bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semi‐strong Hybrid Scaling, a new ordination algorithm
Authors: Belbin Lee 
Published: May 2006

There is a small group of association measures that appear optimal for comparing sites on the basis of their species composition. These measures can accurately estimate affinity between sites when they are ecologically similar. Once sites share few or no species, these measures always under‐estimate the ‘ecological distance’ between them. A new ordination algorithm called Semi‐strong Hybrid Scaling, SHS, uses these features in an attempt to provide a better configuration of the sites. The new method is evaluated by a direct comparison of the structure in simulated data with the Hybrid method of Faith, Minchin & Belbin (1987).To evaluate SHS and compare it with Hybrid Scaling, 3240 datasets were generated using the COMPAS simulator (Minchin 1987). The data were designed to simulate as closely as possible, what is known of the distribution of species on environmental gradients. The factors included the dimensionality of the data, the number of sites and species, the shape of the species response surfaces, positioning of the sites in the simulation space, carrying capacity and level of noise. Recovery of the simulated site positions by SHS and Hybrid Scaling was evaluated using Procrustes rotation. SHS produced a better recovery in 88% of the datasets.
Succession and fluctuation in a wet dune slack in relation to hydrological changes
Authors: Grootjans A. P. , Hartog P. S. , Fresco L. F. M. , Esselink H. 
Published: May 2006

Vegetation changes in a wet dune slack complex have been studied over a period of 23 yr. The vegetation was recorded in 40 permanent plots: all plots in 1964, 1977, 1983 and 1987 and some also in five other years. There were large fluctuations in annual precipitation during this period, including some extremely dry (1976) and wet (1985) years.Many species of wet calcareous and pioneer habitats declined in cover between 1964 and 1977, when there were prolonged dry summer periods, though few species were lost from the sampled quadrats.Practically all calciphilous and pioneer species disappeared between 1977 and 1983, when there were relatively many wet summers. It is suggested that extremely dry conditions temporarily obscure the impacts of hydrological changes in local hydrological systems, by retarding the vegetation succession. After a period of excessive precipitation the (acidifying) effects of ground‐water withdrawal rapidly became evident in the species composition of the dune slack.
Small‐scale variability as a mechanism for large‐scale stability in mountain grasslands
Authors: Herben T. , Krahulec F. , Hadincová V. , Skálová H. 
Published: May 2006

Abstract. Data from a 7‐yr permanent plot study of grassland dynamics were used to address the relationship between processes at two levels of resolution (3.3 cm x 3.3 cm, 50 cm x 50 cm). Grasslands mown and manured in the traditional way in the Krkonose Mts. (Riesengebirge) were used as a model system. Spatial dynamics at the finest scale were very high, as demonstrated by turnover of individual species in 3.3 cm x 3.3 cm subplots and year‐to‐year transition matrices of the same subplots. The direction of these dynamics was not correlated with grassland treatment, although there was some correlation within years. An extrapolation of such year‐to‐year dynamics to larger time scales would result in big large‐scale changes on the community level, and large shifts in species composition of the whole sward. However, dynamics at larger spatial or temporal scales were generally small. Some directional change occurred in manured plots, whereas little change occurred in unmanured plots. Large‐scale dynamics were not correlated with small‐scale dynamics in plots without manuring, but some correlation was detectable in manured plots.There are probably several processes that drive small‐scale dynamics, such as non‐linear interactions and environmental fluctuations. We argue that within certain limits these forces act on species composition so as to make small‐scale dynamics non‐directional. This results in both large‐scale species diversity and apparent large‐scale stability of these grasslands. However, if these forces are beyond these limits, the small‐scale dynamics may become directional, resulting in rapid changes at larger spatial scales.
Pollen representation of vegetational patterns along an elevational gradient
Authors: Jackson Stephen T. 
Published: May 2006

