Anthropogenic influences on the vegetation of Western Rajasthan

ANTHROPOGENIC INFLUENCES ON THE VEGETATION OF WESTERN RAjASTHAN

by

RAj KUMAR GUPTA

Central Arid Zone Research Institute, Jodhpur, Rajasthan.

I N T R O D U C T I O N

Western Rajasthan, forming a part of the Thar desert, is very sensitive to factors of degradation such as climatic crisis or misuse of land. There have been marked changes in the physiography of Rajasthan (PIGGOT, 195o; SMITH, 1949; WADIA, 1954; RODE, 1964; etc.) during geological times. There are geological considerations which seem to have contributed materially, since the close of the last glacial period in northern India, to the deterioration of the desertic conditions (LA TOUCHE, I9O2; WADIA, I960; PASCOE, I950 , I959; DE TERRA, 1939). RAVERTY (1892) is of the view that the desert originated in mediaeval times but the archaeological evidence (GHosH, I952; SANKHALA, 1952 ; VATS, I95 @ indicated that it is at least two millenia old and its nucleus must be older still. The history of the river systems (OLDHAM, 1874 , 1886, 1893 ) shows considerable evidence to indicate that not long ago numerous streams flowed through Western Rajasthan and the climate was less severe than at present. The tract was wooded and there were large settlements along the rivers Saraswati and Drishadvati which have remains of Harappa and Mahenjodaro. Further studies (MARSHALL, 1931 ; LUTHRA, 1936; KOHLI, 1944) showed that there was a highly evolved culture in Rajasthan around 3o0o--4ooo years ago which was characterized by pottery, bricks and copper smelting. It is obvious that these highly cultured people practised agriculture and had domesticated animals. How much of the forest wealth was destroyed by these to burn pottery and to smelt copper could be anybody's guess. With the growth of population and arrival of some foreign tribes like Huns, Gujars etc. from Central Asia and their nomadic ways of life, destruction of the forests continued indiscriminately on a much larger scale even after the drying of the river system and gradual reduction in precipitation. This resulted in the imbalance between the moisture level and the heat which enters the soil and goes to heat the air. Instead of heating the moisture in the soil and evaporating it the radiant energy heated the soil mass in the air and the air layer close to the ground. The loss of plant cover further aggravated the situation and as the amount of radiation at the surface of the earth could not be used in any large amount for evapora-

8o R.K. GUPTA

tion of moisture and transpiration, it heated the air and the soil further, thus creating arid conditions.

These features should not be confused with the present distur- bance of land surface which has been superimposed over this landscape and is sufficiently ominous in its importance to further the productivity of these lands. It is illustrated by the severe dust storms which are prevalent in summer, in the accumulation of sand hum- mocks and sand dunes on cultivated lands and around villages, by large areas of annual vegetation where perennial vegetation should exist, and by the newly active scars of the old fixed sand dunes. These disturbances are the result of excessive cultivation or grazing and axe especially prominent in the vicinity of the villages. Many factors have collectively influenced this long developing process of degradation of resources and the recent serious acceleration of these is the aspect of more immediate concern. Though there may be two opinions about the origin of the deserts, there cannot be different opinions about the role of these factors in the maintenance of the present desertic conditions, like in many parts of the tropical world (SA~J~R, I958).

The anthropogenic influences may broadly be classified as I. Direct influences and 2. Indirect influences. Under the direct influences are included (a) Human population and their socio- economic conditions, including nomadism (b) Land utilization and agriculture and (c) Destruction of vegetation for fuel, fibre, wood and fodder. Indirect influences include (a) Domestication of animals (b) Overgrazing of natural pastures (c) Dissemination of seeds of undesirable species (d) Degradation of the micro-climate following the disappearance of the vegetation (e) Introduction of exotic species at the expense of indigenous species for plantation etc. and (f) The action of chemical products such as pesticides, herbicides etc. These have been reviewed in this article.

