Warblers out of the Woods: Savanna Restoration Creates Bird Habitat
Roach, M. C., Thompson, F. R., & Jones-Farrand, T. (2019). Effects of pine-oak woodland restoration on breeding bird densities in the Ozark-Ouachita Interior Highlands. Forest Ecology and Management, 437 (September 2018), 443–459. https://doi.org/10.1016/j.foreco.2018.12.057
Down in the Ozarks and Ouachita Highlands of the Midwest, dense forests give way to remnants of woodlands and savannas. With a little help from land managers, these fragments are being protected and restored to have a greater range and diversity of plants and animals. But all management actions that change the land favor some species over others. How is this restoration effort affecting birds? Researchers from the Missouri Department of Fish and Wildlife and the University of Missouri looked for answers.
Fires, insect outbreaks, and windstorms disturb the ecosystem– but disturbance isn’t always a bad thing. Disturbances can change the character of the landscape; for example, it could clear out the vegetation on the forest floor, make more standing dead trees known as snags, or favor more fire-resistant tree species, such as pines. These disturbances destroy the homes of some species while creating homes for others. It is because of natural disturbances that savannas, areas covered <30% by tree canopies, and woodlands, areas from 30-90% canopy cover, exist.
However, people have changed these natural patterns of disturbance, for example, by eliminating some natural forest fires. With less frequent or less intense natural disturbances, savannas and woodlands are being edged out by the dense forest––and species that are adapted to the disturbed environment are affected.
Restoration efforts have tried to reverse this, by introducing some disturbances such as controlled burns and tree-thinning. With restored savannas and woodlands comes a diversity of the species that thrive in those habitats.
New Place to Nest
Different bird species like to live in different kinds of places. Some, such as the ovenbird, live their lives
comfortably in a dense canopy. Others, such as the prairie warbler, require ample shrubs to nest in. Still others prefer a nice view of the sky, living in woodlands with an open canopy, like the blue-winged warbler. Knowing this, the researchers wanted to see how different bird species were responding to their new homes from the disturbance regime.
They predicted that, following disturbance that resulted in thinning of forests, bird species that prefer open canopy would increase in numbers, whereas bird species that prefer dense canopy would decrease in numbers
Their 3-year study looked at 352 survey locations that followed different restoration management efforts. They took bird surveys each year and measured the change in vegetation at each site. Finally, they created a computer model to find the relationship between vegetation change and bird species.
What they found supported their initial hypotheses: 10 species, all of which were birds that depended on disturbance, increased with the restored habitat. These species benefit from the open canopy and the lush vegetation that grows beneath it.
Species that prefer the dense canopy were negatively affected by the restoration efforts. However, as the dense forest is still prevalent in nearby areas, these species were found abundantly there.
These results mean that restoring savannas and woodlands, while maintaining some dense forest, creates habitat and breeding ground for diverse groups of birds–– and many of these birds are of concern for conservation. It also underscores the importance of habitat. Changing one aspect of the ecosystem, such as forest cover, can have huge impacts on plants and birds, but also on other diverse aspects of the environment. This study highlights how different management actions impact the ecosystem– and for these birds, things are looking up.