Environmental Engineering Reference
In-Depth Information
FIGURE 2.6
(a) Mean annual precipi-
tation versus mean ANPP for a range of
terrestrial ecosystems and (b) the slopes of
the individual relationships of annual pre-
cipitation and ANPP for the same terres-
trial ecosystems versus mean annual
precipitation.
(Figure replotted from data in
the supplement of
Huxman et al. 2004
.)
(a)
1200
1000
800
600
400
200
0
0
500
1000 1500
Precipitation (mm)
2000
2500
3000
(b)
0.6
0.4
0.2
0.0
-0.2
0
1000
2000
3000
Precipitation (mm)
in biomass (
Figure 2.5d
),
leading to the conclusion that all
three nutrients colimit
production.
Terrestrial primary production is often correlated with precipitation in broad compari-
sons among ecosystems (
Figure 2.6a
)(
Huxman et al. 2004
). The values presented in
Figure 2.6
are annual means of precipitation and ANPP for at least seven years from long-
term study sites. Within a particular ecosystem represented by a point on the graph, the
interannual relationship of precipitation and ANPP is variable. For example, low precipita-
tion ecosystems like deserts and grasslands are generally quite sensitive to variation in
precipitation and there is a positive relationship (positive regression slopes) between pre-
cipitation and ANPP in different years (
Figure 2.6b
). For ecosystems with precipitation
greater than 1000 mm, slopes tend to be near zero; hence, these ecosystems are not sensi-
tive to interannual variation in precipitation, and other factors are more limiting to pri-
mary production.
