Can harvesting trees improve habitat for birds?

Red headed woodpecker (Melanerpes erythrocephalus).

Overview
In a new study, scientists look at the effects of wildlife-friendly silviculture on birds in the bottomland hardwood forests of Louisiana. Wildlife forestry tries to balance economic and conservation objectives by clearing small patch cuts and preserving large live trees and woody debris. The goal is to mimic natural disturbance and maintain structural heterogeneity in the forest canopy thereby benefiting birds and other species while at the same time harvesting wood of economic value.

The researchers found that creating patch cuts and thinning trees seems to improve the habitat for a number of birds compared to untreated forest. This study is particularly timely. While recent rates of bottomland hardwood forest loss have slowed, resident songbird populations continue to decline. It is unclear what role different types of forestry practices are playing in the population loss.

Methods
The study examined wildlife-forestry practices at Tensas River National Wildlife Refuge in northeast Louisiana. Researchers set out to answer two questions: 1) how do species respond to wildlife-forestry treatments and 2) how does this response change over time.

The researchers conducted bird surveys in three types of forest stands: a) nine stands which had not undergone any silvicultural treatment; b) five stands which had undergone thinning and patch cuts, and c) nine stands which had just undergone thinning.  They calculated Avian Conservation Scores (ACS) for the stands based on the species present. They looked at how avian response to the treatments changed over time, by selecting stands of different treatment age for their sample.

Findings
Overall, mean ACS scores were higher in both treated stands, indicating these forested areas provide more viable habitat for songbirds than reference sites. Nine species responded positively to the treated versus the untreated stands. Notably, six of the nine species are listed as Partners In Flight birds of concern. Three out of the nine bird species (Orchard oriole, Red-headed woodpecker, and Yellow-breasted chat) were rarely detected in any of the untreated, control stands. Meanwhile four species responded negatively to the treated stands.

Implications for conservation
According to the researchers, these results provide evidence that wildlife-forestry can enhance the density of birds, including certain species of conservation concern. The most interesting aspect of this study, though, are the findings of how the birds responded to the treatments over time. For those species that benefited, most saw population increases within five to eight years after silvicultural treatment, before decreasing to pre-treatment numbers within twelve to thirteen years. However, not all species responded the same way. These findings are particularly valuable because they allow the researchers to give very specific recommendations to managers on the ideal time-intervals between implementing treatments depending on the birds being targeted for conservation.

--Reviewed by Evyan Borgnis

Twedt, D., & Somershoe, S. (2009). Bird Response to Prescribed Silvicultural Treatments in Bottomland Hardwood Forests Journal of Wildlife Management DOI: 10.2193/2008-441

Comments

[Danny]

What a concise and well crafted review. I found it both informative and interesting.