Does salvage logging erase a key physical legacy of a tornado blowdown? A case study of tree tip-up mounds

While large-scale wind disturbances are rare, they are nonetheless powerful drivers of plant community reassembly in temperate forests worldwide. These disturbances cause the formation of tree tip-up mounds that serve as regeneration niches, but the time scale at which novel plant communities develop on mounds is unknown. Moreover, salvage logging can cause mounds to "tip back down" and could therefore erase these microsites. Here, we test three hypotheses with a replicated field experiment: (1) novel plant communities rapidly form on tip-up mounds; (2) salvaging erases these microsites; and (3) "tipped-down" tip-up mounds are novel intermediate microsites. We salvaged a random half of four 3-6 ha blowdowns created by an F1 tornado, measured 249 mounds, and censused the vegetation on 48 mounds and 48 reference plots. Plant communities on mounds had two to three fewer species, 50% less cover, and lower diversity than reference communities. However, salvaging caused modest increases in species richness and diversity on mounds and caused 40% of mounds to tip back down. The physical characteristics and vegetation of these tipped-down "inclined mounds" were more similar to vertical mounds than to reference plots. Our results suggest that salvaging may increase microsite heterogeneity across the landscape by creating novel intermediate mounds.