DIRECT INFLUENCES

H u m a n p o p u l a t i o n a n d t h e i r s o c i o - e c o n o m i c c o n d i t i o n s

The relation between the distribution of population and the avail- ability of water in arid regions is obvious, but variations do occur on account of difference of topography, soils, landuse, occurrence of economic minerals, accessibility and other socio-economic factors. The density of population in Western Rajasthan is high by the general arid zone standards and is chaxacterised by the practice of nomadism (Bose et al. 1964). In Jhunjhunu, Sikar, Pall, Jalor and Nagaur districts the density is respectively 315, 271, 168, 136 and I I I per sq mile which decreases fairly rapidly towards the west to 103 in Churu, i o I in Jodhpur, 64 in Barmer, 42 in Bikaner and 9 in

ANTHROPOGENIC INFLUENCES IN W. RAJASTHAN 81

Jaiselmer districts (ALl, 1964). It is a paradox that the total population of the Indian desert adds up to 7.6 million (according to i961 census); it was 5.9 million in 1951 . This gives a net increase of 23 during the decade, the corresponding figures for India and Raja- sthan for the same period are 31.5o and 26.2o % respectively.

In the absence of social and financial aid and scientific and tech- nological assistance the population till now tended to overexploit their natural resources. Where large scale water resources from outside the arid regions could not be tapped, the inherently small water resources within the region set the ultimate limits for production of plant material on which both human and animal populations are finally dependent. Furthermore, erratic rainfall results in widely fluctuating production and this in turn leads to famine periods im- posing periodic stress on the population. As population increases, these increases become greater so that tile demand on natural resources is magnified. Eventually, the consequence is an imbalance between the human and animal populations on the one hand and the plant, water and land resources on the other. As the demand by the first is persisting and incerasing, the resources tend to become depleted and as depletion proceeds the stress upon them becomes greater. Thus, there is set into operation a process of progressive degradation of resources which is accelerated during every famine period and immediately thereafter. If continued unchecked, it leads to permanent damage by the loss of valuable plant species through excessive grazing, or cutting for fuel, their replacement by bare land, or at the best by useless plant communities, the loss of surface soil by water and wind erosion, lower soil fertility and ultimately the occurrence of large areas of wastelands cut by deep erosion channels or of barren sand dunes (GuPTA, 1966), which are not only unproductive but may involve considerable expenditure of public money where these encroach on community services. The cumulative effect of all these processes is to make significant changes in both the hydrology of the region and its micro-climate tending towards the creation of more arid and less productive environment than the original status of the region. Thus new deserts are formed. The final outcome, if uncontrolled, must be greater and greater stress on the human populations, less return per unit of effort and lower standard of living.

The practice of nomadic pasturing, though generally condemned, is often considered as the principal cause in the deterioration of arid zone vegetation, which is already poor. The nomads are not in- terested in the conservation of the local vegetation and pastures which do not belong to them and have a tendency to exploit them to their maximum (Bose et al., I964).

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L a n d u t i l i z a t i o n a n d a g r i c u l t u r e

The present land utilization in the arid regions of Western Rajasthan reveals that the cultivated and fallow fields together occupy more than 4/5 of the total area. Tehsils of Barmer, Pach- padra and Sanchor do not have even 1 % of the area under irrigation, in other tehsils the extent of irrigated area is about 5 ~/o; chief source of irrigation is wells. Thus bulk of the cultivated land grows only Kharif crop which is entirely dependent upon the vagaries of the monsoon and subsistence farming is practised. The main crops are Bajra, Moth, Yfong and Guar with wheat, barley, oil seeds; vegetables and fodder crops are grown to a smaller extent. Since the main crops are human food crops their continued production is essential, but if continued according to the present pattern which include many unsuitable land types, further degradation of resources would result. Efforts, therefore, are essential to concentrate crop production on more suitable sites, compensating for smaller areas by improved methods of production, thus further reducing the demand for land and thereby conserving the vegetation. The tradi- tional method of land use which is to concentrate around water sources and carry out extensive instead of intensive agriculture which have been long adopted in the region have further led to the serious degradation of native plant communities.

