bluuebunny/crossref_metadata_2025_split huggingface dataset:
Persistence of a rare aquatic species along gradients of disturbance and sediment richness
Authors: Greulich Sabine , Bornette Gudrun , Amoros Claude 
Published: May 2006

Abstract. This study examines the capacity of establishment of a rare aquatic macrophyte, Luronium natans, within plant communities and habitat types in which it does not occur spontaneously. The species, generally limited to disturbed or nutrient‐poor habitats, was transplanted into a series of sites situated along natural gradients of disturbance (flush‐floods and intermittent sediment exposure) and sediment nutrient‐richness. The transplanted colonies were given a competition‐free establishment period. Colony dynamics of Luronium as well as size structure of the recolonizing macrophyte communities were monitored over three growing seasons. At the end of this period, transplanted colonies still persisted in five out of 12 transplantation sites. Apparently successful integration into the community occurred at both ends of the nutrient gradient, in periodically disturbed habitats. At intermediate to high nutrient richness Luronium maintained one of the highest cover values within the recolonizing community.The study supports previous presumptions that long‐term persistence of Luronium depends on processes limiting community biomass through occurrence of disturbance. But it also reveals the existence of suitable, yet not occupied habitats in which the species can persist as successfully as species from the local species pool. This finding modulates the presumption that Luronium's rarity is mainly caused by a weak competitive ability in the established phase. It thus rises questions about the species’ performance at other stages of its life cycle and on its dispersability.
Diversity and pH changes after 50 years on the boreal mire Skattlösbergs Stormosse, Central Sweden
Authors: Gunnarsson Urban , Rydin Håkan , Sjörs Hugo 
Published: May 2006

Abstract. The Skattlösbergs Stormosse mire was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providing a unique opportunity to quantify long‐term mire dynamics.The results show decreased pH in the richer (high‐pH) parts of the mire, but little or no change in the poor fen and ombrotrophic parts. 14 species had disappeared while two new species were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in 10m x 10m plots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 73% of other bryophyte species and 38% of vascular plant species had decreased by more than 20% in plot frequency.There was a strong relationship between number of species and pH‐value. The mean and standard deviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in more polluted areas.
Long‐term vegetation dynamics mediated by herbivores, weather and fire in a Juniperus‐Quercus savanna
Authors: Fuhlendorf Samuel D. , Smeins Fred E. 
Published: May 2006

Abstract. Long‐term (45‐yr) basal area dynamics of dominant graminoid species were analyzed across three grazing intensity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Research Station on the Edwards Plateau, Texas. Grazing intensity was identified as the primary influence on long‐term variations in species composition. Periodic weather events, including a severe drought (1951–1956), had little direct influence on composition dynamics. However, the drought interacted with grazing intensity in the heavily grazed treatment to exacerbate directional changes caused by grazing intensity.Species response to grazing was individualistic and noisy. Three response groups were identified. Taller, more productive mid‐grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic to weather patterns. Graminoid diversity increased with the removal or reduction of grazing intensity. The moderately and ungrazed treatments appeared most resistant to short‐term weather fluctuations, while the heavily grazed treatment demonstrated significant resilience when grazing intensity was reduced after over 110 yr of overgrazing.Identification of a ‘climax’ state is difficult. Significant directional change, which took nearly 20 yr, appears to continue in the ungrazed treatment after 45 yr of succession. The observed, relatively linear patterns of perennial grass composition within the herbaceous patches of this savanna were generally explained by traditional Clementsian succession. However, when dynamics of the herbaceous community are combined with the woody component of this savanna, the frequency and intensity of fire becomes more important. Across the landscape, successional changes follow several pathways. When vegetation change is influenced by several factors, a multi‐scale model is necessary to demonstrate interactions and feedbacks and accurately describe successional patterns. Absence of fires, with or without grazing, leads ultimately to a Juniperus/Quercus woodland with grazing intensity primarily influencing the fuel load and hence fire intensity.
Nutrient supply in undrained and drained Calthion meadows
Authors: van Duren I.C. , Pegtel D.M. , Aerts B.A. , Inberg J.A. 
Published: May 2006

