Virgen de las Flores

by Carina Kozmich and Hannah Perlinger

Climate and vegetation of the Eastern Cordillera

The eastern Andean forelands in the area of Tucumán are part of the outer Tropics, receiving plenty of rainfall during summer - the savanna landscape of the Gran Chaco starts or ends here. The eastern slopes of the Andes, however, reveive rainfall all year round, as the air pushed against the mountains by the trade winds is forced to lift up and cools down. The impressive result of this situation are the yungas: this humid, evergreen mountain rainforest can be characterized as cloud forest in its upper part, near the condensation level. The yungas extend from southwestern Bolivia all the way to northwestern Argentina. They grow above approx. 800 m asl. The busy road leading from Tafí del Valle down to the forelands suddenly dives into this mysterious world, and winds itself down through the Quebrada de Los Sosa in steep and narrow turns. Only a few places allow for stops. The short trail to the pilgrimage chapel Virgen de las Flores is selected here as an example of such a point of interest.

Another place where you can explore the mountain rainforests in the eastern part of the Andes is Machu Picchu. Also the temperate rainforests of southern Chile show some similarities to this type of ecosystem.

A photographic journey through the yungas

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You can start your journey through the mountain rainforest by clicking on the arrows or into the image.

The trees are lower in the mountain rainforest, compared to the classic lowland rainforests. Temperature decreases with increasing elevation, so that those tree species in need of warm temperatures decrease in abundance. The relative humidity, in contrast, increases with elevation. One common tree species here belongs to a genus which is well-known from mid-latitudes of the Northern Hemisphere: the alder Alnus acuminata. The mountain rainforest is mostly steep, inaccessibe, and hard to penetrate.

The plants of the mountain rainforest

Click on the arrows or into the image and penetrate deeply into the mysteries of the mountain rainforest.

Did you already visit the Observatorio Astronómico de Ampimpa? If yes, you are an expert in the adaptation of plants to water scarcity. Here, in the yungas, however, other criteria decide whether plants can survive or not. Which strategies might be a good choice?

Describe the photos in a first step, and thereby pay attention to the visible characteristics of the plants.
Which environmental factor could be most important here, and how are the plants adapted to this factor?
Attention! One photo does not fit in here. Which one might it be?

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Show solution

In the mountain rainforest, the precipitation is often higher and the evapotranspiration is lower than in lowland rainforests. Usually, enough water is available for all organisms, whereby fog is important particularly near to the condensation level - therefore the term cloud forest. Whereas root competition plays a less important role than in arid regions, the various plants compete among themselves to grow faster and higher, in order to gather as much sunlight as possible. Due to the dense canopy and the frequent cloud cover, a comparatively small amount of sunlight is available for each plant. It has to be used in the best possible way - besides rapid growth, there are at least three more strategies for an optimized use of the sunlight:

The plants form larger leaf areas, in order to compensate the lower irradiation caused by shadowing through other plants, and by clouds and fog (Photo 2).
Some plants do not root in the soil, but high up on other plants (Photo 1). Plants dwelling on stems, branches, or leaves of other plants are called epiphytes. They often only use their hosts as habitat, but do not extract nutrients from them. Epiphytes occur mainly in poorly lit areas with high air humidity and are therefore ideally adapted to the environmental conditions in mountain rainforests - particularly, in cloud forests. Species of the genus Tillandsia are widely distributed in the yungas. They can also grow on rocks, roofs, fences, or power lines (Photo 3). As access to water can be an issue high up on other plants, tillandsias are often succulent and catch water in their leaf rosettes. Photo 3 was not taken directly in the yungas, but in the lowlands near to the eastern margin of the Andes where rainfall is lower, but the humidity of the air is still high.
Lianas, in contrast to epiphytes, root in the soil, but do not invest in the tedious formation of an own stem. Instead, they wind up along the stems of other trees, and reach the well-lit upper areas of the canopy within quite a short timespan.

Mountain rainforests also form ideal habitats for ferns, which prefer shady and damp conditions. Some of them live epiphytic (lower part of Photo 1). The same is true for mosses (left portion of Photo 2).

Buttresses, in contrast, are rather found in the tropical lowland rainforest, and partly still in the lower portions of the mountain rainforest. They provide the required stability to the emergents, which have shallow root systems due to the structure of the soil. Photo 4 was taken in the Amazon Rainforest in Ecuador.

Australien - Queensland - Lianen, Regenwald. www.hansthiele.de [Access source]

Wikipedia article on ferns [Access source]

Wikipedia article on the yungas [Access source]

This contribution was revised, extended, and translated from German by Martin Mergili.