Abstract

The mid-elevation settings of the Andes are important biodiversity hotspots, yet little is known of their long-term ecology or environmental change. Here, we assess 30,000 years of landscape and vegetation dynamics on an alluvial terrace located in a mid-elevation valley of the Ecuadorian Andes (Campo Libre). We used loss-on-ignition and particle size analysis to reconstruct past river dynamics, charcoal analysis to reconstruct past fire regimes, and phytolith analysis to reconstruct vegetation change through time. Our results show that Campo Libre was a part of the active floodplain system of the Quijos River until 18,000 cal yr BP. The biggest vegetation change in vegetation at Campo Libre occurred ca. 13,000 cal yr BP, when the site warmed and dried, transforming the swampy alluvial terrace into a palm forest. As Holocene precipitation increased, the site transformed back into a swamp around 7500 cal yr BP, and it remained that way until maize agriculture began around 4600 cal yr BP. Local and regional fires were absent from the system until regional fires were detected ca. 3300 cal yr BP. By ca. 2700 cal yr BP, maize cultivation became frequent and regular. Climate, tectonic activity, and the human history have shaped the modern vegetation around Campo Libre, although during different periods of the Holocene. Our results demonstrate the ability of phytoliths to reconstruct vegetation change through time, and show that the mid-elevation Andean valley systems were highly dynamic over the last 30,000 years.

Highlights

  • The Eastern Andean Flank (EAF) in Ecuador is a biodiversity hotspot (Myers et al, 2000)

  • This has likely varied through time, but if it were used as an average incision rate, the elevation difference between the current alluvial terrace and the Quijos River would suggest that the historic floodplain became inactive ca. 18,000 cal yr BP

  • Phytoliths preserve in places where pollen grains do not, such as Campo Libre, but so far have only been analyzed in one study containing sediments from the last glacial period (Bush et al, 1990)

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Summary

Introduction

The Eastern Andean Flank (EAF) in Ecuador is a biodiversity hotspot (Myers et al, 2000). Species richness is typically highest along this gradient between 1000 and 2000 m above sea level (masl) (Colwell, 2000; Rahbek, 1995; Terborgh, 1977; Jørgensen et al, 2011). These mid-elevation forests are threatened systems, both in terms of. During the last glacial period, species in Andean systems could live at much lower elevations than in the warmer climate of the current interglacial period The deglaciation, or transition from the last glacial period to the current interglacial period (the Holocene), resulted in spatially variable climate and landscape changes that were abrupt and highmagnitude across South America (Clark et al, 2012)

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