Sensitivity of Boreal Forest Carbon Balance to Soil Thaw

Abstract

We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 ± 0.5 metric ton of carbon per hectare per year (ton C ha −1 year −1 ) from 1994 to 1997, with a gain of 0.6 ± 0.2 ton C ha −1 year −1 in moss and wood offset by a loss of 0.8 ± 0.5 ton C ha −1 year −1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool (∼150 tons C ha −1 ) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.

Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings

“…It is wellknown that if moss cover thickness incieases, thermoisolation of soil also increases, summer soil thawing decreases, and tree growth is suppressed by nearer permafrost. During long warm periods with higher annual and seasonal (June-September) temperatures, owing to deeper soil thawing the moss destruction and organic decomposition in soil may prevail over moss increment on surface and moss thickness decreases [Goulden et al, 1998]. This leads to better thermal conditions tbr roots of trees and finally to the increase of the growth rate.…”

Modeling landscape net ecosystem productivity (LandNEP) under alternative management regimes

“…Many modeling and fieldbased studies have also reported a high interannual variability of ecosystem CO 2 sources and sinks (Woofsy et al, 1993;Goulden et al, 1996;Chen et al, 2002). Researchers conducting fieldbased eddy covariance studies have noted that in some instances a warm winter can switch a boreal forest from becoming a carbon sink to a source due to an increase in ecosystem respiration (Lindroth et al, 1998;Goulden et al, 1998). This has been attributed to climatic variability and the correlation between temperature and ecosystem respiration .…”

Storage and Turnover of Organic Matter in Soil

“…If these soils are warmed, decomposition and emissions of CO 2 and CH 4 will proceed rapidly, leading to a large positive feedback with climate change. Indeed, year-to-year differences in decomposition of old SOM in some boreal forest soils can determine the status of entire forest stands as net sources or sinks of C (Goulden et al 1998). Because gross C fluxes at high latitudes are small compared to those in the tropics, it is unlikely that even large interannual variability in those fluxes could be as important in affecting the short term (annual) C balance of the atmosphere.…”