Spatio-temporal trends of mercury levels in alluvial gold mining spoils areas monitored between rainy and dry seasons in the Peruvian Amazon.

Artisanal and small-scale gold mining (ASGM) in the Amazon has degraded tropical forests and escalated mercury (Hg) pollution, affecting biodiversity, ecological processes and rural livelihoods. In the Peruvian Amazon, ASGM annually releases some 181 tons of Hg into the environment. Despite some recent advances in understanding the spatial distribution of Hg within gold mine spoils and the surrounding landscape, temporal dynamics in Hg movement are not well understood. We aimed to reveal spatio-temporal trends of soil Hg in areas degraded by ASGM.,. We analyzed soil and sediment samples during the dry and rainy seasons across 14 ha of potentially contaminated sites and natural forests, in the vicinities of the Native community of San Jacinto in Madre de Dios, Peru. Soil Hg levels of areas impacted by ASGM (0.02 ± 0.02 mg kg-1) were generally below soil environmental quality standards (6.60 mg kg-1). However, they showed high variability, mainly explained by the type of natural cover vegetation, soil organic matter (SOM), clay and sand particles. Temporal trends in Hg levels in soils between seasons differed between landscape units distinguished in the mine spoils. During the rainy season, Hg levels decreased up to 45.5% in uncovered soils, while in artificial pond sediments Hg increased by up to 961%. During the dry season, uncovered degraded soils were more prone to lose Hg than sites covered by vegetation, mainly due to higher soil temperatures and concomitantly increasing volatilization. Soils from natural forests and degraded soil covered by regenerating vegetation showed a high capacity to retain Hg mainly due to the higher plant biomass, higher SOM, and increasing concentrations of clay particles. Disturbingly, our findings suggest high Hg mobility from gold mine spoil to close by sedimentary materials, mainly in artificial ponds through alluvial deposition and pluvial lixiviation. Thus, further research is needed on monitoring, and remediation of sediments in artificial to design sustainable land use strategies.

The distribution of cadmium in soil and cacao beans in Peru.

Peru is the eighth largest producer of cacao beans globally, but high cadmium contents are constraining access to international markets which have set upper thresholds for permitted concentrations in chocolate and derivatives. Preliminary data have suggested that high cadmium concentrations in cacao beans are restricted to specific regions in the country, but to date no reliable maps exist of expected cadmium concentrations in soils and cacao beans. Drawing on >2000 representative samples of cacao beans and soils we developed multiple national and regional random forest models to develop predictive maps of cadmium in soil and cacao beans across the area suitable for cacao cultivation. Our model projections show that elevated concentrations of cadmium in cacao soils and beans are largely restricted to the northern parts of the country in the departments of Tumbes, Piura, Amazonas and Loreto, as well as some very localized pockets in the central departments of Huánuco and San Martin. Unsurprisingly, soil cadmium was the by far most important predictor of bean cadmium. Aside from the south-eastern to north-western spatial trend of increasing cadmium values in soils and beans, the most important predictors of both variables in nation-wide models were geology, rainfall seasonality, soil pH and rainfall. At regional level, alluvial deposits and mining operations were also associated with higher cadmium levels in cacao beans. Based on our predictive map of cadmium in cacao beans we estimate that while at a national level <20 % of cacao farming households might be impacted by the cadmium regulations, in the most affected department of Piura this could be as high as 89 %.

Habitat Quality Differentiation and Consequences for Ecosystem Service Provision of an Amazonian Hyperdominant Tree Species.

Ecosystem services of Amazonian forests are disproportionally produced by a limited set of hyperdominant tree species. Yet the spatial variation in the delivery of ecosystem services by individual hyperdominant species across their distribution ranges and corresponding environmental gradients is poorly understood. Here, we use the concept of habitat quality to unravel the effect of environmental gradients on seed production and aboveground biomass (AGB) of the Brazil nut, one of Amazonia's largest and most long-lived hyperdominants. We find that a range of climate and soil gradients create trade-offs between density and fitness of Brazil nut trees. Density responses to environmental gradients were in line with predictions under the Janzen-Connell and Herms-Mattson hypotheses, whereas tree fitness responses were in line with resource requirements of trees over their life cycle. These trade-offs resulted in divergent responses in area-based seed production and AGB. While seed production and AGB of individual trees (i.e., fitness) responded similarly to most environmental gradients, they showed opposite tendencies to tree density for almost half of the gradients. However, for gradients creating opposite fitness-density responses, area-based seed production was invariable, while trends in area-based AGB tended to mirror the response of tree density. We conclude that while the relation between environmental gradients and tree density is generally indicative of the response of AGB accumulation in a given area of forest, this is not necessarily the case for fruit production.

