Harvard Forest Research

Carbon retention in woody debris in the face of climate change

Principal Investigator: Colin Orians
Tufts University: Aug 28 2007 - Aug 30 2010:

Abstract:
Carbon retention in woody debris varies under many environmental factors, such as temperature and moisture availability. There is much already understood about the forest carbon cycle, however the effects of climate change (specifically warming) on carbon retention in woody debris is not yet well understood. As the soil is warmed, organisms that decompose woody debris, such as fungi, invertebrates and microbes could be given a longer active season to degrade wood. This in turn would speed the rate of wood degradation in these warmer plots. Such increased decomposition would have significant implications for the carbon cycle as carbon is returned to the atmosphere more quickly than under current soil temperatures. Alternatively, the soil warming could result in a decrease in moisture availability within the woody debris. This would then decrease decomposer activity, slowing decomposition and increasing carbon retention in the wood.

As different tree species have different internal chemistry and wood structure, changes in decomposition will vary between species. From our previous research at Hopkins forest on the decomposition of coarse woody debris, we found that decomposition rates vary with species. While Red Oaks had a long carbon retention time, other trees such as Sugar Maple or American Beech decomposed much faster. Warming could make this variation between species even more distinct. This difference in decomposition between species could be due to wood structure, as more porous woods can retain larger amounts of water for greater periods of time. This in turn could create better environments for decomposers, resulting in higher decomposition rates in these more porous woods. Alternatively, wood chemistry alone could be responsible for decomposition rates. This research question integrates the environmental factor of warming with species-specific wood traits to address carbon retention in woody debris.

Previous data collected at the Harvard Forest soil warming plots has shown that there is no difference in the tree mortality between the soil warming and control plots. In addition, our natural experiment earlier this summer showed that an equal amount of woody debris accumulated in both plots. This suggests that mortality and woody debris accumulation will not change with soil warming. As a result, the decomposition rate alone will become the sole factor controlling carbon retention in the woody detritus carbon pool. In addition, this change in decomposition could correlate with a change in nutrient release into the forest system from the decomposing woody debris. Influenced nutrient cycles could include nitrogen, phosphorous, calcium, potassium and magnesium. This could then change carbon sequestration in the forest as the availability of nutrients is altered.

Our larger research question addresses the amount by which carbon retention in woody debris will change with climate warming. This data is relevant to a larger forest carbon budget. An increase in tree growth (and carbon sequestration) due to soil warming could potentially be offset by a decrease in carbon retention by woody debris in the same forest. However, if carbon retention in woody debris is increased, then there would be a net gain in carbon sequestered by the forest. This is relevant to projections as to how temperate forests will respond to and potentially influence climate change.
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