Successional Series Research Articles

Light partitioning among species and species replacement in early successional grasslands

Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ‘later successional’ species had higher light harvesting efficiencies for the same plant height than ‘early successional’ species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series.

Habitat and successional status of plants in relation to the communities of their leaf‐chewing herbivores in Papua New Guinea

Summary The spatial distribution of 30 woody species (15 species each of Euphorbiaceae and Moraceae) and their associated leaf‐chewing communities (Orthoptera, Phasmatodea, Coleoptera and Lepidoptera) were studied in coastal, riverine and rain forest habitats. A successional series, from abandoned gardens to primary forest, was examined. Host plant records for more than 27 000 insects, all verified by feeding experiments, and spatial distribution of almost 9000 plant specimens were evaluated. Phylogenetic (taxonomic) relatedness of host plants explained 56% of the variability in the composition of their herbivore communities, while the ecological (distribution) similarity of plants explained only 4%. The successional optimum of plant species was not an important determinant of the composition of their herbivore communities. Neither plant successional optimum nor plant palatability to a generalist herbivore were correlated with the number of species, abundance or host specificity of its herbivores, nor was there a correlation between a plant’s palatability to a generalist herbivore and its successional optimum. Herbivore communities became dominated increasingly by a few abundant species in later stages of succession. On average,Ficusspecies had lower palatability and supported more species of herbivores than species of Euphorbiaceae. The abundance of herbivores and their dominance index were not significantly different between the two plant families. These results contradict several previous studies of successional trends in temperate regions. Many tropical successions, however, start with pioneer trees, rather than with annual herbs, and may present a permanent and predictable habitat for insects even at the earliest stages, with no advantage for polyphagous species. Numerous pioneer trees in the tropics possess anti‐herbivore defences, resulting in their low palatability to generalists, increased host specificity of herbivores, and often idiosyncratic composition of herbivore communities. Even plant traits such as species richness of their herbivores or palatability may have a phylogenetic component which should not be ignored.

SUCCESSIONAL CHANGES IN BACTERIAL ASSEMBLAGE STRUCTURE DURING EPILITHIC BIOFILM DEVELOPMENT

Although bacteria are often treated as one entity in ecological studies, bacterial assemblages are composed of individual species populations. Bacterial assemblages can have their own richness and structure, analogous to communities of plants and animals, although few studies have attempted to describe spatial or temporal patterns in their structure. In this study, we examined successional changes in the structure of bacterial assemblages using denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction amplified 16S rDNA fragments. Bacterial biofilm assemblages developing on glass slides in a mesocosm and a small lake showed an initial increase in richness over the first week, followed by a slight decrease and a subsequent increase after two to three months. Functional changes in the bacterial community were examined using most probable number estimates and revealed decreases in the abundance of glucose- and cellulose-degraders during biofilm development, whereas benzoate-degraders became more abundant in the lake biofilms. The banding patterns observed on DGGE gels were used to derive rank-abundance profiles for each stage of biofilm development. These profiles resembled those observed for communities of macroorganisms and could usually be described by geometric series models. These models suggested greater equitability in bacterial community structure as the biofilms developed. A comparison of two successional series of biofilms separated by 30 d revealed that neither successional stage nor time of sampling was the major factor influencing bacterial assemblage structure. Our results allowed us to suggest a general model for the development of bacterial biofilm assemblages that emphasizes the interaction of species and resource diversity. This model suggests that, at least in biofilms, bacterial assemblages may not be structured by the resource competition or niche-driven patterns typical of communities of macroorganisms.

