A new study found that bird diversity increased in North Carolina mountain forest areas severely burned by wildfire in 2016, reinforcing that while wildfires can pose a risk to safety and property, they can be beneficial to wildlife. The study results can help forest managers better predict the birds’ reactions to forest fires, and manage forests for the benefit of birds.
“It’s important for us to understand the relationship between animals and wildfire dynamics as the climate changes because predictions show more of these high-severity wildfires across the landscape in the future,” said study co-author Chris Moorman, professor of forestry and environmental resources at North Carolina State University.
Wildfires burned more than 235 square kilometers of forest in the southern Appalachians in the fall of 2016, following a period of dry conditions and arson. In the study published in the journal Forest ecology and managementresearchers tracked different levels of burn severity in three forest regions in the Nantahala National Forest in western North Carolina.
Researchers counted the abundance and diversity of birds during the breeding season in these forest areas over five years. They used this data to compare bird communities in patches burned to different degrees of severity.
“Birds and other animals are well known to respond to forest vegetation structure, which is the distribution of plants vertically in a forest,” Moorman said. “When forest fire changes the vegetation structure, it affects the animals that live there.”
In heavily burned areas, researchers documented the loss of most of the crown trees, followed by the regrowth of dense shrubs and the regrowth of trees. In areas affected by high-severity fire, 44% of trees died in the first year, and 71% had died by the fifth year. That compared to 7% tree mortality in unburned areas.
“After the severe wildfires, everything was brown and black and seemed dead,” Moorman said. “But changes are happening quickly in the southeastern United States, and vegetation quickly grew back.”
When they compared the number of birds in areas with different fire severity, they found an increase over time in the number of birds, as well as greater bird diversity, in forest areas where the forest fires were high. By the fifth year, total bird abundance and species richness, or the number of different species present, in severely burned areas was twice that of unburned areas.
Although it seems counterintuitive that high-severity patches supported more bird species, researchers said it’s because few species avoided the severe patches, but more species were more abundant or occurred only in those patches. More specifically, indigo sparrows, chestnut-sided warblers, and eastern towhee—all shrub-nesting species in areas with few or no canopy trees—occurred almost exclusively in the severe fire patches.
“When we do low-intensity prescribed fire under an intact tree canopy, we’re not benefiting these bird species that prefer to nest in shrubland,” Moorman said. “In fact, low-severity burns—whether by wildfire or prescribed fire—have little effect at all on nesting bird species or communities.”
One species, the ovenbird, showed a trend of lower abundance in heavily burned areas. However, the abundance of seven species was greatest in areas of higher severity, and 11 species did not differ between areas.
“I think many of the forest birds are not as special as the literature may have previously suggested, as long as there is some vertical structure — like some live trees or standing snags — and cover,” said the study’s lead author Cathryn Greenberg, a research ecologist at the US Forest Service. “Other studies show that even mature forest birds bring their young into recently disturbed areas, where insects and fruits are abundant, to learn how to forage under thick shrub cover for protection.”
Moorman said it’s likely that high-severity patches were small enough, or incomplete enough in the landscape, that it didn’t affect birds that live in the canopy or otherwise depend on the canopy trees.
“Most of the western NC landscape contains continuous closed-canopy forest, so you get this new structural condition associated with canopy removal from fires that benefits shrubland bird species, but you still have the canopy nearby for other birds,” Moorman said.
Researchers said the findings have implications for managing forests to promote bird diversity.
“It is not a practical or logical approach to deal with tall wildfires in the landscape because of the obvious risk to safety and loss of timber revenue,” Moorman said. “But there are types of timber harvesting that can create similar structural conditions to those created by high-altitude wildfires.”
The study “Breeding of bird abundance and diversity greatest in high-severity wildfires in central deciduous forests,” was published in Forest ecology and management. Co-authors included Katherine J. Elliott, Katherine Martin, Mark Hopey and Peter Caldwell. The study was funded by the USDA Forest Service Coweeta Hydrologic Laboratory Southern Research Station; Nantahala Ranger District Southern Region 8; Washington Office Water Resources Program; National Science Foundation Long-Term Ecological Research Program (award #DEB-0823293); USDA Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Program, Agro-Ecosystem Management (award #2017-67019-26544); The Nature Conservancy; and the US Forest Service North Carolina Supervisor’s Office.