Tree hollow parameters and their effects on saproxylic arthropod diversity: A multi‐taxon approach

European beech (Fagus sylvatica L.) forests gain a special interest in Central Europe. The highly competitive species would most likely achieve dominance within a wide range of site conditions. Understanding the natural structure and dynamics of beech forests is of great importance for forest ecosystem research from both a conservation and management perspective. Today, there are only few remnants of virgin beech forests and our knowledge on their structure and especially on structural dynamics is poor. This thesis focuses on gap dynamics processes, their effect on stand structure and the analytical description of stand structures in terms of forest development stages in virgin beech forests. Canopy gap formation is suggested being the main driver of structural processes in in natural beech forests. However, information on spatio-temporal change of gap pattern, released understory structures and their reaction to canopy release are scarce. In the virgin beech forest Kyjov a repeated gap inventory was conducted to quantify differences in gap size frequency and fraction over a 10-year interval (2003–2013). Further, the percentage cover of understory trees and regeneration were estimated in 2013. Gap fraction decreased significantly from 13.6% in 2003 to 8.2% in 2013. Within 10 years the mean rate of gap closure was > 80%. Saplings and trees in lower canopy layers formed a heterogeneous understory in large parts of recently formed gaps. The results indicate considerable variation in disturbance intensity in the past decades. The prevalent heterogeneous tree understory guarantees a high resilience to canopy disturbance. The effects of gap formation on the regeneration process are fundamental for understanding forest dynamics. There are only a few studies from temperate virgin forests on gap regeneration and its natural dynamics over time and results are partly contradictory. The regeneration structure was studied in understory gaps of variable size and age, and under closed-canopy conditions in the Kyjov forest. Further, spatial differences in regeneration structure and height growth within a gap and in the gap periphery were analyzed. Sapling density and cumulative biomass were significantly higher in understory gaps than under the closed canopy. Sapling density was positively affected by high direct radiation but low diffuse radiation intensities, resulting in pronounced spatial differences in sapling density across a gap. Sapling shoot length growth was positively affected by higher levels of diffuse radiation and increased sapling size, while direct radiation was not influential. The results suggest that regeneration in small gaps most likely ends in a suppressed heterogeneous understory while in gaps ≥ 100 m2, regeneration may be capable even at low plant densities to fill the gap center, often forming a rapidly growing cohort-like regeneration layer. V It is suggested that in natural temperate forests gap induced regeneration processes imprint on forest structure in the way that trees establish on the approximate gap area and close the gap over time. This assumption lacks an empirical basis. To verify this assumption neighboring trees of similar size were assigned to tree groups on a continuous 12 ha plot in the Kyjov forest and the group size-frequency of such homogeneous patches was analyzed across diameter classes. The number of tree groups (cohorts) in a particular diameter class decreased exponentially as group size increased. Compared to random distributions, the Kyjov forest exhibited a more clumped distribution especially for small trees. The frequency distribution patterns for group sizes are similar to those for gap sizes reported from the same stand and many others. Even though a direct comparison (number of trees vs. m2) is not possible, the results indicate that gap initiated tree groups may persist through the forest cycle. Researchers defined a succession of forest development stages to explain the diversity of structures encountered in beech-dominated virgin forests. However, existing methods based on empirical stand structural data fail to display structural development comprehensively. A novel approach for determining the extension of development stages is proposed. The Development Stage Index (IDS) assigns living and dead trees to the Initial, Optimum and Terminal stage according to their DBH (7–39 cm, 40–69 cm and ≥ 70 cm, respectively) and quantifies their extension by means of stem density and basal area. It was applied to 40 spaced sample plots (500 m2 each) in three beech virgin forests in East Slovakia (Kyjov, Havešová and Stuižca; 120 plots in total). Based on thorough stand structural analyses in the three virgin beech forests, it is demonstrated that IDS is a promising tool for quantifying the proportion of the three stages on different scales, visualizing the complex mixing of stages and analyzing dynamic changes in old-growth forest structure. The results from the Kyjov forest derived by the IDS are in large agreement with the conclusions on how gap dynamics shape forest structure in this forest. This suggests that it might be possible to infer on past forest dynamics by analyzing stand structure with the IDS.

