The recent windstorms and unusual weather in western Oregon has resulted in lots of tree blow-down and tree failure. What considerations should be taken to salvage this material or prevent bark beetle outbreaks?
It is generally best to salvage as soon as possible. As the warmer weather of spring arrives (late March, and April), many bark beetles and dead tree invading insects will take flight, and fungal spores will also become abundant. These organisms will colonize down trees and begin the decomposition process, including staining the wood and boring into the wood.
There is potential for down ponderosa pine trees on the west side and in SW Oregon to breed bark beetles and cause a bark beetle epidemic. The problem is site specific. Ponderosa pine may be susceptible to bark beetle flare-ups particularly if there is abundant down material that is in close proximity to green standing trees.
Photo by Bob McNitt
Slash piles after harvest can create Ips beetle build ups that attack healthy green trees
The most important bark beetles to ponderosa pine with regard to windthrow are the pine engraver (Ips pini) and the California five-spined Ips (Ips paraconfusus). The mountain pine beetle (Dendroctonus ponderosae) and the western pine beetle (Dendroctonus brevicomis) are not usually associated with wind-thrown trees. The two Ips beetles, especially the California five-spined Ips can have multiple generations in one year. Typically the California five-spined Ips will colonize wind-thrown timber in the spring, and then by mid summer can begin attacking live trees. It can attack and kill the tops of large trees, and also attack and kill smaller diameter trees. But it usually takes a significant amount of down wood to build up the population of beetles. However, with two generations per year (and three in SW Oregon), the populations can build up quickly and may move into nearby trees.
Drought definitely plays a role in increasing the susceptibility of trees to Ips beetles, and therefore the weather this spring and summer can either exacerbate or ameliorate the problem. Salvage of pine should occur before the second-generation of beetles fly in mid-summer 2007, and small diameter (greater than 3 inches) slash should be disposed of by scattering in openings to facilitate drying, or piling and burning. Slash piles that are not burned provide good habitat for beetles, so if you pile slash, be sure and dispose of it. Do not pile slash around the base of live trees, because the volatile chemicals from pine slash attract bark beetles.