The Amazonian forest is a large, ecologically intact area of ancient (or primary) forest. However, the Brazilian Amazon is becoming increasingly fragmented, whereby previously large tracts of forest are reduced to ever-smaller forest patches, interrupted by non-forest areas. Fragmentation leaves the remaining forest exposed to edge effects and vulnerable to increased fires and to climatic change.
Road opening is a principal agent of fragmentation. Roads built through intact primary forest open up the forest to further logging and deforestation, often followed by agricultural settlement. Such agricultural settlement along roads ultimately leads to fragmentation of the remaining forest. Logging is a critical force behind the opening of roads in primary forest. In particular, the extraordinary value of mahogany (Swietenia macrophylla King) makes it financially viable to open up long distances of roads, necessary because mahogany occurs in widely scattered patches. Widespread illegal logging practices compound the problem by increasing the number of roads into intact primary forests. The inclusion of mahogany on CITES Appendix II will allow increased regulation and curtail illegal trade in mahogany.
It is proposed that management plans for mahogany should be certified according to the environmental and socio-economic standards set by the Forest Stewardship Council (FSC), driven by international demand for FSC products. However, efforts to achieve sustainable management of mahogany must also include a network of national forest parks, regional planning for extraction and steps taken to combat illegal logging.
Ancient forests are mature forests that have been shaped largely by natural events and are little impacted by human activities. They are often termed "primary" or "old-growth" forests (see, e.g. Thompson et al. 2002). It is estimated that 80 % of these ancient forests have already disappeared globally (WRI 1997). The remaining large, ecologically intact areas of ancient forest (or frontier forests) are of global importance for their ecosystem services (e.g. climate regulation) and reservoirs of biodiversity (including far ranging species that require large areas). The Amazonian forest is such a large, ecologically intact, ancient forest, containing approximately 40% of the world's remaining tropical rainforests (Laurance et al. 2001a).
The Amazonian forest is threatened by anthropogenic activities including logging, mining and agricultural settlement. The Brazilian Amazon has the highest absolute rate of deforestation in the world (Laurance et al. 2001a). The continuing high rate of deforestation, coupled with planned development programmes such as 'Avança Brazil' have serious implications for the long term stability and ecological integrity of the Amazonian forest area Laurance et al. (2001a). Such activities increase fragmentation of the Amazonian forest, whereby previously large tracts of intact, continuous forest are reduced to patches of forest separated by non-forested lands (Thompson et al. 2002), with serious consequences for the remaining forest. One important threat is the extra-ordinary value of mahogany, which makes it financially viable to open roads into primary forest for extraction of mahogany timber.
This paper examines how the direct and indirect effects of fragmentation are important threats to the Amazonian forest. It then describes how opening roads into primary forest for extraction of timber, especially mahogany timber, leads to further logging, deforestation, agricultural settlement and ultimately, forest fragmentation, compounded by illegal logging. Finally, measures for the sustainable management of mahogany are discussed.
Fragmentation is known to have serious, direct consequences for biodiversity, leading to the genetic isolation of plants and animal species, reducing their genetic diversity (Foreman & Collinge 1996). However, the indirect effects of fragmentation are also of great importance to the Amazonian forest, as they pose a considerable threat to the survival of the remaining fragments. Indirect effects include edge effects and increased vulnerability to fire.
Edge effects: Forest fragmentation increases the relative length of forest edges. Along these edges of forests are strong microclimatic gradients, or edge effects (Gascon et al. 2000). As fragmentation and deforestation continue, the proportion of the remaining total area of ancient forest affected by fragmentation increases.
Edge effects in fragmented forests have now been well documented (e.g. Gascon et al. 2000) and include: increased tree mortality, especially amongst large mature trees of high biodiversity value (Laurance et al. 2000a); impairment of seed germination (Bruna 1999), shift to pioneer tree species; increased vines, which block out light preventing forest regeneration (Laurance et al. 2001b) and negative responses of butterflies, ants, beetles and termites (Laurance et al. 2000b). Edge effects have serious ecological consequences, which may threaten the survival of the remaining forest fragment (Gascon et al. 2000).
