Can plants and animals keep pace with changing climates and habitats?
As climates change, many animals and plants will have to shift their geographical ranges to find suitable living conditions — and in some cases these shifts will have to happen phenomenally quickly. “You can think of it as a kind of sprinting capacity that these plants and animals need if they're going to stay in the climate zone that they're in now,” says Christopher Field, a global ecologist at the Carnegie Institution for Science in Stanford, California. Field, together with postdoc Scott Loarie, also at the Carnegie Institution, and their colleagues have calculated the speed at which climate could change across various landscapes — and how quickly animals would have to move to keep pace.
Loarie first became interested in understanding how climate change might affect species movement as an undergraduate, when he worked at Stanford's Jasper Ridge Biological Preserve with Field and co-author David Ackerly, an ecologist at the University of California, Berkeley. Jasper Ridge provided a model area for climate studies owing to its abundance of diverse, hilly terrain and north- and south-facing slopes, which create complex temperature and precipitation patterns. In particular, it revealed the importance of taking topography into account when making projections.
Until recently, climate data were not sufficiently detailed to quantify the influence of topography on climate change. Taking advantage of finer-scale data, Loarie, Field and their colleagues combined the WorldClim data set, which models current climate globally at 1-kilometre resolution, with climate-change projections from 16 climate models and three potential greenhouse-gas emissions scenarios. In this way, they were able to estimate how quickly climate could change across landscapes at fine scales.
They found that in mountainous regions, which are characterized by heterogeneous terrain, plants and animals don't have to move far to encounter different climates. On a mountain slope, a species might need to move less than one kilometre upwards to encounter a change of several degrees Celsius, says Loarie. By contrast, in more homogeneous regions such as deserts or tropical-forest basins, where the terrain and climate are more uniform, species must travel greater distances to encounter an appreciable difference in climate. “In certain places, like the Central Valley of California, species might have to travel hundreds of kilometres this century to reach the climate zone that they're in now,” says Loarie.
“Species might have to move up to ten times faster to keep pace with future changes in climate.”
Once they had calculated projected velocities required for animals and plants to keep pace with climate change in different scenarios, the authors compared their calculations with changes that plants, animals and ecosystems have undergone in the past. By the end of the last Ice Age, some 12,000 years ago, northward tree migration may have been as fast as one kilometre per year. Across much of the globe, these speeds are comparable with the velocities of climate change calculated by Loarie, which average almost 0.5 kilometres per year in moderate emissions scenarios (see page 1052). But for about 30% of Earth, including homogeneous areas such as deserts and the Amazon Basin, species might have to move up to ten times faster to keep pace with future changes in climate, says Loarie.
The researchers applied their projections globally, including the locations and areas of global preserves. They found that in all but 8% of the world's protected areas, species will be forced out of reserves by shifting temperatures within a century. The authors conclude that by designing reserves that encompass more heterogeneous landscapes — such as mountainous regions with hills and valleys that provide a diversity of climate regimes — and larger, more connected reserves that contain more plants and animals, species might stand a better chance of keeping pace with changing climate. Efforts are already underway in northern California, where Ackerly has been working with state parks and regional and local agencies to devise conservation strategies that facilitate species movement for adaptation to climate change.
Elsewhere, co-author Greg Asner, an ecologist at the Carnegie Institution, is helping the United Nations to enable countries to monitor deforestation in order to combat climate change. “Most tropical species will be better able to move through and persist in continuous forest than through fragments of forest in a sea of soy and cattle pasture,” says Loarie.