Ghosts of Cultivation Past - Native American Dispersal Legacy Persists in Tree Distribution.

Robert J Warren,Gary W Crawford

doi:10.1371/journal.pone.0150707

Abstract

A long-term assumption in ecology is that species distributions correspond with their niche requirements, but evidence that species can persist in unsuitable habitat for centuries undermines the link between species and habitat. Moreover, species may be more dependent on mutualist partners than specific habitats. Most evidence connecting indigenous cultures with plant dispersal is anecdotal, but historical records suggest that Native Americans transported and cultivated many species, including Gleditsia triacanthos ("Honey locust"). Gleditsia triacanthos was an important medicinal/culinary (e.g., sugar), cultural (e.g., game sticks) and spiritual tree for the Cherokee (southeastern U.S. Native Americans). This study tests the hypothesis that a Cherokee cultivation legacy drives current regional G. triacanthos distribution patterns. Gleditsia triacanthos occurs in rocky uplands and xeric fields, but inexplicably also occurs in mesic riverine corridors and floodplains where Cherokee once settled and farmed. I combined field experiments and surveys in the Southern Appalachian Mountain region (U.S.) to investigate G. triacanthos recruitment requirements and distribution patterns to determine whether there is a quantifiable G. triacanthos association with former Cherokee settlements. Moreover, I also investigated alternate dispersal mechanisms, such as stream transport and domestic cattle. The results indicate that a centuries-old legacy of Native American cultivation remains intact as G. triacanthos' current southern Appalachian distribution appears better explained Cherokee settlement patterns than habitat. The data indicate that the tree is severely dispersal limited in the region, only moving appreciable distances from former Cherokee settlements where cattle grazing is prevalent. Human land use legacy may play a long-term role in shaping species distributions, and pre-European settlement activity appears underrated as a factor influencing modern tree species distributions.

Highlights

A simplifying assumption in ecology and biogeography is that species occupy suitable habitat and are absent from unsuitable habitat
Gleditsia. triacanthos recruitment and survival were most limited by vegetation cover, and unaffected by increased soil moisture in the seed addition experiment
The field plantings suggested that mesic bottomland habitat was the least suitable for G. triacanthos recruitment, despite that the tree often is found in bottomlands and mesic habitats [20,21,22,23]

Summary

Introduction

A simplifying assumption in ecology and biogeography is that species occupy suitable habitat and are absent from unsuitable habitat. The veracity of that assumption is undermined, by evidence that species persist in unsuitable habitat [1, 2] and remain absent from. Plants that depend on a mutualist may be strongly associated with habitat suitable for their partner [5,6,7] so that some plant distributions better reflect the niche requirements of the mutualist than the plant itself. The absence (or loss) of a dispersal partner reduces (or eliminates) the plant’s ability to track suitable habitat and may leave it stranded in suboptimal habitat [2]. Plant populations can persist in less than optimal conditions for centuries [8] and may be in disequilibrium with optimal habitat at very large scales [9]

Methods

Results

Conclusion