A new study found that bird diversity increased in North Carolina mountain forest areas that were severely burned by a wildfire in 2016, reinforcing that while a wildfire can pose risks to safety and property, it can be beneficial to wildlife. The study results can help forest managers better predict bird responses to wildfires and manage forests to benefit birds.
“It’s important for us to understand the connections 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 damage 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 regions 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 a forest fire changes the vegetation structure, it has an impact on the animals that live there.”
In severely burned areas, researchers have documented loss of most of the crown trees, followed by regrowth of dense shrubs and regrowth of trees. In areas affected by severe fires, 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 happen quickly in the southeastern United States, and the vegetation grew back quickly.”
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-grade patches supported more bird species, researchers said it’s because few species avoided the high-grade patches, but several species were more abundant or only occurred in those patches. More specifically, indigo sparrows, chestnut-sided warblers, and eastern towhees—all shrub-nesting species in areas with few or no canopy trees—occurred almost exclusively in the severe burns.
“When we do low-intensity prescribed fire under an intact tree canopy, we’re not favoring 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 on breeding bird species or communities at all.”
One species, the ovenbird, showed a trend of lower abundance in severely burned areas. In contrast, 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 with the US Forest Service . “Other studies show that even mature forest birds bring their young to recently disturbed areas, where insects and fruits are abundant, to learn to forage under thick brush cover for shelter.”
Moorman said it’s likely that high-grade patches were small enough, or incomplete enough on the landscape, that it didn’t affect birds that live in the canopy or otherwise rely on 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 high-severity burns that favors shrubland bird species, but you still have the canopy present 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 managing severe wildfires in the landscape because of the obvious risks to safety and the loss of timber revenue,” Moorman said. “But there are types of timber harvesting that can create similar structural conditions to those created by high-severity wildfires.”
The study “Breeding bird abundance and diversity greatest in high-severity wildfire patches in central hardwood forests,” was published in Forest ecology and management. Co-authors were 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; the National Science Foundation’s 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); Nature Conservation Society; and the US Forest Service North Carolina Supervisor’s Office.