Reduce numbers of large herbivores

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

70%
Certainty

30%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

High densities of large herbivores such as deer or non-native feral livestock have been shown to reduce species diversity and limit the regeneration of shrublands in some parts of the world (Perea et al. 2014). Reducing the number of large herbivores in shrubland areas may allow vegetation to increase in height and cover.

Perea, R., Girardello, M. & San Miguel, A. (2014) Big game or big loss? High deer densities are threatening woody plant diversity and vegetation dynamics. Biodiversity and Conservation, 23, 1303-1318.

Study locations

Key messages

One before-and-after trial in the USA found that removing feral sheep, cattle and horses increased shrub cover and reduced grass cover. One replicated study in the UK found that reducing grazing pressure by red deer increased the cover and height of common heather.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A before-and-after trial from 1980 to 2012 in coastal shrubland on Santa Cruz island, USA (Beltran et al. 2014) found that reducing grazing pressure by removing feral sheep, cattle, and horses increased shrub cover and reduced grass cover. After 20 years, cover of woody species was higher after the removal of sheep, cattle, and horses (24%) than before removal (1%), but cover of herbaceous plants did not differ significantly (after: 66%, before: 60%). Cover of bare ground was lower after the removal of sheep, cattle, and horses (9%) than before removal (39%). Sheep, cattle, and horses were removed from the island between 1981 and 1989. In 1980 and 2012 twenty 30 m transects were used to survey vegetation. Every 1 m along the transects the vegetation type was identified and cover was estimated.
Study and other actions tested
Referenced paper
Beltran R.S., Kreidler N., Van V.D.H., Morrison S.A., Zavaleta E.S., Newton K., Tershy B.R. & Croll D.A. (2014) Passive recovery of vegetation after herbivore eradication on Santa Cruz Island, California. Restoration Ecology, 22, 790-797.
A replicated study in 1991–2001 in two moorland sites in the Cairngorms, UK (Welch et al. 2006) found that reducing grazing pressure by red deer Cervus elaphus increased the cover and height of heather Calluna vulgaris. Nine years after the reduction of grazing pressure by deer, the cover of heather had increased by 6% in one site and by 2% in the other. Additionally, mean height of heather increased from 17 cm to 19 cm in one site and from 25 cm to 29 cm in the other. Deer numbers were reduced by culling and, in one site, grazing pressure was also reduced by localized winter feeding. As a result, between 1992 and 2001, the mean number of deer pellet groups on 60 m²plots felt from 26.3 to 22.9 in one site and from 17.2 to 5.7 in the other. Sampling plots of 15 m x 4 m (90 in one site and 96 in the other) were visited annually and, at each plot, 25 measures of heather height were taken. Additionally, heather cover was measured at each plot using a sampling stick with four 8 cm diameter circles at 10 positions and by counting the circles containing heather.
Study and other actions tested
Referenced paper
Welch D., Scott D., Mitchell R. & Elston D.A. (2006) Slow recovery of heather (Calluna vulgaris L.(Hull)) in Scottish moorland after easing of heavy grazing pressure from red deer (Cervus elaphus L.). Botanical Journal of Scotland, 58, 1-17.

Please cite as:

Martin, P.A., Rocha, R., Smith, R.K. & Sutherland, W.J. (2020) Shrubland and Heathland Conservation. Pages 483-525 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Shrubland and Heathland Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Use biological control to reduce the number of problematic invertebrates Action Link	No evidence found (no assessment)	0	Synopsis Link
Use fences to exclude large herbivores Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Reduce numbers of large herbivores Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link