Ecology And Environment

Mountain Pine Beetle



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I first came face to face with Dendroctonus Ponderosae about eight years ago. The company I worked for was interested in the possibility of using satellite imagery to track the spread of the mountain pine beetle epidemic, which at the time was in its early stages in Southern British Columbia. The forester who acted as our guide used an axe to slice into the bark of an infested lodgepole pine, revealing a complex network of passages and galleries just below the surface. Using a knife blade, he removed a tiny black speck, which he then showed to us. Here in front of us was the cause of the devastation which lay all around us. The pine beetle displayed in front of us was about the size of a match head, and looked about as threatening as a speck of dust. Yet this tiny creature has had more of an impact on the forests of British Columbia and the Western US over the last ten years than the combined effects of all logging and all forest fires over the same period.



The scale of the epidemic staggers belief. In central British Columbia an area four times the size of Vancouver Island has been devastated. When you drive North through the Cariboo region, you pass through mill towns such as Williams Lake and Quesnel. Not long ago these towns were surrounded by healthy forests. Today there are only dead trees as far as the eye can see. The mills are still working for now, but they are processing beetle killed wood. In a few more years, the wood from these trees will no longer be of sufficient quality for processing. What will happen to these communities then? The mountain pine beetle epidemic has been an ecological disaster. It is likely to also become an economic disaster for many communities.



To appreciate why the mountain pine beetle epidemic has been so devastating, it is necessary to understand the life cycle of the beetles. Female beetles lay eggs under the bark of the pine trees in the late summer, and larvae hatch within a week or so. These larvae occupy and feed off the phloem area just under the bark of the host tree. They continue feeding off the host tree right though the winter and spring. In June and July they transform into pupae and emerge as adults several weeks later. These adults then leave the host tree and fly off looking for new hosts. The galleries which the larvae create eventually cut off nutrients to the host tree and kill it. Additionally the larvae carry a fungus, which affects the host tree’s ability to ward off the attack. This fungus gives beetle killed timber its distinctive blue colouration.



It is this life cycle which makes the epidemic so hard to control. When a tree infested by mountain pine beetles has recently been killed, it still appears to be a healthy tree to the casual observer. It is only in the following year, long after the beetles have left the host tree that the needles start to turn red, the so called red attack phase. At this stage it is too late to do anything about the problem. The beetles are therefore always a year ahead of any obvious signs of their presence. Control is therefore often ineffective. This is particularly true of the current epidemic, which is unprecedented in scale.



There are a number of reasons why this epidemic has occurred. In the first place the climate has changed in recent decades. We are now seeing milder winters, with hotter drier summers. This has the twin effects of ensuring higher survival rates for beetle larvae and increasing water stress on host trees, making them more vulnerable to attack. A sustained cold snap occurring in autumn would be particularly effective in reducing beetle numbers. However the weather in recent years has resulted in high beetle survival rates.



Another reason for the current outbreak is the logging and reforestation practices which have occurred over the last century. This has lead to large stands of even aged lodgepole pines, with none of the mixing found in natural forests. These conditions are perfect for the spread of the mountain pine beetle. Forest companies love the lodgepole pine, because it is fast growing, straight, and will grow almost anywhere. As a result it has become the tree of choice for reforestation, even where it did not naturally occur in the past.



The signs are that the epidemic is at last slowing. In 2008, 7.8 million hectares were destroyed, compared with 10.1 million hectares the year before. It is not slowing from anything we have done however. The beetle is simply running out of suitable trees to feed on. While it is likely we may soon see the end of this outbreak, the damage it has caused is immense. It will be many years before large tracts of interior BC return to full forest cover. The question is whether we will allow this to happen naturally? If we interfere with nature again we may simply be setting the stage for a future outbreak.

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More about this author: Ken Whitehead

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