bluuebunny/crossref_metadata_2025 huggingface dataset:
Community attributes along a perturbation gradient in a shortgrass steppe
Authors: Milchunas D. G. , Lauenroth W. K. , Chapman P. L. , Kazempour M. K.
Published: May 2006

Abstract. We constructed a perturbation (response) gradient that encompassed several types of disturbances (causes) affecting shortgrass steppe communities, and that was confounded by time scales of initiation and duration. The objectives were to (1) examine the type of disturbance and the relative magnitude of response in relation to the history of the shortgrass steppe, and (2) determine which attributes of the plant communities displayed relationships across the perturbation gradient, rather than across traditional successional ‐ time gradients.

Comparisons of disturbance types indicated that long‐term heavy grazing by cattle resulted in plant communities which differ less from communities resulting from other disturbances than did long‐term ungrazed sites. The removal of grazers from this system promoted attributes of earlier serai stages. Water addition, below‐ground grazing by white grubs, and water‐plus‐nitrogen enrichment had distinct and large impacts on community composition. Nitrogen enrichment resulted in additions but not losses of species. The shortgrass steppe has a high degree of adaptation to both short‐term drought and aboveground grazing. Belowground grazing and semi‐aridity may be considered antagonistic pressures on the community.

Community attributes that displayed a relationship with increasing level of perturbation were decreasing dominance and increasing diversity, and fluctuation in species composition during short‐term wet/dry cycles. The level of perturbation was related to negative impacts on the two primary species and a corresponding increase of other warm‐season species, but was not related to densities of any other species, life‐form, or functional group.
Variation in structure and diversity in Mediterranean grasslands related to trophic status and grazing intensity
Authors: Puerto A. , Rico M. , Matias M. D. , Garcia J. A.
Published: May 2006

Abstract. The spatial organization of Mediterranean grassland in Spain is described, based on samples from 71 sites covering the existing variation in slope exposition and inclination.The whole set can be regarded as representing a trophic gradient, along which gradual variation in soil, species composition, biomass, and coverage were quantified. Corresponding to other studies from varying habitats, maximal species richness, diversity, and heterogeneity were observed on moderately infertile sites. Maximum species richness, over 60 species, occurred on sites with biomass values from 150–350 g / m2. Species richness values are much higher and biomass values are much lower than those found in temperate grasslands. The decrease in diversity towards the mosteutrophic communities is stronger than expected, but can be easily explained by the high grazing pressure here. The variation in diversity observed runs parallel with that in heterogeneity. Zones with a high species richness also have a high heterogeneity, meaning a low amount of dominance.

Grazing is understood as abiotic form of disturbance. Differences in grazing pressure may modify the relation between richness and fertility. While the greatest grazing pressure coincides with the most eutrophic communities, decreasing progressively towards the oligotrophic ones, the trend predicted by the resource availability theory is maintained; species diversity will be maximal at intermediate levels of disturbance. Absence of grazing in the eutrophic communities would lead to an investment in the soil of the unconsumed organic matter.
Soil seed banks and post‐fire seed deposition across a forest ‐ fynbos ecotone in the Cape Province
Authors: Manders P. T.
Published: May 2006

Abstract.The relative sizes and composition of soil seed banks, the influence of fire and the post‐fire deposition of seeds were investigated in a riparian forest and adjacent fynbos and transitional vegetation in Swartboskloof. Brief complementary studies of soil seed banks were conducted in poorly‐developed forest and scree forest soils. Numbers of species in each vegetation type were very similar, but there were fewer seeds in riparian forest soil than in the transitional and fynbos zones. These patterns were not repeated in poorly‐developed forest and scree forest. No effects of fire on soil seed banks were detected. Forest soil had relatively large numbers of seeds stored at 10 to 15 cm deep, with many zoochorous and few myr‐mecochorous seeds.

Anemochorous and ornithochorous seeds of forest species formed a major component of seed deposition within the transitional and fynbos zones in the first year after fire. The numbers of anemochorous forest seeds in the fynbos declined with distance from the forest edge. The deposition of ornithochorous forest seeds was less closely related to distance from the source, and was not exclusively associated with the presence of tall or fruit‐bearing shrubs.

Regeneration after canopy‐destroying disturbance in the forest is likely to emanate from the soil seed banks of pioneer species which now or previously occurred on forest margins. Seed availability does not appear to limit colonization of fynbos by forest species soon after fire.
Comparative seed biology and co‐existence of two fynbos shrub species
Authors: Kilian D. , Cowling R. M.
Published: May 2006

Abstract. Fire‐prone fynbos communities include numerous species which are difficult to distinguish in terms of conventional niche axes since they are morphologically similar and share the same broad life‐history traits. These species compete for space after each fire and lottery theory predicts that those with dissimilar per capita regeneration would not co‐exist in the long‐term.

