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.

Climate change is increasing the weather persistence in the mid-latitudes, prolonging both dry and wet spells compared to historic averages. These newly emerging environmental conditions destabilize plant communities, but the role of species interactions in this process is unknown. Here, we tested how direct and higher-order interactions (HOIs) between species may change in synthesized grassland communities along an experimental gradient of increasing persistence in precipitation regimes. Our results indicate that species interactions (including HOIs) are an important determinant of plant performance under increasing weather persistence. Out of the 12 most parsimonious models predicting species productivity, 75 % contained significant direct interactions and 92 % significant HOIs. Inclusion of direct interactions or HOIs respectively tripled or quadrupled the explained variance of target species biomass compared to null models only including the precipitation treatment. Drought dominated the plant responses, with longer droughts increasing direct competition but also HOI-driven facilitation. Despite these counteracting changes, drought intensified net competition. Grasses were generally more involved in competitive interactions whereas legumes had a stronger affinity for facilitative interactions. Under longer drought, species affinity for nutrient rich or wet environments resulted in more negative direct interactions or HOIs, respectively. We conclude that higher-order interactions, crucially depending on species identity, only partially stabilize community dynamics under increasing weather persistence.

Climate change and other global change drivers threaten plant diversity in mountains worldwide. A widely documented response to such environmental modifications is for plant species to change their elevational ranges. Range shifts are often idiosyncratic and difficult to generalize, partly due to variation in sampling methods. There is thus a need for a standardized monitoring strategy that can be applied across mountain regions to assess distribution changes and community turnover of native and non-native plant species over space and time. Here, we present a conceptually intuitive and standardized protocol developed by the Mountain Invasion Research Network (MIREN) to systematically quantify global patterns of native and non-native species distributions along elevation gradients and shifts arising from interactive effects of climate change and human disturbance. Usually repeated every five years, surveys consist of 20 sample sites located at equal elevation increments along three replicate roads per sampling region. At each site, three plots extend from the side of a mountain road into surrounding natural vegetation. The protocol has been successfully used in 18 regions worldwide from 2007 to present. Analyses of one point in time already generated some salient results, and revealed region-specific elevational patterns of native plant species richness, but a globally consistent elevational decline in non-native species richness. Non-native plants were also more abundant directly adjacent to road edges, suggesting that disturbed roadsides serve as a vector for invasions into mountains. From the upcoming analyses of time series even more exciting results especially about range shifts can be expected. Implementing the protocol in more mountain regions globally would help to generate a more complete picture of how global change alters species distributions. This would inform conservation policy in mountain ecosystems, where some conservation policies remain poorly implemented.

A document by Charly Géron. Click on the document to view its contents.