Successional Changes in Bacterial Assemblage Structure during Epilithic Biofilm Development

Although bacteria are often treated as one entity in ecological studies, bacterial assemblages are composed of individual species populations. Bacterial assemblages can have their own richness and structure, analogous to communities of plants and animals, although few studies have attempted to describe spatial or temporal patterns in their structure. In this study, we examined successional changes in the structure of bacterial assemblages using denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction amplified 16S rDNA fragments. Bacterial biofilm assemblages developing on glass slides in a mesocosm and a small lake showed an initial increase in richness over the first week, followed by a slight decrease and a subsequent increase after two to three months. Functional changes in the bacterial community were examined using most probable number estimates and revealed decreases in the abundance of glucose- and cellulose-degraders during biofilm development, whereas benzoate-degraders became more abundant in the lake biofilms. The banding patterns observed on DGGE gels were used to derive rank-abundance profiles for each stage of biofilm development. These profiles resembled those observed for communities of macroorganisms and could usually be described by geometric series models. These models suggested greater equitability in bacterial community structure as the biofilms developed. A comparison of two successional series of biofilms separated by 30 d revealed that neither successional stage nor time of sampling was the major factor influencing bacterial assemblage structure. Our results allowed us to suggest a general model for the development of bacterial biofilm assemblages that emphasizes the interaction of species and resource diversity. This model suggests that, at least in biofilms, bacterial assemblages may not be structured by the resource competition or niche-driven patterns typical of communities of macroorganisms.

Soil Saprotrophic Microfungi Associated with Roots of Calamagrostis epigeios on an Abandoned Deposit of Toxic Waste from Smelter Factory Processing Pyrite Raw Materials.

Saprotrophic microfungi associated with roots of Calamagrostis epigeios growing in industrial waste contaminated with high concentrations of heavy metals (manganese, iron, zinc) were isolated on three different media. The isolates were obtained from three plots colonized by plant cenoses, representing three different succession series of plant cover: initial, intermediate, and advanced. A total of 60 species of saprotrophic microfungi were found in the roots during three samplings. In addition, unidentified dark and white sterile mycelia were frequently isolated. Trichoderma koningii was frequent in the roots formed under the advanced phytocenose. The abundance of dark sterile mycelium gradually decreased with progressing succession of the plant cover. Chrysosporium merdarium was rarely observed in the roots under the intermediate and advanced plant cenoses. Multivariate redundancy analysis showed that the effect of succession stage of phytocenoses on incidence of saprotrophic microfungi in mycocenoses present in roots was statistically significant. When the similarity of root mycocenoses of the three plots was studied using the similarity coefficients, the results proved that the similarities between the initial and intermediate or intermediate and advanced mycocenoses were higher than that between the initial and advanced mycocenoses. This corresponds to a different speed of succession of the mycocenoses. The results suggest that the dark sterile mycelia, abundant at slowly developing plots, play a dominant role during the first stages of succession where the plant cover is poor.

Enchytraeid communities in successional habitats (from meadow to forest)

The study was conducted in two successional series: natural on mesotrophic soils (a meadow, two birch woods and a mixed coniferous forest), and human-made on sandy soils (old field, birch plantation and pine forest). In both these series species richness and diversity of enchytraeid communities decreased with advancing succession. In the first two successional stages, enchytraeid communities showed a high degree of similarity (the meadow and 30-year-old birch thicket, ore the old field and 10-year-old birch plantation). Variation in soil in the same plant communities cause differences in animal communities. The abundance of enchytraeids varied from 14 to 51 × 103 m−2 individuals. In the majority of habitats C. sphagnetorum was the dominant species. Soil pH showed a positive correlation with species diversity and negative with number of C. sphagnetorum. The body size of this species was small at low pH (presumably as a result of frequent reproduction). It is suggested that the way of reproduction of the dominant species could confer a competitive advantage, thereby accounting for the simplification of enchytraeid communities in later stages of succession.

Legislative Records, 2000

The political scene behind Japan's legislation in 2000 was uneasy and flurried. The ascent to political power by Prime Minister Yoshiro Mori following the sudden death of Prime Minister Keizo Obuchi, the shift in political framework caused by the separation of the Liberal Party from the coalition government, and the general election came one after the other in a series of restless succession.

