The Timing of Forest Treatments

We have come to the last of our four foundations of ecologically based forest management (i.e., context, continuity, complexity, and timing). Below, I discuss how forest land use history impacts future forest management and the important consideration of the timing of forest treatments. As discussed previously, forests are much more than just trees. Forests have living (biotic) and non-living (abiotic) parts. Living organisms include trees, other plants, fungi (mushrooms), and vertebrate and invertebrate animals. Abiotic components include air and water, among other things. Soils are complex, and contain both biotic soil organisms and abiotic minerals. Nonetheless, we often refer to forests based on the most common tree species. Locally common “forest types” include aspen forest or oak forest or red pine forest, for example. While generalities within forest types can be made, what separates nearly every forest from another forest are their unique management histories. In other words, there are aspects of oak forests in northern Michigan that are shared among other oak forests, but that differ significantly with red pine forests in northern Michigan. And one oak forest differs from another oak forest because the land use history of each differ. So how do past events affect a current or future forest? There are generally two reasons a certain type of forest in a certain condition currently exists on a site or might grow on a site in the future: 1) the site’s soil and climate and 2) the site’s history. What happened in the past not only partly explains what type of forest is currently found, but what type of forest may be found in the future. For the most drastic example, consider our ash forests. When the exotic, invasive emerald ash borer moved into these forests and caused wide-spread mortality, these forests were fundamentally changed. Not only are they different now, but they will be different from what they once were for decades to come. The site’s soil and climate didn’t change, but the majority of ash were removed and therefore unable to reproduce more ash in the future. Something similar has happened in the past in some parts of the eastern United States with Dutch elm disease and chestnut blight. What happened in the past influenced what forest currently exists and what forest may be in the future. Now, let’s consider a “forest succession” example. Forest succession is the changing of one forest type to another forest type over time (decades or more). This change occurs because short-lived tree species that tend to need more sunlight naturally die and are replaced by longer-lived tree species that can often exist under lower light scenarios. In many northern Michigan forests, for instance, shorter-lived aspen trees give way over 50 or more years to longer-lived oak and eastern white pine. But how does the timing of forest treatments (logging) impact this? Forest management can dictate whether succession continues to occur and longer-lived tree species predominate or whether the site is reset to the stage comprised of shorter-lived tree species. Some forest treatments can reset succession, have little impact on the current trend in forest development, or actually promote longer-lived tree species. The shorter the time between treatments (logging events), the less likely the forest is allowed to recover and recruit new tree species and develop aspects discussed in my previous article on complexity. To maintain continuity and complexity in forests, the timing of forest treatments is an important consideration. Here again, natural models of how forests historically worked can aid contemporary forest management. Studies have shown that forest types can be grouped by the type of natural disturbances they evolved under and the timing of such events. As previously described, disturbances are anything that impact living material in a forest, with fire and wind and herbivory being common examples. While fires in other parts of the country were historically common on 5-10 year intervals, naturally occurring fires shaped northern Michigan forests at intervals nearly 10x this rate. Thus, some aspects of our forests only occur if the timing of our management activities take into account these greater natural time frames. If maintaining biodiversity within a forest is of interest, context, continuity, complexity, and timing can all be considered during the forest management planning stage. Depending on the forest type and the site’s land use history, aspects of these precepts of ecologically based forest management can then be applied to differing degrees in each forest. Dr. 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 via phone (989.356.3596 x102).