Fungal communities associated with acorn woodpeckers and their excavations

Positive feedback from woodpeckers on deadwood decomposition via invertebrates

Plant matter decomposition is a linchpin of global carbon cycling,1,2 yet the role of vertebrates remains poorly understood.3 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.4 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.5,6,7,8,9.

The internal decay of wood is driven by the interplay between foraging Magellanic woodpeckers and environmental conditions

Although woodpeckers are known to forage in decaying trees, their contribution to internal wood decay is not well known. In this sense, non-destructive techniques for structural wood degradation provide an opportunity to quantitatively assess the role of woodpeckers in tree decay. We used sonic tomography to test that the trunks of living trees pecked by Magellanic woodpeckers show pronounced decay, which accelerates under environmental conditions favorable to wood-decaying fungi. The internal decomposition of wood and its decay rate were measured over four years on 156 living southern beech (Nothofagus) trees belonging to four dominant species of southern temperate forests in northern Patagonia. Half of these live trees had woodpecker feeding holes, while the rest served as controls. The percentage of decayed wood, although not severely decayed, increased in sections with the presence of woodpecker holes, but was also influenced by temperatures and biophysical variables such as elevation and topography. The trunk sections with woodpecker holes and exposed to intensive foraging showed accelerated inter-annual decay. Woodpecker foraging activity interacted with vegetation characteristics, resulting in accelerated wood decay in forest sites with an open canopy and exposed to water stress. Thus, sonic tomography provided evidence of a close relationship between woodpeckers and internal wood decomposition, suggesting a positive feedback mechanism regulated by forest disturbance. The approach used here can be extended to gain insight into the influence of woodpeckers on tree decay and mortality in regions experiencing severe drought and forest degradation, such as northern Patagonia.