Yungas: Subtropical Forest

The Yungas (an Aymara word meaning "Warm Lands") is a narrow band of forest along the eastern slope of the Andes Mountains within Peru, Bolivia and northern Argentina. This humid, subtropical natural region is a transitional zone between the Andean highlands and the eastern forests.

Like the surrounding areas, this region belongs to the Neotropic ecozone; the climate is rainy, humid, and warm. Owing to orographic precipitation, the high rainfall creates a thick jungle on the eastern slopes of the Andes.

In Bolivia, Yungas occupies the eastern slopes of the Andean Cordillera Real and extends northeast and north of the cities of La Paz and Cochabamba. This rainy forested belt of rugged terrain (deep valleys and gorges separated by sharp ridges) has its counterparts in Colombia, Ecuador and Peru.

Settlers have been attracted to the area by gold, coca leaves, coffee, cacao (the source of cocoa beans), and many other crops. Government efforts to improve transportation and colonize the region continue.

These forests are highly diverse, ranging from moist lowland forests to evergreen montane and cloud forests. The terrain, formed by valleys, fluvial mountain trails and streams, is exceptionally rugged and varied, contributing to the ecological diversity and richness. A complex mosaic of habitats occurs with changing latitude as well as elevation.

The World Wide Fund for Nature has delineated three yungas ecoregions along the eastern side of the Andes:

• The northernmost is the Peruvian yungas, located entirely within Peru and stretching nearly the whole length of the country.

• The Bolivian yungas lie to the south, mostly in Bolivia. The Inambari River marks the boundary between the Peruvian and Bolivian Yungas.

• The Southern Andean yungas begin in southern Bolivia and continue to the north of Argentina. It is a humid forest region between the drier Gran Chaco region to the east and the dry, high-altitude Puna region to the west. These are transitional zones between the Andean highlands and the eastern forests.

There are high levels of biodiversity and species endemism throughout the regions. Many of the forests are evergreen, and the Southern Andean yungas contain what may be the last evergreen forests resulting from Quaternary glaciations.