second-growth. 

Several other sets of estimates for carbon in the Tongass National Forest have 

been published. Some of the data used in this report, specifically the 1995–1999 

data, was used in Leighty et al. (2006), in their paper “Effects of Management on 

Carbon Sequestration in Forest Biomass in Southeast Alaska.” The log data used in 

that paper had a systematic error that resulted in overestimates of carbon in logs; 

those errors have been corrected in this report. In addition, this report uses standard 

national FIA methods for statistical estimation, which differ substantially from the 

map-based approach used by Leighty et al. (2006), and this report uses measured 

data for flux rather than modeled approximations. 

The live tree density reported here, of 53.3 tons per acre on average (table 19) 

for the nonwilderness areas, is equivalent to 119.3 Mg/ha. This is very similar to the 

123 Mg/ha reported by Heath et al. (2012) for the Tongass National Forest overall, 

particularly considering the difference in methods of calculation. Estimates in this 

report will also differ somewhat from those published in Barrett and Christensen 

(2011) owing to the addition of data from 2009 to 2010 and improved estimates for 

snags. That report also found a significant decrease in lodgepole (shore) pine; data 

from 2009 to 2010 had relatively little mortality in lodgepole (shore) pine, so that 

while there is still a nominal decrease in lodgepole (shore) pine of 3 percent (tables 

21 and 23) it is no longer significant at the 90-percent CI. However, there was a significant increase in lodgepole (shore) pine snag carbon (table 26), providing indirect 

evidence of higher than normal mortality for this species.
39

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Conclusion

The Tongass National Forest stores substantially more forest carbon than any other 

national forest in the United States, with an approximated estimate of 650 million tons of carbon in live trees, snags, and logs. Both managed and unmanaged 

forest shows nominal net annual increases in live tree carbon (of 0.68 and 0.06 

percent, respectively) that were not significantly different from zero. However, 

changes in species composition have been occurring. On unmanaged lands, there 

were increases in western redcedar and red alder. On managed lands, there were 

increases in red alder and Sitka spruce, and a decrease in yellow-cedar. 

This report provides the first estimates of annual flux and turnover rates in live 

tree and snag carbon pools in Alaska based on remeasured data. Overall, live trees 

in the Tongass National Forest remove about 2,787 lbs of atmospheric CO2

 per acre 

per year through growth and recruitment, which is largely (estimated 90 percent) 

balanced by CO2 returning to the atmosphere from mortality and harvest, assuming eventual decay of those trees. Carbon storage and flux differed substantially 

between managed and unmanaged lands, and by forest type. 

Although the Chugach National Forest stores less carbon in aboveground trees 

than the Tongass National Forest, it also is exhibiting greater change in carbon 

stores. The Chugach’s location on a very major ecoregional transitional zone (boreal 

forests to the north, shrubland to the west and southwest on the Alaskan Peninsula, 

and temperate rainforest to the east and south) may make it much more vulnerable 

to large disturbances and climatic shifts. 
40

general technical report pnw-gtr-889

Common and Scientific Names

Black cottonwood Populus balsamifera L. ssp. trichocarpa (Torr. & 

A. Gray ex Hook.) Brayshaw

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

Lodgepole pine, shore pine Pinus contorta Dougl. ex Loud.

Mountain hemlock Tsuga mertensiana (Bong.) Carr.

Pacific silver fir Abies amabilis (Douglas ex Louden) Douglas

ex Forbes

Paper birch4 Betula neoalaskana Sarg.; Betula kenaica

(W.H. Evans); Betula papyrifera Marshall

Quaking aspen Populus tremuloides Michx.

Red alder Alnus rubra Bong.

Sitka spruce Picea sitchensis (Bong.) Carrière

Subalpine fir Abies lasiocarpa var. lasiocarpa (Hook.) Nutt.

Western hemlock Tsuga heterophylla (Raf.) Sarg.

Western redcedar Thuja plicata Donn ex D. Don

White spruce Picea glauca (Moench) Voss

Yellow-cedar Chamaecyparis nootkatensis (D. Don) Spach

4

 Alaska paper birch, Kenai paper birch, and western paper birch are not recorded as 

different species by FIA and are included together as “paper birch” in this report.

Acknowledgments

Data used in this report was collected and initially compiled by the Forest Inventory 

and Analysis program. I greatly appreciate the dedication of the Alaska FIA field 

crew to collecting high-quality data under arduous conditions, and the contributions of Jane Reid and Kevin Dobelbower to database development. Many thanks 

to Misha Yatskov and Olga Krankina (Oregon State University, agreement JV 

11261917-099) for help with log data and very useful comments on a draft report. 

Thanks also to Olaf Kuegler, who wrote the software used to estimate standard 

errors, and Kurt Campbell, for programming and testing biomass equations. Partial 

funding for this project came from the Chugach National Forest and the Alaska 

Region of the National Forest System. Comments on drafts from Rob Develice, 

Connie Hubbard, James Thomas, Mark Nelson, Dave Azuma, and Robert Pattison 

were very helpful. 
41

Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

Metric Equivalents

When you know: Multiply by: To find:

Acres .405 Hectares

Pounds .453 Kilograms

Pounds per acre 1.12 Kilograms per ha

Tons 0.97 Tonnes or megagrams

Tons per acre 2.24 Megagrams per hectare

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Storage and Flux of Carbon in Live Trees, Snags, and Logs in the Chugach and Tongass National Forests

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