bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of bryophyte associations at different scales in a Norwegian boreal spruce forest
Authors: Økland Rune Halvorsen
Published: May 2006

Abstract. Patterns of associations between 36 bryophytes and their relationships with trends in α‐ and β‐diversity were studied at five spatial scales (from 1 m2 to 1/256 m2) in a Norwegian boreal spruce forest. The range and dispersion of α‐diversity values in the data were significantly higher than in comparable model data sets, indicating varation from favourable to unfavourable conditions for bryophytes at all scales, particularly with increasing cover of the upper layers. The number of positive associations was significantly higher than predicted from a random distribution, for all sample plot sizes except the smallest. For the most frequent species, this number decreased with decreasing sample plot size. The excess of positive associations was due to the presence of (1) α‐diversity trends, as demonstrated by a stochastic simulation, and (2) β‐diversity (variation along environmental gradients). A microscale coenocline from dominance of large forest floor mosses to small liverworts, is added to two broad‐scale coenoclines demonstrated earlier. Facilitation ‐ positive density‐dependence caused by more favourable moisture conditions within dense stands ‐ is discussed as a possible third cause of excess positive associations.

The number of significant negative associations was generally low, and deviated neither from theoretical values assuming random distribution of species, nor from predicted values accounting for α‐diversity trends. The low proportion of negative associations, even in the presence of β‐diversity trends, suggests that interspecific competition is not important in this vegetation. Several alternatives to competition are discussed; (1) static mechanisms for avoidance of competition, (2) mobility, and (3) the importance of density‐independent mortality, in particular due to fine‐scale disturbance.

Simulation studies for assessing the effects of α‐diversity trends on species associations are emphasized.
Vegetation of the Eden Region, South‐eastern Australia: Species composition, diversity and structure
Authors: Keith D. A. , Sanders J. M.
Published: May 2006

Abstract. A classification of plant communities and land systems is presented for the Eden region to assist with the resolution of land use and management conflicts. Vegetation and environmental parameters were sampled at 369 sites and analysed with numerical techniques incorporating elements of the Braun‐Blanquet approach.

Land surfaces in the study area were described by means of a land systems analysis. A total of 41 plant communities, 3 with 2 subcommunities, were defined and described on the basis of floristic composition, structure and environmental variables. Descriptions of communities include information on habitat, structure, floristic composition of various strata, distribution and representation in reserves. The distributions of plant communities are interpreted in relation to characteristics of their land systems.

Plant communities were grouped into 5 major floristic series: Rainforest, Moist Eucalypt Forest, Dry Grassy Eucalypt Woodland and Forest, Dry Shrubby Eucalypt Woodland and Forest and Heath and Swamp. These groupings are distinguished by their structure, physiognomic attributes, composition of their canopy and understorey strata and habitat. Plant communities are differentiated along gradients of moisture availability, soil properties and temperature. A hypothesis is proposed to explain floristic and structural variation in relation to interactions between moisture and soil fertility gradients. Where moisture is high, tall shrubby eucalypt forest, mesic eucalypt forest and rainforest are thought to be segregated along a gradient of increasing soil fertility. On drier sites, dry eucalypt communities with grassy understorey s are thought to inhabit more fertile soils than those with shrubby understoreys.

The biogeographic relations and broad conservation values of the major floristic groupings are discussed. Vegetation patterns in the region are related to a latitudinal sequence which prevails in eastern Australia. A preliminary assessment of plant community distributions shows that the reserve system is not representative of the range of vegetation and landscape types in the region.
Colonization and early succession on anthropogenic soils
Authors: Rebele Franz
Published: May 2006

Abstract. This paper reports on vegetation development on permanent experimental plots during five years of succession. Nine (1 m2) plots were filled with three typical substrates from man‐made habitats of urban and industrial areas in the region of Berlin. The three substrates (a commercial ‘topsoil’, a ruderal ‘landfill’ soil and a sandy soil), differ in organic matter and nutrient contents. Relevés of species composition and percent cover of each species present were made monthly during the growing season from the start of vegetation development. This paper describes the different successional pathways on topsoil and ruderal soil and the colonization process on sandy soil. On topsoil, ruderal annuals are dominant in the first year and are replaced by short‐lived perennials from the second year. Those species were replaced by long‐lived perennial herbs (Ballota nigra or Urtica dioica) from the third year of succession onwards. On the ruderal land‐fill soil the early successional stages are less sharp and the perennial Solidago canadensis is able to dominate within one year after the succession was initiated. On sandy soil there is still an ongoing colonization process, where pioneer tree species like Betula pendula and Populus nigra play a main role. The importance of ‘initial floristic composition’, the role of substrate for community structure and the peculiarities of successional sequences on anthropogenic soils in the context of primary and secondary successions are discussed.
Vegetation patterns, microtopography, and soils on a Chihuahuan desert playa
Authors: Wondzell Steven M. , Cornelius Joe M. , Cunningham Gary L.
Published: May 2006

Abstract. Spatial patterns of vegetation on an ephemeral lake bed (playa) in the northern Chihuahuan desert were closely correlated with elevation. Distributions of species along a 265 m transect from the center to the edge of the playa showed abrupt boundaries at 110 m and 220 m. These boundaries seem related to the maximum elevation covered with standing water following complete flooding, and to an edaphic boundary between heavy clay soils at the center of the playa and adjacent soils.

