Michigan forests provide innumerable benefits. To start, forests help maintain biodiversity and clean air and water. They are also used for hiking, hunting, camping, wildlife observation, and collecting berries and mushrooms. Our forests also feed local economies. How then do we sustain forests ecologically in our quickly changing world? All forests are dynamic; they change in composition and structure over time. Different forests naturally change in different ways by different means over different time frames. As defined before, a “disturbance” is anything that impacts the amount of living material (biomass) in a forest. Jack pine forests, for instance, are as fire-dependent as any forest type in North America. Fire is an essential disturbance for naturally regenerating these forests and providing complexity. Fires shape these forests in dramatic ways every hundred years or so. Fires kill most mature trees and provide for biodiversity. Fires also open up cones so seeds are released. These seeds germinate on the forest floor on which the leaf litter is removed by fire. Not surprisingly, a jack pine rarely lives much more than a hundred years. It is adapted to fairly frequent disturbance. Conversely, our forests of American beech, sugar maple, and eastern hemlock are more stable; natural change occurs in these forests, but less dramatically and over longer time frames. Not surprisingly, trees in this forest type live many hundreds of years. They also commonly grow quite large and become more vulnerable to the effects of wind. “Windthrow” is a natural disturbance and effects not only a single tree, but other trees knocked down as a large tree falls to the forest floor. The downed log provides habitat for many organisms, including male ruffed grouse that “drum” on logs. The “canopy gap” provides an irregular patch of sunlight in the forest. In gaps, saplings and seedlings take advantage of pulses of sunlight and grow more rapidly. Forests regulated by windthrow are structurally complex. While forests have always undergone change of different types and over different time frames, science suggests that forest disturbances are changing in type, return interval, and severity (degree of impact). For instance, many non-native organisms are now competing with native species for space and resources in our forests. Some of these exotic species are causing tree mortality. Oak wilt, Emerald ash borer, beech bark disease, and hemlock wooly adelgid threaten the sustainability of our forests. These new agents of disturbance, and potential changes to fire and wind patterns, require us to reevaluate forest management. “Resistance” is the ability of a forest to remain unchanged when challenged by disturbances. “Resilience” is the ability of a forest to reorganize itself after a disturbance so that it still functions. These two terms can be used as a basis for planning and can guide our forest management actions. In other words, a landowner could have these as specific goals in a forest management plan and can use these to help devise forest treatments. To promote resilience and resistance, early evidence suggests that forest diversity is important. Forest diversity is a product of site conditions of soil and climate, as well as past management activities. To maintain forest diversity, landowners should focus on what will be left behind after logging is done. In other words, think about “desired future condition.” This can include leaving less common tree species in the forest after a treatment. In many of our forests now dominated by oaks, there were once red pine and eastern white pine. If scattered pine trees are still found, these should be retained to provide seed and increase the pine component of the future forest. In cases where no pines or other conifers are found, underplanting seedlings in gaps created by logging would increase diversity. In a similar way, many pine forests historically managed by fire had scattered oaks and aspen. Future management should aim to keep these forests mixed and not solely one species (called a monoculture). When a future disturbance occurs that is not planned for (like a new exotic species), these forests would be provided a greater likelihood of resilience and resistance. A repeated principle in this column has been the importance of forest diversity. While previously discussed in the context of wildlife, tree species diversity is also an important factor in having resilient and resistant forests for the future. Diverse forests theoretically have more potential management options. In the end, however, uncertainty abounds. Understanding what our forests once were like in terms of composition and structure and how they once functioned provides us with ways to understand current conditions and plan for an uncertain future. 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 (firstname.lastname@example.org) or phone (989.356.3596 x102).
The first wildlife management text in the United States was Aldo Leopold’s Game Management (1933). Leopold saw that game populations responded positively to habitat management. He also proposed that species-specific wildlife habitat consists of food, water, and cover. Nearly 100 years later, we know that wildlife populations are impacted by many other things. Nonetheless, food, water, cover, and space (as a newly added fourth variable) still structure how we think about wildlife habitat for individual species. How does space come into play in wildlife habitat? For some wildlife species, including many Neotropical migrant songbirds, space is used differently during the breeding season, during migration, and on the wintering grounds. Throughout migration routes, space provides birds the ability to restore energy reserves by resting and foraging for food. Birds that struggle to find suitable space during migration from their wintering grounds to their breeding grounds may arrive in poorer physical shape, potentially reducing their ability to reproduce successfully. Space is also critical for wildlife species with exceptionally large home ranges or “area-sensitive species”. Area-sensitive species not only require a certain condition of vegetation structure (vegetation arrangement) and composition (mix of plant species), they also require large blocks of habitat (space). In northern Michigan, the upland sandpiper and sharp-tailed grouse are bird species of fire-dependent, pine and oak barrens, as well as pasture and hayfield complexes. Both species require hundreds or thousands of acres of unfragmented open habitat. Similarly, black-throated blue warblers are only found in large tracts of mature, mixed forests of northern Michigan. A forest must be many hundreds of acres or more to be occupied by this migratory bird species. Of the four variables of wildlife habitat, space is perhaps the most challenging to provide in a world increasingly dominated by human land uses. Not surprisingly, many species requiring large spaces are of conservation concern. [Authors note: the importance of “landscape context” previously covered applies here.] How can a landowner provide wildlife habitat, especially when space is limited? Let’s think specifically about our winter wildlife. While wildlife diversity in northern Michigan is reduced during the winter months due to migratory birds wintering elsewhere, it is also during the winter when some species move into our area. Snowy owls, pine grosbeaks, red crossbills, common redpolls, pine siskins, and