bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of sod cutting for restoration of wet heathlands: revegetation and establishment of typical species in relation to soil conditions
Authors: Sansen Ugo , Koedam Nico
Published: May 2006

Abstract. Field observations in sod‐cut wet Molinia caerulea dominated heath lands revealed information on the revegetation process in relation to plot age and soil variables. Data on the most common species; Erica tetralix, Molinia caerulea, Drosera intermedia and Rhynchospora fusca show that Molinia tends to dominate again within a few years. Whereas the other species are affected in their development by either groundwater regime, soil acidity, nutrient availability or cut depth, Molinia caerulea is highly competitive in all situations. Soil acidity is the major factor affecting species diversity.
Changes in Mediterranean plant succession: old‐fields revisited
Authors: Debussche Max , Escarré José , Lepart Jacques , Houssard Claudie , Lavorel Sandra
Published: May 2006

Abstract. Old‐field plots used for a study of succession in Mediterranean France were revisited after 12–14 yr. Our aims were: (1) to verify if predicted patterns of species richness, turnover and composition are confirmed; (2) to compare the development in disturbed plots with that in undisturbed ones; (3) to discuss the impact of management changes.

In undisturbed plots species richness and turnover decreased with successional age. Floristic composition changed in a way consistent with the predicted successional development in most plots. Therophytes decreased and phanerophytes increased; anemochorous species decreased and endozoochorous species increased, as expected. In plots disturbed since the first analysis richness decreased with successional age, but generally remained higher than in undisturbed plots. Floristic composition, species turnover and an increase in therophytes indicated changes towards younger successional stages. Thus, disturbance changed succession but not much. This is probably linked with the regeneration abilities typical of mediterranean species, e.g. resprouting. At the landscape scale, richness did not change and species turnover was low.

The plots studied were situated in two distinct locations. One had not been disturbed between the two observation periods, while the other is a mosaic of undisturbed and disturbed sites. Observations fitted predictions much more closely at the undisturbed location.

We conclude that permanent plot studies are powerful in identifying successional trends and can also provide additional insights into the effects of disturbance some of the mechanisms underlying the dynamics of diversity.
Vegetation heterogeneity and diversity in flat and mountain landscapes of Patagonia (Argentina)
Authors: Jobbágy Esteban G. , Paruelo José M. , León Rolando J.C.
Published: May 2006

Abstract. We studied floristic and diversity patterns and their environmental controls in two landscapes of contrasting topography in the Patagonian steppe. The analyses were focused on the effects of water availability gradients and landscape configuration on plant species distribution and coexistence.

Floristic variation was investigated using Correspondence Analysis. The relationship between floristic and environmental variation was analyzed using Canonical Correspondence Analysis and correlation tests. We explored diversity patterns by relating spatial distance to floristic dissimilarities. The floristic gradient was determined by shrub and grass species and was related to precipitation in the flat area, and to precipitation, elevation and potential radiation in the mountain area. Site species richness increased with water availability in both areas. Mean site species richness and species turnover in space was higher in the mountain than in the flat area. Landscape species richness and floristic gradients were more concentrated in the mountain than in the flat area. In contrast to shrubs and grasses, forb species distributions were uncoordinated and probably independent of any environmental gradient. Our results suggest (1) that landscape configuration affects species composition and diversity through its direct effect on abiotic environmental heterogeneity, and (2) that the environmental controls of the community composition vary depending on the plant functional type considered.
Use of Plant Strategy Ordination, DCA and ANOVA to elucidate relationships among habitats of Salix planifolia and Salix monticola
Authors: Cottrell Tom R.
Published: May 2006

Abstract. Detrended Correspondence Analysis (DCA) was used on a data set of 112 species from 14 stands dominated by Salix planifolia and/or S. monticola. Environmental variables were determined which might be important to explain differences in stand vegetation composition, and willow stature (height), in willow carrs in the Rocky Mountain National Park. Correlation of environmental variables with DCA stand scores indicate that peat depth and soil redox potential are highly related to the primary DCA axis. Soils in stands of S. planifolia are more reduced in the early summer and have greater peat depths, than soils in stands of S. monticola. The second DCA axis is related to a water chemistry gradient of hydrogen ion, sulphate, and ammonium concentration. Four environmental variables selected by correlation analysis were regressed on stand scores from the first two DCA axes. Regression coefficients of August soil redox potential and soil water pH were significantly non‐zero on the primary DCA axis. In addition to overall vegetation relationships elucidated by DCA, the relationships between willow stature and environmental variables were tested by simultaneous ANOVAs. ANOVA results and DCA ordinations indicate that S. planifolia and S. monticola plants achieve the greatest stature in the least reduced soils, and in shallow peat. Competitive, stress tolerant, and ruderal plant strategy theory applied to the vegetation data produced an arrangement of stands highly correlated to the DCA Axis 1 stand arrangement. These correlations indicate that the primary axis of vegetation structure can be extracted either by species composition, or species morphology/physiology relationships. Concurrent use of DCA and plant strategy theory is suggested as a tool for the prediction of community composition.
Shrub emergence and seedling growth in microenvironments created by Prosopis glandulosa
Authors: Franco‐Pizaña Jesus G. , Fulbright Timothy E. , Gardiner Duane T. , Tipton Alan R.
Published: May 2006

