The impact on animals proved more difficult to assess. The giant wave had caught only a very small number of large mammals, like wild boars, and not a single elephant or leopard was found dead. Pruthu's team predicted that many small mammals, land snails, reptiles, and amphibians would have drowned. But the patchy nature of the water intrusion and the large populations of these groups meant there were plenty of opportunities for recolonization. The catastrophe left tangled masses of vegetation that could serve as nesting sites or hiding places for small mammals, reptiles, and birds.

Pruthu and his team designed a grid of markers throughout the area and began carefully surveying the diversity and abundance of plant and animal species. When that was complete, Pruthu began the more ambitious survey of the remote area known as Block II, which no one had been able to visit for a month after the tsunami. Even under normal conditions, the area is inaccessible during the wet season. Some 40 days after the tidal wave hit, an expedition finally made it in. The wildlife conservation department's assistant director for the southern region, Mr. Jayaratne, and Yala's park warden, Mr. Weragama, led a 25-person crew, and Pruthu led the 8-person CCR science team. Sumith Pilapitiya represented the World Bank.

The first site they visited, Yalawela, had been a large and fertile grassland savanna abutting the Menik Ganga estuary. Most of the grass and almost all the herbs in the Yalawela area had dried up and died. Yet, to the expedition members' pleasure, some grass was already regenerating, and herds of wild buffalo were calmly grazing. The group then evaluated the estuaries, which are a critically important habitat for marine life. Some mangroves had been completely uprooted and moved, and others were broken off at the trunk, but most affected stands of trees showed signs of regrowth.

An archaeological surprise awaited the team at their final stop in Block II, an area called Pottana, where the tsunami had come ashore with such force that the freshwater tank there had been breached and emptied. Pieces of terra-cotta pottery, presumably centuries old, had been unearthed by the strength of the wave. Other shards of terra-cotta most likely came from the rims of ancient wells whose existence had been suspected but never previously confirmed. In some places, expedition members also found pieces of shark cartilage, which may once have been used as currency.

Yala's recovery showed that an ecosystem can rebound quickly from a tsunami if the landscape is sufficiently large and hilly. Areas untouched by the tide of destruction can become centers of recolonization, and coastal plants proved to be resilient.

Slowest to recover were bodies of freshwater that had been flooded with salt water. Even so, most small ponds that were inundated returned to a freshwater state during the next rainy season. Some ponds are still salty because that period brought relatively little rain. The three largest lakes inundated, Diganwala, Pattiya Wala, and Mahaseelawa Wala, all remain salty. The Pottana tank is still broken, but the wildlife conservation department is planning to rebuild it. Within a few years, the only trace of a tsunami in Yala National Park will be a historical display. 

Previous Natural Selections Columns:

Roaming Free in the DMZ
(November, 2006)

Brazilian Rendezvous
(October, 2006)

The Potential Pandemic You've Never Heard Of
(September, 2006)