Old-growth forests, such as those found in the H.J. Andrews Experimental Forest Long-Term Ecological Research site supported by the U.S. National Science Foundation, may offer temperature refugia for animals in a warming climate.
In the face of a warming climate, organisms may find at least temporary refuge in cooler nooks and crannies of a landscape. Previous work from the Andrews Forest, located in Oregon, found that sites with concave microtopography and old-growth forest structure tended to be cooler than other locations across the landscape. But how consistent is that effect?
If plants, animals and fungi are to find refuge in hot years, it's critical that such sites are consistent over time, researchers have found. Otherwise, organisms would need to move around the landscape to track refugia. That's where long-term undercanopy data from Andrews Forest come in.
Chris Wolf and Matt Betts of Oregon State University and their colleagues analyzed 10 years of microclimate data from 184 sites across Andrews Forest to test whether there is temporal consistency in thermal refugia. The results are published in Agricultural and Forest Meteorology. Three important findings emerged.
Cool and hot sites were remarkably consistent and predictable across the 10-year study. That's good news for organisms that aren't likely to pick up and move to track microclimates (for example, lungless salamanders, herbaceous plants, tree seedlings, mosses and lichens).
Old-growth forests played an important role in this refugia effect (on the order of 3 to 5 degrees C cooler in summer months). Finally, free-air temperature (how warm it is in the region) overwhelmed the capacity of local sites to stay cool. That is, although the coldest sites across Andrews Forest are consistently so, even these sites warm up considerably in hot years.
Overall, the scientists say, the findings have important implications. To maintain microrefugia in a rapidly changing climate, conservation of old-growth and other structurally complex forest habitat is critical, especially at sites with high elevations relative to their surroundings.
“This study demonstrates the importance of long-term, fine-scale monitoring,” says Doug Levey, a program director in NSF’s Division of Environmental Biology. “The consistently cooler temperatures in old-growth forest refugia are a big deal for many organisms.”