Bark Beetle Infestation

You have probably noticed that many of the trees in view are not green, but either rust-colored, gray, or black. Those that are rust-colored or gray and scattered seemingly at random have in all likelihood been killed by bark beetle infestation. Those trees that are black and distinguished by the large area of destruction are evidence of forest fire. The bark beetle is a flying insect which at maturity is the size of a long grain of rice. The beetles bore through the bark to reach the tree’s cambium layer and lay their eggs. Once hatched, the larvae create feeding tunnels that encircle or "girdle" the tree. This "blocks" the flow of water and nutrients within the tree and it dies. The first growth season the tree is attacked it may appear outwardly healthy and green. After that it will turn rust-red, then gray, as it loses its needles and becomes a dead tree. At this point the larvae have grown to mature adults and migrate to other trees.

Currently, what you see is the results of the largest known insect infestation in North American history. To-date 92 million acres have been destroyed by the bark beetle. Bark beetle infestation has been occurring for a very long time. But, in the past, the population cycle fluctuated, decreasing during times of adequate moisture, freezing temperatures and healthy forests composed of a variety of trees of different species. The past several decades have been distinguished by higher temperatures, drought and same-species forests of a more uniform age. There is no effective form of treatment for a forest infestation, although individual trees may be successfully treated to deter the beetles.

2017 ROUTE GUIDE, Condensed Historical and Natural Science Material from the Complete Resource Guide, Empire Builder – Amtrak Train 8 Between Edmonds, Washington and Havre, Montana, NPS