Dynamics of bog-pine-dominated mires in the Jura Mountains, Switzerland: A tentative scheme based on synusial phytosociology

A description of the bog-pine (Pinus uncinata var.rotundata) dominated vegetation of uncut oligotrophic mires affected by drainage is given. Surveys were carried out at 17 sites along the Jura Mountains (Switzerland and France) in 1993, 1994, and 1995. Raised bogs of the Jura are generally of small size, and most vegetation changes in them have occurred as a result of the indirect impact of peat cutting. This activity led to the peat drying out and to colonization by trees, in particular by bog-pines.Integrated synusial phytosociology was used to describe the vegetation where bog-pine, spruce, and birch occur. Two spatio-temporal levels of organization were considered: the synusia and the phytocoenosis. At the phytocoenosis level, four vegetation types representing bog-pine stands of uncut and deep oligotrophic peats are described with their constitutive synusial composition. They represent: (1) phytocoenoses developing in the open, wet central parts of the bogs, where trees are scattered and of small size, (2) phytocoenoses with layered tree stands of medium size and with a higher density, and (3) phytocoenoses with tall trees, developing generally near the edge of the bogs or close to peat cuttings. A generalized qualitative dynamic model of the vegetation in relation to the development of bog-pine trees was developed. It shows the spatial and temporal organization of the constituent synusiae, as well as other underlying hypothetical functional relations.The different bog-pine-dominated vegetation types described in this study appear to have coexisted since the origin of the Jura bogs as a result of local polyclimaxes induced by differential waterlogged situations. They probably all belong to the same (primary) successional series, but have been affected by both autogenic and allogenic processes. During the development of the bogs the balance between the different communities changed. In particular, the vegetation types with dense and tall pine trees have undergone a drastic expansion since the Jura bogs were first affected by drainage.

The self-organization of trophic structure in ecosystem models: the succession phenomena, trigger regimes and hysteresis

The self-organization of trophic structure in ecosystems during the course of biogenic succession was analyzed using the dynamic ecosystem model with two competing food webs of the type ‘producer–consumer–top predator’. Variants of the model with feeding-specialized and mixed-feeding consumers were considered. The ecosystem development was limited by one biogenic element, recycling in the system, with the total reserve of element M Σ. The biogenic succession was simulated by a slow increase of M Σ from zero to higher values, and after that by a gradual decrease back to zero. The different trophic structures, formed from the initial set of species were analyzed, and analytical conditions of their existence and stability were obtained. The total pool of element M Σ was found to be the key parameter, determining the development of food webs. It was shown analytically that each particular trophic structure, formed from an initial set of species exists and is stable within a strictly defined range of M Σ values; following the gradual increase of M Σ, trophic structures replace each other, thus forming succession series. In the ecosystem model with feeding-specialized consumers, the gradual development of trophic organization from primitive ‘one-species’ structure to the most complicated food webs was demonstrated, and two possible variants of succession series were revealed. In the system with mixed-feeding consumers more than 10 different variants of succession series were found, depending on the ecological parameters of the species. Specific trigger regimes were found, when two different trophic structures existed and were stable within one and the same range of parameters; the actual realization of a particular trophic structure was completely determined by initial values of biomasses of species. For succession series, which contained trigger regimes, a hysteresis phenomena was demonstrated: the successive changes in the trophic structures realized following the gradual increase of M Σ were not reproduced in the same order if M Σ was gradually decreased back to its previous values.

Sulfur-Isotope Characteristics of the Volcanogenic Cu-Zn-Pb Deposits of the Eastern Pontide Region, Northeastern Turkey