D e s t r u c t i o n of v e g e t a t i o n for fuel , f ibre , w o o d a n d t o p - f eed

(I) Fuel and energy: In contrast to the arid regions of Australia, United States, Israel etc. where kerosene, natural gas and petroleum provide the bulk of energy, in Rajasthan natural vegetation forms the chief source of fuel besides contributing to the requirement of small timber for agricultural implements and fencing material. The rapid growth in population has inflated the demand for fuel resulting in the indiscriminate cutting of shrubs and trees. The fuel requirements are generally met by Pros@is cineraria (Khejri); P. juli- fora (Vilayati-babul), Salvadora oleoides (Jal), S. persica (Kharijal), CaUigonum polygonoides (Phog), Tamarix sp. (Jhau); Cassia auriculata (Anwal), Butea rnonosperma (Palas), Acacia jacquemontii (Bawali), Capparis decidua (Kair), Euphorbia caducifolia (Thor) besides the scrap- ings of shrubs and herbaceous vegetation from the ground soon after the monsoons. The fuel value of the various species is P. juliflora 8o5o , P. cineraria 765 o, Zizyphus sp. 7875, Capparis decidua 7825, Euphorbia caducifolia 78oo, Acacia nilotica ssp. indica 77oo, Albizia lebbek 76oo and Salvadora oleoides 7ooo BTU/lb.

The burning of cow dung is another chief source of fuel and we could ill afford it as it represents a loss of plant nutrients which


could well be used to advantage in agriculture in these days of food shortage. The recent development of bio-gas plant though provides a way out but only to those with the requisite capital resources to utilize dung for providing heating and at the same time retaining most of the plant nutrients as fertilizers. Vegetation used for fuel in the arid areas will require regeneration and improved means of harvesting and exploitation than that has been practised in the past. It has been estimated that about 700 maunds of fire wood is required for an average village of 55 ~ people or say IOO families (NcAEI~ 1959).

(~) Wood for agricultural implements: Trees and shrubs are put to multifarious use by households in Western Rajasthan. Plants like Anogeissus pendula, A. sericea, Acacia nilotica ssp. indica, Tecomella undulata are used for making ploughs since the wood is of superior quality. In the construction of huts and semi-pucca structures Prosopis cineraria, Azadirachta indica, Acacia nilotica ssp. indica and Tecomella undutata are put. Socio-economic survey of the Luni basin (Bose 1963, Div. Report, CAZRI) has revealed that locally available trees and shrubs are utilised to the maximum, particularly for meeting the requirements of housing, fencing, animal feed and for making ropes and baskets. For making agricultural implements, however, the timber is purchased when local resources prove in- adequate.

(3) Fibre for cordage, ropes and baskets: Thick ropes for irrigation made of Bauhinia racemosa, Acacia nilotica ssp. indica are used while other plants used for making ropes are Leptadenia pyrotechnica, Crota- laria burhia and Calotropis procera. One outstanding feature in the use of trees and shrubs in the region is their non-commercial use. Branches of Vitex negundo and Acaciajacquemontii are also twisted for making baskets for local use.

(4) Top-feed: BHIMAYA et al. (1964) have shown that intensity of lopping does not affect adversely the growth of trees. Recurrent lopping definitely reduces the leaf fodder yield irrespective of intensity of lopping due to successive reduction in the overall surface of new shoots, thereby suggesting definite need for evolving a system of rotational lopping, giving the trees just the right period of rest which may be needed for sustained leaf fodder yield. Prosopis cineraria (Khejri), besides being a timber, provides valuable fodder. The young coppice form is very difficult to kill and mature trees withstand annual lopping to a remarkable degree. Other top-feed species in order of preference are Acacia nilotica ssp. indica (Babul); gizyphus nummularia (Bordi); Acacia senegal (Kumat), Albizia lebbek (Siris); Azadirachta indica (Neem) ; Maytenus emarginata (Kangkera); Calligonum polygonoide~ (Phog); Prosopis juliflora (Vilayati-babul) and Tecomella undulata (Rohida). From the point of view of palatability

84 R.K. GUPTA

and nutritive value P. cineraria and Zizyphus nummularia are the best top-feed for cattle, sheep and camels, while Calligonum polygonoides, Salvadora oleoides, Salvadora persica and Maytenus emarginata are some of the leaf fodder for camels (GA~QtmI et al., I964). Since some of the top-feed species viz. P. cineraria, Zizyphus nummularia and Acacia sp. remain green during the dry season they add substantially to the fodder resources during the lean period of the year. Though leaves of Salvadora oleoides, Calligonurn polygonoides and to a limited extent Calotropis procera along with twigs of Capparis decidua are un- palatable to the bovine population, they form useful top-feed for sheep during dry weather.

