Deforestation can still be ecologically valuable – if you don’t overdo it

Researchers analyzed data from 127 studies to identify “thresholds” at which deforested rainforests lose their ability to sustain themselves. The findings could broaden the scope of which forests are considered “worth preserving,” but also show how much deforestation is destroying forests beyond the point of no return.

The first study of its kind, led by researchers from the Department of Life Sciences at Imperial College London with collaborators from around the world, was published in NatureThe team examined data from 127 plant and animal surveys covering a period of more than ten years at the same site in Sabah, Malaysia.

The site, called the Stability of Altered Forest Ecosystems (SAFE) Project, covers a full spectrum of landscapes, including unlogged primary forests, selectively logged forests, protected riverbank “buffer forests” and forests converted to oil palm plantations, which account for 99% of the logged forests.

Although no level of forest degradation from deforestation was too small to have an impact on the ecosystem, the results showed that forests that had lost less than 29% of their “biomass” (total weight of organic matter) retained relatively high biodiversity and ecological value and were likely to recover if left alone.

Prevent extinction

However, with biomass depletion of over 68%, many plant and animal species formed that were effectively “disrupted” by extinctions and invasive species. Serious proactive conservation would be needed in these areas to maintain biodiversity. In addition, the forests were rapidly losing their ability to sustain themselves – to function as complete, functioning ecosystems.

Lead researcher Professor Robert Ewers, from the Department of Biological Sciences at Imperial College London, said: “There is a tendency in conservation to view pristine forests as the only ones worth investing in – that logged forests are not worth it.”

“We have shown that the potential ‘nature reserve’ is much larger than we thought. And although pristine forests are shrinking worldwide, that does not mean all hope is lost. There are other forests we can protect to preserve biodiversity.”

Co-author Dr Will Pearse, from the Department of Life Sciences at Imperial College London, said: “Pristine forests will always be the ideal, but there should not be a binary view of what is worth preserving and what is not. Some level of deforestation may always be necessary, and while these forests are not the same as pristine forests, they can still sustain themselves as functioning ecosystems below certain thresholds.”

While the exact thresholds for forest destruction may vary in different environments, the study shows that they can be determined with the right data.

Professor Ewers added: “A study like this, bringing together so much data across landscapes, species and time periods to determine critical thresholds, has never been done before. We now have a framework for assessing where these points of change might be in other ecosystems.”

“This gives hope for nature conservation and gives us the means to find a way out of the extinction crisis more quickly.”

Nature worth preserving

Governments and policy makers in different countries use different metrics to assess the likelihood that deforestation will cause serious harm to local ecosystems, but these can be inaccurate because there is no universal definition of which environments can be classified as forests.

Every environment is different, but the researchers believe their findings are applicable to all tropical rainforests in Southeast Asia.

The Malaysian SAFE project survey counted the occurrence of 590 plant species (including grasses, herbs and woody plants), 88 mammal species (including bats), 161 birds, nine reptiles, 42 amphibians, 26 fish and 635 invertebrates (including 263 beetles, 199 moths and butterflies, 130 ants and 33 spiders) and noted the impact of the extent of deforestation damage for each of these species.

Co-author Dr David Orme from the Department of Life Sciences at Imperial College London said: “Of course we have long known about the impacts of deforestation on biodiversity, but it has been difficult to determine exactly when this damage is felt. This is partly because previous studies have tended to look at disparate taxa such as trees or birds, but here we were able to include much more comprehensive data from across the entire tree of life.”

Dr Pearse added: “Hundreds of hours of work have gone into this result, but it shows that it was worth it. There was a myth that certain species and organisms were only found in pristine forests, so no one looked for them in logged forests. But now that we’ve looked, we’ve found that many of these ‘ravaged’ forests are home to a surprisingly high level of biodiversity.”

Co-author Dr Cristina Banks-Leite from the Department of Life Sciences at Imperial College London said: “Ecological thresholds are great tools that are easy to apply in conservation and management. For example, thresholds established elsewhere have been used to decide how much area needs to be reforested or protected.”

“The thresholds we identified in our study can also provide insight into where restoration projects would pay off most – changes in biodiversity occur more quickly when biomass loss is below 30 percent and above 70 percent. This suggests that any improvement in habitat in these areas would lead to dramatic changes in biodiversity.”

Virtual ecosystem

The team is currently constructing a “virtual ecosystem” that will track the birth, growth, reproduction and death of organisms in a changing ecosystem. They also plan to use data from this study to create a virtual model of a Borneo rainforest.

This allows researchers to address ecological questions that cannot be answered through field observations, such as how to optimize the ecological recovery of destroyed tropical forests.