Forests and Other Vegetation Types of Sri Lanka
BIODIVERSITY: Sri Lanka is one of the world’s bio diversity hot-spots. This means that we have a wide range of biological species, fauna and flora, in a variety of habitats. This article deals with the different forest types in Sri Lanka. It also includes non forest vegetation areas. These forests are among the most floristically rich forests in Asia and are quite unique for a small country. The diversity comes as a result of the wide variations in rainfall, altitude and soil within the country. Our unique geological formation also plays a major role in the diversity of our vegetation. Vegetation reflects the combined effect of topography, climate and soils.
Looking at the geography and topography of the island, we find that there are three peneplains or erosion levels. These are categorized by their height and slope features. The first peneplain is the largest of the three and extends from sea level to 270m (885 feet) above mean sea level (msl). The Uplands or the second peneplain extends from 270m to 900m (885 to 3477 feet) above msl. and the Highlands or third peneplain at 900-2420m (2985 to 7939 feet). The island has also been divided into three climatic zones based on rainfall, the wet, which covers 65% of the country, intermediate covering 12% and the dry zone covers 23%.
The climate is the main factor that determines the distribution and type of forests. In the past, except for a few areas because of their soil, the whole island was covered in forests. With the increase in population and the demand for more and more land, forests were cleared to cater to these growing needs. This changed the forest landscape of the island. It was further altered when, during the British period, large extents of highland forests were cleared for the cultivation of coffee and later tea. There were much more mangrove forests along the tidal mud flats along the coast than are prevalent now. Until the early part of this century, the higher sandy soils also had strips of littoral woodlands. However these have all disappeared now.
The Forest Ordinance of 1885 was the first item of legislation, which enabled the proclamation of Forest Reserves for conservation purposes. At that time the Crown (state) owned 95% of the forests in the island. Further many areas were placed with the Forest Department as Proposed Forest Reserves, since the process of establishing reserves was time consuming. Village forests were placed under the district Government Agents, and other Crown Forests were, at various times, transferred from the Forest Department to the respective Government Agents. In addition, as mentioned in a previous article, the Department of Wildlife Conservation had certain forest areas established for the protection of wildlife, in five categories, under the Fauna & Flora Protection Ordinance. Till 1944 all forest and wildlife conservation came under the purview of the Forest Department. The Department of Wildlife Conservation was formed that year and took over the function of protecting the island’s wildlife.
Considering Sri Lanka’s natural vegetation there is a striking variety of forest types brought about by spatial variations in rainfall, altitude and soil. The forests have been categorised broadly as tropical wet lowland evergreen forests (at elevations between 0-1000 m); wet sub-montane forests (at elevations between 1000-1500m in the wet zone); wet montane forests (at elevations of 1500-2500m); tropical dry mixed evergreen forests in the dry lowlands, with riverine vegetation along river banks; tropical moist evergreen forest in the intermediate zone and thorny scrub in the arid areas. In Sri Lanka and other countries many names are applied to the same forest type making it rather confusing for anyone first interested in forestry. [WL]
The Tropical Rain Forests or Wet Lowland Evergreen Forests
The southwest region and the central hills of Sri Lanka have the most luxuriant forest cover. They have rain during the southwest monsoon and constitutes the lowland rain forests up to an elevation about 900 meters. At higher elevations they change to montane rain forests. Both these are very similar to those of India’s Western Ghats.
Tropical rainforests are characterised by a multi-storeyed vegetation where the crowns of dominant trees form a closed canopy, that covers the full forest, at 25m to 30m on top with with taller species growing to rise up to about 45m. These forests have a relatively sparse undergrowth but are rich in epiphytes and lianas. Epiphytes are those plants that hang on to a big tree, which is its host. It takes its food from the air. On the other hand, a parasite takes its food from the host plant itself. The interior of these forests are dark and dense. They have an understory made of small trees and shrubs and the ground layer consisting of herbs. The tallest trees that rise above the canopy is called the emergent layer. The have a high temperature and a high humidity. They also have a high annual rainfall which exceeds 3000 mm.
