bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence on ecotone concepts from switch, environmental and anthropogenic ecotones
Authors: Lloyd Kelvin M. , McQueen Amelia A.M. , Lee Beatrice J. , Wilson Robert C.B. , Walker Susan , Wilson J. Bastow
Published: May 2006

Abstract. Four contrasting ecotones were sampled to address three questions: (1) Are there ‘ecotonal’ species, (2) Do ecotones possess higher (or lower) species richness than the adjacent communities? and (3) Are exotic species more likely to occur in ecotones? One ecotone was edaphic, one was apparently caused by a positive‐feedback switch, one was environmental/anthropogenic and one was entirely anthropogenic. The exact position of each ecotone was established from the spatial change in ordination scores. Ecotonal species, in the sense of species mainly restricted to the ecotone at the site, were present in all four ecotones. All but one of the ecotonal species were native. The switch ecotone and the purely anthropogenic ecotone also contained native species that were significantly more frequent in the ecotone than in either adjacent community. Species richness was intermediate between that of the two adjacent communities in three of the ecotones. In the environmental/anthropogenic ecotone, species richness was higher than in adjacent communities, but not significantly so. There were appreciable numbers of exotic species in the two ecotones with anthropogenic influence, one of which had a proportion of exotic species intermediate between the two adjacent communities. Contrary to theory, the proportion of exotic species in the second ecotone was significantly lower than in either adjacent community. We conclude that all three features we examined depend on the particular ecological conditions and the ecology of the species present; they are not intrinsic properties of ecotones.
Changes in grassland canopy structure across a precipitation gradient
Authors: Lane Diana R. , Coffin Debra P. , Lauenroth William K.
Published: May 2006

Abstract. In temperate grasslands, the relative importance of above‐ground competition for light compared to below‐ground competition for water and nutrients is hypothesized to increase with increasing precipitation. Thus, competition for light is likely to exert an increasing influence on canopy structure and species composition as precipitation increases. We quantified canopy structure, light availability and changes in species composition at seven sites across the central grassland region of the United States to determine how these properties change across a precipitation gradient. Across the region, there was a disproportionate increase in leaf area and canopy height with increasing precipitation, indicating that plants become taller and leafier across the gradient. Leaf area index increased by a factor of 12 across the gradient while above‐ground net primary productivity increased by a factor of only 5.5. As precipitation increased, there was decreased light availability at the soil surface, increased seasonal variability in light transmission, increased biomass and leaf area at higher canopy layers and an increased proportion of tallstatured species. These observed changes in canopy structure support the prediction that competition for light increases in importance with increasing precipitation.
Simulation of observed types of dynamics of plants and plant communities
Authors: Gassmann Fritz , Klötzli Frank , Walther Gian‐Reto
Published: May 2006

Abstract. Observations of different plant communities over several decades reveal five types of dynamics: constant, fluctuating, growing, decaying, intermittent. With a modelling approach based on interacting particle systems (cellular automata), these distinct types of dynamics can be simulated. In addition, the proposed model shows a strong tendency towards the formation of patches when started with random initial conditions. Further, it gives evidence for dominance resulting from the interplay of plant characteristics and patterns rather than being attributable to certain plant types alone, so making questionable the existence of key species and the usefulness of a constant mapping key over extended periods. The presented model unifies the fundamental dichotomy in vegetation dynamics between determinism (predictability) and disorder (chance effects) by showing the outcome of both classical theories as special cases.
Persistence of a rare aquatic species along gradients of disturbance and sediment richness
Authors: Greulich Sabine , Bornette Gudrun , Amoros Claude
Published: May 2006

Abstract. This study examines the capacity of establishment of a rare aquatic macrophyte, Luronium natans, within plant communities and habitat types in which it does not occur spontaneously. The species, generally limited to disturbed or nutrient‐poor habitats, was transplanted into a series of sites situated along natural gradients of disturbance (flush‐floods and intermittent sediment exposure) and sediment nutrient‐richness. The transplanted colonies were given a competition‐free establishment period. Colony dynamics of Luronium as well as size structure of the recolonizing macrophyte communities were monitored over three growing seasons. At the end of this period, transplanted colonies still persisted in five out of 12 transplantation sites. Apparently successful integration into the community occurred at both ends of the nutrient gradient, in periodically disturbed habitats. At intermediate to high nutrient richness Luronium maintained one of the highest cover values within the recolonizing community.

