- Created on Monday, 05 September 2011 22:55
- Hits: 21310
Sri Lanka, the pearl of the Indian Ocean lays claim to eight of the current 911 UNESCO World Heritage Sites out of which two are endowed owing to rich biological diversity. Biological diversity or Biodiversity in simple terms is the variation of living beings including plants, animals and micro-organisms together with the variation exhibited by the non-living environment and genetic variation. Sri Lanka, even though claims for a relatively small land extent of 65,610 sq km, the geographical terrain, altitude and the climate of the islands display an ample variety that has resulted a extensive array in diversity, which has given rise to different floristic regions. Considering the topography of the country, three distinct peneplains are discernible. The lowest of these, the flat lowland peneplain covering about 75 percent of the land and is referred to as the `Low country' with the altitude rising from sea level to 300 m. Towards the south central parts of the country, the land rises steeply on all sides and the second peneplain, the `Mid country' is identifiable from 300m to 1,000 m. Further inland the land rises very steeply to form the south central mountain massif with several plateaus, which is the third peneplain or `Up country' (1,000 m - 2,500 m). The western, southern and western slopes of the central hills is fed by the southwest monsoons bringing ample rain from May to July and is referred to as the wet-zone while the northern and eastern regions that is fed by the north-east monsoon from December to January with a lesser amount is referred to as the dry-zone. Throughout these different zones one can see plants specially adapted to each set of circumstances, giving rise to a rich floral assemblage.
The diversity exhibited by plants often surprises man, and we are fortunate that by crossing this land stretch in matter of hours one can experience many of the vegetation types with its unique flora; coastal vegetation including mangroves, scrublands, wetlands, tropical rain forests, dry zone forests, montane forests, grasslands, savannahs and pattanas, which is a valuable source of outdoor laboratory.
Sri Lanka harbours over 3500 flowering plants classified under 214 families of which 75% are native (plants that occur naturally, or existed for many years in the wild) and 25% are exotic (plants that have been introduced). Of the total number of native plant species, 27% are confined or endemic to the island. Most of the rich diversity of the flora together with the endemics is confined to the wet-zone, where the virgin tropical rain forests still thrive. The Sinharaja and Kanneliya are our great tropical rain forests, by all accounts is a vast repository of this wealth.
Saved from government sponsored logging operation in the mid-1970s, the Sinharaja Forest was recognized as an international Man and Biosphere Reserve by UNESCO in 1978 and declared a national wilderness area in 1988. The protection of Sinharaja was further strengthened by the subsequent inclusion of the rainforest in UNESCO’s list of World Heritage Sites. Sinharaja Forest is of special importance because of its high species diversity and the larger number of endemic and threatened species that the forest harbours. The species endemism of some plant families such as the ‘Hora’ family (Dipterocarpaceae) exceeds 90 percent. Kanneliya complex is richer in endemicity compared to Sinharaja and is home for more than 60% of Sri Lanka's woody endemic plant species. The tree profile of the wet lowland forest is multi-layered, which is a characteristic of a rainforest. The upper most strata comprise of the emergents or the tallest trees, and in many of these forests they appear as a discontinuous layer emerging above the continuous canopy layer, which is the second tree layer. In some forests the emergent dominants consist mainly of ‘Hora’ trees (Dipterocarps zeylanicus). The associated species include ‘Bu-hora’ (D. hispidus), ‘Dun’ and ‘Beraliya’ (Doona spp.). These giants have a bole trunk that branches at the top, and therefore is supported by buttress and prop roots. The next strata, the continuous canopy is the primary life sustaining layer with an abundance of food and forms a natural roof with their overlapping crowns over the remaining layers. Trees such as ‘Keena’ (Calophyllum spp.), ‘Hadawaka’ (Chaetocarpus castanocarpus), ‘Malaboda’ (Myristica dactyloides), ‘Atamba’ (Mangifera zeylanica), ‘Milla’ (Vitex altissima), ‘Dawata’ (Carallia brachiata) and ‘Aridda’ (Campnosperma zeylanicum) are abundant in this layer. Due to the overlapping crowns, the amount of light that reaches the ground is minimised. ‘Diyapara’ (Dillenia triquetra), ‘Godapara’ (D. retusa), ‘Badulla’ (Semicarpus species), ‘Galkaranda’ (Humboldtia laurifolia), and ‘Uru honda’ (Stemonurus apicalis) are the occupants of the next tree layer which is smaller in stature. The shrubs include ‘Tapasara bulath’ (Thottea siliquosa), ‘Bata’ (Ochlandra stridula), ‘Pera-tambala’ (Gaertner vaginans) and the scandent ‘Wewal’ (Calamus species). The forest also has a profusion of large woody climbers, ‘Weniwelgata’ (Coscinium fenestratum), ‘Rasa-kinda’ (Tinospora cordifolia), and ‘Pus-wel’ (Entada pusaetha) climb often to the very top of the highest trees in search of light. The wet lowlands forests are also rich in epiphytes that include orchids and ferns. A noteworthy feature of the rain forest vegetation is the drip tips of most of the leaves. These pointed tips allow the rain water and moisture that is collected on the surface of the leaves to drain off. Cauliflory, producing flowers and fruits on the leafless trunks or large branches, is another feature exhibited by rain forest species. Towards the higher elevations, the middle slope forest is characterized by the ‘Na-Dun’ (Mesua-Doona) community, that includes ‘Batu-na’, ‘Diya-na’ (Mesua species), and several species of Dun (Shorea species). ‘Kirihembiliya’ (Palaquium spp.), ‘Ketaboda’ (Cullenia ceylanica), ‘Tiniya dun’ (Doona congestiflora), ‘Kekuna’ (Canarium zeylanicum), and ‘Netaw’ (Xylopia parvifolia) are other trees species that are found in the slopes. ‘Bandura’ or the pitcher plant (Nepenthes distillatoria) and ‘Kekkilla’ (Dicranopteris linearis) are a common site along the disturbed roads.
The central highlands of Sri Lanka encompass an array of different vegetation types, Peak Wilderness Protected Area, Horton Plains National Park and Knuckles Conservation Forest being the main contributors. These montane forests are home for extraordinary range of flora including remarkable number of endemics. The area includes the largest and least disturbed remaining areas of the sub-montane and montane rain forests of Sri Lanka, which gained global conservation priority recently as a UNESCO World Heritage Site.
Horton Plains is the highest plateau in Sri Lanka. The most fascinating about this vegetation is the forest-grassland ecosystem, the endless rolling mounts either covered by grassland or trees. In general, forests are seen towards the hill-tops or upper slopes. Plants that occur in these forest are of families belonging to either almost entirely restricted to the tropics and sub-tropics; the ‘Keena’ or the ‘Goraka’/ ‘Mangosteen’ family (Clusiaceae); the Guava or Eucalyptus family (Myrtaceae); the Osbeckia or ‘Bowitiya’ family (Melastomataceae); the Cinnamon family (Lauraceae) and those common to the temperate countries such as the Rhododendron family (Ericaceae); the Michelia or ‘Wanasapu’ family (Magnoliaceae) etc., The tree layer in montane forests is dominated by members of the Cinnamon family together with Guava and ‘Mangosteen’ family. Among them are trees such as ‘Polkatu gas’ or ‘Elephants’ ears’ (Actinodaphne speciosa) with their hemispherical shaped drooping leaves; ‘Mountain Keena’ (Calophyllum walkeri), the tallest trees in the canopy species with a characteristic crown bearing closely arranged leaves; ‘Wana-sapu’ (Michelia nilagirica), a rare canopy species with very fragrant flowers and a large spreading crown and wild relatives of true Cinnamon (Cinnamomum ovalifolium), when the leaves are crushed it too has the characteristic smell. Many other Actinodaphne species, which are endemic to the country occur confined to the montane forests. Towards the summits, the height of the forest trees varies between 10-15m and 1-1.5m, where one could look down on the ‘forest’ and is sometimes referred to as pigmy forests. In appearance most trees do not possess straight stems or buttresses, but are low and profusely branched, twisted where some refer to them as ‘Giant bonsai’. On the whole the leaves of these taller trees are small and show drought resistant features such as hairs or a thick waxy layer on their surfaces. Underneath the trees, the tree-lets and shrub layer is dominated by ‘Nelu’ (Strobilanthes species). This species blooms only once in its life time, after which the plants die. Since the plants being of the same age, as they bloom together, the