Modelling Plant Ecology - Environmental Modelling: Finding Simplicity in Complexity - page 198

12

Modelling Plant Ecology

Rosie A. Fisher
CGD/NCAR, Boulder CO, USA

between the inside and outside of leaves, partitioning
of incoming solar radiation energy into reflected, latent
(evaporated water) and sensible (atmospheric heating)
fractions and the impact of vegetation on atmospheric
momentum. Vegetation models then predict the rate
of assimilation of carbon compounds via the process
of photosynthesis, and determine the fate of these
carbon compounds by simulating allocation to multiple
plant requirements including (a) respiration needed to
maintain active living tissues, (b) the growth of leaves,
roots, transport tissues and woody stems, (c) storage and
defence compounds and (d) reproductive structures.
Fluxes of assimilated carbon into biomass pools, com-
bined with estimates of the loss rates of pools to turnover,
create representations of the size and form of individual
plants. Moreover, the responses of vegetation to stress
from temperature extremes, drought, fire and pest out-
breaks (either death or loss of biomass) must be included,
as they are key controls on plant distribution and size.
In addition to modelling these basic processes, it is
evident that the response of ecosystems to changes in cli-
mate depends upon the properties of the vegetation that
exists prior to the change occurring. In order to predict
the structure of communities and their future changes in
composition demands that land-surface models - those
that are traditionally based on eco-physiological
principles - be combined with representations of more
traditional plant ecology, which is the study of the
composition of entire communities of plants. Therefore,
the impact of plants on the light and water resources
available

12.1 The complexity

The study of plant ecology - the interactions between
plants and between plants and their environment - can
be and is undertaken by scientists at numerous spatial
and temporal scales. In this chapter, I consider the com-
plexities involved in predicting the response of the global
biosphere to climate change - a problem that theoreti-
cally encompasses all spatial and temporal scales up to
and including the impact of the biosphere on the entire
Earth system over geological timescales (Beerling, 2008).
Predicting the response of terrestrial ecosystems to cli-
mate change and altered atmospheric composition is an
increasingly high profile problem (Slingo et al ., 2009):
because of the potential for feedback between the bio-
sphere and climate change (Sitch et al ., 2008); because
many climate impacts on humans are mediated via their
impact on the biosphere, either directly (fires, agricul-
ture, forestry) or indirectly (via the impacts of vegetation
on hydrology, sediment stabilization and local climate),
and finally because of the likely inclusion of national
land-surface carbon-exchange budgets in future carbon-
emission treaties (Gibbs et al ., 2007; House et al ., 2008).
Models of the response of plant ecosystems to climate
change are typically founded upon the physiological
properties of individual leaves, the scale at which our
understanding of plant-atmosphere interactions is
arguably most advanced (Moorcroft, 2006; Prentice et al .,
2007). Relatively well-constrained models exist to repre-
sent the impact that local climate has on leaf interactions
with the atmosphere. These interactions include exchange
of carbon dioxide and water through stomata, the pores

to each other (plant competition) and the

processes leading to different community structures

must also be represented in these models.