Rainforest distribution and vulnerability

There is widespread concern about the decline of forests around the world, especially at lower latitudes. Tropical forests are causing particular concern given that they contain more than 50% of all the species on Earth, and have a large economic value. Even more critically, more than 50 million indigenous people live in tropical forests; Amazonian forests alone hold 400 indigenous groups composed of 1 million people (Bryant et al., 1997). Costanza et al. (2003) calculate that the current economic value of tropical forests collectively is $3.8 x 1012 ($3.8 million million) per year, the most valuable of all terrestrial ecosystems. This is over four times the value of all temperate and boreal forests together even though they are 1.5 times the area of tropical forests. Of all the tropical forests it is the rain forests that are considered most at risk. The plight of tropical rain forests caused particular concern as early as 1850, when the British Association for the Advancement of Science appointed a committee to consider the probable economic and physical effects of the destruction of tropical forests. This concern continues; the strong pressure that has for many years been exerted by both individuals and conservation groups, is recorded in Goldsmith (1998). It is difficult to get an accurate picture of the current rate of loss. As Watson et al. (2000) have pointed out 'for tropical countries, deforestation estimates are very uncertain and could be in error by as much as 50%'. FAO (2005) give an average loss of forest in Brazil of 3.1 M ha per year between 2000 and 2005. Data for just the Brazilian Amazonia has been put forward by Laurance et al. (2004) - see Fig. 11.1- which underlines the general

Threats to forests and the increasing demand for timber


Threats to forests and the increasing demand for timber

European Rain Microorganism

Figure 11.1 Deforestation in Brazilian Amazonia since 1990. The data are from Brazil's National Space Agency. The fitted regression line is the best fit to the data and shows a significant upward increase in annual deforestation. (Redrawn from data from Laurance et al., 2004. Science 304.)

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Figure 11.1 Deforestation in Brazilian Amazonia since 1990. The data are from Brazil's National Space Agency. The fitted regression line is the best fit to the data and shows a significant upward increase in annual deforestation. (Redrawn from data from Laurance et al., 2004. Science 304.)

feeling that globally deforestation is still increasing. This is especially tragic since Amazonia holds over half the Earth's remaining tropical rain forests. The primary underlying reasons are the need for cropland, increasing population density and the need to earn revenue to pay off external debt (Han et al., 1997). A more insidious problem is not just the loss of rain forest but its increasing fragmentation. Estimates suggest that 4% of the boreal forest has been fragmented or removed by humans, compared with over half of temperate broadleaf and nearly one-quarter of the tropical rain forest (Wade et al., 2003). In their pleading letter to the journal Science, Laurance et al. (2004) point out that the Brazilian Government's plans to expand dramatically highways in the Amazon basin will not just lead to further development and forest loss, but will also lead to 'fragmentation of surviving forests on an unprecedented spatial scale'. In 1993, Skole and Tucker published a study that showed that the area of Amazonian forest within 1 km of the numerous edges caused by felling was 1.5 times larger than that of the cleared forest. The effects of fragmentation are considered in Section 10.7.2.

When large areas of primary forest are cut, the successional pathways which occur if the land is subsequently abandoned are of major interest; Mesquita et al. (2001) report studies of such patterns in Amazonia. The pioneer genus which dominated clearcut sites after 6-10 years differed with subsequent land use, being Cecropia (Moraceae) if the land was abandoned directly after clearcut and Vismia (Clusiaceae) if it was subsequently used as pasture before abandonment.

In the Cecropia stands 58 plant families and 300 species were identified, of which 77 species were also found in the 147 (belonging to 43 families) beneath the Vismia canopy, where regeneration was dominated by small Vismia individuals. Regeneration under Cecropia was more diverse and did not include a single small Cecropia. Not surprisingly the number of regenerating plants and plant diversity decreased sharply with distance from primary forest in both cases. This work clearly has important implications for rain forest conservation; if primary forest is to be felled this should be done in relatively narrow strips allowing adequate seed dispersal from the unfelled trees, while the clearcut areas themselves should be left to regenerate directly after felling.

