# ANNEX O Methodology for Estimating Net Ch anges in Forest Carbon Stocks

Thi s anne x p r e s ent s a di sc ussi on of t h e m e th od ol o g yuse dt o cal cul at e net chan ges i ncar b o nst oc ks i ntr ees, un d e r s tory , for e st f l oo r, dow n d e adwo od , for e st so ils, w oodpro ducts an dland f i lled w ood

. Mo r e d e tailed di scussi o n s of sel ect ed t o pi cs m aybe f o un di nth e re fere nce s ci t e d i nth i s anne x. The details of carbon convers i on factor s and proce dures for calculating net CO 2 flux f o r f o rests ar e gi ve n in th ree step s. In ad d ition , t h e USDA Fo re st Serv ice forest secto r m o d e ling proj ec tionsystem is d e scri b e d b r iefly.
Step 1: Es tima te Forest Car b on Stocks a nd Net Cha nges i n Forest Car b on Stocks
Step 1a: Obtai n Forest Inve ntory Data For e st sur v eydat ai nth e Un i t e d St at es by br oa d fo rest type an d regi on fo r 1 9 8 7 an d 1 9 9 7 we re o b t a i n ed fr om USDA F o rest Se rvi ce, For e st Inve nt o ryand A n al y s i s est i m a t e s of f o rest res o urces , pu bl i s he d i n Wad d el l et al

. ( 198 9) andSm ithet al. ( 2 001)

. Th e For e st In v e n t ory and A n alysis d ata i n clud e: (1 ) g r ow ing sto c k vo l um e p e r acr e byfo rest type (refe rre d t o he r e i n aft e r as “g r o wi ng st ock vo lum e s”); and (2) area bytim b erlan dan d oth e r fo rest land , fo r ge neral f o r e st types byregio n( r efe rre d to herei n afte r as “fore s t are a s”). For 2 001, the sam e variables we re obt ai ne d f r o m m odel resul t s as descri bed i nHayn es (2 0 0 2 )

. (See F o rest S ect or M o del i n g Pr o j ect i on S y st em bel o w). Th is in fo rm ati o n was co m b in ed withsep arate esti mates of carb o nde nsi ty(carb on m a ss per uni t are a ) t o est i m at e carb o nst oc ks

. Step 1b : Esti m a te Carb on i n L i ving an d Sta n d i ng Dea d Trees To estim ate live tree biom a ss, equations t h at convert forest tree v o l umes to to tal li v e tree dry b i o m ass (Sm i thet al . in pr ess) were appl i e d t o th e gr owi n g st ock volum es byforest type and r e gi o n( obt ai ne d i nSt ep 1a ). Tree bi om ass i n cl u d es a b ove gr o un dbi om ass and bel o w g r o un dbi om ass of coar se r oot s
. The m i nim u m si zed tr ee i s one -i nc h di am et er at di am et er br east hei g ht (1 .3 m e t e r). Trees l e ss th an one -i nc h di am et er are counte das carbon in
un de rst o ryve g e t at i on. B i om ass est i m at es were di vi de d b ytw o t o o b t a i nest i m at es of carb o ni nl i vi n g tr ees (i .e. , i t was ass um e d th at dry bi om ass i s 50 pe rc ent car bo n)

. St andi ng dea d tr ee bi om ass was cal cul at e d byap pl y i ng equat i o ns t h at est i m at e bi o m ass fo r st an di n g dead tr e e s (S m i thet al ., i npress ) f r o m growi ng st ock v o l u m e s. Agai n , st andi ng dead tr ee bi om ass was di vi de d b ytw o t o est i m at e carbon i nst an di n g dea dtr ees. Ta bl e O- 1 l i s t s th e av erag e liv ing an dstand i n g deadtree carbond e n s ities b y forest typ e , as calcu lated b yap p l ying th e equ atio ns to th e 1 997 d ata.

