bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Vegetation‐environment relations along water courses in the Nile Delta region
Authors: Shaltout K. H. , El‐Sheikh M. A. 
Published: May 2006

AbstractThe 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 reviewsR. 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.
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.‐.
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.
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.
Effects of timing of precipitation and acorn harvest date on emergence of Quercus emoryi
Authors: Germaine Heather L. , McPherson Guy R. 
Published: May 2006

Abstract. Germination of semi‐arid Quercus is strongly correlated with the rainy season. However, the timing and amount of summer precipitation in the southwestern United States is extremely variable. Ongoing and impending changes in global and regional climates are likely to increase this variability. Specifically, anthropogenically induced changes in general circulation patterns may alter the seasonal distribution of precipitation in a directional manner. In addition to climatic variability, the inter‐ and intra‐annual variability of Quercus emoryi Torr. (Emory oak) acorn maturation also is high. Therefore, in light of existing climatic variability and potential future climate change, we conducted a greenhouse experiment to investigate the effects of acorn maturation date and the timing of the onset of the ‘monsoon’ on emergence of Q. emoryi seedlings.Acorns were collected at weekly intervals in July of 1995 and 1996, planted in a greenhouse, and subjected to different watering treatments. Watering treatments were (1) acorns watered the same day as planting; (2) acorns watered two weeks after planting; (3) acorns watered four weeks after planting. Emergence in 1995 was significantly greater in the last week of acorn maturation and decreased significantly as time to the onset of the ‘monsoon’ increased. Emergence in 1996 was very low, presumably because of soil moisture contents that were lower than those observed in 1995. The dependence of Q. emoryi on water for emergence has profound implications for Q. emoryi recruitment in the face of current climatic variability and future climate change. Summers with a delayed ‘monsoon’ and decreased soil moisture may severely constrain recruitment of this woody plant.
Successional trends 219 years after fire in an old Pinus sylvestris stand in northern Sweden
Authors: Engelmark Ola , Hofgaard Annika , Arnborg Tore 
Published: May 2006

Abstract. We present results from repeated analyses (1962, 1993) of a permanent plot established in 1947, combined with retrospective stand age structure data, in an old Pinus sylvestris stand in Muddus National Park, northern Sweden. The study points towards a successional pathway governed by concurrent disturbance effects of climate variability, reindeer grazing and fire. This is intermediate to the two often advocated ideas on dynamics in boreal forests, that is, one of disturbance‐related tree regeneration/mortality and one of continuous regeneration.When the plot was established in 1947 the tree layer (> 1.3 m) consisted of 300 individuals/ha of P. sylvestris and 62/ha of Betula pubescens. Subsequently the stand has become more dense and the species dominance has shifted. In 1993, 362 P. sylvestris and 62 Picea abies individuals were present per ha, while no Betula individuals were found. The number of dead trees increased from zero in 1947 to 200/ha (Pinus) in 1993. Pinus was also the most common species in the sapling layer (< 1.3 m) throughout the study period, though the number dropped from 8912/ha in 1947 to 51% in 1993. Dead saplings decreased from 2650/ha in 1947 to ca. 50% in 1962, and only 9% in 1993. Temporal variations in mortality and sapling mean height coincided with variations in snow depth, indicating a critical period in sapling development when saplings are exposed at the snow/atmosphere interface. The number of living Picea saplings increased slowly until 1993; no dead saplings were found.Most Pinus recruited shortly after the 1774‐fire, and during the second half of the 1900s. The major part of the spruce regeneration took place during the later half of the 1900s. No successful Betula recruitment has occurred after the 1930s, and no live Betula were present in 1993, which might be explained as an effect of increased reindeer browsing – the reindeer stock has grown by 50% since 1961.Although subjected to high mortality, Pinus regenerated and maintained a seedling/sapling bank. In this way Pinus remained dominant in the tree layer after more than 200 post‐fire years. The importance of the shade‐tolerant Picea has slowly increased, while Betula has died off. Thus, even after 219 yr since fire there is an early successional trend in the stand. This suggests that an increased chronic disturbance (grazing/browsing by reindeer) has partly succeeded earlier discrete fire‐disturbance events, and maintained a continuous seedbed favouring the shade‐intolerant pine recruitment.
Long‐term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest
Authors: Segerström Ulf 
Published: May 2006

