Human populations have risen sharply in South Asia in the past century, leading to a greater demand for land for agricultural and other purposes. This has had a profound impact on the wildlife of the region, as areas of uncultivated land have shrunk and become fragmented. Even in areas which have not been formally 'claimed' by Human populations, habitats are often degraded by activities such as fire-setting, Cattle grazing, and the collection of thatch and timber.
The Chitwan National Park in Nepal contains slightly over 950 km² of 'wild' landscape providing a habitat to large Mammals such as Greater One-horned Rhinoceros, Rhinoceros unicornis, Asian Elephant, Elephas maximus, Gaur, Bos gaurus, and Bengal Tiger, Panthera tigris. However, while in theory protected from Human actions, both this environment and the buffer zone surrounding in (in which only a limited range of Human activities are allowed), are coming being altered by Human pressures, leading to changes in the numbers and distributions of the Animals within the park.
Five species of Rhinoceros still survive on Earth. The most numerous of these, the White Rhinoceros, Ceratotherium simum, currently has a population estimated to be between 17 212 and 18 915, and is found in semi-arid grasslands in Southern Africa. The Black Rhinoceros, Diceros bicornis, has an estimated population of between 5366 and 5630 individuals, found in dry woodland savannah, although with a population fragmented and largely confined to protected reserves. The Greater One-horned Rhinoceros, Rhinoceros unicornis, is the most numerous surviving Asian Rhinoceros, with a population of over 3700, inhabit the moist riverine grasslands and alluvial floodplains of Ganges, Brahmaputra, and Sindh rivers and their tributaries. Less than 80 Sumatran Rhinoceros, Dicerorrhinus sumentransis, are thought to be alive today, living in the rainforests of Sumatra, Peninsula Malaysia, and Borneo. An estimated 75 Javan Rhinoceros, Rhinoceros sondaicus, still survive in the lowland forests of the Ujung Kulon National Park, on the westernmost tip of Java.
The Sumatran and Javan Rhinoceros are the two rarest large Mammals surviving, and both are currently classified as Critically Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species. The Greater One-horned Rhinoceros was formerly classified as Endangered, but was downgraded to Vulnerable following a significant recovery of the population of this species in the Kaziranga National Park in India. The Black Rhinoceros is still considered to be Critically Endangered, due to its highly fragmented population, and the threat of poaching, while the White Rhinoceros is Near Threatened.
There are currently 752 known Rhinoceros with Nepal, 694 of which are found within the Chitwan National Park, where they inhabit the riverine grasslands of Reu, Rapti and Narayani rivers, while the remaining 17 are found within the Suklaphanta National Park, where they are found in mixed riverine forests and tall grasslands associated with the Chaudhar and Mahakali rivers. Greater One-horned Rhinoceros favour areas close to rivers, wallowing in riverbeds and feeding grasslands and open woodlands. They will occasionally retreat into more dense woodland to seek shelter during monsoons, and rarely visit croplands to feed on aggricultural products. Their favoured enviroment is grassland dominated by Wild Sugercane, Saccharum spontaneum.
In a paper published in the Asian Journal of Conservation Biology in July 2023, Prayag Raj Kuikel and Khadga Basnet of the Central Department of Zoology at Tribhuvan University, present the results of a study of changing land use by Greater One-horned Rhinoceros in the Chitwan National Park, in response to changing habitats within the park.
Previous studies of Rhinoceros in the Chitwan National Park have shown that their distribution has changed in recent years with the majority shifting from the eastern part of the park to the western part, but no attention has been given to date to the cause of this shift.
The Chitwan National Park was Nepal's first national park, created in 1973, and was made a UNESCO World Heritage Site for the international significance of its unique wetlands in 1984. The park comprises a variety of lowland ecosystems within the wider Inner Tarai ecozone, including the Churia and Someshwor hills, the flood plains of the Reu, Rapti and Narayani rivers, and numerous ox-bow lakes. The eastern boundary of the park abuts the Parsa National Park.
Kuikel and Basnet looked at the way in which the Rhinoceros were using the landscape, and the way in which that landscape changed over time, using field observations, satellite data, and geographical information systems. The landscape was divided into a series of categories, river area, sparse forest, dense forest, riverbed, bushes, cultivable land, and barren land, and Landsat images from 1993, 2000, 2010 and 2014, were used to track the way that these had changed over time.
