Publications by K. Stahl

Climate change could alter the distribution of mountain pine beetle outbreaks in western Canada.

Tue, 06 Mar 2012

Climate change can markedly impact biology, population ecology, and spatial patterns of eruptive insects due to the direct influence of temperature on insect development and population success. The mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae), is a landscape-altering insect that infests forests of North America. Abundant availability of host trees due to altered disturbance regimes has facilitated an unprecedented, landscape-wide outbreak of this pest in British Columbia and Alberta, Canada, during the past decade. A previous outbreak in the 1980s, in central British Columbia, collapsed due to host depletion and extreme cold weather events. Despite the importance of such extreme weather events and other temperature-related signals in modulating an outbreak, few landscape-level models have studied the associations of extreme cold events with outbreak occurrences. We studied the individual associations of several biologically-relevant cold temperature variables, and other temperature/degree-day terms, with outbreak occurrences in a spatial-temporal logistic regression model using data from the current outbreak. Timing, frequency, and duration of cold snaps had a severe negative association with occurrence of an outbreak in a given area. Large drops in temperature (>10°C) or extreme winter minimum temperatures reduced the outbreak probability. We then used the model to apply eight different climate change scenarios to the peak year of the current outbreak. Our scenarios involved combinations of increasing annual temperature and diff erent variances about this trend. Our goal was to examine how spatial outbreak pattern would have changed in the face of changing thermal regime if the underlying outbreak behaviour remained consistent. We demonstrate that increases in mean temperature by 1°C to 4°C profoundly increased the risk of outbreaks with effects first being manifested at higher elevations and then at increasing latitudes. However, increasing the variance associated with a mean temperature increase did not change the overall trend in outbreak potential.

Development of a low-flow hazard model for the Fraser basin, British Columbia

Mon, 25 Jan 2010

The province of British Columbia, Canada, is currently experiencing the largest mountain pine beetle outbreak ever recorded in North America. The most recent surveys indicate that widespread mortality of pine trees has occurred in over 10 million ha of forest (an area roughly the size of Iceland) and the outbreak continues to kill mature pine in the province. The epicentre of the current outbreak is in the Fraser River drainage basin (230,000 km2), where roughly 8 million ha of forest have been affected, approximately 35% of the drainage area. Due to the infestation's area and associated salvage harvest operations, the potential exists for widespread and significant local and regional hydrologic impacts within the basin. However, the scale and physiographic heterogeneity of the Fraser River basin precludes both direct observation and extrapolation of hydrologic impacts observed from a limited number of stand-level and small basin experiments. A low-flow hazard model was developed for third-order catchments within the Fraser River watershed. Baseline and mountain pine beetle-infestation and harvest scenarios were modeled for seven catchments for direct comparison with the Variable Infiltration Capacity modeling results. The model is to be used in risk-based hydrology modeling to produce a comprehensive knowledge of mountain pine beetle-infestation effects on the hydrology of the Fraser River watershed and its major sub-basins in British Columbia, Canada.

Movement of outbreak populations of mountain pine beetle: influences of spatiotemporal patterns and climate

Thu, 16 Apr 2009

Insect outbreaks exert landscape-level influences, yet quantifying the relative contributions of various exogenous and endogenous factors that contribute to their pattern and spread remains elusive. We examine an outbreak of mountain pine beetle covering an 800 thousand ha area on the Chilcotin Plateau of British Columbia, Canada, during the 1970s and early 1980s. We present a model that incorporates the spatial and temporal arrangements of outbreaking insect populations, as well as various climatic factors that influence insect development. Onsets of eruptions of mountain pine beetle demonstrated landscape-level synchrony. On average, the presence of outbreaking populations was highly correlated with outbreaking populations within the nearest 18 km the same year and local populations within 6 km in the previous two years. After incorporating these spatial and temporal dependencies, we found that increasing temperatures contributed to explaining outbreak probabilities during this 15 yr outbreak. During collapse years, landscape-level synchrony declined while local synchrony values remained high, suggesting that in some areas host depletion was contributing to population decline. Model forecasts of outbreak propensity one year in advance at a 12 by 12 km scale provided 80% accuracy over the landscape, and never underestimated the occurrence of locally outbreaking populations. This model provides a flexible approach for linking temperature and insect population dynamics to spatial spread, and complements existing decision support tools for resource managers.