Context Hollow-bearing trees are an important breeding and shelter resource for wildlife in Australian native forests and hollow availability can influence species abundance and diversity in forest ecosystems. A persistent problem for forest managers is the ability to locate and survey hollow-bearing trees with a high level of accuracy at low cost over large areas of forest. Aims The aim of this study was to determine whether remote-sensing techniques could identify key variables useful in classifying the likelihood of a tree to contain hollows suitable for wildlife. Methods The data were high-resolution, multispectral aerial imagery and light detection and ranging (Lidar). A ground-based survey of 194 trees, 96 Eucalyptus crebra and 98 E. chloroclada and E. blakelyi, were used to train and validate tree-senescence classification models. Key results We found that trees in the youngest stage of tree senescence, which had a very low probability of hollow occurrence, could be distinguished using multispectral aerial imagery from trees in the later stages of tree senescence, which had a high probability of hollow occurrence. Independently, the canopy-height model used to estimate crown foliage density demonstrated the potential of Lidar-derived structural parameters as predictors of senescence and the hollow-bearing status of individual trees. Conclusions This study demonstrated a ‘proof of concept’ that remotely sensed tree parameters are suitable predictor variables for the hollow-bearing status of an individual tree. Implications Distinguishing early stage senescence trees from later-stage senescence trees using remote sensing offers potential as an efficient, repeatable and cost-effective way to map the distribution and abundance of hollow-bearing trees across the landscape. Further development is required to automate this process across the landscape, particularly the delineation of tree crowns. Further improvements may be obtained using a combination of these remote-sensing techniques. This information has important applications in commercial forest inventory and in biodiversity monitoring programs.

Leadbeater’s possum (Gymnobelideus leadbeateri) is a critically endangered arboreal marsupial found primarily in the mountain ash forests of Victoria’s Central Highlands in southeastern Australia. It has two very specific and well-known habitat requirements: a dense, connected lower stratum of Acacia spp. for foraging and movement within the forest and hollow-bearing trees for nesting. Early habitat suitability models for Leadbeater’s possum focused primarily on the dynamics of the hollow-bearing tree component, assuming that sufficient Acacia persisted throughout the development of the stand. Recent research has highlighted the transient nature of the Acacia component in these forests and shown that old-growth forests are relatively poor habitat for Leadbeater’s possum. The stand dynamics of mountain ash forests mean that the presence and abundance of Acacia and hollow-bearing trees are largely independent of one another. This presents a fundamental conundrum for the conservation of Leadbeater’s possum – the Acacia component is associated with young, post-disturbance forests, whereas hollow-bearing trees are associated with older forests. Conservation-oriented silviculture needs to accommodate these dynamics and focus on the provision of both habitat elements in close proximity to each other in time and space. A landscape-scale approach that focuses on long-term habitat restoration and management will be critical to the long-term viability of Leadbeater’s possum, particularly in a warming climate.Keywords Acacia dealbata Eucalyptus regnans Habitat suitabilityConservation-oriented silviculture

Assessing the effects of forest gaps on beech (Fagus orientalis L.) trees traits in the logged temperate broad-leaf forest

Land management causes changes in forest structure and thus influences the composition and abundance of communities of forest-inhabiting bird species. However, it is unclear how these changes translate into local habitat suitability for certain bird species given that detailed knowledge on habitat use by forest bird species is still scarce. We have analyzed the habitat preferences of 37 breeding bird species in 19 lowland beech forests, each with an average size of 40 ha. We used Jacobs habitat selection index to quantify preference or avoidance of certain forest developmental phases (fdp). Fdp divide the forest life cycle into different periods, each characterized by a certain combination of habitat parameters (canopy cover, tree dimension, deadwood amount, regeneration cover), thereby integrating several age-specific structural properties. We found that fdp representing the last third of the forest life cycle were significantly preferred by most of the bird species. Of the 37 bird species analyzed, 19 showed the highest preference for the terminal phase or the disintegration phase; this was especially true for hole breeders, semi-hole breeders, ground breeders and beech forest indicator species. Moreover, each bird species showed a characteristic profile of preferred and avoided fdp. Some bird species, such as several free breeders, also preferred younger fdp, such as gaps or regeneration phases. Further, mean fdp patch size turned out to be a strong predictor of bird community composition. Our study confirms that most bird species show a strong preference for later fdp, such as the terminal phase and disintegration phase. However, the simultaneous availability of a mixture of different fdp on local scales meets the habitat preferences of most species and promotes biodiversity of breeding bird communities in lowland beech forests.

