The diversity of life-forms and habitats in Colombia has impressed observers since the days of the German explorer Alexander von Humboldt. The complex pattern of climate, soil, and topography has produced an extraordinary range of plants and plant communities that vary through both vertical and horizontal zones. They range from the mangrove swamps of the coasts, the desert scrub of La Guajira, the savanna grasslands and gallery ecosystems of the Atlantic lowlands and the Llanos, and the rainforest of Amazonia and the Chocó region to the widely diverse and complex montane ecosystems of the Andean slopes.

Human intervention has vastly altered what must have been the original vegetation of the Atlantic lowlands and the Andean region. Forests probably covered all but the highest and driest areas, where the soils were unsuited to support them. Today they are restricted to the steepest, most inaccessible slopes and to areas of especially high rainfall in the inner Andes. Elsewhere pasture, crops, or degraded scrub and grass have replaced the original cover of broad-leaved evergreen trees. The first chroniclers often described the Andes as sparsely wooded, a condition they usually attributed to the agriculture and burning practiced by indigenous people. In more recent times, with the increasing number of European cattle, the area in grassland has been vastly extended, both in the mountains and on the Atlantic lowlands. Introduced grass species of African origin are particularly conspicuous.

Even in the most lush forest tracts that remain, such as those that flank the outer sides of the eastern and western ranges, there is much evidence of earlier human occupation. These wet montane forests are characterized by lianas, mosses, orchids, and bromeliads and by such economically valued plants as cinchona, the latex-bearing balata, ivory nut (tagua), and the giant American bamboo. Lumbering has had a minor role because of the singular difficulty of access as well as the absence of forests of any one commercial species. In modern times technological advances have made possible the exploitation of forest species in accessible parts of the Atrato River basin and on the Pacific coast near Buenaventura.

The distinctive páramo biome of the equatorial high mountains reaches its greatest development in Colombia. This alpine vegetation is characterized by tussock grasses, cushion plants, and the treelike frailejón (Espeletia), a curious-looking hairy-leafed genus of some 50 different species. Fire-resistant and adapted to low temperatures and high humidity, it gives special character to the páramo landscape. The lower páramo, below 12,000 feet (3,650 metres), is a transitional belt in which scattered clumps of trees occur. Despite its bleak and forbidding climate, much of the páramo has been significantly altered by human activity, especially wood cutting and burning to promote better grazing. Agriculture has also impinged on its lower reaches, but extensive tracts remain relatively untouched by humans.

The animal life of the forests of the Amazon and Pacific coastal Chocó regions is particularly rich and has supported a considerable export trade to North American and European zoos. It includes anteaters, sloths, several monkey species, tapirs, peccaries, spectacled bears, deer, and such large tropical rodents as agoutis, pacas, and capybaras. Carnivores include pumas and jaguars, which were considered endangered species by the 1980s, and raccoons.

Bird habitats are influenced by elevation, and many species are specific to narrow altitudinal bands, ranging upward and downward only very short distances. The extremely lush birdlife encompasses more than 1,500 species, including toucans, hummingbirds, and those that migrate annually from North America. Among the reptiles, turtles, lizards, snakes, caimans, and crocodiles abound. Some quite unusual species inhabit the land, including earthworms that grow up to six feet in length. Freshwater fish include catfish, bocachica (“smallmouth”), and characins (small, brightly coloured tropical fishes). Electric eels also inhabit the inland waters. The Magdalena and Cauca once supported rich river fisheries, but pollution and unrestrained commercial exploitation have taken a heavy toll.