Reclaiming the Rajasthan desert from a voracious Mexican plant

Long after a 19th-century English watercolourist painted the massive outcrop of barren volcanic rocks on which the formidable Jodhpur fort is perched, a modernising maharajah went up in his two-seater Tiger Moth plane to scatter bagfuls of mesquite seed in order to green his desert kingdom in Rajasthan. The Prosopis juliflora variety of the mesquite that the flying maharajah planted in the 1930s not only lay siege to his fort, described by Rudyard Kipling as "the work of angels, fairies and giants", but eventually took over large stretches of the Thar desert. The thorny, leguminous mesquite can grow to be either shrub or tree, and was imported by the colonial British to afforest the desert wastelands of western India. It is hardy, drought-resistant and originally from Mexico. Today it dominates over half a million hectares across the country's arid zones, and has been at the centre of debates over the ecological, social and economic impact of introducing exotic species into India. In Jodhpur, villagers have renamed the Prosopis juliflora as baavlia ("the mad one"), with good reason. "It can grow even in the crevices of hard volcanic rocks on little bits of moist soil and it outcompetes and chokes all vegetation," said naturalist Pradip Krishen, who is attempting to bring Rajasthan native plants back. "In the Kutch region of Gujarat it even eliminated Asia's largest grasslands." But scientists at the government's Central Arid Zone Research Institute in Jodhpur look at it differently. While recognising the damage caused by Prosopis juliflora, they emphasise its usefulness in a backward economy – its wood, for instance, is excellent for fuel and its pod provides not just food for cattle but also flour for the poor. But the main reason for the official support for the plant is its invincibility – even Australia is struggling to eradicate it. In the 1890 water-colour of the Mehrangarh citadel, the multi-stemmed cactus-like succulent thhor (Euphorbia caducifolia) and other native plants and shrubs can be seen in between the volcanic rhyolite rock, which geologists say is 750m years old. Once Prosopis juliflora took root, the native plants were ousted, but they have now been reintroduced, thanks to an extraordinary effort at ecological restoration. In 2006, Krishen took up the assignment to convert 70 hectares of the rocky land around the fort into a nature park. The biggest challenge was to uproot the Prosopis juliflora from the hard rhyolite. The "mad one" regenerates unless its roots are destroyed to a depth of 18in (46cm). After compressor-driven corkscrew tools, herbicides and tiny charges of dynamite proved unsuitable, Krishen hired a team of local sandstone miners. Their traditional skills brought success. They could "hear" inside the rocks with their hammers, ascertain the angle and depth of the crevices, and then precisely chisel down to cut the roots. As patches of the rocky landscape got cleared of the deadly Mexican shrub, Krishen had to figure out what to plant in its place. He decided he would only use native species. "The British have a lovely word for it – rewilding," he said. "Native plants have adapted to the harsh local conditions over millions of years. I resolved that no plant deserves to be in the Rao Jodha Desert Rock Park if it doesn't survive on its own. It would be crazy to have to water them." (The region gets just six inches of rainfall annually.) Krishen is not a botanist – he was a film-maker before he turned naturalist and wrote two bestsellers on trees – nor was he familiar with desert flora. But the previous monsoon he had already begun scouring the desert with an octogenarian botanist who proved to be an invaluable teacher and field guide. During the past eight years, dozens of desert species have been brought to Jodhpur, tested in a nursery with different soils and water content, catalogued, and planted in the park. Not one species has been lost. As the sparse monsoon arrives in the coming days, the park will turn verdant green, and then burst into myriad colours as flowers sprout over 300 desert species of trees, shrubs, climbers and herbs, including grasses and sedges. Later, during the dry seasons, desert perennials will beautify the park. Ecologists, botanists and landscape architects have hailed Krishen's creation as an inspiring model for the rehabilitation of native plants. But on the ground the native versus exotic debate remains one-sided – the government continues to import trees and shrubs as sand-binders for the desert, the latest being Israeli babool (Acacia tortilis). "I saw a sand dune completely dominated by this tree," said Krishen. "Who knows how it'll run amuck."