|Thursday, 24 January 2002|
A glimpse into Lanka's verdant forests
by Ravi Ladduwahetty
Sri Lanka was once a land that was blessed with rich natural forests. These naturally abundant eco-systems provided the inhabitants of these areas with their daily needs.
Climate, the principal determinant of forest distribution, has not precluded forests in any part of the country. It is also important that forests are located in watershed areas.
When it is so, the rain that falls permeates into the soil as the trees that cover the soil prevents soil erosion. It is for that reason that the rivers are fed even in drought periods. Forests have also been a tremendous influence in preventing soil erosion. Thick roots have been a catalyst in binding the soil.
The forest cover is also a catalyst in convectional rains. When the atmosphere near the ground gets heated and moves up, the surface and environment gets cooler. This air gets condensed and causes rain. It is carried by the winds.
The classification of forests in Sri Lanka:
Tropical thorn forests
These are found in the oldest areas of the North Western and South Eastern sectors of the country. The rainfall that is derived from these forests from the North East Monsoon is under 1250 mm per annum and a moisture deficit period of 4-7 months from March to September. It is a low open thorny scrub with isolated patches of trees.
The common species in these types of forests are: Heen Karamba (Carissa spirarium), Eraminiya (Zizyphus), Maha Andara (Acacia leucopholea and Acacia planiformis), Andara (Dicrostachys cinera), The isolated patches of trees comprise mainly of Maliththan (Salvador persica) and Palu (Manilkara hexandra)
Dry evergreen forests
These occur mainly in the dry zone such as in Hambantota, Puttalam, Vellankulam and Nachchikadu where the mean annual rainfall varies from 1250 mm to 1900 mm received from October to January with a pronounced dry period from June to September.
The main vegetation in these areas comprise Palu.
Moist Deciduous forests
These too occur in the Dry Zone of which the main characteristic is the emergent dominants which rises above the three metre level. The general canopy is 25 metres in height. Most of the emergent species are: Satin (Burutha- Chrolophylla sweetnia), Milla (Vortex Pinnata), Thel Kaduru (Sapium insignia), Bora Deminiya (Grewia polygama), Halmilla (Berrya cordiflora) and Kotel (Adima cordiflora). Common evergreen species are: Ebony (Diospyros ebenum), Weerawarna (Alseodaphne sermicarpitoa).
The pillar species are abundant which gives it an evergreen character. This is a secondary character of forests which has been developed in the last 400-500 years.
Moist Semi Evergreen Forests
This is characteristic of the intermediate zone where the annual rainfall ranges from 1900 mm to 2500 mm which peaks between October and January followed by a dry season. This is best developed in the Moneragala District. The species ranges from Wal Del (Arterocarpus nobilis), Milla (Vitex pinnata), Pihimbiya (Filicium decipiens), Welang (Pterospermum canescens) and Hulang Hik (Chukrasia tabularis)
Wet Semi Evergreen Forests
This is also characteristic of the dry zone which are found mainly on the eastern slopes of the central hills between 300 metres and 900 metres altitude belonging to both the Intermediate and Dry Zones around Badulla and Bibile. The Savannah Conditions are maintained by repeated burning during drought periods. This is an open plant community of scattered trees amidst a sea of grass. The tree species are: Aralu (Terminalia chebula), Bulu (Terminalia belerica), Kahata (Careyea arborea) and Nelli (Eblica officianalis). The two principle types of grass which are available are: Iluk (Cylindrika) and Mena (Cymbopogan confortiflorus)
Tropical Savannah Forests
This is found mainly in the eastern slopes of the central hills between 300 and 900 metre altitudes belonging to both the intermediate and dry zones around Badulla and Bibile.These conditions are maintained by repeated droughts during drought periods.This is an open plant community of trees amidst a sea of grass.The tree species are: Aralu (Terminalia chebula), Bulu (Terminalia belerica) Nelli (Eblica Offinales) and Kahata (Careyea Arborea)
Tropical Wet Evergreen Forests
These types of forests represent the vegetative climax of the wet zone in the south west sector of the country- characterised by the 2500 mm - 5000 mm of rainfall with no moisture deficits.
These forests are best developed in the lowlands below 900 metres. The canopy is dense with evergreen trees rising from 25-45 metres. The four plant communities those have been identified with these forests are: Hora (Dipterocarpus zelanicus), Nedun (Mesua doona) Aridda (Camphosperma), Milla (Vites) and Hedawaka (Chaetocarpus)
Sub Montane Ever Green Forests
These forests occur in the hills between 900-1500 metres in the Wet Zone. The vegetation is essentially transitional, being immediate in the structure and physiognomy between the Wet Evergreen and Montane Evergreen Forests, occurring in the Adam's Peak's Range around Hatton, Kotagala and the Upper slopes of Sinharaja. The characteristic trees those are found are: Gurendra (Celtis cinnammea) Ubberiya (Calcina) Keena (Caleba) and Sudu Kadumberiya (Diospyros sylvatica)
Montane Ever Green Forests
Montane Evergren Forests is characteristic of the highland hills above 1500 metres in the Wet Zone. The forest is low reaching around 13 metres in the better sites. The trees are in poor form with the dense with dense spread with flat crowns. In exposed situations These forests are characteristic of highland hills above 1500 metres in the wet zone. The forest is low reaching around 13 metres in the better sites.
The trees are in poor form with the dense spread with flat crowns. In exposed situations, the canopy is low and the trees have a marked appearance. The principal species found in these forests are: Maha Rathmal (Rhododendron arboreum) and bamboo (Teaniostachyum attentium)
Grasslands comprise four main types- Damana, Villu, Wet Patnas and Talawas. Damana is a Savannah type vegetation found in the lowland dry zone but differs from tropical Savannah. Villu is a grassland often associated with wetland conditions around abundant irrigation tanks, river banks, water holes and flood plains. Patnas have been classified as wet and Dry lands depending on locations- the former found at an elevation of around 1400 metres with no moisture deficit periods. Tala wa is found in the low country wet zone intermixed with trees which occur in clumps.
Produced by Lake House