bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distance decay in an old‐growth neotropical forest
Authors: Palmer Michael W. 
Published: February 2009

Abstract. Questions: Does distance decay exist in an old‐growth neotropical forest? Is this distance decay stronger than expected due to environmental heterogeneity alone? At what spatial scales are distance decay manifested?Location: La Selva Biological Station, Costa Rica, Central America.Methods: An index of distance decay is applied appropriate for small quadrats (the probability of encountering a conspecific tree) to a grid of 1170 0.01‐ha plots. A null model is provided that accounts for environmental heterogeneity.Results: Significant, but weak, distance decay is found. After correcting for known patterns of environmental heterogeneity, the distance decay almost disappears, except for fine spatial scales.Conclusions: These results are inconsistent with models that predict distance decay at all spatial scales. However, biological processes leading to distance decay may be more relevant and detectable at scales broader than this study. Research utilizing objectively‐located samples over much broader scales is necessary to evaluate the generality and magnitude of distance decay.
Plant traits: Their role in the regeneration of alpine plant communities in sub‐arctic Finland
Authors: Welling Pirjo , Tolvanen Anne , Laine Kari 
Published: February 2009

Abstract. Question: How do the relative frequencies of plant traits (clonality, growth form, seed weight, diaspore morphology) vary during the life cycle and how does this affect regeneration?Location: Alpine meadow and heath communities at Kilpisjärvi, sub‐Arctic Finland.Methods: Control plots and three treatments were used to measure relative species abundances for five life cycle stages: standing vegetation, seed rain, seed bank and seedlings emerging in gaps and in closed vegetation.Results: The relative frequencies of plant traits varied between the life cycle stages. The meadows were dominated by weakly clonal herbs, small or intermediate seeds and unappendaged diaspores, while the heaths were dominated by clonal dwarf shrubs, small seeds and fleshy fruits. In the meadows, species with small seeds dominated during the seed rain and in the seedling stage in gaps, while species with intermediate seeds dominated the seed bank and the seedling stage in closed vegetation. Species with unappendaged diaspores dominated throughout the life cycle. In the heaths, seed bank and seedling stage were practically absent.Conclusions: The observed differences in plant trait spectra between life cycle stages indicate that important environmental factors differ among the stages. Small seeds are advantageous for dispersal, whereas intermediate seeds have a greater probability of germinating and establishing in closed vegetation. Appendages facilitate dispersal, whereas unappendaged diaspores favour seed burial. Although the plant growth form spectrum largely reflects environmental constraints during the regeneration cycle, information on seed weight and diaspore morphology improves our knowledge of the relative importance of morphological adaptations of sexual structures in different stages during the life cycle.
Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems
Authors: Gómez‐Aparicio Lorena , Gómez Jose M. , Zamora Regino , Boettinger Janis L. 
Published: February 2009

Abstract. Question: Is the facilitative effect of nurse shrubs on early recruitment of trees mediated by a ‘canopy effect’(microclimate amelioration and protection from herbivores), a ‘soil effect’(modification of soil properties), or both?Location: Two successional montane shrublands at the Sierra Nevada Protected Area, SE Spain.Method: Seedlings of Quercus and Pinus species were planted in four experimental treatments: (1) under shrubs; (2) in open interspaces without vegetation; (3) under shrubs where the canopies were removed; (4) in open interspaces but covering seedlings with branches, mimicking a shrub canopy.Results: Both effects benefited seedling performance. However, microclimatic amelioration due to canopy shading had the strongest effect, which was particularly pronounced in the drier site. Below‐ground, shrubs did not modify soil physical characteristics, organic matter, total N and P, or water content, but significantly increased available K, which has been shown to improve seedling water‐use efficiency under drought conditions.Conclusions: We propose that in Mediterranean montane ecosystems, characterised by a severe summer drought, pioneer shrubs represent a major safe site for tree early recruitment during secondary succession, improving seedling survival during summer by the modification of both the above‐and below‐ground environment.
Plot shape effects on plant species diversity measurements
Authors: Keeley Jon E. , Fotheringham C.J. 
Published: February 2009

