Land Use, Land-Use Change and Forestry

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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.




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