bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diversity and phenology of weed communities in the Nile Delta region
Authors: Shaltout K. H. , El Fahar R. A. 
Published: May 2006

AbstractThis study evaluates the species diversity and phe‐nological behaviour of the weed communities associated with the common crops in the Nile Delta region (three winter crops: Egyptian clover, broad beans and wheat; and three summer crops: cotton, maize and rice). The weed communities of winter crops are of higher diversity than those of summer crops, presumably due to differences in sowing and weeding processes. The phenological sequences of the weed communities are, in most cases, closely related to those of the crops in which they occur. The correspondence between the crucial periods in the life cycle of the weed and the crop (seedling establishment and fruiting) often leads to severe competition.
Influence of landscape complexity and land management on woody plant diversity in northern Spain
Authors: Rescia A.J. , Schmitz M.F. , Martín de Agar P. , de Pablo C.L. , Atauri J.A. , Pineda F.D. 
Published: May 2006

Abstract. Changes in land use, particularly the type of forest management, and their spatial pattern, especially woody plant diversity, were related to each other in an area in the Basque region (Spain). The number and diversity of boundaries between landscape patches is related to the development of the spatial complexity of the landscape, C(s), measured in bits and defined as: C(s) = H(b) H(l), where H(b) is the boundary diversity H(1) the spatial heterogeneity generated by these boundaries.As to the vegetation types, changes in land use over the last 50 yr have resulted in a less diversified and more fragmented landscape, especially on a small scale. Forest plantation has become the predominant land use. The frequency of land use changes is studied regarding its influence on the present levels of woody plant diversity.
Influence of management on the seed production and seed bank of calcareous fen species
Authors: Schopp‐Guth Armin , Maas Dieter , Pfadenhauer Jörg 
Published: May 2006

Abstract. The dynamics of the seed production and seed bank of two dominant perennial species of calcareous fens were investigated in response to different mowing frequency, fallow or pasture. The production of fertile shoots responded strongly to management practices. On sites where mowing alternated with fallow, autumn mowing led to an increase of fertile shoot density in Schoenus ferrugineus and a decrease in Molinia caerulea in the subsequent season. Repeated annual mowing after long‐term fallow raised the density in Schoenus and inhibited initiation of flowering shoots in Molinia. Seed set and viability were influenced mainly by climatic or other factors. Variation of seed production between sites and in consecutive years at the same site could thus be large.The relationship between total seed production and seed bank was weak, but it improved when germination rates were included in the calculation. As the seed bank was generally smaller than the viable seed production, low survival and a high turnover of seeds in the upper soil layers is assumed for both species. Implications for recruitment strategies are discussed.
Spatial patterns of trees in natural forests of East‐Central Europe
Authors: Szwagrzyk Jerzy , Czerwczak Marek 
Published: May 2006

AbstractThe analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynamics. Three hypotheses concerning distribution patterns in old‐growth stands were tested: (1) fine‐scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old‐growth forest stands in Poland and the Czech Republic were analysed with a modified RipleyKfunction, using distribution maps of tree stems.Fine‐scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15–25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.
Resource availability at three presumed stages of a heathland succession on the Lüneburger Heide, Germany
Authors: Leuschner Ch. 
Published: May 2006

Abstract. The availability of maj or plant resources was investigated in three vegetation types that were assumed to represent different stages of a secondary succession on heathland on the Lüneburger Heide, northwestern Germany. Canopy transmission and absorption of photosynthetically active radiation (PAR), soil‐water availability, and nutrient (Ca, K, Mg, N, P) availability were monitored with high spatial and temporal resolution in (1) a Calluna vulgaris heathland, (2) a pioneer birch‐pine forest and (3) a late‐successional oak‐beech forest, situated close to each other on comparable geological substrate (diluvial). Mean fractional transmission of PAR during summer decreased from 0.48 in the heathland to 0.04 in the oak‐beech forest while the fractional canopy absorption increased from 0.49 to 0.92.Soil‐water availability as indicated by the soil‐water potential, was significantly influenced by differential canopy interception loss and characteristic rooting patterns in the three vegetation types. Annual mean nutrient concentrations in the equilibrium soil solution were similar or, for some elements, increased from the heathland to the birch‐pine and the oak‐beech forest despite a growing demand. A marked increase was found for the total nutrient pools in the soil‐organic layer between early and late successional vegetation types. On the poor glacial parent material, nutrient pools seem to be strongly dependent on stand productivity and litter production which increased with succession. Thus, for nutrients, facilitation seems to be important in this type of succession.
Altitudinal pattern of vegetation variation on Tenerife
Authors: Fernández‐Palacios José María , de Nicolás Juan Pedro 
Published: May 2006

