Research Article

Persistent effects of pre-Columbian plant domestication on Amazonian forest composition

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Science  03 Mar 2017:
Vol. 355, Issue 6328, pp. 925-931
DOI: 10.1126/science.aal0157

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  • Levis et al.’s study on lasting effects of pre-Columbian tree domestication upon Amazonian forests does not adequately control for environmental gradients
    • Stephen J. Tulowiecki, Assistant Professor, SUNY Geneseo
    • Other Contributors:
      • Chris P.S. Larsen, Associate Professor, University at Buffalo

    In “Persistent effects of pre-Columbian plant domestication on Amazonian forest composition” (3 March 2017, p. 925), Levis et al. tested for relationships between current distributions of tree species in the Amazon basin and the distribution of pre-Columbian settlement sites, to assess how environmental and anthropogenic factors shape current distributions. Using multiple linear regression (MLR) they concluded that across the Amazon basin “the relative abundance and richness of domesticated species increase in forests on and around archaeological sites”, and that past human settlement is responsible for roughly half the variation explained in the abundance and richness of domesticated tree species. Distance from archaeological sites and rivers served as proxies for intensity of human land use.
    Levis et al.’s use of MLR is misspecified since it only accounts for linear relationships between explanatory variables and vegetation measures, and therefore inadequately controls for environmental gradients. Results showing that human land-use proxies were prominently and significantly related to domesticated tree species may have occurred because out of all explanatory variables tested, the relationship between human land-use proxies and vegetation is perhaps the only variable that is expectedly linear or at least monotonically decreasing (e.g. as distance from archaeological sites increases, the abundance of domesticate species decreases). Conversely, relationships with env...

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    Competing Interests: None declared.
  • Persistent effects of soils on Amazonian forest composition
    • Gabriela Zuquim, Post-doc Researcher, University of Turku, Finland
    • Other Contributors:
      • Gabriel Massaine Moulatlet, PhD candidate, University of Turku, Finland
      • Carlos Alberto Quesada, Assistant Researcher, National Institute of Amazonian Research, Manaus, Brazil (INPA)
      • Hanna Tuomisto, Lecturer, University of Turku, Finland

    We agree that Amazonia is not as pristine as often imagined, but Levis et al. seem to have taken their interpretations to the other extreme. They argue that the effect of pre-Columbian humans on some aspects of Amazonian tree communities equals the effect of the modern environment (fig. 5, p. 930).
    We argue that their analyses substantially underestimated the importance of soils. Amazonia is known to harbor remarkably diverse edaphic conditions (1), and numerous studies have shown that Amazonian forest composition and plant species distributions reflect soil properties at all spatial scales (2–4). The best predictor variables have generally been physiologically important plant nutrients, such as calcium, magnesium, potassium and phosphorus. However, none of these were included in the analyses of Levis et al., which only used pH and cation exchange capacity (CEC). These are poor surrogates, because soils of any given pH value or CEC can differ greatly in nutrient availability in Amazonia (5), so these variables were probably chosen because they are available as basin-wide digital raster layers rather than because of their ecological relevance. CEC reflects the amount of exchangeable surface charges, which is of interest in agriculture as it indicates the potential of the soil to respond to fertilizers. However, in natural conditions more than 90% of CEC is often occupied by aluminum (1) and, therefore, does not indicate actual nutrient availability. CEC can correlate...

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    Competing Interests: None declared.
  • Insufficient evidence of a “domesticated Amazonia”
    • Crystal McMichael, Assistant Professor, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam
    • Other Contributors:
      • Dolores Piperno, Scientist Emerita, Smithsonian Tropical Research Institute, Smithsonian National Museum of Natural History
      • Mark Bush, Professor, Department of Biological Sciences, Florida Institute of Technology

    Methodological biases predispose Levis et al. (1) to conclude that ancient domestication has shaped Amazonia. Their analysis fails to consider four centuries of European influence, native population recovery in the 1600s, and the Rubber Boom (ca. 1850 - 1920 AD) that followed the pre-Columbian era. Ancient occupation sites have higher likelihoods of subsequent settlement (2); people today still cultivate on Amazonian Dark Earths formed in ancient times (3). The analysis also ignores that Amazonian plant distributions are patchy (4), and the domesticates are native species that were naturally abundant in some areas without human intervention. Levis et al. consider all occurrences of trees identified as domesticates as human-induced. Also, many domesticated species in the study have evidence of cultivation only in the modern era or in geographic regions outside Amazonia, with little to no evidence for their pre-Columbian use in Amazonia.
    Their results, furthermore, did not support their conclusions. Environmental conditions and unknown factors explained a significantly higher proportion of the variance in the dataset compared with the ‘human’ metric (c. 20%)(1, Fig. 5). Domesticates significantly decreased at distances over 20 km from archaeological sites (1, Figs. S7-S8, S10). When forests sitting atop archaeological sites were excluded from the analyses, no relationship existed between humans and domesticates for the entirety of Amazonia, and it remained significant...

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    Competing Interests: None declared.
  • Do multiple origins of domestication matter for Amazon Forest?

    In their Research Article Levis et al (1) provide important new evidence to resolve the controversial debate as to the extent humans, specifically pre-Columbian Societies have influenced tropical forest across the Amazon Basin. Levis et al. demonstrate that domesticated forest tree species are five times more likely to be hyperdominant in forests on or around known archaeological sites. To substantiation their findings Levis et al highlight that “species domesticated in one particular environmental setting had wide geographical distributions and tended to be more abundant in locations not associated with their known or hypothetical origins of domestication”. While we agree that a disassociation of domesticated species hyperdominance with putative origins of domestication is one potentially important signal, it is important to highlight that for many hyperdominant species multiple origins of domestication may well be the case. This has been documented in economically and ecologically important forest tree species such as the Brazil nut and cacao, for which there are at least two independent origins of domestication (2, 3).

    Evidence suggests that two of the three traditional cacao cultivars in the Amazon (the Ecuadorian Nacional cacao and the Amelonado from eastern Brazil), are likely to have been domesticated from different source populations in Western and Central Amazonia, respectively (2, 4, 5). Levis et al (2017) only identify one origin of domestication i...

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    Competing Interests: None declared.