The Valdivian temperate forests and the more hygrophilous vegetation of the Mediterranean area of central Chile, represent a true biogeographic island separated from climatically similar areas by extensive ocean barriers and deserts.
The Valdivian temperate forest is characterized by its extraordinary endemism (e.g., 90% at the species level and 34% at the genus level for woody species) and the great antiquity of its biogeographic relationships.
Its taxons show close philogenetic relationships dating back to the early Tertiary, with Gondwanic taxons of Oceania forming more recent relationships with Neotropical taxons, separated from other biotas in South America by the great mountainous barrier of the Andes.
Location and general description
This ecoregion is located in the southern cone of South America. It covers a narrow continental strip between the western slope of the Andes and the Pacific Ocean, running from 35° to 48° south latitude.
The tree line is at about 2400 metres (m) in central Chile (35°S), descending to 1000 m in the south of the Valdivian region. The Andean mountains at these latitudes rise above 3000 m. At these higher elevations the temperate forests disappear and are replaced by high Andean vegetation. Maximum annual average temperatures vary between 21°C and 13°C in the northern and southern ends of the ecoregion, respectively. Minimum annual average temperatures range from 7°C to 4°C. The most pronounced variations in average temperatures occur from west to east, due to an increase in altitude toward the Andes. This change in temperature often occurs in less than 160 km of longitude, with more moderate temperatures on the coast and more extreme temperatures in the Andes. Annual precipitation varies between 1000 mm in the north and more than 6,000 mm per year in the southern part of the ecoregion. Rain fronts correspond primarily to the belt of westerly winds off the Pacific Ocean, with their activity concentrated on the Chilean slope of the Andes, where high mountains create a screen effect. Precipitation decreases significantly on the eastern slope of the Andes in Argentina, where rainfall of less than 200 mm is recorded only 100 km east of the Andean peaks. These rains are seasonal due to the Mediterranean-like climate with concentrated rains in the winter months. This seasonality declines from north to south.
Three geological accidents define this ecoregion:
- The Andes range, with heights above 3000 m and frequent volcanic and seismic activity, has been the center of glaciation processes which transformed the biota of the temperate forest during the Pleistocene (last two million years).
- The coastal range is a mountainous belt approximately 100 km to the west of and parallel to the Andes. This range is from the Jurassic age, formed on a metamorphic rocky basement from the Paleozoic age. It has moderate heights at a maximum of 1300 m, breaking off toward the south of the Chiloé Archipelago (43.5°S).
- The intermediate depression or central valley is a lower fault zone (100-200 m) covered by volcanic ash and glacial morainic fields lying between the two ranges. The soils of both ranges are poorly developed because the Andean slopes are young and the coastal range is extremely weathered. The soils of the intermediate depression have been formed by sedimentary deposits from both mountain ranges.
The temperate forests of southern South America have been isolated from other continental forest biomes since the mid-Tertiary. The connection with other forest ecosystems in South America was probably broken by the end of the Tertiary, and has remained so during the entire Quaternary. Phytogeographic analyses of the Tertiary fossil record in Chile show that around 60% of the tropical genera in Chilean forests during the early Tertiary disappeared from the territory during the latter half of the Tertiary. These extinctions were due to a remarkable contraction of the tropical vegetation belts in the Southern Hemisphere that took place in the mid- to late-Tertiary.
In the Quaternary, a succession of cooling and warming cycles produced massive mountain glaciers that advanced during the cool glacial periods, causing repeated contractions of the geographic range of temperate forests on the western edge of southern South America. These processes were followed by expansions of the forest during short and warmer interglacial periods. Immigration of species from tropical latitudes was no longer possible due to the extreme aridity established in the subtropical latitudes on the western edge of South America, and the Andean mountain barrier to the east. The increased aridity, reduction in area, and isolation of temperate forests led to the extinction of many congeneric plant species, resulting in the presently high number of monotypic genera in the austral forest flora.
Climatic change and geographic isolation resulted in a net loss of species, particularly taxons with tropical ancestry. At the time when glaciers reached their maximum extension in the southern hemisphere, species-rich rainforests survived near the northern limit of their present distribution. Rainfall in this northern area was probably higher during the glacial period and temperatures were moderate due to oceanic influences. Some areas in the coastal range between 38°S and 40°S including specific places in Argentine Patagonia could have remained free of ice and periglacial processes that restricted the persistence of vegetation in the proximity of glaciers. These plant communities may have represented the sources for the recovery of regional biodiversity following deglaciation.
