Carbon balance of the taiga forest within Alaska: present and future " John Yarie and Sharon Billings Abstract: Forest biomass,rates of production, and carbon dynamics are a function of climate, plant species present, and the structure of the soil organic and mineral layers. Inventory data from the U.S. Forest Service (USFS) Inventory Analysis Unit was used to develop estimatesof the land arearepresented by the major overstory species at various age-classes. The CENTURY model was then used to developan estimate of carbon dynamics throughout the age se- quenceof forest development for the major ecosystem types. The estimatedboreal forest area in Alaska, based on USFS inventory data is 17 244 098 ha. The total aboveground biomass within the Alaska boreal forest was estimatedto be 815330000 Mg. The CENTURY model estimatedmaximum net ecosystem production (NEP) at 137, 88,152,99, and 65 g.m-2.year-lfor quaking aspen (Populus tremuloides Mich.), paper birch (Betula papyri/era Marsh.), balsam poplar (Popillus balsamifera L.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) forest stands, respectively.These values were predictedat stand ages of 80, 60, 41,68, and 100 years, respec- tively. The minimum values of NEP for aspen, paper birch, balsampoplar, white spruce,and black sprucewere -171, -166, -240, -300, and -61 g.m-2.year-1 at the agesof I, I, I, 1, and 12, respectively. NEP becamepositive at the ages of 14, 19, 16, 13, and 34 for aspen,birch, balsam poplar, white spruce, and black spruce ecosystems, respectively. A 5"C increase in mean annual temperature resulted in a higher amount of predicted production and decomposition in all ecosystems, resulting in an increaseof NEP. We estimatethat the current vegetationabsorbsapproximately9.65 Tg of carbon per year within the boreal forest of the state. If there is a 5"C increasein the mean annual temperature with no changein precipitation we estimatedthat NEP for the boreal forest in Alaska would increase to 16.95Tg of carbon per year. Resume: La biomasse forestiere, les raux de production et la dynamique du carbone sont fonction du cHmat,des espe- ces de plantespresentes et de la structure des couches organiques et minerales du sol. Leg donnees d'inventaire de I'unite d'analyse d'inventaire du Service forestier des Etats-Unisant ere utili seespour fournir des estimesde la super- fide du territoire occupee par les diversesclasses d'age des principales essences dominances. Le modele CENTURY a ensuite ete utilise pour fournir un estime de la dynamiquedu carbone venti1ee par classes d'age pour leg principaux ty- pes d'ecosystemes. Sur la base des donnees d'inventaire, la superficie de for8t boreale de l'Alaska est estimce a. 17 244 098 hat La biomasse aenenne locale de la Coree borealede I' Alaska a ere estimee a 815 330 000 Mg. Le modele CENTURY a estime la production maximale nette de l'ecosysteme (NEP) a 137, 88, 152,99 et 65 g.m-2.an-1 respecti- vement pour des peuplemencs forestiers de tremble (Populustremuloides Michx.), de bouleau blanc (Betula papyrifera Marsh.), de peuplier baumier (Populus balramifera L.), d'epinette blanche (Picea glauca (Moench) Voss) et d'epinette noire (Picea mariana (Mill.) BSP). Ces valeurs onE ere preditesrespectivement pour des agesde peuplement de 80, 60, 41, 68 et 100 aDS. Les valeurs minimales de NEP pour Ie tremble, Ie bouleau a papier, Ie peuplier baumier, I'epinette blanche et l'epinette noire etaient de -171, -166, -240, ~300 et -61 g.m-2.an-1 aux agesrespectifs de I, I, I, I et 12 ans. La NEP devenaitpositive aUK agesde 14, 19, 16, 13 et 34 ans respectivement pour les ecosystemes de tremble. de bouleau a papier, de peuplier baumler, d'epinette blancheet d'epinette noire. Une augmentation de 5°C de la tempera- ture moyenne annuelle aboutit a une production et une decomposition predites plus elevees dans tous les ecosystemes, ce qui entraine one augmentationde la NEP. Nous estimonsque la vegetation actuelle absorbe approximativement 9,65 Tg de carbonepar anneedans la for8t boreale de I'etat. s'n y a one augmentationde 5°C dans la temperature moyenne annuellesanschangements dans les precipitations.nous estimons que la NEP des forets boreales de I' Alaska augmenteraient a 16,95 Tg de carbonepar an. [fraduit par 1aRedaction] Received I December2000. Accepted 5 April 2001. Publishedon the NRC Research Press Web site at hup:/Icjfr.nrc.ca on 26 April 2002. J. Yariel and S. Billings. Department of Forest Science. School of Agriculture and Land Resources Management, University of Alaska Fairbanks, Fairbanks, AK 99775, U.S.A. 'Correspondingauthor (e-mail: j.yarie@uaf.edu). Can. J. For. Res. 32: 757-767 (2002) 757 Introduction The primary componentsof forest carbon (C) dynamics are forest biomass, production, and decompositionof the forest floor and mineral soil organic matter. Control and change in the dynamics of these components is a function of climate, plant species,and the structureof the soil organic and mineral soil layers. It is the relationship betweenpro- @ 2002 NRC Canada DOl: 1O.1139JXO1-O75