The study supports previous presumptions that long‐term persistence of Luronium depends on processes limiting community biomass through occurrence of disturbance. But it also reveals the existence of suitable, yet not occupied habitats in which the species can persist as successfully as species from the local species pool. This finding modulates the presumption that Luronium's rarity is mainly caused by a weak competitive ability in the established phase. It thus rises questions about the species’ performance at other stages of its life cycle and on its dispersability.
Spatial micro‐patterns in the steppe of Tierra del Fuego induced by sheep grazing
Authors: Posse Gabriela , Anchorena Juan , Collantes Marta B.
Published: May 2006

Abstract. In the Festuca gracillima tussock steppe of northern Tierra del Fuego there is a physiognomic pattern at the community scale composed of a matrix of tussocks, scrub patches of Chiliotrichum diffusum and lawn patches. In this paper we compared floristic composition, soils, microclimate and sheep use of these three types. Species composition greatly differed among physiognomic types. Lawn patches showed the highest diversity and maximum cover of exotics, grazing escape growth forms and species of high‐fertility habitats. Soil profiles of tussock steppe and lawn were similar but the A‐horizon of the latter contained more clay and cations. Radiation and temperature during daylight at the soil surface in summer were highest in the lawn patches. Soil impedance, a good indicator of trampling, was highest on the lawn patches. According to dung pellet density, lawn patches received much heavier use than the tussock matrix. Our results suggest that lawn patches supported the highest grazing impact and undergo a eutrophication process favoured by high mineral inputs, high mineralization rates in the soil during the warm season and restricted leaching through the profile. They also support the idea that a feedback mechanism between vegetation heterogeneity and sheep grazing behaviour maintains the patches. Although grazing behaviour suggests that the lawn patches favour animal production, their expansion would result in a system less protected against the impact of water deficits and temperature variations and more vulnerable to erosion and to the loss of important species.
Desert grassland dynamics estimated from carbon isotopes in grass phytoliths and soil organic matter
Authors: McClaran Mitchel P. , Umlauf Marcelle
Published: May 2006

Abstract. We document the potential for using carbon isotopes in both soil organic matter (SOM) and grass phytoliths in soil to increase the temporal and taxonomic resolutions of long term vegetation dynamics. Carbon isotope values from both SOM and phytoliths are expected to describe both the age of material through 14C dating, and the photosynthetic pathway of the source plant material through ratios of 12C/13C. Taxonomic resolution is increased because the phytoliths examined are specific to grasses, whereas the SOM reflects the contribution of all the vegetation. Temporal resolution is increased because phytoliths are less mobile in the soil profile than SOM, and can therefore provide older dates from the same soil depth. Our results, from a desert grassland site in southwestern North America, largely confirm these expectations, and show that C4 species have dominated the grass composition for the last 8000 yr, C3 non‐grass vegetation increased about 100–350 yrBP, and no significant C3 grass or non‐grass vegetation existed between 350–2000 yr BP.
Structural and functional changes in Nothofagus pumilio forests along an altitudinal gradient in Tierra del Fuego, Argentina
Authors: Barrera Marcelo D. , Frangi Jorge L. , Richter Laura L. , Perdomo Marcelo H. , Pinedo Luis B.
Published: May 2006

Abstract. Structural (density, height, basal area, above‐ground tree biomass, leaf area index) and functional (leaf phenology, growth rate, fine litter fall, leaf decomposition) traits were quantified in four mature forests of Nothofagus pumilio (lenga) along an altitudinal sequence in Tierra del Fuego, Argentina. Three erect forest stands at 220, 440 and 540m and a krummholz stand at 640 m a.s.l. were selected. Along the altitudinal sequence, stem density increased while DBH, height, biomass, leaf‐size and growth period, mean growth rate and decay rate decreased. Dead stems increased and basal area and fine‐litter fall decreased with an increase in elevation among erect forests, but these trends inverted at krummholz. We suggest that krummholz is not only a morphological response to the adverse climate but is also a life form with functional advantages.
Ocular estimates of understory vegetation structure in a closed Picea glauca/Betula papyrifera forest
Authors: van Hees  , Willem W.S. , Mead Bert R.
Published: May 2006

Abstract. Horizontal/vertical profiling is a method used to assess vegetation space occupancy. This study investigated consistency and repeatability of measurements made on plots designed to describe forest understory vegetation structure. 20 circular, 100‐m2 plots were measured by six independent observers, three times during the summer of 1997. The plots, located in south‐central Alaska, were established in a closed Picea glauca (white spruce)/Betula papyrifera (paper birch) forest. Consistency and repeatability of measurements were evaluated by examining components of variance. Response variables were absolute and relative canopy cover. Results indicate that observers were not consistent relative to each other estimating vegetative cover from one plot to the next and from one measurement period to the next, making measurements unrepeatable.
Diversity and pH changes after 50 years on the boreal mire Skattlösbergs Stormosse, Central Sweden
Authors: Gunnarsson Urban , Rydin Håkan , Sjörs Hugo
Published: May 2006

Abstract. The Skattlösbergs Stormosse mire was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providing a unique opportunity to quantify long‐term mire dynamics.

