Action: Use wire fences within grazing areas to exclude livestock from specific forest sections
Key messagesRead our guidance on Key messages before continuing
- Four of eight studies (including two replicated, randomized, controlled studies) in Argentina, Australia, Belgium, Israel, New Zealand, Spain, West Africa and the USA found that excluding livestock using wire fences increased biomass , species richness, density and cover of understory plants. The other four studies found mixed effects or no effect of livestock exclusion on understory plants.
- Three of four studies (including one replicated, randomized, controlled study) in Mexico, Kenya, Israel and Panama found that excluding livestock using wire fences increased the size and density of regenerating trees and the number of regenerating trees. One study found livestock exclusion decreased tree density but not tree size.
Livestock grazing changes habitats, mainly by changing soil properties, plant composition, structure and diversity (Alkemade et al. 2013). High grazing pressure can degrade understory species diversity. This is mainly due to decreasing the abundance of palatable herbaceous and low woody species. Using wire fences to excluded livestock from regularly grazed forested areas may increase species diversity (Crawley 1983). Other studies aimed to reduce the detrimental effects of grazing are discussed in ‘Prevent livestock grazing from forest areas’.
Alkemade, R., Reid, R. S., van den Berg, M., de Leeuw, J., Jeuken, M. (2013) Assessing the impacts of livestock production on biodiversity in rangeland ecosystems. Proceedings of the National Academy of Sciences, 110, 20900-20905.
Crawley, M.J. (1983) Herbivory: The dynamics of plant-animal interactions. Blackwell Scientific Publications, Oxford, UK.
Supporting evidence from individual studies
A controlled study in 1986-1990 in tropical dry woodland in Kenya (Oba 1998) found that excluding goat grazing decreased the density of umbrella thorn Acacia tortilis trees but did not affect their height. The density of umbrella thorn trees was lower in the fenced than in the grazed transects (377 vs 512 trees/ha respectively), while their height was similar (2.2 and 2.5 m respectively). Umbrella thorn trees were monitored in 1990 in five wire fenced (fenced in July 1986 to exclude goats) and five grazed 200 x 20 m transects, in an area with a long history of goat and other livestock grazing.
A replicated, randomized, controlled study in 1999-2001 in temperate coniferous forest in Oregon USA (Bates 2005) found that cattle exclusion following cutting of western juniper Juniperus occidentalis trees in 1998, increased seed production of perennial grasses, but did not affect herbaceous plant cover. Seed production of perennial grasses was lower in grazed plots (32 kg/ha) than in ungrazed plots (42 kg/ha), while seed production of Sandberg's bluegrass Poa sandbergii was similar (5 kg/ha in both). Herbaceous plant cover was similar in grazed and ungrazed plots (16% in both). In 2001, seed production was estimated in five 9 m2 plots and herbaceous cover was estimated in 0.2 m2 plots in four pairs of grazed (0.86 cattle/ha for 4-5 days in early 1999 and 2000) and ungrazed plots (0.45 ha).
A replicated, randomized, controlled study in 1997-2001 in tropical dry forest in Mexico (Montero-Solís et al. 2006) found that cattle exclusion increased trees density and diversity but not species richness. The total number of woody trees taller than 1.3 m was higher in fenced (650) than in grazed plots (450), the same was true for species diversity (Shannon's index fenced: 1.23; grazed: 0.60). The total number of species was similar between treatments (fenced: 44; grazed: 39). Data were collected in 2001 in eight fenced (with barbwire in 1997) and eight grazed plots (12 × 12 m).
A paired sites, before-and-after trial in 1995-2001 in a Mediterranean Black pine Pinus nigra forest in the Pyrenees, Spain (Casasús et al. 2007) found that grazing exclusion increased the biomass of herbaceous plants and shrubs. Six years after treatment herbaceous plant and shrub biomasses (kg dry matter/ha) had increased in fenced areas (herbaceous plant: 501 to 1,730; shrub: 1,902 to 5,073) but not in grazed areas (herbaceous plant: 417 to 679; shrub: 1,120 to 1,207). At the beginning of the study herbaceous plant and shrub biomasses were similar in the grazed and fenced areas while six years after both parameters were higher in fenced areas. In 1995, a 10 × 10 m area was fenced to exclude grazing in each of four sites (0.2 cows/ha) each spring and autumn throughout the experiment. Biomass was measured within and outside the fenced area at the end of the grazing season in 1995 and 2001.