Table O-1: Average U.S. Carbon Densit ies of Forest Components* (Metric Tons C/ha)
Region a /Forest T y pe Live and St andin g Dead Tr ee Forest Fl oor Soil Organi c Carbon Carbon Carbon b Eastern

White-r ed-j a c kpin e Spruc e -fir Lon gle a f-s l as h pin e Lob lol l y - s hortle a f pin e Oak

- pine Oak

- hic k o ry Oak

- gum-c y p res s Elm-as h-c o tt onwo od Map l e-b eec h-b i rc h As pen-birc h Other for e s tty pes Nons toc k ed 77.1 13.8 196. 1 59.8 40.2 192. 9 42.4 9.2 136. 3 49.3 9.1 91.7 57.3 11.6 82.3 76.3 6.6 85.0 86.0 6.0 152. 2 67.6 23.0 118. 1 82.5 28.0 139. 5 56.0 7.6 237. 0

1.8 2.1 99.6 3.7 3.5 99.6

O-1Western Dougl as -fir Pond eros a pin e Wes t ern wh ite pi n e Fir-s pruc e Hemloc k

- Sitk a s p r u c e Larc h Lod gep ol e pi ne Redwoo d Hardwoo d s Other for e s tty pes Piny on-j uni per Chaparr a l Nons toc k ed 110. 8 30.7 89.6 66.3 20.3 70.4 69.2 25.8 68.3 113. 0 37.4 137. 5 152. 4 34.1 157. 1 97.0 30.2 65.6 67.8 23.9 62.7 186. 6 26.9 85.8 89.0 9.9 79.5 55.4 28.2 90.1 20.8 21.1 56.3 17.5 25.7 58.7 18.1 24.4 90.1 * Bas ed o n 1 9 9 7 d a ta fo r m a j o r for e s tty pes of the c ont ermi nous Un ite d S t ates

. a Eas t ern Uni t ed S t ates is def ine d a s s t ates eas t of, and inc l u d i ng, Nor t h Dak o t a , S out h Dak o ta, Ne bras k a , Kans as , Ok la ho ma, an d Te xa s. Wes t ern Un ite d St ates inc l ud es the r e ma ini ng c o nter mi nous s t at es

. b Soil i n c l ud es bot h min e ral s o ils a nd orga nics o ils (i. e ., his t os ols ) ; c a rb on dens it ies are to a dept h o f 1 me ter. Step 1c: Es tim a te Carb on i n U nderst o ry Vege tation To est i m at e carb o ni n un de rst o ryve get at i o n , eq uat i o ns base d o nB i r d sey(1 99 2 ) we re ap pl i e d t o th e d atab a se t h at was used t o pro d u ce th e co mp iledfo rest statistics inS m i thet al. (2 001 ). Un d e rstory v e g e tationi s defi ned as al l bi om ass of unde r g r o wt h pl ant s i na f o re st , i n cl u d i n g wo o dyshru bs and t r ees l e s s th an o n e-i n c h d i am e t er, m eas ur edat breast h e igh t

. A rati o of un d e rs tory carbo nt o live tree carb o n was calcu lated, an d m u ltip lied b y100 to calcu late th e p e rcen tag e of carbonin th e un d e rsto ry relativ e t o th at inliv e trees. Th ese p e rcen tag e s were then ave r aged for eac h forest type in eac h region. T h is percen tag e was m u l tip lied b yt h e liv e tree carbon d ata in 1 987 an d 199 7 to calcu late un d e r s torycarbo n. Th ese p e rcen t a ges are gi ven i nTabl e O

- 2

. T h i s pr oce dur e was use d instead of appl ying the Birds e y equations directly, becaus e detailed data bases are not available for invent ory years p r i o r t o 1 987

. Using estim ate dav erag e v a lues resu lts inco nsi s t e nt hi st ori cal carb o nest i mates for all survey years. Table O-2: Ratios of Understory and Down Dead Wood Carbon to Li ve Tree Carbon* (Percent) Ratio of Under s t o ry Ratio of Down Dead Wood Region/For est T y pe Carbon to Li ve Tr ee Carbon to Li ve Tr ee Carbon Carbon Northeast White-r ed-j a c kpin e Spruc e -fir Lon gle a f-Sl as h pi n e Lob lol l y - s hortle a f pin e Oak

