Action: Increase number of livestock
- Two site comparison studies in the UK found that cover of common heather declined in sites with a high density of livestock. One site comparison in the Netherlands found that dwarf shrub cover was lower in grazed areas than in ungrazed areas. One before-and-after study in Belgium found that grazing increased cover of heather. One site comparison in France found that areas grazed by cattle had higher cover of non-ericaceous shrubs, but lower cover of ericaceous shrubs. One before-and-after study in the Netherlands found that increasing the number of livestock resulted in an increase in the number of common heather and cross-leaved heath seedlings. One randomized, replicated, paired, controlled study in the USA found that increasing the number of livestock did not alter shrub cover. One replicated, site comparison study and one before-and-after study in the UK and Netherlands found that increasing grazing had mixed effects on shrub and heather cover.
- Three site comparisons in France, the Netherlands and Greece found that grazed areas had a higher number of plant species than ungrazed areas. One before-and-after study in Belgium found that the number of plant species did not change after the introduction of grazing. One replicated, before-and-after study in the Netherlands found a decrease in the number of plant species.
- One before-and-after study in the Netherlands found that increasing the number of livestock resulted in a decrease in vegetation height. One replicated, before-and-after trial in France found that grazing to control native woody species increased vegetation cover in one of five sites but did not increase vegetation cover in four of five sites.
- A systematic review of four studies in North Western Europe found that increased grazing intensity increased the cover of grass species, relative to heather species. One before-and-after study and two site comparisons in the Netherlands and France found areas with high livestock density had higher grass and sedge cover than ungrazed areas. One randomized, replicated, paired, controlled study in the USA found that increasing the number of livestock reduced grass and herb cover. One before-and-after study in Spain found that increasing the number of ponies in a heathland site reduced grass height. One replicated, site comparison in the UK and one replicated before-and-after study in the Netherlands found that increasing cattle had mixed effects on grass and herbaceous species.
Many shrublands depend on disturbances such as grazing to reduce succession that leads to an increase in woody plant species and conversion to forest. However, in many cases grazing by livestock has declined as it is no longer economically viable. Reintroduction of livestock may help to reduce the number of woody species in a shrubland and reduce the possibility of succession to forest.
Supporting evidence from individual studies
A before-and-after study in 1972–1978 in a heathland site in the Netherlands (Bakker et al. 1983) found that increasing the number of livestock resulted in a decrease in vegetation height, but increased grass cover and the number of seedlings of common heather Calluna vulgaris and cross-leaved heath Erica tetralix. After six years vegetation height had decreased by approximately 20 cm when compared to the period before grazing started. Grass cover and the number of common heather and cross-leaved heath seedlings were higher after six years of grazing than before grazing started (no data presented). No statistical tests were carried out in this study. In 1972 sheep were introduced to the area at a density of three sheep/ha. One hundred and nine plots (of undefined size) were placed at the site and vegetation cover was recorded yearly in 1972-1978.
A site comparison in 1967-1987 in 15 heathland sites in the UK (Welch et al. 1995) found that common heather Calluna vulgaris cover decreased at sites with high livestock density. Over 20 years cover of common heather increased in sites with low livestock density but decreased in sites with high livestock density (no data reported). Ten point quadrats were used to estimate vegetation cover at each sites in July or August every two years. Dung was counted to assess herbivore abundance at each site.
A replicated, site comparison study in 1994 at three heathlands in the UK (Bullock & Pakeman 1997) found that increasing the abundance of livestock had mixed effects on the cover of shrubs, grasses, and herbaceous plant species. Increasing the abundance of livestock decreased cover of shrub species in one of nine comparisons (grazed: 45%, ungrazed: 80%) but increased cover of shrub species in three of nine comparisons (grazed: 3–8%, ungrazed: 0–2%). For one of eight comparisons grass cover was lower in grazed (9%) than ungrazed areas (32%) but for three of eight comparisons grass cover was higher in grazed (3–8%) than ungrazed areas (0%). For three of six comparisons cover of herbaceous species was higher in grazed (2–3%) than in ungrazed areas (0%) while for the remaining three comparisons cover did not differ in grazed and ungrazed areas. At each site one area was grazed and another area was not grazed. At each site 5–15 quadrats were located randomly and cover of plant species estimated by eye.
A before-and-after stud y in winter 2006/2007 in a heathland in Northern Spain (Aldezabal et al. 2013) found that increasing the number of ponies present at the site reduced grass height in most cases. After one month and in nine of fifteen areas, grass was shorter in areas that were grazed (9‑21 cm) than in the same areas prior to grazing (13‑–38 cm). In October 2006 fences were constructed around the site. Five Basque pottoka ponies were released at the site in December 2006, giving a density of 6.3 ponies/ha. Vegetation height was measured using a ruler in 120 quadrats before and after grazing (dates unspecified).
