The boreal is cold, the austral warm, and the tropical affords conditions of heat and moisture to which the vegetation of the others would be intolerant.
Limit of numerous austral species, is divided into an eastern humid or Alleghanian area, a western arid area, and a Pacific coast humid area.
Other species are exclusively tropical or austral in their range.
The Upper Austral zone is divided into an eastern humid (or Carolinian) area and a western arid (or Upper Sonoran) area.
Passarge's Die Kalahari (Berlin, 1904) deals chiefly with geological and allied questions; John Mackenzie's Austral Africa, Losing it or Ruling it (London, 1887); John Mackenzie, a biography by W.
This takes account of - (I) the ArcticAlpine zone, including all the vegetation of the region bordering on perpetual snow; (2) the Boreal zone, including the temperate lands of North America, Europe and Asia, all of which are substantially alike in botanical character; (3) the Tropical zone, divided sharply into (a) the tropical zone of the New World, and (b) the tropical zone of the Old World, the forms of which differ in a significant degree; (4) the Austral zone, comprising all continental land south of the equator, and sharply divided into three regions the floras of which are strikingly distinct - (a) South American, (b) South African and (c) Australian; (5) the Oceanic, comprising all oceanic islands, the flora of which consists exclusively of forms whose seeds could be drifted undestroyed by ocean currents or carried by birds.
The varied fauna and flora of Texas may be classified in the following life-zones: the Canadian zone, on the highest parts of the Davis Mountains; the Transition zone, including high parts of the Davis, Chisos and Guadalupe mountains; the Upper Austral zone, Upper Sonoran division, in the Panhandle, E.
Excepting the embayment region, Missouri lies wholly within the Carolinian area of the Upper Austral life-zone; the There has been some controversy as to whether this condition is due to the elevation and corrosion of original flood-plain meanders after their development in a past base-level condition - which theory is probably correct - or to the natural, simultaneous lateral and vertical cut of an originally slightly sinuous stream, under such special conditions of stream declivity and horizontal bedstrata (conditions supposed by some to be peculiarly fulfilled in this region) as would be favourable to the requisite balance of bank cutting and channel incision.
Bird, Annals of Natal,1495-1845(2 vols., Maritzburg, 1888); C. de Mello, Os Inglezes na Africa austral (Lisbon, 1890); E.
Fauna.Differences of temperature have produced in North America seven transcontinental life-zones or areas characterized by relative uniformity of both fauna and flora; they are the Arctic, Hudsonian and Canadian, which are divisions of the Boreal Region; the Transition, Upper Austral and Lower Austral, which are divisions of the Austral Region, and the Tropical.