The level of occlusion of included bark affects the strength of bifurcations in hazel (Corylus avellana L.)

Bark-included junctions in trees are considered a defect as the bark weakens the union between the branches. To more accurately assess this weakening effect, 241 bifurcations from young specimens of hazel (Corylus avellana L.), of which 106 had bark inclusions, were harvested and subjected to rupture tests. Three-point bending of the smaller branches acted as a benchmark for the relative strength of the bifurcations. Bifurcations with included bark failed at higher displacements, and their modulus of rupture was 24% lower than normally formed bifurcations, while stepwise regression showed that the best predictors of strength in these bark-included bifurcations were the diameter ratio and width of the bark inclusion, which explained 16.6% and 8.1% of the variability, respectively. Cup-shaped, bark-included bifurcations where included bark was partially occluded by xylem were found, on average, to be 36% stronger than those, where included bark was situated at the bifurcation apex. These findings show that there are significant gradations in the strength of bark-included bifurcations in juvenile hazel trees that relate directly to the level of occlusion of the bark into the bifurcation. It therefore may be possible to assess the extent of the defect that a bark-included bifurcation represents in a tree by assessing the relative level of occlusion of the included bark

An assessment of the remodelling of bifurcations in hazel (Corylus avellana L.) in response to bracing, drilling and splitting

This paper provides an insight into the ability of bifurcations in hazel trees to remodel themselves after bracing, drilling and splitting. The study uses evidence from field observations and testing the strength of these bifurcations using a universal testing machine alongside wood density tests. This work highlights the importance of the centrally-placed xylem at the apex of hazel forks in supplying tensile strength to the bifurcation. Additionally, it provides evidence that rod-braced bifurcations can atrophy in terms of their tensile strength, growth rate and wood density, suggesting that thigmomorphogenesis plays an important role in the development of a strong bifurcation

Grasses and the resource availability hypothesis: the importance of silica-based defences

The resource availability hypothesis (RAH) predicts that allocation of resources to anti-herbivore defences differs between species according to their growth rate. We tested this hypothesis by assessing the growth and defence investment strategies of 18 grass species and comparing them against vole feeding preferences. In addition, we assessed the effectiveness of silica, the primary defence in many grasses, in influencing vole feeding behaviour. Across species, we found that there was a strong negative relationship between the overall investment in defence and growth rate, thus supporting predictions of the RAH. However, no such relationship was found when assessing the various individual anti-herbivore defences, suggesting that different grass species show significant variation in their relative investment in strategies such as phenolic concentration, silica concentration and leaf toughness. Silica was the most influential defensive factor in determining vole feeding preference. Experimentally induced increases in leaf silica concentration deterred vole feeding in three of the five species tested, and altered feeding preference ranks between species. The strong positive relationship between silica concentration and leaf abrasiveness, when assessed both within and between species, suggests that increased abrasiveness is the mechanism by which silica deters feeding. Although grasses are often considered to be tolerant of herbivore damage rather then defended against it, they do follow predictions of defence allocation strategy based on their growth rates, and this affects the feeding behaviour of generalist grass-feeding herbivores

The mechanical properties of wood and the design of Neolithic stone axes

Despite the importance of wooden tools for early man, and the development of woodworking in the Mesolithic and Neolithic culture, there has been surprisingly little research on how wood can be worked by stone tools or how wooden handles for composite tools were designed. This paper outlines an approach based on an understanding of the structure and mechanical properties of wood. The cell arrangement in wood makes it far less stiff, strong and tough across the grain, especially tangentially. This makes it hard to harvest wood or break it into lengths because it splits down its centre rather than breaking right across. Fortunately, this also makes wood easy to split along the grain, especially radially through its centre into sections and planks. A model of the splitting process predicted that wood is best split using blunt, broad but smooth wedges, as these would use less energy and would be less likely to get stuck in the wood. The predictions were verified in tests in which hazel coppice poles were split using wedges of contrasting angle, width and surface texture. The results help explain the change from the flaked flint Mesolithic tranchet axes to the broader polished stone Neolithic axe and adze heads. However, further experiments are also needed cutting wood obliquely to test this hypothesis. The splitting model also helps to understand the design of socketed axe hafts. Failure usually occurs when the handles split at the distal and proximal ends of the socket. To prevent this, handles are best designed with the growth rings parallel to the socket, and with an expanded head, especially with flanges on the distal and proximal ends of the socket. These designs are seen in some of the Neolithic axe handles that have been found in Britain, including the Etton, Ehenside and Shulishader axes. More experimental research is needed to understand the optimal way of hafting axe heads

