The Science of Vegetation with Reference to India

Pt. I Vegetation is the sum total of plant population covering a region and its descrete units circumscribed by characteristic environment, are communities. The species content is the flora. The physical and the biological surroundings characterise the environmental complex. Both plants and their environment are dynamic systems interacting within and with each other. The amplitude of variations in the environment is generally met with synchronised adaptive responses of the plants in time and space. Differentiation of ecads and ecotypes within the plastic species is the result. However, many forms and invaders may get eliminated also if the situation goes beyond their range of tolerance set by the genetic organisation as the factors may become critical at different stages of the life-cycle. The species around provide the genetic material for recruitment and ecesis within the community.

pt. II Migration of species involving mobility of disseminules, their germination, aggregation, competition and final ecesis-ever continuing processes lead to colonisation and invasions. All these plant phenomena react upon the environment introducing changes therein. Thus newer community-environment-complex equilibria are set up in the dynamic system. The whole process is called, succession in relation to time and the series of succeeding communities for a given area, a sere. When it happens ‘de novo’ with no trace of plant present originally in the area, it is prisere as a result of primary succession and subsere with disturbed communities in which secondary succession is the rule. The mechanism of succession is driven by the reacting and changing environment consequential largely either to the plant processes themselves or to extraneous forces succession is autogenic in the former and allogenic in the latter case. In every case succession terminates into a more stable climax community generally dependant upon the climate and soil. The taxa used for classifying communities differ widely among ecologists but association is the basic unit accepted by all, though with varying concepts. The concept of ecosystem in relation to energy and matter within the community is the most acceptable basis for comprehending;vegetation types in India.

Pt. III Since vegetation evolves out of the flora floristic regions of India should form the basis of its main divisions. For this purpose three main latitudinal belts viz. (1) Eastern and Western Himalayas, (2) Assam, Gangetic Plains and Rajasthan, and (3) Deccan and Malabar are recognised. The seven provinces with their distinct climate including photoperiod can be individually considered for the description of vegetation types along gradients of altitude, humidity-aridity, history and proximity of human settlements and soil fertility. Along these gradients closed, open and desert types of structure within forests, scrub and grass can be described with their combinations wherever necessary. Physiognomy, structure, function, composition, dynamics, habitat relations and history are the important diagnostic criteria of vegetation types. Size, texture and seasonal behaviour of leaves of dominant species may also be given. The hydrophytes can be described in each place as floating, suspended, submerged anchored, floating-leaved anchored and emergent anchored.