In the Eastern Pontide Region of northeastern Turkey, volcanogenic Cu-Zn-Pb deposits of the Kuroko type are widespread within the dacitic series of the Liassic-Eocene volcano-sedimentary succession. Sulfide mineralization within the studied deposits shows four different depositional styles: disseminated ore; polymetallic stockwork ores; polymetallic massive ores; and disseminated pyrite in the hanging-wall tuff units. Only the stockwork and massive ores are economically important, and usually one or the other dominates in each ore body. The δ34S of sulfide minerals belonging to the various styles of mineralization are in the range from −2.6 to +5.2% (VCDT): pyrite has the highest values and the galena lowest values in agreement with the usual isotopic-fractionation trends. Massive ores have heavier sulfur-isotope composition among the mineralization styles and the heaviest values are recorded in barite- and gypsum-rich deposits. The close similarity of the δ34S among the various mineralization episodes in some deposits indicates a single sulfur source having a stable and homogenous composition. The δ34S of sulfates fall into three groups: barites and primary gypsum (15.4 to 20.4%), close to coeval seawater sulfate; one value of barite (25.4%) heavier than coeval sea water; and values of secondary gypsum (2.2 to 8.0%) either very light compared to coeval seawater sulfate, or within the range recorded from sulfide minerals. The δ34S values of pyrite disseminated in the brecciated dacite tuff units are very close to zero and similar to the ones reported for magmatic rocks, suggesting a magmatic source for the sulfur of the earliest sulfide mineralization episode. These δ34S data are not sufficient to calculate the fraction of the reduced sulfur derived from seawater sulfate, as the associated fractionation factor cannot be constrained.

Ecohydrological perspective of phytogenic organic and inorganic components in Greek lignites: a quantitative reinterpretation

A consensus about the development of freshwater wetlands in relation to time and space is urgently required. Our study aims to address this issue by providing additional data for a fine-scaled comparison of local depositional settings of Greek mires during the Pliocene and Pleistocene. Lignite profiles exhibit phytogenic organic components (macerals) that have been used to investigate the past peat-forming vegetation structure and their succession series. The organic petrology of lignite samples from the opencast mines of Komanos (Ptolemais) and Choremi (Megalopolis) was achieved to assess the water supply, wetland type, nutrient status and vegetation physiognomy. A holistic approach (a study of ecosystems as complete entities) was carried out for a paleoecological reconstruction of the mires. Huminite, liptinite and inertinite were traced by means of their chemical and morphological differences together with the morphogenic and taphonomic affinities. The problem of combining independent information from different approaches in a multivariate calibration setup has been considered. Linear regression, non-metric multidimensional scaling and one-way analysis of variance tested the occurrence of palynological and petrological proxies. Although the lignite formation and deposition are less related to humid periods than expected, the resulting differences occurring in the reconstructed development stages appear to be related to astronomically forced climate fluctuations.

Relationships between pikas (Ochotona, mammalia) and vegetation in Tuva

The burrowing and trophic activities of four pika (Ochotona) species proved to be reflected in the horizontal structure of the biogeocenotic cover. Zoophytochores ofOchotona daurica andO. pallasi pricei burrows correspond to previously described ameboid zoophytochores. Burrows of pikas provide for the growth of pea shrubs (Caragana bungei, C leucophloea), with the formation of specific plant groups under their crowns and on rubble dug out by pikas. In ecosystems of placers, zoophytochores are formed owing to the presence of pika food stores and lavatories, which are the main substrate for vascular plants first appearing among the stones. General ecological (and successional) series characterizing the overgrowing of placers is as follows: (1) separate spots of vegetation with poor floristic composition at the sites of pika food stores (stacklets); (2) groups of spots and simplest complexes; and (3) complex plant communities of pika colonies. Food stores of pikas in Tuva were analyzed.

Крупномасштабные карты растительного покрова западного побережья залива Петра Великого (Дальний Восток, бассейн Японского моря)

Two territories on the western coast of Peter the Great Bay were mapped in the large scale. The geobotanical mapping means revealing and displaying the essential regularities of vegetation cover. Both the spatial and temporal regularities of vegetation under natural and anthropogenic influences are well pronounced in the territory under consideration. The concept of the vegetation spatial unit (vegetation complexes) was applied as a basis for mapping. The maps and their legend were worked out as a system of vegetation combination types (vegetation combination is a spatial unit of the supracoenotic level). Such categories, as vegetation of tops and slopes, lowlands and river valleys, sea coasts reflect maximal contrasts in vegetation cover, so they are the highest level divisions of the map legend. Types of succession series and stages of series are developed for construction of the second and third levels of the legend. Communities, similar in ecotope, total species composition, saplings and some other characteristics, are referred to one type of series. 5 types of series have been distinguished: dry, fresh, moist, very moist, wet. The main factor of dynamics in considered territory is fire and the series are mainly pyrogeneous. Series are presented as sequences of vegetation stages. The vegetation stages for tops and slopes are: closed low forest — open low woodland — shrub thicket with saplings — meadow with saplings, for lowlands and river valleys they are: open low woodland — thicket of saplings — meadow or mire with saplings.