Genotypic Variation in a Foundation Tree (\u3ci\u3ePopulus tremula\u3c/i\u3e L.) Explains Community Structure of Associated Epiphytes

Community genetics hypothesizes that within a foundation species, the genotype of an individual significantly influences the assemblage of dependent organisms. To assess whether these intra-specific genetic effects are ecologically important, it is required to compare their impact on dependent organisms with that attributable to environmental variation experienced over relevant spatial scales. We assessed bark epiphytes on 27 aspen (Populus tremula L.) genotypes grown in a randomized experimental array at two contrasting sites spanning the environmental conditions from which the aspen genotypes were collected. We found that variation in aspen genotype significantly influenced bark epiphyte community composition, and to the same degree as environmental variation between the test sites. We conclude that maintaining genotypic diversity of foundation species may be crucial for conservation of associated biodiversity

The impact of fungicide treatment and Integrated Pest Management on barley yields:Analysis of a long term field trials database

This paper assesses potential for Integrated Pest Management (IPM) techniques to reduce the need for fungicide use without negatively impacting yields. The impacts of three disease management practices of relevance to broad acre crops –disease resistance, forecasting disease pressure, and fungicide use – were analysed to determine impact on yield using a long-term field trials database of Scottish spring barley, with information from experiments across the country regarding yield, disease levels, and fungicide treatment. Due to changes in data collection practices, data from 1996 to 2010 were only available at trial level, while data from 2011 to 2014 were available at plot level. For this reason, data from 1996 to 2014 were analysed using regression models, while a subset of farmer relevant varieties was taken from the 2011–2014 data, and analysed using ANOVA, to provide additional information of particular relevance to current farm practice. While fungicide use reduced disease severity in 51.4%of a farmer-relevant subset of trials run 2011–2014, and yields were decreased by 0.62 t/ha on average, this was not statistically significant in 65% of trials. Fungicide use had only a minor impact on profit in these trials, with an average increase of 4.4% for malting and 4.7% for feed varieties, based on fungicide cost and yield difference; potential savings such as reduced machinery costs were not considered, as these may vary widely. Likewise, the1996–2014 database showed an average yield increase of 0.74 t/ha due to fungicide use, across a wide range of years, sites, varieties, and climatic conditions. A regression model was developed to assess key IPM and site factors which influenced the difference between treated and untreated yields across this 18-year period. Disease resistance, season rainfall, and combined disease severity of the three fungal diseases were found to be significant factors in the model. Sowing only highly resistant varieties and, as technology improves, forecasting disease pressure based on anticipated weather would help to reduce and optimise fungicide use

Systematic reappraisal of marsh-orchids native to Scotland

© The Author(s), 2023.This article is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.Summary: The intensively studied Eurasian orchid genus Dactylorhiza has become a model system for exploring allopolyploid evolution, yet determining the optimal circumscriptions of, and most appropriate ranks for, its constituent taxa remain highly controversial topics. Here, novel allozyme data and detailed morphometric data for 16 Scottish marsh-orchid populations are interpreted in the context of recent DNA sequencing studies. Despite being derived from the same pair of parental species, the two allopolyploid species that currently occur in Scotland can reliably be distinguished using allozymes, haplotypes, ribotypes or sequences of nuclear genes. A modest range of diverse morphological characters are shown to distinguish the two molecularly-circumscribed species, but they have in the past been obscured by equivalent levels of infraspecific variation in characters rooted in anthocyanin pigments; these characters are better employed for distinguishing infraspecific taxa. Dactylorhiza francis-drucei (formerly D. traunsteinerioides) is confirmed as being distinct from the continental D. traunsteineri/lapponica, probably originating through allopatric isolation once the continental lineage reached Britain. All Scottish populations are attributed to the comparatively small-flowered, anthocyanin-rich subsp. francis-drucei, which includes as a variety the former D. 'ebudensis'; the less anthocyanin-rich subsp. traunsteinerioides is confined to Ireland, North Wales and northern England. In contrast with D. francis-drucei, only a minority of Scottish populations of D. purpurella are attributed to the anthocyanin-rich race, var. cambrensis. This species most likely originated through an allopolyploidy event that occurred comparatively recently within the British Isles, as it contains allozyme alleles distinctive of British rather than continental D. incarnata (its diploid pollen-parent). In contrast, the rare Scottish population of D. incarnata subsp. cruenta shares with its Irish counterparts a continental genotype, and is most likely a recent arrival in Scotland through long-distance dispersal. Among all European allotetraploid dactylorchids, D. purpurella is the species that most closely resembles D. incarnata, both molecularly and morphologically.Peer reviewe

