bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of grazing on local colonisation and extinction during early succession
Authors: Gibson C. W. D. , Brown V. K. 
Published: May 2006

AbstractEstimates of colonisation of plant species were made at three spatial scales in an old‐field on limestone subject to five experimental sheep grazing regimes. Local extinctions within grazing treatments were estimated in 1‐m2 permanent quadrats. These data were used to assess the effects of grazing treatment and spatial scale on the process of species change over a period of six years. Colonisation of the lOha field was virtually a random draw of plant species from adj acent vegetation, irrespective of plant life‐history traits including dispersal strategy. The effects of grazing on colonisation increased at smaller spatial scales. Colonisation rates changed little during the study on the 10 ha scale, but declined steeply with time at smaller scales. Colonisation rates of short‐lived species declined more than those of perennials, and short‐lived species were subject to erratic episodes of extinction which did not affect perennials.Short periods of grazing enhanced colonisation rates of all species, but extinction rates were the same as in ungrazed controls. Grazing for longer periods further enhanced colonisation rates, but also increased extinction rates. This produced diversity patterns consistent with a ‘hump‐backed model’, except that no grazing treatment was heavy enough to decrease diversity. Ungrazed controls had low species diversity, but areas grazed for longer periods were no more diverse after six years than those grazed for short periods.
Germination and seedling dynamics of Arbutus unedo and Erica arbórea on Corsica
Authors: Mesléard F. , Lepart J. 
Published: May 2006

AbstractAnalysis of the seedling distribution of Erica arbórea and Arbutus unedo, two dominant plant species in the Corsican maquis, and of three tree species (Pinus mesogeensis, Quercus ilex and Quercus pubescens) with which they compete in a mosaic of successional habitats, has enabled the determination of the successional position of the two ericaceous species. Erica arbórea and Arbutus unedo are often considered to be pyro‐phytes, but the distribution pattern of their seedlings, following either abandonment of cultivation or after fire, indicates that fire is unfavourable for their establishment. Field and laboratory studies of the germination of the two ericaceous species indicate that the absence of seedlings following fire is not due to the destruction of seeds by fire but due to the newly created environmental conditions.Erica arbórea invades sites abandoned after cultivation and has thus spread widely since the end ofthe last century. Arbutus unedo, the seeds of which are disseminated in bird droppings, has the ability to establish in denser vegetation, and thus appears to be a mid‐successional species.
Response of a weed community to nitrogen fertilization: a multivariate analysis
Authors: Pyšek Petr , Lepš Jan 
Published: May 2006

AbstractThe effect of nitrogen fertilizers on the composition of a weed community was investigated in a barley field. Two doses (70 and 140 kg N/ha) of three fertilizers (ammonium sulphate, calcium‐ammonium nitrate, and liquid urea) were used. The results were evaluated using the canonical correspondence analysis. Hybrid analyses and various combinations of environmental variables and co variables were used to separate the influence of the dose and the type of fertilizer and to separate the direct and indirect effects of fertilization. The results reveal that both the dose and type of fertilizer have a significant effect on the composition of the weed community. The results suggest that both the direct effect of fertilizer and an indirect effect, through increased competition of the crop, are important determinants of weed community composition.
Patch colonisation in a savanna grassland
Authors: O'Connor T. G. 
Published: May 2006

