Interactions of Grazing History, Cattle Removal and Time since Rain Drive Divergent Short-Term Responses by Desert Biota

Abstract

Arid grasslands are used worldwide for grazing by domestic livestock, generating debate about how this pastoral enterprise may influence native desert biota. One approach to resolving this question is to experimentally reduce livestock numbers and measure the effects. However, a key challenge in doing this is that historical grazing impacts are likely to be cumulative and may therefore confound comparisons of the short-term responses of desert biota to changes in stocking levels. Arid areas are also subject to infrequent flooding rainfalls that drive productivity and dramatically alter abundances of flora and fauna. We took advantage of an opportunity to study the recent effects of a property-scale cattle removal on two properties with similarly varied grazing histories in central Australia. Following the removal of cattle in 2006 and before and after a significant rainfall event at the beginning of 2007, we sampled vegetation and small vertebrates on eight occasions until October 2008. Our results revealed significant interactions of time of survey with both grazing history and grazing removal for vascular plants, small mammals and reptiles. The mammals exhibited a three-way interaction of time, grazing history and grazing removal, thus highlighting the importance of careful sampling designs and timing for future monitoring. The strongest response to the cessation of grazing after two years was depressed reproductive output of plants in areas where cattle continued to graze. Our results confirm that neither vegetation nor small vertebrates necessarily respond immediately to the removal of livestock, but that rainfall events and cumulative grazing history are key determinants of floral and faunal performance in grassland landscapes with low and variable rainfall. We suggest that improved assessments could be made of the health of arid grazing environments if long-term monitoring were implemented to track the complex interactions that influence how native biota respond to grazing.

Small Australian desert vertebrate responses to grazing intensity during La Niña

“…We expected that dragon lizards (agamids) would increase and skinks (scincids) decrease in abundance based on previous work in the region (Read 2002;Read and Cunningham 2010). Limited information exists for mammalian species and taxa that occur in the area, but we postulated that native rodent and dasyurid species abundance would most likely decrease at more intenselygrazed sites (Read and Cunningham 2010;Frank et al 2013). We expected that the exotic Mus musculus would increase in abundance with increasing grazing intensity owing to its generalist life-history and ability to colonise post-disturbance environments (Robinson et al 2000).…”

“…Globally, arid and semi-arid rangelands are dominated by livestock grazing systems that encompass a greater area than any other land use (Frank et al 2013). It has been suggested that the ecological consequences of grazing, particularly in north-western America, are substantial, and include changes in the composition of communities and in ecosystem structure, and disturbance to ecosystem function (Fleischner 1994).…”

“…It has been suggested that the ecological consequences of grazing, particularly in north-western America, are substantial, and include changes in the composition of communities and in ecosystem structure, and disturbance to ecosystem function (Fleischner 1994). However, relatively few published studies have examined the effects of livestock grazing on small vertebrate communities in Australian deserts (but see : Read 2002;James 2003;Read and Cunningham 2010), particularly in wet years (see Frank et al 2013). This paucity of knowledge is peculiar considering that Australia supports the largest area (4.4 M km 2 ) of managed grazing land worldwide (Asner et al 2004), and has experienced the largest global mammal extinction rate in the past 200 years (Woinarski and Fisher 2003;Woinarski et al 2015).…”

“…Direct effects can include activities such as destruction of shelter or burrows (e.g., through trampling; Fleischner 1994) and competition for food resources (Evans et al 2006). E.g., the removal of seed-producing palatable plants by livestock may facilitate declines in granivorous vertebrates; Frank et al 2013).…”

“…Consequently, years during which large rainfall events occur present a rare opportunity to study small mammals that should be most abundant following rainfall-mediated increases in food resources (Dickman et al 1999). In dry El Nin˜o years, many of these species (particularly rodents) are not detected readily as they persist in naturally low numbers (Frank et al 2013). Wet years offer a chance to assess their status and responses to disturbances, such as grazing.…”