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October 2009
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The flowers are blooming, the birds are chirping, and everyone is sneezing. That can only mean one thing, spring has sprung. Now for you Valley folk, it has been spring since October. 70 degree temperatures and nice sunny days, who could complain? Some might argue it is devastating Snowbowl, the Northern Arizona ski resort. However we have a bigger issue when you consider the impact it is having on our national forest. From the Prescott to the Coconino through the Tonto National Forests there are thousands of acres of bug kill trees. How do bark beetles kill trees? According to the Arizona Forest Health Program here’s the explanation: How do pine bark beetles kill trees? Pine bark beetles (Ips sp. and Dendroctonus sp.) feed primarily on the inner bark (phloem tissue). This has the same effect as girdling (peeling off the bark) of the tree. Damage caused by their feeding acts as an internal tourniquet cutting off the flow of nutrients from the leaves to the other parts of the tree. As the damage progresses, sugars and other complex compounds cannot be translocated downward from the leaves to non-photosynthetic areas of the tree. The beetle can also introduce a blue stain fungus which grows into the wood (xylem). This fungus prevents water from being transported upward to the leaves. Both of these factors contribute to the decline and death of colonized trees. What caused the current bark beetle outbreak? The current level of bark beetle mortality has resulted from a combination of natural factors including, but not limited to: drought, dense forest stands, shallow/rocky soils, and relatively large quantities of bark beetles. Human activities such as fire suppression, past forest management practices, past grazing practices, and ongoing urbanization also have also contributed to current conditions. These factors all influence the amount of water, light, and nutrients available to individual trees in the forest. Trees not receiving enough of these resources become stressed. Bark beetles can detect stressed, susceptible trees and they respond by colonizing it and effectively removing it from the population. This inadvertently makes a larger quantity of resources available for the surviving trees, shrubs, and herbaceous plants. So why am I telling you this? All these trees are prime fuel for forest fires and according to the state forester more than 60% of all wildfires in Arizona are human caused. Please be careful while using the forest! |
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