Abstract. Facilitation of the establishment of certain plant species by nurse plants is a common phenomenon in arid and semiarid ecosystems. The most commonly reported mechanisms of facilitation include cooler temperatures and increased soil nutrients beneath the nurse plant canopy, which favor establishment of other plant species. During conversion of upland grasslands to thorn woodland in southern Texas, Prosopis glandulosa appears to facilitate establishment of other woody plants, including Celtis pallida, whereas Acacia smallii occurs only in habitats between P. glandulosa canopies. We tested the hypothesis that light intensity and soils under P. glandulosa canopies facilitate seedling emergence and growth of C. pallida but inhibit seedling emergence and growth of A. smallii. In the field, C. pallida and A. smallii seeds were planted under P. glandulosa canopies and in adjacent interspaces. Percent emergence of C. pallida seedlings was greater under the canopy of P. glandulosa, whereas percent emergence of A. smallii seedlings was greater in interspaces. In a greenhouse experiment, seeds of each species were planted in pots filled with soil from under P. glandulosa canopies or from adjacent interspaces. Two treatments, shade and sunlight, were imposed and plants harvested seven weeks later. Seedling mass of both species was greater in canopy soil than in interspace soil in sunlight but mass of the two species did not differ between soil sources in shade. Canopy soils contained more total and available nitrogen than interspace soils. These results suggest that light is more limiting than nutrients under shaded conditions and so neither species can take advantage of the high nutrients beneath P. glandulosa. Shade and greater soil nutrients beneath P. glandulosa do not appear to be the major factors that facilitate C. pallida or inhibit A. smallii. Aggregation of C. pallida beneath P. glandulosa canopies appears to be a complex process that involves both passive facilitation (seed dispersal by birds) and active facilitation (reduction of seed dormancy by under‐canopy temperatures) operating only during the seed germination stage with successional mechanisms other than facilitation operating during later stages of shrub establishment and growth.
Age structure and dynamics of Rhododendron ferrugineum L. populations in the northwestern French Alps
Authors: Pornon André , Doche Bernard
Published: May 2006

Abstract. The ericaceous shrub Rhododendron ferrugineum occupies large areas at the subalpine level (1600–2200 m) of the northwestern French Alps. It frequently reaches 90–100 % cover, accumulates 60–70t/ha (dry weight) above‐ground biomass and is able to dominate many subalpine landscapes by outcompeting other species. We formulated the hypothesis that the species shows a rapid and invasive seedling establishment and a fast population development. We investigated the age structure and development of two populations. Although classic colonization stages can be identified, and variation did occur depending on the site, R. ferrugineum populations showed a surprisingly slow development compared with other ericaceous species. Curves obtained from polynomial regression equations of cover on age allowed us to predict the future development of populations. Thus, depending on the site, it would take 150 to 250 yr to achieve total cover.

We discuss the factors involved that could explain this slow development and discuss which biotic and abiotic factors may be responsible for the large extension of this species in the subalpine belt.
Early post‐fire regeneration of a Pinus halepensis forest on Mount Párnis, Greece
Authors: Thanos Costas A. , Daskalakou Evangelia N. , Nikolaidou Sotiria
Published: May 2006

Abstract. The post‐fire regeneration of a 45‐yr‐old Pinus halepensis (Aleppo pine) forest, burned in July 1989, has been studied on Mount Párnis, Attiki, Greece. Four experimental plots at various slopes and exposures were established at altitudes of 400 ‐ 450 m, and monitored for 3 yr at 3‐month intervals. Early regeneration took place abundantly, through both resprouting and seed germination of mostly hard‐seeded herbs and shrubs; the floristic richness was high with 80 taxa. Pine seedling emergence took place during the winter of the first post‐fire year. The mean pine seedling density by the end of the recruitment period (March 1990) was 5–6 seedlings/m2. This density decreased slightly during late spring and considerably during summer. During the second post‐fire year only a relatively slight decline was observed; thereafter the density was stabilized to 1 ‐ 2 seedlings/m2. Mortality follows a negative exponential curve that levels off at ca. 20 %. Height distributions throughout the three post‐fire years were all positively skewed as a result of the presence of few very tall saplings. A considerable fraction (20 %) of very short (5–15 cm) saplings were still alive 39 months after the fire; these may constitute the sapling bank. Based on the analysis of height distribution curves, it is concluded that the taller seedlings survived significantly better than the shorter ones.
Geigeria alata in the Namib desert: seed heteromorphism in an extremely arid environment
Authors: Burke Antje
Published: May 2006

