City of San Antonio Parks and Recreation Department’s Nature Preserve Officer Wendy Leonard wrote this piece.
SNAGS = STANDING DEAD TREES
The saying “home is where the heart is” has never been more true than its meaning in nature. For many animals, home can be the heartwood of dead or decaying trees. Dead trees still standing in the forest are called snags. Snags provide home and refuge for many animals including birds, reptiles, and mammals. Snags that fall to the ground are called logs and these downed logs play an important role in forest ecology and diversity as well.
SNAGS = HOMES FOR BIRDS & OTHER ANIMALS
There are over 85 species of North American birds that use cavities in snags and decaying trees as their home¹. A very few species including woodpeckers and nuthatches are Primary cavity nesters who excavate their own cavities; snags provide the perfect medium for this activity. These primary cavity nesters will rarely nest in cavities that they themselves did not excavate. If snags are not available for excavation, they may not be able to nest or to roost².
Many more species are Secondary cavity nesters such as the Eastern Bluebird (Sialia sialia) and the Carolina Chickadee (Poecile carolinensis) who cannot excavate cavities for themselves; thus, they rely on the primary cavity nesters to carve out a home in a dead or dying tree².
Do only birds make use of snags and tree cavities?
These cavities are home not only for numerous bird species, but also for many mammals such as squirrels and ringtails, both of which live in Phil Hardberger Park. Reptiles such as the Texas Spiny Lizard or Tree Lizard (Sceloporus olivaceus) take refuge in these cavities as well.
ROTTEN WOOD IS A HOME, TOO!!
Cavity nesters are an important part of the forest ecosystem, because many of them are insectivorous and keep forest pests in check². After a snag has rotted enough to fall to the ground, it is now called a log and its role of providing a home does not end. Once on the forest floor, the log encourages an entirely new ecosystem to begin. The downed log now becomes home for fungi, earthworms, and firefly larvae. Toads like the Eastern Narrow-mouthed (Gastrophryne carolinensis) and Gulf Coast Toad (Incilius valliceps), as well as skinks like the Ground Skink (Scincella lateralis) all use these downed logs for shelter. As the downed log rots on the forest floor, it is recycling nutrients back into the soil³.
THAT’S WHY WE LEAVE SNAGS
What lessons do we learn from Mother Nature about recycling?
In the past, snags were removed from forest ecosystems. However, as we learn more and more about their importance, retaining snags has become an increasingly important part of maintaining a healthy ecosystem. As you look around the forest floor, know that the dead wood you see like in the two photos below can sustain as much life as a living tree³. Without these snags and downed logs, our forests would not be able to sustain a diversity of wildlife.
1 Wildlife in Connecticut: Wildlife Habitat Series. 1999. Snags for Wildlife. Connecticut Department of Environmental Protection: Wildlife Division.
2 Megalos, M. et al. 2019. Snags and the Downed Logs: Working With Wildlife. North Carolina Cooperative Extension Service.
3 Parker, M.O. 2011. Skill Builder: Dead Wood Supports Life. Texas Parks and Wildlife Magazine.