Forests are complex ecosystems comprised of biotic (living) and abiotic (non-living) components. Forests change constantly due to the interrelationships of different ecosystem components and the timing of environmental events. Some forest changes are dramatic, while most are quite subtle.
Germination is the process whereby stored energy in a plant seed is reactivated. The resulting metabolic activity leads to the development of a seedling. For germination of specific plant species to be successful, certain environmental conditions need to exist. Consequently, some seeds may lie dormant in the soil for years, only to be reactivated when appropriate environmental conditions arise. Seed storage in the soil is referred to as the “seed bank.”
Different tree species have different sizes of seed. Some tree species are termed “heavy-seeded” because their seeds are large and require the assistance of dispersal agents. American beech and red, white, black, and northern pin oaks are local examples. Blue jays and many other bird species can move acorns a long way. Rodents, such as gray, fox, and red squirrels, also disperse seeds farther from the parent tree than would otherwise occur.
Other tree species are termed “light-seeded” and produce very small seeds that can be dispersed significant distances by wind. For some light-seeded tree species that hold their seed into the winter, dispersal can be enhanced when seeds are blown across the crust that forms on top of snow; these tree species also function as natural winter bird feeders. Local examples of light-seeded tree species include paper birch, yellow birch, and ironwood.
Soil scarification is the process of preparing a site for seed germination by exposing mineral soil. And scarification can occur by different means. For instance, windthrow is the process in which whole trees are blown down. The result is exposed mineral soil where the roots once held the tree vertically in place. Windthrow is common on wetter or rockier sites because tree root depth is limited. Conversely, on drier sites with deep sands, fire can scarify the soil by removing the litter layer through the consumption of leaves (needles) and other organic matter. The resulting ash may function as fertilizer for seeds that germinate on the exposed mineral soil.
For some light-seeded tree species, such as paper birch, fire is critical. While fire may kill adult trees, it also prepares the soil for the next generation. Because paper birch seeds are small, they have little energy reserves and can desiccate quickly and become unviable if they fall on leaf litter. Fire removes the leaf litter and prepares a seedbed and increases seed viability. Not surprisingly, many natural fires occur in late summer and paper birch has evolved to drop seed in the fall or early winter when mineral soil is still exposed and moisture is abundant. Because of this, paper birch is one of the more fire-dependent tree species in Michigan. Fire suppression, along with climate change and secondary succession, has been reducing the abundance of paper birch in Michigan forests for decades.
Scarification can also be accomplished mechanically. Logging operations during the growing season can disturb the top layer of the soil when tracked machinery moves across the forest floor. And scarification can be enhanced when tree tops are dragged around the site. However, logging operations are not conducted during the growing season in many Michigan forests in an attempt to limit the spread of oak wilt. Oak wilt is a fungal pathogen that affects red, black, and northern pin oaks in our area. The pathogen moves below ground via comingled roots and above ground by beetles that respond to injured trees and carry fungal spores from tree to tree. To limit above ground spread of oak wilt, oak forests are often managed when snow covers the ground and beetles are inactive. During this time, soil scarification and its benefits are virtually nonexistent.
Forest landowners should consider the important role of soil scarification in some forest types. When done during logging operations, soil scarification can aid the development of diverse forests by promoting the establishment of many underrepresented tree species. Besides birch trees and ironwood, many pine species also regenerate better when scarification occurs. While eastern white pine seeds have the ability to regenerate across a range of soil types and even in the presence of a significant litter layer, red pine and jack pine benefit from exposed mineral soil.
The role of soil scarification in promoting successful tree germination is but one way in which the integration of biological and ecological concepts are incorporated into recommendations for managing for complex forests that are resilient and resistant.
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).
