bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structure and dynamics of Abies magnifica forests in the southern Cascade Range, USA
Authors: Taylor Alan H. , Halpern Charles B. 
Published: May 2006

AbstractAbies magnifica (Red fir) forests in the Cascade Range and Sierra Nevada of California are composed of groups, or patches, of even‐sized individuals that form structurally complex stands. Patches may be even‐aged, resulting from synchronous post‐disturbance establishment, or multi‐aged, reflecting continuous recruitment of seedlings moderately tolerant of shade. We analyze the population structure (i.e. age, size, and spatial patterning) of A magnifica, and associated A concolor, White fir, and reconstruct the disturbance history of two mature to old‐growth A. magnifica forests in order to determine the relationship between disturbance and forest structure.Within both stands examined, the distributions of A. magnifica seedlings, saplings, and small understory trees were clumped, with clump sizes corresponding to the area of canopy gaps. Gaps were created by frequent wildfire (mean fire return interval of 41 yr) and by windstorms. Severe fire initiated mass establishment of Abies magnifica, whereas gaps created by windthrowreleasedalreadyestablishedindividuals. Lowinten‐sity fire stimulated little recruitment, but Red fir established continuously during fire‐free intervals. Thus, the complex age and structures of Red fir forests reflect both episodic and continuous recruitment, as determined by the type and severity of natural disturbance.
Recruitment pattern of Rhus integrifolia populations in periods between fire in chaparral
Authors: Lloret Francisco , Zedler Paul H. 
Published: May 2006

AbstractPopulation structure, fruit production and dispersal, and recruitment of Rhus integrifolia, a gynodioecious sclerophy llous shrub living in coastal chaparral, were studied in two localities in southern California last burned 60 and 90 years ago. Though hermaphroditic plants produce some fruits, only the male‐sterile plants bore significant numbers. Among the sample plants, one individual accounted for 50% of the crop measured. Terrestrial animals, through the loss of some seeds taken for consumption, play a decisive role in the seed dispersal, promoting the establishment of seedlings outside the parent's canopy. Birds have not been demonstrated to contribute to long distance dispersal, but they are responsible for dropping 25% of the fruits collected below the R. integrifolia canopies, 36%) of which were completely destroyed. Allelopathic effects were not observed in laboratory assays, and germination is probably not influenced by the species beneath which seeds have been deposited. This pattern can explain the non‐aggregated distribution of individuals observed in the studied populations. We conclude that establishment of new individuals has been continuous at both localities and that the populations of R. integrifolia are increasing in these long unburned stands. This may be indicative of a successional trend in unburned chaparral and coastal scrub toward a sclerophy llous woodland.
Dynamic aspects of diversity
Authors: Margalef Ramon 
Published: May 2006

Abstract. Ecological diversity is viewed as a measure of information, as the variety of messages compounded with the number of individuals belonging to different species. Two limit situations of diversity are indicated: a chemostat‐like system tending to become monospecific, and a Noah's ark or museum situation with an infinite number of species each represented by just one specimen. In a dynamic approach, two differential equations for S, the number of species, and N, the number of individuals, can be considered. A new index of diversity is proposed based on these two equations.The concept of diversity spectrum is proposed for a series of diversity measurements in samples of increasing size and related to the concept of minimal area. Diversity can also be measured on non‐taxonomic categories, e.g. size classes.The contrast between the two boundary types, limes convergens (ecotone) and limes divergens (ecocline), is emphasized. The nature of the difference between them is compared with that of tension zones between fluids in contact.Differences between ecosystems can be characterized through differences in the ratio P/B (Production/Biomass) and a boundary situation is imagined including two systems with P/B different values and different diversity levels. Some examples are presented from communities in streams.
Shrub architecture and occupation of space in a Mediterranean sclerophyllous shrubland
Authors: Guillén Dolores F. , De las Heras Paloma , Herrera Pedro , Pineda Francisco D. 
Published: May 2006