Abstract.Question:Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies?Location:Grasslands, shrublands and forests in the Mediterranean‐climate region of California, USA.Methods:We compared three 0.1‐ha sampling designs that differed in the shape and dispersion of 1‐m2and 100‐m2nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400‐m2subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire.Results:We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1‐ or 100‐m2. Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self‐similarity at the scale of 400 m2, but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale.Conclusions:At the 0.1‐ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean‐climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below‐ground niche space outside the sample area.
The Circumpolar Arctic vegetation map
Authors: Walker Donald A. , Raynolds Martha K. , Daniëls Fred J.A. , Einarsson Eythor , Elvebakk Arve , Gould William A. , Katenin Adrian E. , Kholod Sergei S. , Markon Carl J. , Melnikov Evgeny S. , Moskalenko Natalia G. , Talbot Stephen S. , Yurtsev Boris A.(†) , The other members of the CAVM Team  
Published: February 2009

Abstract. Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries?Location: The Arctic tundra region, north of the tree line.Methods: A photo‐interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above‐ground biomass.Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 × 106 km2), about 5.05 × 106 km2 is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate‐shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf‐shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low‐shrub tundra.Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land‐use, and climate‐change applications and will make updating the map relatively easy.
Distribution patterns of plant communities on Santiago Island, Cape Verde
Authors: Duarte M.C. , Rego F. , Moreira I. 
Published: February 2009

Abstract. Question: What is the composition, ecology and distribution of the main plant communities on Santiago Island?Location: Santiago Island (Cape Verde archipelago).Methods: 308 plots were established using a stratified sampling system according to habitat type; random sampling was employed in each habitat type. Floristic and ecological (topographic, edaphic, climatic and land use) data were collected and analysed using classification and ordination methods and regression analysis.Results: The classification results led to the recognition often plant communities. Ordination pointed to the importance of altitudinal gradient, slope angle and soil moisture in vegetation variation, as well as some categories of land use, land form or soil type. Regression analysis of sample distributions in ordination space and altitude, according to the two main types of slope aspect — leeward vs. windward — produced altitude differences of ca. 100 m. Variation in rainfall proved more effective at lower altitudes, resulting in the differentiation of more vegetation belts. Slope angle proved to be more important for vegetation differentiation when values exceeded 40°, particularly at medium and higher altitudes. Plant communities are mainly dominated by herbaceous annual species, many of which are exotic.Conclusions: Two main phyto‐ecological zones can be distinguished: a xerophilous zone (up to 300/400 m) and a mesophilous zone (above 300/400 m). The zonal communities (four mesophilous and three xerophilous) were distributed in altitudinal belts (mainly reflected in a precipitation gradient); different altitudinal ranges were estimated for these communities according to aspect. The two hygrophilous and one psammophilous communities presented an azonal distribution.
Effects of microsite conditions on seedling establishment on the foreland of Coleman Glacier, Washington
Authors: Jones Chad C. , del Moral Roger 
Published: February 2009

Abstract. Questions: How do physical microsite conditions of microsites affect germination and seedling survival in different successional stages? Do different species germinate in similar microsites in a given successional stage?Location: Coleman Glacier foreland, Mount Baker, Washington State, USA.Methods: Two methods were used to characterize safe sites. 1. Grids of 300 10 cm × 10 cm plots were located in four different age classes on the foreland. 2.105 pairs of plots, with and without seedlings of Abies amabilis, were located in each age class. For each plot we identified all seedlings and all individuals < 1 m tall. Microsite characteristics such as topography and presence of rocks or woody debris were noted for each plot. Microsite characteristics were compared between plots with and without each species. In addition we examined the effect of distance from seed sources on the presence of Alnus viridis seeds and seedlings in a newly disturbed area.Results: In early successional sites, seedlings of several species were positively associated with depressions and presence of rocks, and negatively associated with ridges. Patterns were generally consistent among species. In later succession, seedlings were not significantly associated with any microsite characteristics. For Alnus viridis, seed density decreased with distance from seed sources but seedling density did not.Conclusions: Because of harsh conditions in early succession, physical microsites are important, and most species have similar microsite requirements. In later succession, physical microsites characteristics are not as important and are more variable. Microsites appear to be more important than seed rain in controlling the distribution of Alnus viridis in early succession.
Border and ecotone detection by vegetation composition along forest‐savanna transects in Ivory Coast
Authors: Hennenberg Klaus J. , Goetze Dethardt , Kouamé Lucien , Orthmann Bettina , Porembski Stefan 
Published: February 2009

