Agriculture Reference
In-Depth Information
compared with communal grazing or game ranching systems in their assessment. In
contrast, Tefera et al. (2007) evaluated semiarid rangelands under communal land,
government ranch, and traditional grazing reserve enclosure land use systems in
Ethiopia, and found that vegetation distribution and grazing intensity was high in
the communal land but more moderate in the government ranch and the traditional
grazing reserves. However, there were no significant differences in vegetation along
the gradient of distance from water for any of the three land management systems,
suggesting that grazing disturbance had exceeded a threshold of degradation. Fterich
et al. (2012) studied soil characteristics for
Acacia
-dominated drylands in Tunisia
and reported that soil pH, electrical conductivity, SOC, microbial biomass carbon,
the microbial-to-organic carbon ratio, and enzyme activities increased as tree size
increased, while soil carbon-to-nitrogen ratio and metabolic quotient were lower
with increasing tree age. In intensively grazed sites, SOC, microbial biomass, and
enzyme activities were lower, while soil carbon-to-nitrogen ratio and metabolic quo-
tient were greater than in ungrazed sites.
4.3
MANAGEMENT PRACTICES AND
STRATEGIES FOR SUSTAINABILITY
4.3.1 e
xtenSIve
G
razInG
S
yStemS
Management practices such as fire and grazing modify the structure and function
of ecosystems, affecting SOC storage (e.g., Piñeiro et al. 2010). In fire-prone eco-
systems of arid landscapes, the largest pools of carbon are typically found in soils
rather than in the aboveground biomass (e.g., Rau et al. 2010). At a global scale, SOC
sequestration represents about 90% of the potential of what is technically feasible
(Gattinger et al. 2012). Grasslands have high SOC stocks (~12% of terrestrial SOC);
thus, it is important to understand the effects of management on SOC in setting
appropriate management intervention and policy. Grass and woody species coexist
in savanna ecosystems in which fire, herbivory, and soil types influence the relative
dominance of grass and woody cover where moisture is a determining environmen-
tal factor (Sankaran et al. 2005).
The potential of African rangelands to sequester SOC is based on the assumption
that they are undersaturated in SOC as a result of overgrazing and excessive use of
fire (Neely and de Leeuw 2011). Consequently, grazing management and control of
fire are considered interventions with the potential to sequester SOC in rangelands
(Intergovernmental Panel on Climate Change [IPCC] 2000; Derner and Schuman
2007; FAO 2010). The potential of these two interventions is further supported by a
number of models that predict enhanced SOC stocks under moderate grazing inten-
sity (e.g., Conant et al. 2001; Conant 2002, 2012).
4.3.1.1 Fire
Fire is an important management tool in African savanna and grassland systems for
both livestock herders and wildlife managers who use it regularly to control bush
encroachment and to remove dead and dying vegetation that has low forage quality
and is unpalatable to animals (Fynn et al. 2003; Sankaran et al. 2005). Fire is an
