Bark coverage and insects influence wood decomposition: Direct and indirect effects

Rates of terrestrial wood decomposition are known to vary widely depending on regional and local climatic conditions, substrate characteristics and the organisms involved but the influence of many factors remain poorly quantified. We sought to determine how bark and insects contribute to decomposition in a southeastern U.S. forest. Open-topped stainless steel pans with screened bottoms were used to prevent subterranean termite (Rhinotermitidae: Reticulitermes spp.) colonization from “protected” logs. After a 20-month study period, we compared mass loss and lignin content between these and logs assigned to “unprotected” treatments that permitted termite colonization. The experiment was repeated for 1) logs from which bark had or had not been initially removed and 2) logs with sealed or unsealed ends. Logs with bark lost significantly (∼2.4-fold) more mass than those without bark, likely due to the moisture-conserving properties of bark. Logs with unsealed ends lost significantly more mass than those with sealed ends. There was no significant difference in mass loss between protected and unprotected logs but logs with visible termite activity lost significantly more mass than those without termite damage. Few differences in lignin content were detected in this study but when logs with bark were analyzed separately, those with visible damage from long-horned beetles (Coleoptera: Cerambycidae) had lower lignin content than those without cerambycid activity. This suggests that cerambycids may promote decomposition indirectly through interactions with fungi or other organisms capable of degrading lignin. Our results suggest that insects can have significant direct and indirect effects on wood decomposition and clearly demonstrate the importance of bark in determining wood decay rates and insect activity.