Fire susceptibility: Fragmentation of Amazonian forests leads to increased fires, especially during periods of drought (Nepstad et al. 1999; Cochrane 2001). Intact Amazonian forest was found to be more resistant to El Niño drought because primary forests retain more moisture more effectively than fragmented or secondary forests (Williamson et al. 2000). Both logging and fires themselves have been shown to increase vulnerability to future burning (Nepstad et al. 1999, 2001). Thus, once fragmented, the forest becomes vulnerable to repeated burning, preventing regeneration.
Forest fragmentation and climatic change: The predicted effects of global climatic change show a marked decrease in rainfall across the Amazon basin, increasing the number of El Niño-like drought periods (Cramer et al. 2001). Fragmented forests are more vulnerable to forest fires induced by droughts. Hence, fragmentation diminishes the resilience of the Amazonian forests to the desiccating effects of climatic change by making them more vulnerable to catastrophic fires (Nepstad et al. 1999; 2001; Laurance & Williamson 2001). In addition, fragmentation of the Amazonian forests decreases the ability of species to migrate in response to regional climatic change (Noss 2001).
Globally, ancient forests represent a significant terrestrial store of carbon (IPCC 2000). Houghton et al. (2001) estimated Brazil's Amazonian forests to contain 10% to 20 % of the total terrestrial carbon stock in the tropics. Additionally, the Amazon is currently a carbon sink (Houghton et al. 2000). Fires cause dramatic releases of carbon to the atmosphere, thereby reducing both the carbon store and ability of the Amazon to absorb atmospheric C. Such effects could contribute significantly to further climatic change (Laurance & Williamson 2001). Thus, the forests of the Amazon are under multiple, inter-related threats from the positive feedback loops driven by fragmentation, an increased incidence of fires and regional climate change impacts (Laurance & Williamson 2001).
In summary, fragmentation has serious consequences for wildlife and the ecosystem function of ancient forests, including large mammals, which require wide ranges and whose absence will disrupt the ecological balance of the forest. The remaining forest fragments are subject to edge effects and, in the Amazon basin, are vulnerable to fire. Fragmentation of the Amazonian forest plays an important role in increasing the vulnerability of carbon stocks, especially with regard to the expected impacts of climate change. Minimising the fragmentation of forests is, therefore, an essential consideration for the future existence of the Amazonian forests.
Historically, mahogany (Swietenia spp.) has always been a valued timber, with overseas demand for timber driving mahogany exploitation since the colonial era, resulting in the commercial extinction of two of the three mahogany identified species (Snook 1996). The one species remaining viable for loggers, Swietenia macrophylla King (hereafter referred to as mahogany), has now been included in CITES Annex II because of rapid depletion and low success with generation (see, e.g. Snook 1996, Greenpeace 2002a). Extraction of mahogany in the Brazilian Amazon began to be significant in the 1960s with the building of highways and decline in availability of mahogany in Central America.
Mahogany timber has extra-ordinary value. A cubic metre of first quality sawn timber was sold in 2001 for US$1200 at port in Belem, Brazil (Grogan et al. 2002). Verissimo et al. (1995) reported a final average profit (including expenses for reconnaissance, road building, felling, log extraction and transportation to saw mill and sawing) of US$200 per cubic metre. Much mahogany timber is destined for export. It is estimated that 70 % of mahogany is currently exported from Brazil, mostly to Europe and the US (Greenpeace 2001).
Mahogany extraction entails the opening up of new roads because mahogany occurs in widely scattered patches (Verissimo et al. 1995; Snook 1996). It is the extra-ordinary value of mahogany that makes it financially viable to open roads into primary forest for extraction of timber. The current high rates of mahogany extraction in the Brazilian Amazon are attributed to powerful machinery now available for road building (Snook 1996). It is estimated that it took more than 200 years for loggers to extract mahogany from a band 60 km wide along rivers in the Yucatan peninsula, Central America (Snook 1996), whilst mahogany loggers have constructed 3,000 km of logging roads in 30 years in the Brazilian state of Pará (Verissimo et al. 1995), the largest mahogany producing and exporting region in Brazil. As mahogany has become increasingly rare in more accessible areas, today there is a continuous penetration of logging roads into primary forests to extract mahogany trees (Snook 1996, Verissimo et al. 2002a). For example, Verissimo et al. (1995) detailed mahogany extraction operations up to 5-600 km from the mill.
