   2003 Bark Beetle Update - November 19, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Although the official 2003 forest health survey data has not been officially released, preliminary data suggests that statewide mortality was ten times greater in 2003 than in 2002. By my unscientific observations in Yavapai County, it appeared that ponderosa pine bark beetle activity actually peaked in late 2002 and may have leveled off or even be on the decline. However, tree mortality due to pinyon and cypress bark beetles appeared greater in 2003 than in 2002. The ten-fold increase in mortality observed in the 2003 surveys is likely related to timing of survey flights. In 2002, surveys were conducted in July and October. The October surveys may not have detected the bark beetle activity in progress at that time. I know in the Prescott area, ponderosa pine trees continued to fade throughout the winter of 2002-03. In other areas, such as Pine/Strawberry and the Mogollon Rim, areas of mortality seemed to expand during the summer of 2003. Interestingly, Payson has not seen a high level of bark beetle mortality either year. Keep in mind that my observations are not hard data, but simply anecdotal information (I recently heard this called anecdata). Irregular distribution of summer rainfall and damage caused by wildfires may partially explain the distribution of beetle killed timber. On average, rainfall was closer to normal between January and October 2003. For the same period in 2002, rainfall was half to two-thirds of normal. Trees damaged by scorching and extreme heat are more susceptible to bark beetle colonization. In localized areas, bark beetle activity often carries over during subsequent year following a severe outbreak. Many other factors that determine bark beetle dynamics are no well understood: interactions of predators and parasites, temperature and precipitation thresholds, differences in precipitation patterns, etc. One question that I have been getting lately is “why are pine trees dropping their needles?” This is normal seasonal (fall) needle drop. Pines (and other conifers) cannot keep all their needles forever. Ponderosa pines usually carry about three years worth of needles. The four year-old needles are dropped during the fall. Other pine species may carry between two and four year’s needles. The needles that drop should always be the oldest (furthest away from the branch tip). Self-shading or competition with neighboring trees can cause lower branches to die. This is also a natural process and is especially prevalent in dense timber. Conversely, open-grown trees that have little or no competition tend to carry branches lower to the ground. This can be seen in pinyon-juniper woodlands where trees are often widely spaced. Open stands of ponderosa pine are thriftier and more attractive. These stands are the goal of many ponderosa pine ecosystem restoration projects. Open stands can withstand periodic, low intensity wildfires. In turn, these fires decrease the number of pine seedlings that survive and perpetuate the open stand structure. If drought continues, we should expect beetle mortality to continue. Remember, the bark beetles are simply bringing the number of trees into balance with the resources (primarily water) available on that site. Our generation is witnessing a unique period where ecosystems are changing before our eyes. Bark beetles are neither good nor bad-they are simply part of the process. Many people resist change and see it as “bad”. As much as we resist it, the change they bring is constant and necessary. This is how we maintain the beauty and diversity of Arizona’s natural landscapes. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |