The Pantanal of Mato Grosso, Brazil

Discovery

The legendary existence of a great inner lake in the centre of South America was believed for several centuries. On the 1559 map by Hondius, the Pantanal is represented as a large lake, “Eupana Lacus”, surrounding an archipelago. In the 1641 improved edition of the Hondius map, the swampy lake is still there, but no name is given. This lake appeared as a common source of the Paraguay, the São Francisco and even of the Amazon (Hoechne, 1936).

The name of the “Sea of the Xaraes” was first mentioned by the Spanish conquistador Nuñes Cabeza de Vaca, who after founding the city of Asuncion, traveled in 1543 upriver till lake Gaiba. There he must have heard from the “sea” from the indian tribe of the Xaraes, which inhabited the shores of another extensive lake, Lagoa Uberaba, further north. Cabeza de Vaca who invented also the tale of the seven golden cities of Cibola in Texas, probably did not check his source too much. To his defense one can admit that a lake, the size of Uberaba, which can reach a surface of over 400 square kilometers, can easily be considered as an “inland seas” even under the present climatic conditions.

For two centuries the swamps of the Pantanal were still the domain of the indian tribes, the Paiaguas, expert boatmen, the Guaicurus who became feared horsemen, and others. During the XVIIIth century, the “bandeirantes” slave-capturing armed bands from the province of São Paulo discovered gold near Cuiabá. In rapid sequence, the present frontier line separating Portuguese from Spanish lands became established and studded with stronghold townships. But the indian tribes remained a fiercely independent menace of the colonists, even during most of the XIXth century. In a typical North American way, these powerful tribes choose either the Portuguese or the Spanish side, even as late as in the Paraguay War of 1864-1870.

Limits and Size

Situated roughly between 16° and 20° S and 58° and 50° W, the limits of the Pantanal are not unanimously accepted. Descending the Serra das Araras, near the border of Mato Grosso with Bolivia, the Paraguay River flows into an immense alluvial plain of the Holocene epoch (of the last 10,000 years). This alluvial plain in Brazil alone measures 770km from north to south and has an area of approximately 139,000 km2 (Ferreira et al. 1993) The western end of this plain is traversed by the Paraguay River. It extends into neighboring countries (Bolivia, Paraguay, and to a lesser degree, Argentina) always along the margin of the river bed.

The alluvial plain of the Pantanal varies between 80-150m in altitude, with a north-south slope of only 2cm/km (Dubs,1992). On the Brazilian side (east, north and west), it is surrounded by the crystalline plateau, approximately 600-700m in altitude, which is covered with Cerrado vegetation. To the south, there is the Paraguay depression, a rolling plain with an extensive hydrographic network, formed by countless tributaries of the gigantic Paraguay River. These alluvial plains are very thick. Drilling in this area has reached 83m without hitting bedrock.

Geological Data

The basin of the Pantanal is an old continental margin of the pre-Cretaceous South American Gondwana. The graben of the Pantanal itself was formed through the fragmentation of an old Cretaceous shield, in a balancing conjunction with the uplifting of the Andes and of the Brazilian highlands. The topography changed from a basically exorheic pre-Tertiary domed shield, to an endorheic syncline. As the orogenesis progressed, the syncline of the Pantanal sunk deeper and deeper and filled up with alluvional sediments. The Pantanal, as we see it today, represent the fluctuations history of the Pleistocenic climates.

The Climate

The annual temperature media fluctuate around 25°C. The highest temperatures occur usually early in the summer and may reach 40°C. According to Valverde (1972), the wet summer regime is due to the penetration of the equatorial continental air mass of Amazonian origin. The climate in the winter is dominated by the tropical-atlantic air mass coming from the Brazilian highland. Since the amphitheater of the Pantanal is open to the south, sometimes polar-antarctic atmospheric fronts advance into the area and winter temperature extremes of around 0°C may occur. These are the so called “friagens” which can provoke frost-bite etiolation of the plants over large swamp areas.

