One minute, my guide and I were alone in the Gabonese jungle — and the next, we were in trouble. The guide — a N’komi tribesman who, to save his blushes, I won’t name — had been explaining how the mysterious Bwiti sect likes to burn the bitter sap of the Aucoumea klaineana tree to keep vampires away, and how to use an ant-infested shrub, known as adultère noire, to extract a confession from an adulterous wife, but he broke off to drag me behind a bush. “Forest elephants,” he grunted, “and they’re drunk!” There were eight of them: big, fat, swaggering tuskers, swaying slightly and clearly having a good time until they spotted us in their path. It was like encountering a Geordie hen party in the Palm House at Kew.

Ten minutes ago, this barefoot encyclopedia had pointed out the oafaca tree, a soaring white trunk elevated on mangrove-like roots that stab through the dark soil like the bars of a cage. “If elephants surprise us, we hide in here,” he said, and I thought he was joking — how could an elephant sneak up on us? Now, 10 yards away, a half-cut pachyderm with tusks like yellow lances closed one bloodshot eye to focus while her lairy, nut-brown companions waved her on with their trunks.

“See how much smaller they are than savanna elephants?” whispered the guide as the big female flapped her ears and stamped her foot. It was like being told the truck that’s about to hit you weighs loads less than a freight train. “They can reach 25mph in a sprint,” he added, unhelpfully.

I looked around for an oafaca tree, wondering if I could make 26mph.

My guide held me back. “Stay put,” he advised. “They’re stoned on that iboga fruit you’ve been eating.

It contains hallucinogens that make them paranoid and aggressive.”

Overhead, a passing troop of red-faced mangabeys hooted in derision before crashing off through the canopy, while a nine-inch millipede with a body like stainless steel crawled across my hand and into the leaf litter. The musty smell of snake was all around, suggesting that somewhere nearby lurked Bitis gabonica — the gorgeous gaboon viper. Typical bites inject up to 600mg of venom through fangs as long as your thumb, and just 100mg will kill a man. So will hallucinating elephants, and so will the vampires. You would expect no less from the Heart of Darkness.

IF YOU’VE been to Africa, the chances are you’ve seen the beige bits, the dry and dusty locales characterised by rain-chasing migrations and shade-seeking predators. This is a tale from the green bit, the dripping jungles of Tarzan and Mary Kingsley, where the beaten track is made by elephants and the only tourist trail is blazed by beach-bound gorillas.

This is Gabon, and as you fly south from the capital, Libreville, to the lodge at Loango, the jungle spreads out to the horizon like a dense green overcast. It only ends at the beach, where hippos come to play in the white surf. Three-quarters of this prosperous, stable West African country is forested, and people disappear here. Three months ago, an American bird-watcher, exhausted by a long climb, volunteered to wait with the rucksacks while the rest of the party continued to a rare nesting site. When they returned, 90 minutes later, the bags were still there. The American wasn’t. He hasn’t been seen since.

Eleven thousand square miles of this Eden have been saved, and for that, the biologists Mike Fay and Lee White, and Gabon’s president, Omar Bongo, will go to heaven. In perhaps the most effective PowerPoint presentation in history, Fay and White persuaded Bongo to create 13 national parks in May 2002, protecting for posterity a paradise unparalleled on earth.

Scattered across the Congo basin, most of these parks are all but inaccessible to tourists, but the unique blend of savanna, forest, lagoon and beach that makes up the Loango reserve is a breeze to reach, if only because the lodge’s owner set up an airline to bring visitors here from Libreville.

From the river, Loango Lodge looks like your typical African safari camp, but sneak behind the bamboo screens and the true nature of this facility reveals itself. Military generators throb beside well-appointed workshops, and a dozen serious men sit at banks of computers, surrounded by test tubes, digicams and an incongruously sinister crossbow. Nick M’badinga uses the medieval weapon in the Herman Melville style, firing hollow-point bolts into humpback whales in the heaving Atlantic, five miles downstream, to collect DNA. If your idea of a holiday involves bobbing around in a tiny rubber boat annoying cetaceans the size of trucks, you’re welcome to join him. If you’d rather wrestle crocodiles, Mitch Eaton, crocodile researcher, could use another pair of hands. Or you could join the Gorilla Girls, three intrepid primatologists studying the elusive western lowland gorilla.

The guides here joke that Loango is a top-end safari destination with a few biologists hanging about, and the resident biologists counter that the lodge is a research station with rooms, but the truth is that here — unlike so many other so-called eco-destinations — conservationists and tourists enjoy a symbiotic relationship. Tourism pays for research and local development projects; in turn, researchers and locals welcome the tourists. Gabon is not ideal for everyone: if you want bougainvillea petals on your bed and the Big Five bagged before breakfast, head south or east. If, however, you’re prepared to sweat it out on the off chance that you spot something before it spots you, the rewards are immense.

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