The complete turnover in species composition across this transect, with an elevation change of only 85 cm, indicates that environmental gradients resulting from flooding and soil development are steep. Vegetative patterns within the lowest part of the playa were patchy, with patch diameters ranging from 2 to 5 m. These patches appear to be produced by differences in the duration and frequency of flooding between small knolls and depressions resulting from gilgai microtopography.
The disturbance regime of an old‐growth forest in coastal California
Authors: Hunter J. C. , Parker V. T.
Published: May 2006

This study deals with the disturbance regime of an old‐growth, mixed‐evergreen forest with a canopy composed of Arbutus menziesii, Lithocarpus densiflora, Pseudotsuga menziesii, Quercus chrysolepis, Q. wislizenii, and Sequoia sempervirens. 80 canopy gaps were randomly selected from throughout a 230‐ha watershed. Of the land area sampled, 11.1 to 16.6 % was within gaps. Gap area had a mode of < 50m2 and a range of 6–3437 m2. Gaps were formed by snags, snaps, tips, and slope failures. Although < 10 % of the gaps sampled were due to slope failures, these accounted for 43 % of the total land area within gaps. All snags resulted from the death of a Pseudotsuga or Arbutus individual, the widely branched trunks of Arbutus individuals accounted for most of the irregularly shaped gaps, and larger gaps resulted from the death of Pseudotsuga and Sequoia individuals, averaging 119 and 111 m2 respectively, than from the death of Lithocarpus or Arbutus, averaging 54 and 52 m2. Gaps were more frequent over concave sections of slopes and large gaps were more frequent on north‐facing slopes. The creation of a gap increased disturbance to the adjacent canopy, with half of the gaps formed through more than one disturbance.

The relationship of disturbance regime to topography, the influence of canopy species biology on gap properties, and the repeated events involved in gap formation all indicate a fine scale variation in the pattern of gaps and their characteristics.
Floristic and structural variation in the Tamaulipan thornscrub, northeastern Mexico
Authors: Reid N. , Stafford Smith D.M. , Beyer‐Miinzel P. , Marroquin J.
Published: May 2006

Abstract. A generalized research strategy is presented for identifying the ecological effects of the physical environment and management in a poorly known region of subtropical, semiarid thornscrub in northeastern Mexico. Vegetation samples were stratified across a small number of climatic subregions, substrate types and topographic situations. Classification analysis and PCo A of the species x site matrix of incidence data after application of the Information Statistic were used. The analyses suggested that the regional variation in climate, substrates and topography was responsible for the major floristic differences in the vegetation. The distributions of most plant species were related to the variation in the physical environment. PCo A of the species x site cover data after application of the Bray‐Curtis dissimilarity metric revealed evidence of vegetation change due to overgrazing in each major floristic group, but not to selective cutting for timber and firewood.
BOOK REVIEWS
Authors: Bornkamm R.
Published: May 2006

Book reviewed in this issue.

Guntli, A. P. Ligningehalt und andere Merkmale des Schilfhalmes (Phragmites australis (Cav.) Trin. ex Steudel) in Beziehung zur Röhrichtbewirtschaftung. 1989. Veroff. Geobot. Inst. Rübel ETH Zürich 103: 1–65. Price: 39 CHF.
Long‐term vegetation changes in stands of Pinus sylvestris in southern Finland
Authors: Nieppola Jari
Published: May 2006

Abstract. Understorey vegetation dynamics in Pinus sylvestris L. stands were examined over 30 yr in southern Finland. Data were collected from 112 permanent sample plots twice, first in 1950–1956 and again in 1983 ‐ 1986. Between the two surveys 52 stands were clear‐felled and in the 60 remaining old stands thinnings of various magnitude were conducted.

In the mature, thinned stands species presence remained virtually unchanged. With the exception of a few species, including Vaccinium vitis‐idaea, Hylocomium splendens, and Dicranum polysetum, the changes in species cover were also slight. In the clear‐felled plots the changes in species presence were minor but the cover of many species changed strongly. The average cover of Vaccinium myrtillus and Hylocomium splendens dropped to near zero and that of Vaccinium vitisidaea and Pleurozium schreberi decreased 2 ‐ 4 times on all sites. The cover of Calluna vulgaris approximately doubled, and Cladina rangiferina and Cladina arbuscula also increased after canopy removal.

