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FRAGMENTATION: A GROWING THREAT TO BIODIVERSITY

Patches of tropical rain forest in Brazil.
Source: Rainer Wirth

Much of the attention given to biodiversity loss has centred on the threat to wilderness areas. New studies in the region, however, show that fragmentation of ecosystems into smaller patches is a major problem.

Islands of natural vegetation, surrounded by areas that have been deforested, burnt or used for agricultural and livestock production, are more and more common, especially in Central American tropical forests, the Amazon, the Cerrado (Brazilian savannah) and the areas that remain of the 'Mata Atlántica' forest in Brazil. It is estimated that only 43 per cent of the original area of the Cerrado (1.96 million km2) and 8 per cent of the Atlantic forest region (1.10 million km2) in Brazil remain, and much of these areas exist only in remnant patches of various sizes (Lopes 2004).

When large forest blocks are broken into smaller ones, not all species are included in all the remaining patches. Rare species and those requiring large areas of habitat are especially vulnerable. Among tree species, because of differences in seed dispersion, slow growing species are lost, while opportunistic species become more common. The life span and reproductive capabilities of mature specimens are affected, along with flows of biomass and dead organic matter, mainly plant litter (Tabarelli and others 2004).

These patches also suffer an 'edge effect' from juxtaposition with a contrasting environment, most commonly cropland or grassland. For example, large trees die three times faster in areas less than 300 metres from the edge of the patches (Laurence and others 2000). Species unable to tolerate the altered microclimate in these edge areas, or facing too much competition from other species, are driven back into a reduced area, while species from outside invade and become more common.

Fragmentation also allows more human access to the forests, leading to increased subsistence and industrial logging, hunting and resource gathering. Human-induced fires are also more frequent. All of these contribute to the decline of many species. For example, new estimates show that 35 per cent of the tree species in the remaining areas of the Atlantic forest of northeast Brazil are likely to become extinct if the current rate of fragmentation continues (da Silva and Tabarelli 2000).

Fragmentation creates gaps between forest blocks that reduce the movement of species, so there have also been some local extinctions of vertebrate species that help disperse plant seeds. This has reduced the rate of plant reproduction further. Fragments smaller than 100 ha typically lose half of their bird species within 15 years (Ferraz and others 2003). Agoutis, primates and fruit-eating birds such as toucans and aracaris are often affected. Fragmentation reduces the genetic flow between isolated populations of a species. In some cases a population as a whole is replaced by other species - including invasive species transported to the area by humans (Lopes 2004, Tabarelli and others 2004).

This understanding demands new perspectives in forest conservation. One response is to establish ecological corridors to allow the movement of fauna and flora between 'islands'. Others include controlling human activity and the entry of invasive species along the edges, controlling fires, and encouraging sustainable land use and local wildlife-friendly management in the adjacent areas. New studies call for a regional conservation approach, going beyond national environmental policies (Lopes 2004).

Countries in Latin America and the Caribbean (LAC) are trying to develop and implement environmental strategies and initiatives of this type. The Mesoamerican Biological Corridor project, a sub-regional project for biodiversity conservation, is being implemented by the Central American Commission for Environment and Development, comprised of ministries of environment and natural resources. Ministers of foreign affairs from the member countries of the Amazon Cooperation Treaty Organization (ACTO) coordinate activities for development and conservation of the Amazon rainforest (Box 1).

Box 1: Relaunching the Treaty of Amazon Cooperation

In September 2004, ministers of foreign affairs from the member countries of the Amazon Cooperation Treaty Organization (ACTO) - Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela - produced the 'Manaus Declaration'. The treaty aims to coordinate activities for development and conservation of the 7.5 million km2 of Amazon rainforest.

In the declaration, the states reiterate their responsibilities to promote the economic and social development of the region and the protection of its cultural and environmental patrimony for the benefit of their populations. They aim to establish cooperation programmes and declare a common interest in issues such as defence and internal security, social development, infrastructure and physical integration, trade and integration, science and technology, protection of biodiversity and intellectual property.

The original treaty produced little tangible result since its signing in 1978. But in 2004 the Secretariat of ACTO was established, headquartered in Brazil. It has signed agreements and implemented projects to promote sustainable development in the Amazon. ACTO has also secured approval of a Strategic Plan outlining actions to be undertaken to the year 2012 by the foreign ministers. The plan establishes four strategic themes, six priority areas of action, and the instruments needed to meet these objectives. Other key developments include:

  • Approval for agreements with the Andean countries and the countries of the Plata River Basin;
  • Launch of a plan to develop sustainable indicators for the Amazon (with FAO help); and
  • Agreement with UNCTAD to promote biotrading, which aims to stimulate trade and investment in biological resources and to further sustainable development, with conservation of biological diversity and equitable sharing of the benefits.

Sources: ACTO 2004a and b


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