Mercury in soils impacted by alluvial gold mining in the Peruvian Amazon.

Gold mining is the largest source of mercury (Hg) pollution worldwide. The discharge of mercury in the environment bears direct human health risks and is likely to increase cascading effects throughout local food chains. In the Peruvian Amazon the mining process consists of slashing and burning trees, followed by extraction of gold-bearing sediment, amalgamation with Hg and gold recovery, leading each year to the degradation of 6,000-10,000 ha and the release of 180 metric tons of Hg per year to the enviroment. The purpose of this study was to determine soil Hg levels in soils of abandoned alluvial gold mine spoils and undisturbed forest in the Madre de Dios region, the epicenter of alluvial gold mining in Peru. We selected gold mine spoils of the two most important technologies locally applied for gold extraction, i.e., Minimally Mechanized Mining (MMM) and Highly Mechanized Mining (HMM), in the native communities of Laberinto and Kotzimba, respectively. We collected 127 and 35 soil samples (0-20cm depth) from potentially contaminated sites and undisturbed forest, respectively. Physicochemical analysis and determination of Hg levels were determined for all soil samples. None of the samples had Hg concentrations above Peruvian, Canadian and British Environmental Quality Standards for Agricultural Soil (6.6mg/kg). Hg levels in MMM and HMM were not significantly different between the two areas. The main variables explaining variation of soil Hg concentrations were the vegetation cover, soil organic matter, soil pH and clay particle content, which explained up to 80% of data set variation. Surprisingly, highest Hg concentrations were found in untouched old-growth forest bordering the mine spoils, but there was also a trend of increasing Hg concentrations with the regenerating vegetation. Our findings suggest that Hg concentrations in old mine spoils are low and shouldn't stand in the way of efforts to restore soil conditions and develop sustainable land uses. However, it is urgent to end the use of Hg in mining operation to decrease human and environmental risks.

Genetic diversity of the rain tree (Albizia saman) in Colombian seasonally dry tropical forest for informing conservation and restoration interventions.

Albizia saman is a multipurpose tree species of seasonally dry tropical forests (SDTFs) of Mesoamerica and northern South America typically cultivated in silvopastoral and other agroforestry systems around the world, a trend that is bound to increase in light of multimillion hectare commitments for forest and landscape restoration. The effective conservation and sustainable use of A. saman requires detailed knowledge of its genetic diversity across its native distribution range of which surprisingly little is known to date. We assessed the genetic diversity and structure of A.saman across twelve representative locations of SDTF in Colombia, and how they may have been shaped by past climatic changes and human influence. We found four different genetic groups which may be the result of differentiation due to isolation of populations in preglacial times. The current distribution and mixture of genetic groups across STDF fragments we observed might be the result of range expansion of SDTFs during the last glacial period followed by range contraction during the Holocene and human-influenced movement of germplasm associated with cattle ranching. Despite the fragmented state of the presumed natural A. saman stands we sampled, we did not find any signs of inbreeding, suggesting that gene flow is not jeopardized in humanized landscapes. However, further research is needed to assess potential deleterious effects of fragmentation on progeny. Climate change is not expected to seriously threaten the in situ persistence of A. saman populations and might present opportunities for future range expansion. However, the sourcing of germplasm for tree planting activities needs to be aligned with the genetic affinity of reference populations across the distribution of Colombian SDTFs. We identify priority source populations for in situ conservation based on their high genetic diversity, lack or limited signs of admixture, and/or genetic uniqueness.

Mapping tree species vulnerability to multiple threats as a guide to restoration and conservation of tropical dry forests.

Understanding the vulnerability of tree species to anthropogenic threats is important for the efficient planning of restoration and conservation efforts. We quantified and compared the effects of future climate change and four current threats (fire, habitat conversion, overgrazing and overexploitation) on the 50 most common tree species of the tropical dry forests of northwestern Peru and southern Ecuador. We used an ensemble modelling approach to predict species distribution ranges, employed freely accessible spatial datasets to map threat exposures, and developed a trait-based scoring approach to estimate species-specific sensitivities, using differentiated trait weights in accordance with their expected importance in determining species sensitivities to specific threats. Species-specific vulnerability maps were constructed from the product of the exposure maps and the sensitivity estimates. We found that all 50 species face considerable threats, with an average of 46% of species' distribution ranges displaying high or very high vulnerability to at least one of the five threats. Our results suggest that current levels of habitat conversion, overexploitation and overgrazing pose larger threats to most of the studied species than climate change. We present a spatially explicit planning strategy for species-specific restoration and conservation actions, proposing management interventions to focus on (a) in situ conservation of tree populations and seed collection for tree planting activities in areas with low vulnerability to climate change and current threats; (b) ex situ conservation or translocation of populations in areas with high climate change vulnerability; and (c) active planting or assisted regeneration in areas under high current threat vulnerability but low climate change vulnerability, provided that interventions are in place to lower threat pressure. We provide an online, user-friendly tool to visualize both the vulnerability maps and the maps indicating priority restoration and conservation actions.

