Impact of cattle on conservation land licensed for grazing in South Westland, New Zealand

Making use of existing fences as ready-made exclosures, this study aimed to assess the long-term effects of cattle grazing on forest margins. Results indicated: 1) that cattle browsing and trampling has an impact on vegetation species composition, structure and regeneration; 2) that the effects of a particular grazing regime may take many decades to dissipate; and 3) that the impacts of cattle change with stock intensity. Some plant species appeared to be highly palatable to cattle and only occurred on sites without cattle. Such species included pate (Schefflera digitata), broadleaf (Griselinia littoralis), pigeonwood (Hedycarya arborea), supplejack (Ripogonum scandens), mahoe (Melicytus ramiflorus), milk tree (Streblus heterophyllus), lancewood (Pseudopanax crassifolius) and hen and chickens fern (Asplenium bulbiferum). A small group of plants appeared to regenerate better under cattle than in their absence, particularly mountain horopito (Pseudowintera colorata) and prickly shield fern (Polystichum vestitum). A few species were encouraged by cattle at one site but suppressed by them at another: kahikatea (Dacrycarpus dacrydioides), wheki (Dicksonia squarrosa), Coprosma rhamnoidesand Blechnum fluviatile. The impact of cattle on most other plant species was not discernible. The results of this study, while somewhat equivocal, indicate that future grazing licences in South Westland should restrict stock to low numbers and be confined to already modified sites where damage to conservation values would be minimal.