Early in my graduate school education, I was studying evolutionary biology. Two competing theories focused on the rate of change in the genetics of populations due to competition and the environment. One theory contended that most evolutionary change occurs slowly; this is called “gradualism.” Charles Darwin promoted this theory in his On the Origin of Species (1859). Others suggested that change is spurred by irregular, dramatic events that result in a “punctuated equilibrium.” The late Harvard evolutionary biologist Steven J. Gould promoted this theory in the 1990s.

While species found in our forests evolve, forests, as ecosystems and not species, only change. Nonetheless, the rate of change in forest ecosystems can be discussed similarly to the above debates in evolutionary theory: some forests typically experience slow and gradual change, while others are prone to change driven by major events.

Northern hardwood forests, for instance, typically experience relatively slow, gradual change with mortality events impacting individual organisms. One of the reasons forest management in these ecosystems produces relatively small (hopefully irregular) canopy gaps is because natural disturbances generally involve a single tree or a small group of trees if a big tree falls and takes others with it to the forest floor. Not surprisingly, the associated tree species in northern hardwood forests have evolved to utilize a broad range of light conditions. Some species, such as yellow birch and northern red oak, require larger gaps for regeneration or substantial diameter growth. Other species, such as eastern hemlock and sugar maple, can conduct photosynthesis at lower light levels in smaller gaps and can often regenerate under these low light conditions, too.

Other forests, such as our dry pine ecosystems, are fire-dependent. When fire gets into the canopy, the disturbance can result in large openings, with only scattered individuals or small groups of retained trees. Species like jack pine and red pine are adapted to these events and often need fire for regeneration and lots of sunlight to grow.

However, even in these fire-dependent forest ecosystems, mortality of different plants is occurring almost all the time, sometimes because of competition for sunlight. When the important natural process of fire is thwarted by fire suppression, an unnatural buildup of dead material can result. This “fuel load” can then cause fires of increased (and atypical!) severity for some of these forests. Mixed-pine forests with an intact fire regime and dominated by red pine and/or eastern white pine do not typically burn with high severity, for example, compared to jack pine-dominated forests.

How has the recent ice storm impacted forests?

The recent ice storm impacted forests differently depending on where the forest was, the type of forest, the age of the canopy, etc. Much of the impacts follow what the scientific literature would suggest (see Greenberg and Collins, eds., 2016, Natural Disturbances and Historic Range of Variation, Springer Press). For instance, my anecdotal observations are that forests lower in elevation, such as those found along Lake Huron, were impacted less than forests on higher ground to the west. The leeward forests were seemingly also impacted less than windward forests.

In many deciduous forests (those that lose their leaves in the fall), the ice storm will promote secondary succession and only a minor change (assuming browse is not severe) in the plant and animal communities. Mortality of some individuals acted like a northern hardwood thinning as discussed above, with the exception that woody material was left behind for the ecosystem, not taken off-site as timber products. While this may look odd, it does not necessarily result in negative effects on the forest. On our better forest soils, much of this coarse woody debris will break down in a few years. Trees left standing and with enough green leaves will grow toward the canopy openings. Plants in the understory will grow up toward the sunlight, too. In most of these forests, the canopy gaps created by the ice storm will be occupied in a couple of years.

In our natural mixed-pine forests, mortality may be increasing an already unnatural buildup of larger fire fuels. Many of these forests have needed prescribed fire for years, if not decades. Now, the management of fire is only more problematic in these forests.

And perhaps most impacted by the ice storm were the pine plantations; many of the red pine plantations I have walked in have significant mortality. The term “entropy” refers to the concept that the natural world works on disorder, randomness, or complexity, not uniformity or homogeneity. In many of our pine plantations, the agriculturally-based, row-by-row patterns produced by planting and subsequent management likely facilitated the high degree of mortality.

Across the forests in northeastern Lower Michigan, the recent ice storm produced complexity in many forests and plantations. Natural complexity is usually correlated with biodiversity. Thus, for those conducting “salvage” harvesting, caution is advisable. Retaining some of the resulting complexity may benefit many plant and animal species (see Thorn et al., 2017, Journal of Applied Ecology, 55:279+).

Dr. 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 Greg: greg.corace@macd.org.