Abstract. Modern pollen assemblages from 16 small lakes (< 2.5 ha) and 11 moderate‐sized lakes (4.5–19.3 ha) arrayed along an elevational gradient (300 to 1320 m) in the east‐central Adirondack Mountains were studied to determine how well the pollen assemblages recorded patterns of forest composition along the gradient. Forest composition ranges from Pinus strobus/Tsuga/ hardwoods forests at low elevations through Tsuga/ hardwoods, hardwoods, and Picea/Abies forests to Abies‐dominated forests at high elevations. Modern pollen percentages for 10 tree taxa were compared with lake elevation using scatter plots and correlation and regression analysis.Differential smoothing of vegetational patterns along the elevational gradient occurred among the 10 taxa owing to differences in pollen dispersibility, pollen production, and spatial pattern of taxon abundance in forests of the region. No differences were observed in pollen‐elevation patterns between small and moderate‐sized lakes. Pollen‐elevation patterns were obscured for most taxa when the gradient was shortened (e.g. to 600–1320 m) owing to increased spatial smoothing by pollen dispersal. Design and interpretation of paleoecological studies of spatial gradients can be improved by careful attention to site spacing, gradient length, and gradient steepness in the context of pollen dispersal and representation models.
BOOK REVIEWS
Authors: Wieder R. Kelman 
Published: May 2006

Book reviewed in this issue.Whigham, D. F., Good, R. E. & Květ, J. (eds.) 1990. Wetland Ecology and Management: Case Studies. Tasks for Vegetation Science Series No. 25. vii + 180 pp. Kluwer Academic Publishers, Dordrecht. ISBN 0–7923–0893‐X. Price: USD 95.‐.
Limitations to species coexistence: evidence for competition from field observations, using a patch model
Authors: Wilson J. Bastow , Gitay Habiba 
Published: May 2006

Abstract. Plant community structure in four dune slacks is examined for evidence of competition, expressed as local constraint on species biomass. Such constraint would result in a low variance in total quadrat biomass, compared to a null model. A method of analysis is introduced, using a patchbased null model, which is intended to discount most of the effects of environmental heterogeneity. The method is applied to data in which previous methods had failed to find such structure.There was significant biomass constraint (i.e. low variance in biomass) examining total plant‐community biomass in Site 1, and there was a trend in this direction also in Site 2. When guilds defined on morphology were examined, significant biomass constraint was found for the Rhizomatous guild in Site 2. There was a trend to low variance for this guild also in Site 4, but it was significant only in a one‐tailed test. After a consideration of other mechanisms, it is concluded that the most likely explanation for this biomass constraint is interspecies competition.Site 2, which showed the strongest evidence of biomass constraint in the present analyses, was also the site that demonstrated a significant deficit of variance in richness in earlier work, and was the most species‐rich of the four sites and the least disturbed.The advantages of the new method, for obtaining evidence on competition, are discussed in comparison to pot experiments and field‐perturbation experiments.We conclude that community structure can be seen in the pattern of species biomasses provided that a suitable method of analysis is used, i.e. examining small‐scale effects and excluding the effects of environmental heterogeneity. In some cases such effects can be related to guild membership. We hypothesise that constraint on biomass is likely to be stronger in more species‐rich and less disturbed communities.
BOOK REVIEWS
Authors: Sykes Martin T. 
Published: May 2006

Book reviewed in this article:Veroustraete, F., Ceulemans, R.J.M., Impens, I.I.P & van Rensbergen, J.B.H.F. (eds.) 1994. Vegetation Modelling and Climatic Change Effects. SPB Academic Publishing bv, The Hague. ISBN 90‐5103‐090‐8. Price: USD 42.‐.; NLG 75.‐.
Interspecific variation in tree seedling establishment in canopy gaps in relation to tree density
Authors: Reader R.J. , Bonser S.P , Duralia T.E. , Bricker B.D. 
Published: May 2006