Soil carbon is a useful surrogate for conservation planning in developing nations.

Defining the optimal placement of areas for biodiversity conservation in developing nations remains a significant challenge. Our best methods for spatially targeting potential locations for biodiversity conservation rely heavily on extensive georeferenced species observation data which is often incomplete or lacking in developing nations. One possible solution is the use of surrogates that enable site assessments of potential biodiversity values which use either indicator taxa or abiotic variables, or both. Among the plethora of abiotic variables, soil carbon has previously been identified as a potentially powerful predictor for threatened biodiversity, but this has not yet been confirmed with direct observational data. Here we assess the potential value of soil carbon for spatial prediction of threatened species using direct measurements as well as a wide range of GIS derived abiotic values as surrogates for threatened plant species in the PEBANPA network of permanent plots in Southern Patagonia. We find that soil carbon significantly improves the performance of a biodiversity surrogate elaborated using abiotic variables to predict the presence of threatened species. Soil carbon could thus help to prioritize sites in conservation planning. Further, the results suggest that soil carbon on its own can be a much better surrogate than other abiotic variables when prioritization of sites for conservation are calibrated on increasingly small sets of observation plots. We call for the inclusion of soil carbon data in the elaboration of surrogates used to optimize conservation investments in the developing world.

Fine-scale processes shape ecosystem service provision by an Amazonian hyperdominant tree species.

Conspecific distance and density-dependence is a key driver of tree diversity in natural forests, but the extent to which this process may influence ecosystem service provision is largely unknown. Drawing on a dataset of >135,000 trees from the Peruvian Amazon, we assessed its manifestation in biomass accumulation and seed production of Brazil nut (Bertholletia excelsa) which plays a keystone role in carbon sequestration and NTFP harvesting in Amazonia. For the first time, we find both negative and positive effects of conspecific proximity on seed production and above ground biomass at small and large nearest neighbour distances, respectively. Plausible explanations for negative effects at small distances are fine-scale genetic structuring and competition for shared resources, whereas positive effects at large distances are likely due to increasing pollen limitation and suboptimal growth conditions. Finally, findings suggest that most field plots in Amazonia used for estimating carbon storage are too small to account for distance and density-dependent effects and hence may be inadequate for measuring species-centric ecosystem services.

NTFP harvesters as citizen scientists: Validating traditional and crowdsourced knowledge on seed production of Brazil nut trees in the Peruvian Amazon.

Understanding the factors that underlie the production of non-timber forest products (NTFPs), as well as regularly monitoring production levels, are key to allow sustainability assessments of NTFP extractive economies. Brazil nut (Bertholletia excelsa, Lecythidaceae) seed harvesting from natural forests is one of the cornerstone NTFP economies in Amazonia. In the Peruvian Amazon it is organized in a concession system. Drawing on seed production estimates of >135,000 individual Brazil nut trees from >400 concessions and ethno-ecological interviews with >80 concession holders, here we aimed to (i) assess the accuracy of seed production estimates by Brazil nut seed harvesters, and (ii) validate their traditional ecological knowledge (TEK) about the variables that influence Brazil nut production. We compared productivity estimates with actual field measurements carried out in the study area and found a positive correlation between them. Furthermore, we compared the relationships between seed production and a number of phenotypic, phytosanitary and environmental variables described in literature with those obtained for the seed production estimates and found high consistency between them, justifying the use of the dataset for validating TEK and innovative hypothesis testing. As expected, nearly all TEK on Brazil nut productivity was corroborated by our data. This is reassuring as Brazil nut concession holders, and NTFP harvesters at large, rely on their knowledge to guide the management of the trees upon which their extractive economies are based. Our findings suggest that productivity estimates of Brazil nut trees and possibly other NTFP-producing species could replace or complement actual measurements, which are very expensive and labour intensive, at least in areas where harvesters have a tradition of collecting NTFPs from the same trees over multiple years or decades. Productivity estimates might even be sourced from harvesters through registers on an annual basis, thus allowing a more cost-efficient and robust monitoring of productivity levels.

