Wolfgang J. Junk

An introduction to South American wetland forests: distribution, definitions and general characterization

This chapter provides an introduction to the ecology of wetland forests, their ecophysiology, distribution, species diversity, classification and use, with emphasis on Amazonia. Wetland forests occur in all continents and all regions except in deserts, high altitudes, and high latitudes. Their importance for humans and the environment is often underestimated because in developed or densely colonized regions such as Europe, North America, Australia, and the Indian sub-continent, many of them have already been destroyed or strongly modified. In other regions, such as Siberia, the Zaire River basin and the Amazon River basin they still cover large areas; however, scientists and politicians have placed little emphasis on their study and protection, or on developing sustainable management practices. In this chapter, we describe the general terminology for wetland forests and provide a classification of Amazonian wetland forests. We discuss the distribution of major wetland forests in South America and the impact of hydrology and nutrient status of water and soils. Distribution, species diversity, and the level of adaptation of trees of wetland forests is the result of long periods of evolution, without major extinction episodes. These conditions prevailed for many millions of years in the Amazon basin as shown by paleo-climatic and paleo-botanical evidence, leading to the development of the most species rich and highly adapted floodplain forest on the globe. In light of this history, we give examples for specific adaptations and survival strategies. Finally, Amazonian wetlands have been colonized by humans since their arrival on the sub-continent, about 12,000 years BP. More recently, European immigrants have used the wetlands for fishing, subsistence agriculture, timber exploitation and increasingly for cattle and water-buffalo ranching. Large scale ranching activities are especially detrimental for the forested Amazonian wetlands, because ranchers destroy wetland forests to increase the area of natural and planted pastures. This is also detrimental for forestry, fisheries, and the maintenance of biodiversity.

A classification of the major habitats of Amazonian black-water river floodplains and a comparison with their white-water counterparts

The Amazon River and its large tributaries are bordered by floodplains covering tens of thousands of square kilometers. Studies on the structure, function, and species composition have allowed a classification of the macrohabitats of Amazonian white-water floodplains, rich in suspended matter and nutrients and of neutral pH (várzea). Here we describe the use of a similar approach to classify the macrohabitats of the black-water floodplains, rich in humic substances, poor in nutrients and acidic (igapó) of the Negro River and its black-water tributaries. With 12 subclasses and 25 macrohabitats, the igapó is less complex than the várzea. Although white-water and black-water rivers are subjected to similar flood regimes, the low sediment load and shallower declivity of the Negro River lead to reduced sedimentation and erosion processes. Differences in nutrient levels between both ecosystems influence species composition, richness, and growth rates of higher plant communities. Species richness is lower in igapó than in várzea, and wood increment and litter production of igapó trees is about half that reported for várzea trees. In addition, igapó lacks highly productive herbaceous plant communities that are common in várzea. The classification of igapó macrohabitats provides a valuable tool for the elaboration of sustainable management strategies and conservation. While many várzea macrohabitats are suitable for small-scale agriculture, animal husbandry, forestry and commercial fisheries, the carrying capacity of igapó is limited and allows only for subsistence-level fishery and agriculture, the capture of ornamental fishes, and ecotourism. We argue that the biota of most igapó macrohabitats is highly sensitive to changes in hydrological cycles as caused by river damming and/or by climate change.

Ecophysiology, Biodiversity and Sustainable Management of Central Amazonian Floodplain Forests: A Synthesis

This synthesis chapter provides an overview of the 23 chapters of this book. With more than 1000 tree species, Amazonian floodplain forests are the most diverse forests of this kind. They occur in different forms and under different hydrological and chemical (water and soil) conditions. Forests in nutrient rich whitewater river floodplains (varzeas) are richer in species, more dynamic, and more productive than those of black- and clearwater rivers. The new species colonization concept explains the relationship between upland and varzea forests. A model of forest succession is provided that indicates the development of different seral stages under different hydrological and sedimentological conditions. Trees react to long-term flooding and water-logging of the soils with many anatomical, morphological, physiological and phonological adaptations, which result in specific life history traits. Seed production, seedling establishment, and sapling survival are of fundamental importance for the regeneration of these forests and their reactions to the frequent set-backs caused by erosion and sedimentation processes. Until now, the use of floodplain forests has been restricted to highly selective timber exploitation, which depletes the stocks of the respective tree species. A management model, based on growth-oriented logging (GOL) is provided here. In this model, the extraction of the logs depends on water levels, the maximums and minimums of which can be predicted using new model based on sea surface water temperatures in the Pacific and the Atlantic Oceans. Such predictions would facilitate the management of the natural resources of the varzea, including management using forestry. When the many riparian forests are included, floodplain forests cover about one third of the Amazonian rain forest area. However, this fact has not been considered in management aspects and climate models for Amazonia. Global climate changes certainly will affect the hydrological cycle in Amazonia. However, we consider the prediction by the Hadley Center of a near “savannization” of the Amazon forest to be without sufficient scientific basis and unhelpful, because it may even accelerate the deforestation of Amazonia. The maintenance of intact wetlands will be very important for the sponge function of the landscape, which acts to retain water and to buffer extremely dry and wet periods. In this context, the floodplain forest is of utmost importance as a refuge for many plant and animal species.

Implementation of the Ramsar Convention on South American wetlands: an update

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Amazonia: Water Resources and Sustainability

Water resources in Amazonia affect all natural and human-altered ecosystems in the region, including their human populations. Evapotranspiration by the Amazon forest provides water vapor that is transported by wind to other regions of Brazil and to neighboring countries. The enormous quantities of water involved in hydrological processes in Amazonia give great importance to the region’s water resources and to potential impacts if these cycles are altered. The diversity of fish and other aquatic organisms is enormous, as is the importance of this fauna as economic and food resources for the human population. There are impacts from pollution, including mercury methylation in hydroelectric reservoirs. Dams also block migration of fish and alter the flooding cycles of rivers. Hydroelectric dams release methane, thereby contributing to global warming. The chemical characteristics of different types of water affect processes such as the transport of organic carbon, the supply of nutrients to the plankton that are the base of the food chain in aquatic ecosystems, and the quantity of bio-available ions that affect sensitivity of organisms to copper and other toxic elements. Several of the major rivers in the region drain more than one country, as is the case for the Madeira River, whose basin drains parts of Bolivia and Peru, in addition to Brazil. International treaties require protecting the rights of other countries that share aquatic resources in trans-border watersheds. The hydroelectric dams under construction in Brazil on the Madeira River imply a variety of impacts in the neighboring countries, including blocking the migration of large catfish. One of the priorities for rational decision making on aquatic resources in Amazonia is expansion of scientific knowledge on aquatic systems in the region. A series of national and international projects are engaged in improving this knowledge, and masters and PhD programs are increasing the capacity for research in the area. The human population in the region depends on the functioning of aquatic ecosystems. People share the fate of these ecosystems, in which they constitute a central component.