- pine Oak

- hic k o ry Oak

- gum-c y p res s Elm-as h-c o tt onwo od Map l e-b eec h-b i rc h As pen-birc h Other For e s tTy pe s Nons toc k ed North Central White-r ed-j a c kpin e Spruc e -fir Lon gle a f-Sl as h pi n e Lob lol l y - s hortle a f pin e Oak

- pine Oak

- hic k o ry Oak

- gum-c y p res s Elm-as h-c o tt onwo od Map l e-b eec h-b i rc h As pen-birc h Other For e s tTy pe s Nons toc k ed 2.5 10.8 2.6 13.3 2.5 10.8 2.5 10.8 2.8 12.9 2.4 10.9 2.6 11.1 2.6 11.1 1.9 11.1 2.7 13.6 8.9 3.8 8.9 3.8
1.8 9.8 2.2 17.4 2.4 7.4 2.4 7.4 1.9 7.2 2.3 9.6 2.3 9.6 2.2 10.8 2.2 10.8 2.8 13.3 5.5 4.1 5.5 4.1

O-2 I n ventory of U.S. Greenhouse Gas Emis sions and Sink s: 1990-2001Southeast White-r ed-j a c kpin e Spruc e -fir Lon gle a f-Sl as h pi n e Lob lol l y - s hortle a f pin e Oak

- pine Oak

- hic k o ry Oak

- gum-c y p res s Elm-as h-c o tt onwo od Map l e-b eec h-b i rc h As pen-birc h Other For e s tTy pe s Nons toc k ed South Central White-r ed-j a c kpin e Spruc e -fir Lon gle a f-Sl as h pi n e Lob lol l y - s hortle a f pin e Oak

- pine Oak

- hic k o ry Oak

- gum-c y p res s Elm-as h-c o tt onwo od Map l e-b eec h-b i rc h As pen-birc h Other For e s tTy pe s Nons toc k ed Pacifi c Northwes t Easts i de of Cas cade s Dougl as -fir Pond eros a Pi ne Wes t ern W h it e Pi n e Fir-Spruc e Hemloc k

- Sitk a s p r u c e Larc h Lod gep ol e pi ne Redwoo d Other h a rdwo ods Unc l as s i fied & ot h e r Piny on-J u n i per Chaparr a l Nons toc k ed Pacifi c Northwes t Wests i de of Ca scad es Dougl as -fir Pond eros a Pi ne Wes t ern W h it e Pi n e Fir-Spruc e Hemloc k

- Sitk a s p r u c e Larc h Lod gep ol e pi ne Redwoo d Other h a rdwo ods Unc l as s i fied & ot h e r Piny on-J u n i per Chaparr a l Nons toc k ed Rocky Mount ain, Northern Dougl as -fir Pond eros a Pi ne Wes t ern W h it e Pi n e Fir-Spruc e Hemloc k

- Sitk a s p r u c e Larc h Lod gep ol e pi ne 6.8 23.9 6.8 23.9 6.8 23.9 6.8 23.9 5.2 28.0 4.4 24.2 2.2 21.8 2.2 21.8 4.4 24.2 2.2 21.8 11.9 2.0 11.9 2.0
5.9 18.6 5.9 18.6 5.9 18.6 5.9 18.6 4.4 17.3 3.7 15.0 2.2 15.7 2.2 15.7 3.7 15.0 2.2 15.7 16.9 1.7 16.9 1.7
1.6 10.0 2.5 12.6 1.6 10.0 1.1 15.7 1.6 10.0 1.6 10.0 2.6 21.3 1.9 25.8 1.4 8.9 2.5 12.6 10.7 3.7 9.7 2.1 9.7 2.1
2.0 11.9 2.5 18.1 2.5 18.1 1.0 13.7 1.0 13.7 2.0 11.9 1.7 16.4 2.0 11.9 4.5 3.9 1.7 16.4 20.2 3.7 14.2 3.0 14.2 3.0
2.6 19.2 2.4 19.6 2.2 9.7 1.7 14.8 2.0 18.7 2.2 9.7 2.4 19.6

