How do damaged tropical forests become vital ecosystems again? Should you rely on nature’s ability to regenerate or is it worth actively supporting it? A long-term study on Borneo now shows that the forests can build up more biomass much faster and if meaningful measures for renaturation are carried out.
Tropical rainforests are dwindling all over the world – the development in Southeast Asia is particularly dramatic: some areas are being completely cleared, others are severely damaged by selective logging. But a rethinking is also emerging – efforts are being made to protect forests or to restore them to their former state. So far, however, it has been assumed that severely damaged tropical forests will only recover very slowly from the interventions. In addition, it seemed unclear to what extent it makes sense to intervene to support the renaturation or to allow natural development to take its course.
Support or leave to nature?
As an international team of researchers are now reporting, their study now provides new information on these aspects. The results are based on studies of a tropical forest in Sabah in the Malaysian part of the island of Borneo. The forest was largely cleared in the 1980s, but then protected from further deforestation or conversion into agricultural land. The research is based on work that began 25 years ago in this area, the scientists report. The long-term study focused on how well the forest can rebuild aboveground biomass using two different strategies. Some parts of the study area were left to their own devices, in others, however, planting and maintenance measures were carried out, which could have a positive effect on regeneration development.
As the researchers report, the results of the long-term study now show that areas that were left for natural regeneration were able to gain around 2.9 tons of carbon in the aboveground biomass per year and hectare. “This basically confirms that damaged forests can recover if they are effectively protected,” says first author Christopher Philipson from the Swiss Federal Institute of Technology in Zurich. But much more important is the knowledge that forest areas in which few simple measures were carried out could regenerate much faster than the areas that were left to natural regeneration. Specifically, this means: per year and hectare, reforested forests build up to 4.4 tons of carbon in aboveground biomass, the scientists report.
Measures show clear effects
As they explain, the measures taken in the study areas of Sabah included planting tree saplings and maintenance measures such as cutting lianas. These plants thrive particularly well in damaged forests and therefore compete with the growing trees. As a further measure, the forest conservationists also weeded other overgrown plants and preferred to plant valuable native tree species. With the latter, they tried to promote those trees in the damaged forests that were particularly severely reduced by the timber industry.
It is important to reforest a diverse forest, emphasize the researchers. Great attention was paid to this in the measures in the test areas. “The restoration of forests, especially in heavily deforested lowland forests, is essential to preserve biodiversity and ecosystem services, as well as to capture carbon from the air,” says Philipson. This makes a contribution to the fight against the loss of biodiversity and also against climate change.
Against the background of the success of the measures to actively restore the damaged tropical forests, investments in corresponding projects now appear sensible. The problem so far, however, is that the current price for carbon in emissions trading does not cover the costs of reforestation. “As a result, restoration as a means of containing climate change is currently limited,” says co-author Mark Cutler of ETH Zurich. “We have to find sustainable funding mechanisms for this,” the scientist concludes.
Source: ETH Zurich, specialist article: Science doi: 10.1126 / science.aay4490