Sri Lanka Rainforests

Category: Forest Biomes.

Geographic Location: Asia.

Summary: This biome is characterized by high endemism, much of which is still unknown, but is critically threatened by direct and indirect human interactions.

Sri Lanka, a large insular landmass off the coast of India, exhibits a rainforest biome in its southwestern portion. These forests exist along an elevation gradient reaching up to more than 8,200 feet (2,500 meters). The stable climate conditions and monsoon rains allow for productive forest environments. Likewise, the isolation from mainland Asia has led to a huge amount of endemism (species found nowhere else) across all taxonomic levels. More new species will undoubtedly be discovered as further exploration and sampling take place.

Sri Lanka comprises about 25,500 square miles (66,000 square kilometers) on the continental shelf of India. Overall, its rainforest ecosystems encompass nearly 15,000 square miles (39,000 square kilometers)—or over half of the southwestern portion of the island. Despite the past geologic land connections between Sri Lanka and India, these rainforests have been isolated from the rainforests of mainland India due to drier, warmer conditions in the areas between them, creating a high degree of endemism on the island.

The two land masses are currently separated by the Palk Straight. While Sri Lanka’s species closely resemble those of the Western Ghats (mountain range in western India), studies have concluded that they are actually quite distinct. Likewise, Sri Lanka and the Indian subcontinent are unique biogeographically because of their Gondwana ancestry, which contrasts with the rest of Asia.

Lowland and montane rainforest ecosystems extend along elevation gradients here. The lowland rainforest falls below 3,300 feet (1,000 meters). Climate in the lowland rainforests remains fairly constant, at 81–86 degrees F (27–30 degrees C) and 80–85 percent relative humidity. Deep valleys radiate away from the central mountains and contain the major rivers of the region.

Montane Sri Lanka rainforests lie above 3,300 feet (1,000 meters) in the Central Massif and the Knuckles Mountains. Overall, there is a trend of a roughly 1-degree F (0.5 degrees C) decrease in air temperature for every 330-foot (100-meter) rise in elevation, making the highlands much cooler. Ground frost is evident frequently during nights from December to February. Likewise, cloud forests characterize many of the high peaks.

Both elevation divisions receive 100–200 inches (250–500 centimeters) of annual rainfall, with most occurring during the May-to-September southwestern monsoon season. The northeastern monsoon also brings rainfall from December to March.

Biodiversity

The biodiversity and endemism of the Sri Lanka Rainforests biome are staggering. Almost all the endemic flora and fauna of the island nation are found in these lowland and montane rainforests. More than 34 percent of the island’s endemic trees, shrubs, and herbs are located in these ecosystems. The lowland rainforests are characterized by two floral communities: the Dipterocarpus-dominated community and the Mesua-Shorea community.

Virgin forests of this ecoregion have four strata: a main canopy at 100–131 feet (30–40 meters), a sub-canopy at 50–100 feet (15–30 meters), an understory at 15–50 feet (5–15 meters), and a sparse shrub layer. Trees of the emergent layer may reach above the main canopy to 150 feet (45 meters).

Generally, montane rainforests host more endemic flora and fauna than lowland rainforests. Among fauna, there are at least 15 endemic or near-endemic mammals; 25 endemic or near-endemic birds; and a mostly unknown but large number of endemic reptiles, fish, and invertebrates, many species of which have not yet been identified.

Few large megafauna call this ecosystem home because of the large areas of habitat they need for survival, but the montane rainforests support a population of the Sri Lankan leopard (Panthera pardus kotiya). The Asian elephant, previously found in the montane forests, is now locally extinct, although there are reports of a few seen in the lowlands. The species, which is classified as endangered, frequently comes into contact with humans as the elephant's range diminishes or fragments. There are 13 endemic and near-endemic species of small mammals here, including shrews, hares, civets, squirrels, and bats.

There are many birds in Sri Lanka, including 20 that are near-endemic, including the Sri Lanka junglefowl (the national bird of Sri Lanka), dull-blue flycatcher, Sri Lanka bush-warbler, Sri Lanka hanging parrot, and the yellow-eared bulbul. Reptiles in Sri Lanka show more endemism than birds and mammals. Frog and lizard species are among those fauna still being newly discovered, along with fish and crab.

Human Impact

Unfortunately, direct and indirect human consequences threaten this biome, with a majority of the rainforest area already lost. Protected areas have been established, but protection and conservation plans are lacking in this rising nation. During the past 200 years, the Sri Lanka rainforests have been cleared for large-scale agriculture under the influence of the British colonizing forces. Human settlements and the development of tea, rubber, and coconut plantations, as well as rice paddies, have encroached on the rainforests. Likewise, exotic trees like Eucalyptus, Cupressus, and Acacia have been planted for construction and firewood. Furthermore, the Mahaweli River Project uses this major river for irrigation and hydroelectric production.

These developments combined have devastated these ecosystems, leaving the majority of lands, habitat, and biodiversity lost or severely affected. Only about 8 percent of the lowland rainforests are not affected; this region contains about 55 percent of Sri Lanka’s human population. Nine protected areas have been established throughout the biome and offer the only real refuge. Unfortunately, adequate enforcement measures and conservation plans are largely absent. The projected effects of climate change on the island are still largely undetermined, but the impact on an already-compromised ecoregion could hardly be positive.

There are several reasons for the conservation shortfalls on Sri Lanka. First, Sri Lanka is emerging from a long period of British colonialism followed by extreme internal conflict, with a civil war between the government and the separatist Liberation Tigers of Tamil Eelam only ending in 2009. However, the country continues to experience regional political turmoil. The 2021 gross domestic product of $84 billion is ranked 73rd in the world. From 2003 to mid-2022 the nation averaged annual growth of 4.88 percent.

Therefore, even as it rockets ahead economically, this fledgling nation needs the support and guidance of international conservation groups, such as the International Union for Conservation of Nature (IUCN). According to the United Nations, 96 percent of the disasters Sri Lanka experiences, including flooding, drought, and landslides, are caused by climate. Continued growth and increasing stability would ideally allow Sri Lanka to protect the huge amount of biodiversity and endemism that exists in its severely threatened rainforests.

Bibliography

Bossuyt, Franky, et al. “Local Endemism Within the Western Ghats-Sri Lanka Biodiversity Hotspot.” Science 306, no. 5695 (October 15, 2004).

Erdelen, Walter. “Forest Ecosystems and Nature Conservation in Sri Lanka.” Biological Conservation 43, no. 2 (1988).

Hanle, Juliana, Balangoda M.P. Singhakumara, and Mark S. Ashton. "Complex Small-Holder Agriculture in Rainforest Buffer Zone, Sri Lanka, Supports Endemic Birds." Frontiers in Ecology and Evolution, vol. 9, 2021. DOI: 10.3389/fevo.2021.608434. Accessed 2 Sept. 2022.

Selvachandran, Jeevethan. "Preparing for the Impact of Climate Change in Sri Lanka." Asia & the Pacific Policy Society, 30 Oct. 2021, www.policyforum.net/preparing-for-the-impact-of-climate-change-in-sri-lanka/. Accessed 2 Sept. 2022.

U.S. Central Intelligence Agency. “The World Factbook 2009: Sri Lanka.” https://www.cia.gov/library/publications/the-world-factbook/geos/ce.html.