Salvage-Logging after Windstorm Leads to Structural and Functional Homogenization of Understory Layer and Delayed Spruce Tree Recovery in Tatra Mts., Slovakia

Stand-replacing disturbance and post-disturbance salvage-logging influence forest succession in different ways; however, limited knowledge regarding how salvage-logging affects vegetation patterns compared to natural development of forest ecosystems is still lacking. In this study, we described the diversity pattern of understory vegetation and tree regeneration in mountain spruce forest of Tatra Mountains, northern Slovakia, where a high severity windstorm affecting over 10,000 ha occurred in 2004. The area was consequently subjected to salvage-logging. We asked how the species composition, vegetation diversity, and its spatial heterogeneity were modified by severe salvage-logging. Vascular plants, deadwood coverage, and tree species densities were monitored on non-intervention (NI; n = 108) and salvage-logged (SL; n = 95) experimental plots (spatially nested design, sample plot area 3.14 m(2)) six and seven years after disturbance, respectively. The NI sites were structurally more diverse with post-windstorms legacies such as deadwood and pit and mound topography being recorded. The NI plots contained more late-successional plant and moss species that are commonly found in the pre-disturbance forest. The NI plots were also more diverse in terms of alpha- and beta-diversity with abundant natural regeneration of Norway spruce (Picea abies (L.) Karst). The structure of SL site was more homogeneous and its species composition shifted towards being dominated by grasses, although the site accommodated a higher number of plant species due to newly established pioneer plant- and tree species. The retreat of late-successional species in favour of grasses can lead to structural and functional homogenization of habitat and to delayed succession towards establishment of spruce forest. We conclude that the removal of wind-disturbance legacies significantly diverts natural successional pathways. We recommend avoiding salvage-logging in protected areas since large-scale application of salvage-logging reduces beta-diversity of the landscape.