People, Soil and Manioc Interactions in the Upper Amazon Region
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People, soil and manioc interactions in the upper Amazon region Clara Patricia Peña Venegas Thesis committee Promotor Prof. Dr P.C. Struik Professor of Crop Physiology Wageningen University Co-promotors Dr T.J. Stomph Assistant professor, Centre for Crop Systems Analysis Wageningen University Dr G.M. Verschoor Assistant professor, Sociology of Development and Change Group Wageningen University Other members Prof. Dr F.J.J.M. Bongers, Wageningen University Dr C.R. Clement, National Institute for Amazonian Research, Manaus, Brazil Dr C.J.M. Almekinders, Wageningen University Prof. Dr R.G.F. Visser, Wageningen University This research was conducted under the auspices of the C. T. de Wit Graduate School for Production Ecology and Resource Conservation People, soil and manioc interactions in the upper Amazon region Clara Patricia Peña Venegas Thesis submitted in fulfillment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. Dr A.P.J. Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Wednesday 1 July 2015 at 1:30 p.m. in the Aula. Clara Patricia Peña Venegas People, soil and manioc interactions in the upper Amazon region 210 pages. PhD thesis, Wageningen University, Wageningen, NL (2015) With references, with summaries in English and Dutch ISBN: 978-94-6257-322-2 Abstract Clara Patricia Peña Venegas (2015). People, soil and manioc interactions in the upper Amazon region. PhD thesis, Wageningen University, The Netherlands, with summaries in English and Dutch, 210 pp. The presence of anthropogenic soils, or Amazonian Dark Earths (ADE), fuels the debate about how pristine the Amazon ecosystem actually is, and about the degree to which humans affected Amazonian diversity in the past. Most upland soils of the Amazon region are very acid, highly weathered, and have a limited nutrient holding capacity; together, these characteristics limit permanent or intensive agriculture. Várzeas or floodplains that are periodically enriched with Andean sediments carried and deposited by rivers that cross the Amazon Basin, are moderately fertile but experience periodic floods that limit agriculture to crops able to produce in a short time. ADE patches in uplands usually are more fertile than non-anthropogenic uplands, providing a better environment for agriculture. Most studies about how people manage a broad portfolio of natural and anthropogenic soils come from non-indigenous farmers of Brazil. There is limited information about how indigenous people use a broad soil portfolio, and how this affects the diversity of their staple crop, manioc. With the aim to contribute to the understanding of the role of ADE in indigenous food production, as compared with other soils, and in order to provide information about how indigenous people use and create diversity in Amazonia, research was carried out among five different ethnic groups living in two locations of the Colombian Amazon. Several social and natural science methods were used during the study. These included ethnography, participant observation, structured and un-structured interviews, sampling of soil and manioc landraces, standardized protocols for the quantification of soil physical and chemical variables, and molecular techniques to assess genetic diversity of manioc and arbuscular mycorrhizal fungi. Results indicate that ADE patches from the Middle Caquetá region of Colombia are not contrastingly more fertile than surrounding, non-anthropogenic upland soils, except for higher levels of available phosphorus in ADE. Indigenous farmers from the Middle Caquetá region do not use ADE more frequently or more intensively than non-ADE uplands. The swidden agriculture practiced on ADE and on non-ADE uplands is similar. Although ADE patches were not specifically important for swiddens and therefore relatively unimportant for the Abstract production of manioc. They were important as sites for indigenous settlements and for maintaining agroforestry systems with native and exotic species that do not grow in soils with low available phosphorus. Várzeas were also used for agriculture, whether farmers had access to ADE or not. Differences occurred between locations in the type of floodplains selected and the way they were cultivated. Those differences were not related to differences in soil conditions but were associated with the cultural traditions of the different ethnic groups who cultivate low floodplains, as well as labor availability when organizing collective work (mingas) to harvest floodplains. Manioc diversity among indigenous communities was not predominantly related with differences in soil types. Complete manioc stocks were cultivated equally on ADE, non-ADE uplands