Old growth forests serve an ecologically important role in Minnesota’s forested landscapes. They provide unique ecosystem services, habitat for many special species, and serve as genetic reservoirs for future old growth forests.
- Ecosystem services
- Snags provide nesting, foraging, and denning sites for more than 40 species of forest birds and mammals.
- Fallen tree trunks and large branches provide shelter, foraging grounds, and travel corridors for salamanders, small mammals, and arthropods (e.g., beetles, spiders). They also provide nursery logs for many plants to grow.
- Old pine trees provide nesting sites for bald eagles and ospreys, and escape routes for young bear.
- Tall trees, variability in forest structure, and abundant dead wood are capable of providing cooler microclimates that wildlife can use to persist in warmer and/or drier climates.
- A larger amount of nitrogen-fixing lichens—organisms providing critical nutrients—is found in old growth forests than in younger forests.
- Because of the lack of disturbance, old growth forests store more carbon in their wood and soils compared with younger forests.
- Species benefits
- More kinds of lichen and fungi species live in old growth forests than in younger forests. Unique fungi species are found in the relatively undisturbed soils old growth forests, which add to the health and complexity of the forest.
- More beetles live in old growth forests than in other forest types.
- Dragonflies are more common and in greater variety where streams and lakes are next to old growth forests.
- Woodpeckers and 39 species of songbirds are more frequent in older forests than in younger forests.
- Several kinds of hawks and owls, red and flying squirrels, porcupines, and other animals prefer older forests.
- Cavities in large trees provide dens and safety from predators and weather for wide-ranging furbearers such as fishers and pine martens.
- Large, downed woody debris provide necessary pathways under the snow for foraging martens.
- Genetic reservoirs
We are just beginning to understand the full implications of preserving genetic diversity. But what is understood points toward the importance of genetic diversity for forest health, forest research, and forest restoration and conservation.
- Old growth forests embody thousands of years of genetic heritage. Having survived many changing conditions over long periods of time, old growth trees may contain genes that will enable them to survive global climate change, new diseases, and the uncertainties of the future better than younger trees. These forests could be invaluable for the restoration of commercial forests, agricultural lands, and urban forests.
- The tallest, straightest trees in Minnesota's forests were cut between 1850 and 1920. Their offspring often were destroyed by fire, plowing, or subsequent timber cutting. Some research has shown that trees in old growth forests are genetically predisposed to grow taller than trees in surrounding, heavily cut landscapes.