Abstract. Seed heteromorphism in annual Geigeria alata in the Namib Desert was investigated in relation to environmental conditions. Geigeria alata shows heteromorphism in seed dispersal distance depending on the position of the seeds on the parent plant. Seeds produced in capitula on branches (aerial) travel long distances, while seeds produced at the base of the plant remain in the vicinity of the parent plant. The ratio of aerial to basal seed production was investigated under different environmental conditions following an aridity gradient. Although there were significant differences in seed and capitula production between seasons and between different positions on the plant, no overall trend was found with increasing aridity.
Species attributes in early primary succession on volcanoes
Authors: Tsuyuzaki Shiro , del Moral Roger
Published: May 2006

Abstract. We predicted that plants that can establish on volcanic soils with similar disturbance histories will have similar growth characteristics. We tested this prediction by a multivariate analysis of 27 traits of 84 species found six years after an eruption on Mount St. Helens, Washington State, USA, and Mount Usu, Hokkaido, Japan. These traits include vegetative, life‐history, phenological and seed‐biology characteristics. Cluster analysis revealed five species groups: annual herbs, perennial forbs, graminoids, shrubs and trees. Each group has distinct vegetative, life‐history, and seed‐biology traits. Except for shrubs, which were lacking on Mount Usu, both floras were well represented in each group. On intensely disturbed sites on both volcanoes, perennial forbs, whose development is dependent primarily on well‐developed below‐ground organs and wind‐dispersal, expanded their cover more rapidly than did graminoids. These graminoids generally produce gravity‐dispersed seeds and have close‐set rhizomes and/or shoots. These results suggest that species that can establish during the early stages of succession on each volcano have similar vegetative, life‐history, and seed‐biology traits.
Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec
Authors: de Blois Sylivie , Bochard André
Published: May 2006

Abstract. Human impact influences patterns of plant distribution and dominates disturbance dynamics in the agricultural landscape of Haut‐Saint‐Laurent, Québec. We investigated the influence of such impact on the dynamics of Thuja occidentalis in the hardwood forest of southern Québec. A bimodal species of either dry or wet habitats, T. occidentalis has successfully invaded mesic sites of the study area where, although generally considered a poor competitor, it persists as dense populations that seem to resist invasion by more tolerant species. As Acer saccharum is expected to be a dominant latesuccessional species under mesic conditions, we first evaluated the relative importance of abiotic and historical factors in the distribution of 34 T. occidentalis stands and 21 A. saccharum stands. We then classified 55 stands that include T. occidentalis and investigated the dynamic relationships between the species and its associates in 13 mixed mesic sites.

Canonical correspondence analysis (CCA) of T. occidentalis and A. saccharum stands suggested that land use and drainage are the most important variables correlated with plant community composition. A partial CCA with drainage as the constraining variable showed that T. occidentalis stands were significantly associated to present or past use as pasture. Correspondence analysis of 55 stands where T. occidentalis is present produced a clear segregation between nearly monospecific stands and mixed communities, but the chosen environmental variables were not significant in explaining the vegetation gradient at this scale. In all mixed stands, Thuja occidentalis was most often associated with Ulmus americana, Acer rubrum, Betula populifolia, Fraxinus americana, A. saccharum, and Tsuga canadensis. Finally, size‐class ordination of 13 mixed mesic stands did not show convergence toward A. saccharum.

Our results suggest that grazing has played a significant part in the appearance of T. occidentalis stands on mesic sites, whereas competition processes and landscape patterns possibly contribute to the maintenance of relatively persistent T. occidentalis stands in the landscape.
Tree competition and species coexistence in a cool‐temperate old‐growth forest in southwestern Japan
Authors: Hara T. , Nishimura N. , Yamamoto S.
Published: May 2006

Abstract. The growth dynamics and mode of competition between adult trees ≥ 4 cm in DBH (stem diameter at breast height 1.3 m) of eight abundant species occupying ca. 90 % of the total basal area were investigated in a 4‐ha study plot (200 m × 200 m) of a cool‐temperate, old‐growth forest on Mount Daisen, southwestern Japan. In the study plot, 30 tree species with individuals ≥ 4.0 cm DBH co‐occurred. A bimodal DBH distribution showing upper and lower‐canopy layers was found for the most dominant and largest species, Fagus crenata (ca. 78 % of the total basal area), whilst other tree species showed unimodal DBH distributions corresponding mostly to the lower‐canopy layer. We developed a model for individual growth incorporating both intra and interspecific competition and the degree of competitive asymmetry. Onesided interspecific competition was detected only from Fagus crenata (upper‐canopy species) to Acer japonicum and Acanthopanax sciadophylloides (lower‐canopy species) on the scale of the 4‐ha study plot. Only Acanthopanax sciadophylloides showed symmetric intraspecific competition. However, a positive (non‐competitive) interspecific relationship between adult trees prevailed over a competitive relationship; for example, individual DBH growth rate of Fagus crenata (especially lower‐canopy trees) was correlated with the abundance of Acer mono. The positive relationship represented a group of species with similar habitat preference [soil type (mature or immature) caused by landslide disturbance and the presence/absence of Sasa dwarf bamboos in the understorey], where tree densities were not so high as to bring about competition. Competitive interactions between adult trees ≥ 4 cm in DBH occurred only locally between a few specific species and were suggested to be almost irrelevant to the variation in species coexistence on the 4‐ha scale of cool‐temperate forest. Rather, the coexistence of 30 tree species (species diversity) on this large scale was suggested to be governed by the regeneration pattern of each component species (habitat preference, seedling establishment, sapling competition) with respect to landslide disturbance.
A coupled carbon and water flux model to predict vegetation structure
Authors: Haxeltine Alex , Prentice I. Colin , Creswell Ian David
Published: May 2006