Abstract. The variation in structure and floristic composition of the vegetation of Tenerife is related to different environmental factors. 200 sample plots, stratified according to altitude, exposure to wind, kind and age of parent rock, inclination and degree of disturbance were analysed throughout the island. The resulting data were analysed using univariate statistics (altitudinal distribution profiles of the more frequent species) and multivariate methods (Correspondence, Cluster and Pattern Analysis).Altitude, exposure to wind and, to a lesser extent, disturbance were found to be the major determinants of vegetational variation, whereas parent rock and inclination were less important. Ordination results show a continuum in structural and floristic variation of the vegetation with species distributions varying continually along the altitudinal gradient. Nevertheless, altitudinally bound plant community types were recognized with Cluster Analysis. Vegetational discontinuities, which were also detected by pattern analysis, are more evident on the windward slope of the island; they have been attributed to the existence of a major underlying environmental discontinuity the ‘cloud sea’‐which is associated with a climatic inversion. On the leeward slope, beyond the influence of the cloud sea, discontinuities are less evident and vegetational variation seems to be closer to a coenocline, i.e. a vegetational continuum.
In situregeneration ofPinus strobusandP. resinosain the Great Lakes forest communities of Canada
Authors: Carleton T.J. , Maycock P.F. , Arnup R. , Gordon A.M. 
Published: May 2006

Abstract.Two extensive forest vegetation survey datasets are explored, using ordination and classification, for evidence ofin situregeneration byPinus strobus(Eastern white pine) andP. resinosa(Red pine). Ordination of tree species contributions to total basal area in 320 upland northern hardwood‐ conifer stands produced distinct stand groups forP.banksiana, P. resinosa,P. strobusand mesic hardwoods in an ascending sequence along the first axis.Quercus rubra(red oak),Q. alba(white oak) and tolerant conifer groups formed segregates from the hardwood complex along the second axis.P. strobusmixes with all other forest types, butP. resinosais restricted to its own group. Seedlings and trees ofP. strobusare more abundant than saplings, which are restricted to the pine and oak forests. Therefore, seed production, dispersal and seedling establishment seem to be less of a barrier toin situregeneration byP. strobusthan subsequent survival and growth.Canonical correspondence analysis of 170 pine‐dominated stands from the Canadian Shield of Ontario, in which tree species variables are segmented into height‐class pseudo‐ species, yielded no linear relationship between environmental features or stand structure and seedling densities ofP. strobus. However, total tree basal area appears to impose an upper limit to seedling density on the forest floor. Strong correlations emerged between pine seedling density and understorey vegetation. Stand classification of the understorey vegetation, using constrained indicator species analysis, yielded distinct high and low seedling groups. Low pine seedling density was associated with abundant broadleaved shrubs, herbs and seedlings as well as feathermosses and tolerant conifers. High seedling density could not be ascribed to the presence of seedbed taxa, such asPolytrichum, but is ascribed to the absence of competition and other forms of inhibition in the understorey vegetation and down through the canopy profile.In situregeneration ofP. strobusdoes, therefore, occur but conditions over the forest landscape are largely restrictive.
Successional status of trees in gallery forest along the river Rhine
Authors: Schnitzler Annik 
Published: May 2006

Abstract. 20 alluvial forest stands of different ages along the river Rhine in central Alsace, France, are described. A natural complex landscape occurs which is formed by erosion activity of the river. Recent human impact (canal construction, cutting) has affected river hydrology: flooding is eliminated over large areas and the underground water levels are stabilized. The forest vegetation varies in species diversity and structure, from young pioneer to older, mid‐successional forests. The forests were classified into four associations: Salici‐Populetum nigrae, Ligustro‐Populetum nigrae, Fraxino‐Populetum albae and Querco‐Ulmetum minoris. The first three communities are ‘softwood’ because of the dominance of Salix and Populus, the fourth, dominated by Quercus robur, Fraxinus excelsior and Ulmus minor, is ‘hardwood’.Differences in structure, species composition and diversity in 10 widely varying stands in 30‐yr and 150‐yr old forests are quantified and interpreted in relation to the processes and gradients (moisture and texture) involved.A model of forest succession is developed as follows:

Whatever the topographic level, Salix and Populus species are the most competitive in colonizing bare sediments.
Under natural conditions, pioneer softwoods are generally replaced by hardwoods in less than 100 yr.
Old Querco‐Ulmetum is basically the terminal stage of the alluvial succession.
Old softwood forests result from an interruption of the natural course of succession. Softwoods may be an intermediate or late‐successional phase depending on the interruption.
Successional processes change according to hydrological and edaphic gradients.
Allogenic processes of flooding are fundamental in the space‐time species pattern.
Allogenic processes are responsible for the high species and community diversity.
Effects of reindeer grazing on understorey vegetation in dry Pinus sylvestris forests
Authors: Väre Henry , Ohtonen Rauni , Oksanen Jari 
Published: May 2006

