by Luisanna Carrillo-Rubio
FOR MASSIVE TREE SLAUGHTER
A photograph of a mountain pine beetle taken from the dorsal view
© Canadian Forest Service / 2005 from: the northeastern slopes of the Rocky Mountains.
Our forests — whether in Sweden, the United States or Canada — are in danger. The outbreaks of mountain pine beetles or spruce beetles, little-5 millimeter insects, are killing more healthy adult pine trees in British Columbia than logging and wildfires. According to a Washington Post report published on February, 2006, "The mountain pine beetle has infested an area three times the size of Maryland, devastating swaths of lodge pole pines and reshaping the future of the forest and the communities in it.". Bark beetles go inside tree trunks and feed on the layer between the bark and wood, killing a tree. The carnage is currently in progress.
Figure 1: British Columbia, Canada. All the brown or yellowish trees
are infested by the bark beetle.
Figure 2: A map of British Columbia and Alberta that shows the mountain pine beetle range and the area of major outbreak in interior of British Columbia.
The Canadian Forest Service calls it "the largest known insect infestation in North American history." According to a forest officer in Quesnel, British Columbia, observations of the pine beetle have shown that it has been acting more aggressively than ever before: "They are attacking younger [and stronger] trees, and attacking timber in altitudes they have never been before." How can a 1/5 of an inch-sized beetle destroy millions of acres of mature, ancient forests? A bark beetle will spend most of its life under the bark of mature trees. First, many female beetles will make J-shaped tunnels inside the bark of an adult tree and deposit their eggs. Once the eggs mature, larvae will hatch. These larvae will tunnel away from the egg chambers and feed off the bark for the whole winter until they develop into pupae to emerge as adult beetles from the host tree. As the larvae eat from the bark, they will kill the tree usually within a year. Each female will release pheromones to attract other beetles, so a large number of bark beetles will colonize a fully grown tree. As the beetle and its larvae eat through the bark, they spread blue stain fungus. Bark beetles carry in their mouths and their bodies the blue stain fungus and its spores. Blue stain fungus then clogs up trees' water-conducting vessels, so this, along with the beetle and larvae feeding, will succeed in annihilating the host tree quickly, so that a century old tree will be dead within a year after infestation.
Figure 3: Dead trees in Alaska.
The presence and threat of the tree beetle are not new occurrences. However, something has changed to allow the beetles to survive in larger numbers enabling them to attack a significant number of adult trees. At the same time, adult trees seem to have become more vulnerable to the attacks of the beetles. Scientists report that "some environmental factor has triggered a rapid population buildup" of the plague. In the far north of the Alaska wilderness, the spruce bark beetle has seen its development accelerated by heat. This beetle's life cycle normally takes two years to come to a conclusion. Extraordinarily warm summers are to blame for the fact that the beetle has been able to complete its reproductive cycle in one year alone. If the bark beetle were to face two consecutive cold winters, its numbers would undoubtedly dwindle. Rising temperatures have allowed the bark beetle outbreak in the Alaska wilderness to get out of control. Research indicates that "recent climate warming in Alaska has removed those limitations [i.e. what has previously prevented severe outbreaks of bark beetles, such as extremely cold winters]; winters especially have been milder and a few summers (e.g. 1989, 1991, and 1993) have been exceptionally warm."
Climate change has also continued to impact the earth's ecosystems as extreme weather and drought have intensified over the last years. This is of significance, since "some of the typical factors in weakening the resistance of spruce [and other tree species] include defoliation, flooding, [and] prolonged drought."
United States officials note that while outbreaks of the mountain pine beetle have appeared only on isolated patches in northern Washington, there have been reports of more severe outbreaks in other areas of the continental United States. Beetles attack trees and then move on to neighboring trees, eventually turning the pine needles of large forest patches to a brown color. The potential of the beetle to spread onto neighboring trees is a reasonable cause for alarm, since a single beetle's eggs can produce enough beetles to invade and colonize 15 more trees. After a short period, all the needles are lost and an eerie, grey skeleton is all that remains from a once healthy adult tree. A century-old pine tree can be killed within a year or less by bark beetle infestation.
Figure 4: Bark Beetle infested trees in Arizona.
A study by scientists from the University of Alaska, Fairbanks reported that in the Alaska forests, the bark beetle has affected 2 to 3 million acres of south central Alaska forest in the last decade. One of the most affected tree species is the highly commercially prized white spruce. Generally, all spruce trees greater than 10 centimeters are killed by the spruce bark beetle (Dendroctonus rufipennis). This is one of the largest cases of tree death ever experienced as a result from an insect outbreak in North America. Tree-ring studies near Fairbanks have been used to demonstrate that "recent warming in Alaska appears to have removed the environmental limitation [or all natural defenses] that prevented outbreaks of spruce budworm in the far north."