A replicated, controlled study in 2002-2006 in temperate mixed forest in Argentina (Blackhall, Raffaele & Veblen 2008) found no effect of excluding cattle grazing after wildfire on plant species richness and cover. The total cover of plants was 124% in grazed and 126% in the exclusion plots. Average plant species richness was 32 species/2 m2 in grazed and 27 species/2 m2 in fenced plots. Four plots were fenced to exclude cattle and other large herbivores and four unfenced 25 ×25 m plots were installed in March 2002 in an area that was burned by wildfire in 1999. Monitoring was in 2006 in twenty 2 m2 subplots in each plot.
A replicated, randomized, controlled study in 1993-2003 in savanna woodland in West Africa (Savadogo et al. 2008) found no effect of grazing exclusion on herbaceous plant richness or diversity. The number of species/0.25 ha (grazed: 14-16; fenced: 13-15) and species diversity (Shannon's index control: 2.7-3.0; exclusion: 2.5-2.8) was similar between treatments. Data were collected in 2003 in four grazed and four fenced (wire fenced to exclude livestock in 1993) treatment plots (0.25 ha) replicated in four blocks, at each of two sites (18 ha).
A replicated, controlled study in 2005-2007 in Mediterranean-type shrubland in Israel (Agra & Ne'eman 2009) found no effect of cattle exclusion on herbaceous plant species richness. The number of herbaceous species/plot was similar between grazed and fenced under tree canopies (grazed: 19; fenced: 17) and in open areas (grazed: 82; fenced: 78). In April 2007 herbaceous species were monitored under tree canopies and in open areas in five plots where grazing had been excluded using wire fences (during December 2005) and five grazed plots (0.1 ha; 0.3 cows/ha).
A replicated, controlled study in 2002-2005 in dry tropical forest in Panama (Griscom, Griscom & Ashton 2009) found that cattle exclusion increased basal area, density and species richness of new regenerating trees. Fenced plots had larger basal area (fenced: 0.03; grazed: 0.01 m2/plot), density (fenced: 19; grazed: 10 stems/plot) and species richness (fenced: 6; grazed: 4 species/plot) of tree regenerations >1 m height compared to grazed plots. Data were collected in 2005 in 48 grazed (0.6–0.8 head/ha) and forty eight 100 m2 plots fenced in 2002.
A replicated, controlled, paired sites study in 2006-2009 in Mediterranean-type shrubland in Israel (Agra & Ne'eman 2011) found that excluding cattle grazing increased the size of regenerating trees after clear cutting. Three years after clear cutting the average height and diameter of regenerating hawthorn Crataegus aronia, terebinth Pistacia palaestina, Boissier oak Quercus boissieri and Palestine oak Q. calliprinos trees were higher in fenced (height: 210; diameter:230 cm) than in grazed plots (height: 70; diameter:110 cm). In 2006, all trees were clearcut in five pairs of grazed (exposed to grazing livestock, 0.3 cows/ha) and fenced (wire fenced in 2005) plots (0.1 ha). Trees were measured in 2009.
A controlled study in temperate mixed forest in New Zealand (Burns et al. 2011) found that grazing exclusion decreased exotic plant species richness but did not affect total plant species richness. The number of exotic plant species/plot was higher in grazed (6.1) and in plots that were ungrazed for 2-10 years (3.8) than in plots that were ungrazed for 10-20 (0.1) or >20 years (0.4). The numbers of native plant species/plot (34, 35, 37 and 34 for grazed, 2-10, 10-20 and >20 years fenced respectively) and total plant species/plot (40, 38, 37 and 35 for grazed, 2-10, 10-20 and >20 years fenced respectively) were similar among treatments. Plants were monitored in 400 m2 plots in forest fragments: 13 grazed, ten fenced for 2-10 years, nine fenced for 10-20 years and nine fenced >20 years to exclude cattle and sheep grazing.
A replicated, controlled study in 1981-2010 in Mulga Acacia aneura dry forest in Queensland, Australia (Fensham, Silcock & Dwyer 2011) found that exclusion of sheep and cattle increased annual grass species richness. Annual grass species richness was higher in fenced (3.5 species/plot) than in grazed plots (2.6). Species richness was similar between treatments for: all plants (fenced: 18.6; grazed: 15.9), perennial grasses (fenced: 3.3; grazed: .3.3), annual herbaceous plants (fenced: 6.2; grazed: 5.4) and perennial herbaceous plants (fenced: 4.5; grazed: 3.2). In 1981-1983 two treatment plots were established (50 × 50 m): grazed and wire fenced to exclude sheep and cattle, but not kangaroos or rabbits were replicated at three sites regularly grazed by cattle and sheep at 0.1-0.9 dry sheep equivalents/ha. Plant species richness was determined in 2008 in twenty 2 × 7 m plots in each treatment.
