Jennifer Watling

Fire-free land use in pre-1492 Amazonian savannas

The nature and scale of pre-Columbian land use and the consequences of the 1492 “Columbian Encounter” (CE) on Amazonia are among the more debated topics in New World archaeology and paleoecology. However, pre-Columbian human impact in Amazonian savannas remains poorly understood. Most paleoecological studies have been conducted in neotropical forest contexts. Of studies done in Amazonian savannas, none has the temporal resolution needed to detect changes induced by either climate or humans before and after A.D. 1492, and only a few closely integrate paleoecological and archaeological data. We report a high-resolution 2,150-y paleoecological record from a French Guianan coastal savanna that forces reconsideration of how pre-Columbian savanna peoples practiced raised-field agriculture and how the CE impacted these societies and environments. Our combined pollen, phytolith, and charcoal analyses reveal unexpectedly low levels of biomass burning associated with pre-A.D. 1492 savanna raised-field agriculture and a sharp increase in fires following the arrival of Europeans. We show that pre-Columbian raised-field farmers limited burning to improve agricultural production, contrasting with extensive use of fire in pre-Columbian tropical forest and Central American savanna environments, as well as in present-day savannas. The charcoal record indicates that extensive fires in the seasonally flooded savannas of French Guiana are a post-Columbian phenomenon, postdating the collapse of indigenous populations. The discovery that pre-Columbian farmers practiced fire-free savanna management calls into question the widely held assumption that pre-Columbian Amazonian farmers pervasively used fire to manage and alter ecosystems and offers fresh perspectives on an emerging alternative approach to savanna land use and conservation that can help reduce carbon emissions.

Environmental impact of geometric earthwork construction in pre-Columbian Amazonia

Significance The discovery of extensive geometric earthworks beneath apparently pristine rainforest across southern Amazonia has fueled debate over the scale of environmental impact caused by ancient human societies. Whereas some claim that these sites are evidence of vast deforestation by populous pre-Columbian (pre-A.D. 1492) societies, others propose a model of small-scale, localized clearance. We tested these contrasting hypotheses by reconstructing environmental change in a region of geometric earthworks in northeast Bolivia over the last 6,000 y. Our unexpected findings reveal a surprising third scenario, in which earthwork builders took advantage of a naturally open savanna landscape, which existed under drier-than-present climatic conditions before ∼2,000 y ago. This finding suggests lower environmental impact, less labor, and possibly a smaller population than previously assumed. There is considerable controversy over whether pre-Columbian (pre-A.D. 1492) Amazonia was largely “pristine” and sparsely populated by slash-and-burn agriculturists, or instead a densely populated, domesticated landscape, heavily altered by extensive deforestation and anthropogenic burning. The discovery of hundreds of large geometric earthworks beneath intact rainforest across southern Amazonia challenges its status as a pristine landscape, and has been assumed to indicate extensive pre-Columbian deforestation by large populations. We tested these assumptions using coupled local- and regional-scale paleoecological records to reconstruct land use on an earthwork site in northeast Bolivia within the context of regional, climate-driven biome changes. This approach revealed evidence for an alternative scenario of Amazonian land use, which did not necessitate labor-intensive rainforest clearance for earthwork construction. Instead, we show that the inhabitants exploited a naturally open savanna landscape that they maintained around their settlement despite the climatically driven rainforest expansion that began ∼2,000 y ago across the region. Earthwork construction and agriculture on terra firme landscapes currently occupied by the seasonal rainforests of southern Amazonia may therefore not have necessitated large-scale deforestation using stone tools. This finding implies far less labor—and potentially lower population density—than previously supposed. Our findings demonstrate that current debates over the magnitude and nature of pre-Columbian Amazonian land use, and its impact on global biogeochemical cycling, are potentially flawed because they do not consider this land use in the context of climate-driven forest–savanna biome shifts through the mid-to-late Holocene.

