Mountain Pine Beetle – climate is the key

The mountain pinebark beetle Dendroctonus ponderosae is a small beetle native to North America from Mexico to British Columbia. This species plays an important ecological role in pine forests by removing old, weak trees, facilitating the growth of saplings. They do this by laying their eggs under the bark of old stressed trees. The larvae, after hatching eat the wood contributing to the tree’s decline. Trees will respond to egg-laying by exuding sap which expels the eggs but also weakens the tree and opens it to infection by pathogenic fungi. In the normal course of things, the ecosystem functions with a high level of predictability.

Recently, pine beetle outbreaks have been more intense, longer in duration and have covered larger and larger areas, resulting in large swathes of mature, usually healthy trees dying. It has been hypothesised that human-induced climate change has been partially responsible. A number of isolated studies in various locations have added weight to that hypothesis. A new study  published in the journal Ecology investigates multiple outbreaks over large spatial areas and models these against known climate and weather variables. The authors report that climate is affecting weather patterns resulting in longer droughts, altered rainfall and increased temperature. These in turn are acting as stressors on mature trees,increasing opportunities for beetles to reach plague proportions. 

More and more studies of this sort will be comingout in the next few years, adding further weight to the copious evidence for biological effects of climate change that already exist.

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