bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in the canopy structure of the Mediterranean shrub Lavandula stoechas after disturbance
Authors: Díaz Barradas M.C. , Mateos M.A. , Orellana R. , Zunzunegui M. , García Novo F. 
Published: May 2006

Abstract. This study attempts to show the dynamics of the canopy structure of the Mediterranean pioneer shrub Lavandula stoechas after man‐made perturbation (i.e. grazing). The development of the vertical structure of the shrub was studied by harvesting the canopy of plants of 2–6 yr old in horizontal layers. The supportive biomass of the canopy was concentrated near the base at all ages. Leaf biomass was evenly distributed all over the vertical profile in 2‐ and 3‐yr old plants. In 4‐yr old plants it presented a maximum near the top of the canopy. For 5‐yr old plants a structural transition started with leaf profiles showing a bimodal distribution. Leaf biomass predominated near the base in 6‐yr old plants, suggesting that the transition was completed.Three canopy stages in the growth processes of the plant were recognized after the first year of growth: in the first one (from 2 to 3 yr old) both leaf and supportive biomass increased; in the second one (from 3 to 4 yr) leaf biomass remained stable and there was an increase in supportive biomass until the plants reached a ‘mature stage’, in 4‐yr old plants; finally, in 5‐ and 6‐yr old plants there was a decrease both in leaf and supportive biomass and plant structure showed evidence of senescence. Early transitions from seedling to 1‐yr old plant and from this to 2‐ to 3‐yr old plants were less obvious.The leaf/supportive biomass ratio always decreased with plant age, from 1.88 in seedlings to 0.01 in 6‐yr old plants. Biomass density followed the pattern of supportive biomass, with an increase from 1.7 g/dm3 (2‐yr old plants) to 2.4 g/dm3 (4‐yr old plants). Thereafter, biomass density decreased to 0.6 g/dm3 (6‐yr old plants).
Plant communities and landscape diversity along a Canadian Arctic river
Authors: Gould William A. , Walker Marilyn D. 
Published: May 2006

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β‐diversity) of communities, or (3) an increase in within‐community richness (α‐diversity) as species‐poor communities are replaced by species‐rich communities.We described 24 community types and analysed the relationship between site vascular species richness (γ‐diversity) and β‐diversity, α‐diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community‐level estimates of environmental factors.We found that an increase in site species richness correlated with an increase in the number of communities (r2= 0.323, P= 0.0173) and β‐diversity (r2= 0.388, P= 0.0075), rather than an increase in the α‐diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r2= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r2= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r2= 0.214, P < 0.0001).We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.
Tornado damage and initial recovery in three adjacent, lowland temperate forests in Missouri
Authors: Peterson Chris J. , Rebertus Alan J. 
Published: May 2006

Abstract. We surveyed tornado damage 14 months after disturbance in three adjacent forest sites in southeastern Missouri, USA: upland, an occasionally‐flooded lowland and a frequently flooded swamp. We analysed three 0.09‐ha plots in the swamp, and three 0.04‐ha plots in the other sites and recorded the herbaceous‐layer in five 1‐m2 quadrats per plot.Overall, 30 % of the individuals and 64 % of the basal area of these sites was blown down. However, mortality was less than structural damage: 20 % of the trees were dead 14 months post‐disturbance, an intermediate level of mortality relative to other wind disturbances. Damage varied widely among species, sites and tree sizes, but large trees of all species were most likely to be damaged and least likely to resprout.While damage was greatest in the wettest site, we attribute the increase to larger tree sizes and lower density there, rather than to inherent rooting instability. This study suggests that different forest composition and structure may be sufficient to cause differential damage, without topographic effects. Herbaceous‐layer response was more rapid than in a previously reported tornado windthrow in Pennsylvania, and was dominated by fast‐growing, shade‐intolerant forbs.
Population strategies in severe environments: alpine plants in the northwestern Caucasus
Authors: Onipchenko Vladimir G. , Semenova Galina V. , van der Maarel Eddy 
Published: May 2006

