7,203 research outputs found
Unexpected understorey community development after 30 years in ancient and post-agricultural forests
1. Land-use change is considered one of the most radical and extensive disturbances that have influenced plant distributions and diversity patterns in forest understorey communities in much of Europe and eastern North America. In forests growing on former agricultural land, local species diversity and community differentiation among sites are generally reduced compared to ancient forests (i.e. forests with no historical record of agriculture). Yet, no study has determined how the compositional differences created by former land use change over time as the forest sites recover from former agricultural use.
2. Here we resurveyed 78 vegetation plots (half of the plots in ancient and half in post-agricultural forest) to demonstrate how three decades of forest development have changed the compositional differences between post-agricultural and ancient forest sites. The impact of land-use history and survey date was tested on two measures of species diversity and two measure of community divergence.
3. The data indicate that the imprint of former agricultural land use persisted over time, yet not through compositional stability. Parallel and strong vegetation shifts occurred in both ancient and post-agricultural forest: the species diversity decreased and local species cover strongly diverged, which indicates community drift. The observed understorey changes did thus not support the commonly accepted model of community development in post-agricultural forests, i.e. the diversity did not increase and the vegetation did not become more similar to the ancient forest vegetation over time. The changes in species composition were associated with an increase of common, competitive species at the expense of ancient forest indicator species. The source populations of ancient forest species have been gradually depleted, so the recovery of post-agricultural forests becomes even more precarious.
4. Synthesis. While land-use history is likely to persist as the primary predictor of local species diversity and community divergence, other environmental drivers may additionally structure forest understorey communities and lead to biotic impoverishment and pervasive species reordering on the time scale of only decades
State of the Art in the Optimisation of Wind Turbine Performance Using CFD
Wind energy has received increasing attention in recent years due to its sustainability and geographically wide availability. The efficiency of wind energy utilisation highly depends on the performance of wind turbines, which convert the kinetic energy in wind into electrical energy. In order to optimise wind turbine performance and reduce the cost of next-generation wind turbines, it is crucial to have a view of the state of the art in the key aspects on the performance optimisation of wind turbines using Computational Fluid Dynamics (CFD), which has attracted enormous interest in the development of next-generation wind turbines in recent years. This paper presents a comprehensive review of the state-of-the-art progress on optimisation of wind turbine performance using CFD, reviewing the objective functions to judge the performance of wind turbine, CFD approaches applied in the simulation of wind turbines and optimisation algorithms for wind turbine performance. This paper has been written for both researchers new to this research area by summarising underlying theory whilst presenting a comprehensive review on the up-to-date studies, and experts in the field of study by collecting a comprehensive list of related references where the details of computational methods that have been employed lately can be obtained
Former land use affects the nitrogen and phosphorus concentrations and biomass of forest herbs
The colonization rates of understorey plants into forests growing on former agricultural land differ remarkably among species. Different dispersal and recruitment largely account for the contrasting colonization rates, but different effects of the soil legacies of former agricultural land use on plant performance may also play a role. Seven herbaceous forest species were sampled in paired post-agricultural and ancient forest stands to study whether land-use history has an effect on the aboveground nutrient concentrations (N, P and N:P ratios) and biomass of forest herbs and, if so, whether slow and fast colonizing species respond differently. Results showed that P concentrations were significantly affected by former land use with higher concentrations in the post-agricultural stands. N concentrations were unaffected and N:P ratios were significantly higher in the ancient stands. Nutrient concentrations varied considerably among species, but the variation was unrelated to their colonization capacity. Six out of the seven species had higher biomass in the post-agricultural stands relative to the ancient stands, and the degree to which the species increased biomass was positively related to their colonization capacity, i.e., the fast colonizing species showed the strongest increase. Such differential responses to past land use may contribute to the contrasting colonization capacity of forest plants. Land-use history thus affected both the nutrient concentrations and biomass of forest herbs, and only the biomass response was related to colonization capacity
When it Pays to Rush: Interpreting Morphogen Gradients Prior to Steady-State
During development, morphogen gradients precisely determine the position of
gene expression boundaries despite the inevitable presence of fluctuations.