Figure 1. Satellite image showing agricultural settlement along roads. The Landsat 7 ETM satellite image (top), September 2001, is of an area adjacent to the Xingu river, Pará. Forested areas are dark and bare soil or rocky areas are light. The larger of these light areas are mostly agricultural fields, as indicated by their straight sides. The sketch (bottom) of the negative threshold image shows areas without forest as black. Only roads clearly visible on the satellite image are drawn on the sketch shown, although smaller roads will also be present. It is clear that much of the agricultural area occurs alongside roads. The progressive expansion of agriculture along these roads is beginning to split the forest into fragments, indicated by F.
Single mahogany clumps have been found to extend over several hundred or several thousand hectares (Snook 1996), leading to the building of many roads and intense forest disturbance in these areas. Not only are roads built but also a relatively large area of forest is usually damaged in the process. Vegetation is damaged by the felling of mahogany trees, opening of skid trails and log landings (Barreto et al. 1998; Verissimo et al. 1995; 2002a). Verissimo et al. (1995) estimated that, on average, 370 m2 of canopy was opened and a total area of 1,500 m2 affected per single mahogany tree extracted. Once roads are built, forests tend to be revisited several times to harvest additional timber species, leading to a loss of 40-50 % of the canopy (Verissimo et al. 2002a). This forest "impoverishment" led Nepstad et al. (1999) to estimate that the annual rate of deforestation for Brazilian Amazon represents less than half of the forest area that is ecologically impoverished. Once impoverished, the area becomes vulnerable to agricultural settlement (Verissimo et al. 1995; 2002a; Watson 1996; Snook 1996). Indeed, Laurance et al. (2002) identified paved roads (highways) as an important predictor of deforestation of the Brazilian Amazon. Although logging roads would not expected to be paved and therefore have a lesser impact, similar sharp increases of deforestation were noted along unpaved roads, such as logging roads. Hence, the building of logging roads for mahogany extraction opens up the area to further deforestation, ultimately leading to complete deforestation and agricultural settlement.
Verissimo et al. (1995) described mahogany logging as the first step in a colonisation process involving slash and burn agriculture and ranching for 200 km surrounding the mahogany logging town of Tucumã, Pará. Colonists advanced in annual increments of 25-50 km along a logging road built by mahogany companies. Forty percent of the land in the colonists' small holdings was deforested within a 7 year period.
Further evidence of the chain of road building, deforestation and agricultural settlement is shown in Fig. 1. The overlay of the satellite image reveals roads, possibly for logging, built into primary forest. Along the road is a ribbon development pattern of a mosaic of agricultural fields. These agricultural fields are beginning to enclose smaller blocks of forests, producing a fragmented forest. Such satellite images can be gained from many areas of southern Amazonia lying in the mahogany belt.
The effects of mahogany logging on further deforestation and subsequent settlement by ranchers and farmers have lead to mahogany being described as a "catalytic" species in the deforestation of the Amazon (Fearnside, 1997; Verssimo et al. 2002a): "Mahogany loggers play a key role in building roads that give squatters and loggers taking less-valuable species access to new areas. The process that this initial step sets in motion eventually leads to destruction of the entire ecosystem." (Fearnside, 1997). This deforestation and subsequent agricultural settlement along logging roads ultimately leads to fragmentation of the Amazonian forest at a landscape scale (see Fig. 1) making the remaining fragments vulnerable to edge effects, fire and climatic change as described above.
Compounding the effects of mahogany logging, illegal logging is widespread in areas of Brazil in the mahogany belt such as Pará (Verissimo et al. 1995; Watson 1996; Greenpeace 2001). For example, Fearnside (1997) reports the building of several hundred kilometres of illegal roads inside a military reserve. This widespread illegal logging increases the number and length of roads built. Illegal logging has been documented in most of the Indian reserves in southern and eastern regions of Pará (Verissimo et al. 1995; 1998; Watson 1996; Greenpeace 2001) and has severe implications for Indian populations. For example, Watson (1996) described the agricultural settlement of 1,500 colonist families along an illegal road in an Indian reserve, threatening the surviving Arara people. This situation is likely to get worse as intensive and predatory logging practices have already depleted the mahogany stocks of the South of Pará and the largest remaining concentrations of mahogany are found on or around Indian lands in Pará State (Greenpeace 2001 & Verissimo et al. 1998).
