Past Antarctica - Paleoclimatology and Climate Change CHAPTER 11 Geoecological responses

Organisms living in polar regions are subject to some of the most extreme environmental conditions on Earth. Antarctic vegetation is mainly composed of non-vascular cryptogams, with bryophytes and mosses, in particular, being the dominant terrestrial flora with lichens and algae (e.g., Øvstedal and Smith, 2001; Ochyra et al., 2008). Survival in Antarctic terrestrial ecosystems is based on the capability to withstand cold temperatures, low and irregular water availability, scarce nutrients, unstable substrata, prolonged snow cover, low radiation receipt, wide seasonal variations in photoperiod and strong winds (e.g., Kennedy, 1993, 1995). In Antarctica growth conditions are extreme and plants exist at the physiological limits of survival, with abiotic factors considered to be responsible for the restrictions imposed upon the distributions of plant populations (Longton, 1988; Davey, 1997). In this harsh context, even slight changes to growth conditions are likely to have a large impact, rendering Antarctic terrestrial communities sensitive to climate change (Robinson et al., 2003). As a consequence of these severe conditions, Antarctic flora is almost entirely cryptogamic. Only two vascular species, Deschampsia antarctica Desv. and Colobanthus quitensis (Kunth) Bartl., occur, both of which are restricted to the Antarctic Peninsula. Biodiversity patterns of the extant Antarctic biota are the result of a complex and long biogeographical and climatic history. Knowledge of these patterns, with special reference to past, present and future geoecological responses of these ecosystems, allows for facing and preventing, when possible, threats to the continent’s biodiversity deriving from climate change, biological invasions and anthropogenic impacts.