Abstract. This study attempts to show a differentiation into strategy types among plant species of four alpine communities in the northwestern Caucasus, Russia. Four groups of population characteristics (traits) were examined: above‐ground biomass, seed size, seed yield and occurrence of a persistent seed bank. In addition, values for relative growth rate and a morphology index were estimated. Agglomerative Cluster Analysis and Principal Component Analysis were applied to a data set with 42 species from these communities and six species characteristics. In the Geranium gymnocaulon meadow, the most productive community, large gaps occur created by wild boars and bears. Here, the response of 13 species to disturbance was also analysed.Strategy types were approached both according to Grime: ‘competitive’, ‘ruderal’, ‘stress‐tolerating’ and according to Ramensky, Rabotnov and Romanovsky: ‘violent’ ≈ dominant (V), ‘explerent’ ≈ explorative (E) and ‘patient’ ≈ endurant (P). Differentiation into strategy types was more obvious in productive alpine grasslands than in lichen heaths and snowbed communities. The grassland dominants Festuca varia, Geranium gymnocaulon and Hedysarum caucasicum showed a more or less ‘violent’ strategy. Species approaching an Estrategy, e.g. Matricaria caucasica, Sibbaldia procumbens and Gnaphalium supinum, were also found in the grasslands but prevailed in the snowbed communities. Species with a ‘patient’ strategy prevailed in the lichen heaths.We conclude that plant strategy types are well‐differentiated, this is also seen in plant communities occurring under severe high‐mountain conditions. We also suggest that the approaches by Grime and Ramensky/Rabotnov/Romanovsky are not so similar as has been assumed earlier and that the R/R/R types are better differentiated and ecologically better interpretable.We emphasize the gradient character of strategy ‘types’ and would characterize plant species by the degree of adaptation to conditions: (1) from small seed size and large persistent seed bank to large seed size and absence of a seed bank; (2) from high to low biomass and seed production, with relative growth rate as a less important partially correlated trait.
Dynamics of Salix caprea L. populations during forest regeneration after strong herbivore pressure
Authors: Faliński Janusz Bogdan 
Published: May 2006

Abstract. Broadleaved forest communities degenerated through strong pressure from large herbivores. Relief of this pressure led to regeneration, in particular of Salix caprea and other light‐seeded pioneer trees: Populus tremula, Betula pendula and B. pubescens. This regeneration proceeded following conservation protection of degenerate stands in a nature reserve and later in Biaowiéza National Park. The emergence and development of the Salix caprea population proceeded following the expansion of Picea abies, which coincided with the period of enhanced animal pressure on the broadleaved forest. Salix caprea filled all the gaps in the tree stand after the destruction of trees and undergrowth by herbivores (in the years 1892–1915). The species also appeared abundantly in old, at the time unforested, clearings and felled areas.Here, S. caprea developed large populations with certain trees in good condition, with a growth form typical of forest trees and attaining considerable heights. The majority of trees were 50 ‐ 60 yr old at the time of death, although some individuals reached 74 yr of age. The process of extinction of the Salix population — observed over 19 yr on permanent plots with marked trees — proceeded very quickly, especially in the first decade of observation. It led to the almost complete disappearance of S. caprea from the forest communities of Biaowiéza National Park. The death of individual trees is preceded by impairment of their health and reduced annual increments in the last 4–9 years of their life.The development of populations of permanent constituents of the forest, notably Carpinus betulus, Tilia cordata, Acer platanoides and Ulmus glabra, under the canopy of light‐seeded trees, and the absence of a new generation of pioneer trees points to the end of the process of regeneration in the forest communities of BiaHwiéza National Park.
BOOK REVIEWS
Authors: Walck Jeffrey L. 
Published: May 2006

Book reviewed in this article:de Kroon, Hans & van Groenendael, Jan (eds.) 1997. The ecology and evolution of clonal plants. xii + 453 pp. Backhuys Publishers, Leiden. ISBN 90‐73348‐73‐0. Price (paper): NLG 120.00/USD 67.00.Günter, Gundula. 1997. Populationsbiologie selterner Segetalarten. Scripta Geobotanica 22, 220 pp. Verlag Erich Goltze, Göttingen. ISBN 3‐88452‐522‐0. Price: DEM 55.‐.Vernet, Jean‐Louis. 1997. L'homme et la forět méditerranéenne de la Préhistoire à nos jours. 248 pp. Editions Errance. ISBN 2 87772 137 X. Price FRF 240.‐.Grabherr, Georg. 1997. Farbatlas Ökosysteme der Erde. 364 pp., 430 colour photographs, 11 colour distribution maps. Verlag Eugen Ulmer, Stuttgart. ISBN 3‐8001‐3489‐6. Price: DEM 44.‐.Kutschera, Ulrich. 1998. Grundpraktikum zur Pflanzen‐physiologie. UTB 2026. 160 pp. Quelle & Meyer Verlag, Wiesbaden. ISBN 3‐494‐02245‐3. Price: DEM 36.80.Randlane, Tiina & Saag, Andres. 1998. Lichens in Estonia and in the rest of the world. Papers dedicated to Hans Trass on his 70th birthday. Folia Cryptogamica Estonica, Fasc. 32, 160 pp. Estonian Naturalists' Society. ISSN 1406‐2070; ISBN 9985‐50‐211‐6. Price not indicated. To be obtained at the address of the Society, 2 Struve Street, EE 2400 Tartu, Estonia.
Dynamics of forests with Araucariaceae in the western Pacific
Authors: Enright N.J. , Ogden J. , Rigg L.S. 
Published: May 2006