A replicated, before-and-after study in 1996-2008 in temperate forest in Belgium (Van Uytvank & Hoffmann 2009) found that excluding cattle grazing increased bramble Rubus sp. cover and that of some other ground forest plant species. Bramble cover decreased by 30% in grazed plots and increased by 19% in ungrazed plots. In grazed plots frequencies of English ivy Hedera helix and common periwinkle Vinca minor decreased (30 vs 0%) (9 vs 0%) respectively, while the cover of oxlip Primula elatior remained similar (13 vs 12%). In ungrazed plots frequencies did not change for ivy (26 vs 24%), common periwinkle (5 vs 7%) and oxlip (16 vs 13%). Percentage cover and the abundance of wood anemone Anemone nemorosa were higher in ungrazed than in grazed plots (36 vs 22% cover, 230 vs 100 flowers/ plot respectively). Bramble cover data were collected in 1998 and in 2008 in four plots (20 × 40 m) each divided to equal grazed and ungrazed subplots. Presence/absence of ivy, common periwinkle and oxlip (in 2002 and 2008), and cover and frequency of wood anemone (in 2008) were monitored in 206 grazed and 206-225 ungrazed 2 × 2 m plots. Grazing (0.25 cows/ha) began in 2004.
- Oba G. (1998) Effects of excluding goat herbivory on Acacia tortilis woodland around pastoralist settlements in northwest Kenya. Acta Oecologica, 19, 395-404
- Bates J.D. (2005) Herbaceous response to cattle grazing following juniper cutting in Oregon. Rangeland Ecology & Management, 58, 225-233
- Montero-Solís F.M., Sánchez-Velásquez L.R., del R.P.M., Martínez-Rivera L.M., Moermond T. & Aguirre J.C. (2006) Livestock impact on dynamic and structure of tropical dry forest of the Sierra de Manantlán, Mexico. JOURNAL OF FOOD AGRICULTURE AND ENVIRONMENT, 4, 266
- Casasús I., Bernués A., Sanz A., Villalba D., Riedel J. & Revilla R. (2007) Vegetation dynamics in Mediterranean forest pastures as affected by beef cattle grazing. Agriculture, ecosystems & environment, 121, 365-370
- Blackhall M., Raffaele E. & Veblen T.T. (2008) Cattle affect early post-fire regeneration in a Nothofagus dombeyi–Austrocedrus chilensis mixed forest in northern Patagonia, Argentina. Biological conservation, 141, 2251-2261
- Savadogo P., Tiveau D., Sawadogo L. & Tigabu M. (2008) Herbaceous species responses to long-term effects of prescribed fire, grazing and selective tree cutting in the savanna-woodlands of West Africa. Perspectives in Plant Ecology, Evolution and Systematics, 10, 179-195
- Agra H. & Ne’eman G. (2009) Woody species as landscape modulators: their effect on the herbaceous plants in a Mediterranean maquis. Plant Ecology, 205, 165-177
- Griscom H.P., Griscom B.W. & Ashton M.S. (2009) Forest regeneration from pasture in the dry tropics of Panama: effects of cattle, exotic grass, and forested riparia. Restoration Ecology, 17, 117-126
- Agra H. & Ne’eman G. (2011) Quercus calliprinos regrowth advantage under grazing in Mediterranean maquis and its management implications. Forest ecology and management, 261, 143-147
- Burns B., Floyd C., Smale M. & Arnold G. (2011) Effects of forest fragment management on vegetation condition and maintenance of canopy composition in a New Zealand pastoral landscape. Austral Ecology, 36, 153-166
- Fensham R., Silcock J. & Dwyer J. (2011) Plant species richness responses to grazing protection and degradation history in a low productivity landscape. Journal of Vegetation Science, 22, 997-1008
- Van Uytvanck J. & Hoffmann M. (2009) Impact of grazing management with large herbivores on forest ground flora and bramble understorey. Acta oecologica, 35, 523-532