Old Growth May Help Protect Northwest Forest Birds from the Impacts of Climate Change

Recent NW CSC Oregon State University Graduate Fellow, Sarah Frey, records information during a point count at the H. J. Andrews Experimental Forest in Oregon. Inset: A black-throated gray warbler- one example of a species commonly detected. Photo by Matt —Matthew Betts, 2015

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Summer hikers in the Pacific Northwest know well how quickly temperatures can change as they walk from a parking lot into the shade of a mature forest. Within a forested habitat, the temperatures that plants and animals experience vary widely with factors like canopy cover, slope and aspect (direction that the slope is facing).
 
It turns out that some habitats can buffer the effects of global warming. Scientists recently found air temperatures in old growth forest to be a surprising 2.5 degrees cooler than in similar closed canopy plantations that were logged 60 years ago.

 “I expected to see a difference, but I was surprised by how big it actually was,” says Sarah Frey, a Northwest Climate Science Center graduate fellow at Oregon State University, and lead researcher on the project. “We compared old growth to other closed forest types rather than to clear-cuts, so we didn’t expect the difference to be so dramatic.”

Climate models predict the global temperature will increase about the same amount, 2.5 degrees, over the next 50 years.

Frey’s temperature measurements help improve on projections made by global climate models because they give a detailed picture of microclimate variations that occur on the landscape- a much more realistic picture of what temperature species actually experience than anything generated from global climate models.
 
Frey gets this detailed picture by hiking into the woods to measure temperature. Under the supervision of her advisor, Matthew Betts, Frey logs temperature at 183 sites across the HJ Andrews Experimental Forest, a National Science Foundation Long-Term Ecological Research site on the west side of Oregon's Cascade Mountains. Frey measures temperature at these sites year-round using temperature loggers that she hangs throughout the forest using fiberglass posts and pvc shields for protection. Twice annually she and her crews of 4-6 people visit the loggers to download data and change batteries as needed.
 
While in the woods the crews also do point counts to record all the birds that they see and hear at each site. Frey used this point count data to take her work a step further by investigating how microclimate influences where forest birds spend time. To her surprise, she found that about half of the species that are common at her sites prefer warmer temperatures than current averages, while the other half prefer it cooler. Hermit warblers, for example, prefer cool sites while Pacific wrens seem to like it warmer. In fact, Frey has found that, overall, differences in temperature are as good or even better predictors of where her birds spend their time than vegetation.
 
Curious as to whether temperature preferences influenced population patterns over time, Frey did a quick test using publically available data collected by citizen scientists. She used data from the annual breeding bird survey organized by Audubon and the U.S. Geological Survey to get population trends from 2002- 2012 for each of the species for which she had determined temperature preference. As expected, the cool temperature associated species were more likely to be declining.
 
Frey’s findings help natural resource managers understand better what impacts to bird populations they can expect from future climate change and also what management measures might help lessen those impacts.

Read a Science Daily story about Frey's work here.

Read her article on old growth buffering warming in ScienceAdvances here and her article about temperature predicting bird distributions here.

Lead Investigator:
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State: OR

Funding Year: FY 2013

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Topic Category: Fellows Projects, Fish & Wildlife

Science Agenda Theme: Response of Biological Systems to Climate Change

Discipline: Biology

Partners: NSF