Abstract. Plant species‐rich Calthion meadows on mesotrophic fen peat soil extensively cut for hay are among the endangered semi‐natural vegetation types in northwestern Europe. They are often badly affected by lowering the groundwater table (drainage) and fertilization.In a comparative study of an undrained site with a Calthion meadow and an adjacent drained site, availability of N, P and K was biologically assessed under field conditions (for two years) as well as in a greenhouse (for 18 weeks) by measuring shoot responsiveness. Also, experimental wetting of intact turf samples taken from both sites was applied in order to study the interaction between nutrient supply and anaerobic soil conditions. It was concluded that the above‐ground phytomass yield in the undrained site was restricted by a major shortage of N‐supply and a moderate shortage of K‐supply by the fen peat soil. The above‐ground phytomass yield of the drained site was only reduced by a strongly limited supply of K by the soil. The extent of K‐deficiency was larger for the drained site. No P‐deficiency was observed in any of the drained or undrained sites. Rewetting turf samples, taken from the drained site, did not change above‐ground phytomass yields, suggesting that nutrient supplies were not affected by rewetting. Leaching has likely resulted in a strong reduction of K‐supply in the drained site. It is assumed that a shortage in K‐supply from the peat soil may have become an important environmental constraint for characteristic plant species of Calthion meadows. This may hamper the development of this meadow type on drained peat soils after rewetting by groundwater discharge.
Deriving functional types for rain‐forest trees
Authors: Gitay H. , Noble I.R. , Connell J.H. 
Published: May 2006

Abstract. A common goal in functional type research is to find a useful classification that defines the dynamic behaviour of groups of species in relation to environmental variation. Long‐term data sets on the dynamics of forests are difficult to obtain; thus, it would be useful if more readily available data, such as that on morphological and life history characters, could be used to derive groups that reflect the dynamics of the species. We used a 30‐yr data set on the dynamics of subtropical rainforests in Australia to derive classification based on the dynamics of the species and compared this classification with groups of species derived by other approaches. Functional types were derived for ca. 80 tree species using subjective, deductive and data‐driven approaches. The subjective classification used was a pioneer to late successional grouping. The deductive classification was an extension of the vital attribute approach.Two data sets were used for the data‐based classifications, one based on morphological, life history and phenological characters (morphological data) readily available from taxonomic descriptions and another based on long‐term observations on the establishment, growth and death of all individuals on permanent plots (dynamic data).SAHN (Sequential, Agglomerative, Hierarchical and Nested) clustering techniques were used for the numerical classifications. There was some similarity between the classification based on dynamic characters and the subjective and deductive classifications. The classification based on the readily available morphological characters showed less similarity with other classifications. However, the morphological data could be used to predict group membership in the dynamic classification using discriminant analysis with 87% accuracy. Thus, it appears that surrogate classifications might be found to describe the dynamics of the subtropical rainforest site. Further exploration and testing at other sites is required, especially to link the functional classification to specific perturbations.
A rule‐based model for the functional analysis of vegetation change in Australasian grasslands
Authors: Campbell Bruce D. , Stafford Smith D. Mark , Ash Andrew J. 
Published: May 2006

Abstract. Grasslands encompass a broad array of vegetation and climatic zones. We describe the first developments towards a rule‐based functional model for predicting vegetation structure in Australian and New Zealand pastures and rangelands. The approach aims to predict the combined effects of climate and disturbance by humans and grazing livestock, and to provide a level of resolution needed for predicting changes in pastures and rangelands. We enlisted expert knowledge to develop: (1) a minimum set of critical traits; (2) rules relating site variables to favoured plant attributes; (3) rules relating attributes to plant functional traits, and (4) rules relating plant functional types to likely plant communities. We tested the resulting model by deriving some simple predictions of plant communities of some existing pasture and rangeland sites in Australia and New Zealand, with differing climatic and human disturbance inputs.The results indicate that this first model is able to predict plant communities with varying success rates, and with the best results in cases where there are extreme climates or high management inputs. Key sensitivities in the model where further research is required include: (1) the urgent need for more explicit understanding of the key plant functional attributes favoured by differing climates and disturbance regimes, (2) the functional relationships between these plant functional attributes and recognisable plant functional types in vegetation, and (3) the assembly rules for the coexistence of these different plant functional types in major plant communities. The same understanding is required for subsequent process‐based modelling development.
Scaling effects of grazing in a semi‐arid grassland
Authors: Fuhlendorf Samuel D. , Smeins Fred E. 
Published: May 2006

