Botanical Evidence of Paleodietary and Environmental Change: Drought on the Channel Islands, California

Abstract

Fluctuations in climatic regimes and biodiversity through time are linked in complex ways to human behavior and socioeconomic processes. We use macrobotanical evidence from Chumash village sites on California’s Channel Islands to investigate the relationship between late Holocene climatic perturbations and one region of the larger Chumash world. Carbonized plant remains provide evidence of the shifting availability of native plants during the Transitional period (A.D. 1150–1300), when droughts impacted island floral diversity and the Chumash had to cope with changes in vegetation regimes that likely curtailed food availability. We find that drought-resistant plant resources appear in higher relative frequencies in proveniences dating to the Transitional era, and at least one food resource was first imported from the mainland around that time. These findings support the proposition that the Chumash intensified cross-channel trade in part to respond to dietary needs during episodic resource stress. This is also the time when several economic specializations blossomed, including intensive shell bead making. These specializations persisted for six centuries and were central to the development of institutionalized leadership and political complexity in the region ca. A.D. 1200. Various strategies to preserve stability in the plant diet were important elements in the broader reorganization of labor in coastal southern California.

Human–vegetation interactions during the Holocene in North America

“…More examples are available from the past 2,000 years; for example, climate changes during the Medieval Warm Period had impacts across the continent, especially in the west where significant droughts were closely tied to cultural changes (e.g. Jones et al 1999;Foster 2012;Arnold and Martin 2014;Schwindt et al 2016;Comstock and Cook 2018). The impacts of climate changes hypothesized to have affected the regional archaeological record have been documented (Fiedel 2001;McWeeney and Kellogg 2001), where the palaeoclimate reconstructions were frequently derived from global-scale palaeoclimate syntheses.…”

Climate Change and Subsistence Exchange in Southern California: Was Western Sea-Purslane a Channel Island Trade Good?

“…There has been a lot of debate recently regarding the role of plant foods in cross-channel Chumash exchange systems (Arnold 2012; Arnold and Martin 2014; Fauvelle 2011, 2012, 2013, 2014; Gill and Erlandson 2014). Much of this discussion stems from the importance of these exchange systems in models of the development of Chumash social and political complexity (e.g., King 1976).…”

“…This inefficiency of transport is also supported by a paucity of acorn remains in island middens. The last three decades of archaeological work on the channel islands have returned only a few hundred acorn fragments from archaeological contexts (Arnold and Martin 2014; Gill 2013, 2015; Martin and Popper 2001; Thakar 2014), and, in terms of density, acorn nutmeat and nutshell remains are rare throughout the islands’ occupation, rarely exceeding .005 grams per liter (Gill 2015; Martin and Popper 2001). Such numbers are hardly indicative of any heavy consumption of acorns in Channel Island prehistory.…”

“…Despite the importance of subsistence exchange in many models of the development of Chumash chiefdoms, there is little information on the paleobotany of the Channel Islands (but see Gill 2013; Martin and Popper 2001). Arnold and Martin (2014) help alleviate this situation by presenting the results of several years of paleobotanical investigations at four sites on Santa Cruz Island. Although Arnold and Martin (2014) report inconclusive evidence for any importation of acorns, they did identify 63 seeds from the species Sesuvium verrucosum , or western sea-purslane (from .01 to .03 count per liter; Arnold and Martin 2014:235).…”

“…Arnold and Martin (2014) help alleviate this situation by presenting the results of several years of paleobotanical investigations at four sites on Santa Cruz Island. Although Arnold and Martin (2014) report inconclusive evidence for any importation of acorns, they did identify 63 seeds from the species Sesuvium verrucosum , or western sea-purslane (from .01 to .03 count per liter; Arnold and Martin 2014:235). Currently, western sea-purslane grows only on the mainland coast, suggesting that this plant may have been traded across the channel to the islands.…”