Natural Selections: Life After the Wave

The 2004 tsunami devastated Sri Lanka's landscape, but ecologists predict it will recover.

By Mary C. Pearl|Tuesday, December 05, 2006
Prithiviraj "Pruthu" Fernando, a wiry, bespectacled biologist, was visiting his home in Colombo, Sri Lanka, for a much-anticipated Christmas vacation in 2004 when one of his friends who lived by the shore called him and said something strange had happened to the sea. At first, he and most people in Sri Lanka—even eyewitnesses—thought it was a localized affair. Then, throughout the day, news came in of more and more destruction and more people injured or dead. Finally, perceiving the magnitude of the tsunami, Pruthu and his colleagues from the Centre for Conservation and Research (CCR) grabbed medical supplies and headed south to the most stricken area to do what they could for the victims.

Little has been written about the impact of a tsunami on the natural landscape. Pruthu had been working on elephant conservation at Yala National Park, a vast 242,000-acre reserve outside Colombo that is home to elephants, leopards, wild buffalo, chital deer, and rare and magnificent birds like the lesser adjutant stork and the Malabar pied hornbill. He had been told the park was completely destroyed, yet when he returned to work two weeks after the tsunami, he saw that the impact was surprisingly patchy.

Members of the Department of Wildlife Conservation asked Pruthu to help them assess the damage. They had decided that cleanup was a priority, but Pruthu saw a different need. A survey of the scientific literature had turned up no published accounts of how a natural ecosystem responds to a tsunami. Because a tsunami is a natural phenomenon, Pruthu persuaded the authorities to postpone clearing away debris after the December 26, 2004 event and instead take the opportunity to monitor how a natural coastal forest recovers from such a catastrophe.

On foot Pruthu and his team immediately began mapping the affected area and collecting information on the severity of the damage in the portion of the park closest to the sea, a sector known as Block I, where an area about 10 miles long had suffered the brunt of the tidal wave. Most of the coastal zone in Yala was protected by sand dunes rising over 25 feet. On the other hand, ocean waters had rushed into areas like lagoon outlets where there were natural or artificial breaks in the dunes. The flooded area totaled three square miles in 12 different segments of the park, and salt water had poured into four freshwater ponds, or "tanks" (man-made water reservoirs up to several miles wide that were created by Sri Lankan kings in the 12th century). The force of the wave, the inundation of salt water, and the deposition of sand had heavily damaged the vegetation of Block I. Most of the grasses and herbs that had been drowned in salt water perished. Trees and bushes, by contrast, were most affected not by the salt water but by the tremendous force of the wave. Fortunately, the vegetation began to recover almost immediately, except for trees that had been completely uprooted.

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. 

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