bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of species interactions on community organization along a trampling gradient
Authors: Ikeda H. , Okutomi K.
Published: May 2006

Abstract. Effects of interspecific interactions on the organization of two trampled communities, Eragrostio ferrugineae ‐ Plantaginetum asiaticae (EP) and Eleusino indicae ‐ Digitarietum violascentis (ED), were examined by 4‐yr field experiments. We compared changes in the relative abundance of the main component species of the communities in monoculture and mixed culture along a trampling gradient. At no trampling in mixed culture, Ambrosia artemisiifolia var. elatior and Erigeron annuus (roadside herbs, RH) predominated and excluded the trampled community species. Severe trampling markedly reduced the predominance of these roadside herbs, promoted Eragrostis ferruginea (a perennial grass of EP), but suppressed Eleusine indica (an annual grass of ED). These results suggest that the differentiation of trampled and roadside herb communities under heavy trampling are caused by asymmetric competition between their main species.

Several species pairs showed a constant rank order of relative cover at high trampling levels. Pennisetum alopecuroides (a perennial grass of both RH and EP) and Eragrostis coexisted, indicating symmetric competition. Eragrostis and Plantago asiatica (a perennial herb of EP) or Poa annua (a winter‐annual grass of both EP and ED) coexisted through separation in phenology. Eragrostis promoted the survival of Plantago by moderating unpredictable drought (commensalistic positive interaction). This suggests that community composition is maintained by several interspecific interactions.
Community composition and soil properties in northern Bolivian savanna vegetation
Authors: Haase Rainer
Published: May 2006

Abstract. Direct gradient analysis (Canonical Correspondence Analysis) of northern Bolivian savanna vegetation revealed correlations between the composition of plant communities and physical and chemical soil properties. Cover/abundance values for 193 species from 27 sites were related to data on eight soil factors. A water‐regime variable and the percentage of sand and silt were correlated with the first axis of the species‐environment biplot and explained most of the variation in community composition. Along this axis, species and sites of flood‐plain vegetation were separated from sites not affected by flooding rivers. The second axis of the biplot was correlated with soil‐chemical variables, namely extract‐able phosphate, base saturation, organic carbon, pH, and effective cation exchange capacity.

Part of the variation in community composition can be explained by these soil nutrient variables. Grassland communities were separated from woody vegetation along the soil nutrient gradient, and floodplain communities of white‐water rivers from those of clear‐water rivers.

The results of the gradient analysis indicate that the soil texture‐moisture gradient is the prime factor determining the variation in the floristic composition of the savanna communities examined, and that, in addition, the soil nutrient gradient accounts for some of the variation.
Environmental correlates of species distributions in a saxicolous lichen community
Authors: John Elizabeth , Dale M. R. T.
Published: May 2006

Abstract. The importance of abiotic environmental factors in determining species distributions in a saxicolous lichen community at Jonas Rockslide, Jasper National Park, Alberta is assessed using Canonical Correspondence Analysis. This technique allows ordination of species on axes determined by measured environmental variables. The suitability of this technique for handling data which may not be normally distributed is confirmed by comparison with the results obtained using a non‐parametric correlation coefficient. The variables found to be most highly correlated with species distributions are altitude on the rockslide and inclination from horizontal of the rockface (slope). These variables are thought to determine temperature and water availability at the rock surface. Using the first two ordination axes, species can be divided into groups, based on shared responses to the measured environmental variables.
Physiognomic development of Pseudotsuga forests in relation to initial structure and disturbance intensity
Authors: Halpern Charles B. , Franklin Jerry F.
Published: May 2006

Abstract. Physiognomic patterns may vary significantly during succession despite a tendency for larger‐growth forms to gradually replace smaller ones. Development of understory structure was observed for 25 yr after harvest of Pseudotsuga forests on two sites in the western Cascade Range, Oregon. We examine the influences of disturbance intensity and initial vegetation structure on the origin, direction, and rate of physiognomic change.

Broad‐scale changes in vegetation structure differed between sites. On Watershed 1, herbs dominated for 11 yr, after which shrubs became co‐dominant. In contrast, Watershed 3 never exhibited a distinct, transitional shrub phase ‐ herbs dominated for 18 yr, after which trees assumed co‐dominance.

The pattern and rate of physiognomic succession also varied among pre‐disturbance plant communities and with disturbance intensity. Differences among communities largely corresponded with initial vegetation structure, reflecting the disturbance tolerance of forest herbs and shrubs. Canopy closure occurred most rapidly in the initially depauperate, but tree‐dominated Coptis community. Along the disturbance gradient, shifts from herb to shrub dominance occurred earlier on burned than on unburned sites due to rapid development of invading shrubs, whose germination and establishment were stimulated by fire. However, subsequent transitions to tree dominance showed no clear relationship with disturbance intensity.

