Environmental Engineering Reference
In-Depth Information
veritable deserts in comparison. Table 22.6 shows additional information. LAI (leaf area
index) is the area of leaves per unit area of ground. It ranges from highs of about 23 in
some swamps and marshes down to about 0.5 in polar deserts. LAI has become an
important factor in explaining differences in productivity both within and between
biomes, as the leaf is the organ of photosynthesis. The length of time a plant can
photosynthesize is equally important (evergreen
v
. deciduous). This is the index LAD
(leaf area duration), which is not shown here. The percentage of NPP consumed by
herbivores is also shown in Table 22.6. There are very real differences between forest
biomes, grassland biomes and aquatic ecosystems,
Table 22.4 World productivity values
Area (10
6
km
2
)
Ecosystem type
Mean NPP (kg
m
−2
yr
−1
)
Mean biomass (kg
m
−2
)
World biomass
(10
9
t)
Tropical rain
forest
17
2.20
45
765
Temperate
deciduous
7
1.20
30
210
Boreal forest
12
0.80
20
240
Savanna
15
0.90
4
64
Temperate
grassland
9
0.60
1.6
14
Tundra and alpine
8
0.14
0.6
5
Desert
18
0.10
0.7
13
Open ocean
332
0.13
0.003
1.0
Reefs
1
2.50
2.0
1.2
Estuaries
2
1.50
1.0
1.4
Table 22.5 Global biomass within individual
ecosystems (%)
Forests
Tropical rain forest
42
Tropical seasonal
14
Tropical evergreen
10
Temperate deciduous
11
Boreal
13
Grassland and desert
Savanna
4
Temperate grassland
1
