not-yet-known not-yet-known not-yet-known unknown Roads in cold climate mountains are known to be important vectors in the introduction and spread of non-native plant species. In the same context, mycorrhizal fungi communities are also altered by roads with a known positive effect on arbuscular mycorrhizal (AM) fungi diversity and abundance in disturbed roadsides. However, to what degree these two effects of roads are intertwined and how they are evolving over time is not well understood. In this study we conducted repeated surveys of non-native plants and AM fungi between 2012 and 2022, in the northern Scandes mountains to investigate temporal changes and interactions between roads, mycorrhizal fungi, and non-native plants. We found that the upward spread of non-native plants and lateral spread away from the roadside into the natural vegetation were so far extremely limited, with only two out of 23 non-native species showing an increase in their upper elevational limit. However, non-native plant species cover did increase over the ten year period, especially at lower elevations, and non-native richness increased from 17 to 23 species. Likewise, we saw an increase in AM fungal abundance over the last four years along the roadsides at lower elevations. Furthermore, our results suggest that increases in non-native species are unlikely to be the driving cause of the observed increase in AM fungal abundance, as AM fungi colonization varied independently of non-native species cover dynamics.

The contemporary interaction of climate and disturbance drives vegetation composition and species distribution shifts, making their respective roles difficult to disentangle. This study describes the long-term ruderal plant species distributions along the ‘Rallarvägen’ in Abisko, subarctic Sweden. This trail currently serves as a hiking trail but was initially created as a construction road for a railroad from 1898 to 1903 and is 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 common along the Rallarvägen shortly after railroad construction in the early 20th century. Interestingly, many of these native and non-native ruderals with relatively high temperature affinity that were present in 1903 and 1913 have since disappeared and have not reappeared, despite the substantial increase in regional temperature in recent decades. In addition, the historical disturbances have 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 species richness – a process we term “Horizontal Directional Ecological Filtering”, in parallel to the established concept of “Directional Ecological Filtering” along elevational gradients. The historical record of ruderal plant species in the region, influenced by a century-old railroad construction, emphasizes the importance of knowing a system’s disturbance history for understanding current vegetation dynamics and anticipating its future in a changing climate.

Aim: We aimed to assess the impact at the global level of physical anthropogenic disturbances on the dominant mycorrhizal types in ecosystems and how this mechanism can potentially lead to lasting plant community changes. Location: Globally distributed study regions Time Period: 2007-2018 Taxa studied: Plants and mycorrhizal fungi Methods: We used a database of coordinated plant community surveys following mountain roads from 894 plots in 11 mountain regions across the globe in combination with a database of mycorrhizal-plant associations in order to estimate the relative abundance of mycorrhizal types in natural and disturbed environments. Results: Our findings show that roadside disturbance promotes the cover of plants associated with arbuscular mycorrhizal (AM) fungi. This effect is especially strong in colder mountain environments and in mountain regions where plant communities are dominated by ectomycorrhizal (EcM) or ericoid-mycorrhizal (ErM) associations. Furthermore, non-native plant species, which we confirmed to be mostly AM plants, are more successful in environments dominated by AM associations. Main Conclusions: These biogeographical patterns suggest that changes in mycorrhizal types are a crucial factor in the worldwide impact of anthropogenic disturbances on mountain ecosystems by promoting AM-dominated systems and potentially weakening biotic resistance against non-native species invasion. Restoration efforts in mountain ecosystems will have to contend with changes in the fundamental make-up of EcM- and ErM plant communities induced by roadside disturbance.