The Andean-Patagonian Forest

The Andean-Patagonian forests, also known as Subantarctic forests, spreads over steep elevations along a thin strip on both sides of the Andes, on southern South America. These are the southernmost forests in the world, and have their origin 45 million years ago on the Gondwana supercontinent, where the forests of South America, Australia, New Zealand, Tasmania and South Africa have their ancestors. The Patagonian forests can be considered a “green island”, as they have been isolated from other forests for the last 10 million years, resulting on a high number of endemism.

The existence of these thick forests in possible thanks to the heavy rains and snows, 2,500 mm/year on average. These precipitations are the result of the humid winds coming from the Pacific Ocean hitting the Andes mountain range barrier. The soils are rich in organic components, although the formation of humus in slow compared to the tropical forests, as temperatures are low so dead trees take much longer to decompose. Glaciations occurred during the Pleistocene (2 millions to 15.000 years ago) carved the landscape resulting in U-shaped valleys with west-east orientation, now occupied by countless lakes.

Two types of trees are the main components of the Andean Forests: the Southern Beeches of the Nothofagus genus and four species of conifers.

THE NOTHOFAGUS

The Nothofagus genus includes forty living species. Nine of them grow in the Patagonian forests of Argentina and Chile, and the other thirty-one in Australasia. The most spread species of Nothofagus in Patagonia are, in this order: Lenga (Nothofagus pumilio), Ñire (Nothofagus antarctica) and Coihue (Nothofagus dombeyii). The first two are deciduous species and they are present on the entire Patagonian mountain range, from Neuquén to Tierra del Fuego. In autumn they offer a real spectacle, as their leaves turn to yellow, orange and red before they finally fall to the ground. While Ñire may live at different altitudes the Lenga is the highest forest at each latitude, where they come in contact with the high-Andean vegetation.

Coihue is the tallest of all of them, it can reach up to 50 m, and as opposed to Lenga and Ñire, is an evergreen tree. Its distribution range goes from Neuquén to Chubut, while in southern Patagonia and in Tierra del Fuego is substituted by the Guindo or “Magellanic Coihue” (Nothofagus betuloides). Of much more restricted distribution are the Raulí (Nothofagus alpina) and the Roble Pellín (Nothofagus obliqua), both deciduous species growing almost exclusively in limited areas of the Lanín National Park, in north Patagonia.

All of them produce seeds massively to improve their reproductions chances, although only a minimal fraction of those seeds will become a tree, as they need big clearings and enough sunlight to develop. The wind is their most important agent of pollination.

THE CONIFERS

While the northern hemisphere forests are made mainly of conifers, the subantartic forests show a predominance of flowering trees. However, nine species of conifers grow on the Patagonian forests. The most iconic is probably the Pehuén or Araucaria (Araucaria araucana), which grows only in northern Patagonia in the province of Neuquén, on rocky and sandy soils generally of volcanic origin. It can live up to 1,000 years and it is considered a “relict species”, as it survives only in reduced areas. Its shape is unmistakable, with the bark divided into polygonal plates, curved branches and strong and coriaceous leaves. The Pehuén is a dioecious species, so generally each tree produces just male or female cones. The female cones, once they are fecundated produce around 200 seeds. Those seeds are very nutritive so they were a very important component of the native Mapuche people diet.

The Alerce (Fitzroya cupressoides), is a giant tree and the most long-living on Earth after the Californian Sequoias (they both belong to the same family, Cupressaceae). In Argentina they can be found in certain areas of Los Alerces and Nahuel Huapi National Parks, while in Chile they are spread across a bigger area. They grow on poor and damp soils and can reach 50 m. and live up to 3,600 years, growing just around 1 mm in diameter per year!

The Andean Cypress (Austrocedrus chilensis) has a wider distribution, growing on poor and rocky soils on north facing slopes from 700 to 1,500 m above sea level between the Neuquén and Chubut provinces. They form pure forest towards the transition areas with the Patagonian steppe so they are considered a pioneer species, pushing the boundaries of the forest before other species can establish themselves.

Lastly the Ciprés de las Guaitecas (Pilgerodendron uviferum) is the southernmost conifer in the world, growing mostly in Chile in the Aysén region and in Tierra del Fuego. In Argentina it can be found in very specific areas of the Nahuel Huapi and Los Glaciares National Parks. It grows on swampy soils and peat bogs up to 1,000 m above sea level, together with lenga, ñire, coihue or alerce. As well as the alerce its wood is decay-resistant so during the colonization of southern Patagonia they were used for ships and houses construction, resulting in a great reduction of their distribution.

OTHER TREES & UNDERGROWTH

Apart from the Nothofagus and the conifers other wide-spread trees on the Andean-Patagonian forest are: Arrayán (Luma apiculata), a myrtle showing a cinnamon-coloured bark that can grow as a shrub or tree, usually found along the margins of rivers and lakes; Maitén (Maytenus boaria) an evergreen tree of dense foliage which grows on transition areas between the forest and the steppe, sometimes forming small pure forests. Also in these transition areas we can find the Radal (Lomatia hirsuta), a shrub or a tree characterized by its globose tops with evergreen big-sized leaves.

