In tropical forests, companies extract timber by selective logging: only taking a few trees from every hectare, leaving the rest of the forest standing. Even though selective logging is a less dramatic change than removing the forest entirely, it still often changes the forest too much for biodiversity to survive. But how much is too much? Sometimes, selective logging in tropical forests can lead to an increases in biodiversity, but other times it has disastrous effects on the fauna. Because there are about as many studies showing a positive impact as those showing a negative impact, reviews that simply calculated an overall effect size found that, on average, logging is benign for biodiversity. We wanted to understand these seemingly controversial case studies and find out what it is about logging that can cause both types of responses. Through a pan-tropical meta-analysis, we found that logging intensity is the most important predictor of species loss. Whereas low logging intensities are relatively benign and cause a local increase in biodiversity, high logging intensities can lead up to 50% species loss. Based on these results, we recommended logging intensity thresholds to maintain tropical forest biodiversity above critical levels.
Logging intensity thresholds to maintain tropical biodiversity.