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.