Abstract. Shrubland communities in Central Spain were studied through classifying growth forms of woody species and determining the shared use of the ground in progressively smaller spaces. 516 plants belonging to the six most abundant species and taken from different sites were included in biometric measurements. Principal Component Analysis (PCA) was used to detect the trends of variation in the architecture of plants. The individuals were classified on the basis of the results of the PCA and different morphological types were detected, mainly ‘elliptical’, ‘spherical’or ‘variable’according to their shape. These morphological types were adopted by most plants depending on their location and community.The horizontal occupation of space seems to be determined by whether or not the species rooted close to each other are able to occupy different strata. The co‐occurrence of two species in a reduced space is not facilitated when the two species have the same architecture. Then a spatial segregation tends to occur at a fine scale. The results can be interpreted as an optimization strategy of the shrubland ‘biomass/horizontal occupied area ratio’, which can be maximized in different environmental situations. It can also help to explain the ‘grain’ size of the pattern of horizontal spatial organization of the shrubland.
Evidence for lottery recruitment in Mediterranean old fields
Authors: Lavorel S. , Lebreton J. D. 
Published: May 2006

Abstract. The hypothesis of lottery establishment (Sale 1977) explains coexistence of species with similar niches through processes of stochastic recruitment. This initial idea forms the basis for a variety of mathematical models, but has not been tested empirically.This study is a field investigation of lottery establishment for plants with a seed bank, using Canonical Correspondence Analysis to compare the compositions of the vegetation and the seed bank according to different hypotheses on the mechanisms of establishment.This method was used for a data set from old fields from southern France. The weighted lottery (i.e. a random draw from the seed pool, weighted by the frequencies of each species) appeared as the best suited hypothesis to explain the high degree of similarity between the vegetation and the seed bank and the relative spatial distributions of the species. Several mechanisms are probably interacting, depending on the life histories of the species. Modelling and experimental approaches are needed to further test the hypothesis of lottery recruitment.
Seed dispersal and vegetation development on a debris avalanche on the Ontake volcano, Central Japan
Authors: Nakashizuka T. , Iida S. , Suzuki W. , Tanimoto T. 
Published: May 2006

AbstractSeed dispersal and early revegetation processes were studied in an area devastated by a debris avalanche that occurred on volcano Ontake, Central Japan in 1984. The avalanche was initiated by a volcanic earthquake, and a 3.4 x 107 m3 land mass destroyed the vegetation over 700 ha. The revegetation of the first five years was slow in the area of higher elevation (subalpine area). Both the speed of revegetation and the species richness of trapped seeds varied with the elevation. The post‐disturbance vegetation on the deposit with surface soil or plant fragments was richer in species than that without any surface soil. Almost all of the seeds caught by sticky traps and most of the species with frequent occurrence in the vegetation after disturbance were wind dispersed. Wind dispersal was especially important on the deposit without surface soil or plant fragments.
Small‐scale plant species turnover in a limestone grassland: the carousel model and some comments on the niche concept
Authors: van der Maarel Eddy , Sykes Martin T. 
Published: May 2006

