Remote Sensing Reveals Lasting Legacies of Land-Use by Small-Scale Foraging Communities in the Southwestern Indian Ocean

Dylan S Davis,Kristina Douglass

doi:10.3389/fevo.2021.689399

Dylan S Davis, Kristina Douglass

Open Access

https://doi.org/10.3389/fevo.2021.689399

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Abstract

Archaeologists interested in the evolution of anthropogenic landscapes have productively adopted Niche Construction Theory (NCT), in order to assess long-term legacies of human-environment interactions. Applications of NCT have especially been used to elucidate co-evolutionary dynamics in agricultural and pastoral systems. Meanwhile, foraging and/or highly mobile small-scale communities, often thought of as less intensive in terms of land-use than agropastoral economies, have received less theoretical and analytical attention from a landscape perspective. Here we address this lacuna by contributing a novel remote sensing approach for investigating legacies of human-environment interaction on landscapes that have a long history of co-evolution with highly mobile foraging communities. Our study is centered on coastal southwest Madagascar, a region inhabited by foraging and fishing communities for close to two millennia. Despite significant environmental changes in southwest Madagascar’s environment following human settlement, including a wave of faunal extinctions, little is known about the scale, pace and nature of anthropogenic landscape modification. Archaeological deposits in this area generally bear ephemeral traces of past human activity and do not exhibit readily visible signatures of intensive land-use and landscape modification (e.g., agricultural modifications, monumental architecture, etc.). In this paper we use high-resolution satellite imagery and vegetative indices to reveal a legacy of human-landscape co-evolution by comparing the characteristics – vegetative productivity and geochemical properties – of archaeological sites to those of locations with no documented archaeological materials. Then, we use a random forest (RF) algorithm and spatial statistics to quantify the extent of archaeological activity and use this analysis to contextualize modern-day human-environment dynamics. Our results demonstrate that coastal foraging communities in southwest Madagascar over the past 1,000 years have extensively altered the landscape. Our study thus expands the temporal and spatial scales at which we can evaluate human-environment dynamics on Madagascar, providing new opportunities to study early periods of the island’s human history when mobile foraging communities were the dominant drivers of landscape change.

Highlights

Among archaeologists, the identification and quantification of feedbacks between past human activities and landscapescale transformations have historically focused on economies of scale that generate highly visible changes to landscapes
Assessments of training datasets and PlanetScope imagery resulted in clear distinctions between archaeological and nonarchaeological points in all four electromagnetic bands (Blue, Green, Red, and near infrared (NIR); Figure 4B)
Normalized Difference Water Index (NDWI) results show the same pattern (W = 8468, p-value = 0.042). This suggests that archaeological sites exhibit vegetative index values that are distinct from non-archaeological areas

Summary

Introduction

The identification and quantification of feedbacks between past human activities and landscapescale transformations have historically focused on economies of scale that generate highly visible changes to landscapes (e.g., monumental architecture, intensive agriculture, shifts from forests to grasslands, etc.). Uses of remote sensing technology (i.e., satellite images) in such contexts have successfully identified these “low-impact” signatures of human action on large geographic scales (Lombardo and Prümers, 2010). Prior remote sensing analyses on Madagascar have focused on the drivers of settlement and mobility (e.g., resource availability and social aggregation) using predictive models based on satellite-derived environmental information and statistical modeling (Davis et al, 2020a,b). In this paper, we focus on identifying and characterizing legacies of forager activities and coastal settlement on the landscape of the Velondriake Marine Protected Area of southwest Madagascar, a region with a history of coastal foraging that extends back at least to 2,000 cal year BP (Figure 2; Douglass et al, 2019). Vegetation in Velondriake is largely xerophytic and classified as a “spiny thicket” ecoregion, which contains some of the highest levels of endemic flora on the island (Gautier and Goodman, 2003)

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