Alejandro de Humboldt National Park

Listen first. Water is moving somewhere close by, over stones you cannot yet see. The air is heavy and damp, and it carries the smell of wet leaves and red earth. Underfoot, the soil is a rusty, iron-dark colour that stains the edges of your boots. Overhead, the canopy drips long after the last shower has passed. This is the green, wet edge of eastern Cuba, and it feels very far from the beaches most visitors picture.

You are standing in Alejandro de Humboldt National Park. It stretches across the mountains of eastern Cuba, shared between Holguín Province and its neighbour, Guantánamo. In 2001, UNESCO added it to the World Heritage List. The reason was not a palace or a cathedral. It was life itself. Scientists consider this one of the most biologically diverse places on any island in the Caribbean, and many of the plants and animals here live nowhere else on Earth.

The name honours Alexander von Humboldt, the German naturalist and explorer. He travelled through Cuba around 1800 and 1801, during his long journey through the Americas. Humboldt measured, sketched and described almost everything he saw. He wrote about the island's geography, its plants, and also its society, including a sharp criticism of slavery. Cubans still remember him warmly. Some call him the second discoverer of Cuba, a title that carries both affection and respect.

Now look again at that red ground. It is the key to the whole park. Much of these mountains rest on serpentine rock, which forms deep in the Earth and contains heavy metals such as nickel, iron and chromium. The soils that come from this rock are poor and even toxic for most plants. That sounds like a disaster for a forest. In fact, it is the opposite. Over a very long time, plants here adapted to conditions that kill their relatives elsewhere.

This is the first surprise of the place. Hardship created variety. Because so few species could cope with these soils, the ones that did became isolated. They changed slowly, separately, on their own path. The result is a remarkable level of endemism, which simply means species found only in one region. Botanists still find plants here that have never been described before. When you walk a trail, some of the leaves beside you may belong to species known only from these hills.

The second ingredient is rain. The mountains face the trade winds that blow in from the Atlantic. Moist air rises against the slopes, cools, and falls as rain. This corner of Cuba is among the wettest parts of the whole island. Rivers run fast and clear down steep valleys. Mist settles in the hollows in the morning. You will notice that mosses and ferns cover almost every surface that stays still for long enough.

The forest is not one single type. As you move through the park, the landscape changes. In some places, Cuban pines stand tall over a thin, open floor. In others, dense rainforest closes in with broad leaves and climbing vines. On the poorest soils, the vegetation becomes low, tough and scrubby, with small hard leaves. Each zone has its own colour of green, and each has its own community of insects, birds and reptiles.

Some of the park's residents are very small. Here is the third surprise. In 1996, scientists described a frog from these mountains called the Monte Iberia eleuth. An adult is roughly the size of a fingernail, and it ranks among the smallest frogs in the world. You are unlikely to see one, because it hides in the leaf litter. But you may hear the thin, high calls of tiny frogs after rain, coming from the ground all around you.

Other animals are even harder to find. The Cuban solenodon lives in these forests. Locals call it the almiquí. It is a small, shrew-like mammal with a long snout, and it is one of very few mammals that produce venom. Its lineage is extremely old. For many years, scientists feared it was gone, until new sightings confirmed that it survives. It comes out at night, so most visitors only know it through stories and photographs.

There is also a story of loss, or perhaps of hope. These mountains were the last place in Cuba where the ivory-billed woodpecker was reliably seen. It was a large, striking bird with a pale bill. The last confirmed sightings here date from the 1980s. Since then, searches have not confirmed it, and most experts believe it is probably extinct. Still, some birdwatchers look up into the old pines and wonder. Absence, here, is part of the history.

The birds you can see are generous with colour. Watch for the Cuban tody, a tiny round bird with a bright green back and a red throat. The Cuban trogon is the national bird, with red, white and blue feathers that match the flag. Parrots pass overhead in noisy groups. Along the coast, the sheltered water of Taco Bay is a known home for West Indian manatees, the slow, gentle sea mammals that graze on underwater grasses.

The same rock that shapes this forest has value for people too. Not far from the park, the area around Moa is a major centre of nickel mining, built on similar mineral soils. Drive through that zone and you see bare red hills where the forest has been removed. It is a sharp contrast. The protected land around you shows what these mountains look like when the soil stays covered and the rivers stay clear.

Visiting here is a slow experience, and that is part of its value. Trails are often steep, muddy and slippery after rain. Local guides lead most walks, and they know which plants are rare and where the birds feed. Ask them questions. Many grew up in the surrounding villages, and their knowledge of medicinal plants and local names often goes beyond any guidebook. Their stories connect the science of the park with the daily life of the region.

Before you leave, stop for a moment and stand still. Notice the red mud on your shoes, the sound of the nearest stream, and the drip of water from the leaves. Look closely at the plant next to the path. It may grow nowhere else in the world. As you walk back, the light will shift through the canopy, and the frogs may start calling again. The forest will keep working quietly, long after you have gone.