Habitat and herbivore density: response of mule deer to habitat management

Published source details Bergman E.J., Doherty P.F., White G.C. & Freddy D.J. (2015) Habitat and herbivore density: response of mule deer to habitat management. Journal of Wildlife Management, 79, 60-68.
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This study is summarised as evidence for the following.

	Action	Category
	Restore or create shrubland Action Link
	Remove vegetation using herbicides Action Link
	Remove vegetation by hand/machine Action Link

Restore or create shrubland

A replicated, site comparison study in 2006–2009 of pine and juniper forests interspersed with grassland in Colorado, USA (Bergman et al. 2015) found that restoring shrubland by sowing seeds and applying herbicide following tree clearance, did not increase densities of mule deer Odocoileus hemionus using these plots compared to plots that were cleared of trees alone. The effects of seeding and herbicide could not be separated in this study. Deer densities in cleared plots that were seeded and sprayed with herbicide (5–31 deer/km²) were not significantly different from those in plots that were just cleared (6–37 deer/km²). Six plots were cleared of trees, 2–8 years before deer surveys commenced, using a bulldozer and by chopping vegetation, or mulching trees to ground level, by hydro-axing. On two plots, at the same time as deer surveys, unpalatable grasses were controlled with herbicides and seeds, mainly of shrub species eaten by mule deer, were sown. The four remaining plots were not further managed after tree clearance. Deer numbers were estimated by sighting marked individuals during aerial surveys, in late winter each year, in 2006–2009 (not all plots were surveyed each year). Areas surveyed were 15–84 km²/plot.

(Summarised by: Nick Littlewood)
Remove vegetation using herbicides

A replicated, site comparison study in 2006–2009 in six pine and juniper forest sites in Colorado, USA (Bergman et al. 2015) found that treatment with herbicide, alongside clearance of trees and sowing seed, did not alter mule deer Odocoileus hemionus densities compared to clearance of trees alone. The effects of herbicide and reseeding could not be separated in this study. In areas that were sprayed with herbicide, cleared, and sown with seeds, deer density was not higher (5–31 deer/km²) than in plots that were cleared but not treated with herbicide or sown with seed (6–37 deer/km²). Six sites were cleared of trees, two to eight years before deer surveys, using a bulldozer and by chopping vegetation into smaller pieces, or mulching individual trees to ground level by hydro-axing. On two of these sites, unpalatable grasses were controlled with herbicides and seeds of plant species eaten by mule deer were sown. The four remaining sites were not further managed after tree clearance. Deer numbers were estimated by sighting marked individuals during aerial surveys, in late winter each year of 2006–2009. Areas surveyed were 15–84 km²/site.

(Summarised by: Nick Littlewood)
Remove vegetation by hand/machine

A replicated, site comparison study in 2006–2009 of pine and juniper forests interspersed with meadows on a plateau in Colorado, USA (Bergman et al. 2015) found that mule deer Odocoileus hemionus densities did not differ between plots where trees were cleared and those where trees were not cleared. Average deer density was 6–37 deer/km² on plots where trees were cleared and 5–85 deer/km² on plots where no trees were cleared. Tree clearance was carried out on four plots, two to eight years prior to deer surveys. This comprised uprooting trees with a bulldozer, followed by mechanical roller chopping to break vegetation into smaller pieces, or hydro-axing, whereby individual trees were mulched to ground level. In two plots, no trees were cleared. Deer numbers were estimated by resighting marked individuals, in late winter each year in 2006–2009, from aerial surveys. Surveys were conducted over 15–94 km²/plot.

(Summarised by: Nick Littlewood)