In addition to intrinsic successional change, a special interest in this study was to investigate vegetation dynamics in relation to forest land classification methods in which understorey vegetation is used as part of the classification criteria. The results support the Cajanderian site classification approach, in the case of boreal Scots pine stands, that sites can be classified on the basis of understorey vegetation at different successional phases. However, because of the strong successional and site‐to‐site variation in species cover, it is suggested that site classification be based primarily on species presence
Resource heterogeneity in oldfields
Authors: Kelly Victoria R. , Canham Charles D.
Published: May 2006

Abstract. Spatial heterogeneity of photosynthetically active radiation (PAR), soil moisture and soil N mineralization in a range of oldfield communities was analyzed using semi‐variograms for transect data. Percent transmittance of PAR was examined in eight communities, and soil moisture and N mineralization were examined in the two most common communities. In general, the sites with the highest resource availability had the smallest coefficients of variation. For light, 63% of the transects showed significant non‐zero spatial autocorrelation with sills at 1 ‐ 70 cm distance intervals. Although the grass‐dominated communities had the highest average PAR levels and the lowest coefficients of variation, they also were among those with the greatest percentage of transects that had non‐zero spatial autocorrelation. For light, the average semivariogram range, or distance within which samples were autocorrelated, was 19 cm and different among communities at p = 0.07. For soil moisture, two of three shrub sites and one of three grass sites showed non‐zero spatial autocorrelation with sills at 10 ‐ 300 cm distance intervals. Average semivariance range was 249 cm for the shrub community and 170 cm for the grass community. For N‐mineralization, none of the shrub and one of three grass sites showed non‐zero spatial autocorrelation with a sill, with a semivariance range of 60 cm. Soil moisture and N‐mineralization were higher in the shrub than in the grass communities. Overall, these results indicate that resource variability occurred within patches of uniform vegetation, and the range of resource spatial dependence was different among resources even within a single community type. Our results suggest that different seedlings invading these communities will experience very different patterns of microsite heterogeneity as a result of their specific resource requirements.
Modeling a solar radiation topoclimatology for the Rio Grande River Basin
Authors: Dubayah Ralph C.
Published: May 2006

Abstract. Key components in the climatology of the Earth are incoming and net solar radiation. Next to clouds, the major modulator of solar radiation at the surface is topography. Variability in elevation, slope, aspect, and shadowing can lead to large gradients in incoming and net solar radiation fields. The response of vegetation to these gradients can often be dramatic, as in the distribution of vegetation on south‐ and north‐facing slopes. Recently much progress has been made in modeling the effects of topography on incoming and net solar radiation. Such models produce fields of radiation that have been adjusted for topography derived from digital elevation data. This paper presents a topographic solar radiation model that combines digital elevation data with surface and satellite measurements. Specifically, a monthly topoclimatology for the Rio Grande River Basin in Colorado is constructed for the hydrological years 1987 ‐ 1990. Using digital elevation models with 30 m x 30 m grid spacing, representing a mosaic of 39 U.S. Geological Survey 1:24 000 Quadrangles, a digital representation of the watershed is created. Hourly pyranometer measurements taken nearby the basin are then used with satellite reflectances to drive the solar radiation model. The results are monthly maps at 30 m x 30 m grid spacing covering the entire basin that show considerable variability by location and season. Such maps may be useful for vegetation modeling, especially for pattern analysis and ecosystem process modeling.
Methods for fitting dominance/diversity curves
Authors: Wilson J. Bastow
Published: May 2006

Abstract. Dominance/diversity curves, displaying the relative abundances of the species within a community, have often been constructed from field data. Several ecological and statistical models of dominance/diversity have been proposed, to explain the curves. Yet, rarely have curves of different models been fitted to field data.

In this paper the appropriate parameters and methods of curve fitting for plant communities are described for the General Lognormal, Canonical Lognormal, Geometric, Broken Stick, Zipf and Zipf‐Mandelbrot models. Distinction is made between fixed and optimised parameters, to clarify para‐meterisation of the models. It is concluded that all should be fitted by minimising the deviance in a ranked‐abundance plot.

Statistical tests of goodness of fit are discussed. It is concluded that consistency of fit between replicate quadrats of a community provide the best test.

Curves of all the models discussed are fitted to data from a species‐rich Spanish hay meadow, and to data from a New Zealand intertidal algal community. The Spanish meadow data are best fitted by General Lognormal. The New Zealand algal data are best fitted by Geometric or General Lognormal. Goodness of fit for a sample is usually relatively good or poor for all models, since much of the deviance comes from steps in the curve which none of the models can fit closely.
BOOK REVIEWS
Authors: Gardner J. A. F.
Published: May 2006

Book reviewed in this issue.

Schulze, E. D., Lange, O. L., Oren, R. (eds.). 1989. Forest Decline and Air Pollution ‐ A Study of Spruce (Picea abies) on Acid Soil. Ecological Studies, Vol. 77. xvii + 475 pp. Springer‐Verlag, Berlin, Heidelberg, New York. ISBN 3–540–50793–0; 387–50793–0. Price: USD 145.00.
BOOK REVIEWS
Authors: Snoeijs Pauli
Published: May 2006

Book reviewed in this issue.