The results show decreased pH in the richer (high‐pH) parts of the mire, but little or no change in the poor fen and ombrotrophic parts. 14 species had disappeared while two new species were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in 10m x 10m plots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 73% of other bryophyte species and 38% of vascular plant species had decreased by more than 20% in plot frequency.

There was a strong relationship between number of species and pH‐value. The mean and standard deviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in more polluted areas.
BOOK REVIEWS
Authors: Miyanishi Kiyoko
Published: May 2006

Ramakrishnan, P.S., Saxena, K.G. & Chandrashekara, U.M. (eds.) 1998. Conserving the sacred for biodiversity management. xxviii + 480 pp. Science Publishers Inc., Enfield, NH. ISBN 1–57808–036–3. Price: USD 79.‐.
Vegetation, environmental characteristics and ideas on the maintenance of alvars on the Bruce Peninsula, Canada
Authors: Schaefer Claudia A. , Larson Douglas W.
Published: May 2006

Abstract.Despite international recognition that alvar habitats are important reservoirs of biodiversity, they remain little studied in North America. In this paper, the results are reported on an investigation of alvars in the central portion of their known distribution on this continent. 210 plots were distributed among seven sites and were quantitatively sampled for vascular plants, lichens, bryophytes and a suite of environmental variables. Detrended and Canonical Correspondence Analyses and other methods were used to investigate differences among alvars, within alvars and between alvars and adjacent forested habitats. The plant communities and environmental conditions were highly similar among sites in the study region, yet very different from surrounding habitats. There were abrupt changes in vegetation and environmental conditions from alvar to forest, without the presence of transition zones in the vegetation or environmental gradients as the forest was approached. The environmental factors associated with the change from alvar to forest and with variation within alvar habitat were examined. Some alvars in the study were found to contain stunted, slow‐growing trees reaching ages of 524 yr. These same sites appear to have remained unburned for several centuries, while other sites likely burned 90 yr ago. The plant communities were very similar between the alvars that lacked a major, biomass‐removing disturbance in centuries and alvars that had experienced catastrophic fire relatively recently. Maintenance of the plant communities and open nature of alvars appears site‐specific rather than habitat specific.
Long‐term vegetation dynamics mediated by herbivores, weather and fire in a Juniperus‐Quercus savanna
Authors: Fuhlendorf Samuel D. , Smeins Fred E.
Published: May 2006

Abstract. Long‐term (45‐yr) basal area dynamics of dominant graminoid species were analyzed across three grazing intensity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Research Station on the Edwards Plateau, Texas. Grazing intensity was identified as the primary influence on long‐term variations in species composition. Periodic weather events, including a severe drought (1951–1956), had little direct influence on composition dynamics. However, the drought interacted with grazing intensity in the heavily grazed treatment to exacerbate directional changes caused by grazing intensity.

Species response to grazing was individualistic and noisy. Three response groups were identified. Taller, more productive mid‐grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic to weather patterns. Graminoid diversity increased with the removal or reduction of grazing intensity. The moderately and ungrazed treatments appeared most resistant to short‐term weather fluctuations, while the heavily grazed treatment demonstrated significant resilience when grazing intensity was reduced after over 110 yr of overgrazing.

Identification of a ‘climax’ state is difficult. Significant directional change, which took nearly 20 yr, appears to continue in the ungrazed treatment after 45 yr of succession. The observed, relatively linear patterns of perennial grass composition within the herbaceous patches of this savanna were generally explained by traditional Clementsian succession. However, when dynamics of the herbaceous community are combined with the woody component of this savanna, the frequency and intensity of fire becomes more important. Across the landscape, successional changes follow several pathways. When vegetation change is influenced by several factors, a multi‐scale model is necessary to demonstrate interactions and feedbacks and accurately describe successional patterns. Absence of fires, with or without grazing, leads ultimately to a Juniperus/Quercus woodland with grazing intensity primarily influencing the fuel load and hence fire intensity.
Nutrient supply in undrained and drained Calthion meadows
Authors: van Duren I.C. , Pegtel D.M. , Aerts B.A. , Inberg J.A.
Published: May 2006

Abstract. Plant species‐rich Calthion meadows on mesotrophic fen peat soil extensively cut for hay are among the endangered semi‐natural vegetation types in northwestern Europe. They are often badly affected by lowering the groundwater table (drainage) and fertilization.