Humidity is usually around the mark of 70%. Reaching maxima of over 80% in the late summer (Tarifa,1986). Concerning the ecological conditions of this immense area, the rainy season is concentrated between October and March, there is a rainfall of 1000-1400 mm (Dubs,1992). Rainfall is slightly less than in the cerrado of central Brazil, but the Paraguay River and its tributaries swell to such an extent that the waters flood the low plain, covering it with a sheet of water 2-3m (sometimes even 4m) deep. The Pantanal therefore, is a large climatic enclave in which the run-off from the surrounding relatively wet highlands, carried by a series of large rivers, succeeds to maintain an allochthonous wetland environment under the conditions of a basically semi-arid climate.

From a different point of view, the Pantanal is probably the most important window of evaporative freshwater loss of the globe.

Flood and Dry Seasons

Farther inland, away from the rivers, the inundations are limited to depressions, know as baías, which may be circular, and may even have an island in the center. These lakes measure from hundreds of meters to more than 10km in diameter.

The depressions are separated from each other by strips of higher terrain, know as cordilheiras. Sometimes, the lakes contain salt water, in which case they are called salinas. During the dry season, these bodies of water dry up and are called barreiros. They are visited by wild animals and cattle hungry for salt. A water course that connects one baía to another is called a corixo.

Since the soil is very permeable, even the larger rivers diminish in volume if the dry season is prolonged.

During the flood season, from December to May, the land is fertilized by the suspended sediments (clay, silt, organic matter) in the waters. Which are deposit on the plains, making one think of the Nile in Egypt. The waters begin to lower in April, but only in the month of July does the soil become enough dry to support a car. From the beginning of July to the end of December, one can drive over the Pantanal without great difficulty. The dry season begins between May and October, and then, gradually, the rain begins again. This rhythm is essential for the life in the area.

How many Pantanals?

It is only natural that a area the size of the Pantanal needs to be subdivided. Administrative, traditional and objective criteria are, however, mixing in all these subdivisions. In 1979 the state of Mato Grosso has been split in two. The frontier between Mato Grosso (MT) in the north and Mato Grosso do Sul (MS) follows the rivers São Lourenço and Cuiabá. Therefore one speaks of a northern and a southern Pantanal. Adámoli (1980) divides the area into 10 pantanals: Cáceres, Poconé, Barão de Melgaço, Paraguay, Paiaguás, Nhecolandia, Abobral, Aquidauana, Miranda and Nabileque, some of these are natural units and Adámoli gives phytosociological reasons for them.

Introduction to the biology of the Pantanal

The Pantanal is a complex of aquatic and terrestrial environments in a permanent shifting interphase. It is difficult to make a clear separation between the biota of the dryland and the wetland and of the waters. With the exception of the isolated mountain islands of the morros, all the terrestrial environments can be subject to flooding, either on a regular, seasonal basis, or exceptionally at high water levels. The rivers are shifting and the baías can occasionally dry out. Terrestrial plants have to cope both with conditions of high groundwater level and with extreme drought. Natural fires selected also plants with pyrophytic adaptations. Aquatic organisms face deficient oxygen conditions and very high summer temperatures in the standing water and the slow flowing streams; on the other hand they have to be resistant to drought. Practically all the plants are capable of amphibious survival.

Under such conditions, territoriality in animals is rare. Terrestrial mammals and birds follow the changing shorelines of the flooded areas, expanding when the swamps dry out. Water fowl adapt their roosting and nesting places to the changes in the distribution of the waterbodies. Fish perform large-scale and long distance migrations, the so-called piracemas. Floating plants accompany the slow streaming of the seasonal network of the vazantes and corixos.

The Pantanal is in a permanent state of successional changes. The sequence of terrestrial plant associations starts with the dry Chaco scrubland, but it does not reach the stage of a mature rainforest. The rivers are all slow-flowing depositional streams. An obvious result of all this is the fact the Pantanal is an area of very little endemism, especially among the terrestrial fauna and flora. The present conditions are too fluctuating on a yearly and a secular basis, and they were probably even more so in the longer range of the Pleistocene climatic history.

Brown (1986) considers the Pantanal to be first of all a biotic corridor and to a lesser extent a biogeographic barrier separating between the surrounding regions. Perhaps the best way to characterize the Pantanal is to consider it as a biotic filter situated in the heart and the crossroads of South America. Only the most resistant species of the surrounding biogeographic provinces could adapt to the imprevisible environmental fluctuations of this region.

