Horton Plains National Park (Sinhala: හෝර්ටන් තැන්න ජාතික උද්‍යානය, romanized: Hortan Thanna Jathika Udyanaya) is a national park in the central highlands of Sri Lanka. It was created in 1988 and covers an area of 31 km² (12 square miles). The park borders the Thotupalakanda Nature Reserve and is located at an elevation of 2,100–2,300 meters (6,900–7,500 feet). It includes highland grasslands and cloud forests. The park has many plant and animal species that are found only in this region.

The Horton Plains are the starting point for three major rivers in Sri Lanka: the Mahaweli, Kelani, and Walawe rivers. In Sinhala, the plains are called Maha Eliya Plains (මහ එළිය තැන්න). Stone tools from the Balangoda culture, which is an ancient group of people, have been found in the area. The land includes grasslands mixed with highland forests and has many plant species that are unique to the region. Large groups of Sri Lankan sambar deer live there, and the park is an Important Bird Area. Many bird species found here are not only unique to Sri Lanka but also only live in the Horton Plains. A major threat to the park is forest dieback, which some studies suggest may be caused by a natural event.

The park is famous for its natural features, such as the steep cliff known as World's End and the waterfall called Baker's Falls.

Physical features

Horton Plains is located on the southern plateau of the central highlands in Sri Lanka. The peaks of Kirigalpoththa (2,389 m or 7,838 ft) and Thotupola Kanda (2,357 m or 7,733 ft), which are the second and third highest mountains in Sri Lanka, are found to the west and north of the area, respectively. The park’s elevation ranges from 1,200 to 2,300 meters (3,900 to 7,500 feet). The rocks in the park are very old, from the Archean age and the high series of the Precambrian era. These rocks include types such as Khondalites, Charnockites, and granitic gneisses. The soil is part of the red-yellow podsolic group, and the top layer is covered with decomposed organic material.

The average yearly rainfall is more than 2,000 mm (79 inches). Thick clouds often reduce the amount of sunlight reaching plants. The average yearly temperature is 13°C (55°F), but temperatures change greatly during the day, reaching up to 27°C (81°F) in the daytime and dropping as low as 5°C (41°F) at night. During the southwest monsoon season, wind speeds can become strong enough to be called gale force. Although rain occurs throughout the year, a dry season happens from January to March. Ground frost is common in February. Mist often lasts most of the day during the wet season. The park has many pools and waterfalls and is considered the most important drainage basin in Sri Lanka. The Horton Plains are the starting point of the Mahaweli, Kelani, and Walawe rivers. The plains also supply water to Belihul Oya, Agra Oya, Kiriketi Oya, Uma Oya, and Bogawantalawa Oya.

World’s End is a steep cliff with an 870-meter (2,850-foot) drop. Baker’s Falls, a waterfall formed by Belihul Oya—a tributary of the Walawe River—is named after Sir Samuel Baker. The waterfall is 20 meters (66 feet) high. Slab Rock Falls is another well-known waterfall in the area.

History

The area was originally called Maha Eliya Thenna, which means "great open plain" in Sinhala. During the British rule, the plains were renamed after Sir Robert Wilmot-Horton, a British governor of Ceylon from 1831 to 1837. He visited the region in 1836 to meet the Ratemahatmaya of Sabaragamuwa. Earlier, in 1834, Lt. William Fisher of the 78th Regiment and Lt. Albert Watson of the 58th Regiment explored the area and claimed to have discovered the plateau. Stone tools from the Balangoda culture, which dates back thousands of years, have been found there. People living in the lowlands climbed the mountains to mine gems, extract iron ore, build irrigation canals, and cut trees for timber. A 6-meter (20-foot) pollen core taken from a wetland showed that during the late Quaternary period, the area had a semi-arid climate and supported a limited variety of plant species.