Round, F. E., Crawford, R. M. & Mann, D. G. 1990. The Diatoms. Biology and morphology of the genera, ix + 747 pp. Cambridge University Press, Cambridge. ISBN 0–521–36318–7. Price: GBP 125.‐.
Long‐term changes in a Wisconsin Fagus‐Acer forest in relation to glaze storm disturbance
Authors: De Steven Diane , Kline Joanne , Matthiae Paul E.
Published: May 2006

Changes in the composition of a Fagus‐Acer (Beech‐Sugar maple) forest in southeastern Wisconsin over a 16‐yr period from 1971 to 1987 are analyzed in relation to a severe glaze (ice) storm disturbance occurring within the census period. Landscape topography created ‘windward’ and ‘leeward’ forest aspects with respect to storm severity, which resulted in greater canopy opening on the windward aspect. In the tree stratum, most species remained stable in density and most of the common species increased in basal area into larger size classes. However, Fagus grandifolia, Ulmus rubra, and the small tree Ostrya virginiana suffered net losses that suggest synergistic effects between glaze storm disturbance and other factors upon tree mortality. In the sapling stratum, canopy opening strongly promoted release of shade‐to levant Acer sac‐charum. On the windward forest aspect, sapling densities of less shade‐tolerant species also increased, in contrast to the absence of such increases on the leeward forest aspect. In the shrub (regeneration) stratum, species responses were heterogeneous. Regeneration of most species increased over the 16‐yr period, and some less shade‐tolerant species showed increased regeneration differentially on the windward forest aspect.

Overall, disturbance appears to have accelerated forest succession toward increased dominance by A. saccharum and persistence of both Fagus and Tilia americana through their capacities for root sprouting. However, forest succession was retarded somewhat on the windward aspect through increased recruitment of less‐shade tolerant species. These results parallel those of other studies of glaze storm disturbance, and they illustrate how spatially heterogeneous disturbance intensity may contribute to maintenance of forest diversity.
Maquis vegetation in the eastern Cantabrian coastal fringe
Authors: Loidi Javier , Herrera Mercedes , Olano José M. , Silván Fran
Published: May 2006

Abstract. The typology and distribution are discussed of hitherto poorly known Mediterranean‐type maquis vegetation from the eastern stretch of the coastal fringe of the Cantabrian Mountains. 51 phytosociological relevés of maquis with Arbutus unedo (‘madroñales’) and Quercus coccifera (kermes oak shrubland or ‘coscojares’) were submitted to Correspondence Analysis and table rearrangement. The results are discussed and interpreted in the light of actual biogeographical and palaeohistorical knowledge. A sharp division between (uniform) acidophilous and (diversified) basophilous communities was revealed. On the basis of the phytosociological classification four new syntaxa are described: the associations Ulici gallii‐Arbutetum unedonis, Phillyreo latifoliae‐Arbutetum unedonis ‐ with two subassociations: arbutetosum unedonis and viburnetosum tini ‐ and the association Genisto occidentalis‐Quercetum cocciferae.
Experimental evaluation of realized niche models for predicting responses of plant species to a change in environmental conditions
Authors: de Swart Evalyne O.A.M. , van der Valk Arnold G. , Koehler Kenneth J. , Barendregt A.
Published: May 2006

Abstract. We estimated, using logistic regression techniques, the realized niches of the four dominant species in an experimental marsh complex located in the Delta Marsh, Manitoba, Canada. These models were then used to predict the probability of occurrence of these species in selected elevation ranges when water levels were raised in 1985 either 0, 30 or 60 cm above the long‐term normal water level. These realized‐niche models were calculated using elevation and species data collected in 1980. After having been eliminated by two years of deep flooding, the emergent vegetation in this complex had been re‐established during a drawdown beginning in either 1983 or 1984. Our hypothesis was that from 1985 to 1989 the frequencies of occurrence of species in selected elevation ranges would converge to their probabilities predicted from the 1980 logistic models.

This was not borne out by our results. Actual frequencies and predicted probabilities of occurrence of a species were similar at best less than 40% and then mostly in the control (0 cm) treatment. The realized‐niche models were not adequate to predict the distribution of emergents after an increase in water level in the short term because the emergent species did not migrate upslope. Emergent species in the medium and high treatments either (1) died out ‐ Scolochloa festucacea and Scirpus lacustris ‐ after 3 yr because they could not survive permanent flooding, (2) stayed where they were ‐ Phragmites australis ‐ because they were unable to move upslope through clonal growth, or (3) became more widespread ‐ Typha glauca only because of the expansion of small local populations already established in 1985 in areas dominated formerly by other species.
How reliable are our vegetation analyses?
Authors: Lepš Jan , Hadincová Všra
Published: May 2006

Abstract. Two sets of 40 relevés, made independently by two observers on the same 5m x 5m sample plots, were compared to estimate the sampling error and to assess the effect of this sampling error on (1) estimates of species richness and diversity (2) results of multivariate analyses, and (3) estimation of species turnover in repeated sampling. The relevés were made according to the standard Braun‐Blanquet method. The sampling error was estimated for (1) recording of species in sample plots and (2) visual estimation of the degree of cover (or of the general population size). Despite the fact that the sample plots were searched thoroughly for 30 ‐ 40 min, the number of overlooked species was high with a discrepancy of 13% between corresponding relevés.