We studied seed production, soil seed bank dynamics, germination and post‐fire seedling establishment and mortality of two obligate reseeding, morphologically similar shrubs which co‐occur in dune fynbos throughout the southwestern Cape. Passerina paleacea produced 30 x more plump seeds and maintained soil seed banks between 1.5 x (pre‐dispersal) and 2.6 x (post‐dispersal) times larger than Phylica ericoides. Seeds of both species showed a high degree of dormancy although germination was stimulated by direct fire‐related cues for Phylica only. Approximately 4 x more Passerina seedlings than Phylica seedlings were counted at the end of the winter germination period after a mild autumn fire. However, seedling mortality in the first five months of the dry summer was more than twice as high for Passerina than for Phylica.

We suggest that the long‐term co‐existence of these two species does not result from similar post‐fire regeneration success but rather from population instabilities arising from differential regeneration in relation to fire regime. The results predict that hot fires followed by dry summers would favour Phylica over Passerina as the former has fire‐stimulated germination and greater drought tolerance; cool fires followed by moist summers would favour Passerina.
Limitation to plant species coexistence at a point: a study in a New Zealand lawn
Authors: Wilson J. Bastow , Roxburgh Stephen H. , Watkins Anni J.
Published: May 2006

Abstract. Limitation in the number of species that can coexist at a single point was examined by point‐quadrat sampling of a lawn. Three treatments were examined: Control, Herbicide‐treated to remove grasses, and Mechanically perturbed to remove all plants, with 10 replicates of each. The Control plots showed an almost constant degree of niche limitation, variance in richness between points being half that expected under the null model. The herbicided plots showed a significantly lesser degree of niche limitation for the first three months after herbiciding, even though the degree of plant overlap had already recovered by the first sampling time. Six weeks after mechanical perturbation, there was no evidence of niche limitation, but the extent of, and statistical evidence for, niche limitation increased until, 10 months after perturbation, community structure was as strong as in the Control.
Some comments on the classification of African vegetation
Authors: Lawesson Jonas Erik
Published: May 2006

Abstract. Problems of naming African vegetation units are discussed, and related to the AETFAT vegetation scheme and other recent publications. Particularly, the distinction is emphasized between the terms forest and woodland, which are often considered synonyms. In other cases, no precise and ecologically meaningful definitions are presented, which leads to confusion and superfluous terms. More strict rules for the definition and application of vegetation terminology are proposed, and suggested as basic information to be given in vegetation literature.
BOOK REVIEWS
Authors: Spada Francesco
Published: May 2006

Abstract. Meurer, H. 1993. Geo‐ und weideökologische Untersuchungen in Mogod‐Bergland Nordwest‐Tunesiens: unter besonderer Beruecksichtigung der kleinbäuerliche Ziegenhaltung. Erdwissenschaftliche Forschung Band 29. 330 pp., 34 Photographs, 90 Figs., 23 Tables, 4 App. F. Steiner, Stuttgart. ISBN 3‐515‐05637‐8. Price: DM 164.‐.
A quantitative study of vegetation ‐ environmei relationships in two Egyptian deserts
Authors: Dargie T. C. D. , El Demerdash M. A.
Published: May 2006

Abstract. Two contrasting Egyptian desert environments are examined by ordination and integrated inter‐pretationmethods. A crude site moisture index is strongly related to vegetation in both desert regions. Water quality is an additional strong control of floristic variation on the Sinai coastal plain and disturbance (by grazing and woodfuel collection) is important in the Eastern Desert. Useful indicator groupings of species are obtained as part of the analysis and are potential aids in the development and conservation of desert areas. Modern numerical methods offer considerable advances on the traditional descriptions of Egyptian desert ecosystems.
Spatial relationships between cacti and nurse shrubs in a semi‐arid environment in central Mexico
Authors: Valiente‐Banuet A. , Bolongaro‐Crevenna A. , Briones O. , Ezcurra E. , Rosas M. , Nunez H. , Barnard G. , Vazquez E.
Published: May 2006

