The tropics are home to the richest terrestrial diversity on the planet. They are also one of the most threatened biomes, with the highest rate of land conversion to agriculture and existing at the forefront of climate change. With many species in the tropics already living at their thermal maximums, climate change means they will be forced to move elsewhere to find suitable habitat.
Where will the suitable habitat be, and what routes will be available to get there? A recent study that looked at climate connectivity in the United States found that only 41% of natural areas in the country are connected enough for species to be able to track changes in climate. Now a new study has expanded these methods, and applied them to the tropics across the globe.
Using high-resolution maps of forest cover and current and projected annual temperatures, the analysis of both past a current climate connectivity shows striking results. On average, if species shifted their ranges as far as possible under current forest cover, they would still experience almost 1˚C of warming under the least severe climate warming scenario and 2.6˚ C warming under the most severe scenario. While average climate connectivity varies by region, this still means that the average tropical forest is not well connected enough for species to avoid at least some degree of climate change.
In addition, 62% of tropical forest – around 10 million km2 – showed no climate connectivity, meaning that it is incapable of supporting range shifts. This is similar to the study of the United States that showed 59% of natural areas with no climate connectivity. Climate connectivity was lowest in regions that have the greatest loss of lowland rainforests, such as Indochina, Brazilian Atlantic forest, and West Africa.
In comparing the change in forest cover over 12 years (2000-2012), 27% of tropical forest area lost climate connectivity while 10% gained it. The largest losses of connectivity over that time were in the Indomalaya region. As forest loss increased, connectivity declined more rapidly.
Although maintaining corridors is not the solution for every species and every region, it can be a strong tool in ensuring climate connectivity. Limiting forest loss, concentrating loss in certain areas, and restoring corridors are all useful methods for protecting tropical forests for the future. Keeping patches connected, particularly along climate gradients, will be key to making sure that numerous species are able to adapt to increasing temperatures and shifting habitats.
Senior, R.A., Hill, J.K. and Edwards, D.P. 2019. Global loss of climate connectivity in tropical forests. Nature Climate Change. DOI: 10.1038/s41558-019-0529-2.