Peru's three-in-one preserve.

• Author: Emery, Alex
• Position: Northwestern Biosphere Reserve

An extensive biosphere reserve near Tumbes, on this country's northwestern coast, conserves the secrets of three diverse ecosystems

The great teeth-lined jaws parted with a hiss as the fifteen-foot-long reptile slid out of the murky waters of the Tumbes Paver in search of sunlight.

"That's it!" someone whispered excitedly. "That's the crocodile? It was a moment of triumph. One of the main aims of this expedition, after all, was to follow up on reported sightings of the American crocodile, believed to be endangered in Peru. The discovery came after a week on the road. Put together by Peru's largest television station, Panamericana, our group had set out from the northern coastal city of Tumbes for a month-long trek across Peru's Northwestern Biosphere Reserve.

Nestled between the Pacific Ocean and the Andean foothills near the Ecuadoran border, the reserve sprawls across 600,000 acres and three radically different ecosystems - the equatorial dry forest, the Pacific tropical forest, and the mangroves. Little known outside hard-nosed ecologist circles, the area is home to a phenomenal variety of flora and fauna, many of which are not to be found anywhere else on earth.

At the end of a four-hour ride through bleak hills and dry brush we arrived at our first campsite, a bluff perched high above the wide and fast-flowing Tumbes River, which cuts through Cerros de Amotape National Park - the dry forest.

Sandwiched between the Andes and the Pacific Ocean currents, the dry forest experiences a short, intense rainy season between December and March. Apart from this, dry forest vegetation is able to survive mainly because every nine or ten years the El Nino current brings heavy rains for six or seven months, replenishing groundwater. One hypothesis regarding the evolution of the dry forest is that most of its plant and animal species originated in the Amazon jungle and came across the Andes at Abra de Porculla, the lowest point in the mountain chain, to the south of Tumbes in the area of Lambayeque.

The road leading into the 225,000-acre park winds between stands of mesquite trees and a shrub that locals call borrachera, or drunkenness. The mesquite is one of the few types of trees that has managed to survive in the dry forest. Its root structure, penetrating deep into the soil in search of water, is far larger than the tree itself. These small mesquite groves that dot the roadside are all that remain of the mighty mesquite forests that once covered...