Abstract. The Zapotitlán de las Salinas valley, central Mexico, harbours a high diversity of cacti. Pattern analysis indicated that the establishment of two columnar cacti, Neobuxbaumia tetetzo and Cephalocereus hoppenstedtii, and of three small globose cacti, Coryphantapallida, Mammillaria colina andM casoi, is aggregated and associated with perennial nurse shrubs. Some nurse species, Castela tortuosa, Caesalpinia melanadenia and Eupatorium spinosarum have a higher number of cacti beneath their canopies than would be expected by chance. A replacement pattern was found between the columnar cacti and their nurses, an aspect which was not found with the globose cacti. Following the assumption that protection against excessive radiation is the main factor determining the nurse effect, the azimuth orientation of the cacti with respect to their nurses was evaluated. Only Coryphanta pallida presented a non‐random distribution with a tendency towards the North and West. The difference in maximum temperature between the soil surface under the different nurse species and of open spaces, which is reached at midday, was 16 °C. No significant differences were found in beneath‐canopy temperatures for the three nurse species considered. Soil nitrogen levels were significantly lower beneath the different nurse plants than in open spaces. This result suggests that soil fertility is not an important factor in the nurse‐plant phenomenon in Zapotitlán.
BOOK REVIEWS
Authors: Cairns John , Atkinson Robert B.
Published: May 2006

Book reviewed in this issue.

Majer, J. D. (ed.) Animals in primary succession: The role of Fauna in Reclaimed Lands. 1989. xii + 547 pp. Cambridge University Press, Cambridge. ISBN 0–521–33400–4. Price: GBP 60.‐.
BOOK REVIEWS
Authors: Travis Joseph
Published: May 2006

Book reviewed in this issue.

Hairston Sr., N. G. 1989. Ecological Experiments: Purpose, Design, and Execution, xiii+370 pp. Cambridge University Press, Cambridge, UK. ISBN 0–521–34692–4 (pbk).
BOOK REVIEWS
Authors: Bock Jane H.
Published: May 2006

Book reviewed in this issue.

Simpson, G. M. Seed dormancy in grasses. 1990. 297 pp. Cambridge University Press, Cambridge. ISBN 0–521–37288–7. Price USD 49.95.
The effects of grazing on local colonisation and extinction during early succession
Authors: Gibson C. W. D. , Brown V. K.
Published: May 2006

Estimates 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

Analysis 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

The 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

Patches (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.
Components of error in predictions of species compositional change
Authors: McCune Bruce
Published: May 2006

Abstract. A method is given for measuring two components of error (rate and direction) in predictions of compositional change through time. Observed compositional change between two times can be represented as a vector between two points in multidimensional species space. The point at the tail of this vector is the species composition at one particular time. A vector of predicted compositional change will diverge from the vector of observed change to some degree. The error in the predicted rate of change is measured by the difference between the lengths of the two vectors. The error in the predicted direction of change is measured by the angle between the vectors. The cosine of this angle is a non‐standardized correlation coefficient (rn) between the predicted and observed species compositions. The quantity 1 ‐ rn2 measures the error in direction of the predicted dynamics without being influenced by the overall rate of change. These measures in Euclidean space have useful counterparts in city‐block space. The method is illustrated by comparing actual long‐term changes in Midwestern old‐growth forests with the changes predicted by a growth and yield model, TWIGS.
Complex effects of grazing treatment on an annual in a species‐poor grassland community
Authors: Silvertown Jonathan , Watt Trudy A. , Smith Bridget  , Treweek Joanna R.
Published: May 2006

Abstract. The effects of grazing upon the establishment, survival, growth and reproduction of a grassland annual Geranium dissectum growing in a sward dominated by grasses were examined in a replicated grazing experiment with sheep. Seeds were sown in both summer and autumn, and grazing was controlled to produce two levels of grazing in winter, two levels in spring, and two in summer, combined in a 2 x 2 x 2 factorial experimental design. Higher intensities of grazing in the period immediately before emergence benefitted plant establishment, but subsequent survival showed many interactions between factors, demonstrating that under certain conditions and at certain times grazing was detrimental. It is suggested that the frequency of G. dissectum in the grassland was low because the heavy grazing conditions that foster seedling emergence also jeopardize subsequent survival. This may also be why productive grassland communities in general contain few palatable dicots.
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.
Effect of nutrient level on competition intensity in the field for three coexisting grass species
Authors: DiTommaso A. , Aarssen L. W.
Published: May 2006

