Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil

Mark Robinson,Luiz Pessenda,Francis Edward Mayle,Rafael Corteletti,Deisi Scunderlick,Paulo De Blasis,Macarena Cárdenas,Keith Prufer,S Yoshi Maezumi,José Iriarte,Jonas Gregorio De Souza

doi:10.1038/s41598-018-24429-5

Abstract

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900 cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifications to forest expansion, but generally lacked high resoltiuon proxies to measure these effects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profiles confirm that in spite of climatic fluctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifications were linked to demographic changes, the effects of which are still visible today.

Highlights

In the face of global climate change and intensifying population pressure, understanding the drivers of vegetation change is critical for developing appropriate conservation practices to secure global biodiversity
In this study we develop and test an interdisciplinary methodology to distinguish human impacts from climate-induced vegetation changes in the southern Brazilian highlands (Fig. 1) during a period of abrupt cultural and environmental change
Results challenge a dominant hypothesis of climatically driven Late Holocene Araucaria forest expansion, questioning the use of pollen datasets as a proxy to reconstruct both climate and vegetation history, and suggesting that regardless of climatic variability, vegetation was stable in areas of low human activity but forest expansion occurred at the expense of grasslands in areas of high archaeological activity

Summary

Introduction

In the face of global climate change and intensifying population pressure, understanding the drivers of vegetation change is critical for developing appropriate conservation practices to secure global biodiversity. In this study we develop and test an interdisciplinary methodology to distinguish human impacts from climate-induced vegetation changes in the southern Brazilian highlands (Fig. 1) during a period of abrupt cultural and environmental change. Isotopic profiles of soil test pits are used to assess localised vegetation histories against a predictive model of natural forest distribution and a robust archaeological dataset[7,8,9,10]. Results challenge a dominant hypothesis of climatically driven Late Holocene Araucaria forest expansion, questioning the use of pollen datasets as a proxy to reconstruct both climate and vegetation history, and suggesting that regardless of climatic variability, vegetation was stable in areas of low human activity but forest expansion occurred at the expense of grasslands in areas of high archaeological activity. Regional vegetation dynamics and species distribution must be understood in relation to anthropogenic inputs

Methods

Results

Conclusion