Rehabilitating boreal forest structure and species composition in Finland through logging, dead wood creation and fire: The EVO experiment

Abstract. Forest structure is an important indicator for evaluating forest ecosystem and an indispensable input parameter for estimating forest carbon sink. Synthetic Aperture Radar (SAR) Tomography (TomoSAR), as a novel microwave remote sensing technique with 3D imaging capability, has been demonstrated to be an valuable tool for accurate inversion of forest structure. At present, the forest vertical structure parameters inversion is almost all concentrated on the forest height estimation. However, the spatial structure of forests is complex, and it is not enough to only use the forest height to express the forest structure. This fails to identify tree canopy, branch layer and underlying vegetation layer, etc., resulting in the partial and inaccurate forest vertical structure information. To solve this problem, this paper constructs 3D structural indices from tomograms, namely Horizontal Structure Index (HS) and Vertical Structure Index (VS). The HS primarily describes canopy density, compensating for the lack of information on the horizontal dimension of forest structure provided by traditional TomoSAR techniques; while VS describes the complexity of canopy distribution in the altitude direction, further enriching information on forest structure vertically. In order to verify their feasibility and validity, HS and VS are extracted using six fully-polarized L-band SAR images covering the Krycklan watershed in Sweden. Moreover, the accuracy is verified by using external high-precision LiDAR data. The results indicate a strong correlation between the structural indices extracted from TomoSAR and those extracted from LiDAR.

AimAquatic‐terrestrial transition zones contain features essential for many species that often benefit wetland biodiversity. Shallow flood‐zone areas and reed beds are indicative of natural wetland habitats; however, how such features affect the native arthropod biodiversity in constructed wetlands is scarcely investigated. We asked how these shoreline features, as well as wetland shoreline properties and grazing management, influence riparian arthropod diversities and habitat specializations.LocationConstructed wetlands, Sweden.TaxaAraneae, Coleoptera, Diptera.MethodsTaxonomic‐, phylogenetic‐ and trait diversities, along with habitat specialist species richness, were measured in riparian spiders, beetles and selected Diptera in 68 constructed wetlands in two regions of Sweden. We ran structural equation models to estimate direct and indirect effects from shoreline slope, flooded grassland, reed areas and grazing management on group diversities, and used multivariate models to determine drivers on habitat specialist species richness.ResultsFlooded grassland and reed area, along with shoreline slope influenced arthropod diversities, and responses differed between arthropod groups and diversity metrics. Spider trait diversity was greater in wetlands with larger flooded grassland areas, whilst beetle trait diversity was reduced. Spider phylogenetic diversity was greater in wetlands containing larger reed areas and in wetlands with steeper shorelines. However, species richness in predatory flies was greater in wetlands with more gentle shorelines. Grazing management had limited effects on arthropod diversities; however, species richness in wetland specialist and generalist predatory dipterans was greater in the absence of grazers in wetlands with greater flooded grassland areas.Main ConclusionsAs requirements vary considerably among arthropods, care must be taken when constructing and managing wetlands to benefit arthropod biodiversity. The present results suggest wetlands with a varied shoreline, albeit with greater proportions of flood areas, or multiple adjacent wetlands with varying shores in a wet landscape and a mild grazing regiment, would accommodate a more diverse arthropod fauna.

Although species richness has been hypothesized to be highest at 'intermediate' levels of disturbance, empirical studies have demonstrated that the disturbance-diversity relationship can be either negative or positive depending on productivity On the other hand, hypothesized productivity diversity relationships can be positive, negative or unimodal, as confirmed by empirical studies. However, it has remained unclear under what conditions each pattern is realized, and there is little agreement about the mechanisms that generate these diverse patterns. In this study, I present a model that synthesizes these separately developed hypotheses and shows that the interactive effects of disturbance and productivity on the competitive outcome of multispecies dynamics can result in these diverse relationships of species richness to disturbance and productivity The predicted productivity diversity relationship is unimodal but the productivity level that maximizes species richness increases with increasing disturbance. Similarly, the predicted disturbance diversity relationship is unimodal but the peak moves to higher disturbance levels with increasing productivity Further, these patterns are well explained by the opposite effects of productivity and disturbance on competitive outcome that are suggested by the change in community composition along these two environmental gradients: higher productivity favours superior competitors while higher disturbance levels favour inferior competitors.

