MANAGEMENT OPTIONS FOR ASPEN TIMBER
Article #104, February 2006
By Bill Cook
Forest management practices vary considerably across forest types, site conditions, market availability, and many other factors. There simply is not any single way or best way to manage all forests, or even a particular kind of forest. While nature is a dynamic system that defies simple categorization, there remains a body of knowledge and experience that can be very effectively applied.
Aspen stands are among the easiest
to manage and regenerate. However, that does not mean they are without potential
difficulties. Aspen requires full sunlight for a new stand to grow. In nature,
these conditions occur following wildfire, epidemics, mass windstorms, and the
like. With management, these conditions are provided through clearcutting.
Of course, some folks react to clearcutting with a gut wrench. However, a healthy ecosystem and the rules of nature have nothing to do with visual quality. As hard as it might be for some folks to accept, clearcutting is the only way that we are going to maintain aspen in our modern forest landscape. Alternatively, forest clearing for land development is not forestry. That's a land use change involving deforestation. Clearcutting, in forestry, is a regenerating activity. It creates a new forest.
Following a clearcut, dormant
buds on the aspen roots respond to the lack of chemical inhibitors from the
overstory and the warmer soil surface. These root suckers grow very rapidly
with the infrastructure of an intact parent root system. With full sunlight,
aspen can grow several feet during each of the first few years.
For a decade or so, the harvested
area appears brushy. This habitat is excellent for a wide variety of wildlife,
including some of our favorite game species. Eventually, the young aspen enter
a natural thinning stage. The less vigorous trees die from the shade cast by
the faster growing individuals.
During the younger periods
of stand development, aspen may appear to be the only species. In fact, in most
cases, there are many other trees mixed with the aspen. Most of these species
will survive in the light aspen shade and outlive the majority of aspen in the
stand. Eventually, the true biodiversity of the stand will stand out. It's usually
there, even if it can't be casually seen.
Of 15 common forest types
in Michigan and northern Wisconsin, aspen ranks the fourth highest in tree species
diversity. The notion that aspen forms monocultural stands is largely the result
of shorter-term visual perception. The stands created through management are
not terribly different from those created by nature.
Quaking aspen matures somewhere
between the ages of 40-60 years. Bigtooth aspen can remain sound for another
decade or two. In either case, the species are considered short-lived as far
as trees go. On better quality sites, the lifespans will be longer. On poorer
sites, the trees won't grow well and will die younger.
Once the stand becomes
mature, the decision to clearcut must be made, again, if aspen is to remain
on the site. Now, without a clearcut, the stand will most likely succeed into
another forest type. This is not necessarily a bad thing, if the new forest
is acceptable to the owner. The succeeding forest type might consist of balsam
fir, red maple, white pine, northern hardwoods, or other more shade-tolerant
trees. The understory will tell you what the next forest might be. In some cases,
the next forest might not consist of trees, but mostly of brush.
While clearcutting is the
only way to regenerate aspen, the area does not have to be in squares and rectangles.
Visual quality can be enhanced by running harvest boundaries along topographical
lines and the edges of different forest types. Islands and corridors can be
left to break-up the harvest area. Sometimes, a limited number of longer-lived
trees can be left dispersed across the area.
The natural ecology of aspen
regeneration calls for very large "clearcuts," sometimes several thousand
acres in size. In today's ownership and user environment, this natural scheme
is unacceptable. With high aspen prices in many regions, clearcuts might be
commercially harvested as small as 10 acres. Pockets under five acres are not
advisable because adjacent trees will shade the regenerating area. It does not
take much shade to significantly retard aspen growth.
Aside from shade, there are
few reasons that aspen regeneration will fail. In areas of very high deer pressure,
browsing has eliminated even vigorous regrowth. Also, if aspen is harvested
when it is overmature, the root systems may not be as successful at supporting
new suckers. If this becomes an issue, it is best to cut aspen during the fall
or winter when the maximum amount of food reserves are in the roots. Lastly,
aspen on inadequate soil types may not regenerate well.
The arguments surrounding
aspen management ought not to be about clearcutting, which is an essential forest
management system, but rather about the amount of aspen we want across the Lake
States forest. Several hundred years ago, there was much less aspen in the landscape
than we see today. Yet today, we have about half the aspen of 75-100 years ago.
Aspen is a critical
habitat for many popular species of wildlife. The wood can be used to produce
a variety of products, such as paper, oriented-strand board, and cardboard.
Solid wood is used in a wide variety of ways. The light gray bark, trembling
leaves, and bright yellow color in the fall make aspen visually appealing. The
species is one of the most utilitarian in the Lake States.
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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at firstname.lastname@example.org or 906-786-1575.
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: email@example.com
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