In a comparative study of an undrained site with a Calthion meadow and an adjacent drained site, availability of N, P and K was biologically assessed under field conditions (for two years) as well as in a greenhouse (for 18 weeks) by measuring shoot responsiveness. Also, experimental wetting of intact turf samples taken from both sites was applied in order to study the interaction between nutrient supply and anaerobic soil conditions. It was concluded that the above‐ground phytomass yield in the undrained site was restricted by a major shortage of N‐supply and a moderate shortage of K‐supply by the fen peat soil. The above‐ground phytomass yield of the drained site was only reduced by a strongly limited supply of K by the soil. The extent of K‐deficiency was larger for the drained site. No P‐deficiency was observed in any of the drained or undrained sites. Rewetting turf samples, taken from the drained site, did not change above‐ground phytomass yields, suggesting that nutrient supplies were not affected by rewetting. Leaching has likely resulted in a strong reduction of K‐supply in the drained site. It is assumed that a shortage in K‐supply from the peat soil may have become an important environmental constraint for characteristic plant species of Calthion meadows. This may hamper the development of this meadow type on drained peat soils after rewetting by groundwater discharge.
A comparative approach to examine competitive response of 48 wetland plant species
Authors: Keddy Paul , Fraser Lauchlan H. , Wisheu Irene C.
Published: May 2006

Abstract. Competitive ability can be separated into competitive effect (ability to suppress neighbours) and competitive response (ability to tolerate suppressive effect from neighbours), but little is known about the competitive response of plants. A screening trial was conducted in outdoor plant pots where competitive response was measured for 48 wetland species during four months grown with seven established sward species: Acorus calamus, Carex crinita, Eleocharis smallii, Lythrum salicaria, Penthorum sedoides, Scirpus acutus and Typha angustifolia. Competitive response was calculated as 100 (x1–x2)/x1, where x1 is the weight of the target plant grown alone and x2 the weight of the target plant grown in the swards. Despite significant differences in biomass and survivorship of the target plants between the sward species, the correspondence, W, of the rank order of the competitive response of target plants grown in the seven sward species was 0.70 (P < 0.001). The competitive response values were not significantly correlated with independent measures of competitive effect, relative growth rate or functional classification. Published competitive effect values, however, were significantly positively correlated with RGR. The results suggest a different approach towards the study of competitive response, with a conceptual model including three different response types: (1) escape; (2) foraging; and (3) persistence.
Pattern and process in above‐ground and below‐ground components of grassland ecosystems
Authors: Titlyanova A.A. , Romanova I.P. , Kosykh N.P. , Mironycheva‐Tokareva N.P.
Published: May 2006

Abstract. This paper describes patterns of below‐ground components in grassland ecosystems. It provides estimates of the contribution of below‐ground organs to the total phytomass of the community and of different species to the below‐ground phytomass; it describes the distribution of above‐ and below‐ ground organs of different species and the spatial and temporal correlation between above‐ground and below‐ground phyto‐mass – both total standing crop and net primary production. 10 Siberian grasslands (meadows and steppes) were investigated during 15 yr. Ca. 70 % of the living phytomass is located in the soil and no less than 70 % of the net primary production is allocated in below‐ground organs. Phytomass distribution in the soil layer is more homogeneous than above‐ground. For some species the spatial distribution within 1‐m2 plots of the green and below‐ground phytomass is similar, for others it is quantitatively or qualitatively different. According to the dominance‐diversity curve, the above‐ground size hierarchy is much stronger than the below‐ground one. The active growth of above‐ and below‐ground organs of a species may occur at different times of the season and it varies from year to year. Allocation of organic substances to rhizomes and roots occurs simultaneously and with proportional intensity.
Deriving functional types for rain‐forest trees
Authors: Gitay H. , Noble I.R. , Connell J.H.
Published: May 2006

Abstract. A common goal in functional type research is to find a useful classification that defines the dynamic behaviour of groups of species in relation to environmental variation. Long‐term data sets on the dynamics of forests are difficult to obtain; thus, it would be useful if more readily available data, such as that on morphological and life history characters, could be used to derive groups that reflect the dynamics of the species. We used a 30‐yr data set on the dynamics of subtropical rainforests in Australia to derive classification based on the dynamics of the species and compared this classification with groups of species derived by other approaches. Functional types were derived for ca. 80 tree species using subjective, deductive and data‐driven approaches. The subjective classification used was a pioneer to late successional grouping. The deductive classification was an extension of the vital attribute approach.