Plant species diversity in an old, traditionally managed hay meadow compared to abandoned hay meadows in southwest Norway.

A chronosequence, representing a successional series, was used for the comparison of a hay meadow site managed in an old traditional way for at least a hundred years, and hay meadow sites abandoned for about 10, 20 and 30 years, respectively. Old traditional management included grazing early and late in the growing season, mowing in August and light or no fertilizing. The tree cover was the most important factor deciding the composition of vegetation. Time since abandonment was not completely correlated to tree cover, as some plots had a dense canopy and others were situated in the open. The total species number decreased with number of years since abandonment in plots > 0.001 m2and <100 m2. The highest species number in 1 m2 plots was recorded in the managed site, with 38 species of phanerogams. Fourtyeight % of the indicators of traditional management present in the managed site was recorded in the site which had been abandoned for 30 years. Frequency — log area curves made it possible to group species according to persistence in the sward. As a result, a group of functional indicators of rare hay meadows in the region was distinguished.

Consequences of abandonment for a regional fen flora and mechanisms of successional change

Abstract. Until the 1960s, species‐rich vegetation on minero‐trophic peaty soüs (fen sites) were characteristic of the alluvial plains in Schleswig‐Holstein (Northwest Germany). Today, many of these habitats undergo successional changes due to abandonment. Vegetation development after abandonment can be characterized as a sequence of different successional stages and described in terms of a successional model. Successional stage I includes grazed, mown and recently abandoned sites without dominants. Stages II and III are characterized by the dominance of highly competitive herbaceous species whüe stage IV consists of woody vegetation.Ca. 3000 phytosociological relevés were assigned to the respective successional stages. Mean cover values were calculated for 250 species of the regional fen flora and assigned to successional categories according to their changes in cover in the successional series. According to our results 141 species decrease during succession, while 100 species were restricted to early successional stages and 85 species increased. Abandonment of all fen sites in Schleswig‐Holstein will probably lead to the regional loss of 23 species of the fen flora.To identify mechanisms underlying successional change, the successional categories were correlated with life history traits and ecological requirements of the species. Results indicate that both light competition and limitation of sexual reproduction of small‐seeded species might play a major role in the decrease and extinction of species during succession.Finally, conservation strategies for endangered species in a cultural landscape are discussed.