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden & Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific.Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape‐scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; >10 cm DBH); 3. A high turnover rate for angiosperms (<100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness > 10 %) for successful recruitment.The evidence presented here supports the temporal stand replacement model, but more long‐term supporting data are needed, especially for the phase immediately following landscape level disturbance.
Effects of germination inhibition on the dynamics of Quercus ilex stands
Authors: Li Junqing , Romane Francois J. 
Published: May 2006

Abstract. Germination of Quercus ilex L. in coppice stands of this species in the western Mediterranean Basin was examined and a germination inhibitory process is proposed to explain some germination traits. Germination rate and seedling biomass of Q. ilex were greatly modified by watering acorns with various concentrations of aqueous soil extracts from a Q. ilex coppice stand but also when the acorns were sown in soil from Q. ilex coppice stands. In the aqueous extract experiment, Q. ilex germination and seedling weight both decreased as the aqueous extract concentration increased. In the soil type experiment, Q. ilex soil decreased the Q. ilex germination rate. Comparative studies with Q. pubescens germination (this species, replaced by Q. ilex around 5 000 B.P., is assumed to form the climax vegetation of the region) revealed that Q. pubescens was less sensitive to the aqueous extracts and soils of Q. ilex coppice stands.Inhibition of Q. ilex seed germination could be a major reason for the poor seed regeneration and suggested a possible comeback of Q. pubescens.
To fix or not to fix the species limits, that is the ecological question: Response to Jari Oksanen
Authors: Austin M.P. , Nicholls A.O. 
Published: May 2006

Abstract. We respond to Oksanen's recent comments in “Why the beta‐function cannot be used to estimate skewness of species responses”. We agree with Oksanen's criticisms concerning correlated parameters when fitting beta‐functions. We argue that response functions can be reasonably estimated using beta‐functions only for those species whose range limits obviously fall within the observed length of an environmental gradient and our original description included explicit recognition of this need. The simulated data used by Oksanen contains only one species that would meet our criteria for defining the limits and the shape of this species is recovered by fitting a beta‐function.Beta‐functions are shown to recover reasonable approximations of the true shapes when fitted to simulated data, generated without error, and representing species with either skewed or symmetrical response shapes if using realistic estimates of the species limits. When arbitrary limits are imposed then distorted shapes result. Using similar data from 500 simulated data sets generated under the assumption of a Poisson error structure, beta‐functions gave conservative estimates of the degree of skewness for those data sets representing skewed species and no evidence of skewness for those data sets representing symmetrical species.We conclude that despite Oksanen's concerns the conclusions drawn by the current authors and colleagues with respect to the degree of skewness shown by species response functions along a common gradient are robust to the fitting procedures used. While we agree that the fitting of beta‐functions is not the best approach to modelling skewed responses we argue that it will not mislead the user as to the presence or extent of skewness if used with reasonable and data driven estimates of the species limits.
Vegetation of the woodland‐steppe transition at the southeastern edge of the Inner Mongolian Plateau
Authors: Liu Hongyan , Cui Haiting , Pott Richard , Speier Martin 
Published: May 2006

Abstract. The vegetation of the woodland‐steppe transition in southeastern Inner Mongolia, where the East Asian monsoon climate reaches its northwestern edge, is described and analysed in this paper. The communities are classified in a phytocoenological way. 12 major types of woodland, shrubland, meadow, fen, open woodland and steppe are differentiated and described on the basis of 133 phytosociological relevés. Detrended Correspondence Analysis shows that precipitation plays a crucial role in the distribution of grassland communities while woodland and shrubland communities are controlled by both warmth and humidity conditions.Four vegetation zones can be distinguished. From the woodland to the woodland‐grassland zone, the temperature decreases and the precipitation increases with increasing altitude, which leads to the conditions suitable for the meadow and fen communities. In the direction of the woodland‐steppe zone the temperature increases while the precipitation decreases with the gradual lowering of the altitude; the steppe communities form a matrix while the woodlands have a patchy distribution. From the woodland‐steppe to the steppe zone, the precipitation rather than temperature decreases; as a result the woodland communities disappear gradually. On a local scale, geomorphologic conditions determine the vegetation pattern of the study area. Due to the existence of a sandy substrate different woodland types occur together in the woodland‐steppe transition. The local distribution of woodland and steppe communities is dependent on slope conditions. In addition, human disturbance has also influenced the composition of plant communities.
Finite Variable Logics in Descriptive Complexity Theory
Authors: Grohe Martin 
Published: May 2006