Use of tree hollows by a Mediterranean forest carnivore

Effect of stand age on bird communities in late-successional Macedonian pine forests in Bulgaria

Old-growth forests are often looked at as reference for close to nature silviculture, which aims to manage forests in a natural way. An important component of these forests is the large amount of deadwood they possess; the role of dead wood in the forest ecosystem has been well recognised. A detailed investigation of dead wood characteristics (the amount per stand, species, dead wood type, decay class, size and spatial distribution) was performed in two Romanian old-growth European mixed beech forests: Runcu Grosi Reserve (sessile oak-beech) and Sinca (silver fir-beech). Dead wood pieces were classified as belonging to one of seven dead wood types and one of five decay classes. The total amount of the dead wood was greater in Runcu Grosi (240.8 m3 ha-1) than in Sinca Forest (135.5 m3 ha-1). The majority of the dead wood in Runcu Grosi was composed of sessile oak (91.7%), whereas in Sinca Forest, the main dead wood species was silver fir (67.0%); both species exhibited higher values of probability density than beech, the second most important species. The dead wood exhibited much variation in tree size and in dead wood type, and covered the entire spectrum of decomposition classes. The main spatial pattern of all standing dead trees was random in both forests (over 55%), with a reduced participation of regularity and aggregation. The results of this investigation could be used as key values derived from natural conditions to enhance the biodiversity related to dead wood in managed temperate beech mixed forests.

Forest ecosystems provide many essential services such as climate regulation and carbon storage, which are important for many industries and for global Earth system health. However, forest ecosystems are endangered by ongoing resource exploitation and climate and land cover changes which could lead to the destruction of large quantities of forest carbon stocks and stand inventory. Nature-based climate solutions are gaining traction in recent years, particularly forest thinning techniques like variable retention harvesting (VRH) which promotes forest growth, biodiversity, and ecosystem function. Still, they require an intensive assessment of their contribution to forest structure and enhanced carbon dioxide (CO₂) sequestration, but traditional inventory-based forest monitoring practices are time-, cost-, and labour-intensive and impractical at a national scale. In this study, we implement a comprehensive methodology of forest monitoring that uses a combination of field measurements, digital hemispherical photography, spectroscopic analysis, and unmanned aerial vehicle (UAV)-derived data to derive canopy structure, light environment, and soil biogeochemistry. We evaluated the impact of four different VRH treatments on the leaf area index (LAI), canopy openness, photosynthetically active radiation (PAR) absorbance, biomass, and soil carbon and nitrogen content of an 84-year-old red pine (Pinus resinosa) plantation forest in Southern Ontario, Canada. The VRH treatments included 33% dispersed crown retention (33D), 33% aggregated crown retention (33A), 55% dispersed crown retention (55D), and 55% aggregated crown retention (55A). Our findings show that the VRH treatments were major controls or drivers of seasonal variation in LAI, canopy openness, PAR absorbance, biomass, and soil carbon and nitrogen content. Our study suggests that the dispersed crown retention of 55% basal area is the ideal forest thinning technique to enhance CO₂ sequestration and preserve forest structure and light environment. This study provides insight into the interactions between forest ecosystem dynamics and silvicultural interventions, which is indispensable for improving our understanding of nature-based climate solutions. It will also help outline the framework for monitoring forest structure and CO₂ sequestration on large spatiotemporal scales.

Drivers of spatial structure in thinned forests

ContextIn northern Europe, changes in forest ecosystem structures are commonly attributed to the ubiquitous impact of modern forestry. However, the starting point for modern forestry was not a pristine forest, but landscapes influenced for centuries by diverse human activities.ObjectivesOur aims were to (1) describe spatial patterns of forest structure and species compositions over large scales in 1920s Finland, and to (2) analyze how these characteristics were influenced by human population and past land-uses.MethodsWe mapped ca. 3000 systematic sample plots measured in the first Finnish National Forest Inventory (1921–1924) and produced a series of maps of large-scale variation in forest characteristics in upland forests. We analyzed forest age and size structures, and species compositions relative to human population and land-use data.ResultsWe found strong geographical and regional gradients in forest age and size structures, and tree species composition. Depending on the variable, these characteristics were at the stand-level best explained by human population density, reflecting the long history of various forest uses. Tree species composition was clearly associated with site productivity, but also with the history of slash-and-burn agriculture and forest grazing.ConclusionsForest landscapes in the early twentieth century Finland exhibited a strong human fingerprint, visible as the abundance of young forests in populated areas, while in remote areas forest characteristics typical of natural forests prevailed. These gradients in human impact a century ago are still reflected as legacies in forest structure, a situation that needs consideration in management and restoration.