Phytogeography

The vegetation changes according to habitat conditions, which vary considerably in the Pantanal, depending on whether or not the area is flooded and the length of time the land is under water. For this reason there is great variety in plant cover. There is a mosaic of aquatic communities, which may be submersed, floating or fixed on the muddy substrate and which may contain even mesophytes and xerophytes.

The so-called cordilheiras, covered by forests and cerrados, are never flooded, cattle and many wild animals seek shelter here during the rainy season. In flooded areas where the water is deep, there is a rich vegetation of hydrophytes, including a sub-specie of the great vitória-régia (Victoria regia cruziana), In areas where the water flows more or less rapidly, there are immense grasslands, used for grazing by the large herds of cattle raised in the Pantanal. Besides the grasses, there are many herbs from many botanical families, and islands of cerrados and semideciduous forests (whose leaves fall during a certain period of the year). Outcroppings of limestone rock in various places and are locally known as serras. The vegetation here resembles the caatinga. Over vast areas, one species may dominate; this generate diverse types of vegetation such as cambarazal (Vochisia divergens), carandazal (Copernicia alba), piuval (Tabebuia sp), pirizal (Cyperus giganteus), tabual (Typha domingensis).

Therefore, there are no plants exclusive to the Pantanal, that we know of at the present time, which have evolved in loco as well as incorporating elements of the chaco.

In short, the Mato Grosso Pantanal is a region undergoing transformation. It is relatively new and unstable from a geological point of view and is dominated by complex mixture of plants and communities. The Pantanal lies at the border area of four floral provinces: Hylaea, Cerrado, Chaco, and southeastern Brazilian forest (Paraná province). The Pantanal plain (PP) is surrounded by the border regions which can be divided as follows:

• Northwestern border area (NW): This sector can be described as Amazonian. In it cerrado is mixed with semideciduous forests which are marked by Amazonian floristic elements.

• Northeastern border area (NE): The northeastern sector is clearly dominated by cerrado. As in the NW sector, Amazonian-influenced semideciduous forests are present, although in smaller areas.

• Southeastern border area (SE): In the southeastern sector there are areas with cerrado and others with semideciduous forests which contain elements of the southeastern Brazilian forest.

• Southwestern border area (SW): In the southwestern border area, elements of the Chaco, such as Copernicia palm forests, dominate as well as semideciduous and deciduous forest; in particularly dry places on limestone outcrops, elements of the Caatinga can be found.

Vegetation

A seasonal climate and high temperatures are the pre-requisites for the formation of tropical savannas. During the months of drought there is a water shortage, so that the plants have to develop strategies to survive the arid months. The grasses dry up so that fires are common. During the rainy period, topographical and edaphic conditions decide whether rainfall is absorbed and stored by the soil, or flows away on the surface to flat areas with impermeable soils, causing flooding. The types of vegetation occurring in the Pantanal are therefore closely related to the seasonality of the climate and conditions of ground - and floodwater.

• Dry campo. Brazilians use the term campo for various types of grasslands. Dry grasslands naturally occur in the higher mountain ranges, often in regions with a shallow layer of topsoil on a rocky basement. Cerrado can be transformed into dry grassland by frequent burning.

• Cerrado. Brazilian designation for “dry tree and shrub savanna”. Enormous stretches of open grassy country with a more or less dense growth of bushes and low, often crookedly formed trees, are found in Central Brazil. Cerrado is usually found on well-drained, leached, acid soil which is poor in nutrients and has a high content of aluminum (Eiten,1972). The woody plants of the cerrado are for a great part endemics; they show a high degree of fire resistance as an adaptation to the frequent camp fires occurring in the Brazilian savanna regions. In the Pantanal plain, cerrado occurs in many places with sandy topsoil not reached by groundwater.

• Cerradão. Brazilian designation for savanna woodland. This type of forest has a closed canopy of trees, but there is no distinct stratification in the tree-layer. The trees are 10-14 m high, often branching low in the middle third of the trunk and with a tendency to twisted growth. The ground cover consists of shrubs and often of many terrestrial bromeliads. Floristically, cerradão consists of a large number of tree species found in the cerrado as well.

• Evergreen Forest. Evergreen forest may occur in areas where the soil is fertile and the groundwater level does not show much fluctuation. Such conditions exist at the foot of mountain slopes, or along rivers in hilly areas. These forest may exist to a greater extent in the northern border areas of the Pantanal.