Abstract. Data on floristic composition and environmental variables were collected in floristically homogeneous oligotrophic pine (Pinus sylvestris) forests with heath‐like under‐ storey vegetation in eastern Fennoscandia, and ordinated by non‐linear multidimensional scaling (NMDS) in order to study the effect of lichen grazing by reindeer on the understorey vegetation. The study sites included areas with varying grazing pressure, as well as 50‐yr old grazing exclosures. Sites rich in respectively bryophytes and lichens were placed at opposite ends of the ordination axes, and heavily grazed sites were placed in between them. Reindeer grazing increased the abundance of bryophytes, especially Dicranum spp. and Pleurozium schreberi. Grazing changed the vegetation to the extent that it resembled more mesotrophic sites, but this did not show any relationship with tree volume or other site productivity indicators. This was observed both in the ordination and, in a more compelling way, when exclosures with adjacent grazed areas were compared. No such signs were evident at ungrazed sites, where especially Cladina spp. spatially replace Cladonia spp. and tiny bryophytes like Barbilophozia spp., Polytrichum spp. and Pohlia nutans during succession. Cladina stellaris had almost disappeared from the most intensively grazed sites.The soil at ungrazed sites was characterized by high Al and Fe concentrations and bryophyte‐rich sites by high Mn concentrations. Shannon's diversity index, depth of humus layer and proportion of bare ground also increased in sites getting richer in bryophytes.
Dynamics of understory vegetation in an old‐growth boreal coniferous forest, 1988–1993
Authors: Økland Rune Halvorsen , Eilertsen Odd 
Published: May 2006

Abstract. Understorey vegetation changes in a South Norwegian old‐growth coniferous forest were studied between 1988 and 1993 in 200 1‐m2 vegetation plots. Our aims were to quantify the amount of between‐year compositional change, and to elaborate the environmental basis for long‐term vegetation change, including the previously identified gradient structure with a major gradient related to topography (and soil nutrient status and soil depth) and a minor gradient reflecting paludification and canopy coverage.Species richness (yearly mean and cumulative species number) and change in species richness differed between vascular plants and cryptogams, and between forest types. The number of vascular plant species decreased in pine forest in dry years; bryophyte species number increased in spruce forest.Statistically significant vegetation change, as tested by constrained ordination (CCA) with time as the constraining variable, is demonstrated for most one‐year periods and for the five‐year period in most forest types. Vegetation change along identified gradients, measured as plot displacement along DCA ordination axes, also occurred. The magnitude of year‐to‐year vegetation change was related neither to forest type nor to one‐year period; different responses to climatic and environmental change were observed in each forest type. The largest average displacement observed, from medium‐rich spruce forest towards poor spruce forest, was interpreted as a long‐term trend. Humus‐layer pH decreased by ca. 0.25 units from 1988 to 1993, most strongly in medium‐rich spruce forest where exchangeable Ca decreased and Al and Mn increased strongly.Our study supports the hypothesis that vascular plants show a long‐term and broad‐scale response to soil acidification. Change in bryophyte composition is linked to some very long growing‐seasons. Detailed analysis of short‐term vegetation dynamics enhances the interpretation of long‐term changes and stresses the complementarity of univariate and multivariate methods in the analysis of vegetation change.
Seed population dynamics on badland slopes in southeastern Spain
Authors: García‐Fayos P. , Recatalá T.M. , Cerdá A. , Calvo A. 
Published: May 2006

Abstract.The dynamics of seed population on slope surfaces were studied to test the hypothesis that the lack of vegetation on badlands is caused by seed removal by erosion. The initial soil seed bank and two years of seed rain and seed removal by erosion were estimated in two small catchments, and a seed balance was constructed. In addition, six rainfall simulation experiments were performed to test the susceptibility of seeds to be removed by overland flow. A variety of soil surface conditions, rainfall characteristics and plot sizes were used in these experiments.Soil seed bank densities are low, but enough for the development of plant cover. Seed losses due to erosion after natural rains were low (< 13 %), and in agreement with seed losses from simulated rainfall experiments. After two years, seed inputs in the seed rain were greater than seed outputs through seed removal, which resulted in a continuous increase in the numbers of seeds in the soil bank. These results point out that seed removal by erosion is not the key factor explaining the lack of vegetation on badlands. It is suggested that other factors, such as those related to seed germination and seedling survival, may play an important role.
Interactive effects of fire and grazing on structure and diversity of Mediterranean grasslands
Authors: Noy‐Meir Imanuel 
Published: May 2006

