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An inventory-based analysis of Canada's managed forest carbon dynamics, 1990 to 2008

ABSTRACT: Canada's forests play an important role in the global carbon (C) cycle because of their large and dynamic C stocks. Detailed monitoring of C exchange between forests and the atmosphere and improved understanding of the processes that affect the net ecosystem exchange of C are needed to improve our understanding of the terrestrial C budget. We estimated the C budget of Canada's 2.3 × 106 km2 managed forests from 1990 to 2008 using an empirical modelling approach driven by detailed forestry datasets. We estimated that average net primary production (NPP) during this period was 809 ± 5 Tg C yr?1 (352 g C m?2 yr?1) and net ecosystem production (NEP) was 71 ± 9 Tg C yr?1 (31 g C m?2 yr?1). Harvesting transferred 45 ± 4 Tg C yr?1 out of the ecosystem and 45 ± 4 Tg C yr?1 within the ecosystem (from living biomass to dead organic matter pools). Fires released 23 ± 16 Tg C yr?1 directly to the atmosphere, and fires, insects and other natural disturbances transferred 52 ± 41 Tg C yr?1 from biomass to dead organic matter pools, from where C will gradually be released through decomposition. Net biome production (NBP) was only 2 ± 20 Tg C yr?1 (1 g C m?2 yr?1); the low C sequestration ratio (NBP/NPP=0.3%) is attributed to the high average age of Canada's managed forests and the impact of natural disturbances. Although net losses of ecosystem C occurred during several years due to large fires and widespread bark beetle outbreak, Canada's managed forests were a sink for atmospheric CO2 in all years, with an uptake of 50 ± 18 Tg C yr?1 [net ecosystem exchange (NEE) of CO2=?22 g C m?2 yr?1].

SUBMITTER: Stinson G

PROVIDER: S-EPMC3597256 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature

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Project description:The forest-steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest-steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m-2 yr-1 ) and isotope composition of organic matter (?13 CTOC ). Forest-steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m-2 yr-1 . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments.

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An inventory-based analysis of Canada's managed forest carbon dynamics, 1990 to 2008

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