Long‐term drivers of vegetation turnover in Southern Hemisphere temperate ecosystems

Abstract

AimKnowledge of the drivers of ecosystem changes in the past is key to understanding present ecosystem responses to changes in climate, fire regimes and anthropogenic impacts. Northern Hemisphere‐focussed studies suggest that climate and human activities drove turnover during the Holocene in temperate ecosystems. Various drivers have been invoked to explain changes in Southern Hemisphere temperate vegetation, but the region lacks a quantitative assessment of these drivers. To better understand the regional drivers of past diversity, we present a quantitative meta‐analysis study of turnover and richness during the lateglacial and Holocene in Australian temperate ecosystems.LocationSouth‐east Australia (Tasmania, Bass Strait, SE mainland).MethodsWe conducted a meta‐analysis study of 24 fossil pollen records across south‐east Australian temperate ecosystems, applying an empirical turnover threshold to fossil records to identify periods of major turnover for the first time in Australia. We tested pollen richness as a proxy for vegetation richness to estimate past richness and applied this to fossil pollen data. The resulting reconstructions were compared to independent records of climate, sea‐level change and fire through generalized linear modelling.Results and conclusionOur results show changes in available moisture and sea level drove turnover and richness in most parts of SE Australia in the past, explaining up to c. 97% deviance. However, fire mainly drove turnover in Bass Strait. Our richness reconstructions also support the intermediate disturbance hypothesis, suggesting that high biodiversity was partially maintained by anthropogenic‐managed fire regimes. While temperature change is considered key to Northern Hemisphere palaeodiversity, past turnover and richness in Southern Hemisphere temperate ecosystems responded mainly to moisture availability and sea‐level change (considering its role in modulating regional oceanic climate).

Holocene heathland development in temperate oceanic Southern Hemisphere: Key drivers in a global context

“…We rarefied pollen data (excluding exotic pollen such as Pinus) in 'R' (R Core Team, 2020) using the 'rarefy' function in 'vegan' package (Oksanen et al, 2018), to estimate past diversity (palynological richness, a proxy for floristic richness in SE Australia, see Adeleye et al, 2020;Felde et al, 2016). Although differential pollen production may bias pollen-based estimates of floristic richness (Birks, Felde, Bjune, et al, 2016), taxonomic richness of pollen records has been shown to significantly reflect floristic richness of an area (Birks, Felde, Seddon, 2016), especially when a single climatic or floristic region is considered, as in our study (Adeleye et al, 2020;Connor et al, 2000;Meltsov et al, 2013).…”

A quantitative synthesis of Holocene vegetation change in Nigeria (Western Africa)

“…Fossil pollen data have been widely used in estimating changes in terrestrial vegetation through time (turnover), which is useful in assessing long-term stability and dynamics in ecosystems (e.g. Adeleye et al, 2020;Carcaillet et al, 2010;Connor et al, 2019;Seddon et al, 2015). In order to quantify Holocene vegetation change in Nigeria, we applied this approach to the 13 selected pollen records from Nigeria and nearby regions.…”

“…This was done to reduce the risk artefact introduction in turnover results (Adeleye et al, 2020;Connor et al, 2019;Seddon et al, 2015). Turnover analysis was conducted using the Squared Chord Distance (SCD) dissimilarity metric, with pairs of pollen samples randomly selected (50 replications) from each bin to calculate the average SCD between samples (Adeleye et al, 2020;Connor et al, 2019;Overpeck et al, 1985;Seddon et al, 2015). A Bayesian Change Point analysis was performed on SCD results to identify significant changes in turnover trends.…”

“…Quantitative studies of fossil pollen records have been used to assess past regional-and continental-scale vegetation and diversity changes in Europe, North America and Australia (e.g. Adeleye et al, 2020;Carcaillet et al, 2010;Connor et al, 2019;Giesecke et al, 2019), thanks to the large number of fossil and modern pollen records available in these regions via public repositories. Extensive studies of past vegetation, fire regimes and climate have also been carried out in many African sites (e.g.…”

Indigenous Fire-Managed Landscapes in Southeast Australia during the Holocene—New Insights from the Furneaux Group Islands, Bass Strait

“…Our results suggest Indigenous land use is mainly reflected in changes in RRFE across regions in the past. Given that fire frequency can shape vegetation structure and composition [92,93], recurrent Indigenous fire-usage likely created open/mosaic diverse vegetation [94], with reduced fuel loads in many parts of southeast Australia during the Holocene. Results for the FGI in particular suggest periods of reduced Indigenous burning allowed biomass accumulation, contributing to an increase in BB on the FGI between~9000 and 5000 years ago and the last~200 years (Figures 3 and 4).…”