Cantão

Igapós are forests which are flooded for four to seven months every year by blackwater rivers. The igapós of Cantão begin to flood in December, and by March the water in the forest is five to eight meters deep, and running between the trees at speeds of one and two knots. Only trees adapted to such extreme conditions grow in the igapós, and the rushing annual floods mean that the understory is unusually open for a tropical forest. Many flooded forest trees flower and fruit during this season, and the fruit fall into the water and are eaten by fish, which disperse the seeds.

The most common large tree species in the igapó forests of Cantão are the landi and the piranheira. Both of these commonly grow over twenty meters in height, and both of them drop their fruit into the water, to be dispersed by fish. The piranheira tree earned its name due to a further contribution it makes to the aquatic ecosystem: it sprouts new leaves after the peak of the floods, which attract great numbers of caterpillars. These drop into the water whenever the wind shakes the tree tops, attracting schools of small piranha and other omnivorous fish.

The igapós of Cantão have a rich bird fauna, including some habitat specialists. One of the most common is the band-tailed antbird, which only nests during the flood season, on the tops of isolated shrubs, only a meter or two above the water. It does so to avoid the abundant predators, which include roaming bands of black-striped capuchin monkeys and coatis.

In Cantão, moist deciduous forest occurs wherever the ground is high enough to remain above peak flood levels in most years. It is lower in canopy height than the igapó forests, and its undergrowth is thicker and more entangled. It also displays high plant species diversity, including abundant epiphytes like orchids and bromeliads. Many of the plant species of this natural community are drawn from the nearby cerrado.

During the dry season, when up to 90 days can go by with no rain at all, many of the trees in the moist deciduous forest drop their leaves. During this season there is a considerable risk of fire, whether natural or caused by man. Natural fires due to lightning are quite common, but tend to be quickly put out by the ensuing rain.

During the annual floods, deciduous forests are the only places where there is dry ground. They become the only feeding grounds available for bird species like the undulated tinamou, the bare-faced curassow, and the several species of wild pigeon that occur in Cantão. Many mammal species that don't do well on trees or in flooded areas also seek refuge in these forests, which consequently become prime hunting ground for the park's two large terrestrial predators, the jaguar and the puma.

A marsh deer grazing among a flock of white-faced whistling ducks

Although forest vegetation predominates in the park, marshes, where grassy and shrubby vegetation is predominant, occur on the inside of river bends, at the ends of oxbow lakes, in channels that are in the process of closing, and at other places where recently deposited sediments are flooded by swift-moving water during the rainy season.

The marshes of Cantão hold a great diversity of plant life, and this becomes evident at the peak of the floods, when vines, shrubs, and floating vegetation flower, covering large areas with a mosaic of color. Most of these plants go on to produce fruit which are consumed by fish. In addition, broad mats of Paspalum repens grass and other floating vegetation with roots suspended in the current create a substrate for a very productive aquatic ecosystem. The roots of the vegetation are shaped so as to act like filters, trapping organic particles brought by the current, and doing so near the surface, where oxygen and sunlight are abundant. As a result, not only fish, but also fish predators like giant otters and the black-collared hawk move into the marshes to forage.

Marshes are also the prime breeding habitat for the park's abundant hoatzin population. The build their stick nests on the tops of isolated trees in the middle of the marshes, safe from terrestrial or arboreal predators. Many other species of bird also nest over marsh waters during the wet season, including the ubiquitous great kiskadee and the peculiar greater ani, which builds its communal nests in tangled vegetation over water.

Cantão State Park includes 24 sandy islands on the Araguaia river, as well as a large number of river sand beaches on bends of the channels that weave through the interior of the park. The sand itself is the primary habitat for a number of species. Black skimmers, yellow-billed terns, yellow-spotted river turtles, the enormous Amazon river turtle, and other species nest directly on the sand in great numbers. Their eggs attract nest predators like the crested caracara, the tayra, and even the jaguar, which also takes adult turtles at night when they climb up onto the beach to nest.

A male tayra emerges from a Sapium thicket to forage for turtle and bird nests on a beach inside the park.

Sandy beaches and mud banks are also the preferred feeding habitat for wading birds like the roseate spoonbill, the whispering ibis, and several species of ducks. Among the more remarkable inhabitants of river islands and large beaches is the northern screamer, which can be seen in the park throughout the year.

The vegetation growing on this sandy, nutrient-poor environment goes through several successional stages, starting with annual grasses and herbs, which are heavily grazed by mammals and ducks in the dry season and by fish when submerged in the wet season. The next stage is dominated by Sapium and Psidium bushes, both of which fruit during the annual floods, and have their seeds dispersed by fish, especially pacús. As the years pass, the ever-thickening mass of roots begins to accumulate detritus brought by the floods, and the formerly barren sands turn into soils capable of supporting a greater variety of plant species. Finally, a canopy of Cecropia trees forms above the bushes. The cecropias fruit year-round, and the dense stands that form in attract a great many frugivores which bring seeds from the surrounding forest. Over the decades, these seeds sprout and grow, overwhelming the cecropias, shading and stifling the undergrowth, and turning into an igapó flooded forest environment. However, further downstream, new sediments are being deposited, pioneer plants are sprouting on the sand, and all the beach and island successional stages are starting anew.

The backwaters of Cantão include oxbow lakes, forest ponds (which dry out completely by the end of the dry season), and hundreds of kilometers of narrow channels which crisscross the delta of the Javaés river. All these waterbodies have in common the fact that during the floods, they are all interconnected as the black waters of the Javaés river rise and flow over the entire landscape, while in the dry season they become isolated from one another.

A five meter long black cayman cruises on a Cantão lake

There are 843 oxbow lakes within the borders of Cantão state park, and about 900 in the Javaés delta as a whole. The entire rest of the Araguaia wetlands contains just over 200 lakes, illustrating the importance of Cantão for the great river's ecosystem. Oxbow lakes are the site of reproduction for many species of fish, and for concentrating 80% of the basin's lakes, Cantão is known as the "nursery of the Araguaia." The peacock bass or tucunaré, one of Brazil's most popular freshwater gamefish, is one of many species which reproduces in the Cantão backwaters during the dry season. Another is the pirarucú, the world's largest freshwater fish, whose numbers are dwindling everywhere in the region due to relentless poaching. The remote and inaccessible lakes of the interior of Cantão are one of the last remaining sanctuaries for this species.

During the floods, almost every aquatic species in the park can be found in the interconnected backwaters. During the dry season, prey fish become concentrated in isolated water bodies, providing a veritable feast for predators like the giant otter, the Amazon river dolphin, the pirarucú, and the black and spectacled cayman. Along lake edges, five species of kingfisher, nine species of heron, and specialists like the sunbittern and the green ibis forage for fish and invertebrates. Neotropical cormorants and anhingas fish away from the shore. Even jaguars join in the feast, diving into forest pools to catch large fish, or sitting in ambush for them as they pass through the shallow water channels that connect deeper lakes.