|
4.4.3. Grazing Lands Management
Grazing lands (which include grassland, pasture, rangeland, shrubland, savanna,
and arid grasslands up to the fringe of hyper-arid deserts-all of which are
referred to here as grasslands) occupy 1,900 to 4,400 Mha, depending on definitions
(Ojima et al., 1993c); recent global estimates have placed the area of
grazing lands at 3,200 Mha (FAO 1999). Grasslands contain 10-30 percent of the
world's soil carbon (Anderson, 1991; Eswaran et al., 1993)-including approximately
200-420 Gt organic C (Ojima et al., 1993c; Scurlock and Hall, 1998; Batjes,
1999) and 470-550 Gt of carbonate C to a depth of 1 m (Batjes, 1999). Management
activities can significantly affect carbon storage by reducing carbon loss in
degradation processes or increasing carbon inputs and residence times (Table
4-6).
|
Table 4-6: Rates of potential carbon gain under
selected practices for grasslands in various regions of the world.
|
|
| Practice |
Country/Region
|
Rate of Carbon Gain
(t C ha-1 yr-1)
|
Time1
(yr)
|
Other GHGs
and Impacts
|
Notes2
|
|
| Reduce degradation |
Global
|
0.5
|
20
|
Increases sustainability. Generally likely to reduce
methane emissions via reductions in animal numbers and increases in diet
quality. Possible improvement in biodiversity, particularly in set-aside
lands.
|
a
|
| |
Global
|
0.024-0.24
|
50
|
b
|
| |
Global
|
0.41
|
110
|
c
|
| - Improve grazing management |
Global
|
0.22
|
40
|
d
|
| |
Global
|
0.7
|
50+
|
e
|
| |
Australia
|
0.24
|
30
|
f
|
| - Protected lands and set-asides |
USA CRP
|
0.52
|
50
|
g
|
| |
China
|
1.3
|
|
h
|
|
| Increase grassland productivity |
Global
|
0.51
|
|
+N2O. Reduced erosion if grazing management appropriate.
|
d
|
|
| Fertilization |
Global average
|
0.23
|
40+
|
++N2O, off-site nutrient impacts, acidification.
|
d
|
| |
N. Australia
|
0.50
|
10
|
i
|
|
| Irrigation |
Global average
|
0.16
|
|
Associated fossil fuel emissions, salinization risks.
|
d
|
|
| Improved species and legumes |
|
|
|
+N2O, ±CH4. Risk of introduced species becoming weeds
in adjacent areas. Biodiversity loss from native pastures.
|
|
| - Legumes |
Global
|
1.09
|
|
d
|
| - Grasses |
Global
|
3.34
|
|
d
|
| - Conversion from native pasture |
Global
|
0.36
|
|
d
|
| |
South America
|
2.8-14.4
|
|
j
|
|
| Fire management |
Orinoco Plains, South America
|
1.4
|
|
-CH4, -N2O. Reduced agricultural production, ± biodiversity
depending on site.
|
k
|
| |
NE Australia
|
0.56
|
50
|
l
|
|
1 Time interval to which estimated rate applies. This interval may or may
not be time required for ecosystem to reach new equilibrium.
2
a. Glenn et al. (1993). 5172 Mh of drylands, halophyte storage over 5
years.
b. Paustian et al. (1998a). Assumes potential carbon sequestration of
1-2 kg C m-2 on an arbitrary 10-50% of moderately to highly degraded land (1.2
Gha globally; Oldeman et al., 1992).
c. Keller and Goldstein (1998). Revegetation of agricultural and pastoral drylands.
d. Conant et al. (2000). Based on literature review.
e. Ojima et al. (1993b). Regressive 50% consumption vs. sustainable 30%
land management for grassland and rangelands.
f. Ash et al. (1996). Average estimate 0-10 cm soil carbon only for transfer
from deteriorated condition to sustainable across northern Australia.
g. McConnell and Quinn (1988); Gebhart et al. (1994); Barker et al.
(1995); Burke et al. (1995).
h. Li and Zhao (1998). Change in top 20 cm of soil.
i. Dalal and Carter (1999). Phosphorus and sulfur fertilization over 56 Mha
in northern Australia.
j. Fisher et al. (1994, 1995). Introduced grass/legume pastures with
deep, dense root systems.
k. San Jose et al. (1998). Extrapolated from one site to 28 Mha region.
l. Burrows et al. (1998); Burrows et al. (1999). Aboveground and
below-ground biomass extrapolated from 47 sites to 60 Mha region.
|
|
|