Until recently, mahogany logging practices have been poorly managed, if at all. Verissimo et al. (1998): "the current model of largely illegal logging followed by unplanned settlement and widespread forest degradation will lead to biodiversity losses and unsustainable timber production across the Amazon Basin, with logging becoming another boom-and-bust economic activity in Brazil."
There is widespread fraudulent use of official documentation at the initial stages of the supply chain, which renders subsequent national and international measures to control the illegal trade in timber such as mahogany almost meaningless (Fearnside 1997; Greenpeace 2001). In 1999, following an evaluation of 65 registered mahogany Forestry Management Plans (FMPs) in Pará State, the Brazilian government suspended 39 FMPs and cancelled 13 FMPs. Reasons included lack of geographical co-ordinates for the FMP, inaccurate maps and overestimation of the volume of mahogany in the forest (Greenpeace 2001). A moratorium on mahogany exploitation is currently in place (Grogan et al. 2002) and has led to seizures of large quantities of mahogany timber both in Brazil and abroad (Greenpeace 2001). However, despite the efforts of Ibama (Brazilian Government Institute for Environment and Natural Resources), mahogany continues to be logged and exported (e.g. Greenpeace 2002b). The inclusion of mahogany in CITES Appendix II (from November 2003), is considered by many the best option to regulate the mahogany market (Snook 1996; Greenpeace 2002a; Grogan et al 2002; IMAZON 2002). Appendix II listing will provide a mechanism to combat illegal trade and would require sustainable management of this resource.
A coherent scheme for the sustainable development of the Amazon has been detailed in several scientific publications. A suite of measures, comprising regional planning with the establishment of regional forests (Flonas) parks and zoning of areas for timber extraction in Pará, with incentives for sustainably managed extraction has been proposed (Verissimo, et al. 1998, 2002a &b); Grogan et al. (2002) suggest a comprehensive inventory of mahogany forests with improvement of regulatory control relating to FMPs; Verissimo et al. (1995) and Grogan et al. (2002) listed specific options that could be taken to improve the sustainability of mahogany harvesting, including steps to aid regeneration of mahogany. As Verssimo et al. (1998) conclude "The present, unsustainable, uncontrolled spread of logging activities throughout Pará could be replaced by a sustainable model that would bring ecomonic returns while protecting biodiversity and Indian rights.".
Careful planning at the stand level can minimise the impacts of logging. For example, Baretto et al. (1998) found that 26 % of the volume of timber felled was wasted, 7 % lost to poor felling techniques and 19 % lost simply because felled trees by not found by tractor operators. In the planned area, only 1 % of the felled timber was wasted. Importantly, it was found that a 33 % reduction in road density could be achieved with planning (road density reduced from 0.92 m m-3 to 0.62 m m-3 harvested). Prospects for future timber extraction were improved. Thus, carefully managed logging operations can be more economic in addition to minimising impacts.
Both Greenpeace and IMAZON have proposed that management plans for mahogany should be certified according to the environmental and socio-economic standards set by the Forest Stewardship Council (Greenpeace 2001; Grogan et al. 2002), driven by international demand for FSC products. Such standards would include minimising road opening and reduced impact felling. However, efforts to achieve sustainable management of mahogany must include a network of regional forest parks, zoning for timber extraction and steps taken to combat illegal logging.
Logging, driven by the high value of mahogany, is the first step in a process of further deforestation followed by agricultural settlement, with the main agent being the opening of roads into primary forest. In addition, roads are opened by illegal logging. Agricultural settlement along roads ultimately leads to fragmentation of the remaining forest, which results in edge effects and increases the vulnerability of the Amazonian forest to fire and climatic change.
The adoption of rigorous controls on mahogany exploitation (i.e. CITES Appendix II) has potential to substantially reduce illegal logging. The establishment of a network of regional forest parks and zoning for extraction of mahogany must be part of any scheme to sustainably manage mahogany extraction.
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