Sri Lanka’s lowland rainforests covering 2.1% of the land area harbour many endemic and threatened species. More than 60% of the 306 tree species that are endemic to Sri Lanka are found only in the lowland rainforests and some more are shared with montane and dry zone forests. Of the twelve endemic genera of flora of the island, eleven are confined to rainforests. The best known tropical rainforest in Sri Lanka is Sinharaja, internationally recognized as a world heritage site.
Kaneliya, Dedugala, Nakiyadeniya complex known as the KDN forest, Bambarabotuwa, Morapitiya Runakanda, Gilimale and Eratne are some of the other reserves. The diverse vegetation of Sinharaja provides habitats to a wide array of fauna. Thiniya, (Shorea congestifolia) Duna (Shorea stipularis), Duna (Shorea zeylanica) are some of the emergents found in Sinharaja. Hora (Dipterocarpus zeylanicus), Honda Beraliya, (Shorea megistophylla)and Batu Naa (Mesua nagasarium)are some of the species that make the canopy. Thapassara bulath (Apama siliquosa) beru (Agrostistachys spp), Galkaranda (Humboldtia spp) are commonly found in the sub canopy. Herbs like Goniva (Acrotrema) Sandaraja (Anoectochilus setaceus), Lianas sucha as Calamus – Rattan palms, Entada pusaetha – Pus wel (Entada pusaetha), Coscinium – veniwel contribute to the variety of the forest.
The vertebrate animals of Sinharaja consists of about 50% of native inland animals of which 30% are endemic. Mammals like the Leopard (Panthera pardus), Purple faced Leaf Monkey (Semnopithecus vetulus)(endemic), Black naped Hare (Lepus nigricollus), Fishing Cat (Prionailurus Viverrinus) and Rusty Spotted Cat (Prionarilurus rubiginosus) are found together with numerous amphibian and reptile species. The vegetation dwelling tree frogs (Genus Philautus), who lay eggs in crevices and leaves and hatch out as tiny adults, are commonly found. All rainforests such as Sinharaja are famous for the colurful array of bird life. Sinharaja has four endemics the Blue Magpie (Cissa oronata), Green billed Coucal (Centrophus chlororhynchus), Sri Lanka Spurfowl (Galloperdix bicalcarta) and Sri Lanka Jungle Fowl (Gallus lafayetti). Mixed foraging bird flocks, that is a group of different bird species of birds moving together through the forest, is something that should not be missed. A mixed flock consists of an average of 40 individuals from more than 12 species.
The soils of rainforests are shallow and poor in nutrients because what ever the nutrients that return to the soil are rapidly recycled or taken back by the plants.
Sub montane and Montane forests
The sub montane forests are distributed at between 1000-1500m and those above that, 1500-2500m, are the montane forests. They are also known as cloud forests. The hot air of the lowlands rise during the morning hours and condense creating huge clouds, which become so heavy that they result in afternoon rains. They cover a total of 1.1% of our land area. The montane forests are characterized by dense growth of epiphytes and lichens. These forests have a lower canopy and dense undergrowth. In these forests twisted, stunted trees are full of orchids, mosses, lichens, climbers and ferns. At lower elevations, the cloud forests give way to a variety of vegetation, consisting of both temperate and tropical plants, and grassland savannas. Half of Sri Lanka’s endemic flowering plants and more than 34% of its endemic trees, shrubs and herbs are restricted to these diverse montane forests.
These forests provide an ideal habitat for many animals including many mammals Leopard (Panthers pardus), Wild Boar (Sus scorfa), Barking Deer (Muntiacus muntjak), Loris (Loris tardigardus) the smaller cats, the Purple faced Leaf Monkey, Porcupine (Hystrix indica) and Golden Palm Civet (Paradoxurus zeylonensis). New species of frogs, lizards, fish and crabs are still being discovered here. One of the smallest terrestrial mammals in Sri Lanka, Kelaart’s Long-clawed Shrew (Feroculus feroculus), is found only in the mountains of this eco region while the endemic Pigmy Lizard (Cophotis ceylanica) is found only in cloud and montane forests above 1300 m.