Regarding multivariate analysis, the error caused by missing species was at least as important as the error in visual estimation of species cover. The estimates of degree of cover using the Braun‐Blanquet scale are sufficiently reliable for use in multivariate analysis when they are subjected to ordinal transformation. When average cover values are used, the patterns detected are based solely on dominants. Species richness and species diversity could be reliably estimated from the relevés, but the estimates of equitability are very unreliable. The classical relevé method remains one of the most efficient survey methods for recognition of vegetation types on the macro‐community and landscape scales.
Semi‐strong Hybrid Scaling, a new ordination algorithm
Authors: Belbin Lee
Published: May 2006

There is a small group of association measures that appear optimal for comparing sites on the basis of their species composition. These measures can accurately estimate affinity between sites when they are ecologically similar. Once sites share few or no species, these measures always under‐estimate the ‘ecological distance’ between them. A new ordination algorithm called Semi‐strong Hybrid Scaling, SHS, uses these features in an attempt to provide a better configuration of the sites. The new method is evaluated by a direct comparison of the structure in simulated data with the Hybrid method of Faith, Minchin & Belbin (1987).

To evaluate SHS and compare it with Hybrid Scaling, 3240 datasets were generated using the COMPAS simulator (Minchin 1987). The data were designed to simulate as closely as possible, what is known of the distribution of species on environmental gradients. The factors included the dimensionality of the data, the number of sites and species, the shape of the species response surfaces, positioning of the sites in the simulation space, carrying capacity and level of noise. Recovery of the simulated site positions by SHS and Hybrid Scaling was evaluated using Procrustes rotation. SHS produced a better recovery in 88% of the datasets.
Succession and fluctuation in a wet dune slack in relation to hydrological changes
Authors: Grootjans A. P. , Hartog P. S. , Fresco L. F. M. , Esselink H.
Published: May 2006

Vegetation changes in a wet dune slack complex have been studied over a period of 23 yr. The vegetation was recorded in 40 permanent plots: all plots in 1964, 1977, 1983 and 1987 and some also in five other years. There were large fluctuations in annual precipitation during this period, including some extremely dry (1976) and wet (1985) years.

Many species of wet calcareous and pioneer habitats declined in cover between 1964 and 1977, when there were prolonged dry summer periods, though few species were lost from the sampled quadrats.

Practically all calciphilous and pioneer species disappeared between 1977 and 1983, when there were relatively many wet summers. It is suggested that extremely dry conditions temporarily obscure the impacts of hydrological changes in local hydrological systems, by retarding the vegetation succession. After a period of excessive precipitation the (acidifying) effects of ground‐water withdrawal rapidly became evident in the species composition of the dune slack.
Small‐scale variability as a mechanism for large‐scale stability in mountain grasslands
Authors: Herben T. , Krahulec F. , Hadincová V. , Skálová H.
Published: May 2006

Abstract. Data from a 7‐yr permanent plot study of grassland dynamics were used to address the relationship between processes at two levels of resolution (3.3 cm x 3.3 cm, 50 cm x 50 cm). Grasslands mown and manured in the traditional way in the Krkonose Mts. (Riesengebirge) were used as a model system. Spatial dynamics at the finest scale were very high, as demonstrated by turnover of individual species in 3.3 cm x 3.3 cm subplots and year‐to‐year transition matrices of the same subplots. The direction of these dynamics was not correlated with grassland treatment, although there was some correlation within years. An extrapolation of such year‐to‐year dynamics to larger time scales would result in big large‐scale changes on the community level, and large shifts in species composition of the whole sward. However, dynamics at larger spatial or temporal scales were generally small. Some directional change occurred in manured plots, whereas little change occurred in unmanured plots. Large‐scale dynamics were not correlated with small‐scale dynamics in plots without manuring, but some correlation was detectable in manured plots.