• Semideciduous Forest. This type of forest has an upper, often incomplete canopy, 18-24 m high. The trees of this storey are completely deciduous during the dry season. The lower storey is made up of mixed evergreen and deciduous trees, 8-10 m high. The ground cover consists of shrubs, palm seedlings, terrestrial bromeliads, and various herbaceous plants. Semideciduos forest generally grow on fertile soils; this type of forest has therefore been destroyed and transformed into pastures on a large scale, especially in the northern border areas.

• Deciduous Forest. This type of forest can be found on hill slopes, especially on calcareous rocks. The trees and the shrubs of the undergrowth are completely deciduous during the arid months. Floristically this type of forest seems to be closely related with semideciduous forests.

• Gallery Forest of lowland rivers. Lowland rivers usually form river banks which lie 1-2 m higher than the surrounding floodplain. On these river banks, which are rarely flooded by highwater, semideciduous forest and/or cerradão may be found.

• Seasonally flooded woodland. This type of woodland commonly occurs on floodplains in the vicinity of major streams. There is usually a lower canopy formed by tall shrubs and low trees, with a few emerging higher trees. In its floristic composition this type of woodland is quite distinct from semideciduous forests and cerradão.

• Seasonally flooded grassland. This type of grassland, which in Portuguese may be called campo alagado, is classified as wet savanna; it is widespread in floodplains with impermeable soils which are flooded for long periods during the rainy season. It consists of Gramineae, Cyperaceae, Burmanniaceae, Scrophulariaceae, and other herbaceous plants together with a few woody plats such as Curatella americana, Bryrsonima orbignyana, Bactris glaucescens, and Licania parvifolia which can tolerate the double stress of seasonal drought and flooding.

• Forest Islands. Areas of forest of varying size from 10-15 m up to several hundred meters in diameter can also be found on patches of elevated ground in typical wet savanna. Usually these areas take the form of small woods, which are scattered about the flood savanna like islands. Measurements of these forest islands showed that their surfaces were higher than the surrounding wet savanna, sometimes by 40-60 cm but in extreme cases by as much as 140 cm. These mounds are therefore out of reach of the wet season floodwaters, so that trees can become established on them. Both trees of cerradão or semideciduous forest may be found; in many parts of the Pantanal, Tabebuia heptaphylla is a typical tree species growing on these mounds. In the centre of these forest islands there is often a termite nest or, more rarely, a nest of leaf cutter ants. It seems probable that the biological influence of the termite or ant constructions produces these higher mounds in the landscape. The forest islands are important shelters for various animals foraging outside in the wet savannas, and certainly play an important role in the distribution of forest animals and birds throughout the Pantanal plain.

• Swamps and pond margins. Permanently flooded swampy areas and the margins of freshwater ponds are usually covered with dense aquatic vegetation; shrubs and herbaceous plants may be rooted in the mud in shallow water.

Wildlife Diversity

As a result of the topography and the seasonal climate the vegetation consist of a many - sided mixture of swamps, grasslands and woodlands, and forests (evergreen, semideciduous, gallery, etc.). This mixture has caused an extremely rich fauna. The Pantanal is the Brazilian ecosystem where the concentration of fauna has reached its peak, with a fantastic quantity of individuals of numerous species, particularly, aquatic and marsh birds.

In the Pantanal and surrounding region 700 species of Birds occur (Dubs 1992). It is one of the most significant breeding grounds for the typical wetland birds such as stork, heron, ibis, and spoonbill that are found in enormous concentrations (Alho et al. 1988). Quite evident are also the 26 species of parrot including the endangered Hyacinth Macaw (Anodorhynchus hyancinthinus). Other characteristic birds are the Greater Rhea (Rhea americana) , and the Bare-faced Curassow (Crax fasciolata). The large quantity of birds of prey, represented by 45 species, indicates a well balanced ecosystem. (Dubs 1992).

The Pantanal is also one of the last refuges for many threatened Neotropical Mammal species (Alho et al. 1988) such as Jaguar (Panthera onça), Ocelot (Felis pardalis), Maned Wolf (Chrysocyon brachyurus), Bush Dog (Speothos venaticus), Giant Otter (Pteronura brasiliensis), La Plata Otter (Lutra platensis), Giant Anteater (Myrmecophaga tridactyla), Giant Armadillo (Priodontes maximus), Marsh Deer (Blastocerus dichotomus), and Brazilian Tapir (Tapirus terrestris) (Schaller 1983/Paiva 1984/ IUCN 1990/ Bernardes et al. 1990/ Emmons 1990). The most visible mammal in the Pantanal is the Capybara (Hydrochaeris hydrochaeris) that during the dry season can be observed in herds of up to 30 individuals. Primates are represented by 5 species (Schaller 1983).

