Deer And Habitat

Press, Volume CIV, Issue 30803, 15 July 1965, Page 22

Deer And Habitat

After a year In New Zealand, the American biologist, Dr. W. E. Howard, completed a report for the D.S.I.R. on the “Control of Introduced Mammals in New Zealand." This report was put forward as the Department’s submission to the Noxious Animals Committee in Parliament. Part of the report deals with Forest Service-Wildlife branch relationships and what Dr. Howard classifies as the “population cycle.” During the four stages of the cycle the habitat changes Into four stages, even, though “these are not really separate entities. “Using red deer as an

example, stage one commences either with their liberation or immigration into a new area. It lasts until the initial peak population density is attained. In New Zealand this often has required 20 to 30 years"’ Dramatic Period Dr. Howard describes stage two as the dramatic period of the initial peak population. The excessive numbers of the deer herd force it to browse, bark-bite and eat various parts of plants that they normally ignore. In New Zealand drastic winter die-offs do not seem to be common. Consequently the stage two “eating-out” effect often persists for five to 10 years even though the deer are obviously suffering from malnutrition and other stresses associated with overpopulation. The entire range, is not depleted uniformly; hence at any one time the various sections of a watershed may not all be in the same stage. “Since in New Zealand the stage two habitat destruction is occurring in geologically young mountains that have a high potential for erosion because of the presence of fragmented rock, sensitive plants and climatic extremes, it is no wonder that animal-vegetation-soil problems result.”

Stage three begins as soon as the density of red deer has declined to where it more nearly matches the current carrying capacity of the habitat. It is the period of adjustment'in which the soil-plant-animal interrelations are in process of reaching a new degree of stability whereby the system will again be reasonably healthy, although greatly modified. Dr. Howard then quotes New Zealand examples in Fiordland in wapiti country: “A change from the natural vegetation towards a new vegetation, still composed of native species but more stable in the face of animal browsing and grazing.” In the North Island, "superimposed changes due to man and introduced animals are extensive and are causing a general deterioration of protective cover, but there is some evidence of the adaptation of vegetation to browsing.” During stage three the plants that cannot withstand the selective browsing pressure of deer are gradually replaced by less palatable ones, hence, the carrying capacity for introduced mammals is reduced.

“Modern game management practices, rather than extreme control measures sometimes can be started during stage three,” Dr. Howard says.