1,720,974 research outputs found
Estimating the distribution of forage mass for ungulates from vegetation plots in Bavarian Forest National Park
No full textHerbaceous ground vegetation is an important pool of biomass and nutrients, which is also used as the major forage source for wild ungulates. Up to now no standard methods exist to estimate herbaceous biomass on a landscape level for temperate forests, which are characterised by deciduous trees with closed canopies. Quantity and quality of the herbaceous forage accessible to herbivores can be estimated from estimated cover in vegetation plot data and information on biomass and element concentrations in plant species. Vegetation was sampled stratified by community types and forest developmental phases in Bavarian Forst National Park, Germany. We adopted the PhytoCalc model to estimate biomass and bioelement stocks from vegetation plot data and adjusted species assignments and absolute levels of biomass to the conditions in the national park. We categorised attractiveness of plant species as forage for red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Multiple controls of total biomass and of plant groups (graminoids, ferns, herbs, Vaccinium, Rubus) were studied by stepwise regression against stand and environmental predictors. Herbaceous mass had a highly skewed distribution in the park, with 75% of plots having less than 231 g m(-2) of biomass or 24 g m(-2) of raw protein. Contributions of plant groups Were site-dependent and variable, but decreased in the order Vaccinium-graminoids-Rubus-herbs-ferns. Biomass appeared to be controlled by deciduous tree cover, by total cover of canopy and coarse woody debris and by site quality, with nutrient-poor, high elevation sites having higher herb biomass. As a consequence, montane beech forests offered less forage mass than coniferous communities of high elevations and mires. Stand disturbances by bark beetles and the corresponding forest developmental phases had no systematic effects on total biomass. Dominant grass and Vaccinium species are of intermediate attraction to foraging deer and reached higher mass in coniferous forests of poorer, colder and waterlogged sites, where higher summer activity. of the intermediate feeder Cervus elaphus were predicted. It is hypothesised that forest sites suboptimal for tree growth raise the park's carrying capacity for deer. Highly attractive, nitrophytic plant species were usually scarce (75% of plots with < 3 g m(-2)) and occurred in clumps after disturbances in mortal and juvenile phases of stand development, where up to 666 g m(-2) of attractive herbaceous plant mass were modelled. High soil fertility, as found in basiphytic beech forests, additionally favours these attractive plants. A relative preference of the selective browser Capreolus capreolus for these transient stages was predicted. The distribution of herbaceous forage mass and quality is subject to complex spatio-temporal patterns, the detection of which requires detailed vegetation data. The results suggest that it is possible to model the distribution of herbaceous vegetation for analyses at the stand and homerange scale. However, for a more comprehensive analysis of habitat choice the proposed method cannot deliver the required extent and accuracy
Rhizosphere hydrophobicity: A positive trait in the competition for water.
No full textThe ability to acquire water from the soil is a major driver in interspecific plant competition and it depends on several root functional traits. One of these traits is the excretion of gel-like compounds (mucilage) that modify physical soil properties. Mucilage secreted by roots becomes hydrophobic upon drying, impedes the rewetting of the soil close to the root, the so called rhizosphere, and reduces water availability to plants. The function of rhizosphere hydrophobicity is not easily understandable when looking at a single plant, but it may constitute a competitive advantage at the ecosystem level. We hypothesize that by making the top soil hydrophobic, deep-rooted plants avoid competititon with shallow-rooted plants. To test this hypothesis we used an individual-based model to simulate water uptake and growth of two virtual plant species, one deep-rooted plant capable of making the soil hydrophobic and a shallow-rooted plant. We ran scenarios with different precipitation regimes ranging from dry to wet (350, 700, and 1400 mm total annual precipitation) and from high to low precipitation frequencies (1, 7, and 14 days). Plant species abundance and biomass were chosen as indicators for competitiveness of plant species. At constant precipitation frequency mucilage hydrophobicity lead to a benefit in biomass and abundance of the tap-rooted population. Under wet conditions this effect diminished and tap-rooted plants were less productive. Without this trait both species coexisted. The effect of root exudation trait remained constant under different precipitation frequencies. This study shows that mucilage secretion is a competitive trait for the acquisition of water. This advantage is achieved by the modification of the soil hydraulic properties and specifically by inducing water repellency in soil regions which are shared with other species
