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 (email@example.com) or via phone (989.356.3596 x102).
We have now covered the first two of the four foundations of ecologically-based forest management (i.e., context, continuity, complexity, and timing). Here, I define forest complexity, describe how and why pine plantations differ from naturally-regenerated pine forests, and finally illustrate how to apply lessons learned. Forest complexity can be defined within the context of “composition” (the mix of tree species) and “structure” (the vertical and horizontal arrangement of live and dead trees). Complexity can also be defined within the context of spatial arrangement of trees; a complex forest differs from point to point and is far from uniform or orderly. While some forest types are generally more complex than others, the general rule applies that complex forests are more biologically rich. How about plantations? In many ways, the history of forestry begins with plantation management. Gifford Pinchot, the first Chief of the US Forest Service, was trained in Europe where even the Black Forest is really a large conifer plantation. Most natural forests were cutover centuries ago in Europe and replaced with plantations primarily managed for timber production. Plantations are forests derived from intensive management and the planting of seedlings or seeds of usually one tree species. These seeds or seedlings are spaced to optimize vertical growth in the early years of the plantation, with subsequent “thinning” by removing some trees to give the remaining trees more sunlight for continued growth. This is how pine trees grow straight and tall, and then put on diameter growth. But plantations differ dramatically compared to naturally-regenerated forests, especially in regards to complexity of composition, structure, and spatial arrangement. In northern Michigan, jack pine and red pine plantations are common and are most often found on dry, sandy sites that historically were fire-prone. These plantations are easily seen through aerial imagery provided by Google Earth and the uniformity of these forests is readily observed. Trees are generally all the same height and diameter and the spacing is nearly the same between each tree. Because light conditions in many young plantations is low, jack pine and red pine plantations are usually devoid of many other plant species. These characteristics of plantations usually dictate wildlife use as well. Most studies suggest that plantations provide for far fewer wildlife species than do natural forests of the same type. Research has indicated how relatively more complex natural red pine and jack pine forests area than their plantation counterparts. This complexity is often produced by fire. As a natural part of these ecosystems, fire regenerates these forests and, for red pine, maintains them. Whereas fire in jack pine tends to be severe and kills most (but not all!) trees, in natural red pine stands fire causes much less mortality. Unlike jack pines, mature red pines have thick bark and lack lower branches. These attributes protect the tree from heat and reduces fire from climbing up a tree into the green foliage. Consequently, fire usually produces a broader array of flora and therefore compositional complexity in these forests compared to plantations. In jack pine forests that are burned, structural complexity is provided by an abundance of dead trees (snags). In red pine forests, fire provides structural complexity by producing a range of different sizes of red pines and fewer, scattered snags. Finally, in both jack pine and red pine forests fire produces complex spatial patterns and a lack of uniformity. But can something be done to make plantations more complex? The simple answer is: yes, many things. For instance, one of the easiest things to do is to consider leaving some remnants of the previous forest as part of the new plantation. This was addressed as “continuity’ in the previous article. Next, consider planting a mix of pine species, including eastern white pine. While planting may still be uniform to get trees to grow straight and tall, thinning stands irregularly can then be done to produce some spatial complexity in older plantations. Also, snags and coarse woody debris can easily be provided at no cost while thinning is done. Logging equipment can simply either girdle or top a selected tree and leave it in place, or cut a tree and place it on the forest floor and provide coarse woody debris. Many lessons can be learned by studying natural forests. Observed patterns in complexity can then be applied through ecologically-based forest management, even in intensively managed pine plantations. Dr. Greg Corace is the forester for the Alpena-Montmorency Conservation District. Greg has spent the last 25 years publishing forest and wildlife research and conducting forest planning, management, inventory, and monitoring on public and private lands across northern Michigan. For more information, including sources used in this article, Greg can be contacted via email (firstname.lastname@example.org) or via phone (989.356.3596 x102).
Dr. Greg Corace
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