AbstractPatches (1 m diameter) were cleared in a heavily grazed and a lightly grazed savanna in South Africa; half of them were covered once with grass litter. The greatest colonisation over three years occurred on heavily grazed patches with litter, the least on open, lightly grazed patches. Annual rainfall affected colonisation rate. Basal cover was lower on patches than in the surrounding vegetation. Patch composition was weakly affected by treatment, and was partly related to the composition of adjacent vegetation, but the proportional representation of species on patches differed from the surrounding vegetation. The stoloniferous Digitaria eriantha and the obligate seed reproducers Aristida bipartita and Heteropogon contortus were major components of patch communities but were uncommon in the surrounding vegetation and in the seed bank. Setaria incrassata and Themeda triandra were the predominant components of the surrounding vegetation and of the seed bank, but Setaria established very poorly and Themeda established well only on heavily grazed patches with litter.The pattern of seedling establishment was the same as that of colonisation. Most seedlings emerged atthe beginning of the wet season, with ca. 50% mortality soon thereafter. The colonising species can be partly predicted from the availability of propagules (vegetative or seed), emergence and establishment success, and subsequent growth.
Guilds and assembly rules in lawn communities
Authors: Wilson J. Bastow , Watkins Anni J. 
Published: May 2006

Abstract. The community structure of 11 lawn sites in New Zealand and Fiji was examined in terms of guilds, seeking assembly rules based on guild proportionality.First, associations were analysed, using a new patch model which examined the mean of associations within patches of about 4 cm x 4 cm. As expected from the previously‐demonstrated existence of niche limitation at this scale in lawns, the majority of associations between individual species were negative. Even in a lawn only four months old there were significant associations (mostly negative, and one positive). At some sites those species with the most negative associations were those whose morphology might be expected to restrict co‐existence with other species.Much ecological theory is based on the assumption that there are limitations to coexistence, related to the resource usage of the species, such that species that are too similar in resource use are less likely to coexist. This theory was tested by looking for evidence of guild proportionality. We defined two guilds, graminoids and forbs. Using these guilds, three of the sites showed significant evenness in proportional representation from the two guilds in quadrats containing four species, i.e. there was less variation in the graminoid:forb ratio than expected on a random basis. Inclusion of species‐poor quadrats in a joint analysis over all richness categories overwhelmed this effect, though there was still a strong trend for two of the New Zealand sites: the two species‐rich grass lawns. Preliminary analyses of alternative guild delimitations gave no indication that other guild delimitations would have revealed stronger community structure. There was a strong and significant tendency in most sites for the graminoid guild to be more strongly represented in species‐poor quadrats, an effect caused by species frequencies.
Structure, productivity and energy flow in an alpine grassland in the Garhwal Himalaya
Authors: Sundriyal R. C. 
Published: May 2006

Abstract. Structure, primary production and energy flow were studied in ungrazed and grazed alpine meadows in the Garhwal Himalaya, India. In grazed grasslands, the cover of graminoids increased, the biomass of palatable species was reduced by about 50%, but the biomass of unpalatable species increased, due to reduced competition from the better‐foraged species. Generally, 32% of live shoot and root biomass was consumed during a growing season. Also, above‐ground plant productivity increased as a result of plant regrowth, while below‐ground productivity decreased.Flow and storage of energy in ungrazed and grazed alpine grasslands showed an accumulation of 10.1 and 8.5 kJ/yr with energy conversion efficiencies of 0.7 and 0.6% respectively. Ca. 46% of the net energy accumulated was consumed by herbivores on the grazed grassland. Only 26% of the net captured energy disappeared from the system in the growing season, mainly via root and litter decomposition.
Study of spatial components of forest cover using partial Mantel tests and path analysis
Authors: Leduc A. , Drapeau P. , Bergeron Y. , Legendre P. 
Published: May 2006

Abstract. Plant species distributions are generally thought to be chiefly under environmental control, although they may be affected by disturbance events or dispersion properties of the species. The relative importance of these different factors is not easy to evaluate because they often share common spatial patterns, such that an inextricable network of relationships occurs between plant distributions, environmental conditions, disturbance events and endogenous factors such as propagule dispersion. In this paper we propose a method for untangling the common spatial component from the relationship between environmental conditions and the distribution of tree species. Using partial Mantel tests and path analysis, we test models of relationships between these data sets.Results show that in our study area, spatial patterns of species associated with hydric conditions remain largely correlated with environmental conditions. However, mesic sites show more complex forest covers, in which a significant spatial component persists when environmental variation is statistically controlled for. This remaining spatial variability suggests that other factors possessing spatial structure partly explain species distributions.
Variation in basal sprouting in co‐occurring shrubs: implications for stand dynamics
Authors: Flinn Robert C. , Scifres Charles J. , Archer Steven R. 
Published: May 2006

