Climatological Analyses of Infestations of the Mountain Pine Beetle Dendrocronus ponderosae in the Crown of the Continent Ecosystem from 1962 to 2014

Mountain pine beetles (MPB) are the most destructive biotic agent of mature pine (Pinaceae) forests in western North America. Over the past century, MPB infestation has reached epidemic levels four to five times in northwestern North America. Bark beetles have caused the mortality of billions of coniferous trees from Mexico to Alaska. It is estimated 1.84 million ha of mature pine forests in western Canada have been lost due to the MPB in the 1980s; in 1999 - 2005 western Canada suffered a loss of an estimated of 7.1 million ha. The current infestation of bark beetles in North America is the most severe and largest in history. Ramifications of this widespread mortality include a huge economic loss, and substantial change in forest composition from dense coniferous stands to a mix of herbs, shrubs, and grasses on the forest floor.

Bark beetles are extremely resilient and their flexibility in life-history strategies have proven to be much greater than previously understood. Importantly, these strategies are impacted by climate. For example, large scale models shows an increasing northward spread into the extreme northern latitudes of Canada and Alaska due to a continuously warming climate.

A challenge for researchers and practitioners is predicting bark beetle outbreaks due to changes in weather and climate. Prediction, however, requires a thorough understanding of those factors that both facilitate or hinder invasions. Given the inherent relationship between topography (e.g., aspect and elevation) and environmental variables (e.g., air temperature and precipitation) this study characterizes the spatial and temporal spread of the bark beetle through a key ecosystem relative to topographic variables and climate factors.

The geographic focus of this study is the Crown of the Continent Ecosystem (CCE), a 1 million ha mountainous ecosystem in the Rocky Mountains extending from northern Montana and into Alberta and British Columbia. Studying outbreak patterns over a relatively small region (the CCE), but over a long time period (1962-2014) will enable a better understanding of climate dynamics that influence mountain pine beetle outbreaks in this particular region from a historical context.

This study uses monthly data at the climate division scale, including Palmer Drought Severity Index (PDSI), temperature, and precipitation, to create seasonal means. In conjunction with climate division data, regional 500 hPa geopotential height anomalies are characterized, along with global climate oscillations to identify any correlations with bark beetle spread.

The specific objectives of this study are to:

1. Use aerial detection survey data to identify at least 10 distinct time periods of the highest and the lowest advances of the beetle during the period 1962 to 2014, while also determining the nature of the pine mountain beetle infestations at these approximate time periods (monotonic; linear v. non-linear).

2. Correlate climate variables (temperature, precipitation, large-scale circulation patterns) with the spread of the mountain pine beetle within the CCE.

A focus on selected case studies through a climate analysis may shed insight into why some outbreaks varied in severity over time and space. Collectively, the aim of these analyses is to identify years of severe outbreaks and to ascertain the climate conditions that may have influenced the spread of the bark beetle.