Arid zone vegetations of Sri Lanka
Arid zone vegetations of Sri Lanka is most evident in the areas of Hambantota in southern Sri Lanka and Puttalam in North-west Sri Lanka, where the rainfall at the minimum level in the island. Usually, the travellers, who take Sri Lanka road trip come across Yala and Hambantota where this type of vegetation can be seen.
Due to the large variation of annual rainfall, vegetation and different topographical features, the forests in Sri Lanka are divided into mainly six categories. Arid zone forest type is the least attractive of all these forest types and it is dominated by thorn and scrub bushes. This forest type can be seen in the north-west coastal belt from Mannar to Jaffna and South-East coastal belt from Hambantota to Yala.
It has no visible layers and the tree canopy is around 5 meters from the ground, due to the thorn bush that grows only up to 5 meters at maximum. Pockets of some taller trees and grassy plains can be seen especially near the water sources such as rivers, tanks and streams.
Riverbank, where the water is available in abundance is occupied by taller and bigger trees such as kumbuk (Termenella arjuna) and it is identified as riverine forest type. Large tree canopy that bent over the watercourse, obstruct the heat of the sun reaching the water surface, thereby lowering the water temperature than average.
Despite the unhealthy green vegetation than the rain forests (Singaraja rain forest) or Montane forests (Horton plain national park), it harbours a large number of animal species, especially large, charismatic species like elephants (Elephas maximus) and deer. One of the best places to see arid zone vegetation is Block 1 of Yala national park. Block 1 of Yala is most popular for leopard (Panthera pardus Kotiya) watching in Sri Lanka and it is inhabited by other animals as well such as elephant, deer, wild boar, buffalo etc.
The thorn scrub forest is the best vegetation that survives in the climatic conditions such as dry, harsh and warm that prevails in the arid zone. The trees are gnarled trees with small leave and the large thorn is an evolution to save water. Especially the small leaves are the distinct character of the dry zone vegetation, which helps to save water.
Having many small leaves instead of a few big leaves allow the trees to survive a destructive attack of the herbivores. Large thorn provides protection against some animal species in the forest. The forest trees that grow among the thorn scrubs are consist of palu (Manilkara hexandra) and drypetes (Drypetes sepiaria).
The former is very popular for its solid, horizontal boughs and are being used by the leopards for resting. These trees have small, thick, dark green leaves and they produce a small, sweet, yellow coloured fruit mainly in May and June. The fruit attracts varied wildlife and sloth bear (Melursus ursus) is one animal that loves most the taste of this fruit.
The Bear is glued to these yellow berries and they break entire branches in their enthusiasm to access the sweet berries. The bear drop berries aplenty, allowing other animals such as wild boar (Sus scrofa), deer and a large number of other smaller animals to have their share in the jungle.
Thorn scrubs can be seen in a variety of shrubby species such as umbrella thorn (Acacia planifrons), equipped with both long, straight spikes and small, hooked spines, thereby doubling its defences. A large number of other spiky species such as hin katu pila (Flueggea leucopyrus), is selectively eaten by deer despite the small leaves and large thorns. Maha geta kulu (Randia malabarica), ranawara (Cassia auriculara), heen karamba (Carrisa spinarum), katu niyada (Azima tetracantha) and andara (Dichrostachys cinerea) which possesses the most lethal-looking thorn of all.
The rain occurs mainly during the North-east monsoon from October to January. During which the whole area is soaked and runoff water ultimately is gathered in small lakes and low land areas. The rest of the year, other than the few months during the monsoon is relatively dry and latter part of the dry season result in the very scarcity of water in the forest.
The wild animal often wandering to nearby areas in search of water and vegetation is dried out. With the advent of the rain whole region come to live and threes, plants, bushes and grass become green and add colour to the beautiful atmosphere.
Thorn scrub jungles are inhabited by a large number of bird species. There are several bird species that are only confined to these areas. Black-necked Stork, Grey Francolin, Indian Courser and Eurasian Collared-Dove are several common species that inhabit the arid zone vegetations of Sri Lanka.