Impact of pre-Columbian “geoglyph” builders on Amazonian forests

Significance Amazonian rainforests once thought to be pristine wildernesses are increasingly known to have been inhabited by large populations before European contact. How and to what extent these societies impacted their landscape through deforestation and forest management is still controversial, particularly in the vast interfluvial uplands that have been little studied. In Brazil, the groundbreaking discovery of hundreds of geometric earthworks by modern deforestation would seem to imply that this region was also deforested to a large extent in the past, challenging the apparent vulnerability of Amazonian forests to human land use. We reconstructed environmental evidence from the geoglyph region and found that earthworks were built within man-made forests that had been previously managed for millennia. In contrast, long-term, regional-scale deforestation is strictly a modern phenomenon. Over 450 pre-Columbian (pre-AD 1492) geometric ditched enclosures (“geoglyphs”) occupy ∼13,000 km2 of Acre state, Brazil, representing a key discovery of Amazonian archaeology. These huge earthworks were concealed for centuries under terra firme (upland interfluvial) rainforest, directly challenging the “pristine” status of this ecosystem and its perceived vulnerability to human impacts. We reconstruct the environmental context of geoglyph construction and the nature, extent, and legacy of associated human impacts. We show that bamboo forest dominated the region for ≥6,000 y and that only small, temporary clearings were made to build the geoglyphs; however, construction occurred within anthropogenic forest that had been actively managed for millennia. In the absence of widespread deforestation, exploitation of forest products shaped a largely forested landscape that survived intact until the late 20th century.

Pre-Columbian land use in the ring-ditch region of the Bolivian Amazon

The nature and extent of pre-Columbian (pre-AD 1492) human impact in Amazonia is a contentious issue. The Bolivian Amazon has yielded some of the most impressive evidence for large and complex pre-Columbian societies in the Amazon basin, yet there remains relatively little data concerning the land use of these societies over time. Palaeoecology, when integrated with archaeological data, has the potential to fill these gaps in our knowledge. We present a 6000-year record of anthropogenic burning, agriculture and vegetation change, from an oxbow lake located adjacent to a pre-Columbian ring ditch in north-east Bolivia (13°15′44″S, 63°42′37″W). Human occupation around the lake site is inferred from pollen and phytoliths of maize (Zea mays L.) and macroscopic charcoal evidence of anthropogenic burning. First occupation around the lake was radiocarbon dated to ~2500 calibrated years before present (BP). The persistence of maize in the record from ~1850 BP suggests that it was an important crop grown in the ring-ditch region in pre-Columbian times, and abundant macroscopic charcoal suggests that pre-Columbian land management entailed more extensive burning of the landscape than the slash-and-burn agriculture practised around the site today. The site was occupied continuously until near-modern times, although there is evidence for a decline in agricultural intensity or change in land-use strategy, and possible population decline, from ~600–500 BP. The long and continuous occupation, which predates the establishment of rainforest in the region, suggests that pre-Columbian land use may have had a significant influence on ecosystem development at this site over the last ~2000 years.

Reply to Piperno et al.: It is too soon to argue for localized, short-term human impacts in interfluvial Amazonia

We welcome the debate opened by Piperno et al. (1) in response to our recent article (2), and thank the editors of PNAS for the opportunity to reply. Although acknowledging that we detected localized human impacts in our study area, Piperno et al. (1) downplay the increases in palms observed at the geoglyph sites, stating it’s “unclear” whether humans actively managed the forest in these locations. Independent of one’s opinion about intentionality, we argue that the rapid decline of palms after geoglyph abandonment suggests that their previously high levels were because of much more regular, longer-term human influences than Piperno et al. suggest. We also reemphasize that … [↵][1]1To whom correspondence should be addressed. Email: jenny.g.watling{at}gmail.com. [1]: #xref-corresp-1-1

Reply to Silva: Dynamic human–vegetation–climate interactions at forest ecotones during the late-Holocene in lowland South America

We are pleased that the publication of our recent study (1) has stimulated further discussion of the complexities of past human–vegetation–climate interactions in the Neotropics, and that Silva (2) considers that our study “fundamentally changes our understanding of the magnitude and nature of pre-Columbian land use in the Amazon region.” However, we wish to address several of the points raised by Silva.

Direct archaeological evidence for Southwestern Amazonia as an early plant domestication and food production centre

Southwestern Amazonia is considered an early centre of plant domestication in the New World, but most of the evidence for this hypothesis comes from genetic data since systematic archaeological fieldwork in the area is recent. This paper provides first-hand archaeobotanical evidence of food production from early and middle Holocene (ca. 9,000–5000 cal. BP) deposits at Teotonio, an open-air site located on a 40 m-high bluff on the south bank of the Madeira river. Such evidence includes the presence of local and exotic domesticates such as manioc (Manihot esculenta), squash (Cucurbita sp.) and beans (Phaseolus sp.), alongside edible fruits such as pequiá (Caryocar sp.) and guava (Psidium sp.) that point to the beginnings of landscape domestication. The results contribute to an ever-growing number of studies that posit southwest Amazonia as an important centre for early crop domestication and experimentation, and which highlight the longue-durée of human impacts on tropical forest biodiversity around the world.