12 GOTILWA: An Integrated Model
of Water Dynamics and Forest Growth
Carlos A. Gracia, Estlbaliz Tello, Santiago Sabate and Juan Bellot
12.1 GOTILWA: an Overview
GOTILWA is a simulation model of forest growth. Its name, GOTILWA, is an
acronym for Growth Of Trees Is Limited by WAter. The name itself defines
the main characteristic of the model. Water is, very often, the limiting factor
for plant growth (Pinol et al. 1991; Sala 1992; Chap. 13) and thus it constitutes
a key factor in the model (Tello et al. 1994). In a standard simulation, daily
climatic data are analyzed. From the interaction between daily rainfall and
the forest structure, the amount of intercepted water by the canopy layer,
throughfall and stemflow are estimated. This effective rainfall increases the
water stored in the soil which is used by the trees. The proportion of sapwood to heartwood, the leaf area of each tree and, consequently, the leaf area
index (LAl) of the forest are all highly dependent on water availability in the
model.
Carbon uptake by trees is computed by using water use efficiency (WUE)
and the water transpired by each tree on a monthly basis. The pool of carbon
gained leads to an increase, primarily, in the mobile carbon stored in the
plant. A fraction of this carbon compensates the maintenance respiration,
while the remaining carbon, if any, is available for storage and for sustaining
growth.
Associated with the formation of new biomass is an additional metabolic
cost which constitutes the growth respiration. The difference between carbon
fixation and maintenance plus growth respiration is net primary production
(NPP). The carbon balance of trees determines the processes of leaf formation and leaf fall, tree ring formation, the rate of change of sapwood into
heartwood and, consequently, the changes in tree structure within each size
class. These changes will affect in turn the hydrological fluxes which will
subsequently take place in what might be described as a feedback process
(Sala and Tenhunen 1994).
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
of Water Dynamics and Forest Growth
Carlos A. Gracia, Estlbaliz Tello, Santiago Sabate and Juan Bellot
12.1 GOTILWA: an Overview
GOTILWA is a simulation model of forest growth. Its name, GOTILWA, is an
acronym for Growth Of Trees Is Limited by WAter. The name itself defines
the main characteristic of the model. Water is, very often, the limiting factor
for plant growth (Pinol et al. 1991; Sala 1992; Chap. 13) and thus it constitutes
a key factor in the model (Tello et al. 1994). In a standard simulation, daily
climatic data are analyzed. From the interaction between daily rainfall and
the forest structure, the amount of intercepted water by the canopy layer,
throughfall and stemflow are estimated. This effective rainfall increases the
water stored in the soil which is used by the trees. The proportion of sapwood to heartwood, the leaf area of each tree and, consequently, the leaf area
index (LAl) of the forest are all highly dependent on water availability in the
model.
Carbon uptake by trees is computed by using water use efficiency (WUE)
and the water transpired by each tree on a monthly basis. The pool of carbon
gained leads to an increase, primarily, in the mobile carbon stored in the
plant. A fraction of this carbon compensates the maintenance respiration,
while the remaining carbon, if any, is available for storage and for sustaining
growth.
Associated with the formation of new biomass is an additional metabolic
cost which constitutes the growth respiration. The difference between carbon
fixation and maintenance plus growth respiration is net primary production
(NPP). The carbon balance of trees determines the processes of leaf formation and leaf fall, tree ring formation, the rate of change of sapwood into
heartwood and, consequently, the changes in tree structure within each size
class. These changes will affect in turn the hydrological fluxes which will
subsequently take place in what might be described as a feedback process
(Sala and Tenhunen 1994).
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999