INDIRECT INFLUENCES

D o m e s t i c a t i o n of a n i m a l s

BHIMAYA (I963) discussed the effect of animals on the conservation of soil in the arid regions of Western Rajasthan. Main domestic livestock of economic importance to the people are draught cattle, milk cattle (milk and ghee), sheep (carpet and rug wool), goats, camels, buffaloes, horses, donkeys, pigs and poultry. Most important are cattle, sheep, goats and camels. Rajasthan is the source of many well known breeds of cattle such as Nagour (trotting and draught), Sanchor or Kankrej (milk and draught), Theri (milk and draught), Rathi (milk), Thar Parkar or Malani (milk), Hariana (milk and draught) and many aninals are exported to other parts of India every year. The density of animal population ranges from 3 per km ~ in Jaisalmer to 12o in Jhunjhunu districts. Its animal production expressed as cattle units has an average density of 177 per ioo grazing hect. (Population statistics office census operation).

O v e r g r a z i n g o f n a t u r a l p a s t u r e s

Animal husbandry is the main occupation of some of the people of the desert tract and they keep large herds which move from place to place in search of new pastures, but this movement is governed by available watering places. The pastures where water is scarce remain ungrazed. A considerable period of the day is wasted on visits to the watering places for drinking. This results in heavy grazing en route and around a few watering places and loss of actual grazing hours. A very large number of herds of goat, sheep, camel and other animals move to eastern districts or outside the state and return on the onset of monsoon.

The influence of these animals modifies in various degrees the plant succession, resulting in the replacement of undesirable species of low nutritive value and palatability at the expense of highly palatable and nutritive fodder species. The fertile lands are converted

ANTHROPOGENIC INFLUENCES IN W. RAJASTHAN 8 5

into desert tracts, continued removal of trees and shrubs and practice of uncontrolled grazing has caused such deterioration. Some of these tracts, denuded of trees, have under favourable climatic conditions tended to evolve permanent grassland cover of good value, sometimes interspersed with a spattering of trees and more often with shrubs. These represent a sub-climax and become stable under a complex of environmental factors favourable for its existence and development. An evolution of this nature has taken place in Western Rajasthan, where in historical times forests inhabited by elephants and Rhinoceros existed (HoRA, I952 ). In places where human and animal activities are restricted excellent stretches of good palatable and nutritive species can be seen, whereas in areas with continued biotic activity there exist over-grazed and almost barren sandy tracts.

D y n a m i s m of the n a t u r a l v e g e t a t i o n

Successional changes and forage production under the influence of grazing from the aspect of pasture ecology has been studied at the range management and soil conservation centres of Central Arid Zone Research Institute, Jodhpur. With the elucidation of the relationship between the pasture species and their edapho-climatic environment, the effect of biotic factors assume increased importance. DAS & BHIMAYA (1964) have shown at Beriganga that annuals in the initial stages constituted 71.o2 % having Aristida funiculata, A. adscensionis as the dominant plant which together contributed 58.4 %. After three years of controlled grazing, percentage of perennial grasses like Eleusine compressa, Cenchrus ciliaris, C. setigerus and Eremopogon foveolatus increased by 12. 9 ~/o over the initial index. Eleusine cornpressa, Cenchrus ciliaris, C. setigerus and Eremopogon foveolatus increased by 12. 9 % over the initial index. Eleusine compressa increased by 7.9 % while Cenchrus recorded an increase of 5.5 %. It is clear that under light intensities of grazing grasslands maintain at a higher level and show positive trends of range regeneration over the initial stages. Taking into consideration the variation in plant cover as influenced by sheep grazing, it was reported that it increased from lO.25 % to 28.27 % during the same period as above. The data regarding the contribution of individual species is given in Table I.

Similar studies on the rocky ranges at Kailana showed similar data on the vegetational changes, floristic composition and plant cover. Under the influence of controlled grazing the percentage plant cover increased from 16.6 to 23.78 %, the perennial grass cover increased from 8. 7 to 14.82 % in the course of three years.

