Natural history of the Upper Paraná Atlantic Forest
The original9 forest of the Upper Paraná Atlantic Forest ecoregion covered the largest area (471,204 km2) of all the ecoregions of the Atlantic Forests Ecoregion Complex, extending from the western slopes of the Serra do Mar in Brazil to eastern Paraguay and the Province of Misiones of Argentina (Figure 5). In the north, the Upper Paraná ecoregion borders the Cerrado Woodlands and Savannas Global 200 Ecoregion. The vegetation of the Cerrado is very distinct and its physiognomy differs from that of the Atlantic Forest. The Cerrado is a mosaic of forest communities, with slow growing tree species adapted to seasonal rains and the presence of fires and savannas. The riverine forests of the Cerrado, however, contain species typical of the Atlantic Forest. In the west, the Upper Paraná Atlantic Forest meets the Pantanal and the Humid Chaco, a large floodplain characterized by gallery forests, savannas, flooded grasslands, and deciduous chaco forests in the non-flooded areas. In the south, the Upper Paraná Atlantic Forest borders an area of grasslands. Finally to the east, it intermingles with the Araucaria Forests, another of the ecoregions in the Atlantic Forest Ecoregion Complex. The boundary with the Araucaria Forests ecoregion is not clearly delineated; it is sometimes difficult to define where one ecoregion begins, and where another ends. Both ecoregions have been sometimes classified as only one. With the exception of a few species that characterize the Araucaria Forests ecoregion — such as two conifers, the dominant Brazilian pine or monkey puzzle tree (Araucaria angustifolia) and Podocarpus sp., and a set of species associated with them such as the tit-spinetail (Leptasthenura setaria)—many species are shared between both ecoregions.
The predominant vegetation of the Upper Paraná ecoregion is a semi-deciduous sub-tropical forest. Variations in the local environment and type of soil allow for the occurrence of other plant communities—gallery forests, bamboo forests, palmito (Euterpe edulis) forests, and araucaria forests. Most of the remaining forests have been exploited for timber, and some are second growth forests recovering from deforestation. Forest fragments are thus composed of both primary and secondary forests at different stages of succession.
The Upper Paraná ecoregion is situated in the southern portion of the Brazilian Plateau. The topography of the ecoregion ranges from relatively flat areas with deep soils near the Paraná and other main rivers at altitudes of between 150-250 m above sea level (asl), to a relatively flat plateau at altitudes of between 550-800 m asl. The areas located between the main rivers and the plateau, at altitudes of between 300-600 m asl have relatively steep slopes and are dramatically exposed to soil erosion when the forest cover is removed (Ligier 2000). Above 700-900 m asl, the Upper Paraná ecoregion gives way to the Araucaria ecoregion in the east and to the Cerrado in the north.
The soils of the ecoregion are relatively nutrient rich. The usually deep red soils near the main rivers become less deep and more rocky at higher altitudes. There is high variation in soil types, varying in texture, chemical composition, and acidity (Ligier 2000, Fernández et al. 2000).
The ecoregion has a subtropical climate. Mean annual temperature ranges from 16-22 ºC with a relatively high annual variation. In the southern portions of the ecoregion, frost is common during the winter months (June-August), especially at high altitudes. Rainfall in the ecoregion ranges from 1,000-2,200 mm per year, usually with less rain in the northern part of the ecoregion than in the south. Rains are not uniformly distributed during the year, and in some portions of the ecoregion there are up to five dry months, usually during the winter. Increased rains during El Niño years produce large inter-annual variations in rainfall.
Rainfall and the strong seasonality in temperature and light determine a seasonal pattern of primary productivity of the forest (Placci et al. 1994, Di Bitetti unpublished). In the Upper Paraná Atlantic Forest there is strong seasonality in the availability of food for folivorous, frugivorous, and insectivorous species. New leaves, fruits and insects are more abundant during the spring months of September to December (Placci et al. 1994, Di Bitetti & Janson 2001).
