  Traditional approaches to ecosystem modelling have relied on spatially
homogeneous approximations to interaction, growth and death. More recently,
spatial interaction and dispersal have also been considered. While these leads
to certain changes in community dynamics, their effect is sometimes fairly
minimal, and demographic scenarios in which this difference is important have
not been systematically investigated.
  We take a simple mean-field model which simulates birth, growth and death
processes, and rewrite it with spatially distributed discrete individuals. Each
individual's growth and mortality is determined by a competition measure which
captures the effects of neighbours in a way which retains the conceptual
simplicity of a generic, analytically-solvable model. Although the model is
generic, we here parameterise it using data from Caledonian Scots Pine stands.
The dynamics of simulated populations, starting from a plantation lattice
configuration, mirror those of well-established qualitative descriptions of
natural forest stand behaviour; an analogy which assists in understanding the
transition from artificial to old-growth structure.
  When parameterised for Scots Pine populations, the signature of spatial
processes is evident, but they do not have a large effect on first-order
statistics such as density and biomass. The sensitivity of this result to
variation in each individual rate parameter is investigated; distinct
differences between spatial and mean-field models are seen only upon alteration
of the interaction strength parameters, and in low density populations. Under
the Scots Pine parameterisation, dispersal also has an effect of spatial
structure, but not first-order properties. Only in more intense competitive
scenarios does altering the relative scales of dispersal and interaction lead
to a clear signal in first order behaviour.
