Canopy Thinning Research Articles

Shifts in light availability driven by dieback across a marsh‐forest gradient

AbstractEcological zonation in coastal forests is driven by sea level rise and storm‐surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest‐marsh edge, canopy cover loss is most severe; trunks of dead trees without canopies form “ghost forests.” Canopy thinning and light from the edge alter conditions for understory vegetation, promoting the growth of shrubs and facilitating establishment and spread of invasive species that were previously limited by light competition. In this research, we present an analysis of illuminance and temperature in a coastal forest transitioning to a salt marsh. Light sensors above the ground surface were used to measure light attenuation of trees and understory vegetation and to observe the effect of reduced canopies at the forest‐marsh edge. Farther from the marsh, where salinity is lower and trees are healthy, dense canopies attenuate light. We estimate that during the growing season, tree canopies intercept 50% of illuminance on average. Closer to the marsh, canopy thinning, and tree death allow greater light penetration from above, as well as from the adjacent marsh. These illuminance values are further increased by light penetration from the forest‐marsh edge (edge effect). Here, higher illuminance may permit Phragmites australis expansion. At intermediate locations, trees intercept between 32% and 49% of light and the understory shrub Morella cerifera intercepts a further 45% of penetrating light based on comparisons of illuminance above and below shrub canopies. Light penetration from the edge can also be felt. The presence of M. cerifera reduces the air temperature close to the soil surface, creating a cooler summer microclimate. The tree health state is reflected in the canopy size. The canopy patterns and the edge effect are responsible for light availability distribution along forest‐marsh gradients, consequently affecting the understory vegetation biomass. We conclude that during forest retreat driven by sea level rise, tree dieback increases light availability favoring the temporary encroachment of Ph. australis and M. cerifera in the understory.

Spatial signatures of an approaching regime shift in Posidonia oceanica meadows

Determining the proximity of ecosystems to tipping points is a critical yet complex task, heightened by the growing severity of climate change and local anthropogenic stressors on ecosystem integrity. Spatial Early Warning Signals (EWS) have been recognized for their potential in preemptively signaling regime shifts to degraded states, but their performance in natural systems remains uncertain. In this study, we investigated the performance of 'recovery length' — the spatial extent of recovery from a perturbation — and spatial EWS as early warnings of regime shifts in Posidonia oceanica meadows. Our experimental approach involved progressively thinning the P. oceanica canopy, from 0 to 100%, at the edge of a dead-matte area — a structure formed by dead P. oceanica rhizomes and colonized by algal turfs — to promote the propagation of algal turfs. We calculated recovery length as the distance from the dead-matte edge to the point where algal turfs colonized the canopy-thinned region. Our results showed a linear increase in recovery length with canopy thinning, successfully anticipated the degradation of P. oceanica. While spatial skewness decline with increased canopy degradation, other spatial EWS, such as Moran correlation at lag-1, low-frequency spatial spectra, and spatial variance, were ineffective in signaling this degradation. These findings underscore the potential of recovery length as a reliable early warning indicator of regime shifts in marine coastal ecosystems.

Opening the canopy to restore spider biodiversity in protected oakwoods

A mosaic of patches in various successional stages is key to maintaining high biodiversity in open temperate woodlands. The abandonment of traditional management, such as once widespread coppicing, has caused biodiversity loss and a shift to ecologically homogeneous communities. Invertebrates are one of the taxonomic groups that suffered the most from the lack of a regular disturbance regime. Despite the obvious importance of active management in maintaining high biodiversity in open temperate woodlands, our knowledge on its contribution to spider conservation is still poor. We investigated how the coppicing restoration affects the diversity of ground-dwelling spiders in the oakwoods of Podyjí National Park in the Czech Republic. We sampled the spider assemblages using pitfall traps within 10 plots in three successional stages: initial, advanced, and late successional stage (control). We collected a total of 9 919 individuals belonging to 143 spider species. The species richness was positively influenced by restoration and reached the highest values in the advanced successional stage. Each successional stage hosted distinct spider assemblages. The trait diversity (RaoQ) was very low in the late successional stage, primarily accommodating small spider species with a preference for shaded and humid habitats. On the other hand, canopy thinning supported high trait diversity of light-demanding and threatened species. Our results showed that the restoration of traditional coppicing could be an appropriate tool for maintaining biodiversity of ground-dwelling spiders in open oakwoods.

