Effects of socioeconomic and human-modified landscape variables on medicinal species richness at a macroscale: the case of the Caatinga, Brazil

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BackgroundEthnobiological studies at local scales have shown that knowledge of medicinal species tends to decrease as socioeconomic status and the extent of human-modified landscapes increase. However, it remains largely unknown whether these same factors can predict knowledge of useful species at broader scales and whether their interaction might create scenarios that enhance knowledge of medicinal species.MethodsTo address this, we tested whether knowledge of woody medicinal species—measured as the number of species known—is influenced by socioeconomic status, human-modified landscapes, and their interaction. We compiled and curated data on woody medicinal species from a systematic review encompassing diverse communities across the Caatinga region in North-east Brazil. Using the locations of these communities, we extracted data on socioeconomic status (measured by the Human Development Index, HDI) and human-modified landscapes (quantified as the percentage of forest loss).ResultsOur results indicate that forest loss reduces the knowledge of medicinal woody species among Indigenous People and Local Communities. The interaction between human-modified landscapes and socioeconomic status revealed a significant nonlinear relationship, with different combinations yielding varying levels of knowledge about woody medicinal species. Interestingly, socioeconomic status alone does not appear to influence this knowledge. These findings underscore that the processes shaping knowledge of medicinal species differ across scales and suggest the existence of yet unidentified emergent properties that influence medicinal species knowledge at broader scales.ConclusionThe conversion of habitats for anthropogenic use poses a significant risk to the well-being of these populations, as it reduces the availability of species used for prophylactic purposes. In contrast, the cultural traditions of Indigenous People and Local Communities, along with the implementation of regional public policies, may explain why socioeconomic status does not affect local knowledge. Moreover, our study highlights that the processes influencing knowledge of medicinal species at broader scales are not simply the aggregation of local-scale observations. Finally, we propose strategies to advance the field of macroethnobiology.