172
Carlos A. Gracia, Estlbaliz Tello, Santiago Sabat!! and Juan Bellot
12.3.11 Growth Respiration
Owing to biosynthesis costs and to the transport of carbon between organs
and across cell membranes, the formation of new biomass in plants from net
carbon uptake has a respiration cost. On average, 1 g of carbohydrates gives
about 0.68 g of new tissues and the difference is consumed during the process of growth respiration.
12.3.12 Net Primary Production and Carbon Allocation
GPP minus total respiration (the sum ofleaf, wood, fine root and growth respiration) is the net primary production (NPP). NPP is allocated to the different parts of the plant following a set of allocation rules. The plant uses a
fraction of this NPP to form new leaves and fine roots to compensate their
turnover. The remaining NPP is allocated to the pool of mobile carbon in
leaves and woody tissu~s. If the NPP exceeds the carbon storage demand it is
used in the formation of leaves and fine roots, in the case that leaf area is
lower than the leaf area that can be supported by the existing sapwood area.
The remaining NPP, if any, is invested in the production of new leaves and
new wood in such a proportion that the new sapwood area and the new leaf
area fit the constant ratio.
12.4 Model Validation
Actual weather data recorded at Poblet Meteorological Station, close to the
Prades experimental area (Chap. 2), between 1981 and 1995 were used to
simulate the growth of the holm oak (Quercus ilex 1.) forest in Prades. To
calibrate the model, a series of field data collected between 1981 and 1995 for
tree density, increase in diameter, litterfall, tree ring width, LAI, basal area,
aboveground biomass (Djema et al. 1994) and streamflow have been used
even if all the series do not cover the entire period (Lled6 et al. 1992).
A thinning experiment began in Prades in 1992 (Chap. 23). This experiment applied four thinning intensities replicated in three plots (0, control;
55 ± 2,72 ± 3 and 79 ± 4% of basal area). The model validation used data
from field measurements obtained from this experiment between 1992 and
1995 (Albeza et al. 1995), long-term series of litterfall recorded between 1982
and 1989 (Bellot et al. 1992) and weather data recorded during the same period. Figure 12.2 shows the agreement between observed and simulated tree
ring increments in the control, minimum and maximum thinning plots as
well as in the observed and simulated monthly litterfall.
Other field-measured variables such as mean diameter, LAI, basal area or
aboveground biomass have been compared with the results obtained in the
Carlos A. Gracia, Estlbaliz Tello, Santiago Sabat!! and Juan Bellot
12.3.11 Growth Respiration
Owing to biosynthesis costs and to the transport of carbon between organs
and across cell membranes, the formation of new biomass in plants from net
carbon uptake has a respiration cost. On average, 1 g of carbohydrates gives
about 0.68 g of new tissues and the difference is consumed during the process of growth respiration.
12.3.12 Net Primary Production and Carbon Allocation
GPP minus total respiration (the sum ofleaf, wood, fine root and growth respiration) is the net primary production (NPP). NPP is allocated to the different parts of the plant following a set of allocation rules. The plant uses a
fraction of this NPP to form new leaves and fine roots to compensate their
turnover. The remaining NPP is allocated to the pool of mobile carbon in
leaves and woody tissu~s. If the NPP exceeds the carbon storage demand it is
used in the formation of leaves and fine roots, in the case that leaf area is
lower than the leaf area that can be supported by the existing sapwood area.
The remaining NPP, if any, is invested in the production of new leaves and
new wood in such a proportion that the new sapwood area and the new leaf
area fit the constant ratio.
12.4 Model Validation
Actual weather data recorded at Poblet Meteorological Station, close to the
Prades experimental area (Chap. 2), between 1981 and 1995 were used to
simulate the growth of the holm oak (Quercus ilex 1.) forest in Prades. To
calibrate the model, a series of field data collected between 1981 and 1995 for
tree density, increase in diameter, litterfall, tree ring width, LAI, basal area,
aboveground biomass (Djema et al. 1994) and streamflow have been used
even if all the series do not cover the entire period (Lled6 et al. 1992).
A thinning experiment began in Prades in 1992 (Chap. 23). This experiment applied four thinning intensities replicated in three plots (0, control;
55 ± 2,72 ± 3 and 79 ± 4% of basal area). The model validation used data
from field measurements obtained from this experiment between 1992 and
1995 (Albeza et al. 1995), long-term series of litterfall recorded between 1982
and 1989 (Bellot et al. 1992) and weather data recorded during the same period. Figure 12.2 shows the agreement between observed and simulated tree
ring increments in the control, minimum and maximum thinning plots as
well as in the observed and simulated monthly litterfall.
Other field-measured variables such as mean diameter, LAI, basal area or
aboveground biomass have been compared with the results obtained in the