The natural characteristics of the region form an extremely rich habitat harboring countless species of plants and animals, among them the spectacular large cats—the jaguar (Panthera onca), puma (Felis concolor), and ocelot (Felis pardalis) (Crawshaw 1995). Other common mammals include the tapir (Tapirus terrestris), three species of brocket deer (Mazama americana, Mazama nana, and Mazama gouazoubira), two species of peccaries (Tayassu pecari and Tayassu tajacu), coati (Nasua nasua), and four species of monkeys (Cebus apella nigritus, Alouatta caraya, Alouatta fusca fusca, and Leontopithecus chrysopygus). About 500 species of birds are found here, including five species of toucans (Ramphastos toco, Ramphastos dicolorus, Pteroglossus castanotis, Baillonius bailloni, and Selenidera maculirostris). Reptiles and amphibians also show high diversity, and include caimans, turtles, boas and other snakes (including several endemic species within the genus Bothrops, such as Bothrops jararacusu), lizards and spectacular amphibians, such as the toad Bufo crucifer, and the frogs Osteocephalus langsdorffi, Hyla faber and Phyllomedusa iheringi. Some animals are considered endangered or threatened, such as the giant river otter (Pteronura brasiliensis), the black lion tamarin (Leontopithecus chrysopygus), the black-fronted piping guan (Aburria jacutinga ), the solitary tinamou (Tinamus solitarius), the Brazilian merganser (Mergus octosetaceus), the vinaceous breasted parrot (Amazona vinacea), the bare-throated bellbird (Procnias nudicollis), and the harpy eagle (Harpia harpyja). Some species, like the jaguar, the harpy eagle, the giant river otter and the white-lipped peccary, require large expanses of continuous forest to guarantee their long-term survival—which represents a big challenge for their conservation in a fragmented landscape. Some species of the Upper Paraná Atlantic Forest ecoregion have very restricted distributions and constitute local endemism, such as the black lion tamarin, restricted to a small area in the western part of the state of São Paulo, Brazil (Cullen et. al. 2001), and the Urugua-í frog (Crossodactylus schmidti), endemic to a small portion of Misiones (Chebez & Casañas 2000).
Levels of alpha and beta biodiversity are quite high in the ecoregion, although there are very few places that have been intensively surveyed. For example, in the San Rafael National Park area in Paraguay, 378 species of birds have been recorded but it is estimated that between 400 and 450 species are actually present in the area (Clay et al. 2000). The areas of Iguaçú National Park in Brazil and Iguazú National Park in Argentina are among the best-studied sites in the ecoregion, with four hundred and sixty species of birds (Saibene et al. 1993) and more than 250 species of trees recorded in these protected areas. Between 53 and 73 species of trees (>10cm dbh) per ha have been recorded in study plots within the Iguazú National Park (Placci & Giorgis 1994, S. Holz pers. com.). Eighty-five species of orchids have been recorded just in the Iguazú National Park, which represents about 1/3 of the species known for all of Argentina (Johnson 2001). Over 3,000 vascular plant species have been recorded for Misiones, representing about 1/3 of the total vascular flora from Argentina (Zuloaga et al. 2000, Giraudo et al. in press).
The Upper Paraná Atlantic Forest plays an important role in the conservation of watersheds, ensuring the water quantity and quality essential for the conservation of the Upper Paraná Rivers and Streams, a Global 200 freshwater ecoregion (Figure 6). With a remarkably diverse fauna, including over 300 species of fish, in addition to diverse aquatic vertebrates and invertebrates, the Upper Paraná Rivers and Streams ecoregion has a high degree of endemism of freshwater species (Olson et al. 2000).
The Upper Paraná Atlantic Forest ecoregion is located over a large portion of the one of the largest groundwater reservoirs in the world —the Guaraní Aquifer. This aquifer extends over a total of 1.2 million square kilometers from the central-west region of Brazil, through Paraguay to southeastern and southern Brazil, northeastern Argentina and central-western Uruguay (Facetti and Stichler 1995). The current volume of freshwater reserves stored is around 40,000 km3. Its depth varies from almost zero in Brazil to more than 1,000m in Argentina (Fili et al. 1998). Despite a large surface water reserve, the drinking water supply in this heavily populated region is increasingly dependent on this groundwater. Future problems may occur if exploitation does not take place in a sustainable manner or if the waters become polluted. Due to its significant average depth, the Guaraní Aquifer is still relatively unaffected by surface pollution (The World Bank, 1997). However, the rapid development of agriculture in the region, especially in Brazil where the aquifer is nearer to the surface, has the potential to pollute this valuable water resource. This is a very clear example of the need for conservation planning and action at the ecoregional scale.
The main causes of fragmentation and degradation of the Upper Paraná Atlantic Forest