Abstract. This study reports on small‐scale changes in the distribution of plant species in a 2.5 m2 plot of grazed, species‐rich Veronica spicata ‐ Avenula pratensis grassland on shallow, dry, nutrient‐poor soil in the Great Alvar area (Stora Alvaret) of southern Öland, southeastern Sweden. Multivari‐ate analysis of 0.001 m2 and 0.25 m2 quadrats within the plot showed that there is little floristic variation without any trend in the plot. Average species richness varied little throughout the study period from 1986 to 1991 with 1986 averages of 7.0 on 0.001m2, 16.3 on 0.01 m2, and 26.1 on 0.25 m2. On 0.001 m2the highest species number found was 12, on 0.01 m2, 27. However, cumulative species richness, i.e. species number in the first year plus new species appearing in later years (averaged over 40 quadrats) increased over the same period, on 0.001 m2 from 7.0 in 1986 to 14.9 in 1991, and on 0.01 m2 from 16.3 to 24.1. Cumulative frequency, i.e. number of quadrats out of 40 where a species occurred in the first year or/and in later years, increased as well; the number of cumulatively highly frequent (> 80%) species increased from 5 in 1986 to 18 in 1991.Species mobility on the scale of the small quadrats used implies both appearance and disappearance from these quadrats. Using six examples, species mobility is shown to vary individualistically, both in rate and degree.We postulate that in homogeneous, grazed, nutrient‐ and water‐deficient environments many species can reach virtually all microsites within the plot, which we express through the idea of the ‘carousel model’. We also question the usefulness of the niche concept and re‐interpret it by stating that all species of this plant community have the same habitat niche, while most of them are short‐lived and have the same regeneration niche. The essential variation amongst the species is their individual ability to establish or re‐establish by making use of favourable conditions appearing in microsites in an unknown, complex spatio‐temporal pattern.
Early primary succession on the volcano Mount St. Helens
Authors: del Moral Roger , Wood David M. 
Published: May 2006

Abstract. Primary succession on Mount St. Helens, Washington State, USA, was studied using long‐term observational and experimental methods. Distance from potential colonists is a major factor that impedes early primary succession. Sites near undisturbed vegetation remain low in plant cover, but species richness is comparable to intact vegetation. Sites over 500 m from sources of potential colonists have as many species, but mean species richness is much lower than in undisturbed plots. Cover is barely measurable after 11 growing seasons. Highly vagrant species of Asteraceae and Epilobium dominate isolated sites. Sites contiguous to undisturbed communities are dominated by large‐seeded species.For a new surface to offer suitable conditions to invading plants, weathering, erosion and nutrient inputs must first occur. The earliest colonists are usually confined to specific microsites that offer some physical protection and enhanced resources. Primary succession on Mount St. Helens has been very slow because most habitats are isolated and physically stressful. Well‐dispersed species lack the ability to establish until physical processes ameliorate the site. Species capable of establishment lack suitable dispersal abilities. Subsequently, facilitation may occur, for example through symbiotic nitrogen fixation, but these effects are thus far of only local importance. Lupinus lepidus usually facilitates colonization of other species only after it dies, leaving behind enriched soil lacking any competitors. Experiments and fine‐scale observations suggest that successional sequences on Mount St. Helens are not mechanistically necessary. Rather, they result from local circumstances, landscape effects and chance.
Multiple species effects and spatial autocorrelation in detecting species associations
Authors: Dale M. R. T. , Blundon D. J. , MacIsaac D. A. , Thomas A. G. 
Published: May 2006

Abstract.The traditional approach to the analysis of species association within a community, based upon co‐occurrence in sampling units such as quadrats, has been to test all pairs of species, using a 2 × 2 contingency table for each pair. It has long been recognised that all these tests are not independent of each other, but there is an additional problem in that the association between any particular pair may depend on the combination of the other species that are present or on the environmental factors that determine that combination. We use a 2kcontingency table to examine this problem and find that pairwise associations are not independent of the other species.The second problem that we consider is the effect of spatial autocorrelation in the data which makes the statistical tests too liberal. In the absence of a derived solution for a deflation factor to correct the test statistic calculated from a 2ktable, we describe a Monte Carlo approach that provides an approximate solution to this problem. In our data the amount of deflation that is necessary for a 2ktable is small compared to the amount required for the 2 × 2 tables used to test pairwise association.
Plant communities of trampled habitats in North Korea
Authors: Mucina L. , Dostálek J. , Jarolímek I. , Kolbek J. , Ostrý I. 
Published: May 2006