A systematic review of four studies of the impact of grazing on lowland heathland vegetation in North Western Europe (Newton et al. 2009) found that grazing increased the cover of grass species, relative to heather species. There was no evidence of publication bias that would influence the outcomes of the systematic review. The systematic review summarised the impacts of grazing at 15 sites from four studies, with 12 of the sites representing before-and-after trials and the remaining three representing site comparisons. Of 266 potentially relevant references only four presented information on the impacts of grazing that could be used by the systematic review.
A replicated, before-and-after trial in 1978–2003 in dry, wet and moist heathland habitat in Flanders, Belgium (Piessens et al. 2006) found that extensive grazing increased vegetation cover of heather Calluna vulgaris but did not increase species richness over a period of 25 years. Vegetation cover of heather was higher after 25 years of extensive grazing than prior to it (data presented in arcsine units). However, species richness did not change significantly (5, 8 and 6 species in 1978 vs 5.5, 9 and 7 species in 2003, for dry, moist, and wet heathland respectively). Extensive grazing (0.1 cow/ha) was conducted annually from May to September in a 220 ha reserve. Vegetation was sampled in 28, 5 and 19 plots in dry, moist, and wet heathland respectively in 1978 (prior to initiation of grazing) and in 2003 (25 years after grazing initiation). Extensive grazing was supplemented locally with mechanical management practices, like tree-cutting or mowing.
A replicated, before-and-after trial in 1996–1998 in coastal heathland in France (Gallet & Roze 2001) found that grazing to control native woody species increased vegetation cover in one of five sites, but did not increase it in four of five sites (data presented as vegetation cover index). Between nine and ten sheep were introduced to each of five paddocks in 1996. Vegetation was surveyed every one to ten months in four 10 m transects in each paddock using a point quadrat
A replicated, before-and-after trial in 1983–1993 in two heathlands in the Netherlands (Bokdam & Gleichman 2000) found that cattle grazing increased cover of heather Calluna vulgaris in one of two sites, the cover of wavy-hair grass Deschampsia flexuosa in one of two sites, and, despite an initial increase, it reduced the number of plant species in two of two sites. After ten years and in one heathland, heather cover increased from 20% before grazing to 95%, while the cover of wavy hair-grass did not change significantly (before: 0% cover, after: 1% cover). However, in another heathland, heather cover decreased from 69% before grazing to 59% ten years later, while the cover of wavy hair-grass increased from 16% to 60% over the same period. In both sites grazing increased the number of plant species from 3–5 species/plot before implementation of grazing, to 9–11 species/plot after 5 years, followed by a decline to 5–9 species/plot 10 years after grazing. In 1983, cattle were introduced in the two heathlands (approximately 0.2 cows/ha). Three 25 m2 plots were located in one heathland and six in the other. Vegetation cover was recorded in each plot annually between 1983 and 1993.
A site comparison study in 2006 in six heathland sites in France (Gechet et al. 2009) found that areas grazed by cattle had a higher number of plant species, higher cover of grass and non-ericaceous shrubs, but lower cover of ericaceous shrubs. Grazed sites had a higher number of plant species and cover of grass (species: 13–14 species/plot, grass: 47–54% cover) than ungrazed sites (species: 7–8 species/plot, grass: 2–24% cover). Grazed sites also had higher cover of non-ericaceous shrubs (66–67%) than three of the four ungrazed sites (9–58%). However, cover of ericaceous shrubs was lower in grazed sites (56–63%) than in ungrazed sites (86–95%). No statistical tests were carried out in this study. Two moderately grazed sites and four ungrazed sites were selected for study. In 2006 four 1 m2 plots were placed at each site and plant cover estimated.
A randomized, replicated, paired, controlled study in 1936-2009 in eight sagebrush steppe sites in Oregon, USA (Davies et al. 2010) found that increasing the number of livestock decreased grass and herb cover, but did not significantly alter shrub cover. Grass and herb cover in grazed areas were lower (grass: 9%, herb: 17%) than in areas that were not grazed (grass: 18%, herb: 24%). However, shrub cover was not significantly different in grazed (16%) and ungrazed (16%) areas. Eight 2 ha fenced areas excluding livestock were established in 1936, and areas adjacent to the fenced areas were grazed by cattle from 1936-2008. Four 20 m transects were established in each study area and vegetation cover was assessed using a line intercept method.
A site comparison study in 2011 in coastal heathland in the Netherlands (Damgaard et al. 2013) found that areas that were grazed had more plant species, as well as higher sedge Carex spp. and grass cover than ungrazed areas, but had lower cover of dwarf shrubs. Grazed areas had a higher number of plant species (6 species/plot) than areas that were not grazed (5 species/plot). Grazed areas also had higher sedge and grass cover than areas that were not grazed (data not reported). However, cover of dwarf shrubs was lower in grazed areas than in ungrazed areas (data not reported). Grazed and ungrazed areas were separated with a fence. Grazed areas were stocked with sheep at a density of 5.7 sheep/ha. Thirty-two plots were located in the ungrazed area and 33 in the grazed area. At each plot a point frame was used to estimate cover of different plant species.
