|Amazonia: Resiliency and Dynamism of the Land and Its People (UNU, 1995, 253 pages)|
|2. Environmental threats|
Contrary to the prevailing idea of a pristine Amazonian forest little disturbed by human activities until recently (Moran 1993a; Revkin 1990: 39; Richards 1977), much of the region has felt the influence of hunters and gatherers and farmers for a considerable time. Many of the forests of tropical America, including the Amazon, are anthropogenic (Denevan 1992; Turner and Butzer 1992). Assertions that the Amazon is being ravaged by development and floods of land-hungry colonists need to be put within the context of a region that has a long history of settlement and human modifications of the environment.
Archaeological research and unusual concentrations of certain economic plants in the forest suggest much higher human population densities in the past than has hitherto been accepted. Even with relatively inefficient stone axes, aborigines have cleared substantial tracts of Amazonian forests in the past (Huber 1910). Charcoal layers in soils of the upper Rio Negro have been dated to 6,000 years B.P. and some ceramic shards mixed with anthrosols are approximately 3,750 years old (Sponsel 1986). Along the Bragantina coast of Pará, charcoal and potsherds have been dated at 5,000 years B.P. (Simões 1981). The oldest recorded pottery in the New World is from the middle Amazon: ceramics from the Taperinha site near Santarém have been dated at 8,000 years B.P. (Roosevelt et al. 1991). Maize reached the Ecuadorian Amazon at least 6,000 years ago, providing farmers with another food option. Upland and flood-plain forests have thus been altered by farming activities for millennia (Bush, Piperno, and Colinvaux 1989).
Population densities reached high levels, particularly along siltladen rivers, well before contact with Europeans (Moran 1990: 148, 1993b: 114). Estimates of human populations in Amazonia around 1500 range from 1 million to 6 million, or even higher (Smith 1980). Only recently has the region's population regained its former numbers, but with a distinct difference: a sizeable proportion of today's population lives in towns and cities. In pre-contact times, the population was much more rural than at present, and therefore more engaged in farming.
The indigenous population did not raise cattle, however, so cleared areas were devoted to crops and managed fallows. The higher population density in rural areas was thus possible with perhaps the same amount of cleared area as today. The overall cleared area in 1500 was probably close to that prevailing in 1990.
If pre-contact aboriginal populations of Amazonia reached in excess of 6 million people, forest fires in the region were probably as common as at present, but on a smaller scale. Indians would not have cleared fields the size of some ranches and plantations being opened up in the region, particularly in southern Pará, northern Mato Grosso, Rondônia, and Acre, but they likely lit many more smaller fires to prepare fields.
Instead of massive fires concentrated in active colonization zones, particularly in the south-eastern and south-western fringes of Amazonia (fig. 2.1), hundreds of thousands of smaller fires would have been scattered over the basin in pre-contact times. Agricultural activities in Amazonia before the arrival of Europeans were akin to a buckshot event (Oldeman 1989); localized, small-scale clearings spread out over a large area. A Dante's inferno characterizes colonization zones today in the dry season, whereas the twinkling of innumerable small fires would have dotted the nocturnal landscape after the main rains in prehistoric Amazonia.
The shift to clearing larger sections of forest is ecologically more damaging than the scattered, insular fires of the past. When thousands of hectares are cleared for a single ranch or plantation, the ecological fabric of the area becomes simpler (Uhf, Buschbacher, and Serrão 1988). Instead of a patchwork quilt of various plant communities, more homogeneous landscapes emerge. Also, seed sources for forest regeneration became scarcer and soil nutrient recycling systems can be disrupted (Buschbacher, Uhl, and Serrão 1987; Nepstad, Uhl, and Serrão 1990,1991; Serrão et al. 1979).
The implications of a dense, pre-contact human population in Amazonia are far-reaching. A salient lesson here is that Amazonia's diverse environments can support relatively large populations, even on nutrient-poor oxisols and ultisols, if resources are managed wisely. Although some have argued that nutrient deficiencies prevent continuous crop production on highly weathered ferrallitic soils of many parts of the lowland, humid tropics (Weischet and Caviedes 1993: 278), pre-contact indigenous populations probably deployed a wide variety of swidden systems that permitted relatively dense populations, even in inland areas.
People in Amazonia have greatly altered plant and animal communities and the distribution and population densities of certain plants and animals, and have probably triggered increased soil erosion and aggrading of smaller rivers and streams for millennia. The notion of a vast, undisturbed wilderness in Amazonia is an artefact of the indigenous population crash after contact with Europeans and the unleashing of introduced diseases such as smallpox and influenza.