Abstract. Sources of basal sprouting for five shrub species representing five plant families common to the Tamaulipan biotic province were quantified, following four intensities of top removal. Among undisturbed shrubs, Celtis pallida and Zanthoxylum fagara were somewhat arborescent, with one or two dominant primary stems per plant. Aloysia gratissima, Ziziphus obtusifolia and Schaefferia cuneifolia were fruticose in architecture, with more and smaller stems. Following top removal, each species exhibited a distinct regenerative hierarchy whereby shoot production following disturbance was primarily from structures immediately subtending the removed tissues, even though more distal tissues had the capacity for shoot production. Thus, removal of stems to a 5 cm residual increased the contribution of primary stems from stem bases, whereas stem removal to ground line typically induced regeneration from root crowns. Schaefferia, Zanthoxylum and Ziziphus were capable of producing shoots from root tissue, yet regeneration from roots was not stimulated until tissues were removed to below root crowns.Field observations indicate that most woody species in the subtropical thorn woodlands of southern Texas, USA, are highly persistent in the face of natural and anthropogenic disturbance, owing to their ability to regenerate vegetatively. Alternative sources of stem replacement contribute to the high resilience of these shrubs following disturbance and may help explain or predict patterns of secondary succession and plant persistence following various intensities of disturbance.
Change in pattern diversity during secondary succession in Estonian forests
Authors: Zobel K. , Zobel M. , Peet R. K. 
Published: May 2006

AbstractComparisons of observed variance in species diversity (exp LT) and in species richness with expectation assuming a random and independent distribution of species are used to assess the relative importance during succession of niche limitation (Wilson, Gitay & Agnew 1987; limitation of the abundance or occurrence of species by competitive interactions) and nucleation (Yarranton & Morrison 1974; the development of a community through chance establishment or persistence followed by vegetative expansion from those nuclei).Wilson, Gitay & Agnew (1987) and Palmer (1987) suggest a deficit (i.e. lower than expected) in variance of richness is consistent with a ‘niche limitation’ process where competitive sorting makes patches more similar in species number than would be expected. In contrast, variance that is greater than expected is consistent with and could result from underlying environmental heterogeneity (i.e. ‘waterhole effect’). We extend these ideas to suggest that, in addition, a deficit in variance of diversity (expLT) can be interpreted as indicating niche limitation. Further, we suggest that a deficit of variance in richness need not be interpreted as resulting from niche limitation, but could result from limited dispersal and establishment followed by localized spread that causes quadrats to have less compositional overlap than might be expected if species were distributed at random. However, there is little reason to expect that such nucleation would cause a similar reduction in the variance of diversity. First, expLT is relatively insensitive to the presence or absence of rare species, and second, if local competitive processes do restrict the values of exp LT through some form of niche limitation, this could well be independent of the specific species involved. Thus, a combination of lower than expected variance in richness and high variance in diversity suggests nucleation to be important, particularly if the mean pairwise similarity between samples is lower than expected.We first examine a secondary successional sere with stands representing post‐logging and mature forest. The variance of diversity is low in the establishment phase, but not in subsequent phases where the tree canopy is well developed. Significantly low variance of species richness is observed in a young forest just entering the thinning phase. Thus, nucleation may be taking place in the establishment phase of forest development, and is almost certainly important in the early thinning phase. Second, we examine communities in the process of equilibration following fertilization, logging, and paludification. All these communities have a low variance in diversity (exp LT) suggesting niche limitation.
Patterned fens in Scotland: evidence from vegetation and water chemistry
Authors: Charman Daniel J. 
Published: May 2006

