Pine Beetles Outbreaks

Background:

 There has been increasing outbreaks of pine beetles due to possible increases in global temperatures.  This outbreak leads to increased tree mortality and decreased forest carbon uptakes(Dymond et al. 2008). With increasing temperatures, the insect distribution and abundance will change as their life cycles are affected from the climate change. Since insect’s life cycle is dependent upon temperature because they are cold blooded, their response to changing climate by shifting their geographical distribution
and population behavior is rapid. (Carroll et al. 2004)

Fig 3: Number of Pine beetle infestation vs year (Fig.3 Carroll et al. 2004)

 In the Pacific Northwest, warmer forest temperatures allow some beetles to reduce their time of reproduction to half. The increase of beetle outbreaks will cause a major destruction in forests. As the restriction upon these insects is based on brood development, climate change is ultimately reducing the time for development. The warmer temperatures are also causing a shift in the pine beetles population northward and eastward as well as toward higher elevations. (Carroll et al. 2004) Figure 3 portrays a model predicting  the increase of pine beetle infestations in a site  over the years in very low climate suitability classes (increased precipitation, minimal August temperature, minimum growth season duration). Very low climate suitability classes are habitats with climatic conditions unsuitable for mountain pine beetles. Before the year 1968 there were 0 infestations in these unsuitable habitats. (Safranyik et al. 1975) However, since then, the increase  in infestations  suggests that there has been enough change in the climatic conditions in these habitats to have allowed the establishment and persistence of mountain pine beetle populations even in prior unsuitable habitat (very low suitability class). (Carroll et al. 2004)  

Warm summers and mild winters as predicted by climate projections play a role in both insect survival and the continuation and intensification of an outbreak. Adverse weather conditions (such as winter lows of -40 °C) can reduce the beetle populations and slow the spread, but the insects can recover quickly and resume their attack on otherwise healthy forests.

Newly attacked pine trees turn red about one year after infestation (Seattle Times)

How will this affect Spotted Owls?

With increasing outbreaks of beetles and increased tree mortality, the already rare old-growth forests could be in more trouble as range expansions are occurring for these beetles and their faster reproduction can deteriorate forests even greater. If old-growth forest become increasingly deteriorated, the endangered spotted owls will have an even less chance for survival. Recall that the studies by Bart, Forsman, and Gutierrez suggest  the owl prefers old growth forests due to the benefits received, so with decline in these forests due to pine beetle outbreaks, outcomes can be catastrophic as this causes another level of stress for these owls to find new territories.

North Cascades above the Methow Valley, WA: Beetle Outbreak (Seattle Times)

This directly is affecting the Pacific Northwest as we speak, from a news article from the Seattle Times of Feb. 2012, Welch states that nearly 3 million acres of forest (1/3 of eastern WA forests) are expected to be endangered or possibly destroyed by these pine beetle infestations. This increase in beetle infestation has doubled from 1990’s and even tripled since 1980s! Since this is occurring in the North Cascades where owl population occurs and overlaps, the pine beetle infestation is directly endangering the owls if the destruction is great.


If we are trying to conserve these owls, further investigation of how to reduce these pine beetle outbreaks, especially in the old growth forests, will be necessary. Since there is a current trend of increasing outbreaks and destruction of forest by these beetles, the pine beetles will be a great future and possibly current threat to some Northern Spotted Owls.