Beetles and the Climate

Climate Change and the Forest

This week I am at the Community Climate System Model Annual Workshop . It is in Breckenridge, Colorado. In Colorado there has been a lot of discussion in the past few years about the pine beetle or the pine bark beetle. ( Archive Article in Denver Post ). These beetles are attacking lodgepole pines throughout the western United States and Canada. Some have even predicted that all of the lodgepole pine forests could be killed on many millions of acres of land.

There have been many discussions on the relationship of the pine beetle infestation and climate change. The analysis of the relationship of infestations of this type to climate change is very difficult. I give a set of links to primary references below.

When thinking about the impact of climate change on forests, attention is first paid to temperature and water. If the temperature is rising, then it is natural to expect that there will be increased water stress, especially in dry environments. Even if there is an increase in precipitation, the extra evaporation often more than offsets this additional water. With regards to the direct impact of temperature, trees have evolved to grow in certain temperature ranges. In a simplistic view, with small, slow climate change one imagines the range of trees following the climate. Of course, over the next 100 – 1000 years we are looking at fast, large climate change; there is little evidence that the forests can adapt quickly.

When the impact of a creature like the pine beetle is injected into the change of forests it gets more complex. There are historic surges of infestation. This is a very common feature in ecosystems, spurts of growth and decline – I often think of rabbits and foxes. It is, however, well known that pine beetle populations are quite sensitive to wintertime temperatures. It needs to get very cold for a period of time in order to kill the beetles. Therefore, if there is a period of sustained warm winters, then the likelihood of an infestation is increased. One question that arises, therefore, is a period of sustained warm winters natural variability or is it part of a secular trend of warming? One can quickly come to the conclusion that the spread of the pine beetle to higher altitudes and to more northern parts of Canada is consistent with warming patterns expected from global warming due to greenhouse gases.

A paper I have found useful in helping me think about climate change impacts on forests is Climate Change and Forest Disturbances: Dale et al. 2001 . For the naïve climate scientist, that’s me, this paper reframes the impact on forests. Rather than the impacts related directly to the parameters of the physical climate, i.e. temperature and water, emphasis is placed on fast disturbances of the forests. From a physical climate point of view, we have the concern of sustained droughts. There have always been droughts, but if the drought takes place when it is warmer, then there will be more stress from drying. This can lead to more dying, which is a situation that is not quickly repaired when the drought ends. Plus - if between drought and water usage the water table falls below the depth of the roots, then all can be lost.

Other types of disturbances are explosive infestations of insects and disease, fire, wind storms, ice storms, and landslides. On various scales these events have enormous, sudden impact. They interact with each other. They are related to climate change, but they are also related to other factors such as forest management, water management, and land use. They are event related, not part of some small, slow process. And this is, in fact, the general way that things work. Specific events occur with strong, regional impact.

It is in this framework of disturbances and events that the impacts of climate change need to be considered. In the next blog, I will revisit a couple of studies that link ecosystems impact to climate change, and then introduce the feedback … what is the impact of forest changes on climate change?

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Damage from the Mountain Pine Beetle. Boreas Pass Road, Colorado, June 2009 (R. Rood)



Primary References:

Climate Change and Forest Disturbances: Dale et al. 2001 class readings

Effects of Climate Change on Range of Pine Beetles: Carrol et al. 2003

Pine Beetle Symposium 2003

Mountain Pine Beetle: US Forest Service, Amman et al. 1990

Previous Stabilization Blogs:

Warm for a 1000 Years

How Much Warming Can we Avoid

Extinction

Removing Carbon Dioxide


Previous Blogs on Phenology and Ranges of Trees

Series of Blogs in 2008 of Spring Coming Earlier

Trees Moving North