Life strategies of epiphytic bryophytes in Mediterranean woodlands and

A life strategy analysis of the epiphytic Brachythecio olympici-Dicranoweisietum cirratae (xeric Pinus woodlands) and the Orthotricho franzoniani-Antitrichietum breidlerianae (Platanus alluvial forests) of southwest Anatolia was conducted, based on a plant sociological analysis. Typical of the drought-resistant, photo- and xerophytic Brachythecio-Dicranoweisietum are xerotolerant cushion- and short turf-forming acrocarpous “generative” perennial stayers with a regular sporophyte production and small spores, providing chance dispersal for colonizing the extensive Pinus woodlands of the area. By contrast, tail-, mat- and fan-forming pleurocarpous mosses and liverworts, belonging to the “passive” or “vegetative” perennial shuttle species and perennial stayers strategy, dominate the shadier, meso- to hygrophytic Orthotricho-Antitrichietum. In addition, in this community short-range dispersal, as indicated by large spores (engy- and achorous tendency) is typical, increasing the chance of establishment within the narrow alluvial forests along the rivers. The great proportion of the Colonists strategy in the Brachythecio-Dicranoweisietum, which is typical of true colonizing and pioneering species of successional series, can be seen as an indicator for disturbing effects caused by fire, that often occur within these xeric Pinus woodlands. Auf der Grundlage einer pflanzensoziologischen Untersuchung wurde im epiphytischen Brachythecio-Dicranoweisietum (typisch für die Pinus-Offenwälder) und im Orthotricho franzoniani-Antitrichietum breidlerianae (Platanus-Auwälder) Südwest-Anatoliens eine Lebensstrategienanalyse durchgeführt. Charakteristisch für das xerophytische, strahlungsexponierte Brachythecio olympici-Dicranoweisietum cirratae sind trockenadaptierte, polster- und kurzrasenbildende, akrokarpe “generative” Ausdauernde mit regelmäβiger Sporogonbildung und kleinen Sporen, durch die Nah- und Fernausbreitung in den ausgedehnten Pinus-Offenwäldern der Region möglich ist. Im Gegensatz dazu zeichnet sich das eher beschattete und feuchtere Orthotricho-Antitrichietum durch schweif-, decken- und wedelbildende pleurokarpe Laubmoose und Lebermoose aus, die den Lebensstrategien “passive” oder “vegetative” Ausdauernde Pendler und Ausdauernde angehören. Die relativ groβen Sporen dieser “Pendler” deuten auf Nahausbreitung (Engychorie) innerhalb der Auwälder hin, wodurch ein Etablierungsrisiko, das auβerhalb der nur schmal ausgebildeten, bachbegleitenden Wälder besteht, vermieden wird. Der relativ hohe Anteil an Besiedlern im Brachythecio-Dicranoweisietum, einer Strategie die charakteristisch für viele Pionierarten verschiedenster Sukzessionsstadien ist, ist möglicherweise ein Hinweis auf die Störungen durch Brände, die in diesen trockenen Kiefernwäldern häufig zu beobachten sind.

Respiration of the belowground parts of vascular plants: its contribution to total soil respiration on a successional glacier foreland in Ny-�lesund, Svalbard

As a part of the study on soil carbon flow in a deglaciated area in Ny-Alesund, Svalbard (79°N), we estimated the contribution of the belowground respiration of vascular plants to total soil respiration in August 1996. Four study sites were set up along a primary successional series, ranging from newly deglaciated moraine to older moraine with well-developed vegetation cover. Respiratory activity of the belowground parts (roots + belowground stems) of three dominant species, Salix polaris, Saxifraga oppositifolia and Luzula confusa, was determined under laboratory conditions. The respiratory activity and the Q10 value of the respiration were higher in S. polaris than in the other two species. Total soil respiration rates measured in the field varied widely. The areas with dense vegetation cover tended to show high respiration rates. Belowground respiration of vascular plants was estimated based on the respiratory activity and biomass of the belowground parts at each study site. The contribution to the belowground respiration to total soil respiration was negligible in the early stages of succession. On the other hand, the respiration of the belowground parts contributed to a significant proportion (?29%) of the total soil respiration in the latter stages of succession.

The role of tree sprouts in the restoration of stand structure and species diversity in tropical moist forest after slash-and-burn agriculture in Eastern Paraguay

