Interacting effects of insects and flooding on wood decomposition.

Michael D Ulyshen,Peter Shaw

doi:10.1371/journal.pone.0101867

Michael D Ulyshen, Peter Shaw

Open Access

https://doi.org/10.1371/journal.pone.0101867

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Abstract

Saproxylic arthropods are thought to play an important role in wood decomposition but very few efforts have been made to quantify their contributions to the process and the factors controlling their activities are not well understood. In the current study, mesh exclusion bags were used to quantify how arthropods affect loblolly pine (Pinus taeda L.) decomposition rates in both seasonally flooded and unflooded forests over a 31-month period in the southeastern United States. Wood specific gravity (based on initial wood volume) was significantly lower in bolts placed in unflooded forests and for those unprotected from insects. Approximately 20.5% and 13.7% of specific gravity loss after 31 months was attributable to insect activity in flooded and unflooded forests, respectively. Importantly, minimal between-treatment differences in water content and the results from a novel test carried out separately suggest the mesh bags had no significant impact on wood mass loss beyond the exclusion of insects. Subterranean termites (Isoptera: Rhinotermitidae: Reticulitermes spp.) were 5–6 times more active below-ground in unflooded forests compared to flooded forests based on wooden monitoring stakes. They were also slightly more active above-ground in unflooded forests but these differences were not statistically significant. Similarly, seasonal flooding had no detectable effect on above-ground beetle (Coleoptera) richness or abundance. Although seasonal flooding strongly reduced Reticulitermes activity below-ground, it can be concluded from an insignificant interaction between forest type and exclusion treatment that reduced above-ground decomposition rates in seasonally flooded forests were due largely to suppressed microbial activity at those locations. The findings from this study indicate that southeastern U.S. arthropod communities accelerate above-ground wood decomposition significantly and to a similar extent in both flooded and unflooded forests. Seasonal flooding has the potential to substantially reduce the contributions of these organisms to wood decomposition below-ground, however.

Highlights

Dead wood accounts for approximately 10–25% of aboveground forest biomass [1,2] and provides habitat and resources for an or even larger proportion of forest biodiversity [3]
Specific gravity Specific gravity varied significantly between forest types and treatments (Table 1), being generally lower in bolts placed in unflooded forests and for those unprotected from insects (Figure 4A and see Table 2 for details on decomposition rates)
At the end of the study, after 31 months, approximately 20.5% and 13.7% of specific gravity loss was attributable to arthropod activity [i.e., (SGprotected2SGunprotected)/(SGinitial2SCunprotected), with SGinitial = 0.45] in flooded and unflooded forests, respectively

Summary

Introduction

Dead wood accounts for approximately 10–25% of aboveground forest biomass [1,2] and provides habitat and resources for an or even larger proportion of forest biodiversity [3]. A wide variety of arthropod taxa are known to consume or otherwise excavate dead wood and some of these–most notably termites [7,8,9,10] and wood-boring beetles [11,12,13]–are thought to significantly accelerate decomposition. Efforts to quantify this effect are few, and it remains entirely unknown how this influence may vary with physical conditions. Such research is needed to refine decomposition models which have generally ignored arthropod effects [14,15] and would help to properly recognize the ecosystem services provided by this diverse and vulnerable fauna [16]

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