here is nothing quite like a well formed, majestic, dark green
sugar maple tree standing proudly in a forest, field or village. It shows
strength. It speaks of resiliency. It has history. When you hear “sugar
maple tree health,” this is the image that comes to mind.
Vermont’s forests are valuable ecologically, economically, and socially.
Covering nearly 80 percent of the state, our ever-evolving woodlands provide
jobs, stability to the landscape, wildlife habitats, biological diversity,
clear water, scenic vistas, and diverse recreational opportunities. These
values are common ground for Vermonters, and make monitoring and protecting
the health of our forests a priority.
Assessing Sugar Maple Health
The health of sugar maple trees, and forest health in general, involves
a complex set of conditions and factors, which often have an effect on
one another. Rarely, can a tree's poor health be traced to a single factor;
normally a tree's health problems result from a number of causes.
Forest scientists use a number of measures to help measure tree health,
Sugar maple trees grow best on deep, moist, fertile, well-drained
soils. Likewise, these trees prefer cool, moist, climates that receive
around 40 inches of rain during the growing season and where average
temperatures range from 0° F in January to 60° F in July. In
New England, sugar maple trees have an elevation limit of around 2500
feet. They are tolerant of shade, and in many recent studies, have been
shown to be tolerant of ozone and acid deposition pollution. Although
sugar maples will reproduce and grow on less than optimal sites, they
will be less vigorous and shorter lived, and may be more sensitive to
stress from insect, diseases, weather or other factors.
Structure, sustainability, and diversity of forests
Diversity in tree size and species tend to promote a stable
forest for the long-term. A natural healthy forest, is a dynamic system
in which new trees are sprouting each year, and older or less vigorous
trees are dying. Weather events such as high winds, lightning and ice
storms may create natural openings in forests. These openings are a fantastic
way for new tree species to take hold: Trees that require more sunlight
than is typical in the understory of dense forests. The abundance of
sugar maple trees of different ages, tree growth rates, and the mix of
sugar maple and other species, are all measures of forest health and
sustainability. In Vermont, these health factors are measured periodically
as part of the Forest Inventory and Assessment Program.
A woodlot tapped for maple syrup production is called a sugarbush. Healthy
trees are essential for good sap production. Sugar maple is
usually the dominant species, since it is desirable to thin out non-maples
trees that can be tapped. However, creating a monoculture of
sugar maple can be detrimental to the long-term health of the forest, should
which attacks sugar maple become established and begin injuring
or killing trees. Other sugarbush management guidelines should also be
into the operation to maintain tree health. See Sugarbush
Management: A Guide to Maintaining Tree Health, for more information.
Reproduction and Leaf Development
Long strands of yellow-green sugar maple flowers are produced
early in the spring, before leaf buds open. Trees begin reproducing at
about 50 years of age, with older trees bearing large quantities of seed
periodically. Bud development in the spring begins in late-April to early-May,
and generally full leaf-out has occurred by early June. Each tree is
unique in the timing of this process. Monitoring of spring bud development
can provide another indicator of tree health, and is a process that can
be altered when trees are under stress. Yearly examination of bud expansion
is part of Vermont's state monitoring program.
Insects and Diseases
If you look closely at a sugar maple leaf you will generally
find some sort of insect feeding or symptom of disease present. Their
presence and abundance ebbs and flows according to natural population
cycles. Insect and disease outbreaks depend on weather conditions that
enhance or deter the organisms, and/or the health of trees themselves
(stressed trees often lack chemical mechanisms to fight off insects and
diseases). Keeping track of what insects and diseases are in abundance
each year, correctly diagnosing the organisms involved, and making management
recommendations to landowners are part of the Vermont
Forest Health Protection program.
Some of the major sugar maple insects that affect tree health include:
Tent Caterpillar, Sugar
Maple Borer, Maple Leaf Cutter, Pear
Prominent and Bruce
Spanworm. Sugar maple diseases include: Anthracnose,
Eutypella Canker, Nectria Canker, Armillaria Root Rot and Sapstreak. Vermont's,
Conditions Report, summarizes the current status of many
of these pests.
The brilliant display of orange, red and yellow fall colors
make sugar maples special. Add sunlight to the mix, and they appear to
glow. Our hillsides become an artist’s palette with a variety of
colors and hues. The science behind this art involves leaf chemistry,
day length, and fall weather conditions. Each
season varies. Along with color qualities, timing
and duration of fall foliage are additional indications of healthy or
stressed forests. Trees or branches under stress can change color earlier
than normal. Drought or damage from insects or diseases can cause early
fall color, or in extreme cases, can cause leaves to turn brown rather
than normal fall color. Fall
foliage monitoring is part of Vermont's
Forest Health Monitoring Program.
Determining Tree Health
There are a few measures of tree health that can be used as
guidelines to determine, with some certainty, that a tree is healthy.
Many of these indicators of tree health are used in statewide forest
health monitoring programs. Remember that a healthy tree can become unhealthy,
and unhealthy trees can improve.
A healthy tree has …
- a live top (live crown) that is greater than one-third the
total tree height,
- newly dead branches that make up less than 15% of the total
- less than 15% of the tree crown with missing branches,
- foliage that is dense throughout the live portion of the
- a tree trunk with open wounds that are less than one-third
the diameter of the tree, no wounds in contact
with the ground, and no wounds that have soft, punky wood (an indication of decay).
For more information:
Health of Sugar Maple in Vermont-2003: a 2-page public leaflet summarizing
tree health, current health problems and news on sugar maple trees.
Vermont Monitoring Cooperative: Ongoing forest monitoring including sugar
maple trees. VMC is a partnership program of long-term data monitoring
and research on forest ecosystems with studies at 2 locations in Vermont,
Mount Mansfield and the Lye Brook Wilderness Area.