Abstract. We tested whether interspecific variation in tree seedling establishment in canopy gaps was significantly related to interspecific variation in tree density, for seven deciduous forest tree species (Quercus alba, Hamamelis virginiana, Acer rubrum, Sassafras albidum, Quercus rubra, Prunus serotina, Ostrya virginiana). For each species, seedling establishment was calculated as the difference in seedling density before experimental gap creation versus three years after gap creation. In each of the six experimentally‐created gap types (33 % or 66 % removal of tree basal area from 0.01‐ha, 0.05‐ha or 0.20‐ha patches), differences in seedling establishment among species were significantly related to differences in their density in the tree canopy. A regression model with loge tree density as the independent variable accounted for between 93 % and 98 % of interspecific variation in seedling establishment.Our results provide empirical support for models of tree dynamics in gaps that assume seedling establishment depends on canopy tree density.
What constitutes evidence of community structure? A reply to van der Maarel, Noest & Palmer
Authors: Wilson J. Bastow , Peet Robert K. , Sykes Martin T. 
Published: May 2006

Abstract. Van der Maarel et al. (1995) — hereafter VNP — criticize our analyses of Öland limestone grassland. They have four general objections, addressed below.1. VNP attribute our significant results to randomness (‘volatility’); however, significant deviation from randomness cannot be explained by randomness. VNP's conclusion of volatility derives from results that are inconsistent with ours. Their ecological interpretation assumes spatial and temporal near‐constancy in the vegetation; we demonstrate that these assumptions are not correct.2. We discussed physical limitations to plant module packing. VNP give estimated module sizes. We appreciate this information, though data on actual module sizes and overlap patterns would be required before the real module packing effects could be determined. If module packing were really the main cause of deficits of variance in richness, the effect would not fluctuate between sites and years, as VNP admit it does.3. The shape of the richness frequency distribution is a potentially interesting additional form of analysis, albeit one that we had chosen not to include in our analysis. However, it is surprising that VNP dismiss analysis of richness variance, but then interpret a more subtle aspect of the richness distribution — the skewness. VNP's redefinition of the terms‘Niche facilitation’for a deficit of low richness values, and ‘Niche limitation’ for a deficit of high values, leads them to misrepresent our arguments. They are mistaken in suggesting that niche limitation will necessarily lead to a skewed curve: they do not allow for the fact that the species frequencies, on which the null model is based already, incorporate effects of species interactions.‘Niche facilitation’, as defined by VNP, would lead to a variance excess, not a deficit as they assume.4. VNP's criticism of a priori guild classifications had already been met by our use of the intrinsic guild approach. Guild analyses offer the best way forward.VNP use principally the methodology of 1987. There have been a number of methodological advances since that time. We used these advances in our original paper specifically to circumvent the kinds of problems that they identify. We agree with VNP that it would be very useful to explore the mechanisms behind assembly rules with experiments, but the logical first step is to identify potential assembly rules, as we have been attempting to do. We conclude that, whilst VNP make some interesting observations, none of their criticisms invalidate our results or conclusions. Our original approach stands as the best known approach, we believe, for searching for community structure in such data, and we reaffirm the validity of our ecological conclusions.
Correlation between richness per unit area and the species pool cannot be used to demonstrate the species pool effect
Authors: Herben Tomáš 
Published: May 2006

Abstract. Significant correlation between the size of the species pool and richness per unit area is usually taken as a demonstration of the effect of the species pool on the species richness per unit area. This is not logically necessary. It has to be emphasized that such a correlation cannot be interpreted as a demonstration of the effect of species pool on the species richness per unit area. More generally, correlation cannot be used to demonstrate a one‐directional effect of one variable upon another, since several types of (functional) relationships could produce correlations between such variables; the same caution has to be taken when analysing the species pool vs. richness per unit area correlation.In this paper, a simple Monte Carlo simulation model is used to demonstrate that (1) statistical processes acting only at the local scale (such as competitive exclusion) can generate exactly the same correlation that has been used to infer the effect of the species pool on richness per unit area; (2) this correlation would be deemed significant even if the mathematical dependency between species pool and richness per unit area is taken into account; and (3) the strength of this relation depends on beta diversity within the contiguous area used to determine the species pool.
Seed banks of grazed and ungrazed Baltic seashore meadows
Authors: Jutila b. Erkkilä Heli M. 
Published: May 2006

