bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age structure and dynamics of Rhododendron ferrugineum L. populations in the northwestern French Alps
Authors: Pornon André , Doche Bernard 
Published: May 2006

Abstract. The ericaceous shrub Rhododendron ferrugineum occupies large areas at the subalpine level (1600–2200 m) of the northwestern French Alps. It frequently reaches 90–100 % cover, accumulates 60–70t/ha (dry weight) above‐ground biomass and is able to dominate many subalpine landscapes by outcompeting other species. We formulated the hypothesis that the species shows a rapid and invasive seedling establishment and a fast population development. We investigated the age structure and development of two populations. Although classic colonization stages can be identified, and variation did occur depending on the site, R. ferrugineum populations showed a surprisingly slow development compared with other ericaceous species. Curves obtained from polynomial regression equations of cover on age allowed us to predict the future development of populations. Thus, depending on the site, it would take 150 to 250 yr to achieve total cover.We discuss the factors involved that could explain this slow development and discuss which biotic and abiotic factors may be responsible for the large extension of this species in the subalpine belt.
Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec
Authors: de Blois Sylivie , Bochard André 
Published: May 2006

Abstract. Human impact influences patterns of plant distribution and dominates disturbance dynamics in the agricultural landscape of Haut‐Saint‐Laurent, Québec. We investigated the influence of such impact on the dynamics of Thuja occidentalis in the hardwood forest of southern Québec. A bimodal species of either dry or wet habitats, T. occidentalis has successfully invaded mesic sites of the study area where, although generally considered a poor competitor, it persists as dense populations that seem to resist invasion by more tolerant species. As Acer saccharum is expected to be a dominant latesuccessional species under mesic conditions, we first evaluated the relative importance of abiotic and historical factors in the distribution of 34 T. occidentalis stands and 21 A. saccharum stands. We then classified 55 stands that include T. occidentalis and investigated the dynamic relationships between the species and its associates in 13 mixed mesic sites.Canonical correspondence analysis (CCA) of T. occidentalis and A. saccharum stands suggested that land use and drainage are the most important variables correlated with plant community composition. A partial CCA with drainage as the constraining variable showed that T. occidentalis stands were significantly associated to present or past use as pasture. Correspondence analysis of 55 stands where T. occidentalis is present produced a clear segregation between nearly monospecific stands and mixed communities, but the chosen environmental variables were not significant in explaining the vegetation gradient at this scale. In all mixed stands, Thuja occidentalis was most often associated with Ulmus americana, Acer rubrum, Betula populifolia, Fraxinus americana, A. saccharum, and Tsuga canadensis. Finally, size‐class ordination of 13 mixed mesic stands did not show convergence toward A. saccharum.Our results suggest that grazing has played a significant part in the appearance of T. occidentalis stands on mesic sites, whereas competition processes and landscape patterns possibly contribute to the maintenance of relatively persistent T. occidentalis stands in the landscape.
Species richness of Argentine cacti: A test of biogeographic hypotheses
Authors: Mourelle Cristina , Ezcurra Exequiel 
Published: May 2006

Abstract. Patterns of species richness are described for 50 columnar, 109 globose and 50 opuntioid cacti species in 318 grid cells (1° x 1°) covering Argentina. Biological richness hypotheses were tested by regressing 15 environmental descriptors against species richness in each group. We also included the collection effort (estimated as the logarithm of the number of herbarium specimens collected in each cell) to estimate the possible error induced by underrepresentation in certain cells. Log‐linear regression models accounted for a large portion of the variation in richness of columnar species, opuntioid species, globose species and all forms combined. Opuntioid and globose species richness was associated with percentage summer rainfall. Columnar species richness was associated with the number of frost‐free days. The distribution of columnar cacti seems to be limited by freezing temperatures. The results are consistent with the climate favourableness and climatic variation hypotheses, but do not support the hypothesis that energy flow limits regional species richness.Altitudinal range (a measure of habitat heterogeneity) was related to richness of globose cacti. A floristic affinity analysis between geographic provinces and the distribution of the different growth forms confirmed the high degree of endemism of globose cacti and the cosmopolitanism of the opuntioid ones. Two cells in the Prepuna and northern Monte Provinces showed species richness values that were significantly higher than those predicted by the log‐linear model. This is interpreted in terms of Quaternary historical events having affected the main South American biomes.
Invasion by Heracleum mantegazzianum in different habitats in the Czech Republic
Authors: Pyšek Petr , Pyšek Antonín 
Published: May 2006

