Logged forests can still have ecological value if logging is not pushed too far, according to a study published in Nature. A team of researchers from Imperial College London analysed data from 127 studies to reveal a threshold for when logged rainforests lose the ability to sustain themselves. The authors believe this could widen the scope of what forests are worth conserving.
For this study, the researchers looked at data from 127 plant and animal surveys covering more than ten years in the same site in Sabah, Malaysia. The site, named the Stability of Altered Forest Ecosystems (SAFE) Project, covers a variety of landscapes, including unlogged forests, selectively logged forests, protected riverside ‘buffer’ forests, and heavily logged forests converted into oil palm plantations.
While logging always affected the forest somehow, forests losing less than 29% of biomass maintained relatively high biodiversity and ecological value and, if left alone, were likely to recover. If biomass removal was more than 29% but less than 68%, many types of plants and animals were affected, some even reaching extinction. In these areas, serious conservation efforts would be needed to recover biodiversity. For values above this, the forests rapidly lost the ability to sustain themselves and act as functioning ecosystems.
“There has been a tendency in conservation to think of pristine forests as the only ones worth investing in – that logged forests were not worth looking at,” said Professor Robert Ewers, from the Department of Life Sciences at Imperial College London. “What we’ve shown is that the potential ‘conservation estate’ is much larger than we thought, and while pristine forests are shrinking worldwide, this doesn’t mean all hope is lost, and there are other forests we can protect to preserve biodiversity.”
“Pristine forests will always be the ideal, but there shouldn’t be a binary view of what’s worth preserving and what’s not. Some degree of logging may always be necessary, and while these forests are not the same as pristine ones, at certain thresholds they can still sustain themselves as functioning ecosystems,” added Dr Will Pearse, from the Department of Life Sciences at Imperial College London.
The authors are keen to use these results in conservation projects. “Ecological thresholds are great tools that can be easily applied in conservation and management. For instance, thresholds found elsewhere have been used to decide how much area needs to be reforested or preserved,” said Dr Cristina Banks-Leite from the Department of Life Sciences at Imperial College London. “The thresholds we identified in our study can also point to where restoration projects would get the best return to investment – changes in biodiversity are faster below 30% and above 70% biomass loss, which suggests that any improvement on habitat in these areas would lead to dramatic changes in biodiversity.”
Ewers, R.M., Orme, C.D.L., Pearse, W.D. et al. Thresholds for adding degraded tropical forest to the conservation estate. Nature 631, 808–813 (2024). https://doi.org/10.1038/s41586-024-07657-w