These long‐term trends suggest that pre‐disturbance community structure and disturbance intensity are major determinants of physiognomic succession, but that their effects may be modified by historical or stochastic factors such as limited seed availability or local fluctuations in weather.
Arranging phytosociological tables by species‐relevé groups
Authors: Bruelheide Helge , Flintrop Thomas
Published: May 2006

Abstract. A newmethod of arranging phytosociological tables by species‐relevé groups (blocks) on the basis of the density of rows and columns (relative species frequency and relative species number) is presented. Each block fulfils a given minimum criterion regarding its density. With a density threshold of e.g. 50 %, blocks are formed with only those species that are present in at least 50 % of the block's relevés, while at the same time the block's relevés comprise at least 50 % of the block's species. The procedure starts with the complete table and iteratively masks species and relevés with the smallest densities. This is performed step by step with species and relevés and continues until the given density threshold for all species and relevés is exceeded. Without any further parameters other than the minimum density, species‐relevé groups of gradually decreasing size are formed. Data processing is performed with a computer program (ESPRESSO). The main application of the method is found in an effective pre‐sorting of relevé data. The blocks formed can be arranged in the final table as desired.
Predicting vegetation types at treeline using topography and biophysical disturbance variables
Authors: Brown Daniel G.
Published: May 2006

Abstract. The relationships between four vegetation types and variables representing topography and biophysical disturbance gradients were modeled for a study area in east‐central Glacier National Park, Montana. Four treeline transition vegetation types including closed‐canopy forest, open‐canopy forest, meadow, and unvegetated surfaces (e.g. rock, snow, and ice) were identified and mapped through classification of satellite data and subsequent field verification. Topographic characteristics were represented using a digital elevation model and three variables derived from topoclimatic potential models (solar radiation potential, snow accumulation potential, and soil saturation potential). A combination of generalized additive and generalized linear modeling (GAM and GLM, respectively) techniques was used to construct logistic regression models representing the distributions of the four vegetation types. The variables explained significant amounts of variation in the vegetation types, but high levels of variation remained unexplained. A comparison of ‘expected’ and ‘observed’ vegetation patterns suggested that some unexplained variation may have occurred at the basin scale. A suite of tools and techniques is presented that facilitates predicting landscape‐scale vegetation patterns and testing hypotheses about the spatial controls on those patterns.
Species‐area relations in a New Zealand tussock grassland, with implications for nature reserve design and for community structure
Authors: Gitay Habiba , Roxburgh Stephen H. , Wilson J. Bastow
Published: May 2006

Abstract. A tussock grassland, in Blackrock Reserve, New Zealand, was sampled thoroughly at scales ranging from 0.01 m x 0.01 m to 20 m x 20 m, to investigate species‐area relations of relevance to plant community structure, and to offer a pointer to reserve design. In total, 96 species were found. Of the native vascular species among these, 20% were new records for the reserve.

For the total and the native vascular flora the observed points fell midway between the Arrhenius and Gleason fitted curves. Cryptogams fitted the Arrhenius model well, with z close to the 0.26 value expected for isolates under Preston's Canonical hypothesis. Extrapolation of the Arrhenius curve to the whole of the New Zealand uplands gave values far too large; the Gleason curve gave values much too low.

A General Root model is introduced. It fits the observed species richnesses at various quadrat sizes considerably better than previous models. When biogeographic limitations on species richness are included, extrapolation of the General Root curve accurately predicts the size of the upland flora. This fit, the lack of an asymptote, and the rarity structure, are compatible with a random and individualistic model of community structure. However, there are differences in species‐area relation between vascular and cryptogamic plants, which cautions against expecting any universal type of community structure.

Extrapolations using the General Root model suggest that if the ideal is a 10 km x 10 km reserve, a reserve one tenth that size would contain 81% of the native species in that ideal, and the present Blackrock Reserve contains 67%.
Vegetation structure and dynamics of Pinus gerardiana forests in Balouchistan, Pakistan
Authors: Ahmed Moinuddin , Ashfaq Mohammad , Amjad Mohammad , Saeed Mohammad
Published: May 2006

Abstract. 44 forest stands, including 42 stands with Pinus gerardiana Wall, ex Lamb dominant and two stands with broad‐leaved trees, were sampled in the Suleiman Range in Balouchistan. Density oi Pinus gerardiana trees ranged from 24 to 930 trees / ha with a mean of 266 individuals / ha; the average basal area was 25.5 m2 ha‐1.

Adequate recruitment of Pinus seedlings was observed; higher seedling density is recorded from east‐facing slopes, while tree density was higher on west‐facing slopes.

The average growth rate was estimated as 0.08 cm / yr radial growth. However, trees on high elevations and cooler slopes grow faster.

Soil variables showed no correlation with density, basal area or importance values. It is suggested that the present degraded stage of the forests in the study area is of anthropogenic origin.
The shrubland vegetation in western Shewa, Ethiopia and its possible recovery
Authors: Zerihun Woldu , Backéus Ingvar
Published: May 2006

Shrubland vegetation and environmental data in western Shewa, Ethiopia have been analysed. Vegetation data include cover‐abundance values of vascular plant species; environmental data comprise physical and chemical properties of the soil, altitude, slope, grazing and browsing pressure.