forest under storey gets a spectacular appearance. Once the ‘Nelu’ plants die and light reach the forest floor, herbs such as Balsam or ‘Kudalu’ (Impatiens), and Coleus grow and complete their life cycle. Several members of the Coffee family (Rubiaceae) are also found abundant in the undergrowth. The grasslands of the plains which have not been disturbed by the potato cultivation are dominated by tussock or clump grass species such as ‘Gavara’ (Chrysopogon nodulibarbis). Scattered among are few shrubs and stunted trees; the most prominent been ‘Ma-ratmal’ (Rhododendron arboreum subsp. zeylanicum) with conspicuous red flowers. The small white flowered ‘Wel-kapuru’ (Gaultheria sp.), whose crushed leaves gives a wintergeno-like aroma and the yellow or white flowered Anaphalis spp. whose stems and leaves are covered with cottony white hairs are other species that occur more less as shrubs and herbs. The Gorse (Ulex europaeus), a very thorny species with bright yellow flowers occurs in large number in the grassland. This is an introduced species and now considered as invasive plant. Aristea ecklonii, with deep blue flowers is abundant along the roadsides. Hidden among the grass are numerous herbaceous plants, ‘Hare Bell’ (Wahlenbergia marginata) and ‘Buttercup’ (Ranunculus spp.) with yellow delicate flowers. On the wet soils on rocks are the carnivorous plants ‘Ada-handa-essa’ and ‘Wata-essa’ (Drosera species). Several species of ‘Kokmota’ (Eriocaulon species) occur towards wet pools, whose white coloured button shaped inflorescences are raised well above by their long slender stalks. Among the plants in the water is a ‘Kekatiya’ species (Aponogeton jacobsenii) confined to this particular habitat, whose flowers are often seen emerging above the water. Along the streams and in the moisture high shallow valleys of the grassland, ‘Kuru una’ or dwarf bamboo (Sinarundinaria densifolia) is seen growing luxuriantly. The occurrence of the Tree fern, (Cyathea crinita), is another characteristic feature in these forests.
The other important highland region that contributes is the Knuckles, home for many endemic flora such as Stemonoporus affinis a member of the ‘Hora’ family, that is confined to the Knuckles region and many other threatened species such as ‘Binara’ or (Exacum species), a highly valued ornamental and many Orchids. ‘Sudu mihiriya’ and ‘Rathu mihiriya’ (Gordonia spp.) are other tree species that are members of the tea family with large flowers white and red flowers that occur confined to the highland forests.
Due to the historical factors, the dry zone forests are disturbed and secondary in nature; however climax forests still thrive on isolated hill ranges such as Ritigala, now recognized as a strict nature reserve. Tree species such as ‘Kiri-mi’/‘Ritigala-mi’ (Madhuca clavata) are endemics confined to Ritigala. Among other such rare plants is a ‘Nelu’ species (Strobilanthes stenodon), and Anodendron rhinosporum, Ipomoea wightii, Cleidion nitidum and Peperomia pseudo-rhombea, where Ritigala serves as a refugium for species which are rapidly disappearing.
The Dry Mixed Evergreen forests that covers the dry zone of the country has no marked stratification or richness in species as compared to the wet lowland forests. As there is no closed canopy layer in these forests light penetrates the ground. The dominants been ‘Weera’ (Drypetes sepiaria), ‘Burutha’ (Chloroxylon swietenia) belonging to citrus family (Rutaceae), ‘Palu’ (Manilkara hexandra) member of the ‘Lawulu’ family (Sapotaceae), ‘Halmilla’ (Berrya cordifolia), ‘Wewarana’ (Alseodaphne semecarpifolia) a member of the Cinnamon family, ‘Kaluwara’ (Diospyros ebenum), a member of the ‘Ebony’ family (Ebenaceae), ‘Milla’ (Vitex altissima) and ‘Kolon’ (Haldina cordifolia). These species are not uniformly distributed; however associations such as ‘Wewarana’ - ‘Halmilla’ - ‘Kaluwara’ could be recognized in moister regions. ‘Kumbuk’ (Terminalia arjuna) is often found along the banks of the rivers. The smaller trees and shrubs below the main canopy or the tree layer include ‘Kunumella’, (Diospyros ovalifolia), ‘Weli-wenna’ (Dimorphocalyx glabellus), ‘Dodan-pana’ (Glycosmis pentaphylla), Mallotus and Croton species. Herbs such as ‘Bin-kohomba’ (Munronia pinnata), and vines such as ‘Iramusu’ (Hemidesmus indicus) and ‘Anguna’, well-known medicinal plants are found in the ground layer. ‘Wara’ (Calotropis gigantea) with unique violet flowers is a common shrub that is found alongside of the roads and disturbed sites.