A site comparison in 10 heathland sites that were subject to grazing in the UK (Pakeman & Nolan 2009) found that the cover of common heather Calluna vulgaris increased in sites with low sheep density and declined in areas with high sheep density. Common heather cover increased in sites where there were fewer than two sheep/ha and declined when there were greater than two sheep/ha (data reported as model results). Heather cover was estimated in seventy four plots across the 10 sites. Stocking density at the sites varied between zero and six sheep/ha.
A replicated site comparison in Greece in 66 shrubland sites (Papanikolaou et al. 2011) found that grazed sites had higher total plant species richness, as well as higher species richness of annual and perennial forbs, annual grasses, but lower species richness of tall shrubs; species richness of perennial grasses and small shrubs was not affected by grazing. Total plant species richness was higher in grazed than ungrazed plots (grazed: 32-38 species/plot, ungrazed: 22 species/plot). The same trend was true for annual forbs (grazed: 9-12 species/plot, ungrazed: 4 species/plot), perennial forbs (grazed: 6-7 species/plot, ungrazed: 6 species/plot), and annual grasses (grazed: 3-4 species/plot, ungrazed: 1 species/plot). However, in one of three cases species richness of tall shrubs was lower in grazed than ungrazed plots (grazed: 2 species/plot, ungrazed 1 species/plot). Species richness of perennial grasses (grazed: 2 species/plot, ungrazed: 2 species/plot) and small shrubs (grazed: 6 species/plot, ungrazed 6 species/plot) did not differ significantly between grazed and ungrazed plots. In each site 100 m2 plots were used and vegetation cover and species richness estimated. Grazing intensity at each site was assessed by expert opinion.
- Bakker J.P., De Bie S., Dallinga J.H., Tjaden P. & De Vries Y. (1983) Sheep-grazing as a management tool for heathland conservation and regeneration in the Netherlands. Journal of Applied Ecology, 20, 541-560
- Welch D. & Scott D. (1995) Studies in the grazing of heather moorland in northeast Scotland. VI. 20-year trends in botanical composition. Journal of Applied Ecology, 32, 596-611
- Bullock J.M. & Pakeman R.J. (1997) Grazing of lowland heath in England: Management methods and their effects on healthland vegetation. Biological Conservation, 79, 1-13
- Aldezabal A., Mandaluniz N. & Laskurain N. (2013) Gorse (Ulex spp.) use by ponies in winter: Is the spatial pattern of browsing independent of the neighbouring vegetation? Grass and Forage Science, 68, 49-58
- Newton A.C., Stewart G.B., Myers G., Diaz A., Lake S., Bullock J.M. & Pullin A.S. (2009) Impacts of grazing on lowland heathland in north-west Europe. Biological Conservation, 142, 935-947
- Piessens K., Aerts N. & Hermy M. (2006) Long-term (1978-2003) effects of an extensive grazing regime on plant species composition of a heathland reserve. Belgian Journal of Botany, 49-64
- Gallet S. & Roze F. (2001) Conservation of heathland by sheep grazing in Brittany (France): Importance of grazing period on dry and mesophilous heathlands. Ecological Engineering, 17, 333-344
- Bokdam J. & Gleichman J.M. (2000) Effects of grazing by free-ranging cattle on vegetation dynamics in a continental north-west European heathland. Journal of Applied Ecology, 37, 415-431
- Gachet S., Sarthou C., Bardat J. & Ponge J. (2009) The state of change of Erica scoparia L. heathland through cattle grazing and oak colonization. Revue d'Ecologie, Terre et Vie, 64, 3-17
- Davies K.W., Bates J.D., Svejcar T.J. & Boyd C.S. (2010) Effects of Long-Term Livestock Grazing on Fuel Characteristics in Rangelands: An Example From the Sagebrush Steppe. Rangeland Ecology & Management, 63, 662-669
- Damgaard C., Thomsen M.P., Borchsenius F., Nielsen K.E. & Strandberg M. (2013) The effect of grazing on biodiversity in coastal dune heathlands. Journal of coastal conservation, 17, 663-670
- Pakeman R.J. & Nolan A.J. (2009) Setting sustainable grazing levels for heather moorland: a multi-site analysis. Journal of Applied Ecology, 46, 363-368
- Papanikolaou A.D., Fyllas N.M., Mazaris A.D., Dimitrakopoulos P.D., Kallimanis A.S. & Pantis J.D. (2011) Grazing effects on plant functional group diversity in Mediterranean shrublands. Biodiversity and Conservation, 20