Distribution, genetic diversity and potential spatiotemporal scale of alien gene flow in crop wild relatives of rice (Oryza spp.) in Colombia.

BACKGROUND: Crop wild relatives (CWRs) of rice hold important traits that can contribute to enhancing the ability of cultivated rice (Oryza sativa and O. glaberrima) to produce higher yields, cope with the effects of climate change, and resist attacks of pests and diseases, among others. However, the genetic resources of these species remain dramatically understudied, putting at risk their future availability from in situ and ex situ sources. Here we assess the distribution of genetic diversity of the four rice CWRs known to occur in Colombia (O. glumaepatula, O. alta, O. grandiglumis, and O. latifolia). Furthermore, we estimated the degree of overlap between areas with suitable habitat for cultivated and wild rice, both under current and predicted future climate conditions to assess the potential spatiotemporal scale of potential gene flow from GM rice to its CWRs. RESULTS: Our findings suggest that part of the observed genetic diversity and structure, at least of the most exhaustively sampled species, may be explained by their glacial and post-glacial range dynamics. Furthermore, in assessing the expected impact of climate change and the potential spatiotemporal scale of gene flow between populations of CWRs and GM rice we find significant overlap between present and future suitable areas for cultivated rice and its four CWRs. Climate change is expected to have relatively limited negative effects on the rice CWRs, with three species showing opportunities to expand their distribution ranges in the future. CONCLUSIONS: Given (i) the sparse presence of CWR populations in protected areas (ii) the strong suitability overlap between cultivated rice and its four CWRs; and (iii) the complexity of managing and regulating areas to prevent alien gene flow, the first priority should be to establish representative ex situ collections for all CWR species, which currently do not exist. In the absence of studies under field conditions on the scale and extent of gene flow between cultivated rice and its Colombian CWRs, effective in situ conservation might best be achieved through tailor-made management plans and exclusion of GM rice cultivation in areas holding the most genetically diverse CWR populations. This may be combined with assisted migration of populations to suitable areas where rice is unlikely to be cultivated under current and future climate conditions.

Conflict in Protected Areas: Who Says Co-Management Does Not Work?

Natural resource-related conflicts can be extremely destructive and undermine environmental protection. Since the 1990 s co-management schemes, whereby the management of resources is shared by public and/or private sector stakeholders, have been a main strategy for reducing these conflicts worldwide. Despite initial high hopes, in recent years co-management has been perceived as falling short of expectations. However, systematic assessments of its role in conflict prevention or mitigation are non-existent. Interviews with 584 residents from ten protected areas in Colombia revealed that co-management can be successful in reducing conflict at grassroots level, as long as some critical enabling conditions, such as effective participation in the co-management process, are fulfilled not only on paper but also by praxis. We hope these findings will re-incentivize global efforts to make co-management work in protected areas and other common pool resource contexts, such as fisheries, agriculture, forestry and water management.

An Integrated Hypothesis on the Domestication of Bactris gasipaes.

Peach palm (Bactris gasipaes Kunth) has had a central place in the livelihoods of people in the Americas since pre-Columbian times, notably for its edible fruits and multi-purpose wood. The botanical taxon includes both domesticated and wild varieties. Domesticated var gasipaes is believed to derive from one or more of the three wild types of var. chichagui identified today, although the exact dynamics and location of the domestication are still uncertain. Drawing on a combination of molecular and phenotypic diversity data, modeling of past climate suitability and existing literature, we present an integrated hypothesis about peach palm's domestication. We support a single initial domestication event in south western Amazonia, giving rise to var. chichagui type 3, the putative incipient domesticate. We argue that subsequent dispersal by humans across western Amazonia, and possibly into Central America allowed for secondary domestication events through hybridization with resident wild populations, and differential human selection pressures, resulting in the diversity of present-day landraces. The high phenotypic diversity in the Ecuadorian and northern Peruvian Amazon suggest that human selection of different traits was particularly intense there. While acknowledging the need for further data collection, we believe that our results contribute new insights and tools to understand domestication and dispersal patterns of this important native staple, as well as to plan for its conservation.

Present spatial diversity patterns of Theobroma cacao L. in the neotropics reflect genetic differentiation in pleistocene refugia followed by human-influenced dispersal.