Below the tree line several vegetal species find their perfect environment. One of the most characteristic is the Colihue Cane (Chusquea culeou), a bamboo that can reach 5 meters forming dense patches on the most humid slopes of the forests, especially under the coihues. Its flowering occurs simultaneously on an entire forest every 18 to 20 years, producing a massive amount of seeds which as a result can multiply by thousands the rodent’s populations on a certain area.

The Notro, or “Fire Bush” (Embothrium coccineum) can grow as a small tree or a bush in open areas with a lot of light and over sandy soils. Its red flowers, arranged in inflorescences, blossom in October and November, providing a beautiful red contrast on the slopes where the Notro grows. The Aljaba or Fucsia (Fuchsia magellanica) inhabits wet areas, forest gaps and the margin of water courses. It’s beautiful hanging flowers are pollinated by the Green-backed Firecrown.

The Calafate and its relatives of the Berberis genus are distributed both on steppe and forest areas over the entire Patagonia. They are shrubs provided with spine-transformed leaves. Their fruits are blue-black berries which are used to prepare syrups and marmalades. On the Patagonian forest the most common species is the Michay (Berberis darwinii), usually found on the Coihue forests.

HEMIPARASITES & CREEPERS

Several epiphytes (plants that grow on other plants, instead of in contact with the soil) thrive on the subantarctic forest. The most common is Myzodendron or “Ñire Flower”, which grows exclusively on the branches of Nothofagus trees. They have no leaves, and the yellowish and greenish colours of their thin branches are difficult to miss among the trees, especially on the stripped bare lengas and ñires during winter. The Quintral (Tristerix corymbosus) is another hemi parasitic shrub which lives on coihue, maiten and fucsia plants, among others. Its flowers feed the Green-backed Firecrown during winter and its seed are dispersed by a marsupial mammal, the Monito de Monte, as described here.

Among the creeper plants we have the Botellita (Mitraria coccinea), which grows on damp forests gripping its roots on to trees to grow. Their beautiful bottled-shaped red flowers are also pollinated by the Green-backed Firecrown. Another creeper is the Mutisia (Mutisia decurrens), whose beautiful orange flowers are well-known an easy to identify.

MOSSES & LICHENS

Mosses are Bryophytes, non-vascular plants that were the first to conquer terrestrial environments when they evolved from green algae just a while ago, circa 500 million years! They can grow on different surfaces, like rocks, over the ground or on fallen or live trunks, but it is in peat bogs where they represent the dominant vegetation. In Los Glaciares National Park, in Tierra del Fuego and in the Aysen Region in Chile we can find peat bogs where mosses of the Sphagnum genus thrives, usually called peat mosses. On these peat bogs we can also find an insectivorous plant, Drosera uniflora. Trapping insects it obtains the necessary nitrogen for its development, which is not present on these poor wet soils.

Lichens are one of the better adjusted mutual relations know in nature, formed by and algae and a fungus. The algae provide the capacity to photosynthesize, while the fungus contribute with protection against drying and solar radiations. As they have no capacity to store water they depend on rain, fog or dampness in the air to survive. The lichen Usnea, also known as Old Man’s Beard is abundant and easy to identity on the Patagonian forest, hanging from the branches of the Nothofagus trees. Its presence is a proof of the extreme purity of the air, as they disappear at the slightest pollution.

FUNGI

Plants are able to produce their own nutrients by utilizing solar energy whereas fungi are devoid or chlorophyll and feed exclusively on organic substances that they break down using enzymes. Fungi and bacteria are responsible for a key step in the trophic chain: decomposing the organic detritus originating both from plants and animals and concentrating substances like nitrogen, phosphorus and carbohydrates in the substrata which are then absorbed by the plants. Without this process the trophic chain would be interrupted, as the energy and nutrients captured by the plants would remain stored on them with no chance of being reutilized. The saprophytic species play this role of breaking down plant material into soil again. An example of this kind of fungi in the subantarctic forest is Hypholoma frowardii.

Other fungus species play a different role on the southern beech forest, building a symbiotic association with the roots of the Nothofagus trees called mycorrhiza . The fungi increase the absorption capacity of the roots and provide certain nutrients that help the trees grow in poor lands. On the other hand they get substances from the Nothofagus that allow then to grow more.

Another fungus, Cyttaria, produce tumors on the branches and trunks of the Nothofagus trees and fruiting bodies that mature in spring. Those fruiting bodies are pale-orange globes from 2 to 7 cm. in diameter. The most common are the Llao Llao (Cyttaria hariotti) and the Pan de Indio (“Indian Bread”), Cyttaria darwinii.

_{* Special thanks to Jouni Issakainen, PhD, Biologist and Chairman of Turku Mycological Society in Finland for his input on fungi.}

BIBLIOGRAPHY

Bartheley, Daniel; Brion, Cecilia; Puntieri, Javier, Plants of Patagonia, Vazquez Mazzini Editores, Buenos Aires, 2008.

Bisheimer, María V. y Fernández Eduardo M., Parque Nacionales de la Patagonia Argentina, Neuquén, 2008.

de la Vega, Santiago G., Patagonia, the Laws of the Forest, Contacto Silvestres Ediciones, Buenos Aires, 2003.

Gamundí, Irma J; Horak, Egon. Fungi of the Andean-Patagonian Forests. Vazquez Mazzini Editores, Buenos Aires.