Abstract. Analysis of pollen, charcoal and loss‐on‐ignition in peat cores from a Picea aèies‐dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500–7000 cal. BP; (B) Open mire period (ca. 7000–4500 cal. BP; (C) Betula period, ca. 4500–2300 cal. BP; (D) Picea period (ca. 2300–1000 cal. BP; (E) Human impact period (ca. 1000–100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr.The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000–500 cal. BP), and subsequently small‐scale cereal growing (ca. 400–100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand.The present high biodiversity, and subsequent conservation interest does not result from long‐term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity.An important issue for maintaining long‐term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.
Ordered Groups: A Case Study in Reverse Mathematics
Authors: Solomon Reed 
Published: May 2006

The fundamental question in reverse mathematics is to determine which set existence axioms are required to prove particular theorems of mathematics. In addition to being interesting in their own right, answers to this question have consequences in both effective mathematics and the foundations of mathematics. Before discussing these consequences, we need to be more specific about the motivating question.Reverse mathematics is useful for studying theorems of either countable or essentially countable mathematics. Essentially countable mathematics is a vague term that is best explained by an example. Complete separable metric spaces are essentially countable because, although the spaces may be uncountable, they can be understood in terms of a countable basis. Simpson (1985) gives the following list of areas which can be analyzed by reverse mathematics: number theory, geometry, calculus, differential equations, real and complex analysis, combinatorics, countable algebra, separable Banach spaces, computability theory, and the topology of complete separable metric spaces. Reverse mathematics is less suited to theorems of abstract functional analysis, abstract set theory, universal algebra, or general topology.Section 2 introduces the major subsystems of second order arithmetic used in reverse mathematics:RCA0,WKL0,ACA0,ATR0and–CA0. Sections 3 through 7 consider various theorems of ordered group theory from the perspective of reverse mathematics. Among the results considered are theorems on ordered quotient groups (including an equivalent ofACA0), groups and semigroup conditions which imply orderability (WKL0), the orderability of free groups (RCA0), Hölder's Theorem (RCA0), Mal'tsev's classification of the order types of countable ordered groups (–CA0)
Optimal Proofs of Determinacy
Authors: Neeman Itay 
Published: May 2006

In this paper I shall present a method for proving determinacy from large cardinals which, in many cases, seems to yield optimal results. One of the main applications extends theorems of Martin, Steel and Woodin about determinacy within the projective hierarchy. The method can also be used to give a new proof of Woodin's theorem about determinacy in L(ℝ).The reason we look for optimal determinacy proofs is not only vanity. Such proofs serve to tighten the connection between large cardinals and descriptive set theory, letting us bring our knowledge of one subject to bear on the other, and thus increasing our understanding of both. A classic example of this is the Harrington-Martin proof that -determinacy implies -determinacy. This is an example of a transfer theorem, which assumes a certain determinacy hypothesis and proves a stronger one. While the statement of the theorem makes no mention of large cardinals, its proof goes through 0#, first proving that-determinacy ⇒ 0# exists,and then that0# exists ⇒ -determinacyMore recent examples of the connection between large cardinals and descriptive set theory include Steel's proof thatADL(ℝ) ⇒ HODL(ℝ) ⊨ GCH,see [9], and several results of Woodin about models of AD+, a strengthening of the axiom of determinacy AD which Woodin has introduced. These proofs not only use large cardinals, but also reveal a deep, structural connection between descriptive set theoretic notions and notions related to large cardinals.