Most evident among the Reptiles are the abundant Paraguayan Cayman (Caiman crocodilus yacare), the Anaconda (Eunectes notaeus), the Iguana lizard (Iguana iguana) and the endemic Cayman Lizard (Dracaena paraguayensis).

The amphibians are relatively poor in species. But fish are remarkably abundant because of the extensive network of lakes rivers and tributaries, at least 260 species (Wetlands for the Americas 1993) including several species of catfish and piranha (Alho et al. 1988).

Few studies have been made of the invertebrates of the Mato Grosso Pantanal, although they are numerous, the biology of most of the species is still unknown.

Piracema

The seasonal migrations of the fish in the Pantanal collectively called “piracema”, are a dominant and extremely impressive phenomenon, in which the most diverse taxa of small and large fish participate. The adult fish move up-river on the average, from May to October, i.e., during the dry period. In November-December with the raising waters, they reproduce and the fingerlings (together with the adults) penetrate into the flooded standing waters. This is a first critical phase, because often the flooded lowlands carry noxious products of decomposition of the plant detritus and are poor in oxygen. This is the phenomenon of fish death called “dequada”. End of March and April, when the rains stop, the now well-fed young fish return to the rivers. This is the so called “lufada”, eagerly expected by many fish predators. During the winter the fish assemble again in swarms and return up-river. The lufada is also a good period for lantern fishing of several economically important species. The piracema migration takes the fish over distances of hundreds of kilometers.

Environmental Worries

Ninety nine per cent (99%) of the Pantanal is privately owned land consisting of “fazendas”, large cattle ranches. The cattle ranching has taken place in the region for more than 200 years (Garcia 1989/ da Silva 1992), and in the recent years the grasslands has fed up to 8 million head of cattle (Alho et al. 1988). Little of the area has been unaffected by the cattle and the activities of the local “Pantaneiros” (Prance and Schaller 1982), but it is generally considered that these activities have left the nature relatively unharmed (Alho et al. 1988/ Dubs 1992).

During the last decades, however, the Pantanal has been under serious attack, the area and its wildlife are threatened by a number of human activities such as:

• POACHING aimed at the international skin and pet trade (Alho et al. 1988). In the beginning of the ‘ 80s, for example, more than 1.5 million caimans were killed per year (da Silva 1992).

• DEFORESTATION to gain grassland for the cattle or land for arable farming. This cause loss of lifedepending habitats and biodiversity, as well as serious sedimentation problems for the river system (da Silva 1992).

• MAN-MADE FIRES to stimulate the growth of fresh grass to the cattle. The fires kill many slow-moving animals, burn bird nest, and cause big damage to the whole ecosystem (Alho et al. 1988/ da Silva 1992).

• OVERFISHING by uncontrolled illegal net fishing (da Silva 1992).

• UNCONTROLLED TOURISM spreading litter and scaring the animals (Alho et al. 1988).

The biggest threat to the Pantanal in the long run, however, is probably the environmental contamination from the surrounding uplands where most of the population and activities in the region are found. Via the rivers the Pantanal receives agrochemicals from intensive monocrop farming, mercury from goldmining, untreated urban sewage and waste, and organic waste with high oxygen demand from various agroindustries (Alho et al. 1988/ Wetlands for the Americas 1993).

Currently there is a big-scale project under consideration: the construction of the waterway, the “Hidrovia”, by hydraulic alteration of the Paraguay river (Wetlands for the Americas 1993). This project would undoubtedly have catastrophic impacts on the Pantanal.

Day by day, the Pantanal ecosystem is being degraded. If the area and its unique wildlife is to be preserved, action must be taken on a much larger scale. It is essential to:

• spread environmental consciousness in the region;

• research, develop, and introduce environmentally as well as economically sustainable use of the land and its natural resources, inside as well as around the Pantanal; and

• establish more protected areas to acutely save important threatened habitats.