An in-depth conversation on the practicalities of implementing natural climate solutions through forest management
RFF Live featuring Robert Bonnie, Jimmy Bullock, Christine Cadigan, Sam Cook, Paul Trianosky, and Laurie Wayburn — June 9, 2020
Successful forest conservation starts with a detailed knowledge of the land, its history, and its capabilities and limitations. Such information is the basis of forest planning. While winter in northern Michigan is a wonderful time for planning, spring is a good time for planting vegetation that enhances composition (plant species on a property) and structure (the vertical and horizontal arrangement of vegetation). The type and abundance of wildlife in a forest are largely determined by vegetation composition and structure. Site capabilities and limitations are based on soil type, water availability, and light levels. After these factors are known, and preferably documented, the next step is to identify wildlife species or communities of interest and whether woody plantings are to provide food, cover, or both. Although some plants benefit many species of wildlife, plantings will be most successful if they are customized according to the food preferences and cover requirements of the target species or community. Browsing is defined as the eating of leaves and twigs of woody vegetation. Browsing differs from grazing which is the eating of herbaceous vegetation. Browsing can be a significant impediment to forest regeneration and is a reason why some forests are not as compositionally or structurally complex as they should be. The park-like conditions that we see around us are often the result of browsers limiting age classes of trees and other woody plants. Rodents, lagomorphs (rabbits and hares), and cervids (deer and elk) are all browsers, but different species of browsers impact plants differently. Rabbits and hares, as well as deer and elk, work from above and browse the terminal end of young stems at different heights. Rodents often eat woody plants below the snowline in the winter and tend to girdle plants. Young woody plants (seedlings and saplings) need to be protected from browsers. For large plantings, fencing the entire area may be required. Where fewer plants are involved, such as apple trees, fences can be constructed around each tree with stakes and welded wire fencing. Seedlings need protection for 5 years or more. To protect woody plantings from deer, tree shelters should be 6’ tall; to protect from elk, tree shelters should be 8’ tall. Barriers 2’ high may deter rabbits and hares. The best protection against rodent browsing is the elimination of taller vegetation near the planting. This reduces food and shelter for the animals and has the additional benefit of suppressing competing vegetation. Alternatively, tree guards can be put around the main stem of the planting. Several sizes and types of tree shelters, including cone-shaped models for conifers, are also available. Homemade models can be constructed with stakes, staples, and construction grade plastic. In addition to protecting seedlings, tree shelters can, under certain circumstances, serve several other functions: increase seedling survival and growth rate through moisture retention and a greenhouse effect, improve growth form of seedling planted for timber production, protect seedlings from herbicide drift and mowing machinery, and help managers locate seedlings. It is important to note, however, that shelters do not eliminate the need for weed management. Problems that are encountered with tree shelter include trapping of other wildlife (now preventable with netted tops), possible attraction of insect pests, winter die-back of terminal shoots, and the continued need to support stems for 1-2 years after they grow above the shelter. Regardless of the type of shelter used, frequent inspection is needed to detect possible problems and to repair or replace damaged parts. Because they have grown here for thousands of years, native woody plant species have two main advantages over non-native species. First, native species are well adapted to our site conditions. Second, non-native plants can become weedy (invasive) and crowd out native species. Autumn olive, glossy buckthorn, Scots pine, and other non-native woody plants can be a serious threat to the ecological integrity of forests. Because of the costs and time involved, it is generally wise to consider plantings as a small part of a broader habitat management program that focuses on existing vegetation.
Conservation District Tree Sale: The 2020 Spring Tree Sale will move forward as planned. Expect to see a postcard in the mail with instructions on the pickup process and a reminder of the dates and times. Dates for pickups will continue to be Friday, May 1 from 9am until 5pm at the Alpena Warehouse located on Airport Rd. and Saturday, May 2 from 9am until 2pm at the Montmorency County Fairgrounds located on M-33. We will still have extras available on the day of pickups. For any questions, contact us at 989.785.4083 x5 or 989.356.3596 x5; or email firstname.lastname@example.org. 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)
I think all the "rules" allow most of us to go out by ourselves or in a small group......if so, it's a great time to observe some unique forest wildlife behavior in northern Michigan.....
Perhaps it's a good time to get out at dusk to hear/see American Woodcock males peent in an opening next to some young aspen?
Or go into some mature mixed conifer/deciduous woods to hear/see male Ruffed Grouse drum on a large, rotting log in the early morning?
Or see male and female Sandhill Crane unison call and dance in pine openings or in hayfields?
Or go to the eastern UP (when allowed) and see male Sharp-tailed Grouse dance in the morning in pine openings or hayfields?
Forest types are largely defined by the dominant tree species within the canopy of a stand. However, the under-story regeneration often varies, sometimes suggesting long-term forest type changes.
Bill Cook, Michigan State University Extension - March 16, 2020
Over decades, forests undergo somewhat predictable changes. Foresters call this “forest succession”. One of the best indicators of where a forest stand might be headed is from examining the regeneration. Without major disturbance, there’s a pretty good chance the seedlings of today will become the dominant forest type of the future.
Different forest types have various track records in their ability to reproduce themselves over time. Northern hardwoods can sustain themselves for centuries. Signature species, such as sugar maple, beech, and basswood, can grow in the shade and will take advantage of small canopy gaps as old trees gradually die.
On the other end of the spectrum, paper birch and red pine stands have very low percentages of their own seedlings in the under-story. These are sun-loving tree species. Without disturbance, other forest types will replace these forest types.
Paper birch stands are likely to become balsam fir or northern hardwoods. Red pine stands will trend more towards red maple, black cherry, and different species of oak. Similarly, aspen stands tend to be replaced by red maple or balsam fir. Aspen is particularly popular with most game species and a growing number of birds with declining populations.
Enter disturbance. Over the decades, the likelihood of a major disturbance increases. Such events as wind, wildfire, and pest outbreaks will open the forest floor to lots of sunlight and soils will warm somewhat. These conditions will favor the light-loving species, which tend to grow faster than the more shade tolerant tree species.
Forester and forest owners can mimic these events through management and timber harvesting. Practices such as clear cutting and shelter woods can help maintain forest types such as aspen, red pine, jack pine, and paper birch. Regeneration strategies of these tree species depend upon major disturbance.
