Climate Change and the Potential Global Distribution of Serrated Tussock (Nassella trichotoma)

We used the process-oriented niche model CLIMEX to estimate the potential global distribution of serrated tussock under projected future climates. Serrated tussock is a drought-tolerant, wind- and human-dispersed grass of South American origin that has invaded pastures in Australia, Europe, New Zealand, and South Africa. The likely effect of climate change on its potential global distribution was assessed by applying six climate-change scenarios to a previously developed model. The projections of climatic suitability under the current climate revealed considerable scope for spread, with the most suitable areas occurring adjacent to existing naturalized populations in Australia, New Zealand, and Western Europe. Under future climates, projected to the 2080s, the land area suitable for serrated tussock contracts globally between 20 and 27%. Changes in projected potential area under the six scenarios were very similar in all geographical regions apart from North America and New Zealand, where the projections range from little change or contraction under the National Center for Atmospheric Research (NCAR) and Centre for Climate Research (MIROC) global climate models (GCMs) to expansion under the Commonwealth Scientific and Industrial Research Organisation (CSIRO) GCM. Elsewhere, contractions occur in Australia, Asia, South America, and Africa under all six future climate scenarios. By contrast, for Europe, the area climatically suitable for serrated tussock increases under all six scenarios (average increase 47%) through expansions into eastern European countries that are currently unsuitable and through increases in the suitable area in England, Ireland, and Denmark. Since pastoralism is a dominant land use in these regions of Europe, a prudent biosecurity strategy would be to contain the nascent foci of serrated tussock in southern France, along the west coast of Italy, and in the United Kingdom. This strategy could consist of a set of policies to limit human-assisted dispersal of the species' seeds and to reduce wind-borne spread through cultural control of the plant.