Abstract. Question: How do properties of different vegetation components vary along ecotones of semi‐deciduous forest islands, and can the depth of edge influence (DEI) of the components be detected using a novel combination of analyses?Location: Comoé National Park (CNP), NE Ivory Coast.Methods: Along eight transects at semi‐deciduous forest islands tree individuals > 20 cm DBH were mapped. At one transect, tree and shrub individuals down to 1 cm DBH were measured and cover of species was estimated. Split moving window dissimilarity analysis (SMWDA) and moving window regression analysis (MWRA) were combined to detect statistical significance of borders in multivariate vegetation data along continuous transects, to determine the width of associated ecotones, and, thus, the DEI towards the forest interior.Results: For trees > 20 cm DBH, a distinct boundary formation was detected, dominated by the semi‐fire resistant tree species Anogeissus leiocarpus. The median of DEI towards the forest interior was 55 m. Ecotone detection with all species present revealed an interlocked sequence of ecotones for grasses, herbs, woody climbers, shrubs and trees, with each of these ecotones being narrower than the overall ecotone. DEI ranged from 10 m for grasses up to 120 m for trees and shrubs.Conclusions: The coherent set of analyses applied proved to be an objective method for detecting borders and the width of associated ecotones. The patterns found may be explained by successional processes at the forest‐savanna border. The DEI measured for the forest islands in the nearly undisturbed semi‐natural system of the CNP is of relevance to concepts of core‐area analysis and the protection of forest interior species in semi‐deciduous forests in tropical West Africa.
Context‐dependent interactions between adult shrubs and seedlings in a semi‐arid shrubland
Authors: Riginos Corinna , Milton Suzanne J. , Wiegand Thorsten 
Published: February 2009

Abstract. Question: In semi‐arid systems, rainfall gradients can cause plant‐plant interactions to shift from negative to positive or vice versa. However, the importance of a second major abiotic factor, soil nutrients, has rarely been considered. We consider different combinations of both factors and ask: do net adult‐seedling interactions become less competitive and more facilitative with increasing overall abiotic harshness?Location: Succulent Karoo, Western Cape, South Africa.Methods: We examined the interactions between seedlings and adult shrubs at two sites. Sites differ in rainfall, and each contain two habitats: Nutrient‐rich mounds associated with underground termitaria and a relatively nutrient‐poor matrix. We carried out a spatial pattern analysis of community‐wide seedling‐adult associations. We then conducted field and greenhouse experiments to test the effects of soil and the presence of neighbouring shrubs on the growth and survival of six seedling species.Results: At the higher rainfall site, both competitive and facilitative effects of adults on seedlings were found but did not differ by habitat, despite the more benign conditions in the mound habitat. At the lower rainfall site, adult shrubs generally had neutral effects on seedlings in the matrix habitat. In the nutrient‐rich mound habitat, however, adult shrubs had strong and consistently competitive effects on seedlings.Conclusion: Seedling‐adult interactions could not be predicted by a simple overall gradient of abiotic harshness, demonstrating the need for more complex, mechanistic models to predict plant‐plant interactions. We suggest that rainfall and soil nutrients affect seedling‐adult relations through their interactive effects on the life‐history attributes of the species involved.
Ginkgo, a multivariate analysis package
Authors: Bouxin Guy 
Published: February 2009