The vegetation data were subj ected to hierarchical and non‐hierarchical classification and ordination with correspondence analysis. The classification resulted in seven different vegetation types, ranging from grassland with scattered shrubs to degenerated forest. Ordination of the data and biplot analysis showed that the vegetation is influenced by anthropogenic factors and altitudinal variation. Sand content is related to a low level of anthropogenic influence whereas silt content is related to a high level. This is explained by historical events rather than by the present situation. Total nitrogen, organic carbon, altitude and slope are positively correlated and these variables are negatively related to anthropogenic influences.

The shrubland vegetation may have expanded from lower altitudes and drier sites as forests gradually disappeared.

The recovery of an economically more rewarding vegetation type may be achieved through pro viding alternative sources of fuel and construction and through prohibiting cultivation and grazing in the shrublands on the hillsides. Regeneration can be accelerated by actively introducing seedlings of tree species that do not need a heavy canopy cover for establishment and growth.
Changes in Cytisus balansae populations after fire
Authors: Fernández‐Santos Belén , Gómez‐Gutiérrez José M.
Published: May 2006

Abstract. Demographic changes in Cytisus balansae populations were studied during the first 10 yr after a fire, by comparing populations of different ages in which different cohorts were considered. In the study area this species constitutes a monospecific formation which undergoes periodic burning. We distinguished both new genets (seedlings or plants originating from seedlings, after the last fire) and three types of ramets (resprout clumps): rootstock ramets, basal‐branch ramets and lateral‐root ramets.

We found that C. balansae regenerated rapidly after fire. Most seedlings, rootstock ramets and basal‐branch ramets emerged in the first year after fire. Lateral‐root ramets appeared mainly after 2 ‐ 4 yr and continued to emerge in the following years. The numbers of ramets and new genets decreased with time, mainly during the first six years. Density variations between quadrats within each population also decreased. Survivorship varied between seedlings and type of ramet, and according to time of emergence. Survival curves for seedlings which emerged in the first year were concave, for rootstock ramets convex, and for the remainder of the ramets intermediate.

The 10‐yr‐old population was dominated by rootstock ramets. Some were entirely dead but most of them had only some dead basal branches. At this age new lateral‐root ramets were still emerging. The future of C. balansae populations is discussed on the basis of results obtained for old (25 ‐ 30 yr) plants, growing in the prolonged absence of fire.
Effects of artificial plant cover on plant colonization of a bare peat surface
Authors: Salonen Veikko
Published: May 2006

Abstract. This paper describes the effect of artificial plant cover on plant colonization of a bare peat surface, resulting from peat harvesting. Plant species colonization was compared on plots supplied with plastic models simulating Vaccinium vitis‐idaea plants and plots without this artificial cover. After two growing seasons, species composition and total biomass of the established plant cover were similar in the two plot types. However, the number of established seedlings in the plots with artificial cover was significantly higher than that in the plots without cover.

Out of 13 species observed four differed significantly in their performance on the two plot types. Betula spec. had both higher seedling numbers and higher biomass on the test plots; Deschampsia cespitosa had a higher biomass, whereas the seedlings were too numerous to be counted; Salix phylicifolia had higher seedling numbers. On the contrary, the number of seedlings of Epilobium angustifoliwn was lower on plots with artificial cover.

It is suggested that colonization by Betula, D. cespitosa and S. phylicifolia was facilitated mainly by the improved microclimatic and soil moisture conditions under the artificial plant cover. On the other hand, germination of E. angustifolium may be negatively influenced by the increased shade on the test plots.
Plant‐species richness and extinction on isolated dunes along the rocky coast of northwestern Spain
Authors: Obeso J. R. , Aedo C.
Published: May 2006

Abstract. Data on distribution and abundance of rare plant species on isolated coastal dunes along the rocky coast of northwestern Spain were compared with the local floristic literature in order to reconstruct past distribution and local extinction of species. Species extinction was not confined to species with a narrow distribution but also included widely distributed ones. Moreover, there was no evidence of colonization. Species number was related to beach and dune area, but species differed in the minimum area required for occurrence. The largest dune reserve possible would probably be insufficient to avoid further extinctions, so also small areas containing particular species should be preserved. There was no significant relationship between abundance of species in the local dune communities and their total distribution, and there were few satellite species. The former might be attributed to low fertility and habitat diversity.
Vegetation‐environment relations along water courses in the Nile Delta region
Authors: Shaltout K. H. , El‐Sheikh M. A.
Published: May 2006

