The transformation of this wasteland into a lush, wildlife haven is a remarkable conservation story which has created an excellent tourist attraction in the process. Richard Snailham has followed the story for more than 10 years.

Sexing crocodiles is one of the odder activities that I've taken part in during a lifetime of expeditions. How do you sex a crocodile? A Kenyan on the staff of the Baobab Farm showed me: "You see that?" he said, pointing to a small slit in the young reptile's underbelly. "Put your finger in and if you catch something he's a boy."

We caught, weighed, measured and sexed 46 metre-and-a-half-long crocs that morning, by throwing wet gunny sacks over their heads and rolling a tough rubber band over their jaws before they could do any harm.

For 25 years there has been a crocodile farm twelve kilometres north of Mombasa, just behind the strip of smart hotels that runs along the Indian Ocean shore in an unbroken line.

A quarter of a million years ago the sea level was eight metres higher than today and along this littoral a fringing reef of coral flourished in the shallow waters. Thirty thousand years ago the sea receded and the reef was exposed. Slowly humus collected and a tropical forest grew. Then in 1952 an Austrian set up a factory at Bamburi to gouge out the dead coral limestone and turn it into cement.

Over twenty years this left an ugly scar on the landscape and in 1971 the Bamburi Portland Cement Company, showing an environmental concern probably unprecedented in the Third World, decided to try to green the sterile floor of the quarry. This seemingly impossible challenge was taken up by staff member René Haller, a 36-year-old Swiss agronomist.

It was a desolate moonscape. Brackish pools of slightly saline water lay in the depressions. Virtually nothing grew in the two square kilometres of airless suntrap which the giant diggers had left behind. Today, a wonderland of trees, lakes, plants, wildlife both endemic and imported, rice fields, banana groves, fish, crocodile and ostrich farms, offers inspiration to local Kenyan farmers and a fascinating day out for Mombasans and tourists alike.

How did Haller achieve this? He proposed a two-pronged rehabilitation programme: reforestation and the farming of salt-tolerant fish in the groundwater ponds.

Scuffing about among the rocks in a remote corner of the quarry he found five casuarina trees. Planting more of them was an act of faith but amazingly Casuarina equisetifolia, the "whistling pine", originally from Australia, took root in the sterile limestone. When the saplings seemed to wither, some micro-organisms and soil from around the roots of other healthy casuarinas were introduced, and they recovered.

But though the casuarina, and some conocarpus, another evergreen, did well, nothing else grew-until Haller noticed large millipedes devouring the needles that casuarinas shed all year round. He brought in more of these formidable monsters, up to eleven centimetres long and known locally as "Mombasa trains". Soon their faeces were producing humus and secondary growth was burgeoning.

It is this sharp observation of nature's processes that is René's forté. No chemicals or pesticides are used. Every problem has its natural solution. Wasps built nests on casuarina branches and stung visitors, so Buffalo spiders were introduced to spin their lethal webs in the trees. When the casuarinas turned yellow René found that Longhorn beetles were boring vertically up the trunks. He then saw carcasses of these beetles in pellets regurgitated by Spotted Eagle Owls. An injured female owl was found, released and soon others joined it. The threatened reforestation project was saved.

verything at Baobab Farm has a use and frequently a spin-off: casuarinas don't like slopes, so algaroba trees from Brazil were planted on the quarry edges. Bees were attracted by their fruit and soon 60 beehives were set up. After the millipedes (which incidentally have 256 legs not 1,000) came other animals and plants, each bringing added value to the park: Egyptian geese and Crowned cranes control snails and insects; storks, pelicans and marabous scavenge. Vervet monkeys and fruit-bats pass seedlings in their faeces; bushbuck and the tiny suni antelope feed off the leaves of Asystasia gangetica.

But it is the waterworld that best shows the symbiotic integration that Haller loves so much. Hippopotamus luxuriate in the deep pools of the original quarry. But their droppings and urine, fanned out in classic fashion by those ridiculous-looking but efficient tails, provide nutrients for fish.

Haller found, however, that the fish (Tilapia were always the best bet) never grew to marketable size in the natural pools, so he built a series of tanks and water was pumped in to keep the fish on the move. Rectangular tanks encouraged aggressive territoriality so now he has cylindrical ones where peaceful tilapia constantly circulate against the current. The water, with their excrement and other tasty micro-organisms, runs on into the crocodile farm, where the saurians are fed with slower-growing female tilapia and other dead fauna.

Everything interlocks. The fish now help to sustain the people of the Mombasa area, to whom Baobab Farm also offers considerable employment. Since 1991 crocodile have furnished skins and meat. It was to sort them into pits appropriate to their age and size that I found myself gingerly catching juveniles in 1988. My visits to the Bamburi Quarry Nature Park since then have witnessed exciting developments.

René Haller has turned his attention to newly excavated areas to the north. Oryx, lovers of arid, stony ground, were brought in from north-eastern Kenya to join some eland which had been successfully domesticated two years earlier. More casuarinas were planted and in the strips left after felling, slow-growing hardwoods, acacia and palm now flourish. Among them run three forest trails, for leisure walks, jungle jogs and cycling. An exotic butterfly-shaped butterfly house, 3,000 enclosed cubic metres of recreated coastal forest and grassland, is home to twelve local species and there is a special nursery producing caterpillar food.

Four years ago ostriches were introduced. Now there are 73 - a popular tourist attraction and meat source. A baby giraffe, born last August, brings their total to seven.

After the riots at Likoni two years ago and last year's disastrous flooding, Kenya's tourist numbers dropped significantly, but René, now 64, and Sabine Baer, his resident Swiss biologist, are planning ahead hopefully.

Anyone holidaying between Mombasa and Malindi would be foolish to miss this astonishing example of a wasteland converted to a paradise. It is a heartening experience. And you can buy ash-trays and book-ends cut and polished from fossilised clamshells or ammonites-even if you don't always get to sex crocodiles.

BAMBURI FACTFILE

Bamburi Quarry Nature Trail, at Baobab Farm, is situated a few kilometres north of Mombasa, behind the row of tourist hotels which line the beach front. It is open from 10:00 to 18:00 (19:00 on Saturday) and a bus from Mombasa stops right by the gate. Opening times can be checked on (254) (0)11 - 485729 / 485754 / 485501, by e-mail: baobabfarm@ swiftmombasa.com or on the internet:http://www.baobab farm.com

Published in Travel Africa Edition Nine: Autumn 1999Text is subject to Worldwide Copyright (c)