Prehistoric deforestation at Chaco Canyon?

Abstract

Ancient societies are often used to illustrate the potential problems stemming from unsustainable land-use practices because the past seems rife with examples of sociopolitical “collapse” associated with the exhaustion of finite resources. Just as frequently, and typically in response to such presentations, archaeologists and other specialists caution against seeking simple cause-and effect-relationships in the complex data that comprise the archaeological record. In this study we examine the famous case of Chaco Canyon, New Mexico, during the Bonito Phase ( ca . AD 860–1140), which has become a prominent popular illustration of ecological and social catastrophe attributed to deforestation. We conclude that there is no substantive evidence for deforestation at Chaco and no obvious indications that the depopulation of the canyon in the 13th century was caused by any specific cultural practices or natural events. Clearly there was a reason why these farming people eventually moved elsewhere, but the archaeological record has not yet produced compelling empirical evidence for what that reason might have been. Until such evidence appears, the legacy of Ancestral Pueblo society in Chaco should not be used as a cautionary story about socioeconomic failures in the modern world.

Eleventh-century shift in timber procurement areas for the great houses of Chaco Canyon

“…A pair of recent studies, however, challenge this idea based on similarities in the 87 Sr/ 86 Sr values for trees in the Chuska Mountains and soil in Chaco Canyon (8,9). They conclude, therefore, that low-elevation sites within and near the Canyon were just as likely sources for ponderosa beams as were the Chuskas, despite a lack of ponderosa pine in the paleoenvironmental record of the Canyon and surrounding areas since ∼5,000 y ago (14)(15)(16)28).…”

“…These massive stone masonry structures required a wealth of resources to erect, including an estimated 240,000 trees incorporated as roof beams, door and window lintels, and other building elements (3). The incongruity of the great houses located in a nearly treeless landscape has led archaeologists and paleoecologists to investigate the origins of timbers used in construction (4)(5)(6)(7)(8)(9). Beyond the simple curiosity driving this question, the answer has important implications for understanding the complexities of human-environmental interactions, the sociopolitical organization, and the economic structure of Chacoan society (10)(11)(12).…”

“…), which account for tens of thousands of construction beams, have been absent from Chaco Canyon for at least 12,000 y and could have only been logged from distant, higher-elevation sites (2,500-3,450 m above sea level) (4 (6,7). Recently, the explanation of long-distance timber transport and the related interpretations of 87 Sr/ 86 Sr evidence have been challenged and an alternative has been proposed that most great-house timbers (particularly ponderosa pine) were just as likely to have originated from nearby and lowelevation sites within, east, and south of Chaco Canyon (8,9).…”

What’s new in Chaco research?

“…It is argued that sufficient food production was achieved by employing technologies, such as water-diversion features, canals, sand dune farming, ak chin fields and gridded gardens (Worman & Mattson 2010; Dorshow 2012; Wills & Dorshow 2012; Wills et al . 2014, 2016; Vivian & Watson 2015; Sturm 2016; Wills 2017). Wills (2017) suggests that the evidence for agricultural features combined with dispersed fields surrounding the canyon would have been sufficient to support the labour required for great house construction, without needing to generate large surpluses.…”

Stable Oxygen Isotope Sourcing of Archaeological Fauna From Chaco Canyon, New Mexico

“…AD 800 to 1200), when the canyon emerged as the core of a regional socioeconomic system extending across the Colorado Plateau (Lekson 2006). Strontium isotope analyses are prominent in these approaches (Benson et al 2003; Benson et al 2006; English et al 2001; Grimstead et al 2015; Guiterman, Swetnam, and Dean 2016; Reynolds et al 2005) but with ambiguous results because 87 Sr/ 86 Sr ratios do not clearly differentiate Chaco Canyon from other potential long-distance sources (Drake et al 2014; Wills, Drake, and Dorshow 2014). Grimstead, Quade, and Stiner (2016) have used oxygen isotope analyses to assess the importation of animal resources into Chaco, but they did not include (or have access to) modern fauna from Chaco Canyon.…”