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Trees that survive disturbances are important biological legacies that facilitate forests' recovery and enhance their structural and species diversity, substantially contributing to the resilience of these ecosystems. The dynamic pattern of legacy syndromes sets the understudied aspects of survivors of wind disturbance into focus. Several factors at tree, stand, and landscape scales alter the susceptibility of the remnant trees, and affect their potential to recover and survive subsequent disturbances. The characteristics of the survivors interact with direct stress and mortality drivers such as changed environmental conditions and pressure by pests and pathogens. Climate change further enhances the post-storm vulnerability of the remaining stand. This literature review analyzes the impact of disturbance parameters (e.g., severity, seasonal timing) and characteristics of the affected forest (e.g., tree species composition, successional stage of a forest stand) on the conditions of survivors through post-windthrow stand development. We attempted to reveal the main agents and processes driving the fate of remnant trees and linked delayed mortality patterns to the main standscale wind disturbance regimes in Eurasian and North American boreal and temperate forests: (1) stand-replacing, (2) partially stand-replacing, and (3) finescale gap disturbance. We found that after stand-replacing wind disturbance, the spatial location of the remaining trees largely determines their onward fate, whereas these survivors are generally more susceptible to subsequent mortality compared to trees that survived less severe events. After partially stand-replacing wind disturbance, the structure of the remnant stand as well as characteristics of the individual remnant trees (e.g., species, age, size) largely determine their survival probability. Following a fine-scale gap disturbance, the trees at the gap edge are more likely to die, compared to the trees situated in the stand interior, but the mortality-causing processes usually operate on a longer time scale. Our findings contribute to the current knowledge on postwindthrow stand development and offer insights into temporal stability of these increasingly important biological legacies. [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]

In the Baltic States region, anthropogenic disturbances at different temporal and spatial scales mostly determine dynamics and development phases of forest ecosystems. We reviewed the state and condition of hemiboreal forests of the Baltic States region and analyzed species composition of recently established and permanent forest (PF). Agricultural deforestation and spontaneous or artificial conversion back to forest is a scenario leading to ecosystems designated as recent forest (RF, age up to two hundred years). Permanent forest (PF) was defined as areas with no records of agricultural activity during the last 200 yr, including mostly forests managed by traditional even-aged (clear-cut) silviculture and salvage after natural disturbances. We hypothesized that RF would have distinctive composition, with higher dominance by hardwoods (e.g., aspen and birch), compared to PF. Ordination revealed divergence in the RF stands; about half had the hypothesized composition distinct from PF, with a tight cluster of stands in the part of the ordination space with high hardwood dominance, while the remaining RF stands were scattered throughout the ordination space occupied by PF with highly variable species composition. Planting of conifers, variability in site quality, and variability in spatial proximity to PF with relatively natural ecosystem legacies likely explained the variable compositions of this latter group of RF. We positioned the observations of RF in a classic quantification of site type conditions (based on Estonian forest vegetation survey previously carried out by Lõhmus), which indicated that RF was more likely to occur on areas of higher soil fertility (in ordination space). Climatic and anthropogenic changes to RF create complex dynamic trends that are difficult to project into the future. Further research in tracing land use changes (using pollen analysis and documented evidence) should be utilized to refine the conceptual framework of ecosystem legacy and memory. Occurrence and frequency of deforestation and its characteristics as a novel disturbance regime are of particular interest. [ABSTRACT FROM AUTHOR]

The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms “material legacy” (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and “information legacy” (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above- and belowground, and biotic and abiotic categories, and information legacies with above- and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by “legacy syndromes” that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscape, depending on how the legacies in each syndrome affect ecological memory. [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]

Several storms have damaged Estonian forests in recent years. Individual tree properties such as diameter at breast height (dbh) and tree height affect the type of damage (stem breakage or uprooting) and influence the formation of postdisturbance forest structure. The aim of this study was to analyse how the risk of uprooting and stem breakage varied with respect to tree diameter, height, species and soil conditions. The data were collected from plots located in storm-damaged forests in eastern Estonia. The probability of uprooting increased with increasing diameter for Norway spruce, European aspen and birch. Black alders with large stem diameter usually suffered stem breakage. A high proportion of stem breakage also occurred among small Norway spruce in the understorey, probably damaged by falling canopy trees. Soil conditions influenced the ratio between uprooting and stem breakage of Norway spruce, the ratio being much higher on gley soils than on podzolic soils. The root plate size of Norway spruce was only slightly correlated with dbh, tree height and volume. [ABSTRACT FROM AUTHOR]

In this review and synthesis paper, we review the resilience of secondary forests to climate change through the lenses of ecosystem legacies and landscape diversity. Ecosystem legacy of secondary forests was categorized as continuous forest, non-continuous forest, reassembled after conversion to other land uses, and novel reassembled forests of non-native species. Landscape diversity, including landforms that create varied local climatic and soil conditions, can buffer changing climate to some extent by allowing species from warmer climates to exist on warm microsites, while also providing refugial locations for species that grow in cool climates. We present five frames that allow forest managers to visualize a trajectory of change in the context of projected regional climate change, which are: Frame 1 (persistence), keep the same dominant tree species with little change; Frame 2 (moderate change), keep the same tree species with large changes in relative abundance; Frame 3 (forest biome change), major turnover in dominant tree species to a different forest biome; Frame 4 (forest loss), change from a forest to a non-forest biome; and Frame 5 (planted novel ecosystem), establish a novel ecosystem to maintain forest. These frames interact with ecosystem legacies and landscape diversity to determine levels of ecosystem resilience in a changing climate. Although forest readiness to adapt to Frame 1 and 2 scenarios, which would occur with reduced greenhouse gas emissions, is high, a business as usual climate change scenario would likely overwhelm the capacity of ecosystem legacies to buffer forest response, so that many forests would change to warmer forest biomes or non-forested biomes. Furthermore, the interactions among frames, legacies, and landscape diversity influence the transient dynamics of forest change; only Frame 1 leads to stable endpoints, while the other frames would have transient dynamics of change for the remainder of the 21st century. [ABSTRACT FROM AUTHOR]