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Forest changes and ice damage

Forests differ based on past management activities and site conditions (e.g., soils, water, climate). Differences in forests can be observed through comparisons of plant and animal communities and other non-living (abiotic) characteristics, such as forest light levels.

Forests can also be arranged on a continuum of natural ecological disturbance. As the reader may recall, an ecological disturbance is a process that impacts the amount of living material in a forest. Common ecological disturbances include fire, windthrow, insect and mammal herbivory, and ice damage. Some ecological disturbances occur more frequently and affect less area (e.g., windthrow of 1 acre in a northern hardwood forest ever 2-3 decades). Other ecological disturbances occur less frequently, but impact greater area (e.g., wildfire over 1,000s of acres of pine forest every century).

Some forest types, such as jack pine, have evolved to take advantage of fire as an ecological disturbance. Fire kills most, but not all, living trees and prepares the area for the next generation of jack pine. Seedlings that germinate post-fire may grow into saplings under high light levels. Those saplings may then grow into adult trees that produce cones with seeds, but under lower light levels. Assuming no fire suppression, fire starts the process over every 50-100 years.

As the forest matures and changes, different plant and animal communities arise. In a 2010 paper in the Natural Areas Journal researchers showed how different bird species associate with different stages of forest maturation. Birds found in young forests dominated by seedlings were often not found in mature forests dominated by older trees. However, overall bird diversity did not change much across forest age classes (20-25 bird species per age class). As found in many other studies in other forest types, overall diversity is achieved when a range of age classes exist either at the stand or landscape scale. Young forests and old forests are both important for maintaining diversity. Complexity is key.

Because forest site conditions are only changed through drastic measures, many professionals suggest that landowners understand the limitations and opportunities imposed by soils, climate, and water on their property. Landowners are often best served by working with (not against) site conditions; a complex forest is not an agricultural crop that can be controlled without losing important biodiversity components. As such, native plant species are usually promoted by most professionals to meet landowner goals. In some instances, landowner may have to adjust their goals if site conditions preclude their attainment.

Forest owners must also be aware that the plant and animal species we work with now are different than the species we worked with 120 years ago, and will likely be different than the species we work with in the upcoming decades. Among other things, climate change influences the distributions and abundances of many plant and animal species directly and indirectly. One way climate change may change forests and the associated species of plants and animals indirectly is by changes to ecological disturbances. While less common here than elsewhere in the eastern US, ice damage is a potential issue for forest landowners in the future.

Many individual trees can be susceptible to ice damage due to the weight of ice, combined with the effect of wind. In a 2000 paper in the Northern Journal of Applied Forestry it was reported that upwards of 5 tons of glaze ice can accumulate on a 50-foot-tall conifer with a 20-foot-wide crown. Studies have also found that conical conifers (e.g., spruces) are more resilient to ice damage than open-crowned conifers (e.g., red pine), and deciduous trees, in general, are more susceptible overall. Aspen, paper birch, and black cherry can be very susceptible to ice damage, with red oak and sugar maple less so. Rather than wood strength, it seems the shape of a tree influences its resistance to ice damage. Trees with horizontal limbs (usually open grown, such as in yards or sugarbushes) are more susceptible to damage. Trees packed into forest patches are generally less susceptible to damage. Management of forest stands that create complex spatial arrangement of vegetation may reduce the risk of ice damage.

The effect of ice storms can also be felt by the forest overall. Mortality of trees or damage to limbs results in increased sunlight to the forest floor and an invigoration of the understory. While ice damage may be unsightly, ice storms can also create complexity and diversity in the forest similar to windthrow. Some plant and animal species can actually benefit. To what degree the landowner can accept ice damage will be part of future forest planning in management in northeastern Lower Michigan.

Greg Corace is the forester for the Alpena-Montmorency Conservation District. For more information, including sources used in this article, Greg can be contacted via email (greg.corace@macd.org) or phone (989-356-3596 x102).

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