Large-scale monoculture plantations have devastated tropical forests worldwide, but a recent study finds that creating islands of native trees can be a way to restore biodiversity on degraded lands.
The Indonesian island of Sumatra is one of the most biodiverse regions in the world. However, the demand for palm oil has led to rapid deforestation for monoculture plantations, leading to a tremendous loss of biodiversity. In the recent study, an international team of researchers wanted to see if creating tree islands, or strategically planting patches of just a few native species within degraded or agricultural lands, can help restore native woody plant diversity.
Researchers cleared 40% of the existing oil palm trees for each of their 52 experimental plots. They then planted between zero and six native tree species on each of their tree islands. They also kept four control plots with oil palms standing. The tree islands vary in area from 25-1,600 square meters (269-17,222 square feet).
Six years after their establishment, the researchers found that the tree islands were home to an additional 2,788 woody plants of 58 different species from 28 families. While most of the plants typically thrive in open habitats, including secondary forests that regrow after a disturbance like agriculture, one-third of the species were associated with tropical forests. Roughly 20% of the plants were endemic and 10% were non-native. The diversity of trees in the islands was also higher than in the rest of the oil palm plantation but still far lower than in undisturbed forest, highlighting the critical conservation value of standing forests.
Furthermore, large tree islands, greater than 400 m2 (4,300 ft2), hosted 94% of the native tree species found in the study and all of the endemic species. In contrast, small tree islands hosted just 45% of native species and a quarter of the endemic species.
Previously, the researchers had found that the tree islands had greater diversity of several groups of animals, including birds and bats. Large tree islands likely provide better habitat for such animal seed dispersers, the authors write. Geographically large tree islands can also create a more stable microclimate, while more leaf litter improves soil conditions; both make it easier for new trees to get established.
In the previous study, the researchers found that tree islands didn’t reduce yields of oil palm. Palms near tree islands actually had improved yields, which made up for trees that were removed.
“This is a landmark study,” Robin Chazdon, a tropical ecologist with the University of Connecticut, U.S., who wasn’t involved in the study, told Mongabay by email.
“The outcome is a hopeful message that it is possible to provide islands of hope for native vegetation within landscapes dominated by large-scale oil palm plantations,” she added.
Banner image: Habitat loss for oil palm is driving orangutans toward extinction. Image by Marc Veraart via Flickr (CC BY-ND 2.0).
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