The rise of a new biome
The Pocket Tundra
While Antarctic ice shelves have completely disappeared, a new habitat is slowly expanding: the Pocket Tundra. It's a low diverse habitat, with no more than 60 species of vascular plants in the richest areas. This can be explained by the strong geographic isolation, but also by the weak disturbance of grazing animals. Due to this, dominant plant species easily outcompete other less competitive species.
Ice sheets frequently separate this biome in small portions (>100 km2 /0,39 square miles), but at least 40 patches are known to exceed 4.000 km2 (1544 square miles). This habitat fragmentation does not allow vertebrates to become significantly large, since the carrying capacity of each patch is very low. Flying animals like insects and birds have a strong advantage in this tough ecosystem. Land animals have drastically increased here since the last update: after all, this is the only hospitable biome of Antarctica, for now!
Tundra bogs are the most diverse ecosystem, with a higher presence of fruity plants and up to 50 species of arthropods. As you can imagine, insects are the most abundant animal group in Antarctica, mostly comprising diptera, both terrestrial and aquatic, with few species of mayflies (Ephemeroptera) and true bugs (Hemiptera). Recently, some species of beetle (Coleoptera) and caddisfly (Trichoptera) have made their first appearance in the northernmost islands.
Aquatic insects usually live in large rivers, where water does not frost completely during winters. At the moment, the largest stream is the Ghiaccio river, found on the mainland and flowing into Ross Bay. It's a braided river and its average length is 120 km, with seasonal debris events that often change its original flow. Most antarctic rivers are seasonal melt-water streams, especially the smaller ones, with low flow rates like the Onyx river, the longest antarctic river of the Holocene. Due to this, most melt-water streams virtually do not possess any fish species, with only anadromous species being able to survive.
The flora
The antarctic flora is extremely poor, due to the presence of a strong current that flows clockwise around Antarctica, which isolates it from the other continents( the Antarctic Circumpolar Current). Due to this, seed dispersal from other areas is hard to occur. Plants are a mix of native austral species and naturalized boreal species. Mosses are the most widespread group of plants, comprising genera like Sphagnum, Conostotum, Saniona and Ceratodon. Cushion plants are also extremely abundant and include genera like Astelia, Donatia, Bolax and Oreobulus. Large ferns are represented by Bleschum and Dryopteris, both arrived from South Georgia.
Grasses include Poa, Carpha, Festuca and Juncus, Marsippospermum and Deschampsia (the last one was originally the only grass genera native to Antarctica). Dicotyledon herbs on the other side comprise important genera like Trifolium, Cytisus, Bellis, Senecio, Tribeles, Colobanthus and Ranunculus, which are more abundant and biodiverse where the grazing action of herbivorous birds is higher.
Aside from grass species, some shrub plants were able to colonize Antarctica, thanks to seed dispersion by birds. The most ecologically important genera are Empetrum (crowberries), Berberis (barberries), Vaccinium (blueberries), Ribes (currants) and Fragaria (strawberries). All of these species, due to short and cold summers, hardly grow more than 50 cm in height.
Fruity shrubs like this snowy blueberry are an important food source for wintering antarctic tyrants
A succesful alien species
The ice willow (Salix nanixenoidea) is the most widespread shrub in Antarctica and also the tallest one, capable of reaching 1 meter of height on the warmest coast of the Antarctic peninsula. It derives from a boreal species of willow, Salix alba, that was firstly introduced in Magellanic moorland and South Georgia island. It was then indirectly introduced in Antarctica by migrating birds, with the first confirmed occurrence being around 1.000 years AP. This willow rapidly adapted to the extremely cold environment of Antarctica, becoming a dwarf shrub. The species can handle temperatures as low as -40 °C/°F, as long as there are at least 2 warm months during the year.
Ice willow is a typical example of pioneer species, colonizing rocky environments and producing soil, creating new opportunities for less adaptable species. Its flower nectar and leaves are incredibly important for insects and birds, which help disperse its pollen and seeds. It often creates small thickets, where lots of migratory passerines make their nest. We can say that, without the ice willow, the pocket tundra would be far less liveable than we know.
The Ghiaccio river, the largest river of Antarctica