grazing

The effects of environment and management on the composition of short-tussock grasslands and the abundance of the invasive weed Hieracium pilosella were investigated in two small catchments. Species composition and site factors were recorded on a total of 182 plots and the management history of each catchment was reviewed. H. pilosella was present on >80% of all plots, but was at an early stage of invasion in one catchment (<5% cover) and dominant in the other (25% cover).

An account is given of the vegetation of Flat Top Hill, in the driest part of semi-arid lowland Central Otago, New Zealand. Although highly modified, the area was acquired for conservation in 1992, following almost 150 years of pastoral use. The vegetation was sampled in a composite scheme using permanent monitoring sites placed to include the majority of habitats and communities present. A number of environmental factors were measured in each sample. Native species comprise 53% of the vascular flora of the area (211 species).

Vegetation changes were investigated on 27 transects in agriculturally unimproved short tussock grasslands dominated by Festuca novae-zelandine in the Harper-Avoca catchment, Canterbury. These were remeasured at 5 or 10 year intervals between 1965 and 1990. Change was widespread. It was characterised by invasions by exotic species, declines in native species (including F. novae-zelandine), and a trend towards vegetation dominated by the flatweeds Hieracium lepidulum and H. pilosella, and the grass Agrostis capillaris.

Hieracium, or hawkweed species, serious weeds in South Island high country, may be controlled by appropriate pastoral management. Experimental trials at Lake Tekapo, related to S and P fertiliser rates of 0-100 kg ha-1 yr-1, 27 different combinations of over-drilled and resident species and different seasons or intensities of grazing treatments on Hieracium dominated fescue tussock were conducted. These were monitored for 9 years in terms of fertiliser inputs used, sheep stocking rates, and vegetation changes.

Chionochloa species vary in the degree to which they are grazed by introduced ruminants. This is presumed to reflect the relative nutritive value and/or palatability of the forage provided by these indigenous grasses. Data are presented here on silicon content, in vitro organic matter digestibility (OMD), metabolisable energy (ME), crude protein and total nutrient mineral (TNM) contents of mature leaves of eleven Chionochloa species in southern New Zealand.

The effect of protection from sheep grazing on indigenous plant species in relatively mesic, strongly modified Poa cita grassland, was examined using paired grazed and ungrazed sites. Ungrazed sites, fenced at times ranging from four to more than 24 years ago, had fewer species, lower indigenous cover and lower tussock density than adjacent grazed sites. The dominance of adventive species, particularly cocksfoot (Dactylis glomerata), in ungrazed sites appeared to be important to these differences.

Since human settlement, wetland ecosystems in New Zealand have been severely modified by fire and reduced by drainage for agricultural development. Those remaining are problematic to manage, with modified water regimes, invasive weeds and grazing by livestock. Before settlement, wetland habitats supported diverse avian herbivores, the majority of which are now extinct. However, introduced birds are increasing in wetlands. We sought to understand the role of grazing birds in the maintenance of local turf communities in a lacustrine environment in Otago, New Zealand.

Leaf functional traits have been proposed as general indicators of plant palatability to ungulate herbivores, identifying which species are likely to be most at risk from ungulates, and how ungulate grazing may change ecosystem processes. However, few studies have tested whether leaf trait–palatability relationships are consistent across different ungulate species.

There has been considerable ongoing debate about the extent to which the impacts of introduced deer on native vegetation have replaced those of moa, and since the 1980s there have been major changes in thinking about the impacts of deer and ratites on ecosystems. Although it has long been known that deer caused a predictable sequence of changes in forest understorey composition, recent work has shown that the foliage of species preferred by deer contains lower concentrations of fibre – and decomposes faster – than avoided species.