The present study analyses the vegetation of canals and drains in the Nile Delta in relation to environmental factors. 30 clusters were generated by the TWINSPAN technique. A DC A (DECORANA) ordination revealed a moisture gradient, and, less clearly, a salinity and a fertility gradient. The resultant clusters were assigned to seven vegetation types arranged according to moisture preference as follows: Imperata cylindrica ‐ Desmostachya bipinnata, Phragmites australis, Panicum repens ‐ Cynodon dactylon, Echinochloa stagninum ‐ Polygonum salicifolium, Echinochloa stagninum, Eichhornia crassipes, and Ceratophyllum demersum‐Pótame geton crispas. Their species diversity is discussed in view of the disturbance and heterogeneity hypotheses.
BOOK REVIEWS
Authors: Leon Blanca , Young Kenneth R.
Published: May 2006

Seeliger, U. (ed.). 1992. Coastal Plant Communities of Latin America. xx + 392 pp. Academic Press, San Diego, CA. ISBN 0‐12 634550‐3. Price: USD 75.‐.

Short reviews

R. Pott (ed.). 1989. Rintelner Symposium I. Berichte der Reinhold‐Tüxen‐Gesellschaft 1, 165 pp. Reinhold‐Tüxen‐Gesellschaft, Institut für Geobotanik, Nienburger Str. 17, D‐3000 Hannover, Germany. ISBN 3‐88452‐775‐4. Price: not indicated.

R. Pott (ed.). 1991. Berichte der Reinhold‐Tüxen‐Gesellschaft 3, 291 pp. ISBN 3‐88452‐776‐2. Price: DEM 55.‐.

Hügin, Gerhard & Henrichfeise, Alfons. 1992. Naturschutzbewertung der badischen Oberrheinaue. Vegetation und Wasserhaushalt des rheinnahen Waldes. 48 pp + maps. Schriftenreihe für Vegetationskunde 24. Bundesforschungsanstalt für Naturschutz und Landschaftsökologie, Bonn‐Bad Godesberg. ISBN 3‐7843‐2072‐4. Preis DEM 10.‐.

Duhme, F., Lenz, R. & Spandau, L. (eds). 1992. 25 Jahre Lehrstuhl für Landschaftsökologie in Weihenstephan mit Prof Dr. Dr. h.c. W. Haber. Landschaftsökologie Weihenstephan 6. Freunde der Landschaftsökologie Weihenstephan, Ziegelgasse 19, D‐8050 Freising, Germany. ISBN 3‐922318‐06‐1. Price: not indicated.
Relations between the floristic composition of isolated young woods and their proximity to ancient woodland
Authors: Dzwonko Zbigniew
Published: May 2006

Abstract. Recent studies indicate that, in the present‐day agricultural landscape, the floristic composition of young woodland communities can be fully developed if the woods are situated adjacent to ancient woodlands. Four 70‐yr‐old deciduous woods in the Carpathian foothills were examined in relation to three adjacent ancient oak‐hornbeam and oak‐pine woodlands, which are the nearest source of woodland species diaspores. On the basis of data from 208 plots, the frequencies of various species groups in the field layer of the woods were analysed. The dependence of vegetation differentiation within the recent woods on (a) distance to the border with the ancient woodlands and (b) light intensity was examined by Partial Detrended Canonical Correspondence Analysis (DCCA). A significant relation between distance to ancient woodland and species composition was found for recent woods on rich brown soils. The vegetatively propagating species, myrmecochores and small autochores attained higher cover values near ancient woodland; endozoochores and anemochores were most abundant further away. Within recent, more open woods on poor podzolic and leached brown soils, colonisation is strongly inhibited by dense growth of Carex brizoides; here, vegetation regeneration is much slower than in woods on rich soils much further away from the source of diaspores.
Tropical rain forest types and soil factors in a watershed area in Guyana
Authors: ter Steege Hans , Jetten Victor G. , Polak A. Marcel , Werger Marinus J. A.
Published: May 2006

Abstract. An inventory was made of the vegetation and soils of a watershed area of 480 ha in the tropical rain forest of Guyana. 252 plots of 0.05 ha were sampled. In total 111 tree species > 20 cm were recorded. A TWINSPAN analysis resulted in seven groupings. Correspondence Analysis revealed that the major environmental differentiation underlying the floristic variation is according to soil type. Finally, five main forest communities were described. Most sites in the watershed area are characterized by the dominance of one or a few species. Species distribution patterns are strongly determined by soil type and drainage class.
Climatic relationships of some New Zealand forest tree species
Authors: Leathwick John R.
Published: May 2006

