Forests of the world

These ecosystems have been substantially modified by hmnan activity as forests have been replaced by agriculture over the milleimia. The temperate forests of Emope are the most altered ecosystems of all in some regions almost no forest remains. Not only have forests been removed for agriculture and fuel but industrialization and mbanization have also exacted a toll. This means that many animals have become extinct, e.g. wolf, and others, such as birds of prey, are rare and/or threatened. 

Boreal forest ecosystems provide the raw materials for lumber/pulp industries in Canada, Scandinavia and Russia. Unlike tropical forests, they receive relatively little publicity but are subject to as many threats deforestation is rife in the Russian Far East and Siberia and there are concerns about the sustainability of North American and Scandinavian boreal forests because of lumbering industries, as discussed in Section 6.2.2 below. 

Savanna communities are present in tropical regions where there is a pronounced dry season of between two and ten months, and where fire is an important component of the ecosystem dynamics. They are varied in structure and composition, the common feature comprising a continuous grass cover. Trees are present in many savanna types, ranging from scattered 

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Table II. Total aboveground biomass (Mg ha ) in selected forests of the world.

Our results suggest that forest degradation is detectable not only in Yungas but also in Chaco. In environments similar to Chaco, discrepancies between these results (lower) and estimations made in similar environments in other forests of the world might be due to structural differences, altitude, latitude and humidity, gradients (24, 32, 33). However, in our case the level of degradation exerted by human activity in this environment might also be responsible for the discrepancies [20, 21, 41] (further details refer to [43]). 

Millions of tons of wood are produced every year in the forests of the world. Observation, however, tells us that the sum-total of wood upon the surface of the earth remains fairly constant from year to year and from century... 

As of 1995, the forest industry in the United States employed about 1.6 million people and produced products valued at over 200 biUion each year, approximately 20 biUion of which was in exports. There were 350 pulp mills, 600 paper and board mills, and ca 4500 converting plants in the United States producing ca 30% of the total world production. The United States and Western Europe, which represent ca 13% of the world population, consumed about 60% of production. 

In recent years, many of the world s forests have been cut down and replaced with shortlived crops. What effect, if any, might this have on the (1) P stored in the land biota reservoir (2) exchange rate of P between the land biota and the land reservoirs (3) exchange rate between the land reservoir and the surface ocean ... 

From an energy perspective, forests are bank accounts that store the results of photosynthesis. When we cut and bum wood, we make withdrawals from these energy accounts. So long as we do not cut more rapidly than trees can replace themselves, forests represent a renewable energy resource. In the past, as well as in some parts of the world today, forests were harvested much more rapidly than they reproduced. Fortunately, attitudes about forest use are changing, and modem forestry practices make it possible to sustain this energy resource. 

According to recent studies, the forests covering about 30% of the earth s surface [1] contain 80% terrestrial biomass and provide habitat for about half of the world s known species of plants and animals [2]. Forests provide a wide range of ecological, economic, and social assets, as well as services such as climate regulation through the storage of carbon in complex physical,... 

During the Late Pleniglacial, between 20,000 and 13,000 BP, some 25% of the land surface became covered with continental ice sheets (versus some 10% today). With so much water stored in ice sheets, the sea level dropped to about 120 meters below the present level and large parts of the world became extremely arid. The Amazon rain forest dwindled to isolated refugia, European forests disappeared but for small sheltered areas, and large parts of the globe turned to tundra, steppe, savannah or desert. 

The vast loess and till plains are now colonized by grasses and/or forest. They are the home of some of the best soils of the world the black earths . Deep, black Chernozems occupy the central parts of the Eurasian and North American steppe zones. Brown Kastanozems are typical of the drier parts of the steppe zone and border on arid and semi-arid lands. Dusky red Phaeozems occur in slightly more humid areas such as the American prairies and pampas. 

The receptors of interest are soils of agricultural (arable lands, grasslands) and non-agricultural (forests, steppes, heath lands, savanna, etc.) ecosystems. In non-agricultural ecosystems, the atmospheric deposition is the only input of heavy metals. Regarding the Forest ecosystems, a distinction should at least be made between Coniferous and Deciduous Forest ecosystems. When detailed information on the areal distribution of various tree species (e.g., pine, fir, spruce, oak, beech and birch) is available, this should be used since tree species influence the deposition and uptake of heavy metals and the precipitation excess. On a world scale, soil types can be best distinguished on the basis of the FAO-UNESCO Soil Map of the World, climate and ecosystem data from NASA database (1989). 

Eurasia is the biggest continent of the World. Because of the huge size of Eurasia, all types of ecosystems and climatic belts are represented, from arctic deserts up to tropical rain forests. Accordingly, some characteristic examples will be given here with special attention to biogeochemical provinces where biogeochemical exposure pathways induce the relevant diseases. 

Globally, it is estimated that there is 3870 million ha of forests (30 % of the Earth s land area), of which 95 % is natural or semi-natural (Table 1.1). At the present time, in most developed countries, the forest area is increasing and this is likely to continue given the present rates of harvesting. However, in tropical parts of the world, the forest area continues to decline, giving rise to serious concerns. It is estimated that between 1990 and 2000, there was a loss of 9.4 million ha per annum of forest worldwide (an annual deforestation rate of 14.6 million ha and an increase in forest area of 5.2 million ha per year Table 1.2). The only way to reverse this trend is to place sufficient economic value on forest resources, with incentives to encourage sustainable forest management. 

FAO (2001). State of the World s Forests. Food and Agriculture Organisation of the United Nations. 

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