There are probably several processes that drive small‐scale dynamics, such as non‐linear interactions and environmental fluctuations. We argue that within certain limits these forces act on species composition so as to make small‐scale dynamics non‐directional. This results in both large‐scale species diversity and apparent large‐scale stability of these grasslands. However, if these forces are beyond these limits, the small‐scale dynamics may become directional, resulting in rapid changes at larger spatial scales.
Mediterranean pasture dynamics: the role of germination
Authors: Espigares T. , Peco B.
Published: May 2006

Abstract. Meteorological patterns have a decisive influence on the inter‐annual dynamics of therophyte pastures under Mediterranean climatic conditions. The germination behaviour of annual pasture species was studied by subjecting two collections of seeds taken from plants and soil‐seed banks to two phytotron‐simulated weather patterns: early and late autumn rains. Species from these pastures were arranged along a gradient of sensitivity to temperature on the arrival of the first persistent rain. This sensitivity was manifested in both the total germination success of the species and the germination time profile. The different germination patterns of the species can provide competitive advantages depending on the autumn weather conditions.
Species diversity patterns in Mediterranean grasslands
Authors: Montalvo J. , Casado M. A. , Levassor C. , Pineda F. D.
Published: May 2006

Abstract. A field experiment involving herbivore exclusion, ploughing, and the combination of both was carried out over a period of 4 ‐ 5 yr in Mediterranean grasslands located along an elevational gradient. The empirical results provide a general hierarchical framework for understanding patterns of plant species diversity in thesegrasslands. In grazed grasslands, plant species density decreased as altitude increased, and this pattern was maintained through time. The reduced seasonality along the climatic gradient is suggested as the extrinsic, indirect control factor. Ploughing caused species loss, but after 4 yr the original diversity was recovered in most grasslands. Our hypothesis is that a negative feedback mechanism regulates species increase towards a characteristic level. A trend of species density reduction was observed in ungrazed grasslands. Plant‐herbivore interaction is considered to be essential for maintaining species diversity in grazed grasslands and for the recovery of diversity in mechanically disturbed grasslands.
Factors controlling the population dynamics of the clonal helophyte Ranunculus lingua
Authors: Johansson Mats E.
Published: May 2006

Abstract. Two marginal and two central populations of the pseudo‐annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life‐history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water‐level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life‐histories with a high reproductive capacity, whereas a large size of ramet would be the most important life‐history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations.
Pollen representation of vegetational patterns along an elevational gradient
Authors: Jackson Stephen T.
Published: May 2006

Abstract. Modern pollen assemblages from 16 small lakes (< 2.5 ha) and 11 moderate‐sized lakes (4.5–19.3 ha) arrayed along an elevational gradient (300 to 1320 m) in the east‐central Adirondack Mountains were studied to determine how well the pollen assemblages recorded patterns of forest composition along the gradient. Forest composition ranges from Pinus strobus/Tsuga/ hardwoods forests at low elevations through Tsuga/ hardwoods, hardwoods, and Picea/Abies forests to Abies‐dominated forests at high elevations. Modern pollen percentages for 10 tree taxa were compared with lake elevation using scatter plots and correlation and regression analysis.

Differential smoothing of vegetational patterns along the elevational gradient occurred among the 10 taxa owing to differences in pollen dispersibility, pollen production, and spatial pattern of taxon abundance in forests of the region. No differences were observed in pollen‐elevation patterns between small and moderate‐sized lakes. Pollen‐elevation patterns were obscured for most taxa when the gradient was shortened (e.g. to 600–1320 m) owing to increased spatial smoothing by pollen dispersal. Design and interpretation of paleoecological studies of spatial gradients can be improved by careful attention to site spacing, gradient length, and gradient steepness in the context of pollen dispersal and representation models.
Defining phytoclimatic units in Galicia, Spain, by means of multivariate methods
Authors: Retuerto Rubén , Carballeira Alejo
Published: May 2006

Abstract. Floristic and climate data from 150 plots in 25 sites in Galicia, Spain, were analysed to test the hypothesis that climate is the major factor governing the distribution of woody plant species. TWINSPAN classification, Detrended Correspondence Analysis and Canonical Correspondence Analysis were applied in successive stages of the data analysis to describe vegetational variation in relation to climatic gradients. Six groups of species were defined, two clearly oceanic (Maritime and Cool Maritime), one mediterranean maritime, and three mediterranean (Cold Mediterranean, Cool Mediterranean and Temperate Mediterranean). An aridity gradient was revealed as the primary factor regulating the distribution of the species considered. This main gradient reflects the transition between the Eurosiberian and Mediterranean bio‐geographic regions. The gradient can be characterized by means of the Vernet bioclimatic index. A value ≥ 4 for this index can be taken to define the mediterranean zone in our study area. The mean minimum temperature in the coldest month was the second most influential climatic variable. Partial ordination analysis revealed that the residual variation was insignificant and that the observed variation in vegetation can be fully accounted for by climatic variables.
BOOK REVIEWS
Authors: Norton David A.
Published: May 2006

Book reviewed in this issue.

Zonneveld, I. S. & Forman, R. T. T. (eds.) 1990. Changing Landscapes: An Ecological Perspective. Springer Verlag, New York. ISBN 0–387–97102–5. Price: USD 69.50.
BOOK REVIEWS
Authors: Wieder R. Kelman
Published: May 2006

Book reviewed in this issue.

