Impact of Forest Fragmentation on Patterns of Mountain Pine Beetle-Caused Tree Mortality

Christopher Bone,Trisalyn Nelson,Joanne White,Michael Wulder,Colin Robertson

doi:10.3390/f4020279

Abstract

The current outbreak of mountain pine beetle, Dendroctonus ponderosae Hopkins, has led to extensive tree mortality in British Columbia and the western United States. While the greatest impacts of the outbreak have been in British Columbia, ongoing impacts are expected as the outbreak continues to spread eastward towards Canada’s boreal and eastern pine forests. Successful mitigation of this outbreak is dependent on understanding how the beetle’s host selection behaviour is influenced by the patchwork of tree mortality across the landscape. While several studies have shown that selective mechanisms operate at the individual tree level, less attention has been given to beetles’ preference for variation in spatial forest patterns, namely forest fragmentation, and if such preference changes with changing population conditions. The objective of this study is to explore the influence of fragmentation on the location of mountain pine beetle caused mortality. Using a negative binomial regression model, we tested the significance of a fragmentation measure called the Aggregation Index for predicting beetle-caused tree mortality in the central interior of British Columbia, Canada in 2000 and 2005. The results explain that mountain pine beetle OPEN ACCESS Forests 2013, 4 280 exhibit a density-dependent dynamic behaviour related to forest patterns, with fragmented forests experiencing greater tree mortality when beetle populations are low (2000). Conversely, more contiguous forests are preferred when populations reach epidemic levels (2005). These results reinforce existing findings that bark beetles exhibit a strong host configuration preference at low population levels and that such pressures are relaxed when beetle densities are high.

Highlights

The recent epidemic of mountain pine beetle, Dentroctonus ponderosae Hopkins, in British Columbia, Canada has led to tree mortality spanning 18.3 million ha [1]
Since the current outbreak began in the late 1990s, the insect, which is native to the pine forests of western North America, has killed a significant component of forests dominated by lodgepole pine, Pinus contorta var. latifolia Engelmann
While past outbreaks have led to widespread tree mortality in British Columbia and other parts of Canada as well as in the United States [6], beetles are selective in their attack strategy, resulting in a patchwork of tree mortality across the landscape [7]

Summary

Introduction

The recent epidemic of mountain pine beetle, Dentroctonus ponderosae Hopkins, in British Columbia, Canada has led to tree mortality spanning 18.3 million ha [1]. While past outbreaks have led to widespread tree mortality in British Columbia and other parts of Canada as well as in the United States [6], beetles are selective in their attack strategy, resulting in a patchwork of tree mortality across the landscape [7]. Such observations have important implications for management as beetles exhibit selective behaviour that, if understood, could guide mitigation efforts to minimize tree mortality. While mitigation in British Columbia is not currently emphasized, observing the outbreak from a number of perspectives will inform on the nature of the year-on-year outbreak development and identify those factors (mitigation or otherwise) that can be seen to have influenced infestation spread

Objectives

Methods

Results

Conclusion