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Mountain Pine Beetle and Carbon Feedback

One obvious sign of climate change and global warming is the continuous spread of parasites into colder areas previously inhospitable. Such an invasion can sometimes have dramatic effects with long term consequences at all sorts of level. A good example of such devastation is presently in progress towards boreal forests of North America. While this infestation is caused by global warming, it is also a formidable global warming accelerator by turning huge carbon sinks into rich carbon sources of decaying matter or by provoking instant release of gigatons (Gt) of carbon in the atmosphere due to forest fires.

Since the mid 1990ís, mountain pine beetle (MPB) populations have erupted across interior British Columbia in Canada to form the largest outbreak ever recorded. For an outbreak to occur, two main conditions must be satisfied. First, there must be an abundance of large, mature pine trees; the beetle's preferred resource. Second, there must be several years of favourable weather for beetle survival; specifically, hot summers that facilitate beetle reproduction, and mild winters that allow their offspring to survive. Recently, it has been shown that largely as a consequence of effective fire suppression, there was >3 times the amount of mature pine in BC at the start of the current outbreak when compared with 100 years ago. Furthermore, climatic conditions during recent decades have been highly amenable for beetle survival. Thus, both conditions for an outbreak have coincided with sufficient magnitude to cause the largest MPB outbreak in recorded history.

Mountain pine beetle invasion

In the past, large-scale MPB outbreaks collapsed due to localized depletion of suitable host trees in combination with the adverse effects of climate. The results of our investigation suggest that in the absence of an unusual weather event (i.e., an unseasonable cold period or an extreme winter), the current outbreak may not entirely collapse as in the past. Expansion by the beetle into new habitats as global warming continues will provide it a small, continual supply of mature pine, thereby maintaining populations at above-normal levels for some decades into the future. (reference)

Historically, MPB populations have been most common in south-central BC and the north-western US. Non-forested prairies and the high elevations of the Rocky Mountains have contributed to confining it to that distribution. Over the last several decades, the amount of climatically benign habitat for MPB has increased significantly, followed closely by rapid invasion of these new habitats by the beetle. More recently, the enormous ongoing epidemic in BC appears to have exacerbated the rate of range expansion. During emergence and dispersal, a small proportion of beetles will fly above the forest canopy and be carried aloft by winds, often travelling tens or even hundreds of kilometres. The sheer size of the current outbreak has ensured that vast numbers of beetles have been available in recent years for long-distance dispersal, thereby increasing the probability that large populations will encounter new climatically suitable pine forests. By this mechanism, MPB has successfully breached the Rocky Mountain geo-climatic barrier and established in north eastern BC and adjacent Alberta.

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