Elephants once roamed in Sri Lanka’s Cloud forests, where they formed tunnel-shaped paths through the undergrowth of mainly Strobilanthes spp. (Sinhala – Nillu). Only a few are left now on the Rakwana side of this forest.
These high altitude forests are the source of almost all Sri Lanka’s major rivers. The protection of these forests, which are catchments, will ensure that the rivers have water right throughout the year especially during the dry weather. A catchment is where the rainwater is absorbed into the soil and released steadily throughout the year.
Dry mixed evergreen forests and riverine forests
Dry mixed evergreen forests are the most extensive type of forests and are found in the dry zone. They are characterized by monsoon forests and thorn scrub lands. Evergreen forests represent the tropical dry forests covering a major part of the dry zone adding up to 16.8% of the land area except for the southwestern quarter, the central mountain range, and the Jaffna Peninsula in the extreme north. Dry mixed evergreens receive about 1,500-2,000 mm of annual rainfall in December to March northeast monsoon period but are mostly dry during the rest of the year. The strong seasonality in rainfall has prompted these forests to be referred to as monsoonal forests.
Topographically, the ecoregion is flat, except for scattered inselbergs. Inselbergs are rocky outcrops in a flat landscape. The evergreen dry forests have no canopy formation and trees seldom exceed 20m in height. Although deciduous species exist in these forests their evergreen character is maintained by a few widespread species. Deciduous is where the leaves fall off periodically and grow again. These forests are dominated by Palu (Manilkara hexandra) (Sinhala – Palu), Satin (Chloroxylon sweitenia) (Sinhala – Burutha), Drypetes sepiaria, Feronia limonia, Vitex altissima, Syzygium spp., Drypetes sepiaria and Chukrasia tabularis.
The scrub and regenerating forests are characterized by Bauhinia racemosa, Pterospermum suberifolium, Cassia fistula and Dichrostachys cineria. Acacia thorn scrub grows in disturbed areas. Ritigala, the isolated hill in central Sri Lanka, is a hotspot of endemic species within this ecoregion with several endemic plants such as Madhuca clavata.
Compared with Sri Lanka’s rain forests, these forests do not have very high levels of endemism. Nevertheless, they harbour one of Asia’s largest elephant populations, estimated at 3,500 to 4,000 animals and many large mammals. Several of the ecoregion’s mammals are also listed as threatened; elephant (Elephas maximus), the Sri Lankan leopard, the vulnerable Sloth Bear (Melursus ursinus), Purple-faced Leaf Monkey and Slender Loris. The richness of bird life is greater, with 270 species, which include several endemic species namely Red-faced Malkoha (Phaenicophaeus pyrrhocephalus), Ceylon Spur Fowl, Jungle Fowl, Brown-capped Babbler (Pelleorneum fuscocapillum) and Ceylon Hanging Parrot or Ceylon Lorikeet (Loriculus beryllinus).
Intermediate forests / Tropical moist evergreen forests
These forests are located in the transition zone or between the tropical rain forests and dry mixed evergreen forests. There are some species that are common to both types of forests, but some are found only in the semi evergreen forests. Lunumidella (Melia duba), Pihimbiya ( Filicium decipiens) and Hulanhik (Chukrasia)are some of these tree species.
Tropical Thorn Forests / Arid zone forests
These forests cover the extreme Southeastern and Northwestern regions of the country, which have very long dry periods. They have low trees and thorny undergrowth dominated by thorny shrubs. They are called Tropical Thorn Forests. Temperatures here are high being over 34C and the rainfall is below 1250 mm. The thorny shrubs have adaptations to store water and are able to live on very little water.