Biogeographic events, temperature and precipitation gradients, the long history of isolation and recent great climatic changes have produced a heterogeneous mosaic of forest types in the ecoregion. The forest ecosystems from north to south were based primarily on a classification proposed by Gajardo and the scheme of Veblen. There are five types of forest ecosystems:
- Deciduous forests of Maula Province (Chile) representing the transition between Mediterranean-type schlerophyllous forests and wet temperate forests further south. These forests are characterized by the dominance of deciduous species of Nothofagus, with many of these species endemic to this area.
- Valdivian laurel-leaved forests dominated by a variety of tree species, including Laureliopsis philippiana, Aextoxicon punctatum, Eucryphia cordifolia, Caldcluvia paniculata, and Weinmannia trichosperma.
- Northern Patagonian forests with a predominance of evergreen species such as Nothofagus dombeyi, Podocarpus nubigena, and Drimys winteri.
- Patagonian Andean forests, include Araucaria araucana and high Andean scrublands with deciduous Nothofagus, which are widely distributed latitudinally.
- Evergreen forests and bogs consist of evergreen forests of Nothofagus betuloides and bogs of Sphagnum.
A World Wildlife Fund analysis of the ecoregion subdivided the region based on criteria of vegetation and woody formations and identified 11 units or sub-ecoregions. Three of these cover both slopes of the coastal range, and two are basically found in the intermediate depression. These five units or sub-ecoregions are found only in Chile. Six sub-ecoregions are confined to the Andean slopes, one of them entirely in Argentina (xeric cyprus forests), and the remaining five are shared by Chile and Argentina.
There is an unusually high diversity of plant families represented in South American temperate forests (nearly 50% of the plant families in the Chilean flora are found in temperate forests), which contrasts with the lower species richness (only 7.8% of the flora of Chile). The main biological value of the southern temperate forests resides in their high endemism. A high number of taxonomically isolated genera belong to monogeneric families including Aextoxicaceae, Gomotergaceae, Desfontaineaceae, Eucryphiaceae, and Misodendraceae. The high percentage of endemic species, close to 90% of the seed plants, suggests geological antiquity, long isolation, and high rates of extinction during the cooler Pleistocene. For the temperate forests of southern South America, endemism at the species level is estimated to be 50% for vines, 53% for hemiparasites, 45% for all vertebrates, 76% for amphibians, 50% for freshwater fish, 36% for reptiles, 33% for mammals, and 30% for birds. The entire ecoregion contains 700 to 800 species of vascular plants, representing more than 200 genera. Of the 32 genera of trees exclusive to the Valdivian forest, 26 (81%) are monotypic. At least one-third of the woody plants are of Gondwanic origin, with their closest relatives being found in Australia, New Zealand, New Caledonia, and Tasmania.
Many of the amphibians in these forests have very narrow distribution ranges, particularly in the coastal range. Some amphibians limited to the Nahuelbuta range at 38°S include Telmatobufo bullocki, Alsodes vanzolinii, Alsodes barrioi, and Eusophus contulmoensis. Other species found further south in the coastal range with narrow distributions ranges include Insuetophrynus acarpicus, Eusophus vertebralis, and Telmatobufo australis. Atelognathus nitoi, the Patagonian toad, has been collected in a very narrow environment on the western Andean slope. Something similar occurs with species of land crustaceans of the genus Aegla, which are highly diversified in the coastal range. Endemic mammal species are also biologically interesting because of their kinship to geographically remote groups. This is the case with Dromiciops gliroides, an arboreal marsupial found in this ecoregion, located in the basal trunk of Australasian and American marsupials. The only animal species known to be extinct in this ecoregion are two species of Aegla (Crustacea) and some species of the family Tenebrionidae (Coleoptera). Both groups of invertebrates used to live in the woody habitats of the coastal range, one of the most critically endangered ecosystems in the ecoregion.