Abstract. A syntaxonomic study of trampled plant communities in North Korea is presented. Analytic and synthetic methods of the Braun‐Blanquet approach together with a numeric‐syntaxonomical analysis (cluster analysis and principal coordinate analysis ordination) were employed. With the exception of the Bryo‐Saginetum japonicae, all the associations, such as the Artemisio asiaticae‐Plantaginetum asiaticae, Plantagini depressae‐Polygonetum avicularis, Polygono avicularis‐Potentilletum costatae, Eragrostio multicaulis‐Plantaginetum depressae, Euphorbio maculatae‐Centipedetum minimae, Digitario pectiniformis‐Eleusinetum indicae and Setario viridis‐Chlorisetum virgatae, are described for the first time. Some communities also include a number of subassociations. Trampled communities are found along edges of paths and in cracks among paving stones. Soils vary from loamy to sandy and skeletal.A phenomenon of seasonality in expression of ruderal communities was observed in North Korea. It is assumed that this seasonality is controlled by pattern of precipitation showing distinct climatic seasons (e.g. pre‐monsoon and post‐monsoon periods). The ruderal vegetation seasonality is supposed to become more pronounced towards tropical regions. Several mesophilous or slightly hygrophilous European species occur frequently in North Korean trampled communities including Chenopodium glaucum, C. ficifolium and Potentilla supina. Their occurrence in trampled habitats is hypothesized as being related to high air humidity and associated wet climate.
Floristic division of the Arctic
Authors: Yurtsev Boris A. 
Published: May 2006

Abstract:The progress in the floristic study of the circumpolar Arctic since the 1940s is summarized and a new floristic division of this region is presented. The treeless areas of the North Atlantic and North Pacific with an oceanic climate, absence of permafrost and a very high proportion of boreal taxa are excluded from the Arctic proper. It is argued that the Arctic deserves the status of a floristic region. The tundra zone and some oceanic areas are divided into subzones according to their flora and vegetation. Two groups of subzones are recognized: the Arctic group (including the Arctic tundras proper and the High Arctic) and the Hypoarctic group.The Arctic phytochorion is floristically divided into sectors: 6 provinces and 20 subprovinces reflecting the regional features of each sector in connection with flora history, physiography and continentality‐oceanity of the climate. Each sector is described and differentiated by a set of differential and co‐differential species. The peculiarities of the Arctic flora are manifest in different ways in the various sectors, and endemism is not the universal criterion for subdivision.
Competition between three Chihuahuan desert species: evidence from plant size‐distance relations and root distribution
Authors: Briones Oscar , Montaña Carlos , Ezcurra Exequiel 
Published: May 2006

Abstract. Using size‐distance data we tested the intensity and importance of competition between Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a succulent) in the Chihuahuan desert. We also compared the vertical and horizontal distribution of roots to assess the potential degree of overlap in the use of soil resources. The relationships between sizes and distances of nearest‐neighbour plants suggested that intraspecific competition is generally more important than interspecific competition. However, evidence of stronger inter than intraspecific competition was found in some cases. Species combinations showing significant interspecific competition involved always Opuntia, whereas Larrea and Hilaria did not influence each other. The analysis of the symmetry of competition showed that Opuntia was adversely affected by the presence of Hilaria or Larrea.Although differences were found in the distribution of roots, the results of the size‐distance study support the idea that, (particularly) Opuntia, below‐ground niche differentiation is not sufficiently important to totally avoid the negative effects of plant competition.
Impact of different sheep grazing intensities on salt marsh vegetation in northern Germany
Authors: Kiehl K. , Eischeid I. , Gettner S. , Walter J. 
Published: May 2006