A mangrove is a swampy area found in the costal areas and at river mouths. They are periodically inundated by sea water. Rich mangrove forests exist in the Puttlam and Kalpitiya areas, and Portugal and Dutch bays. Dense strips of mangroves also occur in the southwest and southern coasts. The total mangrove area in the island is estimated between 6,000 -13,000 ha. Fourteen mangroves species and 12 associated species have been recorded. Mangrove trees have many adaptations to survive in water logged, saline soil with very little areartion. Stilt and prop roots for support, pneumatopores, which are roots for breathing air and which stick out of the water to take in air, salt and to relieve excess salt are such adaptations. There are many types of fauna of which some are adapted to this specific environment. Mud skipper; a fish who enjoys a walk, the Fiddler crab with one big claw, are some. Some mangrove trees exibit viviparity; that is the seed germinates while attached to the mother plant. This longer period of development before release, ensures the survival of the plant.
Mangroves are essential for nutrient retention for certain species of fish and shrimp to breed. However mangroves are being destroyed for the expansion of human settlement and for aquaculture. Poles, firewood, twigs for brush piles etc. are extracted from mangroves. Pollution and siltation affects the quality of the trees Thus we find that the mangroves are fragmented exploited and degraded. Grasslands – savannas, dry and wet patana, damana, talawa and villus.
Different types of grasslands occur in the wet and dry areas. Savannas consist of grasslands scattered with trees. In Sri Lanka there are few stable patches in Haldummulla, Medagama, Bibile, Ekiriyankumbura and Senanayake Samduraya. Elevation ranges between 100-500m and Illuk (Imperata cylindrica) dominates most of these savannah lands. Savannahs are highly inflammable. The tree species that grows on savannah lands include Aralu (Therminalia chebula), Bulu (Therminalia bellirica), Nelli (Phylanthus emblica), Kahata (Careya arborea), Gammalu (Pherocarpus marsupium) etc.
Dry patanas are extensive grasslands found mostly in Uva basin. The dominant grass is Mana (Cymbopogon nardus).
Wet patnas are unique habitats occurring around 2,000m with upper montane forests. They are found in the Horton plains, Moon plains, Sita Eliya plains, Bogawanthalawa etc. Scattered trees and shrubs like Rhododendron (Sinhala Maha rathmal) occur together with characteristic tussock grass Chrysopogon zeylanicum. Many endemic species including Sri Lankaranga, a shrimp endemic to Horton plains, Giant Squirrel (Rafuta macroura) and the Sri Lanka Nellu Rat (Rattus montanus) (endemic) are among the fauna.
The talawa savannas arising through Chena cultivation in the wet zone are found in Kalutara, Galle and Matara. These are characterized by Terminalia chebula, Terminalia belerica, Pterocarpus marsupium, Butea monosperma Gas Kela, Careya arborea, Anogeissus latifolia Deru, Phyllanthus embilica and Zizyphus spp. The dominant grasses in the villus include Cymbopogon spp., Eragrostis spp., Themeda spp., and Imperata spp.
Villus are found in the flood plains of rivers in the dry zone. Villus are periodically inundated during the flooding of the rivers that flow through them. The better known villus are the Mahaweli Flood Plains, Thamankaduwa, Maduruoya and Manampitiya. They are all flood plains of the Mahaweli River. After the villus are inundated by the flood waters of the rivers, the waters recede and leave behind silt which is rich in nutrients and which has come with the waters from upstream. These nutrients nourish the vegetation in the plains.
Department of Wildlife Conservation (DWLC) and the Forest Department (FD) control over 90% of the natural forests in this country. The DWLC is charged with the conservation of various species that are found in the forests in its charge.
They have for management purposes divided their forests into different categories for conservation purposes, with different types of protection afforded to these areas such as Strict Nature Reserves, National Parks, Nature Reserves, Jungle Corridors and Sanctuaries. They cover all the ecological and climatic regions of the country.
The Forest Department is responsible for the forest areas that do not come within the purview of the Department of Wildlife Conservation. The Forest Department conserves many forests in their original condition like the Sinharaja and the KDN forest but they grow trees, on a commercial scale, for harvesting as timber. This is mainly to meet the country’s need for timber products.
