The invaded range of the tree fern Sphaeropteris cooperi is predicted to shrink in two southern hemisphere biodiversity hotspots

• Climate change is expected to affect alien plants. • Garden Route (South Africa) and Reunion Island are biodiversity hotspots. • The Australian tree fern Sphaeropteris cooperi is invasive in these regions. • Niche dynamics showed little overlap between current invaded and native ranges. • However, the range of S. cooperi is likely to shrink under future climate change. Biological invasions are increasing globally, with species demonstrating differing responses to climate change in their native and invaded ranges. Investigating how alien species respond to climate change is important for planning management interventions. This study considered how the distribution of Sphaeropteris cooperi (Hook. ex F.Muell.) R.M.Tryon, a widely cultivated invasive tree fern with a broad climatic tolerance, could alter under climate change in two invaded southern hemisphere biodiversity hotspots: South Africa's Garden Route and La Réunion Island, Mascarene Archipelago. To determine the distributional changes of S. cooperi under future climate change scenarios, its niche dynamics were assessed in its native range (Australia) and two invaded southern hemisphere ranges using Schoener's statistic for niche overlap and principal component analyses. An ensemble modelling approach was used to predict the potential distribution of S. cooperi under future (2041–2070 and 2071–2100) carbon emission scenarios (SSP1-2.6 and SSP 5–8.5) using five global climate models. The results suggest that S. cooperi demonstrates some climatic niche overlap (17.6 %) between the Garden Route and its native range (Australia), but less overlap (3.7 %) was found between La Réunion Island and Australia. On La Réunion Island, little niche overlap together with niche expansion suggests that S. cooperi occupies niches not occupied in its native range, and that niche conservatism does not hold true for this location. Thus, under current climatic conditions, future spread may be anticipated in both the Garden Route and La Réunion Island. However, climatic conditions are shifting making it important to consider climate change when predicting how the range of this invader may change in the future. Species distribution models revealed that for both biodiversity hotspots, regardless of climatic scenario or the time frame considered, the range of S. cooperi is predicted to shrink, although the degree of decline is expected to vary with time and climate scenario.