What impacts do deer have on vegetation and plant biodiversity?

What impacts do deer have on vegetation and plant biodiversity?

Under medium-term deer grazing (i.e.  after the 4 years of the AgResearch study at two locations) both unpalatable woody scrub species such as matagouri and pasture can increase at the expense of tussock. 

Tussock species are highly valued for their soil conservation role, especially on steep and exposed hillsides, and as a hind habitat for resting/ruminating and calving in seclusion.

Typical stocking rates may be too low to restrict scrub growth.  Scrub increased by 6-9% in vegetation areas that likely had less grazing pressure applied.  Scrub offers multiple benefits for extensive deer farming systems such as providing shade, shelter, and a secluded calving habitat for hinds but if it becomes too dense to use it can reduce the overall effective grazing area of a paddock.

Management tip

Increasing the grazing pressure placed on areas adjacent to scrub, e.g by cattle grazing, may help to stem the spread of scrub, but care should be taken to avoid tussock overgrazing.  Temporary single-wire electric fences could be an option to protect such areas from cattle.

Overall plant species diversity is not significantly affected by medium-term deer grazing. While total plant species richness may remain constant, some species may decrease in abundance (e.g. short-tussocks), while others may increase in abundance (e.g. exotic weeds).