AbstractMires with attributes similar to the patterned fens of boreal continental regions have recently been reported from northern Scotland. This paper reports on the vegetation and water chemistry of 18 of these sites. Most of the 18 mires displayed remarkable uniformity in their vegetation, withCarex lasiocarpabeing a main character species. Major variation of plant communities is associated with microtopographical niches, similar to those found on ombrotrophic mire systems and secondarily with pH and conductivity of surface waters.Nine vegetation noda are described and compared with existing phytosociological associations and National Vegetation Classification (NVC) communities. The dominantSphagnum ‐ Carexcommunities are intermediate between theOxycocco‐Sphagneteaand theCaricion lasiocarpaeand are thus difficult to assign to existing associations or to NVC communities. Although there is a large variation in pH of surface waters (3.9–6.6), mean measurements for terrestrial and aquatic communities are 5.12 and 5.51 respectively. pH levels are comparable with poor fen systems elsewhere in Britain and slightly higher than patterned fens in continental regions of Europe and North America. The vegeta‐tional and chemical attributes of these sites therefore confirm the existence of true patterned fen systems in the British Isles.
BOOK REVIEWS
Authors: Bennett Charles F. 
Published: May 2006

Book reviewed in this issue.Vos, W. & Stortelder, A. 1992. Vanishing Tuscan Landscapes. Landscape Ecology of a Submediter‐ranean‐Montane area (Solano Basin, Tuscany, Italy). 404 pp. Pudoc, Wageningen. ISBN 90220–0964–5, Price: NLG 120.‐.
Adaptation of ecological systems: compositional patterns of species and morphological and functional traits
Authors: Montalvo J. , Casado M.A. , Levassor C. , Pineda F.D. 
Published: May 2006

Abstract. The species composition and morphological and functional traits of ecological systems are compared. The significance of the resulting relationship is interpreted considering the underlying spatial environmental variation. Using 60 morphological and functional traits, a gradient of ecological persistence was detected in Mediterranean grasslands along an altitudinal range of ca. 1200 m. This pattern coincides with the one expressed by its taxonomic composition and thus permits ‘styles of adaptation’ of ecological systems to be recognized. Species composition may represent one of the possible combinations which optimises its environmental fit.The relevance to ecological theory of this pattern of grassland organization is discussed in the context of a hypothetical model of evolution.
BOOK REVIEWS
Authors: Minnich Richard A. 
Published: May 2006

Book reviewed in this issue.Goldammer, J. G. & Jenkins, M. J. (eds.) 1990. Fire in Ecosystem Dynamics: Mediterranean and Northern Perspectives. viii + 199 pp. SPB Academic Publishing, The Hague, the Netherlands. ISBN 90–5103–045–2. Price: USD 37.‐.
The influence of spatial heterogeneity on regeneration by seed in a limestone grassland
Authors: Rusch Graciela , Fernández‐Palacios José María 
Published: May 2006

Abstract. The spatial distribution of seedlings in fertilized and non‐fertilized grassland patches (1 m x 2 m) was examined in alvar vegetation on the island of Öland, Sweden. We established whether variation in seedling distribution in grassland patches reflects the distribution of conspecific adults. We also established the significance of microsite turf attributes for prediction of seedling distribution at a small scale (10 cm x 10 cm), and the significance of conspecific adults abundance, assemblage of adult species and cover of lichens, mosses, litter and bare ground.Our results indicate that fertilization reduces the importance of regeneration by seed of perennial species and enhances seedling recruitment of winter annuals and biennials. At the patch scale, enrichment does not affect species richness. Community patchiness contributes to the maintenance of diversity by providing a variety of environments with differential regeneration of the component species. Cover of lichens, mosses, litter and bare ground, accounts, in part, for the spatial variation in seedling numbers of certain species. The strong association of seedlings of some species with conspecific adults indicates that limitations in dispersal and/or the occurrence of a more suitable environment for emergence and/or establishment close to conspecific adult plants are likely to constrain the spatial distribution of new individuals in many cases. For other species, the lack of association of seedling densities with the cover of their conspecific adults, suggests that long‐distance dispersal or a long‐lived seed bank can play a role in counteracting the effect of short‐distance dispersal.
Identifying plant functional types using floristic data bases: Ecological correlates of plant range size
Authors: Kelly Colleen K. 
Published: May 2006