Sir Joseph Dalton Hooker advised the British government to protect all mountain forests above 5,000 feet from being disturbed. In 1873, an official order was issued to stop cutting down trees in the region. Horton Plains was declared a wildlife sanctuary on December 5, 1969, and later became a national park on March 18, 1988, due to its rich biodiversity. The Peak Wilderness Sanctuary, located to the west, is connected to the park. Horton Plains covers an area of 3,160 hectares (12.2 square miles). It has the largest remaining cloud forest in Sri Lanka. In July 2010, the Central Highlands of Sri Lanka, which includes Horton Plains National Park, the Peak Wilderness Sanctuary, and the Knuckles Mountain Range, was added to the World Heritage List.

Flora

The park's vegetation is divided into two main groups: 2,000 hectares (7.7 square miles) of wet patna (Sinhalese: patana), which includes montane grasslands and shrublands, and 1,160 hectares (4.5 square miles) of subtropical montane evergreen forests. Scientists have recorded nearly 750 plant species from 20 different plant families within the park. The forest canopy, or the top layer of trees, reaches up to 20 meters (66 feet) tall and includes species such as Calophyllum walkeri. These trees grow together with plants from the Myrtaceae family, like Syzygium rotundifolium and Syzygium sclerophyllum, as well as species from the Lauraceae family, such as Litsea, Cinnamomum, and Actinodaphne speciosa. The undergrowth layer, or the area beneath the trees, is mostly covered by Strobilanthes plants. This dense growth limits the growth of smaller herb plants. Dwarf bamboo species, including Indocalamus and Ochlandra, also grow in this layer. Rhodomyrtus tomentosa bushes are commonly found near the edges of the forest and on mountain peaks. Some plants, like Gordonia and Rhododendron arboreum, were originally from the Himalayas but now grow in Sri Lanka and along the Western Ghats of South India. About 54 types of woody plants have been recorded in the park, and half of these are found only in Sri Lanka. Grassland areas are shaped by frequent fires and grazing, and are dominated by plants such as Arundinella villosa and Chrysopogon zeylanicus. Low-lying areas have waterlogged swamps or slow-moving streams, where plants like Aponogeton jacobsenii, Isolopis fluitans, and Utricularia species grow. The bamboo Chimonobambusa densifolia thrives near streams and swamps, while grasses such as Juncus prismatocarpus, Garnotia mutica, Eriocaulon species, and Exacum trinervium are common in these areas. Tussock grasses, like Chrysopogon zeylanicus and Cymbopogon confertiflorus, grow in wet hollows. Grasslands also include herb plants such as Ranunculus, Pedicularis, Senecio, Gentiana, Alchemilla, Eriocaulon, and Ipsea speciosa, a rare type of daffodil orchid. Common boreal herb plants in the park include Viola, Lobelia, Gaultheria, Fragaria, and Plantago.

Tree trunks and branches are covered with many types of ferns, Lycopodium, lichens, and orchids. Old man's beard (Usnea barbata), a type of lichen, hangs from branches and adds to the beauty of the forests. About 16 orchid species are unique to Sri Lanka. Other notable plants include Rhodomyrtus tomentosa shrubs, Gaultheria fragrantissima, herbs like Exacum trinervium, E. walkeri, Drosera indica, and tree ferns such as Cyathea species. A foliose lichen called Anzia, which belongs to the Parmeliaceae family, was discovered in the park in 2007 and had not been recorded in Sri Lanka before. Scientists have different opinions about how the grasslands formed. Some believe the grasslands on dry slopes were created by human activities, such as clearing forests and starting fires, while grasslands in low-lying areas likely formed naturally due to wet conditions, frost, and soil erosion.

Fauna

The region has 24 types of mammals, 87 types of birds, 9 types of reptiles, and 8 types of amphibians. The Sri Lankan elephant no longer lives in the area, with the last known sighting in the 1940s. Today, the sambar deer is the largest and most frequently seen mammal. Some studies suggest there are about 1,500 to 2,000 sambar deer, possibly more than the area can support. Other mammals in the park include Kelaart's long-clawed shrews, toque macaques, purple-faced langurs, rusty-spotted cats, Sri Lankan leopards, wild boars, stripe-necked mongooses, Sri Lankan spotted chevrotains, Indian muntjacs, and grizzled giant squirrels. Fishing cats and European otters visit the park’s wetlands to hunt aquatic animals. A subspecies of red slender loris, the Horton Plains slender loris (Loris tardigradus nycticeboides, formerly Loris lydekkerianus nycticeboides), lives only in Sri Lanka’s highlands and is one of the world’s most endangered primates. In July 2010, researchers from the Zoological Society of London photographed this mammal for the first time.

