Plant specialisation may limit climate‐induced vegetation change to within topographic and edaphic niches on a sub‐Antarctic island

Extreme changes in temperature, rainfall and wind regimes have been correlated with plant species range expansion upslope on sub-Antarctic islands. Ongoing climatic changes are expected to continue driving changes in species distributions globally, but niche specialisations may limit the capacity for range shifts. We hypothesised that non-climatic characteristics of ecological niches of vascular plant species could limit climate induced range shifts. We determined the altitudinal ranges of vascular plant species (n=13) on sub-Antarctic Marion Island and measured air temperature, topographic, foliar and soil properties along transects on geologically distinct substrates. Climatic and non-climatic associations were determined using multiple linear regression and boosted regression tree (BRT) analyses. The degree of niche specialisation was determined using outlying mean index analysis (OMI) within the range of species on the island. Several species (7 of 13) exhibited niche-specialisation. Correlation analysis revealed that edaphic properties including soil depth, loss on ignition, the principal component of most soil nutrients (Mg, Cl, K, Ca, Cu, Zn, P, S), Si, Mn and clay dominated the BRT prediction of overall plant cover. Although air temperature was correlated with plant cover in linear models, model simplification dropped temperature in both BRT and linear models. As a consequence, multiple determinants, including temperature, climate, topography and soils control the distribution of vascular plant species on this sub-Antarctic island.