Two data sets were used for the data‐based classifications, one based on morphological, life history and phenological characters (morphological data) readily available from taxonomic descriptions and another based on long‐term observations on the establishment, growth and death of all individuals on permanent plots (dynamic data).

SAHN (Sequential, Agglomerative, Hierarchical and Nested) clustering techniques were used for the numerical classifications. There was some similarity between the classification based on dynamic characters and the subjective and deductive classifications. The classification based on the readily available morphological characters showed less similarity with other classifications. However, the morphological data could be used to predict group membership in the dynamic classification using discriminant analysis with 87% accuracy. Thus, it appears that surrogate classifications might be found to describe the dynamics of the subtropical rainforest site. Further exploration and testing at other sites is required, especially to link the functional classification to specific perturbations.
A rule‐based model for the functional analysis of vegetation change in Australasian grasslands
Authors: Campbell Bruce D. , Stafford Smith D. Mark , Ash Andrew J.
Published: May 2006

Abstract. Grasslands encompass a broad array of vegetation and climatic zones. We describe the first developments towards a rule‐based functional model for predicting vegetation structure in Australian and New Zealand pastures and rangelands. The approach aims to predict the combined effects of climate and disturbance by humans and grazing livestock, and to provide a level of resolution needed for predicting changes in pastures and rangelands. We enlisted expert knowledge to develop: (1) a minimum set of critical traits; (2) rules relating site variables to favoured plant attributes; (3) rules relating attributes to plant functional traits, and (4) rules relating plant functional types to likely plant communities. We tested the resulting model by deriving some simple predictions of plant communities of some existing pasture and rangeland sites in Australia and New Zealand, with differing climatic and human disturbance inputs.

The results indicate that this first model is able to predict plant communities with varying success rates, and with the best results in cases where there are extreme climates or high management inputs. Key sensitivities in the model where further research is required include: (1) the urgent need for more explicit understanding of the key plant functional attributes favoured by differing climates and disturbance regimes, (2) the functional relationships between these plant functional attributes and recognisable plant functional types in vegetation, and (3) the assembly rules for the coexistence of these different plant functional types in major plant communities. The same understanding is required for subsequent process‐based modelling development.
Scaling effects of grazing in a semi‐arid grassland
Authors: Fuhlendorf Samuel D. , Smeins Fred E.
Published: May 2006

Abstract. Previous studies have demonstrated relationships between spatial scale and spatial pattern and developed general hypotheses of scaling effects. Few studies, however, have examined the interactive relationship between scale and pattern‐driving processes such as grazing. The goal of this study is to evaluate scale‐dependent patterns across three spatial scales for three grazing intensities over 45 yr and to identify some mechanisms that may be associated with scale related differences. Correlation analysis and analysis of the coefficients of variation indicate that the relationships between units are dependent upon spatial scale and treatment. Across all grazing treatments, the relationship between units of the same scale becomes stronger as the spatial scale is increased. However, the rate of increase in the correlation coefficient is different for each treatment. The coefficient of variation responded inversely across scales with the greatest variation between small‐scale units and little difference between the intermediate‐ and large scales. In addition to different relationships between units at each scale, differences in heterogeneity within treatments over time is illustrated by the relationship between small‐scale units within each treatment and their associated larger scale units. The strongest relationship occurred in the heavily grazed treatments where correlation coefficients of small‐scale units with intermediate‐ and large‐scale units were ca. 0.60, indicating similar dynamics across scales. For the moderately grazed and ungrazed treatments this relationship varied from 0.40 to 0.47.

Results from this study suggest that grazing alters scaling effects. Variability between small‐scale units was greatest in the ungrazed treatment which had greater heterogeneity and less predictability than grazed treatments because of the influence of grazing on plant morphology, demography and composition. At the intermediate scale, relationships between units were fairly similar with the least variation occurring in the moderately grazed treatment. Alternatively, variation between large‐scale units was greatest in the moderately grazed treatment because of the relationship between rest cycles, weather patterns, and patch grazing. Therefore, grazing can have a positive, a negative, or no influence on heterogeneity between units depending upon the scale of observation. Evaluation of long‐term dynamics across these treatments at the same small spatial scale results in different variances within each treatment which may violate assumptions of some statistical and experimental designs. Therefore, evaluations of temporal dynamics should consider scale relative to the relationship between plant size, density and longevity (relative scale).
Treefall gap characteristics and regeneration in the laurel forest of Tenerife
Authors: Arévalo José Ramón , Fernández‐Palacios José María
Published: May 2006