Tree Effects on Coffee Leaf Rust at Field and Landscape Scales.

Although integrating trees into agricultural systems (i.e., agroforestry systems) provides many valuable ecosystem services, the trees can also interact with plant diseases. We demonstrate that a detailed understanding of how plant diseases interact with trees in agroforestry systems is necessary to identify key tree canopy characteristics, leaf traits, spatial arrangements, and management options that can help control plant diseases at different spatial scales. We focus our analysis on how trees affect coffee leaf rust, a major disease affecting one of the world's most significant crop commodities. We show that trees can both promote and discourage the development of coffee leaf rust at the plot scale via microclimate modifications in the understory. Based on our understanding of the role of tree characteristics in shaping the microclimate, we identify several canopy characteristics and leaf traits that can help manage coffee leaf rust at the plot scale: namely, thin canopies with high openness, short base height, horizontal branching, and small, dentate leaves. In contrast, at the edge of coffee farms, having large trees with high canopy volume and small, thick, waxy leaves is more useful to reduce throughflow wind speeds and intercept the airborne dispersal of urediniospores, an important consideration to control disease at the landscape scale. Seasonal pruning can help shape trees into the desired form, and trees can be spatially arranged to optimize desired effects. This case study demonstrates the added value of combining process-based epidemiology studies with functional trait ecology to improve disease management in agroforestry systems.

High‐diversity seed additions promote herb‐layer recovery during restoration of degraded oak woodland

Abstract Seed limitation represents a fundamental constraint to the restoration of native plant communities, and practitioners often apply seed additions to overcome this barrier. However, surprisingly few studies have experimentally tested whether seed additions can increase diversity in herbaceous communities of oak woodlands, which have undergone large‐scale transformation due to logging, altered fire regimes and invasion by non‐native species. Previous studies suggest that structural (thinning of woody biomass) and process‐based (prescribed fire) restoration treatments alone are unlikely to restore the full breadth of taxonomic and functional diversity in the herb layer, which accounts for most species in woodland ecosystems. To explore whether seed additions can improve restoration outcomes in an oak woodland, we sowed high‐diversity seed mixes in paired transects (seeded vs. controls) along a topographic gradient in a degraded site undergoing restoration with non‐native shrub removal, selective tree thinning and prescribed fire. Seed mixes contained native forbs, grasses and sedges from locally sourced material (n = 169 total species) in the regional species pool, and were designed to match species' habitat affinity to appropriate locations along the topographic gradient. The herb flora was sampled pre‐seeding, and for two consecutive years after additions. Seed additions significantly altered community and functional composition, and increased native species richness by 29% (43.0 vs 55.4), and floristic quality by 30% relative to controls. However, fewer than half of the sown species were established 2 years after planting, suggesting that dispersal and establishment limitation are both important barriers to the recovery of the herb flora in oak woodlands. We also tested if species' sown abundance, conservatism or functional group predicted establishment success. Species sown at high abundances and less conservative species recruited the most reliably. Grass and forb establishment rates were more dependent on seeding rate than sedges or legumes, and the mechanisms behind this trend merit further investigation. We found that adding high‐diversity seed mixes in conjunction with non‐native shrub removal, canopy thinning and burning, can accelerate recovery of herbaceous communities in a highly degraded woodland.

First Report of Beech Leaf Disease, Caused by Litylenchus crenatae mccannii, on American Beech (Fagus grandifolia) in Virginia.

