Effects of protective fencing on birds, lizards, and black-tailed hares in the western Mojave Desert

Limit or exclude off-road vehicle use

A replicated, site comparison in 1994–1996 in desert shrub and grassland in south-central California, USA (Brooks 1999), found that lizard abundance and species richness was higher inside a fenced protected area that excluded vehicles and sheep, compared to outside of the fence, depending on survey month and plot. Lizard abundance was higher in three of six survey comparisons in a fenced protected area with restricted vehicle use (4–10 lizards/transect) compared to outside of it (2–4 lizards/transect) but similar in the remaining three comparisons (inside protected area: 2–5 lizards/transect; outside protected area 1–3 lizards/transect; see original paper for details). Lizard species richness was higher in one of six comparisons inside the protected area (2 species/transect) compared to outside of it (1 species/transect) but similar in the remaining five comparisons (inside protected area: 2–3 species/transect; outside protected area: 1–3 species/transect; see original paper for details). In 1994, two sites were selected near the north-eastern and southern boundary of the Desert Tortoise Research Natural Area (where off-road vehicles were prohibited from 1973, sheep grazing prohibited from 1978 and the boundary was fenced in 1980). Two 2.25 ha plots were established/site: one ≥400m inside the boundary and one outside the boundary (used by off-road vehicles until 1980 and grazed by sheep until 1994). In each plot, lizards were surveyed using 1.25 km transects in July 1994 and May and July 1995 (six surveys/site).

(Summarised by: Katie Sainsbury)

Use fencing to exclude grazers or other problematic species

A replicated, paired sites study in 1994–1995 in the Western Mojave Desert, California, USA (Brooks 1999) found that within an area fenced to exclude livestock grazing and off-road vehicles, abundance of black-tailed hares Lepus californicus was lower compared to unfenced areas. Fewer black-tailed hares were found in fenced plots (0–1.5 animals/transect; 1.5 droppings/1,250 cm²) than in unfenced plots (1–4 animals/transect; 3-4 droppings/1,250 cm²). In the Desert Tortoise Research Natural Area, off-road vehicles were prohibited from 1973, sheep grazing from 1978, and a 1 m high wire fence protecting the area was constructed by 1980. Two sites were selected near the north eastern and southern boundary. At each site, two 2.25-ha plots were established, one ≥400m inside the fenced area and one outside the fence (used by off-road vehicles until 1980 and grazed by sheep until 1994). Plots were matched for environmental variables. In each plot, hare numbers were estimated along four 1.2-km transects in May and July 1994, and at the north eastern site by counting pellets in 120 quadrats (40 × 50-cm) in April 1994 and 1995.

(Summarised by: Phil Martin)

Protect habitat: All reptiles (excluding sea turtles)

A replicated, site comparison study in 1994–1996 in desert shrub and grassland in south-central California, USA (Brooks 1999) found that lizard abundance and species richness was higher or similar inside a fenced protected area compared to outside depending on survey month and site. Lizard abundance was higher in three of six survey comparisons in a fenced protected area (4–10 lizards/transect) compared to outside of it (2–4 lizards/transect) but similar in the remaining three comparisons (inside: 2–5 lizards/transect; outside: 1–3 lizards/transect; see original paper for details). Lizard species richness was higher in one of six comparisons inside the protected area (2 species/transect) compared to outside of it (1 species/transect) but similar in the remaining five comparisons (inside: 2–3 species/transect; outside: 1–3 species/transect; see original paper for details). In 1994, two sites were selected near the north-eastern and southern boundary of the Desert Tortoise Research Natural Area (where off-road vehicles were prohibited from 1973, sheep grazing prohibited from 1978 and the boundary was fenced in 1980). Two 2.25 ha plots were established/site: one ≥400m inside the boundary and one outside the boundary (used by off-road vehicles until 1980 and grazed by sheep until 1994). In each plot, lizards were surveyed using 1.25 km transects in July 1994 and May and July 1995 (six surveys/site).

(Summarised by: Katie Sainsbury)

Exclude livestock from semi-natural habitat (including woodland)

A replicated, site comparison study in 1994 in a desert site in California, USA (Brooks 1999) found that in areas where livestock were excluded, there were fewer black-tailed hares Lepus californicus, compared to in sheep-grazed unfenced areas that were also driven over by off-road vehicles. Fewer black-tailed hares were found in fenced plots (0–1.5 hares/survey; 11 droppings/m²) compared to in unfenced plots (1–4 hares/survey; 22–31 droppings/m²). Two 2.25-ha plots that were fenced in 1980 were compared to two plots that were grazed by sheep (and driven over by off-road vehicles). Sites were matched for environmental variables. Hare numbers were estimated in May and July 1994 by counting the number of hares seen on four 1.25-km-long transects and the number of droppings in sixty 40 × 50-cm sampling units in each plot.

