Natural disturbance regimes as a guide for sustainable forest management in Europe

Dette er den aksepterte versjonen av en artikkel publisert i Ecological Applications. Den blir tilgjengelig fra og med 28.03.2023 etter en embargoperiode på 12 måneder. Du finner den publiserte artikkelen her: https://doi.org/10.1002/eap.2596. / This is the postprint version of the article published in Ecological Applications. It will be available 28.03.2023 after an embargo period of 12 months.You can find the published article here: https://doi.org/10.1002/eap.2596.In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over-regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a “Comparability Index” (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine-dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed toward even-aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven-aged silvicultural systems and key natural disturbance attributes. Even so, uneven-aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe’s portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating NDS with more conventional practices.acceptedVersio

Evaluating structural and compositional canopy characteristics to predict the light‐demand signature of the forest understorey in mixed, semi‐natural temperate forests

Questions: Light availability at the forest floor affects many forest ecosystem processes, and is often quantified indirectly through easy‐to‐measure stand characteristics. We investigated how three such characteristics, basal area, canopy cover and canopy closure, were related to each other in structurally complex mixed forests. We also asked how well they can predict the light‐demand signature of the forest understorey (estimated as the mean Ellenberg indicator value for light [“EIVLIGHT”] and the proportion of “forest specialists” [“%FS”] within the plots). Furthermore, we asked whether accounting for the shade‐casting ability of individual canopy species could improve predictions of EIVLIGHT and %FS. Location: A total of 192 study plots from nineteen temperate forest regions across Europe. Methods: In each plot, we measured stand basal area (all stems >7.5 cm diameter), canopy closure (with a densiometer) and visually estimated the percentage cover of all plant species in the herb (7 m). We used linear mixed‐effect models to assess the relationships between basal area, canopy cover and canopy closure. We performed model comparisons, based on R2 and the Akaike Information Criterion (AIC), to assess which stand characteristics can predict EIVLIGHT and %FS best, and to assess whether canopy shade‐casting ability can significantly improve model fit. Results: Canopy closure and cover were weakly related to each other, but showed no relation with basal area. For both EIVLIGHT and %FS, canopy cover was the best predictor. Including the share of high‐shade‐casting species in both the basal‐area and cover models improved the model fit for EIVLIGHT, but not for %FS. Conclusions: The typically expected relationships between basal area, canopy cover and canopy closure were weak or even absent in structurally complex mixed forests. In these forests, easy‐to‐measure structural canopy characteristics were poor predictors of the understorey light‐demand signature, but accounting for compositional characteristics could improve predictions

Arbuscular mycorrhizal colonization in roots of sand dune plants in relation to soil factors

Abstract Seacoast plant communities represent primary successions characterized by a harsh environment in which mycorrhizal symbioses are known to be important for plant survival and growth. The study was carried in two grey dune areas (Užava and Pāvilosta) on the western coast of Latvia by the Baltic Sea. We examined how root colonization and abundance of arbuscular mycorrhiza differed along a primary dune succession from an early successional primary dune to an overgrowing grey dune, in relation to soil factors. We hypothesized that plant species growing on soil with a poorly developed soil horizon and low C, P and N concentration would have a higher extent of arbuscular mycorrhiza colonization. We also tested the relationship of soil factors and fungal abundance in roots within specific plant species. In a total of 93 plots among 5 habitats, we determined soil carbon, phosphorus and nitrogen concentrations and sampled roots of dominant plants for determination of arbuscular mycorrhizal (vesicules and hyphae) frequency, abundance of arbuscular mycorrhizal vesicules and hyphae, and abundance of arbuscules. The results showed that extent of mycorrhizal colonization was related to soil development, being more important in the most nutrient poor habitats, compared to grassland habitats. However, slight increases in P and N concentration were associated in increased mycorrhizal colonization in early successional stages and disturbed habitats

Estimates of Tree Canopy Closure and Basal Area as Proxies for Tree Crown Volume at a Stand Scale