Key words: Floristic similarity, Forest fallows, Mature forest, Recovery process, ResproutingAbstractThe contribution of tree sprouts to the recovery of tropical moist forest in Eastern Paraguay after swidden agri-culture was examined in 2–15 yr old forest fallows and compared with sprouting in mature forest. The proportionof stems of sprout origin, as individuals arising from stumps or lower parts of live stems (1 m), in the stemdensity declined from 59.5% (stems 1–4.9 cm DBH) and 21.0% (stems 5 cm DBH) in the young regrowthstands (2–5 yr old) to 32.9% and 19.6%, respectively in the older regrowth stands (10 and 15 yr old). Sproutswere absent in the mature forest. Out of 58 species sampled in the regrowth stands, 28 occured both as resproutsand seed regeneration, 7 were only found as resprouts, and 23 were only present as seed-established individuals.No significant relationship was found between the successional status or the growth form of species and apparentresprouting capacity. Seed-established individuals ofTrema micranthawere predominantin the two and three-yearold regrowth stands. In the more advanced successional stages, T. micrantha was replaced by Cecropia pachys-tachia and other secondary species. Species richness increased during succession. Species-abundance distributionin the successional stands followeda log series pattern, whereas the mature forest showed a log normaldistribution.Floristic similarity to the mature forest, calculated with the qualitative Soerensen index, increased from 0.45 (1–4.9 cm DBH) in the young regrowth stands to 0.52 in the older regrowth stands. In the tree stratum (5cmDBH),however, floristic composition approached only 0.28 in the younger regrowth stands and 0.44 in the older regrowthstands, respectively that of the mature forest.IntroductionInitial floristic composition in disturbed tropical forestis mainly determined by the soil seed bank, advanceregeneration, and the resprouting capacity of stumps.In recent times, sprouting has been studied in nat-ural forests after hurricane disturbance (Yih et al.1991; Basnet 1993; Bellingham et al. 1994), after firedisturbance(Kauffman1991),orasa componentofre-generation after natural gap creation (Putz & Brokaw1989; Matelson et al. 1995).In neotropical forests, sprouting is the most com-mon means of regeneration after forest cutting, butburning reduces the amount of sprouts (Uhl et al.1981; Uhl & Jordan 1984). Moreover, repeated weed-ing and prolonged cultivation lead to a steady declinein, or even to the complete exhaustion of, the resprout-ing capacityof trees (Uhl et al. 1982a; de Rouw 1993).However, except for the work of Saldarriaga et al.(1988), who studied sprout density in 9 to 80 yr oldforest fallows and mature forest stands, the long-termrole of sprouts in the overall recovery process afterslash-and-burn agriculture is not well documented.This paper describes resprouting in different-agedforest fallows and mature forest in Paraguay with thefollowing objectives: (1) determining the proportionof sprouts in stem density and basal area with succes-sional age, (2) studying the role of sprouts in canopy

Intrapopulational size structure of the monocarpic species Saxifraga mutata and its relationship to succession

Summary The monocarpic Saxifraga mutata, a locally endangered species in Central Europe, grows at sites which are strongly influenced by erosion. Three populations of S. mutata were investigated in Northeastern Switzerland. Each of the localities is characterized by a succession series from almost bare slopes to sparse Pinus-woods (Molinio-Pinetum). Rosette diameters of vegetative and generative individuals showed L-shaped distributions in two populations. A normal-shaped distribution, indicating low rejuvenation, was found in the third population. Rosette diameters were significantly correlated with other fitness-related traits such as number of flowers, number of leaves, and flowering stem length. A reproductive threshold size of c. 4 cm in rosette diameter was recorded. Investigations of size structures in plots of 1 m2 demonstrated that rosette size, rosette density, recruitment, and frequency of flowering individuals were closely related to successional stages as well as intensity and frequency of erosion. Maintenance of local populations of S. mutata depends on the balance between erosion and succession. Landscape dynamics must be warranted in order to conserve this species.

Soil seed bank composition along a gradient from dry alvar grassland to Juniperus shrubland

Abstract. Dry alvar grasslands on limestone on the Baltic island of Öland, SE Sweden, are very species‐rich as long as the traditional agricultural exploitation of grazing and fire wood collection continues. After abandonment, encroachment of Juniperus communis starts and a closed woodland can develop within 100 yr. A chronosequence, representing a successional series, was used for the comparison of sites still grazed, and sites ungrazed for about 20, 55 and 80 yr, respectively. Out of the 58 characteristic dry alvar grassland species 55 % disappeared from the established vegetation after 80 yr of abandoning, and 80 % also vanished from the seed bank. Arenaria serpyllifolia, Trifolium repens, Agrostis vinealis, Linum catharticum, Polygala vulgaris, Cerastium fontanum, Luzula campestris, Achillea millefolium and Potentilla tabernaemontani were the only species left in the seed bank. More than 75 % of the dry alvar grassland species were classified as having a transient or short‐term persistent seed bank. It is concluded that restoration management, by cutting junipers, of overgrown dry alvar grassland cannot rely on the longevity of seeds in the soil. Seeds have to be dispersed by wind or grazing animals.