Geomorphological disturbance is necessary for predicting fine-scale species distributions

Disturbances related to geomorphological processes are frequent, widespread and often intense at high latitudes and altitudes, affecting the fine-scale distribution of many plant species. While the inclusion of physical disturbances into models of species geographic ranges is widely recommended, no studies have yet tested the utility of field-quantified geomorphological disturbances for terrestrial species distribution modelling. Here we apply generalized additive models and boosted regression trees to examine if the explicit inclusion of terrestrial and fluvial geomorphological variables alters species distribution models for 154 vascular plant, bryophyte and lichen species in north European mountain tundra. The inclusion of these disturbances significantly improved both the explanatory and predictive power of distribution models, with consistent results for all three species groups. Spatial distribution predictions changed considerably for some species after the inclusion of disturbance variables, with fluvial disturbances generating strongly linear features for species influenced by erosion or sediment deposition. As a consequence, models incorporating geomorphological variables produced markedly more refined distribution maps than simpler models. Predictions of species distributions will thus benefit strongly from the inclusion of fine-scale geomorphological variables, particularly in areas of active earth surface processes, enabling more accurate forecasting of future species ranges under changing conditions.