Current Modelling Research Objectives
Given the recognised importance of
C4 grasslands (Hall, 1989), and other related plant communities, to the global
carbon budget and the current lack of direct experimental evidence for the effects of
climate change on these systems predictive mechanistic models are a vital tool in
extrapolating from current information. A few models designed to examine climate change
response have already incorporated broad mechanistic principles, i.e. MAESTRO {Wang, 1990
#1845} and BIOMASS {McMurtrie, 1992 #1853}. However these models were developed for forest
stands and were developed for specialist modellers rather than for non specialist user
groups. There therefore exists a need for an easy to use mechanistically based model
package of C3 and C4 photosynthesis which can be used to explore the
effects of climate change on diverse plant and soil types and in particular C4
grassland and related vegetative systems. The objectives of this work were therefore:
i). Construction of an interactive mechanistically rich model of grassland systems
which allowed prediction of key vegetative parameters, including monthly and annual above
and below ground net primary production, decomposition, water use and nutrient uptake.
ii) To parameterise and validate this model with existing information about grassland savannahs in Kenya and Mexico and to use this model validated under
current ambient Ca and temperature conditions to make predictions about the
potential impact of climate change on grassland systems.
iii). To examine the effects of management practices, such as burning frequency,
herbivory and crop growth, on grassland savannahs and to access
potential implications of climate change for these practices.
iv). To extend this grassland model to include other related natural C3 and
C4 plant communities. In particular to provide a theoretical basis for the
examination of the effects of increased Ca and temperature on a contrasting
wetland species, papyrus (Cyperus papyrus), in which the expected water balance and
nutrient availability for individual plants is diametrically opposed to the semi-arid,
nutrient poor growing conditions typical of grassland savannahs.
Therefore to asses the potential impacts of climate change on a wide range of C4
plants from a drought limited grassland savannah to a nutrient rich
wetland system. Further to use recent advances in both theory and instrumentation to make
detailed non invasive carbon productivity and water balance measurements of papyrus from
the leaf to the ecosystem level and to use these measurements to examine the integrity of
the hierarchical scaling techniques used in the model as a means of scaling the effects of
CO2 and temperature from leaf based physiology to ecosystem fluxes.
v). To examine the predicted role of C4 communities in a global perspective
of source/sink carbon and water dynamics and the potential of such communities to act as
an enhancing or reducing factor for further climate change.
vi). A further objective was to assess the reliability of process based predictions of
photosynthetic productivity in response to climate change by comparative analysis of model
predictions with those observed in long term open top chamber CO2 enrichment
studies. In addition to use documented evidence for acclimation in grassland species to
investigate the potential effects of long term systematic modification of key
photosynthetic properties in response to environmental change.
vii). To modify the C4 grassland model in order to study the potential
impact of climate change on the light, nitrogen and water use efficiencies of potential
energy crops such as the agriculturally important C4 species miscanthus (Miscanthus
sinensis).
