Summary The establishment of exotic species of vascular flora and vertebrate fauna on subantarctic Macquarie Island since its discovery in 1810 has resulted in major changes in the biota. A management programme aims to reduce the numbers of exotic plant and animal species and assist with the recovery of pre‐existing communities and processes. This paper reviews the integrated vertebrate pests management programme on Macquarie Island since 1974 and outlines future management considerations. As part of this programme, the responses of some native and exotic species of vascular flora and vertebrate fauna were monitored following control of European Rabbit (Oryctolagus cuniculus) numbers. Changes in the vegetation recorded over 10 years showed that approximately half of all the vascular species had benefited from rabbit grazing, including several which formed a major part of the rabbit’s diet. After rabbit control, some adversely affected plants responded rapidly to a reduction in grazing pressure while others will require an almost total cessation of grazing in order to re‐establish their former distributions. With the decrease in rabbit numbers it was also necessary to control Feral Cats (Felis catus) due to their increased predation on native burrow‐nesting birds. Feral Cat predation on introduced fauna also increased, one result of which was the eradication from the island of the introduced Weka (Gallirallus australis scotti). Reduced rabbit grazing is leading to re‐establishment of the native Tall Tussock (Poa foliosa) grassland and with it the spread of the introduced Ship Rat (Rattus rattus). This review indicates that an integrated approach to pest management, with monitoring of the responses of both target and non‐target species, is the most effective way to restore pre‐existing communities and processes. Key words grazing pressure, introduced species, predation, recovery, vertebrate pest management.
The responses of vascular plant species to a reduction in grazing pressure were monitored as part of a rabbit-control program on Macquarie Island. The initial response of the vegetation was more luxuriant growth with changes in abundance recorded after 2–3 years. After 8–10 years the relative abundance of several species had changed while species not previously recorded had appeared on study sites and others had disappeared. Of the 32 species recorded on study sites, 11 species (Agrostis magellanica, Deschampsia chapmanii, Festuca contracta, Juncus scheuchzerioides, Luzula crinita, Pleurophyllum hookeri, Poa annua, P. foliosa, Stilbocarpa polaris and Uncinia spp. (two species)) were found to form the major portion of the rabbits’ diet while another four species (Acaena magellanica, Cerastium fontanum, Isolepis aucklandica, Polystichum vestitum) were moderately grazed. The other species were either rarely grazed or occurred too infrequently to assess. Of the 25 species that were recorded over 30 times, 17 were considered to have benefited from the introduction of rabbits.
Summary Australia's sub‐Antarctic Macquarie Island is presently undergoing one of the most ambitious vertebrate pest eradication programmes ever undertaken. The anticipated success of this programme will release the island's tundra‐like vegetation from well over a century of grazing and disturbance from House Mouse (Mus musculus), Ship Rat (Rattus rattus) and most significantly European Rabbit (Oryctolagus cuniculus). This study describes results from 30 years of vegetation quadrat monitoring (prior to the most recent and comprehensive pest eradication programme) when lower level pest animal control programmes were underway. Plant species were assigned to one of five distinct functional plant groups: Indigenous short‐lived perennials, Introduced short‐lived perennials, Indigenous perennials rarely grazed by rabbits, Indigenous perennials occasionally grazed by rabbits and Indigenous long‐lived perennials heavily grazed by rabbits, with one species, Agrostis magellanica, analysed as a sixth monospecific group. Results from monthly rabbit counts were used to compare changes in abundance of these six groups under different rabbit populations. It was found that there were three distinct phases of rabbit activity during the study period, indicated by (i) an initial very high count year in 1980–1981, followed by (ii) 20 years of low counts ending in 2001–2002 after which (iii) counts rose to medium/high until the commencement of the eradication programme in 2010–2011. Vegetation composition and progression were distinct for these three rabbit count phases. The first four of the plant functional groups decreased under lower count periods and increased in cover under higher rabbit count periods. Agrostis magellanica appears to respond primarily to interspecies competition and is disadvantaged under extended periods of low rabbit numbers. Indigenous long‐lived perennials heavily grazed by rabbits, which includes the large tussocks and megaherbs, is inversely related to rabbit numbers. During the study period, there has also been an overall decline in plant species richness with average species count per quadrat falling by between 0.6 and 2.7 taxa. This study attempts to address the observed vegetation change from this long‐term monitoring, to discuss other potential contributing factors and to use the results to predict likely future vegetation changes after eradication of vertebrate pests.
Sphagnum moss has been used globally as an indicator of climate change. Since continuous meteorological recording started in the late 1940s, there has been a marked change in the climates of Southern Ocean islands. The distribution of Sphagnum on Macquarie Island appeared to be expanding through the 1980s. All patches of Sphagnum were mapped in the 1992/93 austral summer, with 112 Sphagnum moss patches (<3 m 2 ) and 12 larger (≥3 m 2 ) patches recorded. The vast majority of sites recorded were lowland coastal, with a few sites around plateau lakes. The area of moss beds ranges from 0.03 m 2 to 32.4 m 2 . A total of 23 sites were pegged and tagged by 1996, but only 14 of these sites still had Sphagnum moss present by 2004. It is considered that the climatic conditions (higher than average temperatures and wind speeds and lower than average humidity and precipitation) that occurred between April 1999 and May 2000 would have resulted in a period of desiccation that accounts for the destruction of the smaller and/or shallower Sphagnum beds on the island. It is highly likely that both the spatial distribution and size of Sphagnum moss beds on Macquarie Island will continue to decline with predicted changes in sub-Antarctic climate.
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