Organic matter decomposition represents a vital ecosystem process by which nutrients are made available for plant uptake and is a major flux in global carbon cycling. Previous studies have investigated decomposition of different plant parts, but few considered the decomposition of bark or its role in decomposition of underlying wood. However, bark can comprise a large fraction of tree biomass and may modify its decomposition.
We used a common-litter-bed approach to investigate factors affecting decomposition of bark and its role in wood decomposition for five dominant tree species in a secondary seasonal tropical rain forest in SW China. For bark, we implemented a litter bag experiment over 12 mo, using different mesh sizes to investigate effects of litter fauna. For wood, we compared decomposition of branches with and without bark over 24 mo.
Results/Conclusions
Initial chemistry of bark and wood differed, with variable patterns among species. In four species, wood contained more carbon, more cellulose and less N and P than did bark. For the fifth species, Kleinhovia hospita, wood contained less cellulose and more water-soluble sugars than did bark. Patterns for K, lignin, hemicellulose and tannin were more variable. For bark, the ranges across species were as follows: C (44.5-49.7%), N (0.42-1.14%), P (0.02-0.15%), K(0.13-1.24%), water soluble sugar (0.34-3.99%), lignin (20.47-42.9%), hemicellulose (6.36-21.26%), cellulose (20.17-49.36%), and tannin (0.33-7.26%); for wood: C (47.1-51.1%), N (0.18-0.62%), P (0.01-0.11%), K (0.10-0.76%), water soluble sugar (0.39-1.17%), lignin (20.75-34.19%), hemicellulose (10.67-16.43%), cellulose (40.45-54.86%), and fiber (65.66-71.28%).
Bark mass loss over 12 mo ranged from 58 to 96% for material in coarse-mesh bags and from 44% to 82% in fine-mesh bags that excluded meso- and macro-fauna. Species and exclusion of litter fauna both had substantial effects on bark decomposition. For wood decomposition, responses to bark removal were species dependent, with two species showing significant negative effects of bark removal, but no effects in other species. Those species with significant bark-removal effect had slowest rates of wood decomposition. After two years, wood mass loss ranged from 28 to 100%.
We found large species effects on bark-decomposition rates, and its effect on wood decomposition. Thus there is a need to document bark traits, especially chemistry, for more tree species. Future research on wood decomposition should also separately examine bark and wood, and consider bark-removal experiments to better understand roles of bark in wood decomposition.