Formal Tests for Resistance-Resilience in Archaeological Time Series

Philip Riris,Jonas Gregorio De Souza

doi:10.3389/fevo.2021.740629

Philip Riris, Jonas Gregorio De Souza

Open Access

https://doi.org/10.3389/fevo.2021.740629

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Abstract

The study of resilience is a common pathway for scientific data to inform policy and practice towards impending climate change. Consequently, understanding the mechanisms and features that contribute towards building resilience is a key goal of much research on coupled socio-environmental systems. In parallel, archaeology has developed the ambition to contribute to this agenda through its unique focus on cultural dynamics that occur over the very long term. This paper argues that archaeological studies of resilience are limited in scope and potential impact by incomplete operational definitions of resilience, itself a multifaceted and contested concept. This lack of interdisciplinary engagement fundamentally limits archaeology’s ability to contribute meaningfully to understanding factors behind the emergence and maintenance of long-term societal resilience, a topic of significant interest that the field is in theory ideally positioned to address. Here, we introduce resilience metrics drawn from ecology and develop case studies to illustrate their potential utility for archaeological studies. We achieve this by extending methods for formally measuring resistance, the capacity of a system to absorb disturbances; and resilience, its capacity to recover from disturbances, with a novel significance test for palaeodemographic data. Building on statistical permutation and post-hoc tests available in the rcarbon package in the R statistical environment, we apply our adapted resilience-resistance framework to summed probability distributions of calibrated radiocarbon dates drawn from the Atlantic Forest of eastern Brazil. We deploy these methods to investigate cross-sectional trends across three recognised biogeographical zones of the Atlantic Forest domain, against the backdrop of prehistoric phases of heightened hydroclimatic variability. Our analysis uncovers novel centennial-scale spatial structure in the resilience of palaeodemographic growth rates. In addition to the case-specific findings, we suggest that adapting formal metrics can help archaeology create impact and engagement beyond relatively narrow disciplinary concerns. To this end, we supply code and data to replicate our palaeodemographic analyses to enable their use and adaptation to other archaeological problems.

Highlights

In this paper, we use radiocarbon frequency data from the Atlantic Forest of eastern Brazil to develop an empirically grounded archaeological test for resistance-resilience, focused on the period of the Medieval Climate Anomaly (MCA)
We suggest that radiocarbon-based estimates of palaeodemographic dynamics are exceptionally well-positioned to provide solutions, as they provide an absolute chronological framework for assessing fluctuations that can be cross-referenced to known perturbations and couched within a hypothesistesting framework
We investigate whether the transient, centennial-scale effects of the MCA, in the form of a weakened South American Summer Monsoon, are reflected in persistent changes to palaeodemographic growth rates across the Atlantic Forest, as in parts of Amazonia (De Souza et al, 2019)

Summary

Introduction

We use radiocarbon frequency data from the Atlantic Forest of eastern Brazil to develop an empirically grounded archaeological test for resistance-resilience, focused on the period of the Medieval Climate Anomaly (MCA). Narrowing data gaps across tropical South America have found support for its expression as a period of abrupt hydroclimate change over central and eastern Brazil too, with precipitation proxies suggesting depressed rainfall due to a northward shift of the Intertropical Convergence Zone (ITCZ) and lowered moisture delivery across the continent (Novello et al, 2018; Deininger et al, 2019; Lüning et al, 2019). Records from the core of the SACZ, which lies astride the central Atlantic Forest, show a strong multidecadal to centennial-scale variability at around ∼900–500 cal BP, on the cusp of the transition between MCA and LIA (Novello et al, 2018). We expand the scope of recent palaeodemographic modelling work in southern Brazil (De Souza and Riris, 2021) and neighbouring regions of South America (Azevedo et al, 2019; De Souza et al, 2019) to encompass the entire Atlantic Forest biome across eastern Brazil and evaluate the resilience of pre-Columbian populations to known climate perturbations that affected this domain

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