Abstract. We conducted a study in the laurel forest of Tenerife (Canary Islands, Spain) to describe the characteristics of natural gaps and to assess the role of treefall gaps in forest dynamics. Very little is left of the natural laurel forest with i.a. Laurus azorica, Ilex canariensis and Prunus lusitanica. We looked for treefall gaps in 80 randomly located 2500 m2 plots. These plots represented ca. 1% of the remaining and protected laurel forest of Tenerife. We recorded the characteristics of the species causing the gaps, gap architecture and gap age in all observed gaps larger than 10 m2. We inventoried the regeneration in each gap and in a neighbouring control plot with the same topography. Large gaps (>75 m2) were not common in the laurel forest. The absence of large gaps could be due to the physiognomy of the vegetation, the mild weather or the rarity of disturbances. Instead of forming gaps, many trees decompose in place and branches from neighbouring trees and suckers from the decomposed trees occupy the free space. Also, the high rate of asexual regeneration could contribute to the fast closing of the gap.

The number of gaps created by Prunus lusitanica was higher than expected (based on canopy composition) while Ilex canariensis and Laurus azorica created fewer gaps. In this evergreen forest, differences between gap and non‐gap conditions are not as distinct as in other forest types. Only 0.4% of the canopy is in the gap phase (0.6% including gaps smaller than 10m2). No differences were found in patterns of regeneration between gap and non‐gap phases in the forest. Gaps do not explain the persistence of pioneer species in the laurel forest.
Composition and seasonal flux of the soil seed bank of species‐rich Themeda triandra grasslands in relation to burning history
Authors: Morgan John W.
Published: May 2006

Abstract. Most species‐rich grasslands dominated by Themeda triandra in southeastern Australia have been ungrazed and frequently burnt for decades. The seedling emergence technique was used to determine the size and taxonomic composition of the soil seed bank of five grasslands that had different fire histories (i.e. burnt at 1 yr, 3 yr and > 10 yr intervals) and this was compared to the standing vegetation at each site. A nested sampling design (subplot, plot, site) was used to determine the effect of spatial scale on the patterns observed in both the vegetation and the seed bank. Temporal variation in the seed bank was assessed by repeated soil sampling over a two year period. 61 native and 30 exotic species were recorded in the vegetation. Richness varied more between sites than within sites. Sites were therefore internally homogeneous for species richness. However, no correlation between burning frequency and richness was found. DCA ordination separated the sites into distinct groups, but sites with similar fire history did not necessarily group closely. 60 taxa germinated from the soil seed bank, comprising 32 native and 28 exotic species; 11 species, mostly therophytes, were restricted to the seed bank. The richness of the seed bank was significantly lower than the vegetation at all spatial scales. No correlation between seed bank richness and fire history was found. The seed bank of species‐rich grasslands is dominated by a limited number of widespread, highly clumped, annual, native and exotic monocots. Most native hemicryptophytes, and perennials in general, were represented in the soil by a transient seed bank. Only 12 % of study species, all therophytes, were considered to form large, persistent seed banks, the size of which was greater in unburnt grasslands at all times of the year. The distinct floristic patterns observed in the vegetation are less clearly represented in the seed bank. The seed bank represents a floristically distinct (and less variable) component of the vegetation when compared to the standing flora. The size of the long‐term soil seed bank suggests that it has little functional importance for many native species and probably contributes little to seedling regeneration processes following disturbance. Altering established fire regimes is likely to only change the composition and small‐scale richness of the existing site vegetation and will not re‐integrate species previously lost from the vegetation due to past management. It is suggested that the maintenance of vegetation remnants and processes that encompass a range of long‐term burning histories will be necessary if the flora is to be conserved in situ. Restoration of degraded grasslands cannot rely on the soil seed bank but rather, will be dependent on the reintroduction of propagules.
Environmental relationships of floristic variation in the alpine vegetation of southeast Australia
Authors: Kirkpatrick J.B. , Bridle K.L.
Published: May 2006