Abstract. A dataset of some 10 000 plots was used to describe the climatic relationships of 33 widespread New Zealand tree species. Estimates of mean annual temperature, temperature seasonality, mean annual solar radiation, and moisture balance were derived from mathematical surfaces fitted to climate station data. Plots were also categorized into five lithological classes and three drainage classes. Generalized additive models were used to examine species/environment relationships. Mean annual temperature and mean annual solar radiation are most strongly correlated with current tree distributions, followed by moisture balance, temperature seasonality, lithology, and drainage. Most broad‐leaved tree species other than Nothofagus spp. reach their greatest levels of occurrence in warm, moist environments with high solar radiation. In contrast, Nothofagus spp. generally reach their greatest levels of occurrence in cooler and/or lower insolation environments, and all have lower levels of occurrence on rhyolitic substrates which have resulted from large‐scale geomorphic disturbance, mostly over the past few thousand years. Although coniferous species have widely differing climatic optima, many are biased towards lithological classes characterized either by large‐scale geomorphic disturbance or harsh edaphic conditions. The relevance of these results to particular synecological questions is briefly discussed. Continuing adjustments in the range of slow‐dispersing Nothofagus spp. are strongly suggested, and the climatic suitability of extensive rhyolitic basins in the central North Island, from which these species are largely absent, is confirmed.
Stand dynamics, regeneration patterns and long‐term continuity in boreal old‐growth Picea abies swamp‐forests
Authors: Hörnberg Greger , Ohlson Mikael , Zackrisson Olle
Published: May 2006

Abstract. The occurrence of macrofossil charcoal (long axis > 0.5 mm) and Picea abies (Norway spruce) pollen in peat stratigraphies, in combination with size and age data from 2976 P. abies trees were used to analyse ecosystem continuity and stand‐structure in ten old‐growth swamp‐forests in northern Sweden. All stands were dominated by P. abies, a species whose abundance increased westwards in Sweden between 3000 and 2000 yr B.P. In three stands no macrofossil charcoal was found and the maximum age of the peat, determined by 14C dating, varied from 1800 to 3600 yr B.P. In the other seven stands the number of levels containing charcoal varied from 1 to 23, but only between 1 and 7 levels were found after the appearance of spruce. Here the maximum age of the peat varied from 400 to 7900 yr B.P. The ten stands had an all‐sized stand structure and a stand continuity of ca. 300 yr. The shape of the age structure was similar to an inverse J‐curve. This indicates a continuous recruitment over time in a self‐perpetuating ecosystem. In a short‐term perspective (< 300 yr), the swamp‐forests are characterized by individual trees continually emerging while others are dying. it is suggested that internal dynamics of continuous small‐scale disturbances in combination with local site‐specific factors determine the structure of these forests. in a long‐term perspective, some of the present spruce swamp‐forests within the northern boreal zone have functioned as true fire‐free refugia since the establishment of P. abies populations while others have been affected by recurring fires, although not as frequently as forests on surrounding drier sites. The hypothesis that Scandinavian spruce swamp‐forests in general have functioned as true longterm fire‐free refugia is thus modified by the present results.
Early gap successional pathways in a Fagus‐Acer forest preserve: pattern and determinants
Authors: Kupfer John A. , Runkle James R.
Published: May 2006

Abstract. Many theories of forest succession imply that terrestrial plant community composition within a region tends to converge toward a climax community. That is, given similar climatic and edaphic conditions, succession at different sites within an area will lead to comparable species compositions, a pattern referred to as successional convergence.

In this study, we examine changes in plant composition within forest canopy gaps over a 17‐yr period to identify potential patterns of successional convergence and to ascertain the factors controlling the successional pathway. To do so, we: (1) sampled 36 forest canopy gaps in Hueston Woods Nature Preserve in 1977, 1981, 1985, 1989 and 1993, (2) evaluated changes in the similarity of gap composition over this period, and (3) examined gap composition in each year as a function of variables describing gap habitat, seed source proximity, and disturbance history. Results indicated an initial pattern of successional divergence, with gaps exhibiting increased dissimilarity over the first 10–12 years of succession. We attribute this initial period of divergence to the effects of differential seed inputs from edge individuals and heterogeneity of available light due to differences in gap size. Recent surveys, however, indicated that gap composition has become more similar as competition within gaps has become more intense. In these samples, gap composition is closely linked to site conditions, including slope, soil conditions, and site exposure. Finally, while these patterns may suggest equilibrium‐oriented dynamics, non‐equilibrium processes such as repeat disturbances are also evident at Hueston Woods and will likely play an important role in determining future successional pathways.
BOOK REVIEWS
Authors: Pickett S. T. A. , Cadenasso M. L.
Published: May 2006

Book reviewed in this article:

Glenn‐Lewin, D.C., Peet, R.K. & Veblen, T.T. (eds.) 1992. Plant Succession: Theory and Prediction. ix + 352 pp. Chapman and Hall, New York, NY. ISBN 0‐412‐26900‐7. Price: USD 59.95.
BOOK REVIEWS
Authors: Grabherr George
Published: May 2006

Book reviewed in this article:

Rundel, P.W., Smith, A.P. & Meinzer, F.C. (eds.) 1994. Tropical Alpine Environments. Plant form and function. xi + 376 pp. Cambridge University Press, Cambridge. ISBN 0–521–42089‐X. Price: GBP 65.‐.
Growth of Halimium halimifolium under simulated and natural browsing in the Doñana National Park (SW Spain)
Authors: Aguilar Silva F.J. , Diaz Barradas M.C , Zunzunegui M.
Published: May 2006