O-3Redwoo d 2.2 9.7 Other h a rdwo ods 1.9 14.2 Unc l as s i fied & ot h e r 2.2 9.7 Piny on-J u n i per 16.1 3.2 Chaparr a l 16.1 3.2 Nons toc k ed 16.1 3.2 Rocky Mount ain, Southern Dougl as -fir 2.8 19.4 Pond eros a Pi ne 4.1 21.6 Wes t ern W h it e Pi n e 2.8 19.4 Fir-Spruc e 2.2 17.4 Hemloc k

- Sitk a s p r u c e 2.8 19.4 Larc h 2.8 19.4 Lod gep ol e pi ne 3.1 12.8 Redwoo d 2.8 19.4 Other h a rdwo ods 9.2 26.7 Unc l as s i fied & ot h e r 10.7 3.3 Piny on-J u n i per 9.8 3.9 Chaparr a l 9.8 3.9 Nons toc k ed 2.6 15.2 Pacifi c Southwe s t Dougl as -fir 2.3 15.5 Pond eros a Pi ne 2.6 15.2 Wes t ern W h it e Pi n e 2.2 11.5 Fir-Spruc e 2.6 15.2 Hemloc k

- Sitk a s p r u c e 2.6 15.2 Larc h 4.6 10.8 Lod gep ol e pi ne 2.6 15.2 Redwoo d 4.4 9.7 Other h a rdwo ods 2.8 11.5 Unc l as s i fied & ot h e r 9.9 3.1 Piny on-J u n i per 15.3 3.5 Chaparr a l 15.3 3.5 Nons toc k ed 2.5 10.8 * Bas ed o n d a ta fr om 1 9 9 7

. Re gi on s are de fin ed in F i gure 6-2 of t he La nd-Us e Cha nge a nd F o res t ryChapt er.
Step 1d: Esti m a te Carb on i n F o rest Floor Fo rest floor carbonis th e poo l of o r g an i c carbon( litter, du ff, hu m u s, andsm all wo ody d e b r is) abov e th e m i neral soi l an d i n cl u d es wo odyf r a g m e nt s wi thdi am et er s of up t o 7. 5 cm . To est i m ate carb on i nth e fo rest fl o o r , equat i o ns de ve l ope d by Sm ith and Heath (i n p r ess ) were a p p lied to the d ataset d e scribedin Step 1 a
. Tab l e O-1 sh ows th e av erag e forest fl o o r carb o n d e n s ities b y forest type, as calcu lated b a sed onth e 19 97 d ata.
Step 1e: Es timate Carbon i n Down Dea d Wood Down dead wood is defi ne d as pieces of de ad wood great er than 7.5 cm diam eter that are not attache dto tr ees. D o wn d ead w o od i n cl ude s st um ps and ro ot s of harves te d trees. To estim ate ca r bonin d o wnd ead wo od , a p r o c edure sim i lar to esti m ati n g carbo n in un d e rstory v e g e tatio n was u s ed

. Down d ead wo od was est i m atedinth e projections by using decay rates applied to l o gging re sidue , along with e q uatio ns that estim ate the am ount of down dead wood from causes othe r th an h arv esting

. Th e p e rcentag e of do wn d ead wo odcarb o nrelativ e t o th at inliv e trees was calculated. As for t h e under st orycarb o n , ave r a g e val u es of do wn dea d w o o d were deri ve d f o r eac h f o rest type in each re gion. This pe rcentage was multiplied by the live tree carbon data from th e dataset desc ribe d in step 1 ato calcu late th e to tal am o un t o f carb on indo wn d e ad wood

. Th ese p e rcen tag e s are g i v e nin Table O-2

. Th is pr oce dur e was used beca use det a i l e d dat ab a ses are not av ai l abl e fo r ol der d at a
. B y usi n g th i s pr oc edur e, car b o n est i m at e s from hi st o r i cal dat a are c onsi s t e nt wi thcarb o nest i m at e s from curre nt F o rest I nvent oryan d A n al y s i s dat a
.

