Effects of grazing and invasive grasses on desert vertebrates in California

Published source details Germano D.J., Rathbun G.B. & Saslaw L.R. (2012) Effects of grazing and invasive grasses on desert vertebrates in California. Journal of Wildlife Management, 76, 670-682.
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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: Use grazers to manage vegetation Action Link
	Cease livestock grazing: Grassland & shrubland Action Link

Exclude livestock from semi-natural habitat (including woodland)

A replicated, controlled study in 1998–2006 in sagebrush shrubland previously affected by wildfire in California, USA (Germano et al. 2012) found that excluding livestock did not alter the abundance of five small mammal species. Over eight years, abundance of San Joaquin antelope squirrel Ammospermophilus nelson did not differ significantly between areas where livestock were excluded (4–38 animals/plot) and grazed areas (2–29 animals/plot). The same pattern was true for short nosed kangaroo rat Dipodomys nitratoides nitratoides (1–55 vs 3–58 animals/plot), Heermann’s kangaroo rat Dipdomys heermanni (0–4 vs 0–22), giant kangaroo rat Dipodomys ingens (0–4 vs 0–3), and San Joaquin pocket mouse Perognathus inornatus inornatus (1–10 vs 1–17). Four 2.6-km² areas were grazed by cattle and four 25-ha areas were fenced to exclude livestock. To estimate antelope squirrel abundance, 64 traps, baited with oats, at 40-m intervals, were established in each plot. To estimate abundance of other small mammals, 144 traps, baited with bird seed, were established in each plot at 10-m intervals. Traps were set for six consecutive days and nights in July–September 1998–2006.

(Summarised by: Phil Martin)
Other biodiversity: Use grazers to manage vegetation

A replicated, controlled study in 1997–2006 in scrub and grassland in central California, USA, found more ground-dwelling invertebrates in cattle-grazed plots, compared to ungrazed plots. The abundances of one of five mammals and one of three reptiles increased faster in grazed plots, compared to ungrazed plots. The abundance of one mammal species was lower in grazed plots, in some years. Less vegetation was left in grazed plots. Invertebrates: Fewer ground-dwelling invertebrates were found in grazed plots, compared to ungrazed plots, in six of nine years (data not provided). Abundances of grasshoppers did not differ between grazed and ungrazed plots (8–1,600 individuals/count). Mammals: Abundances of giant kangaroo rats Dipodomys ingens increased by 1.6 individuals/year in grazed plots, but did not increase in ungrazed plots. The changes in abundances of four other species did not differ between grazed and ungrazed plots. Heerman’s kangaroo rats Dipodomys heermanni were less abundant in grazed plots in some years (0–3 vs 0–22 individuals). Abundances of San Joaquin pocket mice Perognathus inornatus inornatus differed between grazed and ungrazed plots, but not consistently. The abundances of three other mammals did not differ between grazed and ungrazed plots. Reptiles: The abundance of blunt-nosed leopard lizards increased at a greater rate in grazed plots (6.8 vs 1.4 extra individuals/year). The change in abundances of two other species, and the overall abundances of all three species did not differ between grazed and ungrazed plots. Plants: At the end of the grazing season, less vegetation was left in grazed plots, in eight of ten years (20–2,100 vs 900–4,000 kg/ha). Methods: Four 2.6 km² plots were established and grazed from December to leave approximately 560 kg dry matter/ha by April. Therefore, grazing intensity varied over time, and plots were not grazed at all in 2002–2004. Within each plot, a 25 ha plot was left ungrazed. Mammals were surveyed using 64 traps in each plot for six days and six nights in July–September each year. Grasshoppers and day-active lizards were surveyed visually within 9 ha grids, on ten days in May–July each year. Ground-dwelling invertebrates were monitored with pitfall traps. Vegetation was monitored on the same grids as lizards and clipped to assess biomass.
Cease livestock grazing: Grassland & shrubland

A replicated, controlled study in 1997–2006 in scrub and grassland in central California, USA (Germano et al. 2012) found the abundances of one of three reptiles increased more slowly in ungrazed plots compared to grazed plots following burning (natural and prescribed). The abundance of blunt-nosed leopard lizards Gambelia sila increased at a slower rate in ungrazed plots (1 extra individuals/year) compared to grazed plots (7 extra individuals/year). The change in abundances of two other species (western whiptail lizards Aspidoscelis tigris and side-blotched lizards Uta stansburiana), and the overall abundances of all three species did not differ between ungrazed and grazed plots (see original paper for details). Four 3 km² areas in a single site were established and grazed from December–April in 1998–2001 and 2005–2006. Grazing intensity varied between years and the whole site had been burned (natural and prescribed fire) in 1997. Within each area, a 25 ha plot was fenced to exclude livestock (ungrazed). Day-active lizards were surveyed visually within a 9 ha grid in each grazed and ungrazed area on 10 days in May–July in 1997–2006 (800 survey days).

(Summarised by: Katie Sainsbury)