Forecasting the continued naturalization of widely planted alien conifers: On Sitka spruce (Picea sitchensis) in Norway

Abstract

Imported plants frequently spread from where they are planted — forestry conifers being a prime example. A particular species may spread rapidly into many ecosystems across a large area, or its spread may be more gradual and confined. For species that have just begun to spread, it is crucial to know where they will move, and how fast. To make these forecasts, we can look at where the species occurs in its home range, and observe the early stages of naturalization in the introduced range. The home range reveals broad environmental constraints on the species’ spatial distribution, while the introduced range manifests the fine-scale processes underpinning the expansion. But the forecasts will only be good if the inferences are made carefully, this thesis finds. The thesis: (1) introduces software that isolates important environmental constraints from spurious ones, (2) presents a method to handle spatial bias in occurrence data, (3) quantifies spread into ecosystems with unequal levels of exposure, and (4) identifies current bottlenecks that could release populations from their observed trajectories. Sitka spruce in Norway serves as the motivating case throughout.