Enclosed within the ancient city walls of Jodhpur, with the Mehrangarh Fort as its pivot, is the 70-hectare Rao Jodha Desert Rock Park which recently opened to the public. While two trails are complete, six more are expected to come up soon. One trail begins at Singhoria Bari, a renovated ancient gateway to the city that now serves as visitors' centre. The mention of a 'rock garden' conjures up images of a couple of centrally highlighted boulders with gravel raked evenly around it Japanese style. Or at least, aesthetically and deliberately arranged piles of rocks with little plants tucked between them. But the Rao Jodha Park is nothing like that. It's literally a vast expanse of hard, volcanic rhyolite rock emerging out of the sandy Thar Desert with hardly enough soil to grow a dozen coconut trees. It doesn't seem possible for anything to survive on rock that gets oven-hot from the mid-day sun, and the area doesn't even receive enough rain to bring relief. And yet, miraculously, more than two hundred species of plants thrive in these conditions. Called lithophytes, these plants of the rocks, range from the statuesque columns of the perennial leafless spurge to seasonal grasses. But the Mehrangarh rock plateau wasn't always like this. Seven years ago, when Pradip Krishen, the author of Trees of Delhi who subsequently became the director of the park, first arrived here on the invitation of the Mehrangarh Museum Trust, he saw a badly degraded rocky hillock. It was overrun by one species, mesquite or Prosopis juliflora. In the early 20th century, seeds of this hardy tree were dispersed from aircraft to green the landscape and stabilise sand dunes. It made good charcoal for wood stoves prevalent in the area until recently. But this well-intentioned effort was to unleash an ecological nightmare. The Mexican mesquite grew faster than people could harvest, and since its seeds are spread by cattle, thickets were quick to form. Soon, it was the only plant visible in the entire landscape. Pradip's first big challenge was to eradicate mesquite, which is virtually indestructible. It monopolised the few spots where plants could grow and then discouraged others from taking root by releasing toxic alkaloids underground. The choice was simple: mesquite or native plants.

Pradip declared war on the monopolising invaders. But it's one thing to declare war and another thing to win the battle.

Merely chopping the tree at the base made it pop up again like the Lernean Hydra. At least, the monster grew only two heads when one was cut off. Mesquite was worse;it sprouted a dozen branches with renewed vigour.

The Achilles' heel of this terror lies 15 inches below the surface where the first roots sprout. This is the budding zone and the reason mesquite rises afresh even after being chopped to the ground. Uprooting this tree from soil is a challenge. But in Mehrangarh, mesquite grew on hard rock.

When Pradip was at his wit's end, the Trust introduced him to a group of local stone miners, the Khandwalia. Dhan Singh Khandwalia is a short, wiry, dark man with enormous, rough hands. Over four centuries ago, his ancestors had built the Fort and his knowledge of the bedrock is unsurpassed. Could he use his knowledge of stone to solve Pradip's problem?

Pradip recalls, Dhan Singh squatted next to a short mesquite tree and struck the rock with a heavy hammer. The resounding tone told his discerning ear where the faults lay. A few more test soundings and he had a plan of attack. After chiseling the rock for an hour, he exposed the mesquite's roots.

Having found his Hercules, Pradip pitted 13 Khandwalia against the Mexican hydra-headed monster. In a task reminiscent of the Twelve Labours of the Greek hero, the Khandwalia were to rid the area of mesquite.

While the stone miners set to work, laboriously pulling up one tree at a time, Pradip explored rocky hills and sands of the Thar Desert. With help from the man who wrote the definitive book on Marwar's desert flora, Dr MM Bhandari, Pradip found plants that were found only in specific remote locations. The professor was elderly and couldn't walk much. He sat at home and directed Pradip, "Go around this hill, you'll find a big rock and maybe it's still splashed with vulture poo. Go down there and you'll find some plants like this. " As Pradip found out, the professor's memory of geographic features was astonishingly accurate. This was how seeds or stem cuttings of many rare plants were collected and brought back to the nursery in Jodhpur for propagation. Dr
Bhandari's help was so critical that Pradip says, "There's only one plant we haven't been able to lay our hands on. It's a succulent called Caralluma edulis. We'll get there. "

After an experimental two-hectare area had been cleared of mesquite, Pradip says he saw the bare, pitmarked landscape and felt a sudden jolt of fear. He recalls, "What if we don't know how to do it? What if we don't choose the right plants? You could end up with 70 hectares of pits and nothing to take juliflora's place. That's a very frightening thing to contemplate. You are not doing something that has a track record, you can't consult people who've already done it, there are no books to look at. We could fail. That was the big fear. " Other knolls were also degraded and grazed, and their local plant life was also in retreat.

Since mesquite had colonised every favourable location, Pradip decided to use the tree as a whereto-plant guide. Once the unwanted Mexican was pulled up, nursery-grown natives took its place. He explains, "If you assume that juliflora seeds fell everywhere and it is growing wherever it could, that's a reasonable assumption. We took the decision casually to plant only where juliflora showed us it was feasible and it turned out to be a very useful way of proceeding. "

In the end, Pradip needn't have worried. The plants, provided security from cattle and people, and a lot of encouragement, did what comes naturally from millennia of adaptation. Today, the Rao Jodha Desert Rock Park is the only place you can see what rocky hills in the Thar Desert looked like five or six centuries ago. Sadly, Dr Bhandari died last year before he could see the Rock Park in full glory.

A steep flight of stone stairs leads down into an 18th century aqueduct. Flanked by plants like silvergrey wall lindenbergia, pale lavender blossoms of Bandra lepidagathis, and the glossy green-leaved rubber vine, the walk is a lesson on how these creatures have learnt to squeeze water even out of rock.

Some, like heart-leaf indigo, live short fast lives, telescoping their entire existence into the narrow window when rains make living on rock bearable. Once the dry season sets in, they shrivel up, germinating only when the rains come again. Others, like the succulent leafless spurge, send their roots deep into the finest fissures in the rock. Even during blazingly hot summer days, hairline fractures in stone hold moisture and are key to the plants' survival.

Suddenly the steep embankments of the aqueduct fall behind and a spectacularly wide vista opens up. The fort, a reminder of past glory, competes for attention with a gentle hill slope, covered with native vegetation, a living, breathing ecological heritage.
The trail leaves the aqueduct and winds across the rocky plateau back to Singhoria Bari.

Today, unique trees, shrubs, herbs, climbers and grasses of the desert thrive, flower, and fruit in this seemingly inhospitable landscape. And in turn, they provide sustenance to creatures large and small, from moths, butterflies, and ants to raptors and wild boar. It's astonishing how little these tough plants of the Marwar rockscape need to survive, and yet they are at the very core of sustaining an entire ecosystem.