The southern temperate forests are characterized by flora with one of the highest incidences of pollination and dissemination by animals recorded in any temperate biome, particularly in comparison with the northern hemisphere. In temperate forests of southern South America, the flowers of about 85% of woody plant genera are visited and presumably pollinated by animals. This ecoregion has extremely singular bees, in which many important neotropical groups like the Meliponinae and Euglosinae are missing, but characterized by the presence of various endemic and probably relict groups such as Xeromelissinae, Diphaglosa, Cadeguala, Corynura, Neofidelia, Manuelia, and Eucerinoda.
Close to 20% of the woody plant genera produce red tubular flowers that are visited by Sephanoides sephaniodes, the only species of hummingbird that lives in these forests. About 50% to 70% of the woody plant species or genera produce fleshy fruits; these percentages indicate the importance of the seed dissemination by fruit-eating vertebrates.
Upon the arrival of the Spaniards, most of the area defined as the Valvidian ecoregion was effectively covered by forests with few open areas being cultivated by indigenous Mapuche groups. Currently, the forest cover has declined by one-third of the estimated area at the arrival the Spanish colonists, with a current area of about 12,600,000 hectares. The remaining forested area corresponds to an area (about 50%) of secondary forests. There are few remaining primary forests, especially in the coastal range. If the current rates of deforestation outside the areas of protection continue, the forest will disappear within the next 20 years.
The National Parks in the temperate forests of Chile and Argentina are considered pioneer protected areas in Latin America. Some of these Parks were established in the early 1900s. There are more than fifty parks, reserves and monuments protecting more than 10 million hectares in the temperate region of Chile. There is a great disparity between the distribution of these protected areas and the geographic distribution of trees and vertebrate species. The lowest percentage of protected areas (< 10%) is found in the areas with the highest biodiversity in Chile, between 35.6° and 41.3°S. Most of the protected areas within these latitudes contain the greatest wealth of species found above 600 m, where physical processes that produce impoverished speciation and endemism are accentuated. In addition, the areas with the greatest wealth of species are found precisely in areas with high human density, and thus there is great pressure from agriculture and plantation forestry. The protected areas in the Andes of Chile and Argentina represent 99% of the total surface area protected in the southern part of South America, in contrast to protected areas in the coastal range at the same latitude. The Andean forests are more impressive than the coastal forests, due to vistas of imposing volcanoes, great lakes, and small mountain lagoons, based on the prevailing landscape criteria used when creating Andean parks. There are no protected areas in the intermediate depression, with the exception of a small municipal park near Puerto Montt.
Types and severity of threats
The main threats to the Valdivian temperate forest include logging for commercial purposes and firewood. Agriculture is replacing the species-rich native forests with monocrops of exotic species. Areas are deforested for kindling large road works such as the southern coastal highway and the bridge over the Chacao Channel that will link the continent and the Island of Chiloé. Deforestation in the foothills of the Andes and in the coastal range has been one the most massive and rapid in Latin America prior to 1980. About 15,000 to 49,000 hectares of natural vegetation were burned each year between 1970 and 1990. Reptile exports intensified and the number of reptiles exported grew from 3,548 to 60,000 between 1985 and 1992. Approximately 24,064 specimens of amphibians were exported between 1985 and 1992. In Argentina, the main threats are pressure from tourism, replacement and invasion by alien species, the impact of the European deer, and the introduction of freshwater fish.
Justification of ecoregion delineation
The forests of Valdivia represent the a unique assemblage of ancient species, both floral and faunal, which today persist as relicts of Gondwanaland. This ecoregion is also host to many endemic species. The forests are bound to the north by one of the dryest deserts on the continent (Atacama), traverse the southern Andes and are bound on the east by grasslands, and to the west by the Pacific Ocean. The southern delineation marks the gradual change in tree species composition to a Nothofagus-dominated forest, which we have termed Megallanic subpolar forests. The initial linework for these southern temperate rainforests follow a variety of sources and have undergone a number of modifications to reach this final polygon. Expert opinion during several ecoregion priority setting workshops (Valdivia, Chile [April 19-21, 1999], Bariloche, Argentina [October 19 & 20, 1999], and Concepción, Chile [March 24, 2000]) resulted in Chilean winter-rainforests being lumped in with Valdivian forests, and the western linework was extended further into Argentina to encompass the historic range.
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
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