there is high uncertainty in the measured NPP, the C:N ratio map, and other
parameters used for the model prediction (Mitchell and Csillag 2001). In the spatial
Fixed C:N = 24.0
a
b
Simulated NPP (g C m -2 yr -1 )
Simulated NPP (g C m -2 yr -1 )
y = 1.10x - 25.72
y = 1.02x - 8.63
RMSE = 22.6
R 2 = 0.34
R 2 = 0.17
RMSE = 27.0
Observed NPP (g C m -2
yr -1
)
Observed NPP (g C m -2
yr -1
)
160
140
120
100
80
60
40
20
0
160
140
120
100
80
60
40
20
0
0 20 40 60 80 100 120 140 160
0 20 40 60 80 100 120 140 160
SpaƟal C:N
Fig. 8.7 The relationships between observed NPP and simulated NPP
Table 8.1 Descriptive statistics of field NPP (g C m
À2 years
À1
), simulated NPP (g C m
À2
years
À1
) from the model outputs driven by fixed foliar C:N ratio and MODIS derived spatial
foliar C:N ratio
Descriptive
statistics
Observed
NPP
Simulated NPP driven by
fixed C:N
Simulated NPP driven by
spatial C:N
Average
98.29
112.53
107.36
Max
146.00
131.72
135.65
Min
59.15
89.62
65.32
STD
43.49
21.08
35.38
Simulated NPP VS Observed NPP
C:N values used to drive the model
RMSE (g C m -2
yr -1
)
60
55
50
45
40
35
30
5
10
15
17
19
21
23
24
25
27
29
31
33
35
45
Spatial
Fig. 8.8 RMSE between observed NPP and simulated NPP as a function of different leaf C:N
values
166
Y. He et al.