Landscape-scale drivers of glacial ecosystem change in the montane forests of the eastern Andean flank, Ecuador

Nicholas J.D Loughlin,William D Gosling,Angela L Coe,Pauline Gulliver,Patricia Mothes,Encarni Montoya

doi:10.1016/j.palaeo.2017.10.011

Abstract

Understanding the impact of landscape-scale disturbance events during the last glacial period is vital in accurately reconstructing the ecosystem dynamics of montane environments. Here, a sedimentary succession from the tropical montane cloud forest of the eastern Andean flank of Ecuador provides evidence of the role of non-climate drivers of vegetation change (volcanic events, fire regime and herbivory) during the late-Pleistocene. Multiproxy analysis (pollen, non-pollen palynomorphs, charcoal, geochemistry and carbon content) of the sediments, radiocarbon dated to ca. 45–42ka, provide a snap shot of the depositional environment, vegetation community and non-climate drivers of ecosystem dynamics. The geomorphology of the Vinillos study area, along with the organic‑carbon content, and aquatic remains suggest deposition took place near a valley floor in a swamp or shallow water environment. The pollen assemblage initially composed primarily of herbaceous types (Poaceae-Asteraceae-Solanaceae) is replaced by assemblages characterised by Andean forest taxa, (first Melastomataceae-Weinmannia-Ilex, and later, Alnus-Hedyosmum-Myrica). The pollen assemblages have no modern analogues in the tropical montane cloud forest of Ecuador. High micro-charcoal and rare macro-charcoal abundances co-occur with volcanic tephra deposits suggesting transportation from extra-local regions and that volcanic eruptions were an important source of ignition in the wider glacial landscape. The presence of the coprophilous fungi Sporormiella reveals the occurrence of herbivores in the glacial montane forest landscape. Pollen analysis indicates a stable regional vegetation community, with changes in vegetation population co-varying with large volcanic tephra deposits suggesting that the structure of glacial vegetation at Vinillos was driven by volcanic activity.

Highlights

Mid-elevation tropical forests have been identified as some of the most biodiverse yet at risk terrestrial ecosystems in the world due to their high degree of endemism, sensitivity to climate change and anthropogenic impact (Bruijnzeel et al, 2011; Churchill et al, 1995; Hamilton et al, 1995)
The Vinillos section is composed of dark-brown to black organic layers with occasional pale grey lenses of volcanic ash interbedded with pale grey to beige volcanic tephra deposits
These changes in climate likely contributed to vegetation change within the sedimentary snap shot at Vinillos, here we show that the often neglected non-climate drivers of vegetation change are vital in interpreting past ecosystem dynamics driving landscape-scale change in the glacial montane forest of the eastern Andean flank

Summary

Introduction

Mid-elevation tropical forests have been identified as some of the most biodiverse yet at risk terrestrial ecosystems in the world due to their high degree of endemism, sensitivity to climate change and anthropogenic impact (Bruijnzeel et al, 2011; Churchill et al, 1995; Hamilton et al, 1995). Tropical montane cloud forests (TMCF) are distinguished from other types of tropical forest by their association with montane environments immersed in frequent ground level cloud (Grubb, 1971, 1977). TMCF on the eastern Andean flank of northern Ecuador occur between ca. Changes in climate associated with cloud cover play an important role in natural cloud forest structure and composition (Churchill et al, 1995; Fahey et al, 2016; Hamilton et al, 1995). Modern anthropogenic pressures (e.g. land-use change, landcover modification, pollution) arguably exceeded climate as the dominant control on vegetation structure through much of the TMCF of the eastern Andean flank (Sarmiento, 1995)

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