According to Ecological Society of America (1952), “grassland is a community dominated by grasses or grass-like plants”.
Approximately 24 percent of total vegetation cover is grassland. Grasslands occupy about 45.0 million sq. km. area throughout the world in the tropics, temperate and alpine regions (Shantz, 1954).
Natural grasslands occur in temperate zones with annual rainfall 25 to 80 cm, while in tropics they may be found in areas receiving rainfall up to 150 cm. The favourable conditions for development of a stable grassland are frequent rainfall and sufficient warmth during the growing season.
Grasslands do not form a prominent feature of vegetation in tropical part of India because of the following reasons:
(i) In the moist lowlands, grasses face very tough competition from trees and shrubs.
(ii) In the drier parts, the conditions (dry period, high temperature and evaporation), are so severe that they do not permit the extensive development of grasslands. Indian grasslands are not climax formations but they have developed secondarily under the influence of two factors, namely edaphic and biotic. In most cases, grasslands are maintained in their present seral stage due to biotic influences.
Fire alone or fire coupled with grazing and browsing may be very potent factors causing the development of grasslands in forest areas. If a grassland exists in forest territory for a number of years, the forest growth cannot eliminate it even if the fire factor is absent. Once the land is covered with grasses, tree seedlings find it difficult to gain a foothold.
There the grassland may persist as a very stable pre-climax. With the fire and Grazing which destroy seedlings of trees as soon as they enter the grassy stands, pre-climax of grasses persists for indefinite period. Once a forest has been destroyed and grasses have started secondary succession (secondary seres) over there, succession may be arrested in seral stage.
In India, there are no examples of typical subtropical climax grasslands and typical tropical Savannah type vegetation is also absent. In the tropical zone, the grassland is common enough as a secondary seral stage and may be stable pre-climax under the influence of fire and grazing.
The grasses are successful invaders and are capable of colonization in various habitats due to their following adaptabilities:
(1) They can grow in both hydrophytic and xerophytic habitats
(2) Many of the grasses show xeromorphic adaptations
(3) Their life span is from annual to perennial
(4) Habit varies from trailing to erect
(5) Size varies from small to dendroid
(6) Meristematic activity both apical and inter calary.
(7) Superficial rooting habit
(8) High reproductive capacity and capability for both sexual and vegetative reproduction
(9) Wind pollination
(10) They produce light seeds which are easily and quickly dispersed by wind and animals
(11) Position of buds below the soil
(12) Elasticity of internodes to bend
(13) Nodes have ability to produce roots and shoots
(14) Grasses can withstand trampling. Grazing and fire
(15) Grasses have wide ecological amplitudes
(16) Grasses tolerate poor growth conditions
(17) They can act as pioneer colonizer in Primary and Secondary successions
There are several grassy flats and grassy plains of seral nature in Nilgiri, Khasi hills and Naga hills. At elevations higher than 800 metres, the rainfall is heavy, the soil is dark in colour and rich in humus, and the vegetation consists of grasses which grow forming tufts at lower attitude and a turf at higher altitude. In swampy places above 1800 metre elevations, species belonging to Cyperaceae are in abundance. In the regions where forests are destroyed by fire, vegetation consisting of tall grasses with scattered trees (i.e.. Savannah) develops.
Grasses are of two types:
Bunch grasses which form clumps and Sod grasses which develop from rhizomes. Besides grasses, many nongraminaceous herbs, shrubs and trees also occur in grasslands. Depending upon the size of grasses and the abundance of nongraminaceous flora, grasslands have been assigned different names.
These are as follows:
(i) Grassy Plains:
These are with short grasses.
(ii) Prairies:
They contain tall grasses and shrubs
(iii) Pampas or Velds:
They are similar to Prairies but with more scattered bushes and a few trees.
(iv) Savannah or Savanna:
A grassland having tall grasses (1 – 4.5 m tall) and scattered trees (3-10 m tall). Savannahs are found in Africa, South America, Australia, India, and Burma. Savannahs are named after the dominant trees as for example Acacia savannah. Phoenix Savannah, Eucalyptus savannah and so on.
Grasslands of the world are categorized under the following types on the basis of physiognomy and habitat (Table 11.2).
The tropical grasslands of India may be classified into the following types:
(i) Xerophilous grasslands:
These are found in dry regions of North-West India under semi-desert condition. The common species of xerophilous grasslands are Andropogon contortus, Cenchrus ciliaris, C. barbatus, etc.
(ii) Mesophilous grasslands:
They are also called Savannahs. They are extensive grassy flats or grassy plains typically occurring in moist deciduous forests of U.P. The dominant species of such grasslands may be Saccharum munja, S. narenga, etc.
(iii) Hygrophilous grasslands:
These are called wet savannahs adapted to very wet soil. All these types being biotically controlled are inferior to temperate grasslands and suffer considerably from monsoon nature of climate and lack of proper legume mixture. Based on their floral characteristics Indian grasslands have been divided into the following eight major types by R.O. Whyte (1957). (Fig. 11.3). The geographical distribution and environments of these grassland types are given in Table: 11.3.
Ecological status of grassland in India has been discussed by several scientists. N.L. Bor (1942) and Champion (1936) have opined that the climax vegetation of India would be forests, or grasslands or desert vegetation. The existence of grasslands has been possible due to biotic activities such as lopping, burning, shifting cultivation and grazing of the forests for the centuries. Human activities have affected the grasslands all over the world.
The long term human activities have converted much of the land into agro-climax where climax vegetation is now agricultural crop. The biotically disturbed forest land and agri-climax areas provide niche for grasses on Nilgiris in South India. Grasslands or Maldeows are maintained by forest factor which kills trees, seeding’s invading the upper reaches of hill tops and promotes the growth of grassland. In Punjab, the grasslands are cleaned mostly for agricultural purposes. Mohan (1955) has listed the common grasses of Punjab and discussed succession in grassland vegetation.
The pioneer species in the forest clearings were the common grasses like, Conchrus ciliaris, Themeda anathera, Chrysopogon montanus. In the course of succession, with the change of habitat conditions the previous species disappeared and gradually Dichanthium annulatum, Hateropogon contortats. Bothriochloua pertusa, etc. formed dominant community of grasses there. In Madhya Pradesh grasslands have been studied by Tiwari, S.D.N. (1954), Pandeya, S.C. (1955) and some others. The distribution of common grasses in Madhya Pradesh with their habit preferences and economic importance recorded by Tiwari (1954) are presented in Table 11.4.
Pandey (1955) has worked out the Grassland associations of Saugar Distinct of Madhya Pradesh and classified the grassland into 8 types based on apparent floristic similarity, limits of the area occupied, time duration and correlated them with the soil types (Table 11.5).
Seth (1955) recognized 13 types of grasslands in Uttar Pradesh (including Uttaranchal) on the basis of moisture relations of soils and dominant species (Table 11.6).
Rowntree (1954) has described grasslands of Assam in two associes:
(i) Imperata – Saccharum:
Themeda on higher well drained lands throughout Assam.
(ii) Alpinia – Phragmites:
Saccharum on clay alluvium of rivers & flood plains with Salmalia & Albizzia as common tree associates. Rangnathan (1938) considered upland grassy areas of Nilgiris as climatic climax with species of Andropogon pertusus, Themeda imberbis, Cymbopogon polyneuros and Eragrostis nigra as common grasses. Meher Homji (1972) has discussed the phytogeographical aspects of shola grasslands and considers frost as a controlling factor for perpetutation of these grasslands.
Table 11.6. Grasslands of Uttar Pradesh and Uttaranchal (Seth, 1955) Grasslands of U.P. (Uttaranchal Included):