The world distribution, climates and classification of tropical rain forests are described by Whitmore (1998), who provides maps showing outlines of the areas still occupied by them in central and south America, central Africa and Madagascar, and areas running from the west coast of peninsular India through to the Malayan and Australian rain forests. Other, non-tropical, rain forests formerly covered very large areas and some still do. Temperate rain forests occur in five major areas of the world: The Valdivian of Argentina and Chile, the Pacific Northwest of North America, the western Black Sea, New Zealand and Tasmania. All face pressure of felling.

Although small in area, the coastal temperate rain forests of Scotland represent communities whose extent was much greater before the influence of humans. Their relevance globally is discussed by Rhind (2003), who provides illustrations of a boulder-littered oak woodland on the island of Mull, west Scotland, and of rowan trees in Glen Affric, Scotland covered with bryophytes and lichens, including Lobariapulmonaria. This lichen is well known in Sweden as a plant characteristic of primary beech woodland (see Section 6.4.1). The amount of coastal temperate rain forest remaining in north-west Scotland is estimated at 6896 km2 out of 302 227 km2 for the whole earth. These woodlands are typically dominated by sessile oak Quercus petraea and downy birch Betula pubescens; many fungus species abound as well as an abundance of moisture-loving invertebrates. Oceanic bryophytes present include Dicranum scottianum, Frullania teneriffae, Leptoscyphys cuneifolius, Lophocolea fragrans, Metzgeria leptoneura, Radula aquilegia and Sematophyllum micans. 'Old growth' Lobarion lichens often include Lobaria amplissima, L. scrobiculata, Pseudocyphellareia crocata and Sticta canariensis.

11.1.3 Changing patterns of animal distribution

While data concerning the numbers and world distributions of many species of birds are often freely available, less is known concerning other groups of vertebrates. Information about the status of British mammals collected by members of the Mammal Society shows just what is needed not only in Britain, but in many other places, if we are to make informed judgements about forest policy in relation to the animals present. An increase in badgers Meles meles in Britain to a quarter of a million has been accompanied by many deaths through road accidents. Increases in otter Lutra lutra numbers have been accompanied by losses of the alien mink, though not necessarily caused by them. Even so the range and numbers of otter in the UK are considerably less than 50 years ago. The very large increase in the rabbit Oryctolagus cuniculus population to some 40 million is bad news for both farmers and foresters due to their incessant grazing and browsing. The rise in polecat Mustela putorius numbers since World War II is attributed to the loss of gamekeepers, who formerly kept its numbers down. Numbers of feral ferrets, the tamed version of the polecat, are increasing but still relatively small. Due to competition with alien grey squirrels, the still declining red squirrel is extinct in most of England and Wales (Section 5.7.2).

Perhaps even more serious is the decline of the dormouse Muscardinus avellanarius in England, and of the wild cat Felis silvestris in Scotland. Harvest mouse Micromys minutus numbers have also declined by around 75% due to habitat loss, while those of water vole Arvicola amphibius are even worse with a decline of over 90% attributed to mink predation and habitat changes. Deer on the other hand, particularly muntjac, fallow and roe, are increasing markedly and impacting heavily on the shrubs, ground flora and tree regeneration of British woodlands (Section 5.7.1). Besides our interest in their distribution, there is also much to learn about the behaviour patterns of mammals and the use of remote-controlled concealed cameras has recently proved most useful in studying that of the giant panda.

Over the longer term there is great interest in the changing forms of the animals that have inhabited the Earth. Attenborough (1980, 1985, 2002) gives well-illustrated accounts of the animals that inhabit our forests and tree canopies (Fig. 11.2), as well as describing those of the past, including the bizarre grazing mammals which evolved two million years ago when South America was an island. How will evolution go, and how greatly will the human population be affected by global warming or another ice age?

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