Abstract. The annual cycle of vegetative growth in the Mediterranean shrub Halimium halimifolium (Cistaceae) subjected to simulated and natural browsing on the stabilized sands of Doñana National Park (SW Spain) is described. In a drier area without herbivory (Monte Intermedio) plants were subjected to different intensities of clipping. In a more humid area with high herbivory pressure (Monte Negro) plants were isolated by cages. Plants were monitored monthly from February to November 1994. Vegetative growth starts in March and ends in June or July, according to temperature and water availability. Plants intensely clipped and plants subjected to natural browsing responded maximally regarding shoot length, and number of leaves on main shoots and branches. Clipped plants, however, did not reach the height and cover of controls.
Integrated synusial phytosociology: some notes on a new, multiscalar approach to vegetation analysis
Authors: Gillet François , Gallandat Jean‐Daniel
Published: May 2006

Abstract. The integrated synusial approach of the vegetation is based on the differentiation of several spatio‐temporal organization levels. A phytocoenosis (community of the second level) is considered as a complex of synusiae (communities of the first level) and is characterised by a strong tendency to self‐organization. At each level, a typology of the communities can be performed. Ecological indicator values as well as different diversity indices are calculated for each vegetation unit. They are useful for understanding the spatial and temporal organization of the phytocoenoses. As an example. this approach is applied to wooded meadows.
Differences between banded thickets (tiger bush) at two sites in West Africa
Authors: Couteron Pierre , Mahamane Ali , Ouedraogo Paul , Seghieri Josiane
Published: May 2006

Abstract. This paper deals with the influence of edaphic conditions on the spatial structure of banded thickets or tiger bush (brousse tigrée). It is based on two sites in West Africa, with similar climatic conditions but located on contrasting substrates. The spatial structure was described with standardized characteristics including thicket spacing, thicket/inter‐thicket contrast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to understand current dynamics. Data were collected on transects oriented perpendicular to the contours and so to the thickets as well. A standardized analytical procedure was applied to data from both sites to ensure consistent and thorough delineation of thickets.

The overall periodicity of thickets, the woody flora and the dominant species Combretum micranthum were similar at the two sites. However, thicket spacing, thicket/inter‐thicket contrast and upslope/downslope floristic asymmetry of the thickets were higher in the less favourable site. Also seedlings were less abundant, with a greater dependence on pre‐existing thickets.

Not all banded vegetation systems show sharp contrasts and are strongly asymmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more diverse than expected. Quantified inter‐site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.
Reliability of Ellenberg indicator values for moisture, nitrogen and soil reaction: a comparison with field measurements
Authors: Schaffers André P. , Sýkora Karlè V.
Published: May 2006

Abstract. Ellenberg indicator values for moisture, nitrogen and soil reaction were correlated with measured soil and vegetation parameters. Relationships were studied through between‐species and between‐site comparisons, using data from 74 roadside plots in 14 different plant communities in The Netherlands forming a wide range.

Ellenberg moisture values correlated best with the average lowest moisture contents in summer. Correlations with the annual average groundwater level and the average spring level were also good. Ellenberg N‐values appeared to be only weakly correlated with soil parameters, including N‐mineralization and available mineral N. Instead, there was a strong relation with biomass production. We therefore endorse Hill & Carey's (1997) suggestion that the term N‐values be replaced by ‘productivity values'. For soil reaction, many species values appeared to need regional adjustment. The relationship with soil pH was unsatisfactory; mean indicator values were similar for all sites at pH > 4.75 because of wide species tolerances for intermediate pH levels. Site mean reaction values correlated best (r up to 0.92) with the total amount of calcium (exchangeable Ca2+ plus Ca from carbonates). It is therefore suggested that reaction values are better referred to as ‘calcium values'.

Using abundance values as weights when calculating mean indicator values generally improved the results, but, over the wide range of conditions studied, differences were small. Indicator values for bryophytes appeared well in line with those for vascular plants. It was noted that the frequency distributions of indicator values are quite uneven. This creates a tendency for site mean values to converge to the value most common in the regional species pool. Although the effect on overall correlations is small, relationships tended to be less linear. Uneven distributions also cause the site mean indicator values at which species have their optimum to deviate from the actual Ellenberg values of these species. Suggestions for improvements are made.