Cacao (Theobroma cacao L.) is indigenous to the Amazon basin, but is generally believed to have been domesticated in Mesoamerica for the production of chocolate beverage. However, cacao's distribution of genetic diversity in South America is also likely to reflect pre-Columbian human influences that were superimposed on natural processes of genetic differentiation. Here we present the results of a spatial analysis of the intra-specific diversity of cacao in Latin America, drawing on a dataset of 939 cacao trees genotypically characterized by means of 96 SSR markers. To assess continental diversity patterns we performed grid-based calculations of allelic richness, Shannon diversity and Nei gene diversity, and distinguished different spatially coherent genetic groups by means of cluster analysis. The highest levels of genetic diversity were observed in the Upper Amazon areas from southern Peru to the Ecuadorian Amazon and the border areas between Colombia, Peru and Brazil. On the assumption that the last glaciation (22,000-13,000 BP) had the greatest pre-human impact on the current distribution and diversity of cacao, we modeled the species' Pleistocene niche suitability and overlaid this with present-day diversity maps. The results suggest that cacao was already widely distributed in the Western Amazon before the onset of glaciation. During glaciations, cacao populations were likely to have been restricted to several refugia where they probably underwent genetic differentiation, resulting in a number of genetic clusters which are representative for, or closest related to, the original wild cacao populations. The analyses also suggested that genetic differentiation and geographical distribution of a number of other clusters seem to have been significantly affected by processes of human management and accompanying genetic bottlenecks. We discuss the implications of these results for future germplasm collection and in situ, on farm and ex situ conservation of cacao.

Ethnomedicinal practices and medicinal plant knowledge of the Yuracarés and Trinitarios from Indigenous Territory and National Park Isiboro-Sécure, Bolivian Amazon.

AIM OF THE STUDY: We investigated the ethnomedical practices and knowledge of medicinal plant and fungus species of contemporary Yuracaré and Trinitario ethnic groups from Indigenous Territory and National Park Isiboro-Sécure (TIPNIS), located in the Bolivian Amazon region. Our aim was to identify the culturally most significant medicinal plant families, growth forms and species, as well as to assess the current state of knowledge regarding the bioactivity of the most important species, based on available literature data. MATERIALS AND METHODS: Medicinal plant and fungus species were inventoried during homegarden and swidden sampling, walk-in-the-woods and transect sampling. Data on medicinal uses were obtained from 12 Yuracaré and 14 Trinitario participants. RESULTS: We commence by providing a brief overview of Yuracaré and Trinitario ethnomedical systems, highlighting the important shamanistic component of particularly Trinitario traditional medicine. The rest of the paper is dedicated to an analysis and discussion based on the 349 inventoried medicinal plant and fungus species. Contingency table and binomial analyses of medicinal plants used versus the total number of inventoried species per family showed that several plant families are significantly over (Piperaceae, Araceae, Solanaceae, Asteraceae and Siparunaceae) and underused (Chrysobalanaceae, Sapotaceae, Lauraceae, Celastraceae and Annonaceae) in traditional medicine in TIPNIS. Also herbaceous plants are significantly overrepresented in the medicinal plant inventory, which is in line with relevant literature. Our ranking of medicinal species according to cultural significance is based on the Quality Use Agreement Value (QUAV) index we developed and presented in a previous paper. Results indicate that the QUAV index's property to mainly select species that combine multiple ethnomedical uses with high informant consensus, justifies its use as a measure of cultural significance of medicinal plants in TIPNIS. Results of a literature search suggest, on the other hand, that the QUAV(s) score of a species could also be indicative of its bioactivity. CONCLUSIONS: In addition to the QUAV index's value as a tool for assessing the cultural significance of medicinal species, it might also be useful to identify species with a higher likeliness of being bioactive.

Human impact on wild firewood species in the rural Andes community of Apillapampa, Bolivia.

Firewood is the basic fuel source in rural Bolivia. A study was conducted in an Andean village of subsistence farmers to investigate human impact on wild firewood species. A total of 114 different fuel species was inventoried during fieldtrips and transect sampling. Specific data on abundance and growth height of wild firewood species were collected in thirty-six transects of 50 ×2 m(2). Information on fuel uses of plants was obtained from 13 local Quechua key participants. To appraise the impact of fuel harvest, the extraction impact value (EIV) index was developed. This index takes into account local participants' appreciation of (1) decreasing plant abundance; (2) regeneration capacity of plants; (3) impact of root harvesting; and (4) quality of firewood. Results suggest that several (sub-)woody plant species are negatively affected by firewood harvesting. We found that anthropogenic pressure, expressed as EIV, covaried with density of firewood species, which could entail higher human pressure on more abundant and/or more accessible species. The apparent negative impact of anthropogenic pressure on populations of wild fuel species is corroborated by our finding that, in addition to altitude, several anthropogenic variables (i.e. site accessibility, cultivation of exotics and burning practices) explain part of the variation in height of firewood species in the surroundings of Apillapampa.