O-4 I n ventory of U.S. Greenhouse Gas Emis sions and Sink s: 1990-2001Step 1f: Esti mate Forest Soil Carbon To estim ate the am ount of carbon in forest soils, data for soils from the surface downto a depth of 1 m e ter were o b t ain e d fro m th e STATSGO sp atial d atab a se (USDA 19 91 ). Th ena sp atial d ata set d e lin eatin g forest typ e s th ro ugh ou t th e co n t erm i n o u s Un itedStates (Powell et al . 1 993 ) was ov erlaid o n t o th e so il carb on d ata fro m STAT SG O. An est i m at e of th e av era g e am ount of car b o ni nt h e soi l was th en cal cul at e d f o r ea ch f o rest type
. Est i m at e s i n cl ude d b o thm i neral soi l s and or gani c soi l s
. 1 Coarse roots were incl ude d with tree carbon estim ate s rath er than withso ils. Th e so il carbo nesti mates are g i v e ninTab l e O-1. Th ese esti mates were m u lt ip lied b yth e area of forest land in each forest type for all years. Thus , an y chan ge i ns o il carbon is a reflection of c h anges in t h e area of f o rest l and o r c h anges i n fo rest type.
Step 1g: Calc ulate Net Carbon Stock Changes Aft e r cal c u l at i on of al l fo rest carb on st ocks , th e fi nal step was to calculat e the avera g e annual net carbon sto c k ch an g e fo r eachfo r e st car bonpo o l f o r

th e year s from 1 9 9 0 thr ough200 1. Th e n e t annu a l stock ch ang e fo r each pool for 1987 through 1997 was derive d by subtracting the 1987 stock from the 1997 stock, and divi ding by the
num b e r o f years betweenestimates (1 0 years). Th e sto c k s , b y d e fin ition , co rresp ondto t h e sto c k as of Janu ary 1 of th e g i v e nyear
. Th e n e t annual sto c k ch an ges f o r 1 997 thro ugh200 1 w e re d e r i v e d inthe sam e w ay u s in g t h e 199 7 and 2 0 0 2 st ock s
. T h e p r oced ure fo r est i m ati ng carb o nst o c ks i n 2 0 0 2 i s descri bed bel o w un d er t h e he adi n g “F ore s t Secto r Mod e lin g Proj ection Syste m .”
Step 2: Es tima te Harveste d W o od Carbon Fluxes Th e fi rst step inestim a tin g sto c ks andfl u x e s o f h arv ested wood(i.e., woo d p r o du c ts andland filled wo od) was t o c o m p i l e hi st ori cal dat aon: th e p r o d u ct i on o f l um b er, pl yw o o dan d ve nee r , pulp and othe r pr od uct s ; pr o duc t and l og i m port s and e xpo rt s; and fu el w o o d( i n t e rm s of m i ll i on cu bi c feet of ro un dw oo d equi val e nt b e g i nni n g i nt h e year 1 900 , as d e scr i b e d i nSk og an d N i cholso n 1 998 )

. Data w e r e ob tain ed f r o m U S DA (1 964 ) , U l r i ch(1 989 ), an d H o w ard(2 001 ). Pr oj ected v a l u es f o r

w oodpr odu cts and r o undw ood u s e w e r e ob tain ed f

r o m th e m o d e ls u s ed for th e US DA Fo rest Service 2 0 0 0 Resour ce Planni ng Act As sessm en t ( H ayn e s 200 2, In ce 1 994, see “ F orest Sector Mo d e ling Projectio n Syste m ” b e l o w)

