Effects of mesh bag enclosure and termites on fine woody debris decomposition in a subtropical forest

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The role of insects in terrestrial decomposition remains poorly resolved, particularly for infrequently studied substrates like small diameter woody debris. Uncertainty about how mesh bags used to exclude arthropods may affect decomposition rates continues to impede progress in this area. We sought to (1) measure how insects affect the decomposition of small diameter (<2.5cm) Triadica sebifera L. “twigs” and (2) test for unintended effects of mesh bags on wood decomposition using machined wooden dowels of similar size and specific gravity. In subtropical forests, three twig diameter classes plus dowels were enclosed in two mesh sizes (0.3 or 1mm openings) or left unenclosed over a 20-month study period. Unenclosed twigs lost significantly more mass than those within fine mesh bags. Because this effect was consistent throughout the study (reaching nearly 80% mass loss), our findings suggest the invertebrate influence does not disappear or attenuate over time. Our dowel data (limited to dowels with no evidence of insect activity) show that fine and coarse mesh bags accelerate the decomposition of enclosed woody material, suggesting insects contributed even more to the decomposition of tallow twigs than our measure of 9 – 10%. Termites exhibited a strong preference for larger diameter twigs, resulting in temporary differences in decomposition rates among diameter classes. Our findings confirm the importance of insects to wood decomposition and highlight the need to incorporate these organisms in models of carbon and nutrient cycling.