As for the marine environment, pressures on the terrestrial environment operating on a global scale include anthropogenic climate change (e.g. atmospheric warming and changes to water regimes), while local pressures include the introduction of alien species and impact from human activities.
Climate change impacts in Antarctica and the subantarctic include changes in trends in climate parameters (such as air temperature, precipitation and wind speed), as well as increased frequency and impact of extreme or pulse events.207 Both are regionally specific. In Antarctica, flooding from an extreme summer warming event in 2002 altered species abundances in nematode communities in the Dry Valleys,207 and an extreme warming event in the winter of 2009 negatively impacted moss communities in the Windmill Islands (M Ball, Australian National University, pers. comm., April 2011).
The introduction of alien species has significantly altered the landscape, composition of ecosystems, and species interactions on many subantarctic islands not under Australian jurisdiction.208 Studies of the flora at the French subantarctic Kerguelen Island date back to 1874 when three introduced plants were collected209 Large-scale surveys mainly in the 1970s and 1980s discovered a total of 168 introduced plant species on Possession, Kerguelen and Amsterdam islands. During a survey in 2000, 118 of these were still present. On some islands, the alien species are well established and outnumber the native species. For example, at Kerguelen Island, 68 introduced plant species were present in 2000 compared with only 14 native species.209 In addition, there are 30 known invertebrate alien species.
On Australia's Macquarie Island, there are only 3 alien plant species but 28 alien invertebrate species. Recent research has suggested that the presence of some alien invertebrates has a negative impact on native invertebrate species richness and density.210 Australia's McDonald Island appears to be the only island in the subantarctic that is free of introduced species. Nearby Heard Island has one known alien plant, the grass Poa annua, and three invertebrate species: the earthworm Dendrodrilus rubidus, the mite Tyrophagus putrescentiae and the small thrips Apterothrips apteris,211 but no introduced vertebrates.
Climate change and the intrusion of invasive species may combine as pressures.145,212 As global warming progresses and ambient temperatures rise, non-native species formerly unable to survive in the region may now be capable of establishing themselves and outcompeting the native organisms.145 New species that become established in a warming environment tend to be more competitive than native species because of better dispersal mechanisms or lack of predators, or may occupy niches that previously did not exist. Under such circumstances, food webs and ecosystem functioning could be altered dramatically (e.g. Convoy & Lebouvier213).