Heather Lynch (2006)
Spatiotemporal Dynamics of Insect-Fire Interactions
Phd thesis, Harvard University.
Insect outbreaks and forest fires individually represent significant forest disturbances which have long-term effects on the dynamics and composition of forest ecosystems. Although it has long been speculated that forest fires and insect outbreaks may be correlated, there has been little quantitative evidence of statistically significant spatiotemporal correlations between these two contagious disturbances. In chapter 1, I review the literature on insect-fire interactions in order to highlight how little is actually known about this important ecological interaction in spite of the management implications. In chapter 2, I analyze 26 years of data on western spruce budworm outbreaks and forest fires in British Columbia using a spatiotemporal version of Ripley's K-function. This analysis indicates that areas affected by western spruce budworm infestation have a significantly decreased risk of forest fire for nine years following recorded budworm damage. Conversely, forest fires increase the risk of budworm infestation in the year of the fire and then decrease the risk of infestation for a five year period. In chapter 3, I apply a Markov Chain Monte Carlo approach to understand whether or not the previous history of mountain pine beetle damage in Yellowstone National Park affected the spatial pattern of the 1988 Yellowstone fires. This analysis shows that continued mountain pine beetle infestation 12-15 prior to the 1988 fires was associated with a ~11% increase in the odds of burning relative to areas that were not affected in that time period. In chapter 4, I develop a partial differential equation model for mountain pine beetle dynamics based on the historical record of mountain pine beetle dynamics in the park and in chapter 5, I use this model on simulated post-fire landscapes in order to demonstrate that, over a wide range of fire-size regimes, forest fires are too small to significantly impact the risk of a mountain pine beetle outbreak. However, extremely large fires, such as those that occurred in Yellowstone in 1988, are sufficient to prevent mountain pine beetle spread and epidemic-level outbreaks. Finally, in chapter 6, I discuss the potential for remote sensing technologies to map and track insect outbreaks over large areas.