Abstract. A coupled carbon and water flux model (BIOME2) captures the broad‐scale environmental controls on the natural distribution of vegetation structural and phenological types in Australia. Model input consists of latitude, soil type, and mean monthly climate (temperature, precipitation, and sunshine hours) data on a 1/10° grid. Model output consists of foliage projective cover (FPC) for the quantitative combination of plant types that maximizes net primary production (NPP). The model realistically simulates changes in FPC along moisture gradients as a consequence of the trade‐off between light capture and water stress. A two‐layer soil hydrology model also allows simulation of the competitive balance between grass and woody vegetation including the strong effects of soil texture.
Species richness of Argentine cacti: A test of biogeographic hypotheses
Authors: Mourelle Cristina , Ezcurra Exequiel
Published: May 2006

Abstract. Patterns of species richness are described for 50 columnar, 109 globose and 50 opuntioid cacti species in 318 grid cells (1° x 1°) covering Argentina. Biological richness hypotheses were tested by regressing 15 environmental descriptors against species richness in each group. We also included the collection effort (estimated as the logarithm of the number of herbarium specimens collected in each cell) to estimate the possible error induced by underrepresentation in certain cells. Log‐linear regression models accounted for a large portion of the variation in richness of columnar species, opuntioid species, globose species and all forms combined. Opuntioid and globose species richness was associated with percentage summer rainfall. Columnar species richness was associated with the number of frost‐free days. The distribution of columnar cacti seems to be limited by freezing temperatures. The results are consistent with the climate favourableness and climatic variation hypotheses, but do not support the hypothesis that energy flow limits regional species richness.

Altitudinal range (a measure of habitat heterogeneity) was related to richness of globose cacti. A floristic affinity analysis between geographic provinces and the distribution of the different growth forms confirmed the high degree of endemism of globose cacti and the cosmopolitanism of the opuntioid ones. Two cells in the Prepuna and northern Monte Provinces showed species richness values that were significantly higher than those predicted by the log‐linear model. This is interpreted in terms of Quaternary historical events having affected the main South American biomes.
An application of fuzzy set ordination to determine tree habitat suitability of sites from a regional data set
Authors: Fulton Mark R.
Published: May 2006

Abstract. Fuzzy set ordination is employed to evaluate sites on the basis of their suitability for particular tree species. The technique orders sites along an axis defined by the presences and absences of a given species of interest. A rationale is given in terms of noise reduction; in many situations the overall vegetation of a site will reflect habitat conditions better than the presence, absence, or quantitative performance of any single species. A data set of tree presence/absence covering a large part of the southeastern United States was analyzed and habitat suitability scores were calculated for each species. Monte‐Carlo tests were used to measure the statistical power of the data set with regard to habitat preferences; 38 of the 49 species have cumulative frequency distributions showing significant departures from random expectation. Most statistically significant habitat preferences seem to be related to geographic range limits located within the study area, but some species found throughout the area also show significant departures from random expectation. The method may find applications in autecological studies of species, selection of representative site conditions for simulation modeling, and the solution of certain technical problems in ordination.
Spatial patterning in the canopy gap regime of a subalpine Abies‐Picea forest in the northeastern United States
Authors: Battles John J. , Fahey Timothy J. , Harney Ellen M.B.
Published: May 2006

Abstract. Spatial patterning in the disturbance regime of a forest affects the vegetation dynamics. Therefore, the distribution of canopy gaps was examined in detail for a subalpine Abies‐Picea forest in the northeastern United States. Gaps were not randomly distributed. The fraction of forest area in gaps and the abundance of gaps varied significantly with topographic position, elevation, and slope percent. On average, 15 % of the forest was influenced by gaps, but the gap fraction was greater near ridges (23 %) and near streams (27 %) than on the backslope (13 %). Also, gaps were larger and more abundant near streams and ridges. Gap fraction varied with elevation as well: more of the forest was disturbed at lower and higher elevations than at mid‐elevations. Significantly more of the forest on steep slopes (≥ 30 %) was under gaps. As a result of this patterning, some parts of the Abies‐Picea forest were predictably more disturbed than others. A remaining question is whether this patterning is sufficient to influence the regeneration environment and thus forest composition.
Neighbour interaction and stability in subalpine meadow communities
Authors: Kikvidze Z.
Published: May 2006