Abstract. Australian alpine vegetation is confined to the southeast of the continent and the island of Tasmania. It exhibits strong geographic patterns of floristic variation. These patterns have been attributed to variation in edaphic conditions resulting from geographic variation in substrate, climate and glacial history. This edaphic hypothesis is tested using floristic and environmental data from 166 quadrats distributed throughout the floristic and geographic range of Australian alpine vegetation. Environmental vector fitting in three‐dimensional ordination space, the number of significant environmental differences between all pairs of 17 floristic groups and overall statistical analyses of the environmental differences between communities suggest a primacy of climatic variables over edaphic variables in explaining the broad patterns of floristic variation. Continentality, summer warmth, summer rainfall and winter cold all provide a better statistical explanation of floristic variation than the most explanatory of the edaphic variables, extractable P. The environmental variables that best discriminate the groups at each dichotomy of the divisive classification of the floristic data are largely climatic at the upper two levels, with edaphic, topographic and biotic variables being generally more important than climatic variables at the lower levels. Many of the edaphic variables that were most important in discriminating dichotomous groups were relatively insignificant in the broader analyses, suggesting that it is important to partition large data sets for environment/floristic analyses. The results of such partitioning show that the environmental factors most important in influencing floristic variation in alpine vegetation in Australia vary by location and geographic scale.
Flowering regimes of terrestrial orchids: unpredictability or regularity?
Authors: Kindlmann Pavel , Balounová Zuzana
Published: May 2006

Abstract. Empirical data on many species of terrestrial orchids suggest that their flowering pattern over the years is extremely irregular and unpredictable. A long search for the reason has hitherto proved inconclusive. Irregular flowering was attributed to costs associated with sexual reproduction, to herbivory, or to the chaotic behaviour of the system represented by difference equations describing growth of the vegetative and reproductive organs.

Data on the seasonal growth of leaves and inflorescence of Dactylorhiza majalis are used here to test alternative explanations of the irregular flowering patterns of orchids. These patterns are found to be extremely rare in our data set. Neither costs of reproduction nor grazing seem to explain the rare events of a transition from flowering one year to sterility or absence the next year. These transitions are almost exclusively characteristic of one of four experimental sites, the only unmown site, where the mean leaf area and incidence of flowering in the whole population is also in decline. It is therefore hypothesized that irregular flowering regimes may be characteristic of sites with temporarily or steadily declining populations and that they are usually not present in prosperous ones ‐ at least for D. majalis.
Cover versus biomass as an estimate of species abundance: does it make a difference to the conclusions?
Authors: Chiarucci A. , Wilson J. Bastow , Anderson Barbara J , De Dominicis V.
Published: May 2006

Abstract. Different measures of species abundance, particularly cover and biomass, are often used as if they were interchangeable. We ask to what extent the measure of abundance affects conclusions reached in plant community ecology. The test data comprised 35 plots, each 1 m × 1 m, on serpentine vegetation in Tuscany, Italy, in which both cover and biomass were measured. The measure of abundance used made rather little difference when plots were examined in terms of the rank abundance of the species present, and little difference to the results of a DCA‐ordination. Likewise, species showed similar variation across plots in cover as in biomass. In calculating species diversity, agreement between measures of abundance was lower, but still good. For evenness, the correlation between cover and biomass results was lower again, though more so with some indices than with others. For the shape of the RAD (Relative Abundance Distribution), cover and biomass gave quite different results, the Zipf‐Mandelbrot RAD model most commonly giving the best fit to the cover data, but the General lognormal model to the biomass data. These tendencies can be related to the intrinsic characteristics of cover and biomass as measures of abundance. The parameters of the model fits also differed between abundance measures. We conclude that the importance of using biomass as the measure of abundance depends on the ecological feature being examined. The difference between the two measures may be greater in other vegetation; very little information is available. In the current state of knowledge it is dangerous to use another measure as a surrogate for biomass.
Nutrient limitation and vegetation changes in a coastal dune slack
Authors: Lammerts E.J. , Pegtel D.M. , Grootjans A.P. , van der Veen A.
Published: May 2006

Abstract. Basiphilous pioneer species are among the most endangered plant species in The Netherlands. They find most of their refuges in young coastal dune slacks, especially on the Wadden Sea islands. For the purpose of nature management it is important to know which processes control the presence of basiphilous pioneer communities, and to learn about the nature of slacks harbouring the concerning successional sequences.

In a large dune slack on the Island of Terschelling, we assessed soil nutrient status and tested for nutrient limitation in four chronosequential stages: 2, 6, 37 and ca. 80 yr of age. Stage 2 harboured a basiphilous pioneer vegetation; in the stages 3 and 4 a dense vegetation of dwarf shrubs and grasses occurred. Soil organic matter and nutrient concentrations in each stage were measured in 1991. In 1992 and 1993 fertilizers were applied to all stages to detect nutrient limitation. Rates of accumulation of organic matter, nutrients and above‐ground biomass were estimated.