Abstract. The seed banks of three grazed and three ungrazed seashore meadows were studied on the west coast of Finland. 8486 seedlings (mean 13 669 seedlings/m2) germinated from cold‐treated samples (n = 343; depth = 10 cm). Most seedlings and species were monocots and perennials. The seed bank flora included 54 dicots vs. 28 monocots and 66 perennials vs. 16 annuals. The most abundant species were Juncus gerardii, Schoenoplectus tabernaemontani, Eleocharis uniglumis, Agrostis stolonifera, Juncus bufonius and Carex nigra, which made up 73% of the seed bank.Numbers of species and seedlings differed between elevation classes. Species richness was highest in elevation class 50–70 cm. The highest seed density occurred in class 20–50 cm. A model for size and species composition of the seed bank in relation to elevation is presented. The seed bank was larger and richer in species in the ungrazed than in the grazed sites, but not so in the upper elevations and closest to the open sea. Grazing reduced the size of the seed bank of Agrostis stolonifera, A. capillaris, Calamagrostis stricta, Elymus repens, Juncus bufonius, Limosella aquatica and Schoenoplectus tabernaemontani, but increased that of J. gerardii. 32 species germinated only from ungrazed samples and 11 species only from grazed ones. Multivariate classification resulted in nine sample groups. The ordination scatter was best explained by the flooding stress variables, elevation, the distance from the water line and the number of helophyte species in samples.75 species were found both in the seed bank and in the vegetation, but there was a significant lack of resemblance (in the Mantel test) due to over‐representation of some species. Eight species occurring only in the seed bank were mainly annuals or biennials (63%); those occurring only in the established vegetation (86 species) were mainly perennials (86%).
Effects of herbivory on the growth and reproduction of Picris hieracioides in the Mediterranean region
Authors: Escarré J. , Lepart J. , Sans X. , Sentuc J.J. , Gorse V. 
Published: May 2006

Abstract. The impact of herbivorous insects on the growth and reproduction of Picris hieracioides (Compositae) was followed in three consecutive years by comparing plants treated with an insecticide and untreated plants in an old‐field population abandoned for 15 yr (P15). In the third year the interactions between herbivory and competition were analysed as well. Pre‐dispersal seed predation of seed heads was investigated in three adjacent old‐fields abandoned for one (P1), 15 (P15) and 40 yr (P40) in the region of Montpellier, France. Fields differed in vegetation cover and floristic composition and also in density and above‐ground biomass of Picris hieracioides plants (from 246 g per plant in P1, 13.3 g in P15, down to 3.3 g in P40, for the first year of study). The cumulative rainfall between January and July, the period of Picris growth, decreased from 1992 to 1994. Moreover, in 1992, three times as much rainfall occurred in May and June – the period of stem elongation – as in 1993 and 1994. As a consequence, environmental stress increased during the study period.Herbivorous invertebrates had a negative effect on the growth and reproduction of individual plants of Picris hieracioides in P15. The effect was not constant with time, being apparent in only two years out of three. These two years (1992 and 1994) had contrasting climatic characteristics, whereas the year with no apparent effect (1993) was climatically intermediate. When herbivory had effects on growth, the insecticide‐treated plants had a significantly higher above‐ground biomass and produced twice as many seed heads as the control plants. There was no interaction between herbivory and competition.The percentage of damaged seed heads was significantly lower in the P1‐field than in the P40‐field. The P15‐field had intermediate levels of predation. Predation on seed heads increased whereas biomass and reproductive output decreased between 1992 and 1994 in the three old‐fields. Therefore, the results on seed predation (but not for above‐ground biomass and reproduction) tend to confirm‘the environmental stress hypothesis’ of Mattson & Haack (1987) that states that plants under stress are more liable to be attacked by grazers.
Old‐field colonization by Daphne gnidium: seedling distribution and spatial dependence at different scales
Authors: Verdú M. , García‐Fayos P. 
Published: May 2006