Abstract. The ability of a plant community to maintain favourable conditions within its canopy was examined by means of removing the vegetation around individual plants (radius ca. 1 m) and measuring light and temperature relations and rates of net photosynthesis in both isolated and sward plants. The results suggest that neighbour interactions are important for the stabilization of environmental relations within the canopy, at least in hay meadows as compared to intensively grazed pastures. The canopy may maintain optimal conditions for plant life within a wider variation of environmental factors. At the same time, plants have to adapt to contrasting (sunny vs. cloudy) weather conditions occurring with about equal frequency during the vegetation period in the central Caucasus.
A taxonomic, biogeographical and ecological overview of invasive woody plants
Authors: Binggeli Pierre
Published: May 2006

Abstract. Invasive plants are considered to be a major threat to the earth's biodiversity, but have not been sufficiently investigated. To address this problem a relational database on invasive woody plants has been set up. It is based on 2045 bibliographical references and contains records on 653 species representing 110 families. The families with the largest number of invasive species are: Rosaceae, Mimosaceae, Papilionaceae and Pinaceae. Out of 1060 recorded invasive events an equal number are reported from continents and oceanic islands. The highest number of invasive woody species are recorded from Europe, followed by the Pacific islands, North America, New Zealand, Australia, Indian Ocean islands and southern Africa. Included in these regions are areas which have fewer highly invasive species, e.g. islands on continental shelves, such as the British Isles. Although most invasions occur in disturbed habitats, most natural communities are susceptible to woody plant invasions. Data on species attributes are only available for a minority of species but indicate that invasive woody plant species may be either insect or wind‐pollinated, have a wide array of fruit types, fruit and seed sizes, number of seeds per fruit and dispersal agents. The relative frequency of several attributes varies with the degree of invasiveness. Thus it is not yet possible to determine which set of attributes favours invasiveness and therefore it is difficult to make predictions.
Vegetation ecology of flatwoods on the Illinoian till plain
Authors: Taft John B. , Schwartz Mark W. , Philippe Loy R.
Published: May 2006

Abstract. Midwestern flatwoods are open woodlands of level uplands and terraces that occur on impervious subsoil horizons and have seasonally wet and dry soils. Vegetation and soil data from six flatwoods remnants on the Illinoian till plain in Illinois were examined to identify what biotic and edaphic factors control vegetation structure, composition and diversity. Soils at all sites are characterized by the presence of argillic horizons (clay pans). Two soil ordination groups were clearly defined, each characterized by separate parent material origin. Canopy and subcanopy composition are dissimilar at sites with soils developed entirely in loess; more similar at sites on lacustrine soils (including aeolian sand). Quercus stellata was by far the most important tree species followed by Q. marilandica. Q. stellata importance was negatively correlated with Ca, particularly in the A‐horizon. Q. marilandica shows a positive correlation to sand and magnesium, particularly in the B‐horizon, and was most frequent and abundant on soils where Ca/Mg ratios are lower than 1.0 in the E and B‐horizons. Total stem density of woody plants was positively related to total available soil moisture as influenced by depth to clay pan and soil textural differences. Ground‐cover species richness and diversity were inversely related to tree and total woody stem density and tree diversity. One site with a recent history of annual prescribed fire had significantly greater ground‐cover species diversity compared with the unburned sites. Evidence from stand structure and similarity between canopy and subcanopy strata, if reflecting stationary processes of canopy recruitment, suggest that disturbances historically maintained the importance of oak species in most flatwoods. Prescribed fire appears to maintain or enhance ground‐cover species diversity at one flatwoods remnant, suggesting that fire could be used to maintain compositional stability at sites with greater available soil moisture.
Invasion by Heracleum mantegazzianum in different habitats in the Czech Republic
Authors: Pyšek Petr , Pyšek Antonín
Published: May 2006

Abstract. Heracleum mantegazzianum, a tall forb from the western Caucasus invaded several different habitats in the Czech Republic. The relation between invasion success and type of recipient habitat was studied in the Slavkovskù les hilly ridge, Czech Republic. The vegetation of 14 habitat types occurring in an area of ca. 25 km2 was analysed using phytosociological relevés, and the invasion success of Heracleum (in terms of number of localities, area covered and proportion of available area occupied) was recorded separately in each of them. Site conditions were expressed indirectly using Ellenberg indicator values. The hypothesis tested was that Heracleum spreads in the majority of vegetation types regardless of the properties of the recipient vegetation.

