Throughout Western North America coniferous forests are being decimated by pine beetles. Pine beetles, which include variety of species within the genus Dendroctonus, are a natural component of western coniferous forests and their populations have historically been kept at an equilibrium, where the beetles act as important forest thinning agents without affecting the typical community makeup. (Hayes and Lundquist 2007) Previous outbreaks have occurred, but none have been as widespread and detrimental as the outbreak that began in the 1990's and continues today.
(Fig. 2) (Progar 2005) (Carroll, et al. 2003) In the last few decades however there has been an drastic increase in the number of beetles and the extent of their attacks. (Intermountian and Northern Region Forest Service)
As a dominant vegetation type in many areas, the coniferous trees within the North Western forests are integral to the health of their own and the surrounding ecosystems. In many of the areas affected there is greater than 90% mortality rate among the conifers. (Progar 2005) Within the coniferous ecosystems the massive conifer die-off removes important habitats and food sources, disrupts the typical succession cycles, along with disrupting timber production, recreation and CO2 cycling.
Unnaturally large and uncontrollable fires could easily result from the immense fuel loads being created by the dead conifers. (U.S. Forest Service Forest Health Protection 2009) (Hayes and Lundquist 2007)
Many studies and multiple government groups have been created to better understand the causes for the extreme increase in conifer mortality and pine beetle populations. Two causes that are currently being studied are climate conditions and tree vigor.
Climate Change has increased average temperatures and reduced the amount of precipitation deposited into and retained within the coniferous forests. The resulting long term drought conditions have increased tree stress and reduced tree vigor. This reduces the ability of the trees to withstand the beetles attack. (Hayes and Lundquist 2007) (Intermountian and Northern Region Forest Service 2000) (Carroll, et al. 2003)
By understanding that those areas within the coniferous forests that are more susceptible to drought are also more susceptible to decimation by pine beetles, the assorted government agencies and private citizens are able to more efficiently and effectively direct their resources to combat the beetles. This project will create a multi-hazard assessment map for all or part of Ashley National Forest based on a variety of layers containing factors that could affect the drought susceptibility throughout an area.
Many studies have been done on the climactic factors that can effect tree growth and/or vigor, identifying the types of data layers that would be helpful in determining what areas are more susceptible to drought. The most basic of which is the input of moisture into the system in terms of precipitation. Climate change has been seen to cause an increase in summer temperature and a decrease in summer moisture, along with an increase in winter precipitation in areas similar to those in this study. They further found that a decrease in elevation exacerbate these effects (Knutson and Pyke) Another study found that the aforementioned effects are seen quite clearly in Pinus species which are at high risk to beetle attacks. (Schrag, Bunn and Graumlich) Another study found that elevation, while a definite contributor, is secondary to the amount of water deposited into the system, especially for the Pinus species most heavily effected by the pine beetle. (Adams and Kolb) Due to this the study will include layers showing precipitation, slope, aspect and elevation. Another study showed then when a forest begins to be encroached upon by agriculture or urban building, there is a decrease in soil quality and increase of runoff within the forest. After which the overall health of the forest suffers (HernandezGuzman, Ruiz-Luna and Berlanga-Robles) This study will include layers showing land ownership, major roads and land use to account for the encroachment of man into "wild" lands. Another study showed the importance of a high composition of edible tree species within the area as opposed to a highly diverse area. (Barbaro, Rossi and Vetillard) If available the use of a composition ratio layer could make the map more effective.