Abstract.In an effort to identify ‘plant functional types’, the islands floras of Great Britain and Kríti (Crete, Greece) were examined separately for ecological correlates of plant range size. Plant functional types (PFTs) were defined here as categories into which plants could be grouped on the basis of attributes that predict greater or lesser sensitivity to ecological variability. Plant range size indicates commonness of a species and was assumed to be a proxy for ‘ecological flexibility’, i.e. species of larger range sizes can better withstand environmental change and differences than species of smaller range sizes. Using evolutionary comparative methods that account for the effect of taxonomic relatedness, both floras were investigated for the effects on range size of woodiness vs. non‐woodiness, trees vs. shrubs, trees vs. herbs and shrubs vs. herbs. The British flora was examined additionally for the effects of wind‐ vs. non‐wind‐pollination, self vs. animal pollination and animal vs. non‐animal fruit dispersal on range size.Two analyses showed significant effects on range size: for British species, trees had larger ranges than shrubs, and wind‐ pollinated species had larger ranges than non‐wind‐pollinated species. It is suggested that the lack of a similar pattern for shrubs and trees in Kríti is because the lower water availability of Kríti imbues shrubs with an ecophysiological advantage not relevant in plants of Great Britain. That trees have larger range sizes than shrubs in Great Britain is ascribed to the greater importance of competition for light when other factors are not at issue. The greater range of wind‐pollinated than non‐windpollinated species in Great Britain is postulated to be because both mutualists must be capable of invading new areas. This may be termed a ‘cost of mutualism’.In terms of PFTs, the results indicate that ‘life‐form’ is too broad a classification category by which to differentiate relative sensitivity to environmental variability in Great Britain, in that there were significant differences in range size of trees and shrubs, but not between either of the two categories and herbs, or between woody and non‐woody plants. Although pollination type may predict relative sensitivity to variation in Great Britain, dispersal type will not. Finally, differences between Great Britain and Kríti in relative range size patterns suggests that plant functional types may be specific to a region or set of conditions.
Vegetation succession in lakes of West Connemara, Ireland: comparing predicted and actual changes
Authors: van Groenendael Jan M. , Roepers Reinetta G. , Woltjer Inez , Zweers Hanita R. 
Published: May 2006

Abstract. Changes in the vegetation of lakes and wetlands were investigated over a period of 18 years. It was assumed that changes in vegetation were related to changes in agricultural land use resulting in increased phosphate levels in surface waters. Data were collected in 1975, 1988 and 1993. Multivariate techniques were used to relate changes in vegetation to changes in environmental factors. With the use of a Markovian chain model, vegetation development was projected into the future. Projections based on vegetation dynamics between 1975 and 1988 were compared with actual changes in the vegetation.The vegetation dynamics appeared stable on a regional scale but quite dynamic on a local scale. A continuous decline in species diversity was noted as well as an overall increase of phosphate level. However, only minor changes in vegetation could be attributed to this increase of phosphate. Major changes were a result of fluctuations in water level. These changes coincide with periods of drier and wetter climate. Because of the fluctuating nature of these changes, predicted vegetation change did deviate from the observed change.
BOOK REVIEWS
Authors: Wyman Richard L. 
Published: May 2006

Book reviewed in this article:Scluze, E.‐D. & Mooney, H.A. (eds.) 1993. Biodiversity and Ecosystem Function. Ecological Studies Vol. 99. Springer‐Verlag, New York. ISBN 3‐540‐55804‐7. Price: USD 198.‐.