Abstract. The separate and combined effects of fire and cattle grazing on structure and diversity of productive Mediterranean grasslands in northern Israel were examined within a set of climatically and edaphically similar sites. Cover and height of green and dry plants in winter, and species richness and diversity in spring, were measured in paired transects on both sides of cattle fences, and on both sides of boundaries of both incidental and experimentally lit fires.Early in the first growing season after a fire, plant cover as well as height of green plants were reduced, compared to unburnt grassland. These structural effects of fire were similar to the effects of grazing, but they were greater in ungrazed than in grazed grasslands, indicating a fire‐grazing interaction. The effects of fire were considerably attenuated in the second growing season after the fire.Species richness and diversity tended to be higher in grazed than in adjacent ungrazed grasslands. Richness consistently increased after a fire only in grazed grasslands with a strong perennial component. In ungrazed grasslands, and in predominantly annual grasslands, fires reduced species richness and diversity at least as often as they increased it.Fire and grazing should be regarded as two agents with distinct and interactive effects on the community, rather than as two alternative mechanisms of a general disturbance factor.
Classification of vegetation: Past, present and future
Authors: Mucina Ladislav 
Published: May 2006

Abstract. This paper is a report on the past, status‐quo and perspectives of vegetation classification, still a major occupation of many vegetation scientists. The history of vegetation classification is discussed against a background of several controversial issues such as the problem of continuum vs. discontinuum, naturalness vs. arbitrariness of the nature of plant communities, universality vs. ad hoc character of syntaxonomic schemes, as well as classical versus numerical approaches to data analysis for classification purposes.The development of the methodology of vegetation science and the present image of vegetation classification is documented by a bibliometric analysis of the publication record of four majorjournals: Journal of Vegetation Science, Vegetatio, Phytocoenologia and Tuexenia. This analysis revealed a persisting controversy between traditional and numerical approaches to vegetation classification. A series of important changes in vegetation science (foundation of new journals, change of editorial policy by the established, important meetings) punctuate a period called the ‘Innovation period’.Several trends in the development of methods of vegetation systematics are summarized under the headings formalism, pluralism, functionalism, pragmatism and indeterminism. Some new features, such as the development and improvement of numerical tools, use of large data banks and attempts to summarize the theory of vegetation classification are discussed. The new growth‐form system of Barkman initiated a revival of physiognomy‐based vegetation classification. Within this framework the use of the character‐type concept and the development of new numerical methods for studying the hierarchical structure of character‐set types seems to be a promising approach. The achievements of population biology and ecophysiology have affected vegetation science by emphasizing the functionality of species within plant communities. The use of guilds and other functional groups has experienced an increasing interest from vegetation scientists. Applied in vegetation science, fuzzy‐set theory has bridged the techniques of classification and ordination of plant communities.
Transect‐based patch size frequency analysis
Authors: Xiaobing Dai , van der Maarel Eddy 
Published: May 2006

Abstract.A new, transect‐based patch size detection method for species pattern is proposed which improves results obtained with methods described earlier. The method was tested on an extensive artificial data set together with three of the existing methods considered best: Two and Three Term Local Quadrat Variance (T2LQV and T3LQV) and New Local Variance (NLV). The TLQV methods recovered only some of the existing patterns and were heavily dependent on inter‐patch distances, whereas NLV almost always produced curves with oscillations. In addition a significance test is proposed, while such a test is seldom found in the earlier methods.Our method, PASFRAN, determines the frequencies of runs with 1, 2, 3, etc. quadrats containing a certain species and compares those with frequencies based on Monte Carlo simulated random configurations. The comparison is performed for each run length and the significance of the deviation between observed and expected frequencies can be calculated on the basis of a large number of simulations. Because this approach may be considered a case of multiple testing, a Bonferroni correction on the significance level was applied. The method can also be used for the detection of inter‐patch distances. In addition, run lengths can be grouped and the test can be applied to the frequencies of combinations of run lengths.The method can detect dominance patches when quantitative data on the occurrence of plant species are available. In the same way, it can detect multi‐species patterns using sample scores from an ordination analysis such as correspondence analysis. An extension towards composite, higher‐order patterns is under investigation. The new method appeared to be effective in recovering artificial patterns, while it is not influenced by the relative values of patch size and inter‐patch distance. When applied to the distribution of cow dung patches and certain plant species along a transect of 500 quadrats of 10 cm × 10 cm in an alvar limestone grassland, it produced straightforward and realistic results as compared with other methods and field impressions.