GOTILWA: An Integrated Model of Water Dynamics and Forest Growth
177
Allocation of carbon to leaf and wood production differs with thinning
intensity and climate scenario. Although leaf production does not show a
clear pattern according to thinning intensity (Fig. 12.4f), the fraction of NPP
allocated to leaf production decreases as thinning intensity increases under
both climate scenarios (from 46 to 29% in the present climate, and from 74 to
56% with climate change). Thus, the resulting fraction of NPP invested in
wood production increases as thinning intensity increases. The effect of climate change on leaf turnover has important consequences for the final
structure of the forest. Leaf maintenance costs are so high under the climate
change scenario (9.44 and 7.79 Mg DM ha- 1 year- 1 in control and maximum
thinned plots, respectively) that LAI is reduced when compared to the present climate scenario (Fig. 12.4g). The reduction of LAI is more important in
the control treatment (from 3.98 to 3.03 m 2 m- 2 ) than in thinning treatments
(from 3.09 to 2.83 m 2 m- 2 in maximum thinned plots) because the proportional respiratory costs are lower in thinning treatments. Even more important is the reduction of mean leaf life (Fig. 12.4h) from 2.7 years under the
present climate scenario to 1.8 years under the climate change scenario due
to the higher leaf turnover promoted by climate change. Changes in leaf
turnover are also reflected in the final mean stem diameter. Thinning slightly
decreases the proportion of NPP invested in leaf production and allows
wood production to be increased.
The total biomass after 50 years of simulation shows roughly the same
value under the present climate scenario (465 Mg DM ha- 1 ) while under the
climate change scenario the control treatment shows a lower value than the
thinning treatment (219 and 366 Mg DM ha- 1 , respectively). Climate change
promotes a lower final value of total biomass in all treatments. The higher
maintenance respiration and leaf turnover while NPP remains constant leads
to the mortality of a significant number of trees. The density of control
treatment is 7661 stems ha- 1 at the end of the present-climate simulation
while it is 5074 stems ha- 1 under the climate change scenario. The reduction
of density is lower in the case of minimum thinning treatment (from 4775 to
4330 stems ha- 1 ), and there is no mortality in the maximum thinning treatment (2038 trees ha- 1 ).
Thinning effects tend to diminish after 50 years of simulation and most of
the variables tend to converge to their former values, as shown by GPP
(Fig. 12.4a) and total biomass (data not shown). The consequences of thinning differ in some major variables, such as the reduction of the proportion
of GPP invested in maintenance respiration and the percentage of NPP used
in leaf turnover.
Climate change promotes the opposite effects on the former variables.
Even if the GPP increased by about 29%, climate change would promote a
drastic reduction in LAI and total biomass because the temperature rise involves a marked increase in respiratory cost and leaf turnover. This is an important point to take into account if the results are compared with other predictions of the effects of climate change, where the total biomass generally
177
Allocation of carbon to leaf and wood production differs with thinning
intensity and climate scenario. Although leaf production does not show a
clear pattern according to thinning intensity (Fig. 12.4f), the fraction of NPP
allocated to leaf production decreases as thinning intensity increases under
both climate scenarios (from 46 to 29% in the present climate, and from 74 to
56% with climate change). Thus, the resulting fraction of NPP invested in
wood production increases as thinning intensity increases. The effect of climate change on leaf turnover has important consequences for the final
structure of the forest. Leaf maintenance costs are so high under the climate
change scenario (9.44 and 7.79 Mg DM ha- 1 year- 1 in control and maximum
thinned plots, respectively) that LAI is reduced when compared to the present climate scenario (Fig. 12.4g). The reduction of LAI is more important in
the control treatment (from 3.98 to 3.03 m 2 m- 2 ) than in thinning treatments
(from 3.09 to 2.83 m 2 m- 2 in maximum thinned plots) because the proportional respiratory costs are lower in thinning treatments. Even more important is the reduction of mean leaf life (Fig. 12.4h) from 2.7 years under the
present climate scenario to 1.8 years under the climate change scenario due
to the higher leaf turnover promoted by climate change. Changes in leaf
turnover are also reflected in the final mean stem diameter. Thinning slightly
decreases the proportion of NPP invested in leaf production and allows
wood production to be increased.
The total biomass after 50 years of simulation shows roughly the same
value under the present climate scenario (465 Mg DM ha- 1 ) while under the
climate change scenario the control treatment shows a lower value than the
thinning treatment (219 and 366 Mg DM ha- 1 , respectively). Climate change
promotes a lower final value of total biomass in all treatments. The higher
maintenance respiration and leaf turnover while NPP remains constant leads
to the mortality of a significant number of trees. The density of control
treatment is 7661 stems ha- 1 at the end of the present-climate simulation
while it is 5074 stems ha- 1 under the climate change scenario. The reduction
of density is lower in the case of minimum thinning treatment (from 4775 to
4330 stems ha- 1 ), and there is no mortality in the maximum thinning treatment (2038 trees ha- 1 ).
Thinning effects tend to diminish after 50 years of simulation and most of
the variables tend to converge to their former values, as shown by GPP
(Fig. 12.4a) and total biomass (data not shown). The consequences of thinning differ in some major variables, such as the reduction of the proportion
of GPP invested in maintenance respiration and the percentage of NPP used
in leaf turnover.
Climate change promotes the opposite effects on the former variables.
Even if the GPP increased by about 29%, climate change would promote a
drastic reduction in LAI and total biomass because the temperature rise involves a marked increase in respiratory cost and leaf turnover. This is an important point to take into account if the results are compared with other predictions of the effects of climate change, where the total biomass generally