Next-Generation Invaders? Hotspots for Naturalised Sleeper Weeds in Australia under Future Climates

Abstract

Naturalised, but not yet invasive plants, pose a nascent threat to biodiversity. As climate regimes continue to change, it is likely that a new suite of invaders will emerge from the established pool of naturalised plants. Pre-emptive management of locations that may be most suitable for a large number of potentially invasive plants will help to target monitoring, and is vital for effective control. We used species distribution models (SDM) and invasion-hotspot analysis to determine where in Australia suitable habitat may occur for 292 naturalised plants. SDMs were built in MaxEnt using both climate and soil variables for current baseline conditions. Modelled relationships were projected onto two Representative Concentration Pathways for future climates (RCP 4.5 and 8.5), based on seven global climate models, for two time periods (2035, 2065). Model outputs for each of the 292 species were then aggregated into single ‘hotspot’ maps at two scales: continental, and for each of Australia’s 37 ecoregions. Across Australia, areas in the south-east and south-west corners of the continent were identified as potential hotspots for naturalised plants under current and future climates. These regions provided suitable habitat for 288 and 239 species respectively under baseline climates. The areal extent of the continental hotspot was projected to decrease by 8.8% under climates for 2035, and by a further 5.2% by 2065. A similar pattern of hotspot contraction under future climates was seen for the majority of ecoregions examined. However, two ecoregions - Tasmanian temperate forests and Australian Alps montane grasslands - showed increases in the areal extent of hotspots of >45% under climate scenarios for 2065. The alpine ecoregion also had an increase in the number of naturalised plant species with abiotically suitable habitat under future climate scenarios, indicating that this area may be particularly vulnerable to future incursions by naturalised plants.

Risk hotspots for terrestrial plant invaders under climate change at the global scale

“…However, the plant diversity of these CE ecoregions in Australia and New Zealand may be threatened by climate change and the resulting plant invasion (Fig. 1;O'Donnell et al 2012;Duursma et al 2013;Beaumont et al 2014;Bellard et al 2014). Furthermore, herbaceous and woody TPIs had a high potential to expand in the CE ecoregions of South America, Europe, Madagascar and northern and southern Africa (Richardson and Rejmánek 2011;Beaumont et al 2014;Bellard et al 2014;Donaldson et al 2014).…”

“…1; Eskelinen and Harrison 2014;Kremer 2014;Turner et al 2014). Therefore, we should guard against the entry of TPIs into these VU and RI ecoregions to maximize their capacity to prevent and control plant invasion (Foxcroft et al 2011;O'Donnell et al 2012;Duursma et al 2013). The challenge for biological conservationists is to minimize the opportunities for herbaceous TPIs to be introduced into new areas under climate change .…”

A tool to assess potential for alien plant establishment and expansion under climate change

“…These two epochs were chosen as they offer realistic timeframes for planning long-term management goals for alien plant species. The seven GCMs were: ukmohadcm3, mpi-echam5, gfdl-cm20, mricgcm232A, csiro-mk30, ukmo-hadgem1, and ccsr-miroc32med (see Duursma et al, 2013 for further details on the modelling including model calibration and assessment, as well as species' selection). Interactive maps of the projected conditions in each GCM and RCP are available from http://climascope.tyndall.ac.uk/ Map/Details?mapid¼39946&overlayid¼0.…”

“…Given that invasive alien plants may have the potential to respond to changing environmental conditions more rapidly than native species (Willis et al, 2010;Bradley et al, 2012), the potential for human induced climate change to affect the distribution, physiology and management of invasive alien plant species has emerged as a major area for ecological research and as a significant management concern (Dukes and Mooney, 1999;Hellmann et al, 2008). However, relatively few studies have focussed on the potential for future climate to facilitate new invasions by enabling naturalised but presently non-invasive (sensu Richardson et al, 2000) alien plant species to increase in abundance and invade new areas (but see Duursma et al, 2013). As the climate continues to change under human influences, it is increasingly likely that a new suite of alien plant invaders will emerge in different regions, many of which currently reside in the regional pool of naturalised alien plants (Richardson and Py sek, 2012).…”

“…Outputs from species distribution modelling for alien plants that incorporate climate change scenarios (e.g. Thuiller et al, 2007;Beaumont et al, 2009;O'Donnell et al, 2012;Bellard et al, 2013;Duursma et al, 2013), in association with spatial data on current occurrence, could be incorporated into the WRA and WRM processes to assess both the current and future risk as well as the relative change in the risk rating between current and future conditions. The Australian climate is already changing and is expected to continue to alter in coming decades.…”