Can leaving trees behind during harvest help forest biodiversity?

Details

Industrial forestry typically simplifies forest structure and changes species composition. Leaving some trees at harvest was introduced about 25 years ago to reduce biodiversity impacts, mainly those of clearcutting, and is now widely practiced in boreal and temperate regions. Although many studies had examined flora and fauna responses, no comprehensive review had compared its biodiversity effects with both clearcuts and unharvested forests.

Using a systematic review protocol, researchers conducted a meta-analysis of 78 studies containing 944 comparisons of biodiversity between retention cuts and either clearcuts or unharvested forests. Their main aim was to assess whether retention forestry moderates the negative effects of clearcutting on flora and fauna, at least in the short term.

Compared with clearcuts, retention cuts supported higher richness and abundance of forest species. Compared with unharvested forests, they supported higher richness and abundance of open-habitat species. When forest, open-habitat, generalist and unclassified species were considered together, species richness was higher in retention cuts than in clearcuts.

Retention cuts negatively affected some species compared with unharvested forests, suggesting that certain forest-interior species may not survive in them. They were also less suitable than clearcuts for some open-habitat species.

The positive effects of retention cuts on forest-species richness increased with the proportion of trees retained and time since harvest. There were not enough data to analyse possible thresholds at which biodiversity effects diminish. Whether retained trees were aggregated or dispersed had no detected effect on forest or open-habitat species, although limited data may have hindered detection of responses. Results across comparisons were largely consistent among taxonomic groups for forest and open-habitat species, respectively.

Synthesis and applications: The authors concluded that the meta-analysis supports wider use of retention forestry because it moderates negative harvesting impacts on biodiversity. They considered it a promising way to integrate biodiversity conservation with production forestry, while noting that finding optimal solutions between these goals may need further attention. Retention forestry will not replace conservation actions for certain highly specialized species associated with forest-interior or open-habitat conditions.