Spruce beetle, Dendroctonus rufipennis (Kirby)
The spruce beetle, Dendroctonus rufipennis (Kirby), is the most significant natural mortality agent of mature spruce. Outbreaks of this beetle have caused extensive spruce mortality from Alaska to Arizona and have occurred in every forest with substantial spruce stands. Spruce beetle damage results in the loss of 333 to 500 million board feet of spruce saw timber annually. More than 2.3 million acres of spruce forests have been infested in Alaska in the last 7 seven years with an estimated 30 million trees killed per year at the peak of the outbreak. In the 1990's, spruce beetle outbreaks in Utah infested more than 122,000 acres and killed more than 3,000,000 spruce trees. In the past 25 years, outbreaks have resulted in estimated losses of more than 25 million board feet in Montana, 31 million in Idaho, over 100 million in Arizona, 2 billion in Alaska, and 3 billion in British Columbia.
Spruce beetle outbreaks cause extensive tree mortality and modify stand structure by reducing the average tree diameter, height, and stand density. Residual trees are often slow-growing small and intermediate-sized trees which eventually become dominant.
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