An invasive insect that is infesting trees in forested and urban areas of Alaska is the spruce bark beetle. Since 1980, these beetles have accounted for the demise of spruce trees on 4.4 million acres in Alaska. Of these, over 1 million acres were located in the Kenai Peninsula (Joling). In 1996 alone it was estimated that spruce bark beetles killed around 30 Million spruce trees. These beetles attack only wide stem spruce trees of the species Sitka, White, and Lutz. Black spruce trees are very rarely attacked. The beetles ignore other tree species like hemlock, birch, cottonwood, and aspen.
A spruce bark beetle, scientific name ‘dendroctonus rufipennis,’ is very small in size. The typical length of an adult beetle is 6mm. It attacks the spruce tree by excavating a tiny hole in its bark in order to reach the thin inner phloem tissue that lies between the bark and wood of the tree. It consumes the phloem tissue, the loss of which is very harmful to the tree as it is instrumental in the food preparing process – food is prepared in the needles and then transported to the tree roots. Mature spruce trees are particularly in danger of being infested by spruce bark beetles because maturity causes them to rot from inside, thus significantly reducing their resistance against beetle attack.
Adult beetles initially attack a spruce tree by drilling holes in it. Female beetles then lay eggs in the galleries (Alaska Department of Natural Resources). Adopting what is called the ‘pitching out’ maneuver, the spruce tree resists by generating pitch that inundates the galleries and drowns the marauding beetles and their larvae (Rea et al.). The pitch contains hydrocarbons, and as many as 17 varieties of terpene – the mother of turpentine (Joling). However, only young trees are vigorous enough to carry out successful ‘pitching out’ operations. Mature trees cannot generate such pitch, and as a result, are easily killed by a concerted attack of a large number of spruce bark beetles (Rea et al.) that generate chemicals called pheromones to communicate with one another on topics like locating of target spruce trees, mating, or repelling other hordes of invading beetles. A typical downed spruce tree is likely to host around 100 beetles in each square foot of its bark. The spruce bark beetles then move from the downed tree to other living spruce trees. They attack in the period between the middle of May to the middle of July when the prevailing 60 degrees Fahrenheit temperature is favorable to them.
In the forested areas of the Alaska Kenai Peninsula, the loss of spruce trees to beetles has several detrimental effects. The first effect is the loss of tree shade to the Kenai River. This results in increased exposure of river water to the sun. The resultant increase in water temperature makes it less capable of retaining oxygen. The ecosystem is unable to live effectively on a lesser amount of oxygen. The second effect is the loss of wildlife. Tree-living animals that thrive in the marine ecosystem are deprived of their habitats and perish as a result. The third effect is soil erosion. Soil bereft of support from roots of spruce trees become eroded. This results in damage to the fragile riparian areas that traditionally retain water after rainfall or snowfall . The fourth effect is that thick grass grows on the open land created by fallen spruce trees. The grass sucks in a lot of water through their roots, thereby causing serious depletion of river water. The fifth effect is flooding. In winter, the snow that used to earlier gather on spruce tree branches now accumulates on the open ground created by the loss of trees. With no tree shade to protect it, the accumulated snow melts in the sun, with the resultant water entering the river and causing spring floods.
I recommend a series of cost-effective methods to detect and protect spruce trees that are to be carried out on two fronts – in the Alaska Kenai Peninsula forested areas, and in urban Alaska.
In forests, each spruce tree of the 3 species mentioned should be inspected by employees of the U.S. Forest service every day during the period between mid-May and mid-July. Municipal authorities and householders should similarly check such spruce trees in urban areas during that period. A spruce tree not attacked by spruce bark beetles does not bear any perceptible reddish hued boring dust, or small reddish hued globes of pitch mingled with boring dust, on its bark in the area from ground level to a height of about 6 feet. In the case of an infested spruce tree, such dust or globules are clearly visible on the bark in an area up to 6 feet from ground level.
The spruce tree population in forested areas can be saved by 3 methods. Logging around the shores of the Kenai River will lower the number of spruce trees that could be attacked and overcome by spruce bark beetles, fall into the river and tamper with the river bed life pattern. Due to perceived benefits to the marine ecosystem, conducting logging operations along the river shores is more logical than logging in inland areas of the Peninsula. The second method is using trap trees. These are spruce trees with extraordinarily wide stems (more than one foot) liberally spread out among other normal stem spruce trees. An exceptionally large number of spruce bark beetles attack the trap trees while ignoring the other spruce trees. The third method is to let the gestation period of the spruce bark beetles come to a natural end. It is estimated that the natural gestation term is less in the south region of the Kenai Peninsula as compared to the central region . It is more logical to concentrate on spruce tree saving methods in the central region that is more likely to witness beetle outbreaks that would damage the marine ecosystem.
The first method of saving the spruce tree population in urban areas is by boosting the vigor of those trees. This involves watering and fertilizing the trees during their initial growing period. Fertilizers are rich in phosphorous that assist in root creation and leading to increased intake of water and nutrients. A typical dose is one pound of fertilizer per inch tree width applied into the root region. The second method is to spray insecticides such as carbaryl, chlorpyrifos, or lindane on spruce trees in order to repel spruce bark beetles. This should be typically done during spring so that the trees are fortified against beetle attacks. The third method is to prune lower branches of spruce trees. This activity should take place in the fall season. This method is particularly recommended by the U.S. Forest Service as a good way to ward off spruce bark beetle attacks. The fourth method is to cut down trees infested by spruce bark beetles, as this will prevent other healthy trees from being infested. This activity should be carried out either during the next fall season or before May of the next spring season. The fifth method is to dispose of fallen trees quickly. Trees killed by spruce bark beetles should be debarked or fire-scorched immediately upon felling in order to kill the adult and larvae beetles in them. The tree should then be chopped and used as firewood. Stumps of fallen trees should not be allowed to extend above ground level. If this is not possible, then the stumps’ bark should be removed up to an area of 2 inches below ground level. The last method is to refrain from doing unfavorable activities during house construction, such as changing drainage patterns, heaping large quantities of soil over tree roots, and improperly using heavy equipment.
References
Joling, Dan. “Destructive Insects on Rise in Alaska.” The Boston Globe. 2007. Web.
Rea Katie, Bartolowits Jennifer, Moe Madison & Chihuly John. “Spruce Bark Beetles.” University of Alaska Fairbanks School of Fisheries & Ocean Studies. 2007.
“Spruce Bark Beetles: Control Options for the Home or Lot Owner.” Fs.fed.us. (N.d). 2007. Web.
“What’s Bugging Alaska’s Forests: Spruce Bark Beetle Facts & Figures.” Alaska Department of Natural Resources. 2004. Web.