Niche-dependent forest and savanna fragmentation in Tropical South America during the Last Glacial Maximum

TL;DR

This study investigates how forests and savannas in Tropical South America fragmented during the Last Glacial Maximum, using climate and vegetation models.

Contribution

The paper introduces a bias-corrected Dynamic Vegetation Model to test forest and savanna connectivity during the Last Glacial Maximum.

Findings

Forest fragments and savanna connectivity existed in Amazonia during the Last Glacial Maximum.

Drier ecosystems may have merged into continuous savanna/grasslands in Northern Llanos, Caatinga, and Cerrado.

An ecotonal biome may have acted as a corridor for generalist species and a barrier for specialists.

Abstract

The refugia hypothesis, often used to explain Amazonia’s high biodiversity, initially received ample support but has garnered increasing criticism over time. Palynological, phylogenetic, and vegetation model reconstruction studies have been invoked to support the opposing arguments of extensive fragmentation versus a stable Amazonian Forest during Pleistocene glacial maxima. Here, we test the past existence of forest fragments and savanna connectivity by bias-correcting vegetation distributions from a Dynamic Vegetation Model (DVM) driven by paleoclimate simulations for South America during the Last Glacial Maximum (LGM). We find evidence for fragmented forests akin to refugia with extensive tropical humid forests to the west and forest islands in central/southern Amazonia. Drier ecosystems of Northern Llanos, Caatinga and Cerrado may have merged into continuous savanna/grasslands that dominated the continent. However, our reconstructions suggest taller, dense woodland/tropical savanna vegetation and areas of similar bioclimate connected disparate forest fragments across Amazonia. This ecotonal biome may have acted as a corridor for generalist forest and savanna species, creating connectivity that allows for range expansion during glacial periods. Simultaneously, it could have served as a barrier for specialists, inducing diversification through the formation of ‘semi-refugia’.

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