(Summarised by: Phil Martin)

Cease livestock grazing: Grassland & shrubland

A replicated, site comparison study in 1994–1996 in desert shrub and grassland in south-central California, USA (Brooks 1999) found that lizard abundance and species richness was higher or similar inside a protected area fenced to prevent sheep grazing, compared to grazed areas outside of the fenceline, depending on survey month and site. Lizard abundance was higher in three of six survey comparisons inside a fenced protected area without sheep grazing (4–10 lizards/transect) compared to outside of it (2–4 lizards/transect) but similar in the remaining three comparisons (inside: 2–5 lizards/transect; outside: 1–3 lizards/transect; see original paper for details). Lizard species richness was higher in one of six comparisons inside the protected area (2 species/transect) compared to outside of it (1 species/transect) but similar in the remaining five comparisons (inside: 2–3 species/transect; outside: 1–3 species/transect; see original paper for details). In 1994, two sites were selected near the north-eastern and southern boundary of the Desert Tortoise Research Natural Area (where off-road vehicles were prohibited from 1973, sheep grazing prohibited from 1978 and the boundary was fenced in 1980). Two 2.25 ha plots were established/site: one ≥400m inside the boundary and one outside the boundary (used by off-road vehicles until 1980 and grazed by sheep until 1994). In each plot, lizards were surveyed using 1.25 km transects in July 1994 and May and July 1995 (six surveys/site).

(Summarised by: Katie Sainsbury)

Exclude grazers from semi-natural habitats

A replicated study in 1994-1995 in the Mojave Desert, California, USA (Brooks 1999), found that bird abundance and species richness were higher inside two 2.25 ha sites protected from sheep grazing and off-highway vehicles (OHV) since 1978, compared to adjacent sites that were grazed and driven over by OHVs. Significant differences were observed for sage sparrow Amphispizia belli, Le Conte’s thrasher Toxostoma lecontei, loggerhead shrike Lanius ludovicianus, verdin Auriparus flaviceps and ash-throated flycatcher Myiarchus cinerascens.  The authors suggest the increased abundance of bird species within the protected area is linked to a greater food supply.

Other biodiversity: Exclude grazers

A replicated site comparison in 1994–1996 in a desert site in south-central California, USA, found more birds and bird species in plots with grazers excluded, compared to sheep-grazed plots. Fewer black-tailed hares Lepus californicus, but more lizards were found in fenced plots, compared to unfenced plots. Perennial plant cover was higher in fenced plots, compared to unfenced plots. Birds: More bird species were observed nesting in fenced plots, compared to unfenced plots (3 vs 1 species). More birds and bird species were found in fenced plots (0.9–3.1 vs 0.7–2.6 species/survey; 1–11 vs 1–9 birds/survey), and six of 22 species were more abundant in fenced plots. Mammals: Fewer black-tailed hares were found in fenced plots (0–1.5 vs 1–4 hares/survey; 11 vs 22–31 droppings/m²). Plants: There were no differences in species diversity of perennial plants in fenced or unfenced plots (data reported as Shannon-Weiner indices). Perennial plant cover was higher in fenced plots (13–14% vs 6–7% cover). There were no differences in diversity of height, cover, or volume of perennial plants between fenced and unfenced sites (data reported as Shannon-Weiner indices). Reptiles: Fewer lizards were found in ungrazed plots, compared to grazed plots (1–4 vs 2–10 lizards/survey), and two of six species were less abundant in ungrazed plots, in some comparisons. Methods: Two 2.25 ha plots that were fenced in 1980 were compared to two plots that were grazed by sheep until 1994. Sites were matched for environmental variables. Birds were counted using 16 point counts in each plot, four times during breeding seasons (1994–1995) and twice during winter (December 1994, January 1996). Lizards were surveyed using 1.25 km transects three times in summer (1994–1995). Hares numbers were estimated with four 1.25 km transects and in sixty 40 x 50 cm sampling units in each plot. Plants were surveyed at 16 points in each plot in June 1995. Unfenced plots were also driven over by off-highway vehicles.