Plant species richness at archaeological sites suggests ecological legacy of Indigenous subsistence on the Colorado Plateau

Humans have both intentional and unintentional impacts on their environment, yet identifying the enduring ecological legacies of past small-scale societies remains difficult, and as such, evidence is sparse. The present study found evidence of an ecological legacy that persists today within an semiarid ecosystem of western North America. Specifically, the richness of ethnographically important plant species is strongly associated with archaeological complexity and ecological diversity at Puebloan sites in a region known as Bears Ears on the Colorado Plateau. A multivariate model including both environmental and archaeological predictors explains 88% of the variation in ethnographic species richness (ESR), with growing degree days and archaeological site complexity having the strongest effects. At least 31 plant species important to five tribal groups (Navajo, Hopi, Zuni, Ute Mountain Ute, and Apache), including the Four Corners potato (Solanum jamesii), goosefoot (Chenopodium sp.), wolfberry (Lycium pallidum), and sumac (Rhus trilobata), occurred at archaeological sites, despite being uncommon across the wider landscape. Our results reveal a clear ecological legacy of past human behavior: even when holding environmental variables constant, ESR increases significantly as a function of past investment in habitation and subsistence. Consequently, we suggest that propagules of some species were transported and cultivated, intentionally or not, establishing populations that persist to this day. Ensuring persistence will require tribal input for conserving and restoring archaeo-ecosystems containing “high-priority” plant species, especially those held sacred as lifeway medicines. This transdisciplinary approach has important implications for resource management planning, especially in areas such as Bears Ears that will experience greater visitation and associated impacts in the near future.

Local resource abundance is important for determining where in a given landscape humans decide to live. Nearby water, game, soil, and plants provide readily available wild resources for foraging and conditions that allow for cultivation (1–5). However, humans also modify their surrounding environments in order to increase the abundance and diversity of local plant (6–11) and animal (12–15) resources. Such “human niche construction” is a hallmark of ancient and modern societies (16, 17), having positive and negative impacts on global biodiversity while possibly creating enduring ecological legacies (18–21). This may be especially true for more sedentary and dense populations (22, 4) that are more likely to find investment worthwhile (23) and to produce unintentional impacts. Thus, variation in contemporary ecological diversity may in part reflect past land use dynamics and, therefore, be revealed through coupled archaeological and ecological research (24–33).Coupled ecological and archaeological research has led to the discovery of altered patterns of succession resulting from 1) forest clearing and changes in canopy light regime (34, 35), 2) alterations of soil especially linked to food refuse (36, 37), 3) changes in fire regimes (38, 39), and, more rarely, 4) the importation of plant propagules from distant sites of collection (40, 41). Identifying such long-lost dynamics between humans and landscapes can inform conservation aimed at restoring site-specific artifacts, features, and the associated resource base past and present, here termed “archaeo-ecosystems” (42, 43). This would greatly facilitate cross-cultural management of public lands (44) in ways that promote Indigenous health, cultural reclamation, and sovereignty (7, 45). The linkages, however, between ecological legacies, archaeo-ecosystem restoration and cross-cultural management have yet to be systematically tested or practically applied.Here, we offer a formal evaluation of this archaeo-ecosystem approach by using paired archaeological and ecological survey data focused on Puebloan occupation of a region known as Bears Ears on the Colorado Plateau in southeastern Utah (Fig. 1). Puebloan populations modified their environment by constructing terraces and check dams, developing blinds and wing traps, importing exogenous species, and setting fires (4, 22, 46), but investments were not uniform across the region. We test the hypothesis that locations with greater investment indicated by larger and more complex archaeological sites should today have higher richness of culturally significant plant species, here termed ethnographic species richness (ESR), as an enduring legacy of past investment. Our study expands previous work on ecological legacies by using field surveys to develop an explanatory model applied to 265 sites across one million acres of semiarid public lands. It documents the occurrence of uncommon and ethnographically significant plant species associated with those sites and infuses traditional ecological knowledge into proposed management actions for conserving these archaeo-ecosystems. Controlling for underlying environmental variation, our results indicate that past human habitation increases the diversity of plant species important for Indigenous subsistence.Open in a separate windowFig. 1.Location of Bears Ears National Monument in southeastern Utah. The predicted ESR at 265 known archaeological sites across the original and reduced monument boundaries and surrounding region are shown.