GOTILWA: An Integrated Model of Water Dynamics and Forest Growth
175
characteristic of the Mediterranean climate areas. The annual pattern of
other variables is also in agreement with field observations.
12.5 Model Application
GOTILWA has been used to explore how the thinning intensities applied to
the Prades holm oak forest modify the effects of an increase in both atmospheric CO2 and temperature and a reduction in water availability as predicted by most general circulation models (GCM) for the Mediterranean area
(Rotmans et al. 1994). Two climate scenarios have been used in this analysis:
reference (present climate, no change) and climate change in which we assume a linear increase of 150 ppm CO2, a temperature increase of 3°C, and a
decrease of 15% in rainfall over the next 50 years.
Results after 50 years. of simulation show that both climate change and
thinning could have opposite effects on some main variables. This is the case,
for example, for actual evapotranspiration (Ea). Thinning promotes a reduction of LAI (Fig. 12.4g) and might affect transpiration. Ea increases with increasing thinning intensity, 6% under the present climate scenario but only
20/0 under the climate change scenario. The slight differences shown by Ea are
not reflected in the GPP (Fig. 12.4a). Despite the reduction of Ea, an increase
in atmospheric CO2 of 43% promotes a significant increase of 35% in GPP in
all thinning treatments. The difference is due to the counterbalance of water
and temperature stress. This result agrees with the prediction of Mooney
et al. (1991) that in areas where water limits productivity, increased CO2 will
boost water use efficiency and is similar to the predictions obtained from the
SPUR model applied to semi-arid catchments (Skiles and Hanson 1994).
Maintenance respiration involves an important proportion of GPP
(Fig. 12.4b). This fraction decreases from 59% in the control to 48% in the
maximum thinning treatment under the present climate. Under climate
change scenario, the amount of GPP invested in maintenance respiration is
much higher (72% in control and 64% in maximum thinning treatment).
These values show that thinning promotes a proportional decrease of maintenance costs due to the reduction of total biomass. Climate change promotes
an increase (about 62%) in maintenance respiration due mainly to the effect
of increased temperature on the QIO factor. In spite of the increasing GPP, the
NPP does not significantly change due to this higher respiratory cost. Both
climate change and thinning affect in a similar way litterfall (Fig. 12.4e) and
leaf production (Fig. 12.4f). Thinned plots recover the former LAI under
both climate scenarios after a few years. Increased temperature increases leaf
shedding (71, 93 and 104% for control, minimum and maximum thinning
treatments, respectively) and promotes an important increase in leaf production (57, 78 and 97% for control, minimum and maximum thinning, respectively).
175
characteristic of the Mediterranean climate areas. The annual pattern of
other variables is also in agreement with field observations.
12.5 Model Application
GOTILWA has been used to explore how the thinning intensities applied to
the Prades holm oak forest modify the effects of an increase in both atmospheric CO2 and temperature and a reduction in water availability as predicted by most general circulation models (GCM) for the Mediterranean area
(Rotmans et al. 1994). Two climate scenarios have been used in this analysis:
reference (present climate, no change) and climate change in which we assume a linear increase of 150 ppm CO2, a temperature increase of 3°C, and a
decrease of 15% in rainfall over the next 50 years.
Results after 50 years. of simulation show that both climate change and
thinning could have opposite effects on some main variables. This is the case,
for example, for actual evapotranspiration (Ea). Thinning promotes a reduction of LAI (Fig. 12.4g) and might affect transpiration. Ea increases with increasing thinning intensity, 6% under the present climate scenario but only
20/0 under the climate change scenario. The slight differences shown by Ea are
not reflected in the GPP (Fig. 12.4a). Despite the reduction of Ea, an increase
in atmospheric CO2 of 43% promotes a significant increase of 35% in GPP in
all thinning treatments. The difference is due to the counterbalance of water
and temperature stress. This result agrees with the prediction of Mooney
et al. (1991) that in areas where water limits productivity, increased CO2 will
boost water use efficiency and is similar to the predictions obtained from the
SPUR model applied to semi-arid catchments (Skiles and Hanson 1994).
Maintenance respiration involves an important proportion of GPP
(Fig. 12.4b). This fraction decreases from 59% in the control to 48% in the
maximum thinning treatment under the present climate. Under climate
change scenario, the amount of GPP invested in maintenance respiration is
much higher (72% in control and 64% in maximum thinning treatment).
These values show that thinning promotes a proportional decrease of maintenance costs due to the reduction of total biomass. Climate change promotes
an increase (about 62%) in maintenance respiration due mainly to the effect
of increased temperature on the QIO factor. In spite of the increasing GPP, the
NPP does not significantly change due to this higher respiratory cost. Both
climate change and thinning affect in a similar way litterfall (Fig. 12.4e) and
leaf production (Fig. 12.4f). Thinned plots recover the former LAI under
both climate scenarios after a few years. Increased temperature increases leaf
shedding (71, 93 and 104% for control, minimum and maximum thinning
treatments, respectively) and promotes an important increase in leaf production (57, 78 and 97% for control, minimum and maximum thinning, respectively).