Despite the protection that has been afforded, our forest cover has declined from 80% in 1881 to 24 % in 1992. It is now felt that the figure is less than 20%. The human population in the 1880s was around 1.5 million. Now it is almost 20 million. Some of the loss is justified but as detailed below most forest areas have been lost for the wrong reasons.
Deforestation is due to a number of reasons. Planned agriculture and industrial developments, illicit and extensive felling of timber, firewood harvesting, Chena cultivation, Erosive crops like potato which degenerates the land very fast, forest fires, over collection of rare and endemic species are some of the many reasons that cause the loss of forest cover. Degraded forest structure due to logging causes slow rates of regeneration. The primary overarching threats are from deforestation caused by agriculture, resettlements, and small-scale logging. Encroachment into protected areas, several of which lack adequate protection and management, also poses threats that warrant attention. Alien invasive species have displaced more than 30,000 acres of native forests. The loss of forests directly affects the fauna inhabiting them, thus subjecting them to the threat of extinction.
Mangrove ecosystems on the other hand, are threatened by the reclamation of land, urbanization and prawn culture. Clearing mangroves and salt marshes for agriculture, aqua culture, saltpans and building construction lead to a reduction in both habitat diversity and coastal biota.
Dry zone ecosystems are also disturbed by cyclones, which fortunately are not frequent. The construction of large reservoirs continues to reduce the extents of natural ecosystems, particularly in the lowland wet and intermediate zones.
In the northern and eastern part of the Knuckles range, the forest undergrowth in 2,400 ha has been cleared for cardamom cultivation. Although cultivation is now curtailed, the absence of juveniles and sapling of the canopy species to replace adults will require remedial measures. The ideal option is to convert these cardamom plantations to their original vegetation.
Ethnic unrest, particularly in the north of the Island, also contributed to the degradation of natural forests, through clear felling, illicit removal of timber and fuel wood and hunting. Noise pollution adversely affects the animal population.
One of the major problems faced in the management of various forest types are the invasive species that have now proliferated. Invasive species are those species that have come in from elsewhere and take over the habitats and other resources of native species. Invasive species increase their populations drastically at the expense of the existing flora. They are of two categories, the native and the alien. Native plants or animals become invasive when a change of environmental conditions or some other factor causes their ordinary population to multiply drastically suffocating the other species. Aliens are those species that have been introduced deliberately or accidentally from outside.
Invasive species are species that are not normally found in these areas and which have grown to proportions where they are difficult to control. They grow and increase at the expense of the indigenous species, which as a result die out. In many instances these invasive species cannot be consumed or are not consumed by other species and therefore the food available to the food chain is greatly reduced. Then the habitats of many species are degraded and reduced thereby having an adverse impact on their populations.
Invasive species, both fauna and flora have become problematic to many protected areas. In the Bundala National Park there are two invasive species. Proposis Juliflora or Kalapu Andara in Sinhalese. These thorny trees are spreading across the Hambantota and Bundala landscape like wild fire and choking up the natural vegetation. In Bundala it has bee found that all the Palu (Manilkara hexandra) trees close to which this species has now grown, are dying. In Bundala there is also the cactus Opuntia (Opuntia delenii) that has large thorns, which are invading the PA. The DWLC is cleaning out the cactus but it is not an easy task since this species has very long and sharp thorns.
In Uda Walawe NP Lantana camara (Sinhala – Gandapana) an invasive species has taken over large extents of the park and has choked out the indigenous plants. This is plant is propagated by birds, which consume the berries and drop the seeds, which germinate fast. Here too the DWLC is making an attempt to rid the park of this menace.
In the Horton Plains Ulex uropaeus is an invasive species. It is spreading fast and choking the Gorse bushes, which is the habitat of the endemic Pigmy Lizard (Cophotis ceylanica), called Kurubodiliya in Sinhala.
In the Minneriya NP the thorny bamboo (Bambusa bambos)is a big problem as it is in the Victoria Randenigala Randenigala NP. The trees on which the elephants feed on are choked out by these thick clumps of bamboo. Since forests are an essential part of our lives, their nuturing and protection is very important.