Invasive ectomycorrhizal fungi can disperse in the absence of their known vectors

Positive interactions between non-native species can accelerate their invasion rate and exacerbate their impacts. This has been shown for non-native mammals that disperse invasive ectomycorrhizal fungi (EMF), in turn facilitating the invasion of non-native tree species. Mammal-mediated dispersion is assumed to be the main mechanism of EMF long distance dispersal, being particularly critical for truffle-like EMF species. We asked whether the absence of non-native mammals is an obstacle for Pinaceae invasion given the lack of invasive EMF being dispersed. We studied EMF species colonization and Pseudotsuga menziesii (Douglas-fir) trees’ growth in soil from mainland sites where non-native mammals are highly abundant, and lake islets in which they have been historically absent. Contrary to what we expected, we found invasive EMF, including truffle-like species, in sites where invasive mammals have been historically absent. Douglas-fir trees grew equally well and had the same EMF colonization in soil from mainland and islets. Alternative mechanisms of EMF dispersal, such as saltation, bird dispersal, or human dispersal, can be involved in their arrival to native stands. The presence of invasive EMF makes native sites vulnerable to Pinaceae invasion, even in the absence of mammalian dispersers.