It is concluded that the Ellenberg indicator system provides a very valuable tool for habitat calibration, provided the appropriate parameters are considered.
Gradient analysis of the distribution of a fungal disease of Cornus florida in the southern Appalachian Mountains, Tennessee
Authors: Wilds Stephanie P.
Published: May 2006

Abstract: Based on 115 samples collected throughout the western portion of Great Smoky Mountains National Park, southern Appalachian Mts., and on spatial data derived in a GIS (Geographical Information System), the distribution of the disease dogwood anthracnose affecting Cornus florida (flowering dogwood), caused by the fungus Discula destructiva in this portion of the Park was assessed, and factors contributing to the disease's severity were identified through correlation and multiple linear regression analysis. The degree of infection varies considerably locally, and is influenced by elevation, slope curvature, slope position, and potential soil moisture. However, the abundance of C. florida (stem density) alone explains 25 % of the variation in disease severity. Factors contributing to disease severity do not change significantly between disturbed and undisturbed sites. The highest mortality rates are restricted to dense stands in damp, sheltered sites at low slope positions, implying that surviving populations of flowering dogwood may represent a biased genetic subset of the original population.
CO2‐fluxes in different plant communities of a high‐Arctic tundra watershed (Western Spitsbergen)
Authors: Wüthrich Christoph , Möller Ingo , Thannheiser Dietbert
Published: May 2006

Abstract. There is little information on (1) whether the net carbon balance is positive or negative in different habitats in high Arctic ecosystems such as Spitsbergen today, and (2) what effect a cloudier, cooler summer could have on carbon balance. To provide data on this subject CO2‐flux measurements in different plant communities were made in the high‐Arctic coastal tundra of Spitsbergen, using a mobile macro‐cuvette system based on infrared gas analysis. The study area was situated on the exposed west coast, where westerly winds produce precipitation daily in the form of rain, drizzle and fog. During the cold and cloudy measurement period in 1996, light and surface temperatures were limiting for primary producers, resulting in low size and low physiological activity of the plants. Net CO2‐flux measurements showed carbon fluxes from soil to atmosphere in most of the communities even during the brightest hours of the day, when mean photon flux density was 325 mmol m‐2 s‐1. Calculations based on spatial distribution of the plant communities and soils in the watershed combined with C‐flux measurements revealed information on daily carbon loss. For instance, the Drepanocladus community, covering 21 % of the catchment area, was responsible for 42.6 % of the catchment carbon loss. Only two of nine investigated plant communities, the Racomitrium and a Salix‐Saxifraga community on debris, both adapted to frequent fog situations, were able to compensate for respiratory CO2‐losses under the prevailing low light conditions during daytime. Since there were no significant sunny periods in this area in the summer of 1996, the habitats of the investigated coastal tundra finished the season with a marked carbon loss due to increased cloudiness.
Disturbance response in vegetation – towards a global perspective on functional traits
Authors: McIntyre S. , Lavorel S. , Landsberg J. , Forbes T.D.A.
Published: May 2006

Abstract. Previous work on trait correlation patterns has contributed to the identification of broad patterns of plant distribution along environmental gradients in vegetation. However, these general trends may conceal subtle mechanisms of response that are specific to particular types of disturbance. To address this, we propose a generic methodology for the analysis of traits, using herb‐dominated vegetation as a model.

Hypothetical biological traits are identified for testing against disturbance gradients. The traits were selected for their perceived relevance to disturbance response generally, but also include a specific focus on domestic livestock grazing. The analysis is structured hierarchically to enable attributes to be analysed within major life forms. A different selection of traits is identified as being relevant to each major life form.

Flexible adaptation in the use of the trait set is suggested as a way of comparing functional response to disturbance over a series of locations. For example, assemblages will vary in their representation of the major life forms, and it may be relevant to analyse traits within a subset of these life‐form groups. Because individual studies encompass a limited range of environmental variation, and local floras may be constrained by their evolutionary context, similar approaches need to be tested over a range of vegetation types and geographic situations. A significant advance in functional trait analysis could be achieved if individual studies provide explicit descriptions of their evolutionary and ecological context from a global perspective.
On the identification of optimal plant functional types
Authors: Pillar Valério DePatta
Published: May 2006

Abstract. The study of vegetation response to environmental change on a global scale cannot rely on species because most plant species have geographically limited distributions. To allow ecological predictions beyond the scale of the floristic region, models have to rely on vegetation descriptions using plant types other than the species. The crucial problem is how to define the types. Since types are described by traits, the problem translates into one of optimal trait selection. The best plant traits are those that when used to define plant types optimize the perception of association between vegetation and environmental (e.g., climate, disturbance) variation. I consider trait selection as a two‐step procedure. The first step is the selection of a larger trait set based on past experience and known practicality, which is used for community description. The second step, for which the paper describes new methods, is accomplished on the data analytically by suitable computer algorithms that can find the optimal subset among the preselected traits. This subset defines optimal plant functional types (PFTs). The methods involve a fuzzy set approach and community description by plant types. The optimization algorithms described are tested with data from plant communities in South and North America. The utility of the approach in the evaluation of convergence of phylogenetically distant plant communities is discussed.
Do seed predation and dispersal limit downslope movement of a semi‐desert grassland/oak woodland transition?
Authors: Hubbard J.A. , McPherson G.R.
Published: May 2006

