Historic disturbance events may overrule climatic factors as drivers of ruderal species distributions in the Scandinavian mountains

The contemporary interaction of climate and land use change drives vegetation composition and species distribution shifts, making their respective roles difficult to disentangle. In this study, we investigated long-term ruderal plant species distributions along the ‘Rallarvägen’ trail in Abisko, subarctic Sweden – a trail established for railroad construction in 1903 and paralleled by the E10 Highway (since 1982). Using vegetation and climate data from 1903, 1913, 1983, and 2021, we found that warm-adapted ruderal plant species were already common along the Rallarvägen at its initial creation at the start of the 20th century. Interestingly, however, many of these native and non-native ruderals with relatively high temperature affinity that were present in 1903 and 1913, disappeared since then and did not return, despite the substantial rise in temperature in the region over the last decades. The historical disturbances also had long-lasting effects on the current spatial distribution of the ruderal vegetation. Most ruderals still reside close to the railroad tracks and are progressively filtered out with increasing distance from anthropogenically disturbed introductory points, such as train stations, where they peak in richness – a process we coined Horizontal Directional Ecological Filtering, in parallel to the established concept of Directional Ecological Filtering along elevational gradients. We conclude that it is important to know the disturbance history of a system to get a good understanding of the long-term dynamics in the vegetation community, and thus its possible future in a changing climate.