Mountain Roads Across the Globe Significantly Alter Local Soil Thermal Microclimates

Aim: Mountain roads host plant communities that differ strongly from the adjacent natural vegetation. Besides the effect of propagule pressure, altered disturbance and soil processes, one of the reasons given for the strong influence of mountain roads on species distributions is a significantly altered soil thermal microclimate in the roadside compared to the adjacent vegetation, as a direct consequence of road disturbance. However, the thermal microclimatic differences between roadside and natural vegetation have rarely been quantified, particularly across large spatial extents. This study provides the first global quantification of roadside soil temperature patterns along elevational gradients. Location: Mountain roads in eight mountain regions from the Mountain Invasion Research Network (MIREN): Argentina, Chile, Czech Republic, Norway, Spain (Tenerife and La Palma), Switzerland, and the USA. Methods: In this study, we analysed in situ measured topsoil temperatures (< 10 cm) and forest cover of roadsides and adjacent natural vegetation plots, in a systematically paired design. Results: Across most regions, roadside soils exhibited consistently warmer maxima (3.62°C ± 2.61°C) and colder minima (1.39°C ± 1.40°C) than soils in adjacent vegetation. Although temperature distributions between roadside and natural habitats largely overlapped, these systematic shifts indicate increased thermal variability and higher frost risk in roadside environments. Main Conclusions: Roadsides create distinct thermal microhabitats even within heterogeneous mountain landscapes. These altered temperature regimes, particularly when combined with vegetation structure and other environmental factors such as soil moisture, may influence plant performance and distribution. Our findings highlight the ecological relevance of thermal microclimates in understanding biodiversity patterns along mountain roads.