Add-ons to the standardized protocol
In addition to long-term monitoring of plant communities, the MIREN survey design is well suited for additional projects (‘add-on’ projects) that test more detailed or region-specific questions about the drivers of plant species redistributions. For example, soil temperatures have been recorded with a high temporal resolution for a year or longer in several MIREN regions to document how disturbance along roadsides affects microclimate, including consequences for species redistributions (for the first regional results see Lembrechts et al., 2019). Plant functional traits have additionally been collected for species in Tenerife, Canary Islands, to assess contrasting patterns of intraspecific trait variability of native and non-native species and the change of community mean traits and functional diversity with elevation (Kühn et al., 2020). Another add-on project has focused on soil chemical properties and mycorrhization of native and non-native species in the mountains of Norway (Clavel et al., 2021), and survey plots have also been used to assess the distribution of plant pathogens (Phytophthora species) in Australia (Khaliq, 2019). Once participants begin contributing data to the MIREN global road survey database, they can suggest add-on studies to apply across all regions that go beyond the existing scope of the survey protocol – as long as it is based on a standardized protocol that is fast, simple and low cost to implement by collaborators. To maximize participation and to discuss new proposals, data quality and complementarity, ideas for add-on projects should be developed together with the MIREN steering committee.