Additional implementation notes added by:
Alex Lancaster <alex@santafe.edu>

You can write screenshots for certain rasters for each update to PNG
files if you build like this:

   make CPPFLAGS=-D<name-of-widget>_SCREENSHOT

Where <name-of-widget> is one of:

FIRE
FOREST
YOUNG_FOREST
POPGRAPH
SPECIESGRAPH
ENTROPYGRAPH

You can make screenshots for multiple rasters, by adding a new
-D<name-of-widget>_SCREENSHOT to the  CPPFLAGS argument,
i.e:

  make CPPFLAGS='-DFIRE_SCREENSHOT -DFOREST_SCREENSHOT'

Note the additional quotes.

-----------------------------------------------------------------------------
                                ARBORGAMES

        Arborgames is a model of forest dynamics whose goal is to examine the
role of fire on species diversity.  It is a member of a long lineage of
individual-based, spatially explicit models of forests which assume discrete
cells with one individual per cell.  The local interaction of trees in a
neighborhood, however, allows Arborgames to generate landscape dynamics that
respond to disturbance in a recursive way: the behavior of fire is governed by
the contagion of local forest structure, which in turn is governed by the
pattern of past fires.

        Arborgames follows a minority of forest models in which species are
based on idealized species traits.  As such, they are abstract species, but
they mimic a rational gradient of life history traits from highly opportunistic
to late successional forest tree species.  These life history traits are:  seed
dispersal capability, seed longevity, fecundity of seeding, seed longevity,
germination shade tolerance, tree longevity, length of life stages, age at
reproductive maturity, flammability and heat output while burning.

        The model has three landscape spaces, one for trees, one for seedlings
and saplings, and one for seeds.  Each grid cell can be occupied both by a tree
and a potential replacement baby.  In addition, there are spaces for seeds
dispersed through time by reproducing trees, and visible in a separate window
for each species.  The pattern in each space is a mosaic of continually
changing patches, where seeds are cast into the landscape and seedlings
germinate, grow, and die, either from old age or by burning.  Fires ignite from
random lightning strikes and propagate only when trees burn hot enough to
transfer fire to neighbors.  Tree mortality is thus not a fixed probability,
but depends on susceptibility of the tree and the intensity of the disturbance,
measured by the proportion and heat of burning neighbors.

        There are several windows to track the shifting forest mosaic: 1. total
populations numbers of trees by species, 2. landscape entropy, and 3.  number
of species.  The system can be probed at any time to establish the species and
age of an individual at any location.  The community dynamics of Arborgames
depends on simple, local interactions based on species rules which produce
complex patterns at larger scales.  We are currently analyzing patterns of
species and landscape diversity produced by different intensities of
disturbance.  Ecological theory suggests that intermediate levels of
disturbance play a role in generating and maintaining higher levels of
diversity.  The model reflects this hypothesis and there are suggestions that
landscape trajectory is dependent on interactions that happen early in the
game.

-- 
Melissa Savage
Department of Geography
UCLA
Los Angeles, CA 90095-1524
(310) 825-1912
savage@margay.sscnet.ucla.edu
