In the past decades, large areas of forest in Sumatra, Indonesia have been replaced by cash crops like oil palm plantations and rubber. Now a team of scientists led by the University of Göttingen, Germany, have found out that these changes in land use increase temperatures in the region. The added warming could affect plants and animals and make parts of the country more vulnerable to wildfires. The results are reported in the European Geosciences Union journal Biogeosciences.
Palm oil is the most widely used vegetable oil in the world. Indonesia, the world’s largest producer of palm oil, has seen large swathes of rainforest cleared away and replaced by oil palm plantations. The island of Sumatra has had the highest loss of native rainforest in all of Indonesia. In the framework of the University of Göttingen’s Collaborative Research Centre “Ecological and Socioeconomic Functions of Tropical Lowland Rainforest Transformation Systems (Sumatra, Indonesia)”, the research team, led by Clifton Sabajo and Alexander Knohl, have established that the expansion of oil palm and other cash crops in Sumatra has made the region warmer. “Not only does the land use change impact biodiversity and stored carbon, it also has a surface warming effect, adding to climate change,” says Knohl, a professor in bioclimatology.
The team studied differences in surface temperature for various types of land cover, such as forests, clear-cut land, and cash crops, in the Jambi province of Sumatra. They used satellite data collected between 2000 and 2015 as well as data collected on the ground. They found that clear-cut land was up to ten degrees Celsius warmer than forests. “Clear-cut land is the phase after the forest has been cleared away and before the start of commercial plantations or farming,” says Sabajo, a PhD student and the lead author of the study.
Mature palm oil plantations were about 0.8 degrees Celsius warmer than forests, while young palm oil plantations were six degrees Celsius warmer. “Young palm oil plantations have fewer and smaller leaves and an open canopy, thus they transpire less water. Also, the soil receives more solar radiation and dries out faster,” explains Sabajo. Mature palm oil plantations, which are older than five years, have a closed canopy and larger and more abundant leaves, which results in a cooler ground compared to a young plantation. The team found the coldest surface temperatures in forests, which results mainly from evaporative cooling.
Overall, the average mid-morning surface temperature in Jambi province, Sumatra, increased by 1.05 degrees Celsius between 2000 and 2015, the experts say. Some of this warming is a result of climate change, but some is a direct consequence of the changes in land use. “We compared the average land-surface temperature increase in the province with a site that was covered by forest over the entire period and that can be considered as a control area that is unaffected by direct land-use change. The land-surface temperature of the forest sites in-creased by only 0.45 degrees Celsius, suggesting that at least 0.6 degrees Celsius of the 1.05 degrees Celsius increase is due to land-use change,” says Knohl.
To the scientists, the strong warming effect in Jambi province may serve as an indication of future changes in land-surface temperature for other regions of Indonesia that will undergo land transformations towards oil palm plantations. “Land surface temperature is an important part of the microclimate, which shapes habitat conditions for plants and animals,” says Knohl. “The observed warming may affect ecosystems in many ways. Current land-use developments in Indonesia need to carefully evaluate and consider all aspects of environmental and socio-economic consequences.”
(University of Göttingen/wi)
Sabajo, C. R., le Maire, G., June, T., Meijide, A., Roupsard, O., and Knohl, A.: Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia, Biogeosciences, 14, 4619–4635, https://doi.org/10.5194/bg-14-4619-2017, 2017