Beech leaf disease (BLD) was first reported in 2012 in Lake County, Ohio on American beech trees (Fagus grandifolia Ehrh.). Since then, it spread across the Northeastern United States and has been reported from Ohio, Pennsylvania, New York, New Jersey, Connecticut, Rhode Island, Maine, West Virginia, and Ontario, Canada (Carta et al. 2020; Mara and LaMondia 2020, Reid et al. 2020). The symptoms of BLD are characterized by dark interveinal banding of leaves appearing soon after spring flush that become chlorotic and necrotic through autumn, resulting in canopy thinning in advanced stages, followed in some young trees by death. Litylenchus crenatae mccannii has similar morphological characteristics with Litylenchus crenatae (Kanzaki et al. 2019) reported on Fagus crenata from Japan. However that beech species has not shown BLD symptoms or yielded any L. crenatae mccannii in North America. There are several morphological differences between the two. The North American subspecies have shorter post-uterine sac, narrower body width in mature females, shorter tail in immature females, longer tail in mature females, and longer stylet in males when compared to the Japanese subspecies (Carta et al. 2020). BLD symptoms were found on American beech trees in Prince William Forest Park, Prince William County, Virginia in June, 2021. The affected leaves contained females, males, and juveniles with morphometrics consistent with L. crenatae mccannii (Carta et al. 2020). The crude genomic DNA from a live single Litylenchus was prepared with freeze-thaw lysis (Carta and Li, 2019). The ITS PCR were performed by using the procedures and primer set, ITS-CL-F2 and 28S-CL-R described in the previous study (Carta and Li, 2020). The visualization, the cleanup and the direct DNA sequencing of the PCR products were performed by using the procedures described in the previous studies (Carta and Li, 2018 and 2019). Sequences were submitted to GenBank as accessions MZ611855 and MZ611856. This represents the first report of BLD in Virginia. It is also approximately 300 miles south of the 2020 detection of BLD from New Cumberland, WV, and represents the southernmost detection of the disease and nematode in North America. The author(s) declare no conflict of interest. References Carta, L.K., Li, S. 2018. Improved 18S small subunit rDNA primers for problematic nematode amplification. Journal of Nematology. 50, 533-542. Carta, L.K., Li, S. 2019. PCR amplification of a long rDNA segment with one primer pair in agriculturally important nematodes. Journal of Nematology. 51, e2019-26. Carta, L.K., Li, S. 2020. Improvement of long segment ribosomal PCR amplification for the molecular taxonomic identification of Litylenchus crenatae mccannii in beech trees with beech leaf disease. Journal of Nematology. 52, e2020-016. Kanzaki, N., Ichihara, Y., Aikawa, T., Ekino, T., Masuya, H. 2019. Litylenchus crenatae n. sp. (Tylenchomorpha: Anguinidae), a leaf gall nematode parasitising Fagus crenata Blume Nematology 21 (1), 5-22. http://www.brill.com/nematology doi: 10.1163/15685411-00003190 Marra, R.E., LaMondia, J. 2020. First report of beech leaf disease, caused by the foliar nematode, Litylenchus crenatae mccannii, on American beech (Fagus grandifolia) in Connecticut. Plant Disease (early view). https://doi.org/10.1094/PDIS-02-20-0442-PDN Reed, S. E., Greifenhagen, S., Yu, Q., Hoke A., Burke D. J., Carta L. K., Handoo Z.A., Kantor, M.R., Koch, J. 2020. Foliar nematode, Litylenchus crenatae ssp. mccannii, population dynamics in leaves and buds of beech leaf disease-affected trees in Canada and the US. Forest Pathology 50 (3), e12599.

A gigantic vertical zoo

Why is it that when we see images of major new urban developments today – whether housing units, office blocks, or shopping malls – those developments are as likely as not to be covered in a thin canopy of trees? In this paper, I approach this question by thinking about the long history of the idea that cities are somehow bad for human beings, and especially that they are bad for our mental health. From Shanghai to Paris, from Biophilia to “cheap nature”, from Donna Haraway to Thomas Heatherwick, I examine the growing entanglement between the psychologically restorative city and the green city. I ask: what does it mean, for historical cultures of both madness and the city, that we now ask our urban spaces, recast as centres of nature and biological life, to have even a reparative relationship to mental health?

Functional responses of mangrove fauna to forest degradation

Structural degradation of mangroves through the partial removal of trees is globally pervasive and likely to affect ecological functioning, including habitat provisioning for biodiversity. Biodiversity responses will depend on the severity of degradation, yet few studies have contraste and quantified several degradation states. Addressing this knowledge gap, we sampled faunal diversity across a range of mangrove forests in southern Kenya. Canopy cover was the strongest predictor of faunal responses among forest structural variables. Faunal abundance, species richness and biodiversity all decreased with reduction in canopy cover, and taxonomic and functional composition changed. The trophic diversity of crabs peaked at intermediate canopy cover, with degraded habitats having more generalist species and fewer specialists. Functional redundancy was unaffected by canopy thinning. The decline in functional diversity and richness of brachyuran crabs with canopy cover implies that resource-use efficiency weakens with increasing degradation. Our results are indicative of significant alterations to forest functioning with degradation, because epibenthic fauna are important regulators of mangrove ecosystem processes, including nutrient cycling and carbon.

