Action: Remove coarse woody debris from forests
- One of two replicated and controlled studies from the USA found that overall breeding bird abundance and diversity were lower in plots where woody debris was removed, compared to control plots. Several individually-analysed species showed lower abundances. A replicated, controlled before-and-after study from the USA found lower nest survival for black-chinned hummingbirds following debris removal.
- Some species in both studies increased after debris removal.
Removal of coarse woody debris (i.e. dead woody plant material >5mm diameter, including bark > 5mm thickness) from forests is a practice most commonly undertaken in North American and Australian forests to reduce risk of intense wildfires by reducing the fuel-load. It may be undertaken as a deliberate conservation intervention to benefit certain bird species, but with the potential to adversely affect understorey species that utilise accumulated dead wood for foraging or nesting.
Supporting evidence from individual studies
A randomised, replicated controlled study in 1996-1999 in loblolly pine Pinus taeda stands at the Savannah River Site, South Carolina, USA (Lohr et al. 2002), found that breeding bird abundance, species richness and diversity and resident bird abundance were lower in plots where coarse woody debris was removed, compared to control plots (17-21 territories and 11-13 species/9.3 ha plots with debris removal vs. 31 territories and 20 species for control plots). Midstorey-, canopy- and cavity-nesting species such as red-headed woodpecker Melanerpes erythrocephalus, great crested flycatcher Myiarchus crinitus, eastern towhee Piplio erythrophthalmus and eastern wood-pewee Contopus virens were found at lower densities in removal plots. Pine warbler Dendroica pinus and indigo bunting Passerina cyanea were found at similar densities and summer tanagers Piranga rubra were found at higher densities. Debris removal did not appear affect winter bird community.
A replicated, controlled before-and-after study in riparian forest along the Middle Rio Grande, New Mexico, USA (Smith et al. 2009), found that black-chinned hummingbird Archilochus alexandri nest survival was lower after fuel reduction treatments, including the removal of coarse woody debris from forests, but was no lower in control plots. There were, however, population increases at sites with debris removal, compared to burned or control plots. This study is discussed in detail in ‘Manually control or remove understorey and midstorey vegetation’, ‘Plant native shrubs following fuel reduction’ and ‘Use prescribed burning’.
- Lohr S.M., Gauthreaux S.A. & Kilgo J.C. (2002) Importance of coarse woody debris to avian communities in loblolly pine forests. Conservation Biology, 16, 767-777
- Smith D.M., Finch D.M. & Hawksworth D.L. (2009) Black-chinned hummingbird nest-site selection and nest survival in response to fuel reduction in a southwestern riparian forest. The Condor, 111, 641-652