Employ grazing in non-grassland habitats
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 8
Background information and definitions
In many parts of the world, the native grazers that would have helped maintain a balance between woody and herbaceous plants in a habitat have been lost or greatly reduced in numbers. Introducing domestic grazers is a potential way to re-establish the ecosystem dynamics.
Supporting evidence from individual studies
A replicated controlled trial in a cottonwood Populus sargentii bottomland in northeast Colorado, USA (Sedgwick & Knopf 1987), found that moderate late-autumn cattle grazing had no impact on breeding densities of six selected migratory songbirds over three study years. Five 16 ha cottonwood floodplain plots were fenced and cattle-grazed in October-November 1982-1984, and five were unmanaged. Analysis focussed on six species dependent on the grass-herb-shrub layer for foraging, nesting, or both: house wren Troglodytes aedon, brown thrasher Toxostoma rufum, American robin Turdus migratorius, common yellowthroat Geothlypis trichas, yellow-breasted chat Icteria virens and rufous-sided towhee Pipilo erythropthalmus.Study and other actions tested
In a replicated study in four oak- Quercus spp. hazel Corylus avellana woodlands (average size 5.3 ha) in 1996-1999 in Uppland and Åland, Sweden (Hansson 2001), breeding and migrant birds were found to be more numerous in sites grazed from spring to autumn than in some abandoned sites (average of 12 breeding and 5 migrant birds in grazed sites vs. 2-4 in abandoned sites). However, abundances did not differ between grazed sites and those subject to brush cutting and tree thinning (average of eight breeding bird species and seven migrants), and migrants were less abundant than in sites under simulated traditional management (16 breeding birds and 12 migrants). Traditional management involved sites being cleared in spring, mown in mid-late summer and grazed in autumn. A total of 65 bird species were observed. Birds present in spring did not differ in abundance between management types.Study and other actions tested
A replicated, controlled trial in spring and summer 1997 in Kent, England (Hart et al. 2002), found that northern lapwings Vanellus vanellus had smaller clutches, lower nest survival and higher nest loss to predation on four coastal marshes with low-intensity (0.2-0.5 livestock units/ha) grazing, compared to four areas without grazing (higher proportion of four egg clutches on ungrazed marshes; 34% survival and 58% predation for 36 nests on grazed marshes vs. 64% survival and 36% predation for 50 nests on ungrazed sites). Three of the 15 unpredated nests on the grazed marshes were also trampled by livestock. Livestock presence was also found to have a weak impact on the density of lapwing nesters in 1995 and 1997, but not 1996.Study and other actions tested
A controlled before-and-after study on a reserve in Lincolnshire, England (Ausden et al. 2005), found no significant changes in redshank Tringa tetanus breeding densities on two saltmarsh plots following the introduction of light (approximately 0.2 cows/ha) or medium (0.4-0.6 cows/ha) grazing in 1996-1997. In addition, redshank densities in 1998-2004 were no different on the medium-grazed plot (0.7 pairs/ha), compared to an ungrazed plot (0.8 pairs/ha) or a heavily-grazed plot (0.6 pairs/ha). The light-grazed plot, however, had significantly lower densities (0.4 pairs/ha) than the ungrazed plot.Study and other actions tested
A replicated trial in the UK (Vale & Fraser 2007) found that songbirds and invertebrate-feeding birds were recorded more often on semi-natural rough grazing than on upland improved pasture, but the opposite was true for crows. Bird numbers and species were recorded in plots of improved upland pasture grazed by cattle and sheep (ten with and ten without the seasonal removal of grazing in summer) and in plots of semi-natural rough grazing grazed by cattle from June to September (six replicates). The proportion of surveys where songbirds and invertebrate feeders were recorded was greater on semi-natural rough grazing than on improved pasture. However, the effect on the number of individuals varied over the year. The number of birds of invertebrate-feeding species was greater on semi-natural grassland between May and July (338 birds, compared to 52 and 41 on improved treatments, with and without seasonal grazing removal), but greater on improved treatments between October and January (5,833 and 1,458 birds on improved treatments compared to 606 birds on semi-natural grassland). There were fewer crows on semi-natural rough grazing plots at all times of year, but the difference was greatest during July to September (16 birds on rough grazing compared to 496 and 77 on improved plots).Study and other actions tested
Referenced paperVale J.E. & Fraser M.D. (2007) Effect of sward type and management on diversity of upland birds. Pages 333-336 in: J. Hopkins, A.J. Duncan, D.I. McCracken, S. Peel & J.R.B. Tallowin (eds.) High value grassland: Providing biodiversity, a clean environment and premium products. British Grassland Society Occasional Symposium No.38. British Grassland Society (BGS), Reading.
A before-and-after study in Oostvaardersplassen reserve in Flevoland, the Netherlands (Bijlsma 2008), found significant changes in the bird community in a 1,900 ha area of wet and dry grasslands, reedbeds, scrub and small woodlands, following increased numbers of grazing animals. The number of breeding species declined from 92 to 70 and of the 41 species with more than ten breeding pairs, eight increased and 33 decreased. Shrub-dependent species declined, as did those requiring tall reeds to nest. The authors suggest that declines in some grassland species were due to increased trampling. The number of Heck cattle Bos taurus, Konik horses Equus ferus and red deer Cervus elaphus increased from 390, 284 and 246 respectively (in 1997) to 497, 982 and 1,898 in 2007 (with cattle peaking at 580 in 2002). This reduced the areas of reedbeds from 844 to 377 ha and of shrub and woodland from 97 to 50 ha. The area of dry grassland increased from 527 to 1,019 ha.Study and other actions tested
A replicated site comparison study on 1,031 agricultural sites across England in 2004-2008 (Ewald et al. 2010) investigated the impact of rough grazing on grey partridge Perdix perdix. However, the study does not distinguish between the impacts of grazing, scrub control and the restoration of various semi-natural habitats. There was a negative relationship between the combined intervention and the ratio of young to old partridges in 2008. This study describes the effects of several other interventions, discussed in the relevant sections.Study and other actions tested
In Laikipia District, Kenya, a replicated controlled study in 2005-2007 (Gregory et al. 2010) found that five plots of savanna which were recently abandoned after grazing had, on average, but not consistently, higher densities of birds and held more species than four unmanaged control areas, but fewer than five burned areas (5-8 birds and 4-6 species/100 m2 for grazed areas vs. 3-17 birds and 3-8 species for burned areas; 4-6 birds and 3-4 species for controls;). The authors note that drought removed differences between treatments, and that the yearly variations in burned plots was greater than in grazed plots, suggesting that grazing may have longer term benefits. In addition, some species were only recorded in unmanaged areas. Burning is further discussed in ‘Use prescribed burning’.Study and other actions tested