or várzeas. One issue that could be related with this non-specificity in manioc-soil combinations was the similar arbuscular mycorrhizal fungi diversity of soils and the high number of arbuscular mycorrhizal symbionts associated to manioc roots; these were shown to be independent from the physicochemical composition of the soil or the manioc landrace. Differences in the diversity of manioc stocks among ethnic groups were predominantly related to cultural values attached to different manioc landraces. This study of indigenous agriculture in environments with natural and anthropogenic soils indicates that people have had an important role in transforming the Amazonian ecosystem through agriculture, with consequences on forest composition and forest dynamics. Pre-Columbian people contributed to this by creating an additional soil- the Amazonian Dark Earths. Although ADE are not presently considered to play a major role in indigenous food production, indigenous people believe that ADE have had an important role in the management of the first maniocs cultivated by their ancestors. The domestication of manioc and the creation and maintenance of hundreds of different landraces by indigenous people contributed, and still contributes, to the region’s plant diversity. Table of contents Chapter 1 General introduction 1 Chapter 2 Challenging current ADE knowledge: Indigenous agriculture 21 in different soils of the Colombian Amazon Chapter 3 Classification and use of natural and anthropogenic soils by 45 indigenous communities of the Upper Amazon region of Colombia Chapter 4 Differences in manioc diversity among five ethnic groups of 75 the Colombian Amazon Chapter 5 Arbuscular mycorrhization of manioc in natural and 121 anthropogenic soils of the Colombian Amazon region Chapter 6 General discussion 153 References 171 Summary 193 Samenvatting 197 Acknowledgements 201 List of Publications 205 PE&RC Training and Education Statement 207 Curriculum vitae 209 Funding 210 Chapter 1 General Introduction Chapter 1 The Amazon forest is the biggest patch of continuous tropical forest and also one of the most bio-diverse regions of the world (Peres et al., 2010). The high diversity of the Amazon region is the product of natural events that occurred during the history of Planet Earth such as forest fragmentation during the Pleistocene, marine incursions during the Mid-Miocene and encrustation of Amazonian rivers acting as natural barriers to gene flow (Solomon et al., 2008); human interventions, however, also shaped Amazonian diversity. The Amazon forest has been inhabited for thousands of years by native societies which have been interacting with the environment, changing the floristic composition of the vegetation through agriculture and creating new environments by modifying soils (Balée, 2014). There is a debate among scientists, however, about how much people contributed to shaping diversity in the Amazon region. On the one hand, some scientists affirm that human interventions were heterogeneous and mainly limited to areas near floodplains along the main rivers (Meggers, 2003; McMichael et al., 2012). Therefore, people had little effect on the diversity of interfluvial areas, the diversity there being the product of long-term evolutionary and ecological processes. On the other hand, other scientists affirm that the Amazon landscape was highly impacted by humans. Therefore, many areas of the Amazon region can be considered constructed or ‘domesticated’ landscapes, constituting ‘hotspots’ of bio-historical diversity in the Amazon region (Denevan, 1992; Balée, 1993; Heckenberger et al., 2007). A better understanding of how people use and create diversity would provide important hints to dimension the effect of people in the Amazonian diversity. 1.1. Amazonian landscapes for food production The Amazon Basin is composed of different environments with a range of conditions and soils (Quesada et al., 2010). Most uplands of the Amazon Basin are dominated by very acid, highly weathered soils, originating from parental materials rich in kaolinite with a naturally limited nutrient holding capacity (Sombroek, 1966; Cochrane and Sanchez, 1982; Ma and Eggleton, 1999; FAO, 2006). Under these conditions indigenous people usually cultivate through swidden agriculture. Swidden agriculture, also known as slash-and-burn or shifting cultivation, consists of a system in which forested areas are “slashed and burnt” to establish polycultures for a short period of time. Cultivation is subsequently followed by a long fallow period. During the fallow, the agricultural field returns into a (secondary) forested area while a new forested area is opened for a new swidden (Hammond et al., 1995; Perreault, 2005; 2 General introduction Bonilla-Bedoya et al., 2013).