Many people have probably heard about the Mountain Pine Beetle (MPB) epidemic in western Canada. But the pine beetle is just the most visible face of a larger issue. In the past few decades, several species of beetles have girdled and killed more than thirty billion lodgepole, pinyon, ponderosa, and whitebark pines, as well as white spruce and Engelmann spruce. This sort of devastation is actually quite normal for forests, when Nature is left alone to do its work, but the economic consequences of this destruction have caused the current epidemics to be labelled as a “problem.”
Beetles are probably one of the most successful examples of life on our planet. Beetles (Coleoptera) make up a third of all life on Earth, and a quarter of all animals. Estimates for the number of different species of beetles are in the vicinity of ten million. If you took just one part of the beetle family, the bark beetles, there are more than a thousand more species than there are types of mammals on Earth. Beetle fossils exist that are a third of a billion years old (significantly older than dinosaurs), and various species can live in almost every environment: in rivers, lakes, jungles, caves, forests, deserts, and mountaintops. Bark beetles cooperate on a social level, and bury their dead. If you look globally at species of animals that are smart enough to hunt in packs, there is a very short list: humans, wolves, hyenas, lions, killer whales, piranhas, ants, and bark beetles.
One interesting thing is that bark beetles themselves do not kill the trees they inhabit. Beetles, like some other insects, act as a sort of mobile zoo, carrying all kinds of other life forms with them. The spruce bark beetle, for example, can carry up to ten different species of fungi, six different kinds of mites, and nine different types of bacteria. All of these organisms work together as a complex mini ecosystem, as the life cycle of the beetle continues. It is the effects of these various organisms, in concert, that lead to eventual conifer mortality.
The interesting thing is that beetles are not necessarily bad for the forests. Some people would disagree, particularly those who focus on an immediate snapshot of the forests, and who worry about the current economic potential. But in the long term, over decades and centuries, beetles are unquestionably an important part of forest maintenance. You see, beetles basically act to keep a forest healthy overall, in the longer term. There is no need to protect the trees from the beetles; the beetles and the trees have been living in a symbiotic relationship for millions of years.
Starting about a century ago, North Americans began to focus some efforts on fire suppression within the forests. The obvious rationale was that if forest fires were fought, there would be more wood. But nature relies on regular fires (every few decades) to keep a forest “tidy” and healthy. By putting out the small fires, what happened was that fuel loads began to increase. When a fire eventually came along that couldn’t be put out right away, it could grow to enormous size.
Many people have mistakenly assumed that beetle-killed trees would lead to increased forest fire risks. I actually believed that myself, several years ago. It seems that that would be obvious, because when you look at a dead tree that has been killed by a beetle, it is dry and reminds you of firewood. But when you start to get experience with forest fires, you quickly realize that the majority of major forest fires are “crown” fires. Rather than the coarse wood (the thicker primary branches and trunks of the trees) burning, it is the “fines,” the needles and leaves, that provide the quick fuel that burns fast and hot. Although you would think that living green trees would be moist and less prone to fire than dry and dead stems, the exact opposite is true. Fire likes smaller pieces of fuel with more relative surface area that is exposed to oxygen, and fire also likes density, so flames can jump from fuel source to fuel source. You get this with living trees, but not dead ones. When a tree has first been killed by beetles, yes, it is a high fire risk for the first year or so. But once the needles drop off, it is not a high fire risk. The lesson here is that determined fire suppression eventually guarantees either a catastrophic fire or a bark beetle epidemic.
Any competent forester or woodsman will tell you that a diverse forest is the best kind. But logging companies like to work with monocultures, large tree stands where all the trees are the same species and the same relative age. When forests are harvested and replanted, they are usually planned as a plantation of just one or two dominant species (spruce, pine, fir, or cedar) and all the trees end up having the same approximate age. But it is this kind of forest that is most susceptible to damage from beetles. Basically, the beetles see these forests as a massive free lunch, and in attacking the trees, they are really just protecting the trees from themselves (from overcrowding). When forests are left to themselves, beetles attack a very small number of trees each year, in a system which promotes diversity and balance. It is only when “unnatural” large concentrations of a single species are allowed to grow together that true epidemics become possible. As foresters said in East Texas in the 1980’s, when southern pine beetle growth exploded, “What we have here is not an epidemic of southern pine beetles, but rather, an epidemic of southern pine.”
At this point, the decision about what to do with beetle-killed forests is what concerns me. Many foresters prefer the “mow it down and salvage the wood” approach, resulting in more clear-cutting than would have otherwise been the case. As a tree planter, I initially wished that the BC government would take more of the beetle-killed areas that they couldn’t salvage log and just bull-doze the standing dead wood, and then let our industry replant new forests (preferably multi-species). But since then, I’ve learned a lot more about the interplay between various parts of the forest ecosystem. The northern boreal forests are very efficient carbon sinks, perhaps more so than tropical rainforests. A beetle-killed forest left standing to rot slowly will also release carbon slowly, over a period of many years. As that gradual release takes place, the carbon loss is offset by new undergrowth, which happens very quickly as the sunlight can easily penetrate through to the forest floor. So effectively, leaving dead trees standing is an effective carbon sequestering strategy, probably much more wise in the long run than cutting the dead wood for use by wood pellet factories, where the product gets shipped halfway around the world. Of course, we tree planters could probably still speed up that renewal process by planting a mix of several species in these understory plants.
I won’t go any further into the ground that the book covers, because that would spoil things for people who are planning to read the book. But I should note that a 2001 provincial review in British Columbia suggested that in terms of the “costs and benefits of clear-cutting beetle-kill ... a forest renewed by bark beetles was a much smarter economic proposition than a monster clear-cut designed by humans with forestry degrees.” I personally don’t want to suggest that the pine beetle epidemics are a good thing in an absolute sense. But I do think that a moderate level of pine beetles is an important part of natural renewal, and beetle renewal does have positive aspects that politicians and logging companies sometimes seem to ignore in favour of short-term economics. I guess the best thing though, would be for you to read the book and form your own opinions. Here's a link to buy the book:
