Environmental Engineering Reference
In-Depth Information
50
40
30
20
10
Oak understorey
Canopy edge
Open grassland
Note:
Mean standard error and range have been drawn.
Source:
Marañon (1986).
Figure 4.2
Average species richness (number of species in 4m
2
plots)
in three habitats: oak understorey, canopy edge and open
grassland
herbivore systems, such as game ranches on the savannas of Africa, may
include up to 20 dif erent mammal herbivore species (Cumming, 1993).
Managers exploit dif erences in grazing habits that can lead to a degree of
complementarity in the use of forage resources where the total productiv-
ity of the range is seen to increase. Short grass (concentrate) grazers benei t
from the modii cation of sward structure brought about by long grass
(bulk) grazers, for example, sheep generally perform better when grazed in
mixed systems than when grazed alone (Nolan and Connolly, 1977). This
is usually only the case when large quantities of unpalatable poor-quality
fodder are available. McNaughton (1984) reports that in the Serengeti,
the larger bulk grazers consume long grass and these are then followed by
smaller ungulates that create 'grazing lawns'. These lawns are sources of
high-quality forage and so herbivores are seen to inl uence the quality and
productivity of the grazing resource. Mixed species grazing systems may
also be preferred to single species systems because they improve yields and
do not over-exploit productive herbaceous species. It has been reported
that sheep and cattle may af ect the plant community in dif erent ways.
Bedell (1973) has shown that sheep can reduce the abundance of clover in
a sward but they also increase the amount of
Poa trivialis
(Conway et al.,
1972). In contrast, a high proportion of cattle has been shown to increase