American tree sparrows are encountered more often during our winter as birds from farther north move south. For many of these and other species, cover and food are very important during the winter. Fortunately, cover and food can be provided in a number of ways, regardless of whether a property is in the city or in the country. For example, landowners can provide cover by having patches of their land devoted to native coniferous trees. When a property has coniferous trees of different ages, sizes, or species, a “layering” of vertical structure results. In the winter, these areas provide some refuge from the wind and precipitation, while still retaining heat. One of the reasons white-tailed deer seek swamps of northern white-cedar, black spruce, and tamarack is the “thermal cover” and reduced snow depth these areas provide. Private landowners can also provide cover by retaining large live or dead trees with flaking bark or cavities. Wildlife such as southern flying squirrels and white-breasted nuthatches find refuge from harsh winter conditions in these spaces. And dead material, like a pile of decomposing leaves and branches on the forest floor or in the corner of a backyard, can provide many small mammals, such as meadow voles and deer mice, with cover. Some reptiles and amphibians may use these warm, quiet places to hibernate. Mature coniferous trees, such as red pine and eastern white pine, also provide energy-rich seeds. Red crossbills evolved with beaks that are offset from one another. These beaks allow the birds to pry open pine cones. Birds then extract seeds with their strong tongues. Some deciduous trees also provide winter food. Young aspen is browsed readily by white-tailed deer, elk, and snowshoe hare; ruffed grouse eat the buds of more mature trees. While not a favorite for those interested in timber products, ironwood is favored by many birds in the winter because it retains seeds throughout the year. Like all professional fields grounded in science, our knowledge of forest and wildlife ecology is dynamic. As our forests change due to succession, management activities, or other reasons out of our immediate control, wildlife use can also change. By studying and understanding how the natural world operates, forest managers can devise wildlife habitat management activities best suited for a forest and the suite of native wildlife species adapted to its conditions. 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 phone (989.356.3596 x102).
For many forest landowners in northern Michigan, wildlife habitat management ranks as a primary ownership goal. While white-tailed deer, black bear, ruffed grouse, American woodcock, and other game species are usually of primary interest, the majority of vertebrate wildlife species in our forests are non-game species. In fact, most of our forest wildlife are secretive, cryptic, and/or migratory, spending only the breeding season in northern Michigan. To introduce the reader to some of these species and how specific forest structures provide wildlife habitat, below I will describe a hypothetical forest wildlife community inhabiting a hypothetical 40-acre forest property during late Spring. Our imaginary forested property has 30 acres of northern hardwoods and 10 acres of lowland conifers. The property has both mature trees (40 feet tall or more and 40-100 years old) and immature trees (seedlings and saplings less than 20 feet tall). The northern hardwood forest is comprised of big-tooth aspen, red maple, and sugar maple, with a few scattered large eastern white pine and red oak trees. It once had eastern hemlock and white spruce, but these species were removed decades ago and are no longer represented. White ash was also part of this forest, but non-native, invasive emerald ash borer killed all the trees. The lowland conifers include black spruce, balsam fir, tamarack, and northern whitecedar. The first wildlife species encountered on our property is the gray treefrog. Because our property has “vernal ponds” (seasonally wet spots that dry out come summer in the northern hardwoods) and some standing water in the lowland conifers, a number of different species of amphibians exist on the property. Our gray treefrog is one of the more cryptic. We hear it, but don’t see it. The color of its skin blends in perfectly as it sits on a limb of a red maple on the edge of the northern hardwood patch. Only the trained ear can discern the odd song of this species from other sounds in our forest. The male’s odd song will attract a female that will lay eggs in our vernal ponds and other standing water. The next wildlife species we encounter on our property is a strikingly colored, and consistently vocal, male American redstart. This small, migratory songbird is one of the more common forest bird species in the eastern United States and males are dramatically colored with orange, black, and white. Our male is defending a breeding territory in a 1-acre patch in our northern hardwood forest, spending most of its time in young maple saplings less than 1 inch in diameter. Its mate, yellow-brown and secretive, is sitting on three eggs in a small nest in a sapling sugar maple only 6 feet off the ground. When the young hatch, they will be fed protein-rich insects collected by both parents. Because of the water and the cover in the adjacent lowland conifers, there are lots of insects in our forest and the young grow quickly. Come August, they all will migrate to the Caribbean. Our final two wildlife species are using one tree, just different parts of it. A large big-tooth aspen has formed a perfect crown into which a great-horned owl pair nested the previous February. Now, the two chicks are nearly full grown and are out of the nest, looking for small mammals as prey. Because this aspen is over 100 years old, decay has started to cause some of the limbs to break off and fall to the forest floor. Here, the fallen limbs provide cover for an array of plant, fungi, and animal species, including the pygmy shrew that hides from the owl. This shrew is a member of the second smallest species of mammal in the world, and is most active at night. Because of its high metabolism it eats continuously and is now searching for insects and other invertebrates that are using the fallen limb as well. All told, our 40-ac property provides conditions for many more wildlife species than space allows us to mention here. While game management can provide habitat for some non-game species, forest wildlife diversity is usually a result of complexity provided by “composition” (the mix of tree species) and “structure” (the vertical and horizontal arrangement of live and dead trees) specific to a given forest site. Composition and structure for the present and the future can be a focus of forest planning and management. And if identified as a landownership goal, forest planning that takes into account natural models of how forests form and function can provide a blueprint for maintaining forest wildlife diversity. 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 (firstname.lastname@example.org) or phone (989.356.3596 x102).
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
Want to hear about what is new in the science world? Maybe get more information on the birds around us? Or maybe you want to keep up to date on what is happening in our current environment and with the natural resources we love. Check out some interesting articles shared by our Forester, Dr. Greg Corace.