Snag for wildlife a good thing

By Ashley M. Long

Louisiana’s forests cover more than 50 percent of land and 99 percent of forested land is used for timber production, an industry that supports nearly 20,000 jobs and adds more than $12 billion to the state’s economy each year.

Beyond the direct financial benefits, Louisiana’s forests help maintain water, air and soil quality; support biodiversity; provide opportunities for outdoor recreation; prevent erosion; and store carbon, among many others. Our state’s trees also represent a source of pride, and they symbolize a legacy we hope our children will value for generations to come.

Given the importance of trees to our economy, environment and culture, it can be challenging to view dead and dying trees as more than a painful loss, nuisance or sign of an unkempt forest. However, a closer look reveals that decay may actually be the foundation on which all healthy forests reside, especially for the fish and wildlife that call Louisiana home. Can retaining snags, woody debris, and downed logs really benefit our forests, and the animals that live there, as management recommendations suggest?

To answer this question, we must first identify the species that depend on dead wood for protective cover, nesting sites, roosting sites and food. Perhaps the most visible wildlife that use dead and decaying trees are woodpeckers, but songbirds like titmice, bluebirds, wrens, chickadees and nuthatches also use these features for foraging. In addition, songbirds use cavities excavated by woodpeckers for nesting, as do wood ducks, kestrels and many others. Interestingly, primary and secondary cavity nesters tend to have shorter incubation periods relative to other birds, which researchers suggest may be possible due to the warmer temperatures inside their well-insulated nests. Beyond the bole, smaller birds use branches of dead and dying trees to keep an eye out for predators, while larger birds, like raptors and owls, use the branches to locate potential prey.

Bats, snakes, squirrels, salamanders, raccoons, among others also utilize dead and decaying trees throughout the year.

For example, squirrels build dens and nests called “dreys” in or on dead trees to stay warm in winter and raise their young in spring, and some bat species use different tree cavities as bachelor pads, maternity roosts and hibernacula.

In addition, dead wood in streams, creeks and rivers provide food, cover, and breeding sites for fish and aquatic invertebrates, which are important natural resources in their own right, and serve as food for other wildlife.

The decay process itself breaks down organic materials, which enrich our soils and support the growth of plants and fungi that wildlife, including white-tailed deer and wild turkey, depend on to survive and reproduce.

The insects that use dead and decaying wood are especially important for nutrient cycling, but also represent an important food resource for many wildlife species associated with forests. A woodpecker or a songbird may search for insects under flaking or peeling bark and in moist crevices created by rotting wood. In addition, omnivorous species like squirrels and opossums consume large numbers of insects and insect larvae, and species like armadillos and frogs rely almost exclusively on insect prey. Ants, beetles, caterpillars and earthworms — you name it — these invertebrates are key to successful wildlife populations in Louisiana’s forests.

Given how closely all wildlife are linked, managing our landscapes for biodiversity, including retention of snags, woody debris and downed logs, will inevitably help support all wildlife in our forests. In turn, foresters benefit from having these animals utilize our trees.

For example, insects are important pollinators; they carry seeds from one location to another, which assists with germination; and they can help improve soil quality.

Because so many species that depend on snags for protective cover and nesting are insectivorous, the wildlife that use dead and decaying trees can help control unwanted insect pests. By providing protective cover and food from associated plants, downed wood can also benefit game species that provide recreational opportunities for hunters and represent potential income for forest landowners. In addition, snags, woody debris, and downed logs provide cover and foraging opportunities for the scavengers and predators that remove carrion from the land and help keep our wildlife populations in check.

Beyond the immediate benefits, having a structurally diverse forest ecosystem, which includes dead trees and downed wood, can result in higher property values, provide added income through enrollment in conservation programs and protect species from becoming rare, thus reducing the need for regulatory constraints. The best way to maintain these features is to leave naturally occurring snags and downed wood alone, unless they pose a risk to personal safety or property. If they aren’t currently being used by wildlife, they could be in the future, and if they are being used, maintaining them can prevent wildlife from moving to less desirable locations.

Many suggest retaining at least three to five snags per acre, but more important than numbers, try to keep a range of sizes, species and decay stages, and ensure that they are located along both edges and the interior of forests, as these areas support different wildlife.

Larger snags are particularly valuable, as they will last longer — some wildlife use the same snags over a period of years or generations, and large snags can provide greater varieties of temperatures for roosting and nesting species. In addition, larger dead trees with shredding bark can provide protective habitat for bats, butterflies, lizards and more. However, for the reasons described above, almost any snag or downed tree will provide habitat for something, so work with what you’ve got.

When a property has few natural snags, leaving live trees with poor form and low economic value can provide future snags. It also is possible to create artificial snags by trimming branches or girdling a few trees. In addition, creating small canopy gaps can provide snags, woody debris and downed logs while improving habitat conditions for game species. Management techniques that reduce woody growth in the understory (e.g. herbicides, prescribed fire) and encourage native plant regeneration also can increase the density of snags and downed wood in forests. Finally, consider installing nesting boxes, artificial bat roosts, or other wildlife structures to provide supplemental habitat for species that utilize snags during some portion of their life cycle.

In combination with other best forestry management practices, retention of snags and downed wood on the landscape can help keep Louisiana’s forests healthy and productive for years to come.

Dr. Long is an Assistant Professor of Wildlife Ecology at Louisiana State University’s School of Renewable Natural Resources. You can contact her by email at amlong@agcenter.lsu.edu or phone at 225-578-4940.