In Pall, Jalor and Sikar districts, where the rainfall is from 30--4 ~ cm, the hills support Anogeissus pendula sometimes pure and often

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TABLE I

Trend in changes in plant cover from 1957--6o as influenced by sheep grazing (after DAS & BHIMAYA, 1964)

S. No. Plant species % plant cover % variation under grazing

Before 1957 After 196o impact

Aristida sp. 2.81 4.71 1.96 Eleusine compressa 2.09 9.07 6.98 Cenchrus sp. 1.o 4 o.6o -o .44 Eremopogon foveolatus o. o i 3.15 3.14 Oropetium thomaeum O.Ol o.77 o.76 Melanocenchris jacquemontii 30 o. 12 - o. 18 Non grasses ~.86 9.oo 6.i 4 Others o.97 - - - o.97

Changes in the botanical composition from 1957--6o under light intensities of grazing (after DAS • BHIMAYA, 1964)

S. No. Plant species % composition % difference

Before 1957 After 196o

i. Aristida sp. 54 .8 49.5 - 5 . 3 2. EIeusine compressa I9.3 27.2 7.9 3. Melanocenchris jacquemontii 9,7 o.8 - 8 . 9 4. Eremopogon foveolatus 3.9 3.2 - o . 7 5. Cenchrus sp. 5.6 I I.I 5.5 6~ Schonefeldia gracilis 2.4 - - - 2 . 4 7. Brachiaria ramosa 2. I - - -- 2. I 8. Tetrapogon tenellus 0. 9 - - --o. 9 9. Oropetiura thomaeum 0.5 8. i 7.6

Io. Dactyloctenium sindicum 0.2 - - - 0 . 2 I I. Schina ischaemoides 0.2 - - - o.2 !2. neteropogon contortus 0.2 - - -0 .2 13. Sporobolus sp. 0.2 - - -0 .2

m i x e d wi th Acacia senegal. Shrubs like Zizyphus a n d Grewias occur . A m o n g the grasses Sehirna nervosum, Haekelochloa granularis, Bothri- ochloa pertusa a l o n g w i t h n o n - p a l a t a b l e grasses o f regressive stages like Aristidas (A. mutabilis, A . adscensionis, A . funiculata) are present ; less p a l a t a b l e grasses are Andropogon pumilus, Cymbopogonjawarancusa, C. martinii, Heteropogon contortus, Tetrapogon tenellus a n d Eremopogon

foveolatus. O t h e r annua ls , i n c l u d i n g l egumes a n d forbs are few. T h e r e are b a r r e n hills w i t h o u t a n y vege t a t i on excep t a few shrubs o f Euphorbia caducifolia, Grewias a n d Zizyphus nummularia c o m i n g u p ; in crevices a n d val leys w h e r e some soil has col lected, s tun ted trees o f Acacia leucophloea a n d A. senegal wi th infer ior grasses c o m e up .


The Euphorbias appear to come up whereever the original tree vegetation has been cut down. It affords protection to seedlings of tree species from being browsed offby livestock and allows them to estab- lish themselves. In addition to cattle, sheep and goat, animals like Sambhars, Neelgai, Chinkara, wild Boars, Hyena, Hares, Jackal along with few game birds like Francolin, Painted Francolin, Painted sand gourse, Rock quails, Bush quails and green pigeons are associated in the eco-system. The successional trends in the ecosystem are represented in the Schematic diagram. These hills are subjected to severe water and wind erosion as a result of constant grazing and cutting of bush and tree species. The soils are shallow and strewn with pebbles and boulders. Folds of the hillocks where most of the eroded soil gets deposited have deep silty soils with some amount of moisture. Pioneer species to appear first on bare rocks are Oropetium thomaeum, Melanocenchris jacquemontii and Aristida sp. and last to survive in downward trend when the area is subjected to extreme biotic influence. Eleusine compressa, Cynodon dactylon and Dactyloctenium are of medium fodder value but of great significance in soil conservation and are the seral species under reversal progress of retrogression to climatic climax.