Urbanization Leads to Increases in pH, Carbonate, and Soil Organic Matter Stocks of Arable Soils of Kumasi, Ghana (West Africa)
Get PDFTropical soils typically have low cation exchange capacity and nutrient contents. Both are enhanced by soil organic matter (SOM), which is thus particularly important for the fertility of these soils. In this study, we assessed the influence of urbanization on SOM, carbonate contents and pH of arable soils of Kumasi (Ghana, West Africa), since rapid urban sprawl is widespread in West Africa, whereby in many West African cities urban farming is pivotal to the food security of their population. Based on satellite imagery for the year 1986, we defined long-term and short-term urban arable soils, whereby long-term urban soils were urban already in 1986 (thus ≥30 years, as soil sampling took place in 2016), and short-term urban soils became urban afterwards (<30 years). We took 618 undisturbed topsoil samples (0–10 cm) from 206 urban arable fields. The factors land-use (maize fields) and soil (Ferric Acrisols) were kept largely constant. The fine-earth was analyzed for pH (water), carbonate contents, loss on ignition (LOI), total C (TC) and N (TN). SOM contents were obtained from LOI (SOMLOI). All element contents were transformed to bulk soil element stocks per m2. Differences between short-term and long-term urban soils were identified by a set of linear mixed models. Coarse fragments were more abundant in the long-term (16%) compared to the short-term (10%) urban soils, because of solid municipal waste that accumulates over time in urban soils. TC and SOMLOI concentrations of the fine earth, pH and C/N ratios were all significantly higher in the long-term urban soils. SOC concentrations in the fine earth, as well as bulk soil stocks of TC, SOC, and SOMLOI were also higher in the long-term urban soils, but at a lower degree of confidence, due to variable bulk densities and contents of coarse fragments. We conclude that dumping of organic and inorganic waste (including ash, bones, egg shells, concrete and mortar) increases SOM stocks and soil pH, but also leads to accumulation of non-degradable solid materials (including plastic, metals etc.). These findings point to the need of an improved urban waste management system, separating degradable and non-degradable waste
Habitat selection by a large herbivore at multiple spatial and temporal scales is primarily governed by food resources
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Intensive cattle browsing did not prevent fallow recuperation on smallholder grass-capoeira pastures in the NE-Amazon
No full textIn northeastern Para, extensive fallow-based agriculture systems are still common on smallholdings. Soil fertility is maintained by permitting the recuperation of the capoeira forest fallow. Much of the capoeira, however, has been eliminated, e.g. for permanent pastures but grass-monocultures usually ecologically degrade within a decade and lead often to barren pasturelands. To avoid these biologically degraded pastures, an innovative organic agro-forestry-system-model has been proposed, temporarily integrating pastures/cattle into the slash-and-burn cycle. The new approach assumes that cattle impact such as browsing and trampling would not alter the capoeira. This hypothesis was tested in researcher-managed on-farm experiments, by floristically comparing grass-capoeira pastures (GCP) against undisturbed capoeiras (UC) and traditional grass pastures (GP). Therefore, each pasture treatment was replicated three times on 0.36 ha pasture plots, respectively. Cattle were introduced at a stocking rate of 667 kg/ha, being reduced by one animal after 38 months to 410 kg/ha. Cattle impact was ascertained by comparing total capoeira phytodiversity, species similarity, life form structure, and vegetation cover. It was found that even intensive cattle impact on young capoeiras was neglectable and did not alter phytodiversity nor species composition. GCPs just showed a slight retardation in comparison to UC so that the botanical evidence of the ecological sustainability of a GCP could be proved. A PerMANOVA revealed that only 4.7 % (F = 5.513; RA(2)A = 0.047) of the differences between GCP and UC are attributed to the cattle impact/slashing regime. Our preliminary results suggest that the biodiverse system approach is worth pursuing as an alternative to degraded pastures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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