Carbon allocation plays a critical role in forest ecosystem carbon cycling. We reviewed existing literature and compiled annual carbon budgets for forest ecosystems to test a series of hypotheses addressing the patterns, plasticity, and limits of three components of allocation: biomass, the amount of material present; flux, the flow of carbon to a component per unit time; and partitioning, the fraction of gross primary productivity (GPP) used by a component. Can annual carbon flux and partitioning be inferred from biomass? Our survey revealed that biomass was poorly related to carbon flux and to partitioning of photosynthetically derived carbon, and should not be used to infer either. Are component fluxes correlated? Carbon fluxes to foliage, wood, and belowground production and respiration all increased linearly with increasing GPP (a rising tide lifts all boats). Autotrophic respiration was strongly linked to production for foliage, wood and roots, and aboveground net primary productivity and total belowground carbon flux (TBCF) were positively correlated across a broad productivity gradient. How does carbon partitioning respond to variability in resources and environment? Within sites, partitioning

Abstract Carbon-use efficiency (CUE), the ratio of net primary production (NPP) to gross primary production (GPP), describes the capacity of forests to transfer C from the atmosphere to terrestrial biomass. It is widely assumed in many landscape-scale carbon-cycling models that CUE is a constant value of ~0.5. To achieve a constant CUE, tree respiration must be a constant fraction of canopy photosynthesis. We conducted a literature survey to test the hypothesis that CUE is constant and universal among forest ecosystems. Of the 60 data points obtained from 26 papers published since 1975, more than half reported values of GPP that were not estimated independently from NPP; values of CUE calculated from independent estimates of GPP were greater than those calculated from estimates of GPP derived from NPP. Values of CUE varied from 0.23 to 0.83 for different forest types. CUE decreased with increasing age, and a substantial portion of the variation among forest types was caused by differences in stand age. When corrected for age the mean value of CUE was greatest for temperate deciduous forests and lowest for boreal forests. CUE also increased as the ratio of leaf mass-to-total mass increased. Contrary to the assumption of constancy, substantial variation in CUE has been reported in the literature. It may be inappropriate to assume that respiration is a constant fraction of GPP as adhering to this assumption may contribute to incorrect estimates of C cycles; a 20% error in current estimates of CUE used in landscape models (i.e. ranging from 0.4 to 0.6) could misrepresent an amount of carbon equal to total anthropogenic emissions of CO 2 when scaled to the terrestrial biosphere. 2

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 estimates of the land area represented by the major overstory species at various age-classes. The CENTURY model was then used to develop an estimate of carbon dynamics throughout the age sequence of forest development for the major ecosystem types. The estimated boreal forest area in Alaska, based on USFS inventory data is 17 244 098 ha. The total aboveground biomass within the Alaska boreal forest was estimated to

and forest ecosystems: knowledge gaps

Abstract. It is necessary to develop new satellite methods to monitor boreal forests responses to climate warming. Remotely sensed maps derived from hyper-spectral Advanced Visible/Infrared Imaging Spectrometer (AVIRIS) data were developed and compared for the four conifer forest ecosystems at the Bonanza Creek Experimental Forest, a long-term ecological research site on the Tanana River ood plain near Fairbanks,Alaska. The site was rst strati ed into montane, lowland alluvial plain, and ood plain zones based on topography. A classi cation of six forest and three non-forest types was created from AVIRIS images and compared on a pixel-by-pixel basis to a published vegetation map, a classi ed SPOT (Satellite Pour l’Observation de la Terre) image, and a hybrid SPOT image and digital elevation model classi cation. A comparison of AVIRIS with SPOT results showed that the AVIRIS classi cation was consistently more accurate (74, 43, and 43 % overall accuracy, respectively). Hyperspectral classi cation methods have promise for mapping forest ecosystems in other boreal regions when little or no ground data are available for validation. The time diVerence between the creation of these maps show that substantial ecosystem changes have occurred over the past 15 years, demonstrating the need for developing a capability to obtain cost-eVective landscape characterization. 1.

Empirical models are standard tools in forest management. They provide quantitative information for management and planning that is accurate within the limits of sampling and measurement accuracy, but they are generally site-specific and cannot simulate the results of changing conditions. Mechanistic, or process-based models, based on the physiological processes that govern tree growth can, in principle, provide estimates of the potential productivity of sites for which no mensuration data exist, calculate realized growth and evaluate the effects of actions such as fertilisation or thinning, or the impact of pests and diseases on productivity. It should also be possible to use these models to evaluate the probable effects of climate change on forest growth. However, most process-based models contain too many poorly known parameters and their projections are not as reliable in practice as those of empirical models. In addition they have not, up to now, produced outputs of interest to those concerned with forest management. The reasons for this state of affairs are considered and a brief historical survey of some of the physiological research that, over the last 30 years, has produced the knowledge and information needed to produce useful, practical process-based forest models, is presented. The survey deals with light interception, photosynthesis, stomatal

