You probably don't even think about it, but our forests get sick, too. But when the forest catches a "bug," it just might be a real
Forest health problems also can be caused by parasitic plants and fungus infections. Insects, fungi, and parasites are all natural parts of the forest ecosystem. And just like the bacteria in our bodies, they only become a problem when something gets out of whack.
Some of the things that bug the Idaho forest are: Bark Beetles, Defoliators,
Dwarf Mistletoes, and Root Diseases.
Bark beetles cause a lot of visible damage to the trees in the Idaho
forest. They attack trees that are weakened by old age, drought, overcrowding,
root disease, or weather damage. Bark beetles bore through the bark to eat
the tasty nutrients in the inner bark ("phloem") and "cambium"
layers. If they eat all the way around the tree, (called "girdling"
the tree) the tree will die -- its food tube will have been cut and it will
be unable to send nutrients up and down the trunk.
Idaho's bark beetle population includes the western pine beetle, mountain
pine beetle, Douglas-fir beetle, and fir engraver.
Defoliators hurt trees by eating the green needles that take in carbon
dioxide and release oxygen into the atmosphere. Damage to the needles impairs
the tree's ability to "breathe" and to collect sunlight for manufacturing
sugars, weakening it and making it more vulnerable to damage from other
pests and diseases.
In Idaho's forests, most defoliators are moths, such as the Douglas-fir
tussock moth and the western spruce budworm. The tussock moth has caused
significant damage to the forest in recent years, affecting 15% of
the forested area of the Boise National Forest.
These clumpy, parasitic growths rob nutrients from the host tree. By
robbing nutrients, dwarf mistletoes impair the tree's ability to grow. Trees
that are heavily infected by dwarf mistletoes can be permanently stunted
and can die. Because of their scraggly looks, tree branches that have been
infected with dwarf mistletoe are sometimes called "Witch's Brooms."
Root diseases are the "hidden killers" of Idaho's forests,
because they attack the underground roots of trees. Root diseases are caused
by fungi that live in the soil. When a tree is healthy, its natural defenses
prevent infection by these naturally occurring fungi. But when a tree is
weak, damaged, or otherwise diseased, the fungi can attack the roots, and
can quickly move up the tree causing a great deal of damage.
In Idaho's forests, root diseases include laminated, black stain, annosus,
and armillaria -- the most widespread of all root diseases in the northwest.