Whigham, D. F., Good, R. E. & Květ, J. (eds.) 1990. Wetland Ecology and Management: Case Studies. Tasks for Vegetation Science Series No. 25. vii + 180 pp. Kluwer Academic Publishers, Dordrecht. ISBN 0–7923–0893‐X. Price: USD 95.‐.
Floristics, systematics, and the study of arctic vegetationa commentary
Authors: Murray David F.
Published: May 2006

Abstract. Some remarks are made on the special problem encountered in arctic plant geography and vegetation studies, viz. the circumpolar distribution of many taxa, which may have been described independently in different countries. 80 % of the arctic bryophytes, 70 % of the lichens and 50 % of the vascular plants have a circumpolar distribution and especially amongst the vascular plants there are several cases of confusion. Special attention is paid to Dupontia fisheri s.l., Carex aquatilis s.l. and C. bigelowii s.l. Especially for a classification of vegetation based on floristic data, having a list of accepted plant names and knowing their synonyms is of paramount importance. An electronic database for arctic vegetation will foster, if not require, more unified approaches to the description of plant communities.
Numerical classification of the coastal vegetation of Attu Island, Aleutian Islands, Alaska
Authors: Talbot Stephen S. , Talbot Sandra Looman
Published: May 2006

Abstract. This phytosociological study of the beaches, dunes, and associated lower mountain slopes of Attu Island is the first effort to identify the major coastal vegetation types of the Aleutian Islands using numerical methods. It is the first attempt to use the relevé method in southern coastal Alaska and provides a basis for future comparison with other areas. 76 relevés represent the range of structural and compositional variation in the matrix of vegetation and landform zonation at 16 locations. Data are analyzed by multivariate methods using the MULVA‐4 computer package and ordered with Wildi's numerical procedure to produce results similar to traditional phytosociological tabular classification. Nine major community types are distinguished in four physiognomic groups: 1. Dwarf‐shrub mire: Vaccinium uliginosum‐Empetrum nigrum; 2. Meadow: Athyrium filix‐femina‐Streptopus amplexifolius, Artemisia tilesii‐Veratrum album, Elymus mollis‐Montia (Claytonia) sibirica, Ligusticum scoticum‐Elymus mollis; 3. Beach meadow: Elymus mollis‐Senecio pseudo‐arnica, Lathyrus maritimus‐Elymus mollis; and 4. Beach: Mertensia maritima and Arenaria (Honckenya) peploides. These community types are described and interpreted in response to a complex, topographic gradient. Phytogeographic comparison of Attu Island with neighboring areas suggests close relationship to the beach and beach‐meadow types of eastern Kamchatka and to the mesic meadows of the Alaskan Semidi Islands; there is a slightly lower relationship to the mesic meadows of nearby Buldir Island.
Limitations to species coexistence: evidence for competition from field observations, using a patch model
Authors: Wilson J. Bastow , Gitay Habiba
Published: May 2006

Abstract. Plant community structure in four dune slacks is examined for evidence of competition, expressed as local constraint on species biomass. Such constraint would result in a low variance in total quadrat biomass, compared to a null model. A method of analysis is introduced, using a patchbased null model, which is intended to discount most of the effects of environmental heterogeneity. The method is applied to data in which previous methods had failed to find such structure.

There was significant biomass constraint (i.e. low variance in biomass) examining total plant‐community biomass in Site 1, and there was a trend in this direction also in Site 2. When guilds defined on morphology were examined, significant biomass constraint was found for the Rhizomatous guild in Site 2. There was a trend to low variance for this guild also in Site 4, but it was significant only in a one‐tailed test. After a consideration of other mechanisms, it is concluded that the most likely explanation for this biomass constraint is interspecies competition.

Site 2, which showed the strongest evidence of biomass constraint in the present analyses, was also the site that demonstrated a significant deficit of variance in richness in earlier work, and was the most species‐rich of the four sites and the least disturbed.

The advantages of the new method, for obtaining evidence on competition, are discussed in comparison to pot experiments and field‐perturbation experiments.

We conclude that community structure can be seen in the pattern of species biomasses provided that a suitable method of analysis is used, i.e. examining small‐scale effects and excluding the effects of environmental heterogeneity. In some cases such effects can be related to guild membership. We hypothesise that constraint on biomass is likely to be stronger in more species‐rich and less disturbed communities.
Effects of nutrient availability and neighbours on shoot growth, resprouting and flowering of Erica multiflora
Authors: Vilà Montserrat , Terradas Jaume
Published: May 2006

Abstract. To test if low soil fertility and competition limit the performance of Mediterranean shrubs, and if the effects of competition on plant performance were modified by soil fertility, we subjected shrubs of Erica multiflora to a factorial field experiment of fertilization and removal of neighbours around target plants. After 18 months of treatment, fertilization had stimulated the growth of pre‐existent sprouts and biomass allocation to stems into new sprouts, but decreased the frequency of sprout flowering. Removal of neighbours increased the number and biomass of new sprouts, the probability of sprout flowering and the biomass of flowers. Fertilization slightly enhanced sprout recruitment and the probability of sprout flowering when neighbours were removed, but did not modify the other parameters of plant performance. According to our results, both low soil fertility and competition limited plant performance. Competition was slightly more intense in fertilized plants, but only in determining sprout and flowering bud stimulation.
Global vegetation models: incorporating transient changes to structure and composition
Authors: Steffen William L. , Cramer Wolfgang , Matthias Plöchl , Bugmann Harald
Published: May 2006