The Semi-evergreen forests situated between the tropical rain forest and the dry mixed evergreen forests, is intermediate between the two in appearance. Tree species such as ‘Lunu-midella’ (Melia azedarach), ‘Pihibiya’ (Filicium decipiens), ‘Hulanhik’ (Chukrasia tabularis) and ‘Murutha’ (Lagerstroemia speciosa) are common in these forests. Many of these dry and intermediate zone trees are reputed timber species.
Another interesting vegetation type is the Savannas that consist of grasslands with scattered trees. They occur towards Haldumulla, Medagama and Bibile areas. ‘Aralu’ (Terminalia chebula), ‘Bulu’ (Terminalia bellirica), ‘Nelli’ (Phyllanthus embalica), ‘Kahata’ (Careya arborea), ‘Kudumberiya’ (Diospyros melanoxylon), ‘Gammalu’ (Pterocarpus marsupium) and ‘Dawu’ (Anogeissus latifolius) are dominant tree species while ‘Iluk’ (Imperata cylindrica) covers the grassland. These trees are richly branched and have gnarled twisted trunks and their thick barks are resistant to fire which is a common occurrence.
The Riverine forests associated with rivers and their flood plains are important components harboring rich vegetation. Species of ‘Athiudayan’ (Cryptocoryne spp.) and ‘Kethala’ (Lagenandra spp.) both members of the Anthurium family (Araceae) and Pandanus species, a member of the ‘Rampe’ family (Pandanaceae) occur associated with the water along the banks. An important remnant marsh forest is the Waturana forest located in the ‘Kalu ganga’ (river) basin of the wet zone. ‘Suwanda’ (Mesua stylosa), Stemonoporus mooni, ‘Lenatherya’ (Areca concinna) and several ‘Athiudayan’ species are rare endemics found in this unique forest patch.
The countless water bodies both natural and man-made encompass a rich aquatic flora. Even though the native flora is masked by the spread of invasive alien species such as ‘Japan Jabara’ (Eichhornia crassipes) and Salvinia molesta that have conquered the water bodies, the island inherit rich wetland vegetation. The water lilies, both ‘Manel’ (Nymphaea nouchali) and ‘Olu’ (N. pubescens), ‘Nelum’ (Nelumbo nucifera), and ‘Kumudu’ (Nymphoides spp.) bring in a spectacular site into large water bodies while in bloom.
Orchids are another group of plants that exhibit an incredible range of diversity in size, shape and colour, and valued as ornamentals for their longer lasting and beautiful flowers. Sri Lanka is also considered as a heaven for orchids where more than 170 orchid species grow in the wild in the forests or grasslands, either epiphytic or saprophytic with a remarkable percentage that is unique to the island. Some of the wild orchids include the ‘Wana-raja’ (Anoectochilus setaceus), ‘Foxtail orchid’ (Rynchostylis retusa), ‘Vesak orchid’ (Dendrobium maccarthiae) and ‘Pitcher orchid’ (Acanthephippium bicolour). Many of the wild orchids are in the verge of extinction due to over-collection from the wild.
