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Wind disturbance and climate change increase the risk of major European spruce bark beetle (ESBB) outbreaks. In order to understand the drivers behind the spread, we used a combination of the Random Forest algorithm and logistic regression mixed modelling to generate robust results. We analysed tree and stand characteristics, level of infestation, and nearness to eight major blowdown areas from a summer storm in 2016 in two conservation areas in south-eastern Estonia, Karula National Park and Otepää Nature Park. The two areas differ in forest site quality (tree growth conditions) and topographical features, spatial distribution of protected and managed patches, and management history, and were therefore analysed separately. Data collection, in 2020, was based on a network of transect-based circular plots surrounding the blowdowns. By the time of the inventory, four years after the storm, the wind-induced spread had largely come to a halt, with only a few freshly infested Norway spruce trees recorded. The study revealed that, besides the often-mentioned factors tree diameter and share of Norway spruce, intensity of initial infestation in the first 10 m outside the storm area was positively correlated with ESBB infestation probability in the surrounding forest in Karula, where forest cover is more contiguous and under more severe management restrictions. Conversely, distance to any type of open area and tree species diversity decreased infestation probability in Otepää. Furthermore, trees in patches with average site quality class had a significantly higher infestation risk, compared to those in a low site quality class. Distance to the storm area was not a driver behind the outbreak, and neither did the number of infested trees in the initial storm area affect surrounding stands, at this stage. Differences in significance of factors for infestation probability between the two conservation areas were considerable, which hints at even higher complexity of Norway spruce vigour-bark beetle-climate relations at an international level. Since storm area infestation levels and vicinity did not directly affect spatial distribution of ESBB, but infestation levels in our study were nonetheless high, this suggests that research should focus on early detection and prevention strategies at the landscape scale. In that respect, further investigation is required into the role of tree species diversity, stand structural heterogeneity and growth conditions in reducing outbreak risk and favouring a fast recovery from disturbances. • Climate change facilitates outbreaks of European spruce bark beetle in several ways. • GLM(M) and RF algorithm revealed post-storm bark beetle outbreak drivers. • Norway spruce tree dbh and stand basal area remain most important. • Site quality class, infestations around storm gap indicate risks of further spread. • Species diversity and stand structure can enhance stand resilience and response diversity. [ABSTRACT FROM AUTHOR]

Climate change accompanied by altered natural disturbance regimes threatens the resilience of boreal and hemiboreal forests. Bryophytes, an important part of plant biomass and diversity, fulfill numerous important functions in forests, thus markedly contributing to the resilience of these ecosystems. We studied abundance, richness, diversity and community composition of bryophyte species 20–21 years after wind disturbance in moderately damaged, heavily damaged and heavily damaged and subsequently salvage-logged stands; overmature forest stands with similar tree species composition were included in the study as a reference group. The community characteristics were linked with treatment and accompanying environmental variables. Altogether, 108 bryophyte taxa (81 mosses and 27 liverworts) were identified in study plots. We found that bryophytes responded to windthrow severity level and salvage logging in terms of species richness, diversity, and composition; diversity of microhabitats was the most important environmental variable explaining the variation in diversity metrics. Besides exhibiting greater overall species richness, uncleared wind-disturbed plots contained more bryophyte species with high conservational value as well, compared to salvage-logged and control plots. The largest number of bryophyte taxa was associated with deadwood substrates. Ordination analysis further emphasized the importance of deadwood substrate for liverworts. In order to fulfill the objective of biodiversity conservation, wind-disturbed forests should be left to recover naturally, to ensure a favorable status of all naturally occurring species and to improve the status of endangered and rare species. Retaining a proportion of surviving and/or wind-damaged trees while salvaging might also alleviate the unfavorable environmental conditions for bryophyte species while "lifeboating" some species through the following successional stages. • Uncleared wind-disturbed stands host highly diverse bryophyte communities. • Bryophytes responded strongly to variation in substrate diversity. • Abundance of deadwood substrate is especially important for liverworts. • Salvaged and control plots had similar mean richness, but distinct compositions. • Retention of deadwood and live tree legacies during salvaging is recommended. [ABSTRACT FROM AUTHOR]

• Wind damage severity and salvage logging affected understory species composition. • Salvaged stands had greatest canopy openness and lowest microsite richness. • Salvage logging did not reduce species richness nor diversity. • Moderately disturbed stands had highest variation regarding species composition. • Resilience after wind disturbance was faster in non-salvaged areas. The herbaceous understory is a key component of forest biodiversity. Moreover, it holds the capability to alter the dynamics and composition of the overstory. Severe wind disturbance changes the conditions in a forest ecosystem radically, causing alteration of understory characteristics as well. In this paper we analyze impacts of different storm damage levels and post-storm management on understory vegetation richness, diversity and composition in mixed spruce–hardwood forest stands located in hemiboreal Estonia. We examined understory vegetation in moderately damaged (n = 4), heavily damaged (n = 4) and post-storm salvage-logged stands (n = 4) 19–20 years after storm disturbance. Mature mixed spruce–hardwood forests were included as a reference group (n = 4). Study plots were also assessed regarding canopy openness, richness of microhabitats and coverage of woody species. A total of 98 herbaceous and 2 dwarf shrub taxa were found on 208 vegetation quadrats (1 m2 square each). Total coverage of the herb layer and species richness were greatest at salvage-logged plots when compared to other treatments. However, we found no significant effect of treatment on diversity (Shannon's H') nor evenness (Pielou's index) of herbaceous species. Our results indicate that approximately-two decades after wind disturbance, the understory communities differ from each other as a response to different storm damage levels and post-storm management. Compared to control plots, salvage-logged plots demonstrated greatest contrast regarding species composition. Salvage-logged plots had greatest light levels, but lowest estimates for microsite richness and woody species coverage. Moderately damaged plots demonstrated greatest within-group variation regarding light conditions and species composition. Our findings suggest that salvage logging after severe wind disturbance might induce delayed succession toward a closed canopy due to intense understory competition and lack of opportunity-providing microhabitats for tree regeneration. [ABSTRACT FROM AUTHOR]

Abstract: The regeneration patterns in wind-damaged areas are largely influenced by damage severity and varied microrelief. Regeneration was studied in Picea abies dominated stands with total and partial canopy destruction and in harvested areas in Myrtillus and Filipendula site types in Estonia 4–5 years after a storm, examining particularly the influence of microsites on regeneration establishment and growth. The seedling densities of regeneration were highest in harvested plots compared to heavily and moderately damaged areas. The seedling densities were lowest on mounds and highest in pits among microsites in heavily and moderately damaged sites. The most common tree species regenerating in pits were birch (Betula pendula Roth., Betula pubescens Ehrh.) and alder (Alnus glutinosa (L.) J. Gaertn.). Birch and alder seedlings that survived to 2005 were taller in 2004 than those that died. Trees were also taller with lower regeneration density. Spruces (Picea abies (L.) Karst.) did not prefer any particular microsite, but those growing in pits were smaller than those in other microsites. The plots harvested regenerate more rapidly with hardwood species. [Copyright &y& Elsevier]