Abstract. The Ginkgo software is a subset of the VegAna (for Vegetation edition and Analysis) package that contains three programs named Quercus, Fagus and Yucca. Ginkgo is a multivariate analysis tool; it is oriented mainly towards ordination and classification of ecological data. Quercus is a relevé table editor; it handles community data to perform a phytosociological analysis. Fagus is a floristic citation editor; it can handle data coming from field surveys, bibliographic sources or collections. Yucca is a cartographic tool; it allows plotting distributions of taxa or syntaxa.VegAna is produced by the Department of Vegetal Biology, University of Barcelona. The general project is directed by Xavier Font I Castell, the Ginkgo module by Francesc Oliva I Cuyàs. Programmers are Miquel De Cáceres and Richard Garcia. This review deals primarily with Ginkgo.
Rejecting the mean: Estimating the response of fen plant species to environmental factors by non‐linear quantile regression
Authors: Schröder Henning K. , Andersen Hans Estrup , Kiehl Kathrin 
Published: February 2009

AbstractQuestion:Is quantile regression an appropriate statistical approach to estimate the response of fen species to single environmental factors?Background:Data sets in vegetation field studies are often characterized by a large number of zeros and they are generally incomplete in respect to the factors which possibly influence plant species distribution. Thus, it is problematic to relate plant species abundance to single environmental factors by the ordinary least squares regression technique of the conditional mean.Location:Riparian herbaceous fen in central Jutland (Denmark).Methods:Semi‐parametric quantile regression was used to estimate the response of 18 plant species to six environmental factors, 95% regression quantiles were chosen to reduce the impact of multiple unmeasured factors on the regression analyses. Results of 95% quantile regression and ordinary least squares regression were compared.Results:The standard regression of the conditional mean underestimated the rates of change of species cover due to the selected factor in comparison to 95% regression quantiles. The fitted response curves indicated a general broad tolerance of the studied fen species to different flooding durations but a narrower range concerning groundwater amplitude. The cover of all species was related to soil exchangeable phosphate and base‐richness. A relationship between soil exchangeable potassium and species cover was only found for 11 species.Conclusion:Considering the characteristics of data sets in vegetation science, non‐linear quantile regression is a useful method for gradient analyses.
Supervised classification of plant communities with artificial neural networks
Authors: Černá Lenka , Chytrý Milan 
Published: February 2009

AbstractQuestions:Are artificial neural networks useful for the automatic assignment of species composition records from vegetation plots to a priori established classes (vegetation units)? Is the assignment more accurate (1) if the classes are defined by numerical classification rather than by expert‐based classification; (2) if the training data set is selected to include plots that are richer in diagnostic species of particular classes?Material:Species composition records (relevés) from 4186 plots of Czech grasslands.Methods:Plots were classified into 11 phytosociological alliances (expert classification) and into 11 clusters derived from numerical cluster analysis. Some plots were used for training the classifiers, which were the multi‐layer perceptrons (MLP; a type of artificial neural network). Other plots were used for testing the performance of these classifiers. Plots used for training were selected (1) randomly; (2) according to higher representation of diagnostic species of particular classes.Results:Different MLP classifiers correctly classified 77–83% of plots to the classes of the expert classification and 70–78% to the classes of the numerical classification. The better result in the former case was mainly due to two classes in the expert classification, which were well recognized by the classifiers and at the same time contained a large proportion of the plots of the entire data set. Correct classification of the plots belonging to these large classes resulted in a good overall performance of the classifiers. After training with randomly chosen plots, the classifiers produced better results than after training with plots that contained more diagnostic species. This indicates that the biased selection of the training plots disables the classifiers to recognize the entire variation within the classes and results in errors when new plots are to be classified.Conclusions:MLP is suitable for assigning vegetation plots to already established classes. Unlike some other methods of supervised classification, it performs well even in communities that are poor in diagnostic species. However, the method does not provide clear assignment keys that could be used for class identification in field surveys. It is therefore more appropriate in applications that aim at a reliable class assignment rather than understanding the assignment rules.