Abstract. We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above‐ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.
A functional classification for predicting the dynamics of landscapes
Authors: Noble Ian R. , Gitay Habiba
Published: May 2006

Abstract. Functional classifications have been derived for various purposes using subjective, objective and deductive approaches. Most of the classifications were derived to describe a static state of a region or landscape rather than to predict the dynamics of the system. Here, we suggest a simple, but comprehensive functional classification based on life history parameters that can predict the dynamics of plant communities subject to recurrent disturbances. The predicted dynamics are described in terms of survival and local extinction of the functional groups. The groups derived from the classification are probably largely independent of functional groupings that may be derived for other aspects of community composition (e.g. structure, phenology) and community interactions (roughness, albedo etc.). We emphasize that functional classification is context‐dependent and we should not expect to find a useful, universal classification into functional groups. Software has been developed to help classify the species into functional groups, to derive successional sequences and to predict community composition under different disturbance regimes both in point and landscape models.
Degeneration of species‐rich Calthion palustris hay meadows; some considerations on the community concept
Authors: Grootjans A.P , Fresco L.F.M , de Leeuw C.C , Schipper P.C
Published: May 2006

Abstract. An overview of the vegetation history of Calthion palustris meadows is presented with special emphasis on the natural habitats of the character species. The response of meadow species under the influence of drainage was calculated using species‐environment response curve techniques. The changes were monitored in permanent plots situated on sites with various intensities of drainage. The similarity with an undisturbed local reference type of the hay meadow community was calculated for all plots and years. On this basis a half‐life time of the Calthion palustris stands could be assessed. The half‐life time was small in the plots which are most affected by drainage. The response to drainage of character species of the Calthion palustris was very different. This imposes problems for some definitions of the community concept.
BOOK REVIEWS
Authors: Sykes Martin T.
Published: May 2006

Book reviewed in this article:

Veroustraete, F., Ceulemans, R.J.M., Impens, I.I.P & van Rensbergen, J.B.H.F. (eds.) 1994. Vegetation Modelling and Climatic Change Effects. SPB Academic Publishing bv, The Hague. ISBN 90‐5103‐090‐8. Price: USD 42.‐.; NLG 75.‐.
Leaf phenology and herbivory along a temperature gradient: a spatial test of the phenological window hypothesis
Authors: Aizen Marcelo A. , Patterson William A.
Published: May 2006

Abstract. In this study, we documented patterns of variation in leaf phenology and leaf herbivory in scrub oak (Quercus ilicifolia Wang) along the slope of a closed topographical depression, 15 m deep and 400 m wide, in the pine barrens of eastern Massachusetts. Minimum temperatures over the growing season averaged 6.5 °C lower at the bottom of the depression than at the top. Bud break at the bottom of the depression was 2–3 weeks delayed compared with the top. In both years of this study, 1988 and 1989, leaf damage by thrips increased down slope producing differences of about 10 % in the proportion of leaf area damaged between the top and the bottom of the depression. Because thrips fed exclusively on the youngest leaves, this pattern could be attributed to a closer synchrony between the timing of leaf flushing and the period of insect feeding activity towards the bottom of the depression. Average differences in leaf damage between years could also be accounted for by variation in leaf phenology. These patterns support the hypothesis that the degree of temporal overlap between availability of high quality foliage and the period of insect feeding activity may greatly determine spatial and temporal variation in leaf damage by insect herbivores.
Disturbance regimes and vegetation dynamics: role of floods in riverine wetlands
Authors: Bornette Gudrun , Amoros Claude
Published: May 2006

Abstract. This study tested whether the frequency of flood disturbances was able to slow down or stabilize vegetation succession in former braided channels over a decade. According to the Patch Dynamics Concept and to succession theory, species richness and diversity should be high but stable in the frequently (40 days/year) flooded channel, and should change over time in the infrequently (1 day/year) flooded one. Within the frequently disturbed channel, composition of vegetation as well as species richness and diversity appeared stable through dynamic equilibrium over the decade. Only one zone, because of particular geomorphological features that decreased disturbance intensity, developed highest diversity and richness as expected from the Intermediate Disturbance Hypothesis. The highest disturbance effect decreased species richness and was related to a higher spatial heterogeneity of the substrate (number of grain‐size classes). In the other zones, richness and diversity appeared to be lowest where disturbance frequency was lowest or disturbance intensity was highest. From 1981 to 1987, the infrequently flooded channel underwent succession, and species richness increased in the major part of the channel, whereas diversity increased only in its extreme parts.