Until European settlement, New Zealand alpine grasslands were grazed only by native birds and invertebrates. In the uplands of Fiordland (South Island) by the 1930s, wapiti Cervus elaphus nelsonii and red deer C.e.scoticus (and their hybrids) introduced for hunting, were well established. By the late1960s, high deer numbers had strongly modified alpine grasslands. The effect of reducing deer numbers, mainly by aerial hunting by helicopter (and also live-capture removal) on vegetation was assessed in Fiordland National Park, Southland.
The study grasslands (c.900-1,500 m altitude) are dominated by five species of snow tussock Chionochloa spp. Aerial hunting began in 1973, rapidly reducing deer numbers. Continued hunting (with live-capture in latter years), reduced numbers in the alpine grassland zone to near zero by 1984.
In 1969, 174 permanent (20 x 20 m) alpine grassland plots (spaced at 61 m altitudinal intervals) were established throughout northern Fiordland, and major grassland types were mapped. These were resurveyed in 1975. In 1984, 86 of the plots were within the central range of the wapiti herd (central Wapiti Area). Of these, 57 (covering the range of grassland types) were resurveyed to assess vegetation recovery. The following were recorded:
1. Percent frequency of species and bare ground in subplots along a 20 m transect running through each plot;
2. ‘Top cover’ of vegetation and bare ground (estimated from photos);
3. Tussock stature (maximum leaf length) of Chionochloa pallens or C.flavescens nearest the photo centre and its nearest same-species neighbour;
4. The number of faecal pellets in 10 randomly positioned circular subplots (1.26 m diameter in 1969 and 1975, 1.14 m in 1984) in each plot, to calculate a deer density index.
5. Site factors e.g. soil, altitude, aspect, slope.
A significant recovery of plants preferentially grazed by deer occurred on the 57 plots surveyed in 1969, 1975 and 1984. Deer showed a strong preference for grassland on more fertile soils characterised by C.pallens and large-leaved herbs, especially at lower altitudes (c. 900-1,100 m). Little change occurred in less-favoured grasslands on infertile soils characterised by C.crassiuscula and C.acicularis.
Between 1969 and 1984, the main overall trend was a large increase in frequencies of the large-leaved herbs Anisotome haastii, Celmisia verbascifolia, Gentiana spp. and Senecio lyallii/S.scorzoneroides, with less significant increases apparent for numerous other species. Most recovery occurred between 1975 and 1984, the period when deer numbers declined to near zero.