SRI LANKAN SALT MARSH

The presence of saltmarsh in Sri Lanka seems anomolous since it seems to be outside the recognised global distribution of this habitat. It was thought to be confined to temperate and high latitude zones.  In Sri Lanka is mainly confined to arid parts of north-western and south-eastern coasts where it may represent the most southerly saltmarsh in the northern hemisphere. 

In a study of saltmarsh on a small islet between Mannar Island and mainland Sri Lanka on the north-western coast several major vegetation types were recognised.  In simplified terms these comprised Suaeda Saltmarsh, Arthrocnemum Saltmarsh, Saltmarsh Pasture, Thorny Salt Scrub, Cynodon-Cyperus Depressions and Cyperus Depressions.

Suaeda Saltmarsh

This vegetation was found to be composed of two physiognomically but phytosociologically distinct vegetation types, one in low strongly maritime zones (described as the maritime community) and one on more inland areas on damp saltmarsh pasture (decribed as the inland community). The maritime community was dominated by Suaeda maritima, forming shrubs unto 75 cm high, together with sporadic patches of Suaeda monoica and Suaeda nudiflora. Other less common species included Cynodon dactylon, Evolvulus alsinoides, Portulaca tuberosa, Portulaca wightiana and Salicornia brachiata. In the inland communities Suaeda monoica and Suaeda nudiflora were the dominant species forming shrubby vegetation up to 1.5m high. Less common species here included Arthrocnemum indicum, Cynodon dactylon and Salicornia brachiata.

Arthrocnemum Saltmarsh

Situated between the inland Suaeda saltmarsh and thorny salt scrub this vegetation largely comprised almost mono-specific stands of Arthrocnemum indicum. However, up to 50% of this zone was bare ground. The few other species included Cynodon dactylon and Salicornia brachiata.

Saltmarsh Pasture

This complex of grass-dominated vegetation could be further divided in dry saltmarsh pasture, damp saltmarsh pasture and mixed saltmarsh pasture.

Dry saltmarsh pasture
These pastures comprise dwarf turf with up to 40% bare ground. It can become very parched during draughts and is rarly influenced by sea water. Other scattered species included Acacia planifrons, Aloe barbadensis, Asparagus racemosus, Coccinia grandis, Calotropis gigantea, Dactyloctenium aegyptium, Dyschoriste madurensis, Enicostema verticillare, Epaltis divaricata, Euphorbia antiquorum, Euphorbia hirta, Evolvolus alsinoides, Grewia tenax, Hybanthus enneaspermus, Ocimum canum, Portulaca tuberosa, Portulaca wightiana, Salvadora persica, Sida retusa and Zornia diphylla.

Damp saltmarsh pasture
Forming in relatively low lying areas this largely comprise closed turf of Cynodon dactylon. The vegetation is generally flooded in wet months and occasionally inundated by sea water. Other species such as Arthrocnemum indicum, Cressa cretica, Cyperus pumilus, Cyperus rotundus and Salicornia brachiata occur sporadically.

Mixed saltmarsh pasture
This vegetation represents a transition zone or ecotone between the main saltmarsh pasture types and other communities. For example, in the transition zone to thorn scrub mixed swards of Cynodon dactylon, Eragrostis tenella and Zoysia matrella were found in association with Acacia eburnea, Acacia planifrons, Aloe barbadensis, Asparagus racemosus, Hibiscus macranthus, Hybanthus enneaspermus, Ocimum canum, Portulaca tuberosa and Portulaca wightiana.

Thorny Salt Scrub

Representing the final stage in saltmarsh succession these scrub zones form an almost continuous belt at the top of the saltmarsh. They are never inundated by seawater but all the species are adapted to the dry maritime conditions. In places they show clear stratification with up to three distinct layers. The uppermost tree layer includes Acacia eburnea, Acacia planifrons, Azima tetracantha, Cassia auriculata and Coccinia grandis. Underneath is a discontinous layer of shrubs mainly comprising Aloe barbadensis, Asparagus racemososus, Calotrophis gigantea, Euphorbia antiquorum and Ocimum canum.  The field layer comprises small herbs such as Enicostema verticillare, Evolvulus alsinoides, Hibiscus micranthus, Hybanthus enneaspermus, Portulaca tuberosa Portulaca wightiana and thegrasses Cynodon dactylon and Zoysia matrella.

Cynodon-Cyperus Saline Depressions

In stabilised depressions scattered in low-lying regions up to 2 m below the level of other communities and regularly flooded by high tides, the vegetation comprised closed but dwarf swards dominated by Cynodon dactylon, Cyperus pumilus and Cyperus rotundus together with Salicornia brachiata. In the rainy season therophytes such as Cressa cretica and Heliotropium supinum would appear. The presence of tubers on Cyperus rotundus is thought to help it overcome prolonged exposure to floods and tides.

Cyperus Saline Depressions

Occupying brackish depressions with the thorn-scrub belts are stands of Cyperus rotundus together with occasional individuals of Cynodon dactylon, Ocimum canum, Portulaca tuberosa and Zoysia matrella.

References

Pemadasa, M. A., Balasubramaniam, S., Wijewansa, H. G. & Amarasinghe, L. 1979. The ecology of saltmarsh in Sri Lanka. Journal of Ecology, 67: 41-63.