Recent experiments suggest that some morphogen gradients may be interpreted
prior to reaching steady-state. Theoretical work has predicted that such
systems will be more robust to embryo-to-embryo fluctuations. By analysing two
experimentally motivated models of morphogen gradient formation, we investigate
the positional precision of gene expression boundaries determined by
pre-steady-state morphogen gradients in the presence of embryo-to-embryo
fluctuations, internal biochemical noise and variations in the timing of
morphogen measurement. Morphogens that are direct transcription factors are
found to be particularly sensitive to internal noise when interpreted prior to
steady-state, disadvantaging early measurement, even in the presence of large
embryo-to-embryo fluctuations. Morphogens interpreted by cell-surface receptors
can be measured prior to steady-state without significant decrease in
positional precision provided fluctuations in the timing of measurement are
small. Applying our results to experiment, we predict that Bicoid, a
transcription factor morphogen in Drosophila, is unlikely to be interpreted
prior to reaching steady-state. We also predict that Activin in Xenopus and
Nodal in zebrafish, morphogens interpreted by cell-surface receptors, can be
decoded in pre-steady-state.Comment: 18 pages, 3 figure
Implantation of Subcutaneous Radio Transmitters in the Harbor Seal (\u3ci\u3ePhoca vitulina\u3c/i\u3e)
Radio telemetry has become a standard tool for studying the behavior, physiology, life history traits, and population dynamics of marine mammals. Radio transmitters typically are attached to the hind flippers of pinnipeds or glued to the fur using marine epoxy or other cyanocrylare adhesives (Fedak et al. 1983, Bengtson 1993, Jeffries et al. 1993). Longterm data acquisition is difficult, however, because radio-flipper transmitters commonly tear from the webbing of the flipper and instruments that are glued to the fur are shed during the seasonal molt
Glypican Gene GPC5 Participates in the Behavioral Response to Ethanol: Evidence from Humans, Mice, and Fruit Flies
Alcohol use disorders are influenced by many interacting genetic and environmental factors. Highlighting this complexity is the observation that large genome-wide association experiments have implicated many genes with weak statistical support. Experimental model systems, cell culture and animal, have identified many genes and pathways involved in ethanol response, but their applicability to the development of alcohol use disorders in humans is undetermined. To overcome the limitations of any single experimental system, the analytical strategy used here was to identify genes that exert common phenotypic effects across multiple experimental systems. Specifically, we (1) performed a mouse linkage analysis to identify quantitative trait loci that influence ethanol-induced ataxia; (2) performed a human genetic association analysis of the mouse-identified loci against ethanol-induced body sway, a phenotype that is not only comparable to the mouse ethanol-ataxia phenotype but is also a genetically influenced endophenotype of alcohol use disorders; (3) performed behavioral genetic experiments in Drosophila showing that fly homologs of GPC5, the member of the glypican gene family implicated by both the human and mouse genetic analyses, influence the fly’s response to ethanol; and (4) discovered data from the literature demonstrating that the genetically implicated gene’s expression is not only temporally and spatially consistent with involvement in ethanol-induced behaviors but is also modulated by ethanol. The convergence of these data provides strong support to the hypothesis that GPC5 is involved in cellular and organismal ethanol response and the etiology of alcohol use disorders in humans
Effect of tree species mixture on earthworm communities on a continental scale
The belowground food web represents a major part of associated biodiversity in forest
ecosystems, and plays a significant role in the ecosystem processes of litter decomposition and
nutrient turnover. Past research has demonstrated overwhelming evidence of strong tree
species identity effects on earthworm communities. It has been proposed that increased plant
community diversity would be beneficial to the abundance and diversity of the belowground food
web, but effects of tree species diversity on earthworm communities have seldom been
reported, and are inconclusive.
In this study at continental scale we evaluated whether tree species diversity positively affects
earthworm biomass and diversity. For this purpose the FunDivEUROPE Exploratory Platform
was used with 209 plots in 6 regions well spread over Europe with a low within-region site
variability, but a within-region tree species diversity gradient from monocultures to 3 or 4
species plots. In every plot earthworms were sampled using a combined method of mustard
extraction and hand sorting of litter and a soil monolith. Data are being analysed with
multivariate tools and mixed effects models.
First results suggest only limited influence of tree diversity on the biomass of earthworm
communities at continental scale. Tree diversity effects are weak, context specific and
interacting with tree identity. In nutrient poor soils we found a negative tree diversity effect on
earthworm biomass when deciduous monocultures are enriched with coniferous species, while
in rich soils we found a positive tree diversity effect which could be related with the food security
this provides to the earthworm community.FUNDIVEUROPE - Functional significance of forest biodiversity in Europ
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