Research Highlights: Studies on tree canopy dwelling species often require simple proxies of tree canopy volume estimated at a stand level. These include allometrically related tree crown parameters such as crown area and basal area, and canopy cover. Background and Objectives: In monoculture Scot’s pine and mixed pine/Norway spruce forest, we aimed to test the relationships between tree diameter at breast height (DBH) and tree crown volume at a tree level and between densitometer canopy closure estimates and tree crown volume at a stand level. Materials and Methods: The study was carried out in eastern Latvia (hemiboreal zone) in monoculture pine and mixed coniferous stands. On a subset of trees in 22 forest stands (88 100 m2 plots), we determined the best regression model that described the relationship between tree DBH and crown volume for spruce and pine. Tree crown volume at a stand level was determined from the individual tree volume estimates calculated from these regression models. On a stand level, we also calculated regression models for densitometer closure estimates versus total crown volume for pine and mixed stands. Results: Linear mixed effects models showed significant relationships between DBH and crown volume for pine (R2 = 0.63) and spruce (R2 = 0.40), indicating that basal area could be used as a predictor of crown volume at a stand level. Variance explained by a regression model of canopy closure versus tree crown volume at a stand level was R2 = 0.52. Conclusions: Tree basal area and crown closure can be used as proxies of tree crown volume at a stand scale in monoculture stands. In mixed stands estimates of crown volume based on basal area need to be calculated separately for each tree species, while canopy closure will provide an estimate of total crown volume

Tree Species Establishment in Urban Forest in Relation to Vegetation Composition, Tree Canopy Gap Area and Soil Factors

The study of density and growth of pine, birch and oak seedlings and saplings in canopy gaps in the urban boreal forest in Riga, Latvia, indicates that natural regeneration can increase diversity in small gaps caused by tree mortality, and can ensure conversion from even-aged pine forest. Abundant regeneration in small gaps showed that light (gap area) was only one of the factors affecting tree regeneration in the gaps. The depth of the O layer and pH were suggested to be important factors for the establishment and growth of pine and birch. For oak, the main factors for establishment and growth were favorable moisture, higher pH and N concentration. Knowledge of ecological factors affecting the establishment of seedlings and growth of saplings of the most common trees species in the urban boreal forest is needed to predict successional trajectories and to aid management

Effects of afforestation of agricultural land with grey alder (Alnus incana (L.) Moench) on soil chemical properties, comparing two contrasting soil groups

Abstract Background Natural afforestation of former agricultural lands with alder species is common in Europe. Symbiotic nitrogen fixation by actinomycetes associated with alder species has been widely used for improvement of soil properties of abandoned agricultural lands, but relatively little is known of the interactions of these processes with soil type and chemical composition. We conducted a space-for time study with soil sampling under and outside grey alder tree canopies on two different soil groups to explore effects of colonisation of former agricultural lands by alder on soil properties. Results The results were analysed using analysis of variance. During the first 25 years after afforestation of former agricultural lands there was a significant increase in content of Ctot, Ntot, K+, Fe3+, Mn2+ and available P in the topsoil (0–10 cm and 11–20 cm) of Dystric Arenosols soils, which are deficient in organic matter. Such trends were not evident in organic matter rich Endostagnic Umbrisols soils, in which exchangeable K+ concentration decreased and exchangeable Fe3+ and Al3+ concentration increased. Conclusions The results show that the effects of grey alder on soil chemical properties depend on initial soil properties. The invasion of agricultural land by grey alder leads to spatial variability of soil chemical properties creating a mosaic pattern

The role of forest certification for biodiversity conservation: Lithuania as a case study

The Forest Stewardship Council (FSC) forest certification system is a globally widespread market-driven mechanism that aims at responsible use and governance of forests, and its application is growing. However, the extent to which forest certification contributes effectively to maintaining forest biodiversity is an unresolved issue. We assessed the role of FSC certification for forest biodiversity conservation in Lithuania’s state forests. First, we analysed the indicators related to biodiversity conservation at dif- ferent spatial scales in the FSC standard used in Lithuania. By applying morphological spatial pattern analysis and habitat suitability modelling, we explored the structural and functional connectivity of forest habitat patches of formally and voluntarily set-asides for biodiversity con- servation. According to the Lithuanian FSC standard, active measures in forest management for biodiversity should be imposed at three spatial scales: ‘trees in a stand’, ‘stands in a landscape’, and ‘landscape in an ecoregion’. The total area set aside for biodiversity was 18.6 %, including 4.9 % voluntary set-asides. The quality of habi- tats in terms of forest stand age was low, only 9.4 % of all set-asides constituted older forests. The proportions of voluntary set-aside area varied among the different state forest enterprises, and the results indicated a clear trend to set aside non-forest or low productivity forest habitats. Small (\1 ha) habitat patches formed a major part of all set-asides, including formally protected areas. FSC certi- fication alone was not able to maintain structural and functional connectivity of forests for species at multiple spatial scales in Lithuania. By keeping a minimum stan- dard of 5 % forestland set aside for biodiversity, the state forest enterprises certified according to the FSC can only satisfy forest species with small habitat requirements. To maintain biodiversity, place-based learning among stake- holders for representative functional green infrastructures in concrete landscapes and regions, combined with trans- parent knowledge about the net effect of pressures and responses on the state of biodiversity, are necessary.JRC.H.3-Forest Resources and Climat