Tropical montane rain forests sensitive to temperature increase
An increase in temperature usually stimulates photosynthesis and growth for plants at our latitudes. However, in areas that are already warm, where seasonal changes in temperature are small or non-existent, warming can instead have a negative effect on plants.
"Tropical species have adapted to a stable climate with small variations in temperature, both over the course of a year and between different years. This is why there is concern that such species will not be able to adapt to rising temperatures," says Johan Uddling, senior lecturer at the Department of Biological and Environmental Sciences at the University of Gothenburg.
Although tropical rain forests are the world's most productive and species-rich type of ecosystem, at present there is great uncertainty about how they are affected by climate change.
Rwanda's montane rain forests particularly vulnerable
Johan Uddling, Angelica Vårhammar and Göran Wallin and their colleagues at the University of Gothenburg and the University of Rwanda have studied the temperature sensitivity of tropical tree species in Rwanda. Rwanda is called "the land of a thousand hills" and the forest Nyungwe at 1,600-3,000 metres above sea level is Africa's largest remaining montane rain forest.
Rwanda is located in the "Albertine rift", an area with an immense diversity of species, many of which are tied to this particular area. Global warming is a particularly serious threat to the species that currently grow at high altitudes because in many areas, there is nowhere higher up where they can move to when temperatures rise.
High-altitude species extremely sensitive to temperature
In order to study species in montane rain forest and their ability to adapt to a warmer climate, the researchers studied the species when they were cultivated at a lower altitude where the temperature was about five degrees higher. It became apparent that the plants were very sensitive to high temperature:
"Species from the montane rain forest had a drastic drop in photosynthesis when they grew at a lower altitude. The negative effect was partly purely biological and partly a result of these species not being good at cooling themselves down by transpiring water," says Johan Uddling.
In the middle of the day, the optimal temperature for photosynthesis for these montane rain forest species was exceeded by about ten degrees, while the transcendence was considerably less for the species from lower altitudes that were also part of the study.
Consequences for productivity and biodiversity?
Johan Uddling and Göran Wallin are now going to study, together with colleagues from the University of Rwanda, what consequences the various species of trees' differences in sensitivity to temperature have for productivity and composition of species in the montane rain forests of Rwanda in the future. By using a natural height gradient as a type of laboratory, the researchers can investigate how different species and the competition between them are affected by a warmer climate, that is to say, one step further down the gradient.
"The question then is whether certain species will be pushed aside by others and what consequences that will have for the forests' productivity and biodiversity. "This is something we hope to investigate further in future studies," says Johan Uddling.
Johan Uddling, Senior Lecturer, Department of Biological and Environmental Sciences, University of Gothenburg
Tel: 031-786 3757, mobile: 073-8267104
E-mail: johan.uddling [at] bioenv.gu.se
Photographs: Göran Wallin