Invasive alien species (IAS) are a recognised threat to biodiversity and ecosystem services. With increasing tourism and projected 21st century climate changes across the mid- to high-latitudes of the southern hemisphere, subantarctic islands are potentially highly vulnerable to IAS, but suffer from a dearth of baseline monitoring. Here we report tree-ring measurements from a lone exotic Sitka spruce (Picea sitchensis (Bong.) Carr) on subantarctic Campbell Island to determine past growth rates and likely future response to climate changes.
Mid to late 20th century expansion of Dracophyllum scrub into tussock grassland on subantarctic Campbell Island has been attributed to the collective effects of global warming, cessation of farming in 1931, and continued grazing by feral sheep. To determine the importance of these, we dated the timing of scrub expansion by aging 241 Dracophyllum plants in 17 plots chosen to sample the range of environments this shrub/ small tree occupies on Campbell Island.
Growth of Avena sativa L. and Agrostis tenuis Sibth was measured on peat and mineral soils from sites on Campbell Island in the New Zealand subantarctic. For the peat soils, growth was strongly positively correlated with both pH and Mg levels and less strongly with Ca and Na. With the inclusion of the mineral soil data, only the fit between growth and Ca levels was significant.