Eddy-covariance and biometeorological methods show significant net annual carbon uptake in an old-growth Douglas-fir64 forest in southwestern Washington, USA. These results contrast with previous assumptions that old-growth forest eco-systems are in carbon equilibrium. The basis for differences between conventional biomass-based carbon sequestration estimates and the biomete-orologic estimates are discussed. Annual net eco-system exchange was comparable to younger ecosystems at the same latitude, as quantified in the AmeriFlux program. Net ecosystem carbon uptake was significantly correlated with photo-synthetically active radiation and air temperature,

rain forest

Abstract: Carbon (C) stocks were assessed for hybrid interior spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.)-dominated upland forests within the Aleza Lake Research Forest in central British Columbia, Canada. Four old-growth (141-250 years old) and four young second-growth (<20 years old) forest plots were established on the two dominant soil texture types, coarse and fine, for a total of 16 plots. Mean total C stocks for oldgrowth stands ranged from 423 Mg C·ha -1 (coarse) to 324 Mg C·ha -1 (fine), intermediate between Pacific Northwest temperate forests and upland boreal forests. Total C was lower in second-growth stands because of lower tree (mostly large tree stem), forest floor, and woody debris C stocks. In contrast, old-growth forest-floor C stocks ranged from 78 Mg C·ha -1 (coarse) to 35 Mg C·ha -1 (fine), 2.9-and 1.2-fold higher than in corresponding second-growth stands, respectively. Woody debris C stocks in old-growth stands totaled 35 Mg C·ha -1 (coarse) and 31 Mg C·ha -1 (fine), 2.7-and 3.4-fold higher than in second-growth stands, respectively. Mineral soil C to 1.07 m depth was similar across soil type and age-class, with totals ranging from 115 to 106 Mg C·ha -1 . Harvesting of old-growth forests in sub-boreal British Columbia lowers total C stocks by 54%-41%. Résumé : Les stocks de carbone (C) ont été évalués pour les forêts de montagne dominées par l'épinette hybride de l'intérieur (Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.) dans les limites de la forêt expérimen-tale du lac Aleza située dans le centre de la Colombie-Britannique, au Canada. Des parcelles-échantillons ont été éta-blies dans quatre vieilles forêts (141-250 ans) et quatre jeunes forêts de seconde venue (<20 ans) sur les deux types dominants de texture du sol, grossière et fine, pour un total de 16 parcelles-échantillons. Les stocks totaux moyens de C pour les vieilles forêts variaient de 423 Mg C·ha -1 (grossière) à 324 Mg C·ha -1 (fine), à mi-chemin entre les forêts tempérées du Pacifique Nord-Ouest et les forêts boréales de montagne. Le C total était plus faible dans les peuplements de seconde venue parce que les stocks de C étaient plus faibles dans les arbres (surtout des arbres avec de grosses tiges), la couverture morte et les débris ligneux. À l'inverse, les stocks de C dans la couverture morte des vieilles forêts variaient de 78 Mg C·ha -1 (grossière) à 35 Mg C·ha -1 (fine), soit respectivement 2,9 et 1,2 fois plus que dans les peuplements de seconde venue correspondants. Les stocks de C dans les débris ligneux des vieilles forêts totalisaient 35 Mg C·ha -1 (grossière) et 31 Mg C·ha -1 (fine), soit respectivement 2,7 et 3,4 fois plus que dans les peuplements de seconde venue. Le contenu en C du sol minéral, jusqu'à une profondeur de 1,07 m, était similaire pour tous les types de sol et toutes les classes d'âge avec des totaux variant de 115 à 106 Mg C·ha -1 . La récolte des vieilles forêts dans la zone sub-boréale en Colombie-Britannique réduit les stocks totaux de C de 54 % à 41 %. [Traduit par la Rédaction] Fredeen et al. 1421

ABSTRACT: Changes in soil C and total N stocks were investigated following reforestation of previously cultivated soil in compariso n with soil subjected to continuous cultivation and soil under an adjacent natural forests in south central highlands of Ethiopia. Two of the most widely planted tree species in the highlands of Ethiopia, namely Eucalyptus saligna and Cupressus lusitanica, were considered in the plantation treatments. Soil C and total N contents in the upper 0–10 and 10–20 cm soil layers were significantly different in the order: Natural forest> C. lusitanica> E. saligna> Farmland. Differences in soil C and total N contents among the sites for soil depths greater than 20 cm were negligibly small and statistically not significant. Soil C and total N stocks in the upper 0.80 m mineral soil also varied significantly in the same order as above. Estimated average annual soil C accruals were 156 and 37 g C m-2 yr-1 for Cupressus lusitanica and Eucalyptus saligna, respectively. The results demonstrate that reforestation of former arable soils in the dry Afromontane region of Ethiopia could yield significant restoration of soil C and total N that are lost in the process of natural forest conversion into arable lands and subsequent cultivation. However, the two plantation species differed considerably with respect to the rate of soil C and total N accrual. This suggests that proper selection of tree species will considerably affect the magnitude and rate of soil C sequestration.