Abstract. Mainland salt marshes in Schleswig‐Holstein (northern Germany) have been grazed intensively by sheep for several decades. In 1988 experimental sites were established in the lower and middle salt marsh of Sönke‐Nissen‐Koog and subjected to different grazing intensities. From 1989 to 1993 the impact of sheep grazing on the composition and structure of the salt marsh vegetation was studied through the yearly analysis of permanent plots, vegetation mapping and measurements of the vegetation height.The intensively grazed site (10 sheep/ha) is covered by a short monotonous Puccinellia maritima sward with Salicornia europaea and Suaeda maritima. Halimione portulacoides and Aster tripolium, especially flowering plants, are rare.On the sites with 1.5 and 3 sheep/ha Puccinellia maritima remained dominant. The population density of Salicornia europaea decreases after reduction of the grazing intensity, whereas Suaeda maritima finds optimal growing conditions. Stands of Halimione portulacoides and flowering Aster tripolium plants are rare near the sea dike but their cover and size increases further away from the dike. In the plot with 1.5 sheep/ha the height of the vegetation increases along the gradient from the dike towards the tidal flats, due to local differences in actual grazing intensity.When grazing is stopped, Puccinellia maritima is successively replaced by Festuca rubra, Halimione portulacoides and Aster tripolium. High variability of vegetation height indicates structural diversity. Patches of higher and lower vegetation correspond with the distribution pattern of different plant species.In terms of nature conservation cessation of grazing is recommended.
Ecological responses of dominant grasses along two climatic gradients in the Great Plains of the United States
Authors: Epstein H.E. , Lauenroth W.K. , Burke I.C. , Coffin D.P. 
Published: May 2006

Abstract. Few empirical data exist to examine the influence of regional scale environmental gradients on productivity patterns of plant species. In this paper we analyzed the productivity of several dominant grass species along two climatic gradients, mean annual precipitation (MAP) and mean annual temperature (MAT), in the Great Plains of the United States. We used climatic data from 296 weather stations, species production data from Natural Resource Conservation Service rangeland surveys and a geographic information system to spatially integrate the data.Both MAP and MAT were significantly related to annual above‐ground net primary production (ANPP). MAP explained 54% to 89% of the variation in ANPP of two C4 short‐grasses, Bouteloua gracilis and Buchloë dactyloides, and two C4 tall‐grasses, Andropogon gerardii and Schizachyrium scoparium (= Andropogon scoparius). MAT explained 19% to 41% of the variation in ANPP of two C4 grasses, B. gracilis and B. dactyloides, and 41% to 66% of the variation in ANPP of two C3 grasses, Agropyron smithii and Stipa comata. ANPP patterns for species along both gradients were described by either linear, negative exponential, logistic, normal or skewed curves. Patterns of absolute ANPP (g/m2) for species differed from those of relative ANPP (%) along the MAP gradient. Responses were similar for species with common functional characteristics (e.g. short‐grasses, tall‐grasses, C3, C4).Our empirical results support asymmetric responses of species to environmental gradients. Results demonstrate the importance of species attributes, type of environmental gradient and measure of species importance (relative or absolute productivity) in evaluating ecological response patterns.
Regeneration of a dominant Mediterranean dwarf‐shrub after fire
Authors: Seligman No'am G. , Henkin Zalmen 
Published: May 2006

Abstract. The regeneration after fire of the dominant east Mediterranean dwarf‐shrub Sarcopoterium spinosum was studied under various habitat and geographic conditions in northern Israel, northern Crete and the Aegean coast of Turkey. Age structures of regenerating stands were determined 3–9 yr after fire on 13 1 mx 1 m sample stands by analysis of growth rings in the taproot crown of 874 plants. S. spinosum regenerated either by massive seedling recruitment in some habitats or by resprouting from surviving meristems in others. This versatility facilitates adaptation of the species to widely different environmental conditions and is a factor in the maintenance of its dominance after fire at occupied sites.In the years after fire, the growth of younger plants within the stand at all sites was severely suppressed by the older shrubs. Consequently, the age structure of the stands was dominated by one or two older cohorts that became established soon after fire. In addition, on most habitats, older shrubs (usually older than 6 yr) were often composed of clusters of plants that suggested clonal proliferation of ramets. The strongly peaked age structure, together with the appearance of clonal regeneration on the older plants, suggests that subsequent maintenance of the stand was not dependent on recurrent seedling recruitment. This can explain the persistence of S. spinosum in stands of herbaceous vegetation despite the extreme sensitivity of the seedlings to competition under such conditions.