In the bar chart, the green bars (lighter gray on the left) indicate a forest type’s ability to regenerate under its own canopy. There is a high percentage of signature species already in the under-story The red bars (darker gray on the right) suggest a need for a major disturbance in order to regenerate, as little regeneration of the signature species exists. Left alone, these “other” species will eventually replace the existing trees.
Most of the Lake States forests are adapted to natural disturbances. Since the glaciers melted about ten thousand years ago, the forest area has ebbed and flowed. Our forests have needed to be flexible. The region historically tends to have large sweeping storms, fires, and major insect outbreaks Native American intervention increased the role of wildfire.
As certain forest types matured, the trees served as host to widespread insect epidemics. Thousands of acres of fir-spruce would be killed by the spruce budworm. Large expanses of old jack pine fell prey to the jack pine budworm. Periodic outbreaks of forest tent caterpillar would defoliate and kill great swaths of aspen.
Wildfire would often result from the huge fire loads created by so many dead trees.
After these catastrophes, the fir, spruce, jack pine, and aspen forests would grow back Such is the way of natural cycles.
With human infrastructure spread nearly everywhere, these calamities came with unacceptable risk to people. Forest management has been developed to reduce the negative effects of natural disasters while maintaining those benefits that different forest types depend upon.
Red pine and paper birch still need major disturbances in order to maintain themselves. However, forestry has provided the solutions to help those forest types and humans coexist. So, the next time you see a clearcut jack pine stand, be grateful the jack pine is being regenerated without a forest fire.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).
The study of cyclic changes in the natural world based largely on climate’s effects on plants and animals is called “phenology.” In northern Michigan, many of us welcome the cyclic change we observe this time of year as the days get longer and warmer. And perhaps nothing is more a harbinger of spring than sap flow in our sugar and red maples, when cold nights are followed by warm days. But how does the process of sap flow work and what can a private landowner do to promote vibrant trees from which sap can be collected and syrup made? “Physiology” refers to the mechanical and chemical workings of plants and animals. Sap flow in maple trees is a physiological process driven by phenological change. To understand how and why sap flows in a tree one must understand how a tree produces and stores its energy and how it transports water and other materials from its roots to its leaves. Most green plants, including trees, produce energy through “photosynthesis.” Plants are called “phototrophs” because they use light energy (photons) to combine the gas carbon dioxide and water to produce sugars. In this process, oxygen is released. Without green plants, animals would not have oxygen they need to live. And without the sun, plants would not be able to produce energy. While all green plants need sunlight, some tree species need more sunlight than others. We refer to tree species that require less sunlight as “shade tolerant” species, and those requiring more sunlight as “shade intolerant” species. All native maples, as well as American beech, ironwood, and a few other of our deciduous tree species, are shade tolerants. These species are able to produce energy with relatively little sunlight. This energy (in the form of sugars) produced by photosynthesis is used to meet the demands of tree growth and maintenance. When excess sugars are produced, they are stored in the tree roots. Conversely, other tree species, such as aspen and oaks, are shade intolerant and need more sunlight. These tree species rarely produce extra sugars and do not typically store much energy. Tree sap is primarily a mix of water and sugars. Tree sap move in tubes in a manner slightly similar to the way blood moves in our arteries and veins. The tubes in which maple sap typically flows is called “xylem” tissue. Dead xylem is the “heartwood” of a tree and living xylem is the “sapwood”. Most of the material used in making lumber from a tree is xylem tissue. In other tree species, sap can also flow in the other tubes (phloem). Syrup made from other tree species has a distinctive taste quite different than maple syrup. During the spring of each year, sap flows from the roots, where sugars are stored in the winter, to the crown of the tree. Sap flows because of the pressure in the roots is greater than the pressure in the crown. What can a landowner do to promote vigorous maple trees form which syrup can be made? Tree vigor is the primary consideration for syrup production. Vigorous trees with large, healthy crowns tend to make and store more energy and produce more sap. Site (soil type) and location, as well as tree genetics, are factors that influence tree vigor. On sites with well drained, upland soils and plenty of sun (often south facing slopes), maple trees can thrive and be vigorous, especially if competition with other trees is reduced. When provided more sunlight, a maple tree will respond by growing more leaves and a bigger crown. This is the type of tree that if not impacted by disease or physical harm can produce sap for decades. Thinning a forest to produce trees of 10-25 inches in diameter separated by 20-25 feet is a good starting point. Removing diseased trees or trees of low vigor can promote more diameter growth on the retained trees. Do not, however, reduce overall stand tree diversity. Forests with more tree diversity tend to be healthier overall, and a vibrant maple stand (sugarbush) produces more maple sap. To capture sap, the general recommendation is that trees less than 20 inches in diameter should have one tap, while trees over 25 inches may have up to 3 taps in a given year. Just like all types of forest management, managing a sugarbush depends on many factors and involves a great deal of art guided by science. In the end, an understanding of how a tree, and a forest, forms and functions provides a solid foundation for planning and management. 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)
Long Term Considerations for Managing a Sugarbush
How to Manage a Woodlot for Sugar Maple Syrup Production...Fewer Trees, Bigger Crowns
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 (email@example.com) or 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.