Benefits of protective fencing to plant and rodent communities of the western Mojave Desert, California

Published source details Brooks M.L. (1995) Benefits of protective fencing to plant and rodent communities of the western Mojave Desert, California. Environmental Management, 19, 65-74.
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This study is summarised as evidence for the following.

	Action	Category
	Exclude livestock from semi-natural habitat (including woodland) Action Link
	Other biodiversity: Exclude grazers Action Link

Exclude livestock from semi-natural habitat (including woodland)

A replicated, site comparison study in 1990–1992 in a desert in south-central California, USA (Brooks 1995) found that excluding livestock led to more small mammal species, and higher densities of some small mammal species, compared to sheep-grazed areas. More species of small nocturnal rodents were found in ungrazed (3.7 species/sample) than in grazed areas (2.5 species/sample), and diversity was higher in ungrazed areas in all three years (data reported as diversity indices). The densities of three of five species were higher in ungrazed than in grazed plots (long-tailed pocket mouse Chaetodipus formosus: 26 vs 6 animals/ha; Merriam’s kangaroo rat Dipodomys merriami: 31 vs 13; southern grasshopper mouse Onychomys torridus: 3 vs 0 respectively). The densities of the other two species did not differ significantly between grazed and ungrazed plots (little pocket mouse Perognathus longimembris: 29 vs 30 animals/ha; deer mouse Peromyscus maniculatus: 1 vs 0). Two pairs of 65-ha plots were established in 1990 with one plot inside an area fenced since 1978–1979 and one outside, in an area grazed by sheep (grazing intensity not stated). Over five periods of four to six nights, in May 1990–March 1992, mammals were caught in 64 Sherman traps/plot, 10 m apart.

(Summarised by: Phil Martin)
Other biodiversity: Exclude grazers

A replicated site comparison in 1990–1992 in a desert in south-central California, USA, found more species, and higher densities, of some small mammal species, in plots from which sheep were excluded, compared to grazed plots. More plant biomass was found in ungrazed plots, compared to grazed plots. Plants: Similar plant diversity was found in ungrazed and grazed plots (3.5–4.3 vs 1.5–3.7 species; diversity reported as diversity indices). More plant biomass was found in ungrazed plots (12–199 vs 5–57 kg/ha). Plant biomass was higher in ungrazed areas, in 21 of 23 species, in at least one year, and the two species with lower biomass were non-native. The cover of two of 13 species of perennial shrub was higher in ungrazed areas (Ambrosia dumosa: 2.8% vs 1.5% cover; Lycium andersonii: 0.9% vs 0.1%). The density of one of 13 species of perennial shrubs was lower in ungrazed areas (Acamptopappus sphaerocephalus: 85 vs 333 plants/ha). The density of seeds was higher in ungrazed plots, in one of three years (1992: 193 vs 56 kg/ha; other years: 50–121). The biomass of non-grasses was higher than that of non-native annual grasses in all years in the ungrazed area, but only in one year in the grazed area. Mammals: More species of small nocturnal rodents were found in ungrazed areas (3.7 vs 2.5 species/sample), and diversity was higher in ungrazed areas in all three years (data reported as diversity indices). The densities of three of five small, nocturnal rodents were higher in ungrazed plots (long-tailed pocket mouse: 26 vs 6 animals/ha; Merriam’s kangaroo rat: 31 vs 13; southern grasshopper mouse: 3 vs 0). Methods: Two pairs of 65 ha plots were established in 1990 (one plot inside an area fenced since 1978–1979 and one outside). Vegetation was sampled in ten 1 m² plots and at ten points on each of ten 100 m transects in April and June 1990–1992. Seeds were sampled in the top 2 cm of the soil in ten 6 cm diameter circles. Mammals were caught in 64 Sherman traps in each plot (in five periods of 4–6 nights).