Abstract. Semi‐desert grasslands and dryland forests are typically arranged along elevation gradients, with low elevation grasslands and savannas separated from higher‐elevation woodlands by a diffuse boundary. Recent (< 200 yr) woody plant encroachment into adjacent semi‐desert grasslands appears to be a cosmopolitan phenomenon, and has been attributed to disturbance by humans (e.g., livestock grazing, fire suppression); however, little is known about rates, patterns and mechanisms. Are observations of increased woody plant abundance in semi‐arid grasslands indicative of a downslope shift in the boundary zone? Experimental plots were established in adjacent oak woodlands and semi‐desert grasslands in southeastern Arizona, to determine if mechanisms of acorn predation and dispersal would facilitate or limit downslope movement of oak woodlands. We recovered acorns that had been dispersed 50 m into adjacent grasslands, which suggests that they were cached by acorn predators. Acorns in grassland plots were more than twice as likely to escape predation than acorns that remained in woodland or cleared woodland plots. Contrary to previously published research, simulated perturbations (gap formation, understory and below‐ground vegetation removal) did not affect seed predation, suggesting that generalizations from mesic, deciduous oak forests may not be accurately extrapolated to xeric, evergreen oak forests. Recently published studies indicate that xeric conditions limit survival of oak seedlings across the boundary zone, suggesting that observed patterns of acorn dispersal and predation provide the potential for colonization of adjacent grassland only during infrequent years with cool, moist conditions during late summer months.
High‐Andean vegetation and environmental gradients in northwestern Patagonia, Argentina
Authors: Ferreyra Marcela , Cingolani Ana , Ezcurra Cecilia , Bran Donaldo
Published: May 2006

Abstract. We analysed the heterogeneity of high‐elevation vegetation on three mountains along a west‐east transect at 41 °S lat. in the Andes of northwestern Patagonia, Argentina. In this area, high‐Andean vegetation occurs as islands on mountain tops above Nothofagus pumilio forests ? with the timberline at ca. 1700 m a.s.l. We recorded floristic, topographic and substrate data in 166 sites stratified according to longitude, altitude, slope and aspect. Vegetation data were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis. The relationship between environmental and floristic variation was analysed using Canonical Correspondence Analysis. In order of importance, geographical longitude, altitude and aspect were the major determinants of vegetation variation, whereas substrate texture and slope appeared less important. The combination of these factors resulted in two main vegetation gradients. The first gradient is related to a moisture availability gradient, primarily determined by longitude and secondarily to variation in wind exposure (east vs. west aspect). The second vegetation gradient is related to variation in temperature, primarily determined by altitude, and secondarily by variation in insolation related to the contrast between north and south aspects. The four communities obtained with TWINSPAN are therefore associated with four characteristic habitat types: moist‐cold, moist‐warm, dry‐cold and dry‐warm. The community of warm and dry environments is the richest and has elements in common with dry steppe communities situated at lower elevations to the east, while the vegetation of the cold‐moist habitat type has unique elements that are typical of the southern Andes. Although current climatic factors appear to be the major determinants of high‐Andean vegetation gradients, historical events of Pleistocene times probably also affected the vegetation patterns we see today.
The effects of NPK fertilization for nine years on boreal forest vegetation in northwestern Canada
Authors: Turkington Roy , John Elizabeth , Krebs C.J. , Dale M.R.T. , Nams V.O. , Boonstra R. , Boutin S. , Martin K. , Sinclair A.R.E. , Smith J.N.M.
Published: May 2006

Abstract. Plant productivity is limited by mineral nutrient availability in many boreal forest ecosystems. This study is an analysis of the growth responses of components of a boreal plant community (cryptogams, herbaceous and woody perennials, the dominant shrubs Salix glauca (grey willow) and Betula glandulosa (bog birch) and the dominant tree Picea glauca (white spruce), to the addition of an NPK fertilizer over a nine‐year period. The study was carried out in a low‐nutrient boreal forest ecosystem in the Yukon territory in northwestern Canada. The following predictions were tested: (1) that there would be an overall increase in abundance (measured either as cover, density, or dry mass) of all components of the vegetation, (2) that vegetation composition would change as more competitive species increased in abundance and (3) that initial community changes in response to fertilization would be transient. In general, all predictions were found to be true. Species composition changed rapidly in response to fertilizer. Graminoids (e.g. Festuca altaica) and some dicots (e.g. Mertensia paniculata and Achillea millefolium) increased in cover, while other dicots (e.g. Anemone parviflora), dwarf shrubs (e.g. Arctostaphylos uvaursi), bryophytes and lichens declined. There was a significant increase in the growth rate of the two dominant shrubs and of Picea, but not in the cone crop or seed production by Picea. Surveys after 1 or 2 years showed responses by the vegetation but more stable patterns of response did not emerge until after 5 or 6 years. There were consistent and directional changes in the percent cover of some of the herbaceous species on control plots. Growth rates of Salix and Betula varied considerably from year to year, independently of treatment. Long‐term studies are essential if we are to understand the role of nutrient limitation in this ecosystem.