Susto etiology and treatment according to Bolivian Trinitario people: a "masters of the animal species" phenomenon.

This article addresses two concepts that are quite widespread among Latin American cultures: susto or "'fright sickness," and the "masters of the animal species" philosophy, whereby individual animal spirits are believed to be "owned" by species-specific spiritual masters. This is the first article to integrate both these aspects, drawing from ethnographic data from the Trinitario people in Bolivia collected through participant-observation and semistructured ethnobotanical interviews on medicinal plants. Although Trinitarios have a long history of agriculture, their worldview is still partly one of animistic hunter and fisherman societies. This worldview is reflected in Trinitario susto etiology and treatment. Susto is locally believed to originate through soul theft by a variety of masters of the animal species and landscape spirits. Treatment is partly based on the principle of similia similibus curantur or "like cures like" and magicoritual ceremonies, but ethnopharmacological preparations are also well known and frequently used.

Cultural significance of medicinal plant families and species among Quechua farmers in Apillapampa, Bolivia.

ETHNOPHARMACOLOGICAL RELEVANCE: Medicinal plant use was investigated in Apillapampa, a community of subsistence farmers located in the semi-arid Bolivian Andes. AIM OF THE STUDY: The main objectives were to identify the culturally most significant medicinal plant families and species in Apillapampa. MATERIALS AND METHODS: A total of 341 medicinal plant species was inventoried during guided fieldtrips and transect sampling. Data on medicinal uses were obtained from fifteen local Quechua participants, eight of them being traditional healers. RESULTS: Contingency table and binomial analyses of medicinal plants used versus the total number of inventoried species per family showed that Solanaceae is significantly overused in traditional medicine, whereas Poaceae is underused. Also plants with a shrubby habitat are significantly overrepresented in the medicinal plant inventory, which most likely relates to their year-round availability to people as compared to most annual plants that disappear in the dry season. Our ranking of medicinal species according to cultural importance is based upon the Quality Use Agreement Value (QUAV) index we developed. This index takes into account (1) the average number of medicinal uses reported for each plant species by participants; (2) the perceived quality of those medicinal uses; and (3) participant consensus. CONCLUSIONS: According to the results, the QUAV index provides an easily derived and valid appraisal of a medicinal plant's cultural significance.

Comparison of health conditions treated with traditional and biomedical health care in a Quechua community in rural Bolivia.

BACKGROUND: The objective of the present study was to reveal patterns in the treatment of health conditions in a Quechua-speaking community in the Bolivian Andes based on plant use data from traditional healers and patient data from a primary health care (PHC) service, and to demonstrate similarities and differences between the type of illnesses treated with traditional and biomedical health care, respectively. METHODS: A secondary analysis of plant use data from semi-structured interviews with eight healers was conducted and diagnostic data was collected from 324 patients in the community PHC service. Health conditions were ranked according to: (A) the percentage of patients in the PHC service diagnosed with these conditions; and (B) the citation frequency of plant use reports to treat these conditions by healers. Healers were also queried about the payment modalities they offer to their patients. RESULTS: Plant use reports from healers yielded 1166 responses about 181 medicinal plant species, which are used to treat 67 different health conditions, ranging from general symptoms (e.g. fever and body pain), to more specific ailments, such as arthritis, biliary colic and pneumonia. The results show that treatment offered by traditional medicine overlaps with biomedical health care in the case of respiratory infections, wounds and bruises, fever and biliary colic/cholecystitis. Furthermore, traditional health care appears to be complementary to biomedical health care for chronic illnesses, especially arthritis, and for folk illnesses that are particularly relevant within the local cultural context. Payment from patients to healers included flexible, outcome contingent and non-monetary options. CONCLUSION: Traditional medicine in the study area is adaptive because it corresponds well with local patterns of morbidity, health care needs in relation to chronic illnesses, cultural perceptions of health conditions and socio-economic aspects of health care. The quantitative analysis of plant use reports and patient data represents a novel approach to compare the contribution of traditional and biomedical health care to treatment of particular health conditions.