Substantial heritable variation for susceptibility to Dothistroma septosporum within populations of native British Scots pine (Pinus sylvestris)

The threat from pests and pathogens to native and commercially planted forest trees is unprecedented and expected to increase under climate change. The degree to which forests respond to threats from pathogens depends on their adaptive capacity, which is determined largely by genetically controlled variation in susceptibility of the individual trees within them and the heritability and evolvability of this trait. The most significant current threat to the economically and ecologically important species Scots pine (Pinus sylvestris) is dothistroma needle blight (DNB), caused by the foliar pathogen Dothistroma septosporum. A progeny-population trial of 4-year-old Scots pine trees, comprising six populations from native Caledonian pinewoods each with three to five families in seven blocks, was artificially inoculated using a single isolate of D. septosporum. Susceptibility to D. septosporum, assessed as the percentage of non-green needles, was measured regularly over a period of 61 days following inoculation, during which plants were maintained in conditions ideal for DNB development (warm; high humidity; high leaf wetness). There were significant differences in susceptibility to D. septosporum among families indicating that variation in this trait is heritable, with high estimates of narrow-sense heritability (0.38–0.75) and evolvability (genetic coefficient of variation, 23.47). It is concluded that native Scots pine populations contain sufficient genetic diversity to evolve lower susceptibility to D. septosporum through natural selection in response to increased prevalence of this pathogen

Spring phenology shows genetic variation among and within populations in seedlings of Scots pine (Pinus sylvestris L.) in the Scottish Highlands

Background: Genetic differentiation in phenotypic traits is often observed among forest tree populations, but less is known about patterns of adaptive variation within populations. Such variation is expected to enhance the survival likelihood of extant populations under climate change. Aims: Scots pine (Pinus sylvestris) occurs over a spatially and temporally heterogeneous landscape in Scotland. Our goal was to examine whether populations had differentiated genetically in timing of bud flush in response to spatial heterogeneity and whether variation was also maintained within populations. Methods: Two common-garden studies, involving maternal families of seedlings from 21 native pinewoods, were established and variation in the trait was measured at the beginning of the second growing season. Results: Populations showed genetic differences in the trait correlated with the length of growing season at their site of origin, but the majority of variation was observed within populations. Populations also differed in their levels of variation in the trait; a pattern that may be influenced by spatial variation in the extent of temporal climate variability. Conclusions: Our findings suggest that populations have adapted to their home environments and that they also have substantial ability to adapt in situ to changes in growing season length

An interdisciplinary method for assessing IPM potential:Case study in Scottish spring barley

A method is proposed which considers Integrated Pest Management (IPM) through several lenses, in order to obtain a more holistic view of the potential for IPM, and is described using a case study of Scottish spring barley. Long-term experimental field trial databases are used to determine which management methods are best suited to the system at hand. Stakeholder engagement provides insight into which of these methods are most likely to be taken up by farmers. Finally, a database of commercial practice allows an estimate of the potential for improving management patterns, based on current levels of IPM uptake across a wider sample of Scottish farmers. Together, these diverse sources of information give a more complete view of a complex system than any individual source could and allow the identification of IPM methods which are robust, practical, and not already in widespread use in this system. Bringing together these sources of information may be of particular value for policy and other decision makers, who need information about strategies which are both practical and likely to have a large positive impact. In the case of Scottish spring barley, there is good potential to reduce the need for fungicide use through the increased use of highly resistant barley varieties