Deep sandy plains with shifting sand, stabilised and unstabilised sand dunes in Jaisalmer, Nagaur, Bikaner, Churu and Jhunjhunu districts, where the rainfall varies from 3o to less than 5 cm are subjected to severe wind erosion. The soils are deep coarse sand to sandy loam with poor water holding capacity. The areas remain dry, since whatever precipitation occurs it passes underground and remains nnutilised by the vegetation. Scattered trees of Pros@is cineraria, Acacia senegal and xerophytic scrubs of Zizyphus , Acacia jacquernontii, Ca[otropis proeera, Aerva tomentosa, Cal[igonum polygonoides, Indigofera oblongifolia are the characteristic plant species. Here occurs the vegetation which does not require much soil moisture or is capable of producing deep root system to conserve its own moisture and use it during periods of drought. The most important grasses in the successional ladder are Lasiurus sindicus, Cenchrus ciliaris, C. setigerus, Panicum turgidum and Panicum anlidotale. Eragrostis, Aristida and Cenchrus biflorus are the pioneers as they are first to appear on pure sands and last to disappear under heavy biotic influences. Cynodon dactylon, Eleusine cornpressa and Dactylocteniurn sindicum along with Crotalaria, Aerva and Calligonum occupy middle steps of the successional ladder. The perennials provide excellent fodder for the cattle. Soon after the monsoons the annuals dry and disappear and only few patches of Lasiurus, Panicum and Bothriochloa remain green and provide grazing.

The saline soils with excessive soluble salts of sodium and calcium and alkaline soils with excess of free sodium and insoluble sulphates

88 R .K . GUPTA

and carbonates of sodium, calcium and magnesium occupy very little area. In places where salt concentration becomes milder because of natural leaching, halophytic vegetation consisting of Salvadora persica, Suaeda fruticosa, Tamarix and Haloxylon sp. occur. Common grasses are Sporobolus helvolus, Chloris barbata, Chloris virgata

Euphorbia cadudfolia < (Biotic cllsclimax)

Acacia senegal Anogeissus pendula (climax)

Cordia gharaf Commiphora wightii Grewia tenax

Barleria prionitis Lepidagathis trinervis

T Cymbopogon Eremopogon foveolatus

T Gisekia pharnacoides Tephrosia pterosa

I Protection from grazing

Aristida sp. Oropetium thomaeum

Hackelochloa granularis

t Bothriochloa Brachiaria sp.

Sehima nervosum (climax)

T �9 Eremopogon foveolatus

Heteropogon contortus Cyrnbopogon sp.

Cynodon dactylon Dactyloctenium sindlcum Eleusine compressa

Eragrostis sp. - Aristida sp.

T Oropetiurn thornaeum Melanocenchris jacquernontii

(Skeletal soils)

(After SATYANARAYAN, I964)

(Bare rock and shallow soils)

(Modified from PRAKaSI~ & NANDA, I961)

Schematic diagram I. Succession in the grassland and forest ecosystems on Detached hills of granite, Rhyolite and sand stones. (Precambrian and Vindhyan).

etc. Since the trees and shrubs are sparsely distributed, most of the area is covered by grass species. The successional stages are shown in the schematic diagrams.

D i s s e m i n a t i o n o f t he s e e d s o f u n d e s i r a b l e s p e c i e s

The socio-economic conditions of the inhabitants in this part are such that the native vegetation is a part and parcel of their daily life. Undesirable species which are less in demand are only left. The


Prosopis cineraria- Salvadora oleoides

Zizyphas nummularia- Capparis decidua

t Balanites aegyptiaca Fagonia cretica

t Dactyloctenium sindicum Eleusine compressa

Zizyphas nummularia

T Indigofera cordifolia Cassia auriculata

t Dichanthium annulatum Gemhrus setigems Dactyloaenium sindicum

t

Prosopis cineraria Acacia nilotica sp. indica

t Zizyphas nummularla

T Cassia auriculata Indigofera cordifolia

t Dichanthium annulatum Cynodon daaylon

f Aristida - Melanoeenchris jacquemontii

(Coarse loamy sand) (Sandy clay loam) (Irrigated sandy loam) (After SATYANARAYAN, 1964)

Schematic diagram 2. Successional I stages in the grassland and forest ecosystems on the older alluvial plains.

Proso~Ois cineraria- Salvadora oleoides (climax)

t t Tamarix troupg Salvadora persica

l Tamarix dioica

t Sar spontaneum Capparis deddua Desmostachya bipinnata Vitex negundo

t t Xanthium stmmarium CrotaIaria burma Solanum surattense Tephrosia #urpurea

1 Launaea nudicaulis Desmostachya bipinnata

Saccharum spontaneum

T Desmostachya bifinnata

t C. ciliaris Dactyloctenium sindicum

t Eragrostis sp. Cenchras bifloras

t Cyperas - Aristida

(Coarse gravelly sand) (Deep loamy sands) (River bed terrace)

(after SATYANARAYAN, 1964)

Desmostachya bipinnata Sporobolus helvolas

salinity

Genchras biflorus

T Cypems - Aristida

(Sandy soils liable to inundation)

Schematic Diagram 3. Successional stages in the grassland and forest ecosystems on younger alluvial plains of Western Rajasthan.

