Posted on July 05 2016
Summer is wildfire season, and has been forever. Residents of the western half of our country are keenly aware of the danger and destruction that the dry hot months bring. Lately though, the season of flames starts earlier and stretches beyond the fall. In many places there is hardly an off-season — fire can strike at almost any time, and it’s getting more dangerous. The eight years of greatest wildfire activity since 1960 all happened since 2000. It’s no coincidence that this increased burning is accompanied by the drought. When moisture levels dwindle for lack of rain, vegetation turns to tinder and burns ferociously. California, especially the southern half, is in its fifth year of drought, and the greater Southwest has had drought in many areas for 12 of the last 15 years. Droughts are cyclical, but on top that routine, climate change is bringing new severity to both dryness and heat.
These factors turn brush to brittle twigs and weaken trees. While trees, with their deep roots, can hang on through a few years of drought, extended dryness diminishes their ability to produce sap. Sap is a key defense against insects that burrow into them, like bark beetles. In wet years, trees simply drown invading beetles in sap. But when the trees are unable to produce enough sap, the beetles lay eggs that hatch larvae which eat long winding tunnels in the inner bark. If the infestation is large enough, these channels can cut off the tree’s vascular system, killing it. Dead trees, especially conifers, are proliferating throughout the mountains of the West. Recent surveys of California forests estimate that since 2010, 66 million trees have died and stand as rust-colored patches in the Sierra and other ranges. That number is up from 29 million in 2015, and way up from a mere 3.3 million in 2014.
So the common concept is that drought gives the bark beetles a chance to do their thing, and the dead trees that mount up create massive amounts of fuel to stoke wildfires of ever-greater proportions. To lessen the danger and harvest the wood, timber companies have encouraged state governments to implement programs for removal of dead wood. But is all this wise or necessary?
Recent and ongoing research tells a more complicated story regarding wildfires, their behavior, and the reasons for it. A Colorado University study, for instance, has found that by comparing maps of beetle infestations with maps of wildfire incidence, there is no close correlation between the two. Bark beetles and other boring insects do kill trees but those dead trees are not the cause of runaway forest fires. Chad Hanson, a research ecologist with the John Muir Project recently wrote in the LA Times that scientific consensus is that dead trees or “snags” do not supercharge a fire. Dry as they are, the needles of dead tree do not contain the volatile oils of a fresh tree. Indeed, if they have been dead for long enough, all their needles will be on the ground, not feeding a canopy fire. Fires in forests containing many dead trees may actually burn less virulently than healthy green stands. And trees of more than a few inches in diameter do not fully burn in a fire – only the outer bark and needles are consumed. Dead trees of this greater size do not present a massive new source of fuel. However, an abundance of small trees resulting from years of successful fire suppression do provide a fuel store that can stoke the inferno.
What then is fueling the terrible growth of wildfire? It goes back to the drought and climate change. High temperatures, low humidity, and hot winds are the biggest factors. Topography, tree type, and that ample supply of small trees that grew while fire was kept from doing its job of thinning also figure into the success of a wildfire. Removing large snags from the forest makes sense where danger exists from their falling on structures or across roads, and these should be cut down. But the forest flora and fauna rely on the expired trees, both fallen and still standing, for food, shelter, nesting sites, and eventually as soil enrichment as they decompose. Hauling them away enriches a different kind of entity, but timber company profits, or the money they pay the government to access the snags does little to enhance the health of the forest.