Community invasibility appeared to be affected by site conditions and the composition of the recipient vegetation. The species is not found in acidic habitats. Disturbed habitats with good possibilities of dispersal for Heracleum seeds are more easily invaded. Communities with a higher proportion of phanerophytes and of species with CS (Competitive/Stresstolerating) strategy were more resistant to invasion. The invasion success was bigger in sites with increased possibilities of spread for Heracleum diaspores. Communities invaded by Heracleum had a lower species diversity and a higher indicator value for nitrogen than not‐invaded stands. It appears that species contributing to community resistance against invasion of Heracleum, or capable of persisting in Heracleum‐invaded stands, have similar ecological requirements but a different life strategy to the invader.
Classification of peatland vegetation in Atlantic Canada
Authors: Wells E. Doyle
Published: May 2006

Abstract. The peatlands of Atlantic Canada are classified in four plant alliances, consisting of 10 plant associations. The four plant alliances comprise the dry bog communities (Kalmio‐Cladonion Wells 1981), wet bog communities (Scirpo‐Sphagnion Wells 1981), hummock and ridge communities of slope and string fens (Betulo‐Sphagnion Wells all. nov.), and poor, intermediate and rich fen plant communities (Scirpo‐Myricion Wells 1981). Distribution maps are presented for relevés in each of the 10 associations. Based on species distributions, floristic regions are defined for peatlands in Atlantic Canada. Nutritional characteristics are also described for each plant association. pH and total soil concentrations of calcium, nitrogen and iron proved reliable in separating bog from fen. A boundary between ombrotrophic peatlands and minerotrophic peatlands is suggested, based on a soil pH of 4.0, total soil concentrations of 3.0 mg g−1 Ca, 4.0 mg g−1 Fe, 13.0 mg g−1 N and a Ca/Mg ratio of 2.5. Comparisons between the syntaxa for peatlands in Atlantic Canada and those in Europe are discussed for higher taxa. The possibility of establishing a new order (Chamaedaphno‐Scirpetalia Wells ord. nov.) for peatlands in Atlantic Canada is also discussed.
Understorey foraging and habitat selection by sheep in mixed Atlantic woodland
Authors: Garin I. , Aldezabal A. , Herrero J. , García‐Serrano A.
Published: May 2006

Abstract. The main objectives of this study were to investigate sheep foraging behaviour in mixed Atlantic woodland and to assess its impact on the forest understorey. We established 89 plots along four forest types: Fagus woodland, Quercus woodland, riparian gallery forest and conifer plantations. The presence of plant species in the forest understorey and their foraging damage was surveyed bimonthly from July 1996 to June 1997. In addition, we estimated the selection of woodland types by sheep through the pellet‐group count technique. The intensity of foraging by sheep was negligible for most of the plant species, however several species showed substantial damage in some woodland types. Among the species that were abundant and widespread in the entire study area, Rubus ulmifolius, graminoids and Ilex aquifolium were consumed most. Sheep selected only larch plantations, where grasses and Rubus were very abundant. This grazing behaviour reduced browsing damage of the understorey of woodland stands with higher conservation value, such as Quercus and Fagus woodlands.
Carbon balance gradient in European forests: Interpreting EUROFLUX
Authors: Piovesan G. , Adams J.M.
Published: May 2006

Abstract. A latitudinal trend in forest carbon uptake across Europe has been described by the EUROFLUX group, suggesting a considerable uptake in Italian Quercus ilex, Fagus sylvatica and Picea abies forests while a much lower C sink is reported in Scandinavian Picea abies forest. These results are discussed on the basis of the existing literature, and considered to be open to considerable doubt.
Impact of cattle dung deposition on the distribution pattern of plant species in an alvar limestone grassland
Authors: Dai Xiaobing
Published: May 2006

Abstract. Seed banks in cattle dung, soil under cattle dung and soil under vegetation and growth response of plant species to the changes in soil nitrogen availability were studied in an alvar limestone grassland on Öland, Sweden, in order to analyse the impact of dung deposition and decomposition on the formation of patches of plant species. Results suggest that patches of four plant species could result from cattle dung deposition and decomposition. Impact of dung could proceed in three ways: (1) by changing the relative abundance of species in the soil seed bank under dung, and/or (2) by influencing the deposition of seeds in the dung, and/or (3) by intensifying the growth of some species through nutrient release. Species patches could result from one or more of these aspects. For instance, patches of Arenaria serpyllifolia may be induced by dung deposition because of the dominance of its seeds in dung, while the pattern of Cerastium semidecandrum and Festuca ovina may be due to the abundance of their seeds in the soil seed bank under dung and their positive growth response to increased nitrogen availability.
Biomass accumulation over the first 150 years in coastal Oregon Picea‐Tsuga forest
Authors: Acker Steven A. , Harcombe Paul A. , Harmon Mark E. , Greene Sarah E.
Published: May 2006