9 ~ R . K . GUPTA

Sporobolus Dichanthium annuIatum

t Echinochloa colonum

t Chloris vorgata

t Eragorstis sp. Trianthema sp. Aristida-PortuIaca

t Cressa cretica

t Cypems roomdus

(Depressional saline areas)

Leaching l Leaching I

Genchrus ciIiaris- G. setigerus G. preurii - Desmostachya bipinnata

t t Sporobolus sp.

T Cynodon daaylon- Chloris barbata Chloris virgata - Cenchrus biflor~

(Bare kallar soils) (modified after Pr.a1~Asa & NA_~A, i96i ).

Schematic Diagram 4. Showing succession on the saline and alkaline soils in the grassland ecosystem of Western Rajasthan.

Prosopis cineraria ~ Salvadora oleoides

(climax)

t Prosopis cineraria TecomeIla undulata

Maytenus emarginata Acaeia jacquemontii Balanltls aegyptia~a Maytenus emarginata

Balanites aegyptiaca

l t Cymbopogon sp. Calligonum polygo~ides Leptadenia pyrotechnica Panicum turgidum Grotalaria burhia Leptadenia pyrotechnica Lasiurus sindicus l Panicum antidotale

Cenchrus biflorus Lydum barbarum Dactyloctenium sindicum Crotalaria burhia

Aerua persica

I t Mollugo nudicaulis Indigofera argentea Indigofera argentea Cyperus arenarius

Sandy plains Sand dunes (Deep fine sands) (Deep fine sands)

(after SAT'Z~ARA'ZA~, 1964)

Panieum turgidum Lasiurus sindicus

T Cenehrus setigerus G. preuril- C. ciliaris Panicum antidotaIe

Cynodon dactylon Eleusine compressa Dactyloctenium Cymbopogon sp.

t Aristida- Eragrostis Cenchrus sp.

Sand dunes

(modified from P~AKASH & NANDA, I96I )

Schematic Diagram 5. Successional stages in the grassland and forest ecosystems on the sandy plains and sand dunes of Western Rajasthan.


result is that they propagate themselves freely and the seeds are con- stantly disseminated making them dominant over vast areas. On the hills may be seen Euphorbia caducifolia, which is only used sometimes for fuel, on piedmont slopes and plains Tephrosia purpurea is the most dominant species and is hardly of any use. Other such species in the plains are Cassia auriculata, which to some extent is exploited for tannin, Crotalaria burbia, Calotropis procera, Fagonia cretica etc. On saline soils Suaedafruticosa, Cressa cretica may be mentioned. In general, it has been observed that among such plants members of the families Asclepiadaceae, Leguminosae, Compositae are most common and have also suitable contrivances for the dissemination of their seeds over vast areas.

D e g r a d a t i o n o f t he m i c r o - c l i m a t e f o l l o w i n g t he dis- a p p e a r a n c e o f v e g e t a t i o n

The destruction of vegetation, particularly the forests, radically modifies the micro-climate of the region, especially the wind speed, temperature and humidity of the air near the ground. The climate becomes less favourable for the existing vegetation and also for the regeneration of plants. It is this situation which was created during the past and is continuing even today. The progressive denudation of land exposes the soil to the furry of the wind and direct impact of rain results in rapid erosion. Inter-relationship of the micro-climatic zones and vegetation in this part has been discussed by RAI-IF.JA (I965). In consequence of the changes from intergacial climate in the upper Pleistocene to the present-day hot arid climate the vegetation must have changed from temperate evergreen forest growth to present-day xerophytic plants (LAKI-IANPAL & BOSE, I95 I). Forest vegetation according to THORNTnWAIT~. (1958) loses 5--10 % of the incoming radiation reflected, while grass, shrubs and cultivated green crops lose 15--3o %. The albedo of bare dry sand is 18 %, that of wet sand is 9 %- Thus the loss of plant cover aggravates the disequilibrium between the moisture level and the heat so that micro-climate of the region previously copiously watered and having considerable vegetation tends to be arid.