Throughout the development of finite model theory, the fragments of first-order logic with only finitely many variables have played a central role. This survey gives an introduction to the theory of finite variable logics and reports on recent progress in the area.For each k ≥ 1 we let Lk be the fragment of first-order logic consisting of all formulas with at most k (free or bound) variables. The logics Lk are the simplest finite-variable logics. Later, we are going to consider infinitary variants and extensions by so-called counting quantifiers.Finite variable logics have mostly been studied on finite structures. Like the whole area of finite model theory, they have interesting model theoretic, complexity theoretic, and combinatorial aspects. For finite structures, first-order logic is often too expressive, since each finite structure can be characterized up to isomorphism by a single first-order sentence, and each class of finite structures that is closed under isomorphism can be characterized by a first-order theory. The finite variable fragments seem to be promising candidates with the right balance between expressive power and weakness for a model theory of finite structures. This may have motivated Poizat [67] to collect some basic model theoretic properties of the Lk. Around the same time Immerman [45] showed that important complexity classes such as polynomial time (PTIME) or polynomial space (PSPACE) can be characterized as collections of all classes of (ordered) finite structures definable by uniform sequences of first-order formulas with a fixed number of variables and varying quantifier-depth.
Alonzo Church and the Reviews
Authors: Enderton H. B. 
Published: May 2006

The journal of symbolic logic began publishing in 1936. From the outset, the Journal included a Reviews Section, edited by Alonzo Church. The very first issue carried three pages of reviews, written by Bernays, Church, Rosser, and Quine.As the first issue stated, “It is intended that this section of the Journal shall serve as a complete bibliography of current literature in the field of symbolic logic, from January 1, 1936. To this end an effort will be made to include in it, at least by title, all publications in this field, both books and articles in journals, and as far as possible these will be accompanied by signed reviews.” Thus the purpose of the Reviews Section was two-fold. For one, there was its bibliographical function: to provide a complete, suitably indexed, listing of all the publications—both books and journal articles—in symbolic logic, wherever and in whatever language published. And secondly, the reviews were to provide critical, analytical commentary on these publications, whenever possible.The Reviews Section should be viewed as a continuation and expansion of Church's A bibliography of symbolic logic. The Bibliography was a listing, with some annotations, of the publications in symbolic logic prior to 1936. It was published as volume 1, number 4 of the Journal. Church made the listing as complete as he could, of course.
Developments in Constructive Nonstandard Analysis
Authors: Palmgren Erik 
Published: May 2006

AbstractWe develop a constructive version of nonstandard analysis, extending Bishop's constructive analysis with infinitesimal methods. A full transfer principle and a strong idealisation principle are obtained by using a sheaf-theoretic construction due to I. Moerdijk. The construction is, in a precise sense, a reduced power with variable filter structure. We avoid the nonconstructive standard part map by the use of nonstandard hulls. This leads to an infinitesimal analysis which includes nonconstructive theorems such as the Heine–Borel theorem, the Cauchy–Peano existence theorem for ordinary differential equations and the exact intermediate-value theorem, while it at the same time provides constructive results for concrete statements. A nonstandard measure theory which is considerably simpler than that of Bishop and Cheng is developed within this context.
Brouwer and Fraenkel on Intuitionism
Authors: Dalen Dirk Van 
Published: May 2006

In the present paper the story is told of the brief and far from tranquil encounter of L.E.J. Brouwer and A. Fraenkel. The relationship which started in perfect harmony, ended in irritation and reproaches.The mutual appreciation at the outset is beyond question. All the more deplorable is the sudden outbreak of an emotional disagreement in 1927. Looking at the Brouwer–Fraenkel episode, one should keep in mind that at that time the so-calledGrundlagenstreitwas in full swing. An emotional man like Brouwer, who easily suffered under stress, was already on edgewhen Fraenkel's bookZehn Vorlesungen Über die Grundlegung der Mengenlehre, [Fraenkel 1927] was about to appear.With theGrundlagenstreitreaching (in print!) a level of personal abuse unusual in the quiet circles of pure mathematics, Brouwer was rather sensitive, where the expositions of his ideas were concerned. So when he thought that he detected instances of misconception and misrepresentation in the case of his intuitionism, he felt slighted. We will mainly look at Brouwer's reactions. since the Fraenkel letters have not been preserved.The late Mrs. Fraenkel kindly put the Brouwer letters that were in her possession at my disposal. I am grateful to the Fraenkel family for the permission to use the material.I am indebted to Andreas Blass for his valuable suggestions and corrections.Abraham Fraenkel (then still called Adolf) was one of the first non-partisan mathematicians, if not the first, who developed a genuine interest in intuitionism.