When interpreted as successional stages, the different stages represent a sequence as expected on the basis of general successional theory. There was a peak in yearly nutrient accumulation between the 6‐ and 37‐yr old stage and a steady state after ca. 80 yr. Between the first two and the latter two stages a shift occurred from allogenic to autogenic succession which correlated with a shift in emphasis from available nutrients to light availability as limiting resources.

Basiphilous pioneer species suffered only deficiency of nitrogen, probably because of their low phosphorus requirements. It is concluded that in dune slack habitats, in addition to a low nutrient availability in general, a very low phosphorus availability favours basiphilous pioneer species to species showing co‐limitation of nitrogen and phosphorus as found in some grasses and dwarf shrubs. A comparison between the effects of lime addition and the effects of nitrogen and phosphorus additions suggests that, in the early stages, soil buffering increases the availability of nitrogen and inhibits the availability of phosphorus.

Sod cutting is an effective technique for restoring basiphilous pioneer vegetation, when slacks are acidified only superficially and buffering‐mechanisms can be reactivated. Yearly mowing and removing of standing crop may prolong the life‐span of basiphilous pioneer vegetation, when soil acidification has not yet dropped below pH 6.
On the variation explained by ordination and constrained ordination axes
Authors: Økland Rune Halvorsen
Published: May 2006

Abstract. Total inertia (TI), the sum of eigenvalues for all ordination axes, is often used as a measure of total variation in a data set. By use of simulated data sets, I demonstrate that lack‐of‐fit of data to the response model implicit in any eigenvector ordination method results in polynomial distortion ordination axes, with eigenvalues that normally contribute 30–70% to TI (depending on data set properties). The amount of compositional variation extracted on ecologically interpretable ordination axes (structure axes) is thus underestimated by the eigenvalue‐to‐total‐inertia ratio. I recommend that the current use of total inertia as a measure of compositional variation is discontinued. Eigenvalues of structure axes can, however, be used with some caution to indicate their relative importance.

I also demonstrate that when the total inertia is partitioned on different sets of explanatory variables and unexplained variation by use of (partial) constrained ordination, (35) 50–85% of the variation ‘unexplained’ by the supplied explanatory variables represents lack‐of‐fit of data to model. Thus, the common interpretation of ‘unexplained variation’ as random variation (‘noise’) or coenoclinal variation caused by unmeasured explanatory variables, is generally inappropriate. I recommend a change of focus from the variation‐explained‐to‐total inertia ratio and ‘unexplained’ variation to relative amounts of variation explained by different sets of explanatory variables.
Disturbance history and tree establishment in old‐growth Pinus koraiensis‐hardwood forests in the Russian Far East
Authors: Ishikawa Yukio , Krestov Pavel V. , Namikawa Kanji
Published: May 2006

Abstract. Dendro‐ecological studies were undertaken to document the disturbance history in two old‐growth mixed Pinus koraiensis‐hardwood forests in the southern part of the Sikhote‐Alin mountains in the Russian Far East. Establishment of four common canopy conifers, Abies holophylla, A. nephrolepis, P. koraiensis and Picea ajanensis, and three common canopy hardwoods, Acer mono, Betula costata and Tilia amurensis, were also inferred from population age structures and spatial dispersion patterns.

Growth releases on increment cores suggested that peak periods of growth releases indicating partial canopy disturbances have repeatedly occurred over the past 230 yr at intervals from ca. 35 to 100 yr. Slight releases and suppressions other than the peak releases occurred in many years of both histories, suggesting the formation of smaller‐scale canopy gaps. Despite the predominance of anthropogenic fires in Primorskiy Kray at present, destructive fires had not affected either forest. Wind disturbances and low intensity fires are likely factors controlling the dynamics of the forests. Under the disturbance regime, P. koraiensis has maintained its populations through its dependence on canopy gaps for establishment. Age distribution and gap dependence of P. ajanensis, A. nephrolepis and A. mono suggested continuous establishment of these species under a closed canopy, whereas occasional establishment of T. amurensis was derived largely from vegetative reproduction. Restricted establishment of A. holophylla and B. costata suggested a variety in kinds of disturbance throughout the histories. Continuous habitation of the study area by P. koraiensis is likely under the disturbance regime without destructive fires.
Key variables controlling the vegetation of a cool‐temperate mire in northern Japan
Authors: Yabe Kazuo , Onimaru Kazuyuki
Published: May 2006

Abstract. In the cool‐temperate Bibi Mire, Hokkaido, Japan, valley fens and flood‐plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood‐plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood‐plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone.

The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire ‐where the non‐inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.