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Evaluation of tree diversity and utilization: the role of acculturation

Evaluation of tree diversity and utilization: the role of acculturation
Maximilien Guèze

2011

Institute of Environmental Science and Technology, Autonomous University of Barcelona, 08193 Bellaterra, Barcelona, SPAIN.

ABSTRACT

To date, the association between biological and cultural diversity has mostly been analyzed at regional or global scales. However, studying the link at the local scale is crucial to get a thorough understanding of the processes that determine this association. This PhD thesis aims at filling a gap between ecological and cultural studies at such a scale in the territory of a native group of the Bolivian Amazon, the Tsimane’, whose culture is relatively well documented but whose territory lacks of reliable ecological data. The four chapters of this thesis answer to the following research questions: 1) what are the differences in plant diversity in the forest surrounding indigenous villages and what are the factors determining such differences? 2) How can we relate differences in plant diversity to indigenous intracultural variation?

Fifty-five 0.1-ha plots were inventoried for trees ≥2.5 cm diameter at breast height in seven Tsimane’ villages, and soil variables were analyzed in each plot. First, I quantified oligarchic patterns across villages using diversity and composition indicators, i.e., species and family importance value index (IVI and FIVI). I found a floristic gradient with north-south orientation, likely due to biogeography and to the flooding history in the area. Second, I used Mantel analyses to quantify correlations between tree diversity, proxied by species turnover broken down into different tree categories, and edaphic and geographic factors. Tree species turnover was strongly associated with geographic distances and soil variables, mainly exchangeable cations, pH, C/N and texture; canopy trees were more strongly associated to environmental variables than understory trees, but phosphorus explained only understory tree distributions.

In six of the inventoried villages I measured individual acculturation of household heads as a proxy for intracultural variation. I used multivariate analyses to relate acculturation values to alpha diversity and forest structure in the inventoried plots. I found a significant inverse U-shaped relation between acculturation and diversity, but no significant relation with structure. I discuss how acculturation can act as a cultural disturbance through the modification of traditional ecological knowledge, having only subtle effects in old-growth forests. Lastly, to collect data on uses of 58 tree species expert informants were interviewed in 22 villages with overlapping territory with the villages inventoried for ecological data. I used multivariate analyses to highlight association patterns between the ecological importance of the species in the inventoried plots (IVI) and their overall and categorical usefulness. There was a significant positive relation between overall usefulness and IVI, but a negative association for medicinal uses and edible species. I explain these differences by discussing the likelihood that the Tsimane' substitute species according to their properties.

The results of this dissertation illustrate the importance of the association between intracultural variation and biological diversity in indigenous territories. Natural factors primarily explain tree diversity and composition patterns, but indigenous traditional ecological knowledge and management also seem important determinants of these distributions. Policy implications of this study include the need to consider indigenous people as drivers of part of the biodiversity, which has to be taken into account for future territorial planning and biocultural conservation.