Yanomami Mobility and Its Effects on the Forest Landscape

Abstract

The Yanomami are a hunter-gatherer and gardener people with high mobility, which influences the regeneration of forest in agricultural clearings. Increasing contact with the wider Brazilian and Venezuelan societies may lead to sedentarization. Population groups and clearings were mapped in the Yanomami Land in Brazil using four mosaics of Landsat images from within a two-year period. The mosaics were separated by intervals of 7 years. Few groups were sedentary, and most of these maintained alternative residences. The Yanomami cleared 16,856 ha (0.17% of the Yanomami territory in Brazil) over the 21 years covered by this study. Individuals in mobile groups deforested more than those in sedentary groups, but secondary-forest regeneration occurs mainly in clearings made by mobile groups. Permanent settlements had impeded regeneration of 48% (2,025 ha) of the area cleared prior to 1988. Access to health care has led to population growth but has not increased sedentarization.

Appendix

Each of the four Landsat mosaics corresponds to at least twelve scenes (Table A-1), for a total of 67 scenes. A tolerance of 2 years per mosaic was adopted due to the difficulty of finding satisfactory coverage without cloud cover. Clearings are areas of forest felled for cultivation that are detectable on Landsat images. Yanomami clearings rarely exceed 3 ha (equivalent to approximately 33 pixels); these are difficult to detect and the difficulty can increase with partial cloud cover or with atmospheric interference. The age of regeneration detectable on Landsat images can vary from a minimum of 7 years (in cases of ephemeral openings in continuous forest, with the regeneration reaching a height up to 8 m in the TIY) up to an undefined limit that depends on the degree of disturbance and the dimensions of the clearing. Scenes from intermediate years were used to resolve doubts, allowing a refinement of temporal dynamics of opening swiddens, insuring greater certainty in the interpretation with greater convergence of evidence (Jensen 2009).

Table A-1 Landsat 5 and 7 satellite images: Path, row and dates of passage from each of the four Landsat mosaics used to interpret Yanomami clearings

Treatment of Images

The images were georeferenced using a Geocover2000 mosaic, scene N 20 00, converted to decimal degrees. Since the region is located near the Equator (0 to 4° N), the distortion caused by the map projection should be minimal because it is distributed uniformly throughout the study area.

Channels 3, 4 and 5 were treated individually to maximize the gain in contrast. The progressive decline in the sensitivity of the sensors since the satellite was launched in 1984 was considered (Chander and Markham 2003), producing differences between the images of the two initial mosaics as compared to the images of the two most recent mosaics.

The Geocover image that provided the basis for georeferencing was geometrically corrected to Universal Transverse Mercator (UTM) units, which allows good accuracy in the calculation of area. The conversion factor was:

$$ {\text{Area}}\left( {{{\text{m}}^2}} \right) = {\text{polygon}}\;{\text{area}}\;\left( {{\text{in}}\;{\text{square}}\;{\text{decimal}}\;{\text{degrees}}} \right) \times 12,484,703,500. $$

The conversion factor was calibrated using measures of the circumference of the Earth at the equator (NASA, IBGE, UFRJ) for calculating the distance corresponding to one degree of longitude. The distance corresponding to one degree of latitude was calculated using the same sources. Values were calibrated empirically with existing databases for the region using the numbers closest to the official calculations (area of the state of Roraima from IBGE, areas of indigenous lands from Funai/ISA, and areas of conservation units from MMA/ICMBio).

Categories of Alteration

Two categories of legend were established, to distinguish types of alteration:

• A) “Altered/in regeneration”—areas that are vegetated but where the spectral response indicates vegetation of lower stature than the forest (highest reflectance value in channel 4);

• B_) “open”—open areas, indicating a clearing opened near the date of passage, burning of the vegetation producing the spectral behavior of exposed soil (highest reflectance value in channel 5).