Abstract. Production and mortality are the component processes that together determine the biomass dynamics of forests. Due to the significant role of forests in the global carbon cycle, it is important to assess how these two processes affect the maximum biomass attained by forests, as well as the dynamics leading up to and following peak biomass. We address these questions for two sets of plots in Picea sitchensis‐Tsuga heterophylla forest on the northern Oregon coast that originated from a catastrophic wildfire in the 1840s, using new data on dynamics of live trees and stocks of coarse woody debris (CWD). The set of plots closest to the ocean and occupying steeper, more dissected terrain with areas of thin soils has lower biomass, lower net primary production (NPP) of bole wood and higher tree mortality as a fraction of standing biomass. The two sets of plots have similar CWD levels, most of which has accumulated in the last 25 yr. The present disparity in biomass between the two sets of plots appears to be the result of lower NPP on the low‐biomass plots for the entire 140+ yr history of the forest. Over the 58 yr that the high‐biomass plots have been measured (from stand age 85 to 143 yr), NPP of bole wood has declined by 41%. Only ca. 6% of this decline can be accounted for by an increase in maintenance respiration of woody tissues. For both sets of plots relative constancy of biomass in the long term appears likely, due to a short time lag in tree regeneration, asynchronous tree mortality and little overall decline in NPP of bole wood in recent decades. However, since tree mortality as a fraction of standing biomass is higher on the low‐biomass plots, and NPP of bole wood is slightly lower, the difference in biomass between the two sets of plots should increase if current rates of production and mortality persist.
Static and dynamic approaches to landscape heterogeneity in the Hungarian forest‐steppe zone
Authors: Fekete Gábor , Virágh Klára , Aszalós Réka , Précsényi István
Published: May 2006

Abstract. This paper describes the successional status of the vegetation in a clear‐felled dry oak woodland at the edge of the Hungarian forest‐steppe zone on the basis of a vegetation map. Due to a varied geomorphology of the colline landscape several so‐called landscape units can be distinguished. The patchwork on the vegetation map is evaluated using several, morphology‐based attributes (static morphological indices) traditionally applied in landscape ecology. In the ca. 100 years that elapsed since forest clear‐cut, xeric grassland species and steppe elements became more abundant and the former xeromesophilous vegetation – containing even some woodland components – is slowly turning into xeric grassland communities. The vegetation units mapped can be arranged into a hypothetical succession scheme in which successional distances (the number of steps between two stages) are determined. Based on the distances thus obtained, a new dynamic morphological index is introduced. This is applied to each landscape unit for the dynamic evaluation of successional vegetation, its results being compared with those obtained by static morphological indices.
Plant responses and herbivory following simulated browsing and stem cutting of Combretum apiculatum
Authors: Bergström Roger , Skarpe Christina , Danell Kjell
Published: May 2006

Abstract. Time and mode of herbivory on savanna trees and their subsequent responses are dependent on, among other things, earlier herbivory and fire. We used clipping (simulated browsing) and stem cutting (simulated heavy browsing and to some extent simulated fire) to evaluate such interactions. Study organisms were a deciduous, broad‐leaved tree species, Combretum apiculatum (Combretaceae), browsing large herbivores and leaf‐eating insects. The treatments were done in the late dry season before bud break. Late in the following wet season, we recorded plant responses to treatment and browsing. The treated trees, especially the cut ones, responded by producing larger and fewer annual shoots. Compared to control trees, there was a slight increase in shoot biomass of clipped trees and a strong reduction of cut ones. Leaf area increased in clipped trees, but decreased in cut ones. A marked increase in the number of browsed trees was recorded amongst treated trees. Number of bites, consumption and utilization also increased with severity of treatment. In contrast, insect herbivory was reduced on both clipped and cut trees. The observed patterns are discussed in relation to current ideas on plant ‐ herbivore interactions.
Dynamics of submersed aquatic vegetation on shallow soft bottoms in the Baltic Sea
Authors: Idestam‐Almquist Jerker
Published: May 2006

Abstract. Persistence and colonization of submersed aquatic plant species were studied in permanent plots (20 cm × 20 cm) at three shallow sites adjacent to Askö island, in the northern Baltic Sea. The study started in 1991 at two of the sites, in 1992 at a third site and continued until 1997. Two major weather‐induced disturbances occurred during the study: a long, stormy period during a mild winter and a cold winter with extreme low water levels. The stormy period caused a large loss of species from plots (95 ± 5% SE) at the most wave‐exposed site, resulting in a low species number per plot (0.8 ± 0.2) the following summer. During the three following years the mean species number increased to 3.6 ± 0.2. The cold winter caused high species turnover and increased species number per plot at the two most wave‐exposed sites. The species turnover at the sheltered site was highest in the two years with low water level in May, possibly due to increased waterfowl herbivory. Annuals, loosely anchored and highly reproductive species had significantly higher plot colonization rates and lower persistence than perennials, well‐anchored species and species with none or low reproduction. The extent of lateral growth had no significant effect on colonization or persistence.