. Roun dwo o d pr oducts in clud e l o gs, b o lts, and o t h e r ro undtim b e r g e n e r ated fr om harvest i n g tr ees f o r

i n du stri al or co ns um er use. T h e har v est e d w o o d -t o-carb o nc o nve rsi o n fact o r s p r esent e d by Sk og an d Ni c h ol so n ( 1 99 8) were a p pl i e d t o annu al est i m at e s and pr o j e c t i ons t o est i m at e th e am ount of carb o ni n roundwood an d wood produc ts. T h e am ount of roundwood c o nsum ed was categ orize d according t o product s u c has lum b er, railroadties, an d p a p e r, b ecau s e th e leng th o f tim e th at carbonrem a in s inth ese p r o d u c ts d i ffers substantially. The dynam i cs of carbonloss through decay or t h ro ugh dis pos al of t h e product is summarized as t h e hal f-l i f e o f eac h p r od uct ( S k o g and Ni ch ol s o n 1 9 9 8 )

. Th e r e sul t i ng e s t i m a t e s were a p pl i e d t o p r o d u ct s t o d e ri ve th e n e t carb o nchan g e in w ood p r odu c ts and lan d fills. Note th at, un lik e forest carbo n sto c k esti m at e s, carbo ni n h arv ested w oodpr odu cts estimat es are derived as a carbon stoc k chan ge. In ot her w o r d s, th e annu al roun dw o od pr o duct i o n i s a change vari abl e al ready be fo r e i t i s co nve rt e dt o car b o n
. Step 3: S u m the Results from Step 1 an d Ste p 2 fo r the To ta l Net Fl ux fr om U.S. Fores ts In t h e fi nal st e p , net chan ges i nf o re st car b o nst oc ks ar e adde d t o net c h an ges i n har v est e d w o od carb o n sto c k s , to ob tainestim ates o f to tal n e t forest flu x (see Tab l e O-3 )

. Table O-3 : Net CO 2F l ux from U.S. Forest Carbon Stocks (Tg CO 2 Eq .) Descriptio n Forests (773. 7) (773. 7) (773. 7) (773. 7) (773. 7) (773. 7) (773. 7) (546. 3) (546. 3) (546. 3) (546. 3) (546. 3)

Trees (469. 3) (469. 3) (469. 3) (469. 3) (469. 3) (469. 3) (469. 3) (447. 3) (447. 3) (447. 3) (447. 3) (447. 3) Unders t ory(11.0) (11.0) (11.0) (11.0) (11.0) (11.0) (11.0) (14.7) (14.7) (14.7) (14.7) (14.7) Fores tFl oor (25.7) (25.7) (25.7) (25.7) (25.7) (25.7) (25.7) 29.3 29.3 29.3 29.3 29.3 Down Dea d Wo od (55.0) (55.0) (55.0) (55.0) (55.0) (55.0) (55.0) (58.7) (58.7) (58.7) (58.7) (58.7) Fores tSo ils (212. 7) (212. 7) (212. 7) (212. 7) (212. 7) (212. 7) (212. 7) (55.0) (55.0) (55.0) (55.0) (55.0) 199 0 199 1 199 2 199 3 199 4 199 5 199 6 199 7 199 8 199 9 200 0 200 1

1 Organic soils, otherwise known as histos ols, ar e soils that d e velop in wetland areas and hav e gr eater than 20 to 30 percent org anic matter b y weight depend ing on clay cont ent.

O-5Harvest ed Wood (209. 0) (198. 0) (202. 8) (203. 9) (210. 5) (205. 3) (205. 3) (212. 7) (205. 3) (216. 3) (209. 0) (212. 7) Wood Prod uc ts (47.7) (40.7) (46.6) (54.6) (60.9) (55.0) (55.0) (58.7) (51.3) (62.3) (58.7) (58.7) Lan dfil le d Wo od (161. 3) (157. 3) (156. 2) (149. 2) (149. 6) (150. 3) (150. 3) (154. 0) (154. 0) (154. 0) (150. 3) (154) Total (982. 7) (971. 7) (976. 4) (977. 5) (984. 1) (979. 0) (979. 0) (759. 0) (751. 7) (762. 7) (755. 3) (759. 0) Not e : Parent heses in dicat e netcarbon “se quest r at ion” (i. e

. , accumulat i on int o t he ca rbon pool minus emi ssions or st oc k removal f r om t he carbon pool). The sum of

t he netst ock changes in t h is t able (i.e. , t o t a l net f l ux) is a n est i mat e of t he act ual netf l ux between t he t o t a l f o restca rb on pool and t he at mosphere. Light ly shaded areas indica t e values based on a comb inat ion of his t orical dat a and proj ect i ons. Forestvalu es are based on periodic me asurement s; harvest ed woo d est i mat e s are based on annual survey s. To t a ls may notsum due t o independentrounding.


