1 research outputs found
LPJ-GM 1.0: simulating migration efficiently in a dynamic vegetation model
Dynamic global vegetation models are a common tool to assess the effect of
climate and land use change on vegetation. Though most applications of
dynamic global vegetation models use plant functional types, some also
simulate species occurrences. While the current development aims to include
more processes, e.g. the nitrogen cycle, the models still typically assume
an ample seed supply allowing all species to establish once the climate
conditions are suitable. Pollen studies have shown that a number of plant
species lag behind in occupying climatological suitable areas (e.g. after a
change in the climate) as they need to arrive at and establish in the newly
suitable areas. Previous attempts to implement migration in dynamic
vegetation models have allowed for the simulation of either only small areas or have
been implemented as a post-process, not allowing for feedbacks within the
vegetation. Here we present two novel methods simulating migrating and
interacting tree species which have the potential to be used for simulations
of large areas. Both distribute seeds between grid cells, leading to
individual establishment. The first method uses an approach based on fast
Fourier transforms, while in the second approach we iteratively shift the
seed production matrix and disperse seeds with a given probability. While
the former method is computationally faster, it does not allow for
modification of the seed dispersal kernel parameters with respect to terrain
features, which the latter method allows.
We evaluate the increase in computational demand of both methods. Since
dispersal acts at a scale no larger than 1 km, all dispersal simulations
need to be performed at maximum at that scale. However, with the currently
available computational power it is not feasible to simulate the local
vegetation dynamics of a large area at that scale. We present an option to
decrease the required computational costs through a reduction in the number of grid cells
for which the local dynamics are simulated only along migration transects.
Evaluation of species patterns and migration speeds shows that
simulating along transects reduces migration speed, and both methods
applied on the transects produce reasonable results. Furthermore, using
the migration transects, both methods are sufficiently computationally
efficient to allow for large-scale DGVM simulations with migration.</p