Although these disturbances have a large effect on the dynamics, species mobility was also high in other years. Relative to other, similar, studies in terrestrial vegetation mean persistence in plots was remarkably low and mean mobility and species turnover rates were very high.
Geomorphic principles of terrain organization and vegetation gradients
Authors: Bridge S.R.J. , Johnson E.A.
Published: May 2006

Abstract. Moisture and nutrient gradients consistently explain much of the variation in plant species composition and abundance, but these gradients are not spatially explicit and only reveal species responses to resource levels. This study links these abstract gradients to quantitative, spatial models of hill‐slope assembly. A gradient analysis in the mixed‐wood boreal forest demonstrates that patterns of upland vegetation distribution are correlated to soil moisture and nutrient gradients. Variation in species abundance with time since the last fire is removed from the gradient analysis in order to avoid confounding the physical environment gradients. The physical‐environment gradients are related to qualitative positions on the hill slope i.e. crest, mid‐slope, bottom‐slope. However, hill‐slope shape can be quantitatively described and compared by fitting allometric equations to the slope profiles. Using these equations, we show that hill‐slope profiles on similar surficial materials have similar parameters, despite coming from widely separated locations. We then quantitatively link the moisture and nutrient gradients to the equations. Moisture and nutrients significantly increase as distance down‐slope from the ridgeline increases. Corresponding vegetation composition changes too. These relationships characterize the general pattern of vegetation change down most hill slopes in the area. Since hill slopes are a universal feature of all landscapes, these principles may characterize landscape scale spatial patterns of vegetation in many environments.
Limitations to plant establishment on eroded slopes in southeastern Spain
Authors: García‐Fayos Patricio , García‐Ventoso Belen , Cerdà Artemi
Published: May 2006

Abstract. The possible causes for the lack of vegetation in five badland sites from southeast Spain were experimentally tested. The main factors affecting seed germination and seedling survival considered were seed availability, regolith water dynamics in relation to rain events, regolith salinity, seedling predation by herbivores and seedling removal by erosion.

Four issues are addressed: 1. Both rainfall and the temporal and spatial dynamics of regolith water during the seedling emergence period were monitored in five different zones at one site (Petrer, Alicante). 2. Effects of salinity and water potential on the rate and speed of germination of local seeds were determined. 3. Seed reserve and seedling emergence and mortality were followed throughout one season. 4. Regolith characteristics of all five sites were compared and the consequences for plant colonization discussed.

The main factor limiting plant colonization in these sites was the very short duration of available water in the soil, due to the physical and chemical characteristics of the regolith. In addition, high regolith salinity and its effects on seed germination, the aspect of the site and the pattern of rain events, played a very important role reducing germination and survival. Herbivory and erosion were seldom responsible for seedling mortality. However, there were no highly erosive rain events during the study period, although several have been measured during the past few years.
Fine‐scale vascular plant species richness in different alpine vegetation types: relationships with biomass and cover
Authors: Grytnes John Arvid
Published: May 2006

Abstract. Vascular plant species richness was related to biomass and vegetation cover in nine different alpine vegetation types on the Hardangervidda mountain plateau, western Norway. Each vegetation type was sampled within an 8m × 6m area, and the species‐richness pattern analysed. Evidence for a unimodal relationship between species richness and both biomass and cover was found at the within‐vegetation type scale. Cover was a better predictor for species richness than biomass, suggesting that light may be an important factor influencing species richness at this scale in alpine vegetation. The possibility that the results are an artefact of small grain size is also discussed, and several arguments for an ecological explanation of the humpback relationship between species richness and cover are discussed.
Effects of surface disturbance and light level on seedling emergence in a Japanese secondary deciduous forest
Authors: Kobayashi M. , Kamitani T.
Published: May 2006

Abstract. The effects of soil surface disturbance and light level on seedling emergence were examined by creating experimental conditions differing in soil surface treatment and light level in a temperate deciduous broadleaved secondary forest in central Japan. The results of MANOVA showed that soil surface disturbance exerted a favourable influence upon the seedling emergence of many species. Effect of soil disturbance on total density and number of emerged species was greater than that of a high light level. The interaction between soil surface disturbance and light level revealed significant positive effects for seedling emergence, especially for small‐seeded species. The relationship between the percentage of emerged seedlings and seed weight was significantly negative in the soil‐surface disturbed and high light level condition, suggesting that minute‐seeded species largely depend on both factors for seedling emergence. Both soil surface disturbance and high light level had a positive effect on the number of emerged species, suggesting that these factors contributed to species richness at the stage of seedling emergence.
Effects of repeated burning on species richness in a Florida pine savanna: A test of the intermediate disturbance hypothesis
Authors: Beckage Brian , Stout I. Jack
Published: May 2006

Abstract. We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaike's Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model.