Phytogeography Topics: • Principles • History • Description of earth • Theory of tolerance • Endemism • Brief description of major terrestrial biomes (sp. Tropical, temperate and tundra) • Phytogeographical divisions of India • Vegetation of Delhi Phytogeography or plant geography deals with the geographical distribution of plants on earth. Phytogeography is defined by Good (1964) as ‘that branch of botany that deals with the spatial relationships of plants both in the present and the past’. Plant ecology + phytogeography= geobotany In systematics plants are grouped into taxa. In ecology…………………….into communities etc In phytogeography………..into phytochoria. • Phytochoria are natural floristic areas that broadly correspond to climatic types, and are based on the total number of species with the same concentric distribution pattern. • A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both regions overlap. The region of overlap is called a vegetation tension zone. • Earliest definition was given by Schouw (1823) he divided the earths surface into 25 kingdoms represented by geographical areas named after their most characteristic plants. • Eg Kingdom of Saxifrages and mosses (Alpine Arctic) • Eg Kingdom of Umbelliferae and Cruciferae (Eurasia); it was further divided into provinces. • Turrill (1959) used the term ‘realm’ instead of Kingdom. • Good divided the earth into 6 Kingdoms and 37 regions. Good (1947) floristic kingdoms HISTORTY: • Study is quite old. • Even Theophrastus gave information regarding plants in Mediterranean region. • Linnaeus and de Candolle described geographical distribution of many plants. • However the first structural approach (as a separate subject) was made by Humboldt (1817). • He is credited to be the father of phytogeography: he studied the relationship between plants and environment, both latitudinally and altitudinally. • Important contribution by Sir JD hooker too. Studied plants from different parts of the world. AIMS: • To find out and record the distribution of plants in geographical regions of the world on the basis of latitudinal and longitudinal positions. • To determine the units into which the Earth can be divided on the basis of the similarity of ranges of taxa. • To name and classify these units into phytochoria. • To determine the causes which result in these ranges. Physical geography of the earth: Layers: • Crust • Mantle (upper and lower) • Core (outer and inner) • Core (3500kms) is the densest. It is mainly metallic iron with some nickel and other elements. • Core is surrounded by mantle (2900kms). • Crust is topmost (50kms). Divided into continental (granite rock) and oceanic crust (Basalt rock) • Granite rock (light)- Silica + aluminum (sial) • Basalt rock/felsic rock (dark)- Silica + Magnesium • Granite rock is less dense than basalt hence continental platforms float over the oceanic crust. • Lithosphere includes crust and top portion of mantle. • The line of separation between crust and mantle is called MOHO or mohorovicic discontinuity (after the seismologist Andrija Mohorovicic) CONTINENTAL DRIFT THEORY
