The botany of the southern oceanic islands

Abstract

Botanical interest in the islands of the southern ocean has centred largely on the geographical relationships of their floras, problems of long-distance dispersal, and on the larger questions which their floras raise concerning the past distribution of land and sea in the southern hemisphere and the origins and migration-routes of the continental floras (references in Turrill 1953, pp. 184-88). This paper will deal with the vegetation types of the southern islands. The major types of native vegetation on the islands are compared with one another, and with similar types on the southern continents, and some of the ecological consequences of their insularity are discussed. Geographically, the islands considered all lie between the Tropic of Capricorn and the Antarctic Circle (figure 10). With the exception of the mid-Atlantic and mid-Indian Ocean groups, all he within about a thousand kilometres of the nearest continental shelves. Most of them consist wholly or partly of volcanic material. Islands of both continental and oceanic origin (Wallace 1895) are included. Their climates are all extremely oceanic, with small temperature ranges, evenly distributed rainfall, constantly high humidities, and strong westerly winds. Air temperatures at sea level closely follow those of the surrounding seas (figure 11).