Everything about Balsam Woolly Adelgid totally explained
Balsam woolly adelgids are small wingless
insects that infest and kill
firs, especially
Balsam Fir and
Fraser Fir. They are an invasive species from
Europe introduced to the
United States around
1900.
Because they're not native, the Fraser fir hasn't evolved any type of defense against this predator. These insects typically lay about one hundred eggs and have three generations per year. The adelgid attacks the tree by feeding in
fissures within the bark of trees larger than about four
centimeters in diameter at breast height. As it feeds, it releases
toxins contained within its
saliva. These toxins reduce the conductance of
sapwood being built, which causes water stress and kills the trees.
The
Great Smoky Mountains National Park, in North Carolina and
Tennessee contains about 75% of all spruce-fir
ecosystems. These ecosystems covered vast portions of the Southeast during the last
ice age, when the climate was cool and moist. Since the retreat of the
glaciers, this ecosystem has been confined to the higher elevations in the mountains of the
Southeastern United States. The spruce-fir forest has evolved as an island, away from any other ecosystems of its type. This has presented valuable research and a unique habitat. These forests have a very dense
canopy and a moist
understory.
Since the invasion of the balsam woolly adelgid, discovered in
1957, Fraser fir mortality rates have been 90-99%. Although some areas are being regenerated by young firs, there's much change in understory composition, including invasion by both woody and
herbaceous species.
Red Spruce, the spruce component of the spruce fir ecosystem, has also been suffering declines. Some researchers attribute these declines to damage from wind, which is usually blocked by the firs. Balsam woolly adelgids have destroyed about 95% of the Fraser firs in the Great Smoky Mountains National Park, creating "ghost forests". One concern is that
acid rain and the deterioration of the
ozone, among other
pollutants are contributing to a weak immune system for the Fraser firs and making them more susceptible to the balsam woolly adelgids. The
Spruce-fir moss spider, which lives on moss mats below the forest canopy, is considered endangered due to the decline of the Fraser fir.
The Balsam woolly adelgid also has a significant impact on Pacific Northwest forests. Specifically,
grand fir,
silver fir and
subalpine fir in
Washington and
Oregon all can serve as a host. Extensive mortality due to this pest in the
Cascade Mountain range was recorded during the 1950s and 1960s. Land area affected by the adelgid in the Pacific Northwest has increased from
83,325 acres (337 km²) in 2004 to
108,128 acres (438 km²) in 2005.
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