Isotria medeoloides, a North American Threatened Orchid: Fungal Abundance May Be as Important as Light in Species Management.

The management of endangered or threatened plant species is difficult if protocols are not developed to propagate species for the purpose of restoration or the enhancement of existing populations. The management of endangered and threatened orchids is especially difficult because of the obligate interactions between orchids and orchid mycorrhizal fungi. Isotria medeoloides is a federally threatened forest-dwelling orchid species with a wide distribution in eastern North America. Seeds have not been successfully germinated and current management is based primarily on using subcanopy thinning to increase light in areas where monitoring demonstrates that populations are declining. We report the results of long-term monitoring efforts, canopy thinning, and orchid mycorrhizal fungus abundance studies at two locations in Virginia. The declining populations responded positively to the experimental and natural thinning of the canopy. At one site, the response was the result of understory canopy thinning. At the second site, the response was due to the natural death of a canopy tree. In light of the dramatic increase in fungal abundance following death of the canopy tree, we propose the Fungal Abundance Hypothesis as an additional approach to the management of endangered plant species. The removal of canopy trees in or adjacent to Isotria populations results in an increase in dead belowground biomass (i.e., roots of the dead canopy tree) that provides substrates for microbial growth, including orchid mycorrhizal fungi, that benefit Isotria.

PENGARUH KADAR AIR SERASAH KAYU SUNGKAI TERHADAP KEBAKARAN HUTAN DI AREAL IUPHHK-HT PT. AYA YAYANG INDONESIA

This study aims to determine the effect of Sungkai litter water content (Peronema canescens) on forest fires. The benefit of this research is to provide information and input on related institutions to take actions to prevent forest fires. The research object is Sungkai litter in the IUPHHK-HI area of PT. Aya Yayang Indonesia on 26-year-old plants, with 4 treatments and 5 groups. Sampling with the Stratified Random Sampling (layered random) method, data analysis using Randomized Block Design (RCBD). Based on the results of the study note that the largest average water content is in the dense canopy treatment and there is an understorey (29.67%) and a thin canopy treatment there is an understorey (27.07%) then dense canopy there is no understorey (21.80 %) and the treatment with the least water content is thin canopy treatment and no undergrowth (17.30%). The average of all samples of Sungkai litter water content (23.96%) is known to be less than 30% so according to. Ministry of Forestry and Forestry (1999), can be categorized as very vulnerable to forest fires. Based on the Diversity Analysis test, it is known that the treatment has a very significant effect, for the normality test (using Liliefors test) it is known that the data is spread normally while through the Bartlett Variety homogeneity test it is known that the data is homogeneous. Through Honestly Significant Difference test (BNJ) it is known that each treatment has a significantly different effect.Keywords: Kadar air; Serasah; Kebakaran hutan; Sungkai

Positive impact of traditional coppicing restoration on biodiversity of ground-dwelling spiders in a protected lowland forest

Lowland forests of Central Europe had been managed by diverse traditional practices for millennia. Such management helped to maintain heterogeneous habitat conditions suitable for a wide variety of arthropod species. Modern approaches to conservation, however, with their strategies of nonintervention, unintentionally caused an overall habitat homogenization within protected areas in many ecosystem types during the20thcentury. As a result, the diversity of organisms, including several large groups of arthropods, has gradually declined. Active interventions that would diversify homogenized lowland forest reserves are increasingly being reintroduced. A question remains as to whether the traditional management restoration at various intensities will maintain conditions suitable for high diversity of functionally important groups of arthropods. Here,we studied the effect of canopy thinning, aimed at coppice restoration, on ground-dwelling spider assemblages. Sampling was based on experimental plots distributed equally in an abandoned coppice-with-standards among three canopy thinning intensities: strong thinning, moderate thinning, and nonintervention as a control. We recorded 116 species of spiders, including a high proportion of Red-listed and threatened species. The species richness and presence of rare and threatened species increased with the intensity of canopy thinning. The abundance of spiders was greater in plots with moderate thinning than in control plots. Functional richness was greatest in open habitats with strong canopy thinning, however functional traits were equally distributed across allhabitats. Although ordination analyses revealed that species of conservation concern tended to be associated with open habitats, some conservation-valuable species had affinities alsofor nonintervention plots. Overall, our results indicated that the best silviculture practice for biodiversity conservation is a combination of various management intensities that would support functional groups ranging from open habitat specialists to species typical for dense and more humid forest patches. We demonstrated that returning to active coppicing management can be a successful strategy for biodiversity restoration in lowland forests.

