Proc. Indian Acad. Sci. (Plant Sci.), Vol. 94, Nos 2 & 3, April & May 1985, pp. 505-523. 9 Printed in India. Strand plant communities of the Indian sub-continent T ANANDA RAO and V M MEHER-HOMJI * The Karnataka Association for the Advancement of Science, Central College, Bangalore 560001, India ~ Fran~:ais, Pondicherry, India Akstraet. Strand plant-communities, other than the mangroves, composed of psammo- phytes, halophytes have been desc¡ along with bioclimatic, edaphic factors for the seven coastal biogeographic sub-dtvisions of the sub--continent. Keywords. Strand plant communities; psammophytes; halophytes; bloclimatic factors; edaphic factors. 1. Introduction Coastal landscapes of the Indian sub-continent comprises of an array of ecosystems. The wet coastal ecosystem or the mangrove swamps and the dry coastal ecosystems or strand or beaches are recognised on sight based combined physiognomic and topographic criteria. That these studies are not only of great theoretical but also of practical interest has been recently shown by detailed reviews (Rao 1971; Rao and Sastry 1972, 1974 a, b; Blasco 1975, 1977). Since the mangals or mangroves have already been studied (Chapman 1977), we will review in this article the strand or beach plant-communities (other than the mangals) composed of psammophytes, facultative halophytes or salt toierant glycophytes and also mention briefly the potential terrestrial vegetation in the immediate vicinity of the strand. At the very outset it may be mentioned that the environmental terms 'dry' and 'wet' as applied to the coastal ecosystems appear rather conflicting. Mangrove which in a strict sense of the term cannot be treated asa 'wet' ecosystem because of the physiological dryness of the habitat, however, has been included in the volume on Wet Coastal Ecosystems. Dry and wet categories are distinguished on the basis of the general climatic features like annual average rainfall and length of the dry season. Thus on one hand lie very dry stations like Pasni, Karachi, Bhuj, Dwarka in the northern extremity of the west coast with rainfall less than 500 mm and dryness for 10 to 11 months of the year. In the southern part of the west coast, Kozhikode (Calicut) and Trivandrum represent very wet conditions with very high rainfall (exceeding 3000 mm) and with only 3-4 months of dryness. However, such a climatic division is rendered ineffective in view of the overwhelming edaphic influence of sandy and salty milieux in the immediate vicinity of the sea, imparting floristic and physiognomic homogeneity to the plant communities of the mafitime strand. It is true that the plant formations beyond the confines of the maritime influence show closc relationship with the macro-climatic features. 505 506 T Ananda Rao and V M Meher-Homji The maritime strand is that strip ofcoast extending from just above mean high water to the end of the sandy relief. This area is characterised by a maritime climate, high exposure to salt spray and shifting sand dunes. They are lithologically different and can be categorised under calcareous and non-calcareous zones with significant plant indicators. Rao and Sastry (1972) have attempted ah improvement on the informal strand ecosystem classi¡ of the past workers. They have recognised three major types, namely strand sand, strand rock and strand coral based on combined physiognomic and topographic criteria. Further, these have been subdivided on the basis of zonation, dominant species and substrate features. This has revealed apparent zonation in some sectors and disturbed mosaics in others speciaUy at the woodland stage mostly due to anthropogenic influences such as agricultural practices (paddy cultivation), raising of plantations of Casuarina, coconut and cashewnut in climat- ically humid zones. 2. Biogeographic sub-divisions The coastline of the Indian sub-continent which extends for more than 6000 km may be divided into the foUowing sub-divisions according to the climatic and general floristic features. Geologically, the entire coastline may be broadly placed under recent aUuvium. (i) Coastal tract of Pakistan, Kutch and north-western part of Kathiawar formin O eastern extremity of the Saharo-Sindian region of Eig (1931). The climate as exempli¡ by the stations Karachi and Bhuj (figure 1) is arid with annual average rainfall of less than 500 mm and 9 to 11 months ofdryness as per definition of Bagnouls and Gaussen (1953). Natural vegetation in the sub-coastal plains is a thicket of Prosopis cineraria (L.) McBride-Salvadora oleoides Decne. type. The thicket aspect is given particularly by the bushes of Euphorbia caducifolia Haines which is the main species in the degraded areas where the soil is shallow and there ate outcrops of rocks. Ir withstands the effect ofsalty winds. (ii) South-eastern Kathiawar and Gujarat north of the river Narmada may be included in the eastern half of the Sudano-Rajasthanian reoion of Meher-Homji (I965). The climate of this tract is semi-arid