Abstract. Heracleum mantegazzianum, a tall forb from the western Caucasus invaded several different habitats in the Czech Republic. The relation between invasion success and type of recipient habitat was studied in the Slavkovskù les hilly ridge, Czech Republic. The vegetation of 14 habitat types occurring in an area of ca. 25 km2 was analysed using phytosociological relevés, and the invasion success of Heracleum (in terms of number of localities, area covered and proportion of available area occupied) was recorded separately in each of them. Site conditions were expressed indirectly using Ellenberg indicator values. The hypothesis tested was that Heracleum spreads in the majority of vegetation types regardless of the properties of the recipient vegetation.Community invasibility appeared to be affected by site conditions and the composition of the recipient vegetation. The species is not found in acidic habitats. Disturbed habitats with good possibilities of dispersal for Heracleum seeds are more easily invaded. Communities with a higher proportion of phanerophytes and of species with CS (Competitive/Stresstolerating) strategy were more resistant to invasion. The invasion success was bigger in sites with increased possibilities of spread for Heracleum diaspores. Communities invaded by Heracleum had a lower species diversity and a higher indicator value for nitrogen than not‐invaded stands. It appears that species contributing to community resistance against invasion of Heracleum, or capable of persisting in Heracleum‐invaded stands, have similar ecological requirements but a different life strategy to the invader.
Dynamics of submersed aquatic vegetation on shallow soft bottoms in the Baltic Sea
Authors: Idestam‐Almquist Jerker 
Published: May 2006

Abstract. Persistence and colonization of submersed aquatic plant species were studied in permanent plots (20 cm × 20 cm) at three shallow sites adjacent to Askö island, in the northern Baltic Sea. The study started in 1991 at two of the sites, in 1992 at a third site and continued until 1997. Two major weather‐induced disturbances occurred during the study: a long, stormy period during a mild winter and a cold winter with extreme low water levels. The stormy period caused a large loss of species from plots (95 ± 5% SE) at the most wave‐exposed site, resulting in a low species number per plot (0.8 ± 0.2) the following summer. During the three following years the mean species number increased to 3.6 ± 0.2. The cold winter caused high species turnover and increased species number per plot at the two most wave‐exposed sites. The species turnover at the sheltered site was highest in the two years with low water level in May, possibly due to increased waterfowl herbivory. Annuals, loosely anchored and highly reproductive species had significantly higher plot colonization rates and lower persistence than perennials, well‐anchored species and species with none or low reproduction. The extent of lateral growth had no significant effect on colonization or persistence.Although these disturbances have a large effect on the dynamics, species mobility was also high in other years. Relative to other, similar, studies in terrestrial vegetation mean persistence in plots was remarkably low and mean mobility and species turnover rates were very high.
Limitations to plant establishment on eroded slopes in southeastern Spain
Authors: García‐Fayos Patricio , García‐Ventoso Belen , Cerdà Artemi 
Published: May 2006

Abstract. The possible causes for the lack of vegetation in five badland sites from southeast Spain were experimentally tested. The main factors affecting seed germination and seedling survival considered were seed availability, regolith water dynamics in relation to rain events, regolith salinity, seedling predation by herbivores and seedling removal by erosion.Four issues are addressed: 1. Both rainfall and the temporal and spatial dynamics of regolith water during the seedling emergence period were monitored in five different zones at one site (Petrer, Alicante). 2. Effects of salinity and water potential on the rate and speed of germination of local seeds were determined. 3. Seed reserve and seedling emergence and mortality were followed throughout one season. 4. Regolith characteristics of all five sites were compared and the consequences for plant colonization discussed.The main factor limiting plant colonization in these sites was the very short duration of available water in the soil, due to the physical and chemical characteristics of the regolith. In addition, high regolith salinity and its effects on seed germination, the aspect of the site and the pattern of rain events, played a very important role reducing germination and survival. Herbivory and erosion were seldom responsible for seedling mortality. However, there were no highly erosive rain events during the study period, although several have been measured during the past few years.
A new measure of fidelity and its application to defining species groups
Authors: Bruelheide Helge 
Published: May 2006

Abstract. The first objective of this paper is to define a new measure of fidelity of a species to a vegetation unit, called u. The value of u is derived from the approximation of the binomial or the hypergeometric distribution by the normal distribution. It is shown that the properties of u meet the requirements for a fidelity measure in vegetation science, i.e. (1) to reflect differences of a species’relative frequency inside a certain vegetation unit and its relative frequency in the remainder of the data set; (2) to increase with increasing size of the data set. Additionally (3), u has the property to be dependent on the proportion of the vegetation unit's size to the size of the whole data set.The second objective is to present a method of how to use the value of u for finding species groups in large data bases and for defining vegetation units. A species group is defined by possession of species that show the highest value of u among all species in the data set with regard to the vegetation unit defined by this species group. The vegetation unit is defined as comprising all relevés that include a minimum number of the species in the species group. This minimum number is derived statistically in such a way that fewer relevés always belong to a species group than would be expected if the differential species were distributed randomly among the relevés. An iterative algorithm is described for detecting species groups in data bases. Starting with an initial species group, species composition of this group and the vegetation unit defined by this group are mutually optimized. With this algorithm species groups are formed in a data set independently of each other. Subsequently, these species groups can be combined in such a way that they are suited to define commonly known syntaxa a posteriori.
Plant response to disturbance in a Mediterranean grassland: How many functional groups?
Authors: Lavorel Sandra , McIntyre S. , Grigulis Karl 
Published: May 2006

