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Climate and species controls on decomposition of coarse woody debris: Radiocarbon dating of decaying logs.
Kueppers, Lara*,1, Southon, John2,3, Harte, John1, 1 University of California, Berkeley, Berkeley, CA2 Lawrence Livermore National Laboratory, Livermore, CA3 University of California, Irvine, Irvine, CA
ABSTRACT- Forest ecosystems cycle carbon through reservoirs with a wide range of turnover times. While turnover times for living biomass, fine litter and soil carbon have all been widely reported, coarse woody debris turnover times are not as frequently measured. Standing stocks of coarse woody debris can range from less than 10 to more than 500 Mg ha-1 depending on forest type, disturbance regimes, forest productivity and conditions for decomposition, making it an important reservoir for carbon and carbon isotopes in many forests. Coarse wood decomposition rates are difficult to determine in any single site; good estimates rely on accurate knowledge of disturbance history, dendrochronological records, or decades of foresight. Lacking this knowledge, we used radiocarbon dating to estimate the year of death for 42 logs along a climate and forest type gradient in the Rocky Mountains of Colorado. Year of death ranges from 2001 AD to 1430 AD. Wood density in the same logs ranges from 0.45 g cm-3 in newly fallen trees to 0.09 g cm-3 in completely fragmented logs and correlates well with traditional decay classes. Combining time since death with measurements of wood density, we can generate separate decay curves for Picea engelmannii and Pinus contorta logs at the same elevation, and for each species at two different elevations. This allows us to investigate the relative importance of climate and species on coarse woody debris decomposition.
KEY WORDS: coarse woody debris, decomposition, radiocarbon