Stability of rectangular cantilever plates with high elasticity

The problem of cantilever plate stability has been little studied due to the difficulty of solving the corresponding boundary problem. The known approximate solutions mainly concern only the first critical load. In this paper, stability of an elastic rectangular cantilever plate under the action of uniform pressure applied to its edge opposite to the clamped edge is investigated. Under such conditions, thin canopies of buildings made of new materials can be found at sharp gusts of wind in longitudinal direction. At present, cantilever nanoplates are widely used as key components of sensors to create nanoscale transistors where they are exposed to magnetic fields in the plate plane. The aim of the study is to obtain the critical force spectrum and corresponding forms of supercritical equilibrium. The deflection function is selected as a sum of two hyperbolic trigonometric series with adding special compensating summands to the main symmetric solution for the free terms of the decomposition of the functions in the Fourier series by cosines. The fulfillment of all conditions of the boundary problem leads to an infinite homogeneous system of linear algebraic equations with regard to unknown series coefficients. The task of the study is to create a numerical algorithm that allows finding eigenvalues of the resolving system with high accuracy. The search for critical loads (eigenvalues) giving a nontrivial solution of this system is carried out by brute force search of compressive load value in combination with the method of sequential approximations. For the plates with different side ratios, the spectrum of the first three critical loads is obtained, at which new forms of equilibrium emerge. An antisymmetric solution is obtained and studied. 3D images of the corresponding forms are presented.

Factors influencing efficacy of an area-wide pest management program in three urban forests

Managing exotic invasive pests like emerald ash borer can strain budgets and the capacity of cities to protect their urban forest. Area-wide management approaches, like SLAM (SL.ow A.sh M.ortality), can potentially protect trees at a greatly reduced cost. We tested this strategy in three urban forests in Indiana by treating 40 % of the ash trees with insecticides. While the urban SLAM approach reduced overall mortality of untreated ash trees, survivorship varied considerably between sites. SLAM was most successful (54 % survival) where initially < 10 % of the ash trees were moribund (canopy thinning > 30 %) and 40 % of all trees were treated with emamectin benzoate every two years. The approach was less successful (38 % survival) in a site with similar initial ash morbidity but where 15 % of trees were treated with emamectin benzoate and 25 % with annual applications of imidacloprid. In the third site, where 51 % of ash forest were initially moribund and 40 % of the ash trees were treated, only 23 % survived. Overall survival of treated ash trees declined by 18–22 %, and trees that were not moribund were most likely to survive. Although many treated trees that were initially moribund regained their health by the end of the project, this was not the case for untreated ash trees. Where SLAM was most successful, both untreated and treated white ash were more likely to survive than green ash trees. Untreated ash trees at all three sites were more likely to survive when closer to trees treated with emamectin benzoate, but not to those treated with imidacloprid. Our findings suggest that the SLAM approach can protect urban ash trees, but its success is strongly influenced by initial tree condition, species composition and proximity to treated ash trees.

Coarse Woody Debris’ Invertebrate Community is Affected Directly by Canopy Type and Indirectly by Thinning in Mixed Scots Pine—European Beech Forests

