USA — The current pine beetle outbreak that has led to higher tree mortality among Colorado forests has prompted some people to suggest that beetle-kill trees will invariably lead to larger wildfires and destroy our forests. At the heart of this issue are flawed assumptions about wildfires, what constitutes a healthy forest, and the options available to humans in face of natural processes that are inconvenient and get in the way of our designs.
While it may seem intuitively obvious that dead trees will lead to more fires, there is little scientific evidence to support the contention that beetle-killed trees substantially increase risk of large blazes. In fact, there is evidence to suggest otherwise.
Implications for wildlife
Bark beetles tend to focus on larger trees, and not all trees are killed. This has important implications for fire risk. Fine fuels not large snags are the prime ingredient for sustained fire. After a major beetle outbreak, and once the red needles and small branches have broken off the trees, all that remains are upright big boles that do not burn well. To sustain a blaze among a snag forest you usually need fine fuels to maintain the heating process. That is why one uses small kindling and other fine fuels to start a campfire, and must continuously feed small wood under the bigger logs to keep the fire going.
Lodgepole pine, the primary species attacked by beetles in the Rockies, tend to be found at more moist, higher elevations which simply do not dry out enough to burn well in most years. That is why lodgepole pine forests typically have long rotations between burns on the order of hundreds of years in some places.
Climate/weather events, not fuels, largely control large blazes. If the climate/weather isn’t conducive for fire spread, it doesn’t much matter how much dead wood you have piled up, you won’t get a large fire. As an extreme example, think of all the dead wood lying around on the ground in old growth West Coast rainforests lots of fuel, but few fires because it’s too wet to burn. But it’s even more complex than that generalization.
Even more surprising to many is that a forest dominated by bug-killed snags may be less vulnerable to a blaze than a green forest. Just as a recently burned forest often acts as a fire break due to limited fine fuels, bug-killed trees affect fire spread in much the same way. In fact, green trees stressed by drought can have internal moisture levels drop lower than kiln-dried lumber, but because they still possess flammable resin-filled needles and small branches that burn almost explosively, green trees are sometimes more flammable than dead trees.
Beetles are ecosystem engineers
Even more importantly, bark beetles are increasingly recognized by ecologists as ecosystem engineers much as beaver are now recognized as important to the creation of wetlands and riparian areas. Beetles are essential to maintaining biodiversity in our forests. One study of bark beetles found that bark beetles created habitat for a wide array of other insect species, including many pollinating bees and wasps that maintain flowering species in the forest. Beetle created snags provide important habitat for birds, with as much as 45 percent of all bird species dependent on dead trees for home and other habitat needs. Snags are used by many small mammals for shelter. When snags fall into streams, they contribute to fish habitat and stream bank stability. Suffice to say removal of beetle-killed trees from the forest actually leads to a reduction in forest ecosystem health.
Reduce home flammability
The most cost effective strategy to safeguard homes involves modest thinning of trees near buildings (typically 100-150 feet), combined with the installation of metal roofs, screens on attic vents, and other measures that protect homes from a fire should one occur. Focus fire risk reduction in and near homes, not out in the backcountry.
Beetles are not destroying our forests. Rather, they are creating new ecological opportunities, increasing biodiversity, and improving ecosystem health and perhaps even reducing fire risk.
George Wuerthner has published 35 books including Wildfire: A Century of Failed Forest Policy plus Colorado-Rocky Mountain — A Visitor’s Companion and Rocky Mountain–A Visual Interpretation. He lives in Montana and Vermont.