Abstract. Data referring to changes in vegetation composition resulting from cattle exclosure and ploughing in a Portuguese pasture dominated by annuals were used to test hypotheses regarding the biology of species favoured or eliminated by disturbance in semi‐natural herbaceous communities. These hypotheses were tested in two ways. First we compared the distribution of six a priori groups – grasses, small rosettes, large rosettes, small species with leafy stems, large species with leafy stems, legumes – across grazed, ploughed and undisturbed plots. In a second set of analyses we examined changes in the frequencies of individual biological attributes in response to grazing and ploughing. These analyses were carried out separately for grasses and dicot forbs. Overall, the species composition showed little response to either grazing or ploughing, though species dominance changed. This lack of responsiveness of species composition was attributed to the long history of intensive land use which has resulted in the loss of disturbance‐intolerant species over entire landscapes.When considering a priori groups, small rosettes were indifferent to disturbance. grazing and ploughing showed that dominated. Large rosettes, large species with leafy stems and legumes were generally intolerant to both grazing and ploughing, though individual species may increase in response to disturbance. Small species with leafy stems were the only group favoured by grazing whereas ploughing favoured grasses.As to individual traits, grazing excluded large grass species with heavy seeds and promoted a flat rosette canopy structure and a small size, along with a moderate dormancy and protected inflorescences. In forbs, grazing favoured small species, as expected, while it excluded tall species, and, in contrast to earlier results, a rosette canopy. These attributes were consistent with responses of the a priori groups, though it would not have been possible to reconstruct groups directly from the attribute list. Ploughing had no effect on any of the forb traits. As to grass traits, flat‐ and short‐statured species increased and heavy‐seeded species decreased.Our analysis revealed two advantages of establishing plant functional classifications within life forms. Subgroups within forbs had contrasting types of behaviour. For the same trait patterns could differ within the grass group from within the forb group. Finally, this analysis emphasizes the need for plant functional classifications aiming at the identification of syndromes of co‐occurring attributes rather than of lists of isolated traits of which actual combinations are not specified.
Patterns of invasion of an urban remnant of a species‐rich grassland in southeastern Australia by non‐native plant species
Authors: Morgan John W. 
Published: May 2006

Abstract. The invasion by non‐native plant species of an urban remnant of a species‐rich Themeda triandra grassland in southeastern Australia was quantified and related to abiotic influences. Richness and cover of non‐native species were highest at the edges of the remnant and declined to relatively uniform levels within the remnant. Native species richness and cover were lowest at the edge adjoining a roadside but then showed little relation to distance from edge. Roadside edge quadrats were floristically distinct from most other quadrats when ordinated by Detrended Correspondence Analysis.Soil phosphorus was significantly higher at the roadside edge but did not vary within the remnant itself. All other abiotic factors measured (NH4, NO3, S, pH and % organic carbon) showed little variation across the remnant. Non‐native species richness and cover were strongly correlated with soil phosphorus levels. Native species were negatively correlated with soil phosphorus levels. Canonical Correspondence Analysis identified the perennial non‐native grasses of high biomass as species most dependent on high soil nutrient levels. Such species may be resource‐limited in undisturbed soils.Three classes of non‐native plants have invaded this species‐rich grassland: (1) generalist species (> 50 % frequency), mostly therophytes with non‐specialized habitat or germination requirements; (2) resource‐limited species comprising perennial species of high biomass that are dependent on nutrient increases and/or soil disturbances before they can invade the community and; (3) species of intermediate frequency (1–30 %), of low to high biomass potential, that appear to have non‐specialized habitat requirements but are currently limited by seed dispersal, seedling establishment or the current site management. Native species richness and cover are most negatively affected by increases in non‐native cover. Declines are largely evident once the non‐native cover exceeds 40 %.Widespread, generalist non‐native species are numerous in intact sites and will have to be considered a permanent part of the flora of remnant grasslands. Management must aim to minimize increases in cover of any non‐native species or the disturbances that favour the establishment of competitive non‐native grasses if the native grassland flora is to be conserved in small, fragmented remnants.
Relative abundance distributions in plant communities: effects of species richness and of spatial scale
Authors: Wilson J. Bastow , Gitay Habiba , Steel John B. , King Warren McG. 
Published: May 2006