Research Highlights: Thinning and tree species alter the forest floor microclimate by modifying canopy cover, radiation, wind, and humidity. Thus, forest management can directly influence the edaphic mesofauna responsible for decomposing coarse woody debris (CWD). Background and Objectives: This research was carried out in the Southwestern Pyrenees Mountains (Northern Spain) and aimed to determine the influence of forest thinning and canopy type (pure Pinus sylvestris L. or a mix of P. sylvestris and Fagus sylvatica L.) on CWD colonization by edaphic fauna. Materials and Methods: CWD samples were collected belonging to intermediate and advanced decomposition stages, approximately 10 cm long and 5 cm in diameter. Using a design of three thinning intensities (0%, 20%, and 40% of basal area removed), with three replications per treatment (nine plots in total), four samples were taken per plot (two per canopy type) to reach 36 samples in total. Meso- and macrofauna were extracted from CWD samples with Berlese–Tullgren funnels, and individuals were counted and identified. Results: 19 taxonomic groups were recorded, the most abundant being the mesofauna (mites and Collembola). Mixed canopy type had a significant positive influence on richness, whereas advanced decay class had a positive significant influence on total abundance and richness. In addition, there were non-significant decreasing trends in richness and abundance with increasing thinning intensity. However, interactions among thinning intensity, canopy type, and decay class significantly affected mesofauna. Furthermore, some taxonomic groups showed differential responses to canopy type. CWD water content was positively correlated with total invertebrate abundance and some taxonomic groups. Our results suggest that stand composition has the potential to directly affect invertebrate communities in CWD, whereas stand density influence is indirect and mostly realized through changes in CWD moisture. As mesofauna is related to CWD decomposition rates, these effects should be accounted for when planning forest management transition from pure to mixed forests.

Predicting Occurrence, Abundance, and Fruiting of a Cultural Keystone Species to Inform Landscape Values and Priority Sites for Habitat Enhancements

Environmental niche modeling is an increasingly common tool in conservation and management of non-timber species. In particular, models of species’ habitats have been aided by new advances in remote sensing and it is now possible to relate forest structure variables to understory species at a relatively high resolution over large spatial scales. Here, we model landscape responses for a culturally-valued keystone shrub, velvet-leaf blueberry (Vaccinium myrtilloides Michaux), in northeast Alberta, Canada, to better understand the environmental factors promoting or limiting its occurrence, abundance, and fruit production, and to guide regional planning. Occurrence and abundance were measured at 845 and 335 sites, respectively, with both strongly related to land cover type and topo-edaphic factors. However, their influence varied widely, reflecting differences in the processes affecting occurrence and abundance. We then used airborne laser scanning (ALS) to characterize horizontal forest canopy cover for the study area, and related this and other geospatial variables to patterns in fruit production where we demonstrated a five-fold increase in fruit production from closed to open forest stands. We then simulated forest canopy thinning across the study area to identify places where gains in fruit production would be greatest following natural disturbance or directed management (e.g., thinning, prescribed burning). Finally, we suggest this approach could be used to identify sites for habitat enhancements to offset direct (land use change) or indirect (access) losses of resources in areas impacted with resource extraction activities, or simply to increase a culturally-valued resource through management.

Ecological restoration by canopy thinning in a Quercus robur forest can cause development of a dense shrub layer

Ecological restoration by canopy thinning in a Quercus robur forest can cause development of a dense shrub layer

Understanding the dynamics of forest understorey: Combination of monitoring and legacy data reveals patterns across temporal scales

AbstractAimsThe dynamics of plant communities varies across temporal scales. A correct understanding of temporal patterns is crucial for the interpretation of monitoring outputs. Focusing on the understorey community of an ancient coppice at three temporal scales, our aims were to: (a) assess the link between year‐to‐year variations and a decadal successional change; (b) estimate how seasonal cyclical dynamics could interfere with the changes at interannual and decadal scales; and (c) account for the effects of coppicing restoration.LocationMt Děvín, S Moravia, Czech Republic.MethodsComposition of a temperate forest understorey was monitored in 26 permanent plots on a year‐to‐year basis for a decade (2008–2018) and monthly (2015–2016). Adjacent semi‐permanent plots (23 in total) were resurveyed in 1953–2003. The three scales of temporal variation were statistically analyzed and compared looking at the vascular plant diversity (species richness) and compositional turnover (dissimilarity measures and patterns in multivariate space).ResultsEach of the three temporal scales captures specific patterns in herbaceous understorey species richness and turnover. The interannual variation shows fluctuations rather than trends and is lower than the magnitude of changes on a decadal scale. However, canopy thinning was responsible for rapid changes compatible with the long‐term trend of biodiversity decline following the abandonment of coppicing decades ago. The seasonal dynamics showed a distinct cyclical development typical of temperate forests. It exceeded the magnitude of interannual changes, pointing at the potentially significant source of error from the timing of data collection.ConclusionsComparison of the monitoring and legacy data revealed complex patterns in the forest understorey dynamics. Contrary to general assumptions, the short‐term dynamics of forest understorey can be significant. It is recommended that monitoring designs consider not only permanent plots but also resurveys of semi‐permanent plots. Considering more than one temporal scale will improve our understanding of the plant community dynamics.

Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America

AbstractSymptoms of beech leaf disease (BLD), first reported in Ohio in 2012, include interveinal greening, thickening and often chlorosis in leaves, canopy thinning and mortality. Nematodes from diseased leaves of American beech (Fagus grandifolia) sent by the Ohio Department of Agriculture to the USDA, Beltsville, MD in autumn 2017 were identified as the first recorded North American population of Litylenchus crenatae (Nematology, 21, 2019, 5), originally described from Japan. This and other populations from Ohio, Pennsylvania and the neighbouring province of Ontario, Canada showed some differences in morphometric averages among females compared to the Japanese population. Ribosomal DNA marker sequences were nearly identical to the population from Japan. A sequence for the COI marker was also generated, although it was not available from the Japanese population. The nematode was not encountered in Fagus crenata (its host in Japan) living among nematode‐infested Fagus grandifolia in the Holden Arboretum, nor has L. crenatae been reported in American beech in Japan. The morphological and host range differences in North American populations are nomenclaturally distinguished as L. crenatae mccannii ssp. n. from the population in Japan. Low‐temperature scanning electron microscopy (LT‐SEM) demonstrated five lip annules and a highly flexible cuticle. Females, juveniles and eggs were imaged within buds with a Hirox Digital microscope and an LT‐SEM. Nematodes swarmed to the tips of freshly cut beech buds, but explants could not be maintained. Inoculation of fresh nematodes from infested leaves or buds to buds or leaves of F. grandifolia seedlings resulted in BLD leaf symptoms. Injuring dormant buds prior to nematode application, in fall or spring, promoted the most reliable symptom expression. The biogeography and physiology of anguinid nematode leaf galling, and potential co‐factors and transmission are discussed.

Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe.

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.

Mean pressure coefficient distributions over hyperbolic paraboloid roof and canopy structures with different shape parameters in a uniform flow with very small turbulence

The hyperbolic paraboloid with two high and low corners is the most basic anticlastic double curved shape of tensile surface structures. However, this shape is currently not considered in the existing wind load standards and only very few investigations are documented in literature. Therefore, this study aims to map the mean aerodynamics over hyperbolic paraboloid roofs and extremely thin canopies to help engineers understand the general aerodynamics of these structures. In this study, scaled wind tunnel testing is performed on rigid models of a roof with enclosing walls and a canopy without enclosing walls to draft mean Cp-distributions and standard deviations for various wind orientations. These mean Cp-distributions are validated with the limited studies in literature and used to calibrate and benchmark a numerical wind tunnel, using CFD RANS simulations, that allows to further reduce the thickness of the canopy compared to the wind tunnel models. The numerical wind tunnel is used to study the mean wind load distributions for hyperbolic paraboloid roofs and canopies with different surface curvature for the most important wind orientations. The results in this paper show good agreement between wind tunnel experiments and CFD simulations, with similar variations as established by different studies of the Silsoe cube. First mean Cp-distributions obtained with scaled wind tunnel testing are presented for hyperbolic paraboloid canopies of only 5 mm thick, with similar mean net Cp and only slightly larger suction over the upper and lower face compared to the numerical results for a zero-thickness canopy. The numerical study of different surface curvatures indicates different geometrical patterns in the mean Cp-distributions when the flow starts to separate for highly curved hypars. In general, suction and pressure increase for higher surface curvature, with similar geometrical patterns in the mean Cp-distributions, as long as the flow remains attached. If the flow separates for highly curved hypars, the geometrical pattern differs and the mean Cp drops due to the different behavior of the flow. Finally, the presented mean Cp-distributions give insight in the aerodynamics of hypar roofs and canopies with different surface curvature and could form a basis for future analysis towards peak loads for the design of these structures.