A field experiment encompassing both neighbour‐ and nutrient‐manipulations was conducted in a nutrient‐impoverished old‐field habitat to investigate how the intensity of plant competition was affected by soil nutrient level. Three perennial grasses were used as target species: Agropyron repens, Poa pratensis and Phleum pratense. Neighbour manipulations involved the removal (through herbicide application) of all neighbouring vegetation within a 20 cm or 40 cm radius around target plants. Target performance was measured under five levels of added nutrients (N‐P‐K) in both the neighbour‐removal plots and in non‐removal (control) plots. Both neighbour and nutrient manipulations had a highly significant effect on both biomass and tiller production but the interaction between these treatments was generally insignificant. Below‐ground/above‐ground biomass quotient was affected only by neighbour manipulations and was greatest in the control plots (with no neighbours removed) for all three species. The suppressive effect of neighbours was not markedly affected by nutrient level. However, yield suppression showed a significant decreasing trend with increasing nutrient level for biomass production in Agropyron and an increasing trend for tiller production in Phleum. For Poa, there was no trend in the intensity of competition across nutrient level. The results suggest that the general intensity of competition within this community neither increases nor decreases with increasing nutrient level. Rather, coexisting species appear to respond individually in terms of the intensity of competition that they experience. These results conflict with predictions from the triangular C‐S‐R model of plant strategies. However, they are consistent with a recently modified ‘habitat templet’ model for vegetation.
Change in pattern diversity during secondary succession in Estonian forests
Authors: Zobel K. , Zobel M. , Peet R. K.
Published: May 2006

Comparisons 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

Mires 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.
Germination and regeneration mechanisms in Mediterranean degenerate forests
Authors: Bacilieri R. , Bouchet M. A. , Bran D. , Grandjanny M. , Maistre M. , Perret P. , Romane F.
Published: May 2006

Abstract. Germination and developmental behaviour during juvenile stages are of importance in relation to succession mechanisms acting on plant communities. This is particularly so in the Mediterranean region, where the climatic summer drought causes stress. We investigated and compared germination and development of four tree species in two parts of the French Mediterranean region where the original dominant tree species (Quercus pubescens) has been largely replaced by Quercus ilex in the southern part, and Castanea sativa in the northern part. Observed differences in germination rates and developmental behaviour, especially shootroot ratio and the role of water supply, suggest that other species may eventually replace the current dominant species.
Plant distribution patterns during early succession on an artificial protosoil
Authors: Schmidt Wolfgang , Briibach Martina
Published: May 2006

Abstract. Plant succession has been studied since 1977 in permanent plots on a calcareous protosoil in the northern outskirts of Göttingen (Central Germany). At the beginning the substrate was extremely poor in organic carbon and nitrogen. On 128 plots of 100 m2, the temporal and spatial distribution of the most conspicuous plant species showed remarkable changes and correlations to soil site factors. While presenting data on Melilotus alba, Medicago lupulina, Agropyron repens, Arrhenatherum elatius, Dactylis glomerata, and Picris hieracioides the mechanisms of successional changes on nutrient‐poor soils are discussed. It is demonstrated that a high cover of legumes favours the accumulation of soil nitrogen. Grassland species were more abundant in areas with low humus content whereas ruderal plant species preferred those parts of the area which contained more humus in the substrate. Life‐form, colonization and population strategies play an important role in the described successional processes, in addition to resource competition. Finally, some methodological conclusions for permanent plot studies are presented.
Changes in the chemical composition of mire‐water samples during storage
Authors: Proctor M. C. F.
Published: May 2006

Abstract. Solutes in mire‐water samples vary greatly in their tendency to change on storage. In repeated analyses of samples from Malham Tarn, Yorkshire, U.K., concentrations of Na+ and Cl‐ proved very stable on storage, and Mg2+ hardly less so, whether the samples had been filtered or not. K+ concentrations declined slowly in filtered samples kept at room temperature, falling after two years to about two‐thirds of the original value. In unfiltered samples, K+ concentrations rose on average by about 25 % over a period of two months. At low concentrations Ca2+ changed little on storage, but above 40 ‐ 50 mg/l equilibration of CO2 with the air led to precipitation of carbonate and loss of dissolved Ca2+. Fe concentrations were rather stable in ombrogenous bog waters, but in fen waters showed rapid decreases on storage. SO42‐ showed little change in most samples, but there were a few large increases in unfiltered samples probably due to oxidation of sulphide. Unfiltered fen water samples generally developed high concentrations of NO3‐ (rarely NH4+) on storage; by contrast acid bog waters typically developed high NH4+ concentrations, but did not nitrify. Bog waters showed a small rise in pH and some reduction in colour (dissolved humic substances). Fen waters changed erratically in pH, depending on the balance of production and loss of CO2 in the sample. Some recommendations are given for storage and analysis of samples.
Effects of herbivory and herb interference on oak establishment in a semi‐arid temperate savanna
Authors: McPherson Guy R.
Published: May 2006