Abstract. Previous studies have demonstrated relationships between spatial scale and spatial pattern and developed general hypotheses of scaling effects. Few studies, however, have examined the interactive relationship between scale and pattern‐driving processes such as grazing. The goal of this study is to evaluate scale‐dependent patterns across three spatial scales for three grazing intensities over 45 yr and to identify some mechanisms that may be associated with scale related differences. Correlation analysis and analysis of the coefficients of variation indicate that the relationships between units are dependent upon spatial scale and treatment. Across all grazing treatments, the relationship between units of the same scale becomes stronger as the spatial scale is increased. However, the rate of increase in the correlation coefficient is different for each treatment. The coefficient of variation responded inversely across scales with the greatest variation between small‐scale units and little difference between the intermediate‐ and large scales. In addition to different relationships between units at each scale, differences in heterogeneity within treatments over time is illustrated by the relationship between small‐scale units within each treatment and their associated larger scale units. The strongest relationship occurred in the heavily grazed treatments where correlation coefficients of small‐scale units with intermediate‐ and large‐scale units were ca. 0.60, indicating similar dynamics across scales. For the moderately grazed and ungrazed treatments this relationship varied from 0.40 to 0.47.Results from this study suggest that grazing alters scaling effects. Variability between small‐scale units was greatest in the ungrazed treatment which had greater heterogeneity and less predictability than grazed treatments because of the influence of grazing on plant morphology, demography and composition. At the intermediate scale, relationships between units were fairly similar with the least variation occurring in the moderately grazed treatment. Alternatively, variation between large‐scale units was greatest in the moderately grazed treatment because of the relationship between rest cycles, weather patterns, and patch grazing. Therefore, grazing can have a positive, a negative, or no influence on heterogeneity between units depending upon the scale of observation. Evaluation of long‐term dynamics across these treatments at the same small spatial scale results in different variances within each treatment which may violate assumptions of some statistical and experimental designs. Therefore, evaluations of temporal dynamics should consider scale relative to the relationship between plant size, density and longevity (relative scale).
Treefall gap characteristics and regeneration in the laurel forest of Tenerife
Authors: Arévalo José Ramón , Fernández‐Palacios José María 
Published: May 2006

Abstract. We conducted a study in the laurel forest of Tenerife (Canary Islands, Spain) to describe the characteristics of natural gaps and to assess the role of treefall gaps in forest dynamics. Very little is left of the natural laurel forest with i.a. Laurus azorica, Ilex canariensis and Prunus lusitanica. We looked for treefall gaps in 80 randomly located 2500 m2 plots. These plots represented ca. 1% of the remaining and protected laurel forest of Tenerife. We recorded the characteristics of the species causing the gaps, gap architecture and gap age in all observed gaps larger than 10 m2. We inventoried the regeneration in each gap and in a neighbouring control plot with the same topography. Large gaps (>75 m2) were not common in the laurel forest. The absence of large gaps could be due to the physiognomy of the vegetation, the mild weather or the rarity of disturbances. Instead of forming gaps, many trees decompose in place and branches from neighbouring trees and suckers from the decomposed trees occupy the free space. Also, the high rate of asexual regeneration could contribute to the fast closing of the gap.The number of gaps created by Prunus lusitanica was higher than expected (based on canopy composition) while Ilex canariensis and Laurus azorica created fewer gaps. In this evergreen forest, differences between gap and non‐gap conditions are not as distinct as in other forest types. Only 0.4% of the canopy is in the gap phase (0.6% including gaps smaller than 10m2). No differences were found in patterns of regeneration between gap and non‐gap phases in the forest. Gaps do not explain the persistence of pioneer species in the laurel forest.
Flowering regimes of terrestrial orchids: unpredictability or regularity?
Authors: Kindlmann Pavel , Balounová Zuzana 
Published: May 2006

Abstract. Empirical data on many species of terrestrial orchids suggest that their flowering pattern over the years is extremely irregular and unpredictable. A long search for the reason has hitherto proved inconclusive. Irregular flowering was attributed to costs associated with sexual reproduction, to herbivory, or to the chaotic behaviour of the system represented by difference equations describing growth of the vegetative and reproductive organs.Data on the seasonal growth of leaves and inflorescence of Dactylorhiza majalis are used here to test alternative explanations of the irregular flowering patterns of orchids. These patterns are found to be extremely rare in our data set. Neither costs of reproduction nor grazing seem to explain the rare events of a transition from flowering one year to sterility or absence the next year. These transitions are almost exclusively characteristic of one of four experimental sites, the only unmown site, where the mean leaf area and incidence of flowering in the whole population is also in decline. It is therefore hypothesized that irregular flowering regimes may be characteristic of sites with temporarily or steadily declining populations and that they are usually not present in prosperous ones ‐ at least for D. majalis.
Nutrient limitation and vegetation changes in a coastal dune slack
Authors: Lammerts E.J. , Pegtel D.M. , Grootjans A.P. , van der Veen A. 
Published: May 2006

