Contrasting effects of insect exclusion on wood loss in a temperate forest

Abstract

Abstract. Experimental efforts to determine how insects influence terrestrial wood decomposition are few, especially in temperate regions. To address this need, a five-year exclusion study was conducted in northern Mississippi, U.S.A., to quantify insect contributions to wood decay using one-meter loblolly pine (Pinus taeda L.) bolts. The study included three treatments: (1) ''partially protected'' bolts that were placed on cypermethrin-treated soil to exclude subterranean termites (Isoptera: Rhinotermitidae: Reticulitermes spp.) while permitting colonization by beetles (Coleoptera) and other saproxylic taxa, (2) ''fully protected'' bolts that were placed on cypermethrin-treated soil and enclosed within screen cages to protect against all insects and (3) ''unprotected'' bolts that were not subjected to either exclusion treatment. The full insect community consumed approximately 15-20% of wood volume in unprotected bolts, about six times more than in partially protected bolts from which termites were excluded. There were no differences in specific gravity (based on initial wood volume) or mass loss among treatments, however. It is not clear whether these findings are due to an inhibition of microbial decomposers by insects (e.g., antimicrobial compounds secreted by termites or ants), a stimulatory effect of the exclusion treatments (e.g., cypermethrin stimulating fungal growth or cages favorably altering wood moisture), or some combination of both. When based on final water-displaced volume, specific gravity was significantly higher for unprotected bolts than for those fully protected, probably because termites selectively consume the least dense wood. By the end of the study, about 20% of the final dry weight of unprotected bolts consisted of termite-imported soil. Wood volume consumed and soil content decreased with distance from the ends of the bolts whereas water content exhibited the opposite pattern. We detected a significant negative relationship between water content and volume consumed by termites, possibly because water content decreases with increasing wood density and termites tend to avoid high density wood. While insects clearly consume large volumes of wood in southeastern U.S. forests, our results suggest they do not act to accelerate mass loss beyond what is achieved by microbial decomposers. More research is needed to confirm this, however-especially given the uncertainties inherent to exclusion studies.

Changes in the Contribution of Termites to Mass Loss of Dead Wood among Three Tree Species during 23 Months in a Lowland Tropical Rainforest

“…nitrogen-rich cambium, or the softest rings of spring wood), they can selectively forage for new dead wood after consuming the parts (Shellman-Reeve, 1994;Stoklosa et al, 2016;Traniello & Leuthod, 2000;Ulyshen et al, 2014). Finally, as dead wood loses its specific traits during the decomposition, the termite activity could be suppressed because of the invasion of non-tree specific termite predators on dead wood.…”

Below‐ and above‐ground effects of deadwood and termites in plantation forests

“…Native subterranean termites (Rhinotermitidae) belonging to the genus Reticulitermes are the most important wood‐feeding insects in southeastern U.S. loblolly pine forests where they have been shown to consume up to a fifth of the wood volume (Ulyshen et al. ), accelerate wood mass loss (Ulyshen , Stoklosa et al. , Ulyshen et al.…”

“…The movement of these insects between the wood and soil, including their importation of large amounts of soil into wood (Ulyshen et al. ), raises questions about how they impact soil properties and microbial activity below woody debris. By disrupting fungal networks in decomposing wood and by promoting the fixation of atmospheric nitrogen by both free‐living and endosymbiotic prokaryotes, termites may have a fertilizing effect in forests (Ulyshen ), with potentially important below‐ and above‐ground implications.…”

“…Final measurements were collected after 51 months when, based on previous research conducted in the same area, the experimental logs should have been more than half‐decomposed (Ulyshen et al. ). Below‐ground measurements focused on soil properties, plant‐available forms of N, and ectomycorrhizal diversity associated with fine tree roots.…”

Consistent effects of eastern subterranean termites (Reticulitermes flavipes) on properties of a temperate forest soil

“…As a decomposer of woody material, native subterranean termites (Reticulitermes spp.) provide an important role in forest ecosystems (La Fage and Nutting, 1978;Ulyshen and Wagner, 2014). It is conceivable that factors such as climate warming will permit these species to increase their abundances and hence ecosystem effects at more northerly latitudes (Maynard et al, 2015).…”