The drought in California has been in the news for awhile, especially since the ban on watering lawns is starting to affect the behaviors and preferences of individuals. The drought will eventually end, but the California landscape will be changed. Large numbers of California conifers are dead or dying and more succumb as the drought lengthens. Healthy trees with ample water are able to produce pitch as a defense against bark beetles. When the beetles attack a healthy tree, pitch fills tunnels where beetles live and forcibly “pitches” the beetles from the tree. Severe drought causes trees to be stressed, unable to produce sufficient pitch to eject attacking beetles. As large numbers of stressed trees are successfully attacked, beetle populations explode. Beetles become numerous enough to successfully attack healthy trees as not enough pitch can be made to eject all the beetles.
Large numbers of California conifers are dead or dying; killed by bark beetles including mountain pine beetle, fir engraver beetle, western pine beetle, Jeffrey pine beetle and pine engraver beetles. These are not invasive species but native species gone wild under environmental conditions that are favorable for the beetles. Lack of cold winter temperatures allow more beetles to survive until spring. Large numbers of stressed trees provide abundant food.
The US Forest Service has a number of publications that provide information for homeowners and land managers on bark beetles and drought. What should be done about dying trees? Until trees drop their dead needles, standing dead trees can promote crown fires. Once the needles drop, the standing trees are less fire hazard but a threat to people and property when they eventually topple. For homeowners, removal of dead and dying trees near their property is recommended. Once a tree is successfully attacked by bark beetles, it cannot be saved. Stress on existing trees can be reduced by thinning stands of trees. Trees will compete with each other for limited water, making the stand less healthy. Thinning may allow remaining trees to survive.
Climate change is causing ecological changes all over the world. Recent events have demonstrated the important role of climate-dependent interactions between insects and plants in maintaining healthy ecosystems. When ecosystems change, human improvements and economic activity built around the old ecosystem can suffer negative consequences.