Abstract. Relative abundance distributions (RADs) are an important feature of community structure, but little is known of the factors affecting which type of RAD is observed in a particular community. We examined the influences of species richness and of spatial scale on the RAD of plant communities.The effect of species richness was examined by analysing simulated communities generated under the Broken stick model, the Sequential breakage model, and a randomized version of Niche pre‐emption model. In all cases, when there were few species in the community the data only occasionally gave the best fit to the model that was used to generate it. With 40–65 species, a best fit was obtained for the correct model in about 75 % of cases, almost irrespective of the model.Effects of spatial scale were examined in data from four dune slacks and from two semi‐arid grasslands, by analysing biomass values at a range of sample sizes. The model that best fitted the whole sample differed between the four slacks and between the slacks and the semi‐arid grasslands. The change in which model of RAD fitted best, as sample size was reduced, varied between sites and between habitat types. At the smallest sample sizes, the Zipf‐Mandelbrot model often fitted, and in the slack sites the Broken stick also, though neither fitted (in the vegetation examined) at larger spatial scales.It is concluded the RAD is affected by species richness and by spatial scale, in ways that currently do not enable simple prediction. RADs can theoretically give information on the processes such as resource partitioning, immigration and competition that have structured the community, but they are a blunt tool for this purpose.
Occurrence of pollen and spores in relation to present‐day vegetation in a Dutch heathland area
Authors: Mulder Christian , Janssen C. Roel 
Published: May 2006

Abstract. Pollen, spores and fungal remains in moss cushions along a transect, traversing a Betula‐Quercus forest and a surrounding heathland, were analysed in order to study the relation between present‐day vegetation and recent pollen deposition. Pollen and spores are divided into local types from plant species encountered along the transect and regional types, not present along the transect. Relative percentages and absolute concentration of the palynomorphs were estimated. Radiocaesium activity in the moss was measured to assess the minimal duration of palynomorph accumulation (i.e. the age of the moss samples).The absence of simultaneous trends in the regional pollen types indicates that the samples do not have major differences in age. The moss represents the later stages in the heath mosaic cycle. This is supported by the radiocaesium content of the moss. Thus, in this case the concentration values of regional pollen approach deposition values. The values of the local pollen types calculated on such a rather constant regional pollen flux is considered to represent real differences in the local deposition.The local pollen types can be arranged topographically into five groups characteristic of the local vegetation types and their ecotones. The arrangement of the curves of types from phyco‐, zoo‐, and myco‐coenoses suggests their possible origin, either locally from the heath area or from the Betula‐Quercus forest, or regionally from elsewhere. Analyses and topographical arrangement of the curves of unknown types contribute in this way to their identification and their possible source of origin.
Burrowing activities of kangaroo rats and patterns in plant species dominance at a shortgrass steppe‐desert grassland ecotone
Authors: Fields Mark J. , Coffin Debra P. , Gosz James R. 
Published: May 2006

Abstract. Our objective was to evaluate the effects of burrowing activities by banner‐tail kangaroo rats (Dipodomys spectabilis Merriam) on plant community structure and species dominance for two patch types at the ecotone between shortgrass steppe and desert grassland in New Mexico, USA. 10 mounds produced by kangaroo rats were selected in patches dominated by Bouteloua gracilis (the dominant in shortgrass steppe communities) and 10 mounds were selected in patches dominated by B. eriopoda (the dominant in Chihuahuan desert grasslands). Plant cover and density by species were sampled from three locations associated with each mound: the mound proper, the edge of the mound in the transition area, and the off‐mound vegetation. Similar cover of B. eriopoda for the edges of mounds in both patch types indicates the ability of this species to respond to animal disturbances regardless of the amount of cover in the surrounding undisturbed vegetation. By contrast, cover of B. gracilis was low for all mounds and mound edges in patches dominated by this species. Much higher cover of B. eriopoda on mound edges compared to the undisturbed vegetation in B. gracilis‐dominated patches indicates that kangaroo rats have important positive effects on this species. Lower cover of perennial grasses and higher cover of forbs, shrubs, and succulents on the edges of mounds in B. eriopoda‐dominated patches compared to patches dominated by B. gracilis indicate the importance of surrounding vegetation to plant responses on disturbed areas.Our results show that kangaroo rats have important effects on both species dominance and composition for different patch types, and may provide a mechanism for small‐scale dominance patterns at an ecotone; thus providing further support for their role as keystone species in desert grasslands.