A Spatiotemporal Ripley's K-Function to Analyze Interactions between Spruce Budworm and Fire in British Columbia, Canada

Abstract

In this paper, we extend traditional methods of spatial statistics to study spatiotemporal correlations between two different point processes. After introducing the methodology, we apply this analysis to a particular case study of interest in ecology, the interaction between damage by a particular forest pest (western spruce budworm (Choristoneura occidentalis)) and forest fires. Our analysis, which covers parts of British Columbia in the 26-year period from 1970 to 1995, indicates that areas affected by budworm infestation have a significantly decreased risk of forest fire for the 7 years following the infestation. Conversely, forest fires decrease the risk of infestation for at least 6 years after the fire. These temporal correlations extend over a spatial range of at least 25 km. Our study rejects the common assumption that insect infestation necessarily results in increased fire risk. This case study illustrates the utility of point process modeling and spatial statistics to understanding ecosystem dynamics extending over both space and time.