Healthy forests are complex ecosystems comprised of biotic components that live and die (including trees!) and abiotic components, such as water and air.

Different forest types have different plant and animal communities and different abiotic environments.

The interaction of biotic and abiotic components of a forest is called an “ecological process.” For instance, photosynthesis is an ecological process that green plants use to produce food as “autotrophs.” “Heterotrophs,” including most animals, obtain energy by preying on other plants or animals. Predation is also an ecological process.

For some of us, squirrels represent our first hunted species.

Sitting quietly in a forest, waiting for a squirrel to expose itself taught many of us the patience required to hunt larger mammals, like white-tailed deer.

But squirrels are much more than table fare or pests at bird feeders or invaders of attic spaces. Squirrels are integral parts of many forest ecosystems, interact with many other forest components, and drive several ecological processes.

Eight native species of squirrels (family sciuridae) are found in Northeast Michigan. Three of these species are primarily ground dwellers: woodchuck, 13-lined ground squirrel, eastern chipmunk. The other five species are “arboreal,” or live primarily in trees: gray squirrel (the black squirrel is simply a melanistic phase), fox squirrel, red squirrel, northern flying squirrel, and southern flying squirrel (1957, “Mammals of the Great Lakes Region,” the University of Michigan Press).

Arboreal squirrel species have a role in animal predator-prey relationships in a forest based on their activity patterns.

Most squirrels are diurnal, or active during the day. Flying squirrels are primarily nocturnal. Many raptors, such as red-tailed hawk or northern goshawk, focus on squirrels as prey items during the day, with barred owls and great horned owls being major predators of flying squirrels at night.

Squirrels also impact forest ecosystems by predating other animals and plants. While most squirrels are observed foraging on nuts and seeds, some squirrel species are omnivorous. They eat both plant and animal matter.

Flying squirrels, for instance, regularly prey on gypsy (spongy) moth caterpillars, especially during outbreaks of that forest pest (1974, U.S. Agricultural Information Bulletin 381). Red squirrels, on the other hand, have been shown to be effective predators of bird eggs and young (2010, “Oikos,” volume 119, pages 841-plus).

In oak forests, gray squirrels impact tree regeneration by altering the population of acorns of northern red oaks and white oaks differently. Northern red oak acorns need to overwinter before germinating, while white oak acorns do not. Thus, northern red oak acorns can be stored (cached) by gray squirrels more effectively than white oak acorns, as the delayed development of northern red oak acorns keeps them viable longer. Furthermore, white oak acorns are a preferred food item as they have less tannins.

The result is that squirrels may store more northern red oak acorns and thereby plant more future northern red oaks than white oaks. Squirrels also disperse northern red oak acorns farther from the parent tree than they do white oak acorns (2020, “Frontiers in Ecology and Evolution,” volume 8, pages 1-plus).

Forest management can impact the number of squirrel species found in a forest and their populations.

For instance, data from a study in Ontario indicated that older forests with larger coniferous trees and cavities in both living and dead trees had more northern flying squirrels and red squirrels than did managed forests which had simplified forest structure used by more southern flying squirrels (2006, “The Journal of Wildlife Management,” volume 70, pages 1,735-plus).

Whether being a food source for other animals or preying upon native and exotic animals or burying acorns across a forest stand, squirrels impact forests in many ways and thereby impact the lives of many of us.

Understanding the effects squirrels have on different plants and animals illustrates forest complexity and can help guide us in managing our forests for biodiversity and more.

Greg Corace is the forest and wildlife ecologist for the Alpena-Montmorency Conservation District. For more information, including assistance with the Qualified Forest Program and related forest planning and management, email him at greg.corace@macd.org.