Abstract. Early establishment of Quercus emoryi seedlings in the grassland phase of a semi‐arid temperate savanna was evaluated in southern Arizona, USA. Controlled‐environment experiments indicated that Quercus seedlings are tolerant of frequent clipping, but undipped seedlings produce more biomass than clipped seedlings. Seedlings were much less tolerant of clipping or defoliation in the field than in the growth chamber, and most seedlings died after being clipped or defoliated by herbivores. Invertebrate herbivory, which is rarely mentioned as an important factor limiting seedling establishment, was the leading cause of seedling mortality in the field study. Below‐ground interference from herbs had a greater impact on seedling survival and growth than above‐ground interference.
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.‐.
Snowbed vegetation of far northeastern Asia
Authors: Razzhivin V. Yu.
Published: May 2006

Abstract. Two main types of snowbed habitat with their typical vegetation in far NE Asia are described. In extreme snowbeds, snow depth is ≥ 5 m; the vegetation is sparse and characterized by Salix polaris and arctic and arctic‐alpine taxa adapted to a very short growing season. In moderately snowrich habitats, with a snow depth of 1.5 — 5 m, the environment is more favourable for plant growth as compared to both extreme snow‐rich and mesic habitats, because of snow protection in winter, little permafrost, high organic matter accumulation, and no major reduction of the growing season. Within each snowbed habitat there are two series of community types for lime‐rich and lime‐poor habitats. Along with a large number of pH‐amphitolerant species including the dominants Salix polaris, Cassiope tetragona, Artemisia tilesii which occur in both habitat types, acidic sites usually also have stenoacidophytes (Carex nesophila, Loiseleuria procumbens), and hemiacidophytes (Salix chamissonis, Artemisia arctica). Differential taxa of circumneutral and basic soils are the stenobasiphytes Salix rotundifolia and Dendranthema integrifolium and the hemibasiphytes Salix reticulata and Carex scirpoidea. Ten Chukotka snowbed associations are provisionally described and a diagnostic table is presented according to the Braun‐Blanquet approach. The syntaxonomy and evolution of Beringian snowbed vegetation are discussed.
Effects of fire on abundance of Eragrostis intermedia in a semi‐arid grassland in southeastern Arizona
Authors: Bock Carl E. , Bock Jane H. , Grant Michael C. , Seastedt Timothy R.
Published: May 2006

Abstract. Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi‐arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Arizona, after a period of declining precipitation, but only in areas that had not burned in the previous three years. Lovegrass abundance subsequently increased on both undisturbed and burned sites, but remained substantially higher on the burned area. Long‐term abundance of plains lovegrass may depend on episodic fire, particularly during periods of reduced precipitation.
Coexistence of Banksia species in southwestern Australia: the role of regional and local processes
Authors: Richardson David M. , Cowling Richard M. , Lamont Byron B. , van Hensbergen H.J.
Published: May 2006

Abstract. 60 of the 75 Banksia species are confined to southwestern Australia where five or six species often coexist. We explored the role of regional species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in actual assemblages at 40 sites throughout southwestern Australia. Diversity indices at each site were compared with those from null communities assembled on the basis of the abundance and sociability of taxa in regional species pools. The relationship between local and regional species richness suggests that processes at the scale of 100‐m2 quadrats limit local richness and therefore coexistence. However, there was no consistent evidence that taxa are differentiated by growth form or regeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat specialization is an important factor contributing to lower local richness than would be predicted from niche differentiation of taxa in regional pools. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits suggested by simple niche theories. Variability in the fire regime also provides a mechanism for maintaining local species richness because different fires favour recruitment of different taxa.
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.
Patterns of diversity in the strata of boreal montane forest in British Columbia
Authors: Rey Benayas Jose M.
Published: May 2006

Abstract. Patterns of diversity were analyzed in a boreal coniferous forest and its strata (tree, shrub, herb and bryophyte layers): number of species per community — α‐diversity, total species richness — γ‐diversity, mean similarity — β‐diversity, and mosaic diversity, a measure of complexity. These four measures of diversity consistently decreased from lower to upper vegetation layers. To study the effect of juveniles of larger life forms on diversity of lower layers, they were removed from the data and the measures of diversity reanalyzed. Number of species per community and mosaic diversity decreased substantially, but β‐diversity did not change. So, the effect of juveniles on γ‐diversity is due to the greater number of species per community. Multiple regression models revealed that the relationships between α‐diversity and the environmental variables were the same for the whole forest and for the herb layer. Elevation and soil pH were the major variables explaining α‐diversity in the whole community. Climate was the only environmental gradient related to species richness in all individual strata. Tree and herb richness values were negatively related to soil drainage and acidity, respectively. Species richness of the plant community was affected by environmental variability mostly through the herb layer. Various explanations of the observed diversity patterns included: environmental constraints, resource competition, generation time, and colonization processes.