Authors: Harald Bugmann Christof Bigler
Publish Date: 2010/11/23
Volume: 165, Issue: 2, Pages: 533-544
Abstract
Experimental studies suggest that tree growth is stimulated in a greenhouse atmosphere leading to faster carbon accumulation ie a higher rate of gap filling However higher growth may be coupled with reduced longevity thus leading to faster carbon release ie a higher rate of gap creation The net effect of these two counteracting processes is not known We quantify this net effect on aboveground carbon stocks using a novel combination of data sets and modeling Data on maximum growth rate and maximum longevity of 141 temperate tree species are used to derive a relationship between growth stimulation and changes in longevity We employ this relationship to modify the respective parameter values of tree species in a forest succession model and study aboveground biomass in a factorial design of growth stimulation × reduced maximum longevity at multiple sites along a climate gradient from the cold to the dry treeline The results show that 1 any growth stimulation at the tree level leads to a disproportionately small increase of stand biomass due to negative feedback effects even in the absence of reduced longevity 2 a reduction of tree longevity tends to offset the growthrelated biomass increase at the most likely value of reduced longevity the net effect is very close to zero in most multi and singlespecies simulations and 3 when averaging the response across all sites to mimic a “landscapelevel” response the net effect is close to zero Thus it is important to consider ecophysiological responses with their linkage to demographic processes in forest trees if one wishes to avoid erroneous inference at the ecosystem level We conclude that any CO2 fertilization effect is quite likely to be offset by an associated reduction in the longevity of forest trees thus strongly reducing the carbon mitigation potential of temperate forests
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