Positive feedback from woodpeckers on deadwood decomposition via invertebrates.

Plant matter decomposition is a linchpin of global carbon cycling, yet the role of vertebrates remains poorly understood. Woodpeckers are ubiquitous vertebrate inhabitants of forests, where they hack into deadwood to forage for small animals. Our study in a temperate forest revealed not only how this behavior significantly impacts deadwood decomposition through mechanical breakdown but also how its species specificity leads to positive feedback on decomposition rates. Investigating large logs from six conifer species over 6 years in a tree cemetery, we found that woodpeckers accelerated decomposition (both mass and volume losses) selectively in softer, more decomposable deadwood like that of Norway spruce (Picea abies), which hosted abundant wood-boring beetle larvae relative to the abundances in other tree species. This selectivity triggers a positive feedback loop: bottom-up drivers (low wood density and high water-holding capacity) foster abundant invertebrate prey, promoting top-down woodpecker foraging that fragments logs and exposes inner tissues to microbial decay. Positioning woodpeckers as a potential keystone wood decay agent, our study supports the growing call for integrating vertebrate contributions into global carbon cycling models. As the first study to elucidate the complex interactions between deadwood traits, invertebrate populations, and woodpecker activities, we aim to galvanize further research into their often-overlooked functional role as deadwood fragmenters. The conservation implications of these findings are profound, especially in light of the historical context where vertebrates that once performed key ecological functions are now endangered or extinct due to widespread anthropogenic activities..