In the Kenai Peninsula of Alaska, the spruce tree beetle has already wiped out between 70-80% of the spruce trees. This translates into 2.3 million acres since 1992 and represents "the largest loss to insects ever recorded in North America." According to Ed Holsten, an entomologist with the U.S. Forest Service in Alaska, about two million acres were infested between 1920 and 1990, in contrast with three million acres in the 1990's alone. During 1996, one million trees were infested and subsequently killed.
Figure 5: Aerial view of the once lush forests of the
Kenai Peninsula, Alaska.
The impact that a loss of millions of acres of forest has upon an ecosystem is severe. Many animal species depend on trees for their refuge and food. Trees on high elevations, such as the white bark and other pine trees in the Rocky Mountains, serve as headwaters for all the main rivers in North America, since a lot of the water accumulates as winter snow. It is in the arid west that this snow accumulation is critical. The less the number of trees in high elevations, the less water can be retained as snow pack. Many species of wildlife also depend on the nutritious pine seeds of white bark pine trees in the Rockies, from small rodents to the endangered Grizzly bear in Greater Yellowstone. The more trees the white bark pine beetle destroys, the more much of the wildlife will lack an essential part of their diet. It has been noted by the U.S. Forest Service that in years of reduced white bark pine seed production resulting from droughts or bark beetle outbreaks, detrimental encounters between grizzlies and humans increase dramatically.
Michael Fastabend, of the Kenai Borough's Spruce Bark Beetle Mitigation Office, has expressed his concern in regards to the increased potential of wildfires: "as dead trees drop needles and limbs, fuel and tinder accumulate on the ground, making conditions ripe for a fire. The Environmental Protection Agency (EPA) says the increase in forest fires due to beetle outbreaks and global warming 'is of particular concern for wildlife species that make extensive use of mature and old-growth forests."
Scientists attribute the beetle outbreak in Alaska not only to the mismanagement of forests (where too many trees compete for sunlight and resources weakening individuals), but also to global warming. According to EPA: "the average temperature in Anchorage has increased 3.9 degrees Fahrenheit over the last century, and [it estimates] that by 2100, temperatures in Alaska could increase by five degrees in the spring, summer and fall and by ten degrees in the winter"
Unfortunately, outbreaks of tree beetles are not unique to the forests of North America. Recently, North European forests have seen a dramatic increase of tree beetle infestations. The beetle had caused problems before in Central Europe, however, in Northern Europe, the long cold winters kept bark beetle numbers low. For the present and the upcoming years, experts predict that up to 60 million cubic meters of trees will die as a result from bark beetle infestation in Northern Europe.
In Alaska, British Columbia or Northern Europe, as the destruction takes its course, individuals continue to see the ruinous aftermath of the tree beetle epidemic. Unfortunately, as the Mountain Pine Beetle Emergency Task Force in British Columbia avows: "only cooler weather can stop the mountain beetle epidemic [. . .]. But if the warming trend continues, so will the potential for insects, fire and loss of forests." In the words of Allan Carroll, a research scientist at the Pacific Forestry Centre in Victoria: "It's pretty gut-wrenching." Dr. Carroll has been studying the links between warmer winters and the ability of the beetle to spread further causing the carnage. He further admonished that "people say climate change is something for our kids to worry about. No [it's not]. It's [to worry about it] now." Dr. Carroll also warns that it is the rapid rising in temperatures that is increasing the range and survival rate of the pine beetles, and further recommends that "all the data shows there are significant changes over widespread areas that are going to cause us [a] considerable amount of grief. Not only is it coming, it's here"
How pressing is this problem? Forestry experts say that in Canada, "the weather [. . .] has not been cold enough for long enough to kill the beetle," since average winter temperatures have risen by more than 4 degrees in the last century. The chief forester in British Columbia, Jim Snetsinger, concludes: "Global warming is happening. We have to start to account for it."
Figure 6: All the brown coloring in the forest indicates parts
of forests killed by bark beetles in Mount Swanell,
British Columbia, Canada.
For educators, you can find activities regarding tree beetles and their impact at:
For more information:
International Herald Tribune: Global warming blamed for Swedish beetle-infestation
Colorado State University: Mountain Pine Beetle
North Forty News: Giant blue spruce falling to tiny beetle
The New York Times: New Tree Disease May Afflict California's Giant Redwoods
High Beam Encyclopedia: Battling the Bark Beetle.(spruce tree infestations fatal)
University of Alaska: Spruce Beetles, Budworms, and Climate Warming
US Global Change Research Program: Increased Risk of Fire and Insect Damage to Forests
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