Salix herbacea, as other arctic-alpine species, likely found a refuge from the Ice Age in the Apennines. As the climate changed around them, the trees survived in a fragmenting population. This fragmentation has genetic consequences.
For conservation of rare riparian species, avoiding an impact to hydrodynamic processes, such as water tables and flooding dynamics, may be just as critical as avoiding direct impacts on the number of plants.
Even though P. virginiana is a widespread species, fragmented populations experience significant reductions in fruit set and pollen limitation.