Plants moving downhill in response to climate change
Higher temperatures are forcing species to take to cooler climes at higher elevations, the prevailing wisdom goes. But changes in precipitation also drive change, and in the case of plant species in the Northern Hemisphere, the movement may be driven downhill, not up.
That’s according to a recent study published in the journal Science by a team of researchers led by Shawn Crimmins at the Department of Forest Management, at the University of Montana. The study looked at the distribution of 64 plant species by altitude since the 1930s in California and found a “significant downward shift in species’ optimum elevations” due to wetter conditions, even when temperatures had gone up in those areas.
They studied areas encompassing about half the state, including most of the mountain ranges in northern California, where temperatures have shot up more than 1 degree Fahrenheit during the study period and the “water deficit” has declined by almost 4 inches.
The researchers say that the assumption that temperature is the driving force in climate change ignores the fact that water availability and energy are also determining factors.
The authors write that the plant species seem to be tracking their “climatic niche” downhill with increased water availability, rather than changes in temperature.
The implications are important to understanding regional differences in climate change impacts. Global climate models predict that areas north of 45 degree latitude have had increased precipitation over the last century, a trend that’s expected to continue. That means species may be moving into unexpected areas, where water, rather than temperature, may increase their growth and distribution.