Abstract
AbstractAimPalaeoecological data provide an essential long‐term perspective of ecological change and its drivers in oceanic islands. However, analysing the effects of multi‐scalar and potentially co‐occurring disturbances is particularly challenging in dry islands. Here, we aim to identify the ecological consequences of the integrated impacts of a regional drying trend, volcanic eruptions and human mass migrations in a spatially constrained environment—a small, dry oceanic island in Macaronesia.LocationBrava Island, Republic of Cabo Verde.TaxaTerrestrial vegetation and fungi.MethodsWe use palaeoecological analyses applied to a caldera soil profile that dates back to 9700 cal yr BP (calibrated years before the present). Analyses include pollen (vegetation history), non‐pollen palynomorphs (changes in fern and fungal communities), grain‐size distribution, loss‐on‐ignition and geochemistry (sedimentology and erosion regimes), microscopic tephra shards (volcanic ash deposition) and charcoal (fire regime).ResultsA regional drying trend after c. 4000 cal yr BP caused increased erosion but had limited immediate impacts on highland grassland vegetation. The expansion of fern‐rich woody scrubland was contemporaneous with significant deposition of volcanic ash and erosion between 1800 and 650 cal yr BP. About 300 cal yr BP, exogenous plants expanded, grazing and fires increased, and there was a decrease of native vegetation cover.Main conclusionsThroughout the Holocene, highland vegetation in Brava was characterized by the presence of open landscapes dominated by herbaceous species (e.g. Poaceae, Forsskaolea), with some presence of woody native taxa (e.g. Ficus, Dodonaea). A regional drying trend was a driver of erosion since the Mid Holocene but did not have an immediate influence on highland vegetation. Tephra deposition is a possible driver of vegetation change. Inter‐island mass migration after volcanic events in Fogo Island c. 1680 CE potentially triggered land use change and intensification, causing a reduction of native vegetation in Brava.
Highlights
Oceanic islands worldwide have been identified as frontline sites of major socio-ecological challenges (Baldacchino & Niles, 2011)
For changes in organic matter content we carried out Loss on Ignition analysis (LOI), for identifying the occurrence of fire we quantified charcoal particles, for shifts in sedimentology we used X-ray fluorescence (XRF) and grain size distribution (GSD) analysis, and to assess the occurrence of significant episodes of deposition of volcanic ash we studied the abundance of microscopic tephra shards
Pollen evidence suggests that taxa such as Ficus sur, Ficus sycomorus, Dodonaea viscosa and Dracaena draco subsp. caboverdeana were native to this small dry island before human settlement
Summary
Oceanic islands worldwide have been identified as frontline sites of major socio-ecological challenges (Baldacchino & Niles, 2011). Dry (climatically arid) island environments can be highly sensitive to disturbances such as an increase in extreme weather events or long periods of drought (Holmgren et al, 2006), and these natural factors can interact with and aggravate human impacts (Lindskog & Delaite, 1996). A comparison of disturbance dynamics before and after human arrival can increase our understanding of how human impacts overprint –or interact with–naturally occurring features of the island environment (Dearing et al, 2006; Paine et al, 1998). It is challenging to develop records of long-term environmental change in dry regions due to poor microfossil preservation and a scarcity of undisturbed sediment archives (Brunelle et al, 2018). Palaeoecological research carried out in dryland soil stratigraphic sequences can provide an essential historical perspective on ecological change in dry islands Palaeoecological research carried out in dryland soil stratigraphic sequences can provide an essential historical perspective on ecological change in dry islands (e.g. van Leeuwen et al, 2008)
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