Recent studies (RAHEJA, 1965, BHIMAYA et al., 196o , 1961 ) have shown that the extension of area under irrigation and regeneration of extensive area with suitable grass and other species influence the wind speed, flux of heat from the soil and other micro-climatic factors. The technique of regeneration and suitable species for afforestation, techniques of planting, survival percentage of species and nursery techniques have been separately recorded (BHIMAYA et al., 1961 , BHIYIAYA & KAUL, 196o ). These studies have shown that rehabilitating the areas with vegetation which at present are de- teriorating is likely to influence the micro-climate of different parts of Western Rajasthan.

92 R.K. GUPTA

I n t r o d u c t i o n o f e x o t i c spec ie s

The reforestation of the desert regions with suitable quick growing species in order to check the spread of desertic conditions to other parts of the country and sand dune stabilisation has been attempted in this part and many exotics such as Eucalyptus, Acadas and Prosopis juliflora and other species from analogous climatic regions of the world have been tried (KAuL, I964). Prosopis juliflora has been introduced in the region as far back as I877 and is perhaps the only exotic capable of growing on a wide variety of soils and situations and micro-climatic effects become favourable. In I94o it was de- clared as the "Royal plant" and was placed under government protection. I t forms one of the main species in the dry zone afforestation programme. Its phytotoxic effects on the underground vegetation does not seem to be very encouraging (SA?qKHALA et al., I965; LAHIRI, I966 ). Though during the recent years many species have been introduced in the region it is difficult to say what their effects will be on the natural regeneration of the vegetation and how they will compete with the indigenous species. Moreover, experi- ments at some places have been successful in the first rotation but in second or/and subsequent rotations the species may either not show sufficient growth or may suffer from ill effects of climate, or fungus or insect attacks. This is a basic factor met with even in commercial plantations with species like teak and forms no basis for discouraging plant introduction as when this happens solutions can be found.

A c t i o n of t he c h e m i c a l p r o d u c t s s u c h as h e r b i c i d e s a n d p e s t i c i d e s

The action of herbicides and pesticides, though used on a mod- erate scale in agriculture, disturbs the vegetation to some extent although it may not be very appreciable.

SUMMARY

Western Rajasthan, forming a part of the That desert, is admit-- tedly dry, very hot in summer and is generally poor in vegetation. Though various causes for the origin of this desert have been attributed by climatologists, geographers and geologists, based on anthropological evidences it seems that there has ~been severe destruction of vegetation during the past. Over this landscape was superimposed the present day conditions, mainly the human influences, direct and indirect, on the vegetation, thus making the conditions still arid. From the observations it is seen that the water table in tube wells in some villages is good, patches of good density of vegetation are present where managed properly or dedicated to some deity. The rainfall, though scanty, is sufficient to support


vege ta t ion and i f some rest is g iven the c l imax is r eached especial ly where the nucleus exists. T h o u g h cl imat ical ly the a rea is d ry bu t no t arid, soils are poor bu t not infertile a n d evidence is said to be there tha t in the past it suppor t ed good evergreen vegeta t ion . I m - med ia t e es tabl i shment of vegeta t ion, even on act ive sand dunes, can be seen even t oday i f an a rea is p ro tec ted r igidly f rom h u m a n and a n i m a l influences. D u r i n g d rough t periods there m a y not be a n y a u g m e n t a t i o n of vegeta t ion, yet those a l r eady establ ished live, stabilise the soil a n d pe rpe tua t e the progress o f vegeta t ion. W i t h p ro tec t ion not only the grasses a n d r ank vege ta t ion come up bu t even species like P. cineraria come up. I t m a y therefore be safe lysa id t ha t R a j a s t h a n desert, i f no t a " m a n m a d e deser t" is surely a " m a n m a i n t a i n e d deser t" .

ACKNOWLEDGEMENTS

T h e au tho r is deep ly indeb ted to SI-mi C. P. BI-IIMAYA, Di rec to r a n d Dr . B. B. RoY, H e a d of the Division, Basic Resource Studies, Cen t ra l Ar id Zone Resea rch Ins t i tu te for thei r cons tan t he lp a n d encouragemen t . T h a n k s are also due to SI-IRI S. K . SAXm~A, Senior Resea rch Assistant, for his help dur ing the tours.

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Anthropogenic influences on the vegetation of Western Rajasthan

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