Abstract. This paper deals with the spatial distribution pattern of the bird‐dispersed plant Daphne gnidium in a 10‐yr abandoned field under Mediterranean conditions. Colonization of Mediterranean old‐fields by bird‐dispersed plants is expected to fit a theoretical model in which (1) seed dispersal follows a negative exponential curve with the distance from the seed source and (2) seedlings are better established under perches (nucleation sensu Yarranton & Morrison 1974). However, post‐dispersal processes such as seed predation, seed germination and seedling establishment are also spatial‐dependent and can lead to spatial autocorrelation in the seedling distribution within an old‐field.Results show that both processes in the model (curve of seed dispersal and nucleation) significantly explained the spatial distribution of the seedlings, but some spatial variance remained unexplained. The semivariogram with the statistical residuals of the model detected spatial dependence at small (< 20 m) and large (> 250 m) distance intervals, indicating that some mechanisms with spatial components, apart from the curve of seed dispersal and nucleation under perches, also determined the distribution of seedlings colonizing fields. At scales below 20‐m intervals, semivariance increased indicating that similarity between plots is lost when distance increases between them. This pattern may be explained because the favourable micro‐environmental conditions for establishment produced under perches could be extended towards neighbour plots where perches were absent. A flat semi‐variogram between 20‐m and 250‐m intervals shows spatial independence along this range. From 250 m on, the semivariance increased again, indicating spatial dependence at coarse‐scale. It is possible that the colonization model failed at this scale because different spatial processes to those included in the model (perch presence and distance to the shrubland) could be controlling seed colonization at coarse‐scale.
Effects of cutting and rainfall pattern on resprouting vigour and growth of Erica arborea L.
Authors: Riba Miquel 
Published: May 2006

Abstract. This study analyses the effects of recurrent cutting and rainfall pattern on sprout and genet growth in the resprouting shrub Erica arborea. Three different intervals between consecutive clear‐cutting events were applied: 30, 5 and 2 yr. Above‐ground genet biomass after 2 yr of treatment application was correlated with burl size and decreased with increasing recurrence of cutting, indicating that more than 5 yr were needed to re‐establish the resprouting potential of genets.The effect of rainfall on growth was evaluated through the correlations between sprout RGR and several variables related to the rainfall pattern at different regeneration stages. The effect of the rainfall pattern on sprout RGR was dependent on the regeneration age, suggesting that water availability becomes more limiting after two years of regrowth.
Effects of species partition on explanatory variables in direct gradient analysis ‐ a case study from Senegal
Authors: Lawesson Jonas E. 
Published: May 2006

Abstract. Species‐environment data from Senegal, West Africa, are used to study the effects of partition of a large species data set into subsets corresponding to rare and common species respectively. The original data set contains 129 woody plant species from 909 plots and 60 explanatory variables.By applying Canonical Correspondence Analysis to data subsets, marked differences in the forward‐selected variables were detected. The highest resemblance was found between the complete species set and the common species subset. Only one of eight selected variables was common to all species and the rare species groups. These findings were tested with partial ordination, applying the selected variables from the original species group (Vb), as variables and covariables to the analyses of common and rare species. For the common species this application resulted in a constrained ordination with higher eigenvalues as compared to the set of variables selected with reference to the common species group. Using the rare species group, the application of Vb gave a much lower sum of eigenvalues than did the ordination with selected variables based on the rare species group only. Evidently, the set of variables selected on the basis of the rare species data were more significant.Hence, the resulting gradients depend on the frequency of the species. Gradient analysis is apparently only valid for groups of species with closely resembling characteristics. This implies that different functional types of species, with different distributions and abundances, respond individually to environmental variation. Extrapolating deduced gradients from one species group to another maybe risky, particularly when used in vegetation modelling.