The CASA model defines the constant values of e 0 as 0.55 g C m
-2 MJ
-1
APAR (Potter 1999; Potter et al. 1993) or 0.389 g C m
-2 MJ
-1 APAR (Potter
et al. 2003; Potter 2012) for global biome types, and e n is determined by Eq. 5.18
e n ¼ e 0 Â T Â W
ð5:18Þ
where T is the temperature stress scalar computed with reference to the derivation
of the optimal temperature (T opt ) for production; and W refers to the monthly
relative soil moisture deficit based on the difference between actual and potential
evapotranspiration estimated by a soil/water balance model (Nayak et al. 2010;
Potter and Klooster 1997; Potter et al. 1993, 1998).
5.3.2 The Global Production Efficiency Model (GLO-PEM)
The GLO-PEM model estimates both GPP and NPP based on the production
efficiency concept. It includes the components that describe the processes of
canopy radiation absorption, utilization, autotrophic respiration, and the regulations of these processes by environmental factors (Goetz et al. 2000; Prince and
Goward 1995). The GLO-PEM model estimates FPAR canopy with NDVI. NDVI of
bare soil is approximately 0.05, and NDVI of the closed, thick, and green vegetation canopy is usually 0.9 or higher (Goward and Huemmrich 1992).
FPAR canopy ¼ 1:08 Â NDVI À 0:08
ð5:19Þ
e g is estimated through a modeling approach based on plant physiological
principles (Prince and Goward 1995). Plant photosynthesis depends on both the
capacity of photosynthetic enzymes to assimilate CO 2 (Collatz et al. 1991; Farquhar et al. 1980) and the stomatal conductance of CO 2 from the atmosphere into
intercellular spaces (Harley et al. 1992). These two processes are affected by
environmental factors such as air temperature (T), water vapor pressure deficit
(VPD), and soil moisture (SM).
e g ¼ e 0 Â T Â SM Â VPD
ð5:20Þ
Detailed approaches for modeling e g are described in earlier publications
(Collatz et al. 1991, 1992; Goetz and Prince 1998, 1999; Prince and Goward 1995).
5.3.3 The Terrestrial Uptake and Release of Carbon (TURC)
Model
The TURC model calculates NPP as the difference between GPP and autotrophic
respiration (Cramer et al. 1999; Lafont et al. 2002; Ruimy et al. 1996a, 1999). The
linear relationship between FPAR canopy and NDVI is defined with Eq. 5.21:
5 Gross Primary Production of Terrestrial Vegetation
133
-2 MJ
-1
APAR (Potter 1999; Potter et al. 1993) or 0.389 g C m
-2 MJ
-1 APAR (Potter
et al. 2003; Potter 2012) for global biome types, and e n is determined by Eq. 5.18
e n ¼ e 0 Â T Â W
ð5:18Þ
where T is the temperature stress scalar computed with reference to the derivation
of the optimal temperature (T opt ) for production; and W refers to the monthly
relative soil moisture deficit based on the difference between actual and potential
evapotranspiration estimated by a soil/water balance model (Nayak et al. 2010;
Potter and Klooster 1997; Potter et al. 1993, 1998).
5.3.2 The Global Production Efficiency Model (GLO-PEM)
The GLO-PEM model estimates both GPP and NPP based on the production
efficiency concept. It includes the components that describe the processes of
canopy radiation absorption, utilization, autotrophic respiration, and the regulations of these processes by environmental factors (Goetz et al. 2000; Prince and
Goward 1995). The GLO-PEM model estimates FPAR canopy with NDVI. NDVI of
bare soil is approximately 0.05, and NDVI of the closed, thick, and green vegetation canopy is usually 0.9 or higher (Goward and Huemmrich 1992).
FPAR canopy ¼ 1:08 Â NDVI À 0:08
ð5:19Þ
e g is estimated through a modeling approach based on plant physiological
principles (Prince and Goward 1995). Plant photosynthesis depends on both the
capacity of photosynthetic enzymes to assimilate CO 2 (Collatz et al. 1991; Farquhar et al. 1980) and the stomatal conductance of CO 2 from the atmosphere into
intercellular spaces (Harley et al. 1992). These two processes are affected by
environmental factors such as air temperature (T), water vapor pressure deficit
(VPD), and soil moisture (SM).
e g ¼ e 0 Â T Â SM Â VPD
ð5:20Þ
Detailed approaches for modeling e g are described in earlier publications
(Collatz et al. 1991, 1992; Goetz and Prince 1998, 1999; Prince and Goward 1995).
5.3.3 The Terrestrial Uptake and Release of Carbon (TURC)
Model
The TURC model calculates NPP as the difference between GPP and autotrophic
respiration (Cramer et al. 1999; Lafont et al. 2002; Ruimy et al. 1996a, 1999). The
linear relationship between FPAR canopy and NDVI is defined with Eq. 5.21:
5 Gross Primary Production of Terrestrial Vegetation
133