  Invasive pine trees pose a threat to biodiversity in a variety of Southern
Hemisphere countries, but understanding of the dynamics of invasions and the
factors that retard or accelerate spread is limited. Here, we consider the past
models of wilding pine spread and develop a new model of pine invasion. We show
that many prior models feature parameter estimates which are not biologically
supported and rely on a conjecture to obtain an asymptotic spread speed of
invasive pine populations, the main output of these models. In contrast to
prior approaches, we use partial differential equations to model an invasion.
We show that invasions are almost static for a significant period of time
before rapidly accelerating to spread at a constant rate, matching observed
behaviour in at least some field sites. Our work suggests that prior methods
for estimating invasion speeds may not accurately predict spread and are
sensitive to assumptions about the distribution of parameters. However, we
present alternative estimation methods and suggest directions for further
research.
