Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
fragmentation prevents both livestock and wildlife from reaching parts of
the landscape ; often the fenced parts contain key resources like swamps and
riverine areas. Impacts on wildlife are not entirely known, but decreases in
population sizes and viability can be expected. Eventually, fragmentation can
completely exclude species from an area.
Impacts of expansion of cultivation and settlement
Recent evidence suggests that the impact of cultivation on vegetation , wildlife
and soils in pastoral ecosystems is greater than that of livestock. Expansion of
cultivation fragments rangeland landscapes when farmers convert rangeland into
cropland (Hiernaux, 2000). Land degradation through crop cultivation has been
documented (Niamir-Fuller, 1999), but the impacts of livestock use and crop
cultivation (or any other land uses) has rarely been compared. The conversion
of savannah to cultivation in parts of the Mara ecosystem of Kenya, along
with poaching and drought , has caused more than a 60 percent loss in resident
wildlife populations in the Mara ecosystem in the last 20 years (Ottichilo et al.,
2000; Homewood et al., 2001; Serneels, Said and Lambin, 2001).
In non-cultivated areas, mixed livestock-wildlife systems may be more
productive than either wildlife-only or livestock-only systems (Western,
1989). These mixed systems, when maintained at moderate livestock grazing
levels, coupled with pastoral rangeland burning , may support higher levels of
plant and animal biodiversity than livestock-only or wildlife-only systems,
analogous to the increase in plant diversity seen at the edge of wildlife reserves
frequented by pastoralists and their livestock (Western and Gichohi, 1993).
Further, it is hypothesized that when livestock populations are moderate in
size or mobile , pastoralism produces significant global benefits in the form
of biodiversity conservation , carbon sequestration , soil retention, soil fertility
maintenance and catchment protection.
Estimates of how the expansion of cultivation will affect pastoral systems
over the next half century are based on scenarios of human population growth
and climate change for the year 2050 from Reid et al. (2000a) and Thornton et al.
(2002). Surprisingly, these changes may bring about an absolute expansion of cultivation
of only 4 percent, or a relative increase of about 15 percent (Figures 2.8
and 2.9). Most of the change will probably occur around the edges of currently
cultivated land in areas with the most rainfall . Thus pastoral areas are expected to
continue to contract further in the future and pastoral peoples to either continue
to adopt agropastoralism or become restricted to drier and drier land.
Carbon sequestration
It is not clear whether current changes in the eastern Africa n rangelands
(land use change, overgrazing, fragmentation) are causing a net release or net
accumulation of carbon, either above or below ground. Expansion of cultivation
into rangelands probably strongly reduces carbon below ground, but may