### Forest Sector Modeling P r ojection System The m odel i n g pr oject i o n sy st em i s a set of m odel s th at has bee nuse df o r th e U S DA F o r e st Servi ce, Resource Planning Act Ass e ssm ent since the late 1980s (F igure O-1). The m odels include anarea change m odel (Al i g 1 9 8 5 ) , a t i m b er m arket m odel (TAM M ; Adam s an d Hayn es 1 9 8 0 ) , a pulp an d pa per m odel (N AP AP; I n ce 1 994 ) andani n v e n t ory m o d e l (ATLAS; Mills an d Kin cai d 199 2). Many o f th ese m o dels are econo metric m o d e ls, desi g n e dt o p r oject th e dem a nd and s u ppl y and pri ces i nt h e forest sector. Results of th e proj ectionin clude tim b er vol um e, forest areas, har v est s, and p r i m aryp r o d u ct pr od uct i on. F o r a des c ri pt i o n of th e assum p t i ons and resul t s o f th e m o d e lin g syste m , see H ayn es ( 200 2)

. The F O R C A R B m odel (Pl ant i nga and B i r d sey19 9 3 , Heath an d B i r d sey 19 9 3 , an d Heath et al . 1 9 9 6 ) uses dat aon t i m ber vol um e, fore st areas, and har v est s fr om th e m odel i ng sy st em t o est i m at e carbon i ntr ees usi n g bi om etri cal rel at i ons hi ps bet w eencar b o nan d l i v e tr e e vo lum e
. FORCARB estim a t es carb on inall o th e r fo rest eco system co mp on en ts, pr oducin g carbo n d e n s ity esti m a tes si m i lar to th o s e inTab l e O

- 1 an dTab l e O- 2. Th e m o d e l WOODCARB (Skog and Nichols o n 1998) us es harvested roundwood product sta tistics, along with e n d-use, decay rate, an d durati o ninform atio nto estim ate carb o ni n h arv ested wood

. Fig ure O-1 illu strates t h e co nn ection s b e t w een th e v ari o u s m o d e ls, data inpu ts, and d ata o u t p u t s th at com p rise the forest sector modeling pr oject ion system

. Na m e s of m odel aut h ors ar e i nparent heses in each m odel b o x t o facilitat e id en tification of m o d e l citati o n s
. Data t h at are ex ternal to th e m o d e ls are mark ed with do ub le lin es. F i gure O-1: F o rest Sector Mode l i n g Projecti on System

O-6 I n ventory of U.S. Greenhouse Gas Emis sions and Sink s: 1990-2001

## Figure O-1: Forest Sector Modeling Projection System

Macro Economic F orest Inventory Data Data (consumption & (1) private T imberlands production of wood products) (2) estimated forest growth parameters

AREA MODELS

(Alig)

A TLAS (Mills) TA M M (Haynes/ Adams)

FORCARB

(Heath) NAP AP (Ince) timberland area

estimates of

fuelwood harvests annual forest growth

timber removals Data for private Ti mberlands and some W oodlands: (1) area (acres) (2) harvested area and volume (3) growing stock inventory and increment

Carbon stocks in private T imberlands and some W oodlands Carbon stocks in: (1) public T imberlands (2) orest Land (3) orest Land WOODCARB (Skog)

Carbon stocks in harvested wood

Historical harvested roundwood statistics

Harvest, production, trade, end use, recycling

Reserved F Other F

Harvest data estimated Soils data from exogenously to (1) ST A TSGO database TA MM/A TLAS (harvests (2) FIA ecosystem data on public T imberlands (3) Other ecosystem data Reserved F orest Land, from the literature and Other F orest Land)