Fieldwork was carried out in the Chitwan National Park between December 2016 and September 2017, both on foot, by canoe, and on Elephant back. This was done to provide ground truth of environmental interpretations of landscape type, as well as to carry out direct observations of Rhinoceros. Direct observations of Rhinoceros were made in both the eastern and western regions of the park, while the presence of Rhinoceros on islands in the Narayani River was confirmed by the identification of dung. Animals were classified as calves if they were under four years old, subadults if they were four-to-six-year old, and adults if they were over six. Sightings of Rhinoceros were mapped against landscape type using Arc GIS software.
Most prior studies of Greater One-horned Rhinoceros have concluded that their preferred habitat is riverine grasslands, so Kuikel and Basnet concentrated their efforts on the grasslands associated with the Reu, Rapti and Narayani rivers. The use of each landscape type was calculated by the number of Rhinoceros sightings there as a total of the whole. Areas infested by the invasive Climbing Hemp Vine, Mikania micrantha, was also mapped, as was the condition of the land, state of water bodies, and areas of drought or flood, and variations in vegetation cover.
Kuikel and Basnet found that dense forest cover increased by 196 km² between 1993 and 2014, while grassland and sparse forest decreased by 154 km², and cultivatable land decreased by 56 km². Baren land increased by 56 km², and river cover increased by 14 km², while other land cover types remained roughly constant.
In line with predictions, 49% of all Rhinoceros sightings occurred in open forest or grassland environments, with 38% in riverine forests, 10% in rivers, and 3% in dense forests. The two land cover forms which increased the most in the park were both largely unused by Rhinoceros.
While the over the entire area of the park the areas favoured by Rhinoceros decreased, in the western part of the area there was an increase in river area, and therefore also in land in close proximity to rivers, as well as in the amount of land covered by pure stands of Wild Sugarcane. Infestations of Climbing Hemp Vine covered 23.3% of the land area in the eastern area and 18.3% in the western area, with this particularly affecting rivers, riverine forests, and grasslands. The eastern area was also affected by drought, which was apparently driven by vegetative succession; forms of vegetation which were not washed away by the annual floods had taken hold, leading to the formation of new dykes, which altered the flow of waterways. Only seventeen areas where found in the eastern area where the annual flood cleared areas of vegetation in the eastern part of the park, compared to 32 in the western part. These areas were those colonised each year by Wild Sugarcane, creating the favoured environment for Rhinoceros.
The habitat favoured by Rhinoceros in the Chitwan National Park is steadily decreasing, and it is likely that following current conservation practices will cause it to decrease further. Dense forest and baren areas, both avoided by Rhinoceros, are increasing within the park, while grasslands and mixed woodland, which are important Rhinoceros habitats, are decreasing. Human behaviour is generally assumed to be the major cause of habitat loss for species such as Rhinoceros, though in the case of the Chitwan National Park, the major problem appears to be vegetative succession in undisturbed land. This has been made words by the rapid spread of the invasive Climbing Hemp Vine, as well as indiscriminate fire setting and overgrazing of domestic Animals (leading to the formation of barren areas.
Greater One-horned Rhinoceros require flood plain grasslands and open forest in order to thrive. They also utilise the rivers themselves. In the Chitwan National Park areas formerly utilised for agriculture have been returned to nature, creating new habitats, but over time flood plain grasslands develop into open woodland, and then dense woodland, effectively excluding the Rhinoceros.
Over time the eastern part of the park has dried and become more heavily forested, while the amount of wetlands in the western part of the reserve has increased slightly, causing the Rhinoceros to shift towards the western end of the park. While the Rhinoceros are currently finding suitable habitats in the west of the park, the general trend is towards drying and afforestation across the whole area, with the spread of the invasive Climbing Hemp Vine, which supplants native species such as Wild Sugarcane, the main food of the Rhinoceros also impacting the available space for the species.
Kuikel and Basnet recommend that future conservation efforts in the Chitwan National Park include the maintenance of stable wetlands and a management plan for the invasive Climbing Hemp Vine.
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