with rainfaU of 500-600 mm and dryness of 8 months. Ombrothermic diagram of the station Veralval in figure 1 illustrates this type of climate. Thickets of Acacia spp. and Capparis decidua (Forsk.) Pax are encountered in the areas beyond the strand. The branching palm, Hyphaene dichotoma (White.) Furtado is dominant in the Delvada-Kodinar sector. (iii) Konkan coastal strip extending from southern Gujarat up to Goa. Climate varies from dry (e.g. Surat) to subhumid (Bombay) to humid type (Ratnagiri, figure l). The dry or moist deciduous forests with teak (Tectona grandis L.f.) form the potential natural vegetation beyond the maritime influence. Strand plant communities 507 ~ ) li o I ooo ,,; ~ . ~ "~" i=~t_,,s> : .I/,," ..... ~ ~. = = . _ ~= 7 > 1~{= \ ~ ~ i LI - -"1 i ~~176 ~ . ~-~=--_~~-~ o <a ~ .... ~-~,~ . :<~ o ~ - ~-.~o o . ~~ i ~.-~,~ , ~, 9 ~ 9 I= . "<~ ~o="~" o . Ÿ " .... ~~'73 Q N Ix ....... ~ ~ ~~ ~'-. ~~ " --------,w~: ~ / ~ ~ ~ - ~t ",i ~ - I 91/ : ,~~ o Q :. =n = == . - _ ~= , ; _ ~'~7--- '-~=: .u 508 T Ananda Rao and V M Meher-Homji (iv) Malabar region extendin 9 from Goa southwards up to Kanyakumari (Cape Comorin). The climate is humid (Mangalore) to perhumid (Kozhikode and Trivandrum, figure 1). The areas beyond the limit of the coastal sands have the potentiality to bear evergreen forests but through human interference the original forests are much degraded in the coastal tract and much of the arca is brought under cultivation. (v) Coromandel-Circar coastal plains of Tamil Nadu and Andhra Pradesh of the South- eastern part of India, characterised by tropical dissymetric regime of rains. South-west monsoon brings only light rains during June-September; heavy rains occur in October-November due to the depressions formed in the Bay of Bengal. Climate is dry (Paraban) to subhumid (Madras and Visakhapatnam, figure 1). Potential vegetation of this tract is peculiar: dry evergreen forest (Champion 1936; Meher-Homji 1973, 1974; Blasco and Legris 1973; Sprangers and Balasubramanian, 1978; Werger and Sprangers 1982). (vi) The islands between India and Sri Lanka though climatically similar to the Coromandel coast differ from the mainland in having coral sand and distinct vegetation (Rao et al 1963a, b). (vii) Utkal and Bengal coastalplains The Utkal coast is the northern prolongation of the Circar region in Orissa state. It is formed of the Mahanadi delta and the coastal plains of Bhadrak, Balasore and Kunthi. The Chilka lake of Puri district which though only a few metres deep varies in size from 900-1200 km' and is a!ternately salty and fresh. The Medinipur coast marks the extension of the Utkal coast into Bengal. The climate as exemplified by the stations of Puri and Balasore (figure I) is humid. The potential vegetation of the interior areas is typified by deciduous sal (Shorea robusta Gaertn.) forests, Along the sandy fringes, Borassusflabellifer L. and Phoenix sylvestris Roxb. are commonly met with. Figure 1 shows the c•astal habitats of the sub-continent. The strand sand type is dispersed on the sandy relief beyond the mean high tide limit. Zonation of the vegetation into an outer pioneer zone, a closed herbaceous zone, middle mixed or bushy zone and inner woodland zone can be made out (Rao and Sastry 1972). The outer pioneer zone is characterised by the community of lpomoea pes-caprae (L.) R. Br., Spinifex littoreus (Burm.f.) Merr, Cyperus arenarius Retz., Canavalia maritima (Aubl.) Thw. and Launaea sarmentosa (Willd.) Alston throughout the sub- continenc 3. Pakistan, Kutch, North-western Kathiawar The coastal area may be divided into three sub-divisions: shore, coastal and sub- coastal plain (Rao and Aggarwal 1964). (a) Sandy strandflora: The pioneer plant is lpomoea pes-eaprae, a strand creeper. Closely following it on the back shore in order of relative abundance are Cyperus arenarius, Launaea sarmentosa, Borreria articularis (L.f.) F. N. Will, and Boerhavia diffusa L. (figure 2). Strand plant communities 509 10 Z~t 91 ort/cu[oris I i Co/otropt$ 9rocBro LounoBo sarmentosa i] Ah':I j ~ P$ilo$lochy$ $OflC~ Se$ovtum porluloco~trum Ipo~aeo ~~=coproo DUNE PROF[LE o Jo Ÿ :5o 40 so 60 7o so ~o [o~ qlO IZO 130 140 rSO q6O r?o I$0 I~)O ~o0 Figure 2. Percentagecover and zonal pattern of the strand, dune plants in a belt transect over a coasta[ strip, Kathiawar. Near Dwarka and Okha, Asparagus dumosus Baker is a localised strand species. Around Gharo village in the Indus delta (Pakistan), the sand and sand-dunes are covered with Convolvulus seindicus Stocks, Leptadenia pyrotechnica (Forsk.) Decne., Launaea resedifolia (L.) O. Ktze., Aerva persiea (Burm.f,) Merrill and Asparagus 9haroensis Blatter besides Ipomoea pes-eaprae, Launaea sarmentosa and Cyperus arenarius (Blatter et al 1929). Soils are sandy to sandy loamy in texture, moderately alkaline (pH 8-8-4), low in organic matter which ranges from 0"25-0"64 ~/o- Calcium carbonate ranges from 13- 92 ~. Sodium chloride from 0-01-0.19 ~£ (Rao and Shanware 1967).