Extensive clonal reproduction drives liana proliferation following forest fragmentation

Large-scale anthropogenic disturbances, including forest fragmentation, are increasing worldwide. Lianas often proliferate after such events, yet the mechanisms underlying these increases-- particularly their demographic sources--remain unclear. Here, we quantify the extent to which clonal expansion, rather than seed recruitment, accounts for post-disturbance proliferation of Wisteria floribunda (Fabaceae), the dominant liana in the study area. In a 21.6-ha fragmented forest landscape in Japan, we divided the study area into 20 x 20 m grid cells and randomly sampled up to one W. floribunda ramet per cell, and genotyped 273 ramets at 10 microsatellite loci to assign ramets to genets and quantify genet areas and their spatial distribution. Genotyping revealed a substantial contribution of extensive clonal reproduction: 94% of ramets were clonal, resolving into 47 genets. These genets collectively occupied 58% of the 21.6-ha study area, and expansion produced extensive genets--the largest covered 9.5 ha. Several genets spanned multiple forest patches; three multi-patch genets accounted for 43% of all ramets, including one spanning seven patches. Multi-patch genets were concentrated within areas covered by forests prior to fragmentation (odds ratio = 6.83; P < 0.001). These observations indicate that clonal expansion accounts for most post-disturbance proliferation, that some genets attain landscape-scale coverage in a fragmented forest, and that part of this dominance likely reflects legacy effects of genets established prior to fragmentation. Explicitly accounting for clonal contributions and genet spatial scale is critical for accurate prediction of disturbance-driven liana dynamics.