In 2016, rusty-spotted cats (Prionailurus rubiginosus) were first recorded in Horton Plains National Park at altitudes of 2,084–2,162 meters.

Horton Plains, along with Ohiya, Pattipola, and Ambewela, is one of Sri Lanka’s Important Bird Areas (IBAs). Together with the nearby Peak Wilderness Sanctuary, Horton Plains is home to 21 bird species found only in Sri Lanka. Three of these—dull-blue flycatcher, Sri Lanka white-eye, and Sri Lanka wood pigeon—are found only in Horton Plains. Other endemic birds include Sri Lanka blue magpie, Sri Lanka spurfowl, Sri Lanka junglefowl, yellow-fronted barbet, orange-billed babbler, Sri Lanka bush warbler, and Sri Lanka whistling-thrush. Migrating birds such as swiftlets and alpine swift visit the area in winter. Birds of prey found here include crested serpent eagle, mountain hawk-eagle, black-winged kite, and peregrine falcon. Harriers, which are migratory raptors, also live here. This area is a key wildlife habitat. All six highland endemic birds, including the dull-blue flycatcher, Sri Lanka white-eye, Sri Lanka wood pigeon, and Sri Lanka bush warbler, are found here. Yellow-eared bulbul and black-throated munia are common in the highlands.

Sri Lanka is known for having many amphibians and reptiles. About 15 amphibian species live in the park, including Microhyla zeylanica, Uperodon palmatus, Zakerana greenii, Hydrophylax gracilis, Pseudophilautus alto, Pseudophilautus femoralis, Pseudophilautus frankenbergi, Pseudophilautus microtympanum, Pseudophilautus schmarda, and Taruga eques. De Silva has identified five reptile species in the plains: Calotes nigrilabris, Rhino-horned lizard, Cophotis ceylanica, Lankascincus taprobanensis, and common rough-sided snake. Two fish species, common carp and rainbow trout, live in the park but were introduced by humans. Horton Plains is also home to several endemic crustaceans, such as Caridina singhalensis and Perbrinckia species. The freshwater shrimp Caridina singhalensis lives only in streams with temperatures below 15 degrees Celsius and is now found in only a 10-kilometer stretch of one stream.

Threats and conservation management

Horton Plains was part of a large area that included Agra-Bopats, Moon Plains, and Elk Plains. From 1831 to 1948, it was used for hunting Sambar deer. Elephants and wild boars were also hunted, but less often. During this time, the lower slopes were cleared first for coffee and later for tea plantations. This made Horton Plains and Peak Wilderness separate from other forests and grasslands. Potatoes were grown in the grasslands, but farming stopped in 1977. After becoming a National Park, these areas were restored as grasslands. Problems caused by tourism, such as removing plants, littering, fires, and noise, are major concerns. Other threats include gem mining, logging, collecting plants for decoration or medicine, people moving into the area, poaching, and vehicle traffic. Non-native plants like gorse, Mist Flower, Crofton Weed, Blue Stars, brackens, and Pennisetum species harm local plants. Introduced rainbow trout may also affect native fish, amphibians, and crustaceans.

Because Horton Plains National Park is small, most male leopards have activity areas outside the park. Protecting the park and managing areas outside it are important for saving these animals. Some Sambar deer have died after eating plastic that blocked their digestive systems. Visitors are not allowed to bring plastic into the park. Sambar deer have benefited from the introduced Pennisetum grass.

A new threat, first reported in 1978, is forest dieback. In some areas, especially the edges, this has caused nearly 50% of vegetation to die. Lack of water is the main cause, as droughts are more common now. Frost, which is getting worse, stops new plants from growing. Forest dieback has harmed 22 plant species, with Calophyllum walkeri being the most affected. A study suggests that low calcium in the soil may cause acidification and increased toxicity from metals like aluminum. Loss of nutrients and imbalances in soil micronutrients may also contribute to dieback.