Repeat photography reveals long-term climate change impacts on sub-Antarctic tundra vegetation

Abstract

QUESTIONS: At high latitudes, anthropogenic climate change and invasive species threaten biodiversity, often with interacting effects. Climate change not only impacts native plant species directly by driving distribution and abundance of species, but indirectly through the influence on community dynamics and habitat suitability to invasive species. A key obstacle to quantifying vegetation change in the sub-Antarctic is the scarcity of cloud-free satellite imagery in a region with near-permanent cloud cover and lack of long-term plot data. In this paper, we aim to address the following QUESTIONS: how has vegetation in the sub-Antarctic changed between 1965 and 2020? What are the roles of climate change and invasive species in driving these changes? LOCATION: The study was conducted on Marion Island in the sub-Antarctica. METHODS: We quantified vegetation change by analysing repeat ground photography between 1965 and 2020, accompanied by an analysis of climate trends and invasive plant species’ cover changes over the same period. RESULTS: Total vegetation cover was significantly higher in 2020 than in 1965 in all habitats other than in the coastal saltspray habitat, indicating an increase in overall biomass on the island. The more responsive ‘generalist’ plant species have expanded across the island, whilst the more ‘specialised’ plant species have not significantly changed in cover, with the exception of the mire graminoids, which have declined. Marion Island has thus undergone significant vegetation change, showing a greening trend across most habitats in the last five decades. This has been accompanied by aridification, an increase in mean air temperature, changes in wind direction and wind speed, and an increase in invasive mouse populations. The three most widespread invasive plant species have also expanded their ranges, especially in areas influenced by animal disturbance and nutrient input. CONCLUSIONS: In congruence with research from Northern-hemisphere tundra and other islands in the sub-Antarctic, these results provide substantive empirical evidence for the interacting effects of climate change and invasive species on subAntarctic tundra vegetation, as has long been predicted.