Trivia question: What species is capable of changing an ecosystem the fastest? If you guessed human beings, surprisingly enough, you’d be wrong. That accolade goes to the bark beetle.
Since the 1990s, vast swarms of about 12 species of bark beetle have eradicated nearly 30 billion conifers, changing entire watersheds as a result and leaving vast, red and gray arboreal graveyards in their wake. The beetles prey on conifers in teeming swarms, up to 20,000 tons worth of them – equivalent to a wolf pack a half million strong, preying on trees rather than elk.
The beetles typically target old or drought-stricken trees with degraded wood that’s easier to burrow into than young or healthy trees. First, a female selects a tree. She then releases pheromones which attract hundreds of other beetles to the tree. Once they beetles attack a tree, a savage biochemical battle ensues, the product of over 300 million years of co-evolution. The tree produces copious quantities of resin to try and entomb the insects and, failing that, poisonous hydrocarbon gas. However, when the beetles attack in sufficient numbers to overcome the tree’s defenses, they burrow in (carrying along various molds and fungi), and lay their eggs. When they eggs hatch, the larvae finish the tree off by eating it from the inside out, helped along by the fungal nourishment their parents brought into the tree.
More and more, the beetles have been winning (hence the tens of billions of trees murdered by beetles in the past two decades). They have also been acting in unusual ways: where 600 beetles might attack one tree before, now up to 6,000 might, in a suicidal rush heedless of the lack of room to breed. Where they used to attack only old or drought-damaged trees, beetles now attack young pines as well. What is going on to cause these changes?
Biologists believe that human intervention is largely to blame for the tree genocides. First, forest fire-fighting efforts have drastically increased the number of old trees in a forest from about 25% to 50% of a population. These trees represent the equivalent of an all-you-can-eat buffet and love nest for bark beetles. Second, global warming may also exacerbate the problem (is there anything it doesn’t make worse?); when the climate heats up, even a couple degrees, insect activity increases. The increased insect activity, combined with heat stressed trees, creates a recipe for disaster.
Once the trees are gone, they often don’t return, with grasses growing up in their place and preventing regrowth. Worse, there isn’t a lot people can do to stop it; scientists have tried everything from electrocuting trees, to chemical cocktails, to plastic explosives, but with little to no success. One approach has been clearcutting trees in the beetles’ path to stop the spread, but this seems to be an instance where the cure is as bad as the disease.
It remains to be seen in the years to come whether the scourge will continue to spread across North America (and throughout the world – this isn’t only an American problem), or whether the trees can turn the tide. Either way, it gives us one more reason to think about our place in Earth’s ecosystems, and to do what we can to stem global warming.