Decay classes of coarse woody debris in a lowland Dipterocarp forest: implications for volume, density, and carbon estimates

摘要

Coarse woody debris (CWD) is a critical structural and functional component of forest ecosystems. In tropical forests, developing a decomposition classification is required for vigorous estimates of the role of CWD in carbon (C) and nutrient cycling and habitat diversity. This study considered the relationship between decay class, termite infestation, wood density, and C content of CWD in a lowland Dipterocarp forest in Southern Vietnam. The termite infestation averaged 73% by number and 32% by volume of all CWD pieces. Microbial- and termite-driven decomposition was separated in the suggested decay classification system. Five decay classes were assigned to CWD items based on the proportion of wood consumed by invertebrates, as well as softness and moisture of the remaining wood. The proportion of wood volume consumed by termites in the 1st, 2nd, 3rd, 4th, and 5th decay classes averaged 2, 5, 15, 48, and 77%, respectively. The bulk density of wood of the 1st, 2nd, 3rd, 4th, and 5th decay classes averaged 0.628, 0.501, 0.332, 0.169, and 0.071 g cm(-3), respectively. The C concentration in wood averaged 42% and did not depend on decay class. The total C content in CWD decreased with decomposition and averaged 0.259, 0.199, 0.121, 0.037, and 0.009 g cm(-3) in the CWD of the 1st, 2nd, 3rd, 4th, and 5th decay classes, respectively. We conclude that in Dipterocarp forests the inventories of CWD by decay classes should include estimates of proportions of wood, termite soil substrate, and wood voids.