Sri Lanka is bestowed with a wealth of medicinal plants, most of which have been used in indigenous medical systems. Robert Knox, an English sailor in his work ‘An historical relation of Ceylon’ (1681), commenting on the Sri Lankan herbs states that, “The woods are their apothecaries shops, where with herbs, leaves and the rinds of trees they make all their physic and plaisters with which sometimes they will do noble cures ..”. Among the native flora of the island are over 500 species that are used in traditional medicine. Of these over 200 species are used commonly in traditional medicines; ‘Weniwel’ (Coscinium fenestratum), ‘Katu-wel-batu’ (Solanum virginianum), ‘Kohomba’ (Azadirachta indica), ‘Inguru’ (Zingiber officinale) and ‘Pavatta’ (Justicia adhathoda) are common medicinal plants often used in home remedies. Plants such as ‘Komarika’ (Aloe vera), ‘Kaha’ (Curcuma longa) and ‘Nil-awari’ (Indigofera tinctoria) are medicinal plants that are also popular in the cosmetic industry. Many of these medicinal plants are extracted from the wild and many of them are at the verge of extinction.
The island has been well-known from ancient times for producing many spices that are been used in adding subtle flavours and aromas for food. In the 16th century Ceylon, as it was then known, was discovered by Portuguese who soon began trading in cinnamon and other spices. Cinnamon or ‘Kurundu’ is the dried bark of various laurel trees in the Cinnamon family. Cinnamon sticks are made from long pieces of bark that are rolled, pressed and dried. True Cinnamon, (Cinnamomum verum) is native to Sri Lanka. The seeds of Cardamom (Elettaria cardamomum) is a member of the ginger family, that grows in the under storey of the forests. Cloves or ‘Karambu-neti’ are the dried unopened flower buds of Syzygium aromaticum, an evergreen tree belonging to the the Guava family. Nutmegs are single seeded fruits of the nutmeg tree or Myristica fragrans which produce two different spices, mace and nutmeg. Vanilla, one of the most expensive spices with a high aromatic fragrance, is derived from the pod of a climbing orchid, Vanilla fragrans.
Consequently the untapped genetic potential of the island is almost out of proportion to the country's size. The islands’ natural flora is further enriched by the of crop wild relatives, the wild relatives of crop plants include the progenitors of crops as well as species more or less closely related to them. Crop wild relatives are important both for improving agricultural production and for maintaining sustainable agro-ecosystems. Sri Lanka harbors several crop wild relatives of rice, Oryza eichingeri , O. nivara , O. rufipogon, O. rhizomatis and O. granulata; two wild relatives of Musa or ‘Kesel’, Musa acuminata or ‘Gal-kehel/Unel’ and Musa balbisiana or ‘Eti-kehel’ and many wild relatives of other important crops including Pepper, Vigna and Cinnamon.
The islands’ natural flora has been enriched by the addition of plantation crops, food crops, spices, and other ornamental plants. However many of the plantation crops were established on the expense of clearing natural vegetation during the colonial period. The highlands have lost much of their natural vegetation and have become tea plantations, midlands for rubber plantations, while wet lowland forests in the coastal areas were cleared for coconut and cinnamon plantations. Many other food crops such as ‘Jak’ (Artocarpus heterophyllus), ‘Del’ (Artocarpus incises), ‘Siyambala’ (Tamarindus indica), ‘Caju’ (Anacardium occidentale), ‘Amba’ (Mangifera indica), ‘Rambutan’ (Nephelium lappaceum) and ‘Mangosteen’ (Garcinia mangostana), are grown in various parts of the country. Several seasonal, ornamental trees give glamour to the flora, ‘Pink tabebuia’ and ‘Yellow tabebuia’ (Tabebuia spp.), variously coloured ‘Murutha’ (Lagerstroemia spp.), Queen of flowering trees (Amherstia nobilis), ‘Mal-mara’ (Delonix regia), ‘Erambudu’ (Erythrina spp.), and ‘Ehela’ (Cassia fistula).
Many plant species plays an important role in ritual and cultural activities. Bo tree (Ficus religiosa) famously associated with the enlightenment of Siddhartha Gautama (Buddha), has the greatest religious significance amongst all of Sri Lanka’s plants. Offering a sheaf of Betal (Piper betle) leaves is a traditional practice in the Sinhalese culture. ‘Pol mala’, the flowers and ‘Gok-kola’ the young leaves the coconut tree (Cocos nucifera) are used in traditional decorations including cultural and religious events. In fact the essence of Sri Lanka has often been associated with the greenery of the island. We, being the custodians of this rich green heritage, should be considerate enough to hand them over to the future generations with protected and preserved purity.
Prof. Deepthi Yakandawala
Department of Botany
Faculty of Science
University of Peradeniya