Climate change pushing tropical trees upslope 'exactly as predicted'
Tropical tree communities are moving up mountainsides to cooler habitats as temperatures rise, a new study in Global Change Biology has found. By examining the tree species present in ten one-hectare plots at various intervals over a decade, researchers found that the proportion of lowland species increased in the plots at higher elevations. The study, which was undertaken in Volcan Barva, Costa Rica, adds to a growing body of evidence that climate change is having an impact on species range distributions.
As climate change leads to warmer temperatures, species must respond if they are to survive. One way to do this is to migrate to new habitats that become suitable (and away from old ones that become unsuitable); another way is to adapt to hotter temperatures, but the speed of climate change may be too fast for some species to evolve to keep up. In some cases, if their physiology permits it, species may be capable of tolerating increases in temperature, but the likelihood of this is unknown.
The researchers first turned to herbarium records to calculate the preferred temperature of thousands of tree species, by looking at the geographic location of sampling locations and the temperature ranges they encompassed. With the temperature preferences for each species known, it was then possible to calculate a 'community temperature score' for each of the ten study plots, by averaging the preferred temperatures of all species present. A high community temperature score indicated an abundance of species found in the hot lowlands, whereas a low community temperature score reflected the presence of high altitude species from cooler habitats.
Plots were monitored over the course of a decade, and in nine of the ten plots the community temperature score increased. This indicates a shift in species composition, with the relative abundance of lowland species increasing over time "exactly as predicted under climate-driven upward species migrations," Kenneth Feeley, lead author of the study with Florida International University and Fairchild Tropical Botanic Garden, told mongabay.com.
These changes corresponded to a mean thermal migration rate of 0.0065Â°C per year. However, over the past 60 years regional warming has been 0.0167Â°C per year, so the average migration rate observed across plots is not fast enough to keep up with the rate of warming. Still, encouragingly, when looked at individually, migration in 4 of the 10 plots did keep pace with regional warming.
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Tropical trees image via Shutterstock.