Abstract. Basiphilous pioneer species are among the most endangered plant species in The Netherlands. They find most of their refuges in young coastal dune slacks, especially on the Wadden Sea islands. For the purpose of nature management it is important to know which processes control the presence of basiphilous pioneer communities, and to learn about the nature of slacks harbouring the concerning successional sequences.In a large dune slack on the Island of Terschelling, we assessed soil nutrient status and tested for nutrient limitation in four chronosequential stages: 2, 6, 37 and ca. 80 yr of age. Stage 2 harboured a basiphilous pioneer vegetation; in the stages 3 and 4 a dense vegetation of dwarf shrubs and grasses occurred. Soil organic matter and nutrient concentrations in each stage were measured in 1991. In 1992 and 1993 fertilizers were applied to all stages to detect nutrient limitation. Rates of accumulation of organic matter, nutrients and above‐ground biomass were estimated.When interpreted as successional stages, the different stages represent a sequence as expected on the basis of general successional theory. There was a peak in yearly nutrient accumulation between the 6‐ and 37‐yr old stage and a steady state after ca. 80 yr. Between the first two and the latter two stages a shift occurred from allogenic to autogenic succession which correlated with a shift in emphasis from available nutrients to light availability as limiting resources.Basiphilous pioneer species suffered only deficiency of nitrogen, probably because of their low phosphorus requirements. It is concluded that in dune slack habitats, in addition to a low nutrient availability in general, a very low phosphorus availability favours basiphilous pioneer species to species showing co‐limitation of nitrogen and phosphorus as found in some grasses and dwarf shrubs. A comparison between the effects of lime addition and the effects of nitrogen and phosphorus additions suggests that, in the early stages, soil buffering increases the availability of nitrogen and inhibits the availability of phosphorus.Sod cutting is an effective technique for restoring basiphilous pioneer vegetation, when slacks are acidified only superficially and buffering‐mechanisms can be reactivated. Yearly mowing and removing of standing crop may prolong the life‐span of basiphilous pioneer vegetation, when soil acidification has not yet dropped below pH 6.
On the variation explained by ordination and constrained ordination axes
Authors: Økland Rune Halvorsen 
Published: May 2006

Abstract. Total inertia (TI), the sum of eigenvalues for all ordination axes, is often used as a measure of total variation in a data set. By use of simulated data sets, I demonstrate that lack‐of‐fit of data to the response model implicit in any eigenvector ordination method results in polynomial distortion ordination axes, with eigenvalues that normally contribute 30–70% to TI (depending on data set properties). The amount of compositional variation extracted on ecologically interpretable ordination axes (structure axes) is thus underestimated by the eigenvalue‐to‐total‐inertia ratio. I recommend that the current use of total inertia as a measure of compositional variation is discontinued. Eigenvalues of structure axes can, however, be used with some caution to indicate their relative importance.I also demonstrate that when the total inertia is partitioned on different sets of explanatory variables and unexplained variation by use of (partial) constrained ordination, (35) 50–85% of the variation ‘unexplained’ by the supplied explanatory variables represents lack‐of‐fit of data to model. Thus, the common interpretation of ‘unexplained variation’ as random variation (‘noise’) or coenoclinal variation caused by unmeasured explanatory variables, is generally inappropriate. I recommend a change of focus from the variation‐explained‐to‐total inertia ratio and ‘unexplained’ variation to relative amounts of variation explained by different sets of explanatory variables.
Disturbance history and tree establishment in old‐growth Pinus koraiensis‐hardwood forests in the Russian Far East
Authors: Ishikawa Yukio , Krestov Pavel V. , Namikawa Kanji 
Published: May 2006

Abstract. Dendro‐ecological studies were undertaken to document the disturbance history in two old‐growth mixed Pinus koraiensis‐hardwood forests in the southern part of the Sikhote‐Alin mountains in the Russian Far East. Establishment of four common canopy conifers, Abies holophylla, A. nephrolepis, P. koraiensis and Picea ajanensis, and three common canopy hardwoods, Acer mono, Betula costata and Tilia amurensis, were also inferred from population age structures and spatial dispersion patterns.Growth releases on increment cores suggested that peak periods of growth releases indicating partial canopy disturbances have repeatedly occurred over the past 230 yr at intervals from ca. 35 to 100 yr. Slight releases and suppressions other than the peak releases occurred in many years of both histories, suggesting the formation of smaller‐scale canopy gaps. Despite the predominance of anthropogenic fires in Primorskiy Kray at present, destructive fires had not affected either forest. Wind disturbances and low intensity fires are likely factors controlling the dynamics of the forests. Under the disturbance regime, P. koraiensis has maintained its populations through its dependence on canopy gaps for establishment. Age distribution and gap dependence of P. ajanensis, A. nephrolepis and A. mono suggested continuous establishment of these species under a closed canopy, whereas occasional establishment of T. amurensis was derived largely from vegetative reproduction. Restricted establishment of A. holophylla and B. costata suggested a variety in kinds of disturbance throughout the histories. Continuous habitation of the study area by P. koraiensis is likely under the disturbance regime without destructive fires.