Assessment and management of hare impact on high-altitude vegetation

Abstract

In New Zealand, introduced brown hares (Lepus europaeus) are present in many sub-alpine and alpine habitats. In 1995, five Department of Conservation conservancies documented their concerns that hares may be causing unacceptable damage to such areas, particularly in the alpine grasslands. It was acknowledged, however, that hare impacts are difficult to separate from those of rabbits, possums and larger grazing mammals. In response, the Department of Conservation commissioned this review of the existing literature on assessment and management of hare impacts on high altitude vegetation. The average density of New Zealand's hare population is estimated to be 0.1 hares ha⁻¹. Densities are highest in sub-alpine areas and much lower in alpine areas. Hares are most abundant along the dry, eastern side of the Southern Alps, where densities of 2-3 hares ha⁻¹ are reached. Hare diet tends to reflect the composition of the vegetation community that they are feeding in, although preferences for certain plant species are evident. To date, three studies have attempted to quantify hare impacts on high altitude vegetation. These suggest that hares reduce plant growth and inhibit regeneration in some habitats but have relatively little impact in others. In certain parts of their range, hares are probably the 'main' introduced herbivore, in that they consume more forage per hectare than possums, chamois, thar, deer or domestic livestock. In many other areas, however, the impact of these other grazers is likely to exceed that of hares. If conservation managers require specific information about hare impacts in areas of high conservation value, then additional studies on hare diet and density assessment, and experiments using exclosure plots and population reduction techniques, will be needed. A critical issue for managers will be to determine how intensively hares need to be controlled to achieve conservation goals in an area - this needs to be known before the appropriate methods and likely costs can be evaluated. Any expenditure on hare control should be supported by longterm vegetation monitoring to assess the benefits of such control. Hares are only one of numerous issues affecting high altitude habitat management, and so need to be considered within a broad management framework for such areas.