The Spread of the Mountain Pine Beetle: Challenges and Solutions in Large-scale Spatial Ecological Modeling

Abstract

The mountain pine beetle (MPB) is among the most destructive eruptive forest pests in North America. A recent increase in the frequency and severity of oubtreaks, combined with an eastward range expansion towards untouched boreal pine forests, has spurred a great interest by government, industry and academia into the population ecology of this tree-killing bark beetle. Modern approaches to studying the MPB often involve the analysis of large-scale, high resolution datasets on landscape level damage to pine forests. This creates a need for new modelling tools to handle the unique challenges associated with large sample sizes and spatial effects. In this thesis, I develop some of these tools and apply them to studying the spread and attack behaviour of MPB. Chapter 2 introduces a statistical framework for handling spatial autocorrelation based on the geostatistics paradigm of explicit covariance functions, known as covariograms. This extends previous work on computationally feasible models for covariances in lattice data, and introduces a powerful new estimator for the angle of anisotropy in stationary random field representations of autocorrelation. Chapter 3 unifies a number of previously unconnected results on redistribution kernels, by presenting a novel mechanistic derivation of a widely-applicable kernel for isotropic movement patterns. Phenomenological extensions are proposed to account for anisotropy as well as an approximation with superior computational properties, which is well suited to model-fitting on extremely large samples. In Chapter 4, these ideas are combined to construct a comprehensive model for the spatial spread of infested stems, coupled by MPB dispersal flights. This model facilitates the landscape-level inference of subtle properties of MPB attack behaviour based on aerial surveys of killed pine. Among these result is an accurate estimate of the size of the cryptic endemic MPB population, which formerly has been measurable only by means of costly and time-intensive ground surveys.