The relationship between the climates, ecology and plant geography of the southern cold temperate zone and of the tropical high mountains

Abstract

This asymmetry of the two hemispheres may be demonstrated by drawing a profile-diagram of the climatic vegetation belts from the northern to the southern polar regions, or by constructing a ‘summarized continent’ (i.e. a world map showing the proportions of land and sea in the different latitudes of the globe). The typical boreal vegetation types—tundra, coniferous forests and caducous broadleaved forests—are restricted to the continental, winter-cold climates of North America and Eurasia, while in the high-oceanic cold temperate zone of the southern hemisphere tussock grasslands, communities with cushion plants, and luxuriant evergreen scrubs and forests exist. The cool-temperate forests of Patagonia and New Zealand have a striking similarity to the upper montane forests of tropical mountains (Ceja de la Montaña of the Andes; moss-forests, and elfin forests of East Africa and Malaysia). Similarly the tussock grasslands of the subantarctic have their counterparts in the tussock and cushion formations of equatorial high mountains (páramos). The same arrangement of zones may be observed vertically, between lowlands and mountains, in New Guinea, as is encountered when proceeding from north to south at one level in New Zealand. In each case the succession passes from tropical rainforests through lower montane forests with Weinmannia, Podocarpus and Nothofagus to upper montane forests with Libocedrus and Dacrydium and then to tussock grassland with Danthonia (Troll 1947). These contrasts and similarities can be correlated clearly with temperature conditions, and this is best illustrated by comparing so-called thermoisopleth diagrams for Macquarie Island, Quito, McMurdo Sound (Antarctica) and Oxford.