Abstract: (1) Seed-bank species composition and seed density were determined in an annually ploughed field at the Kellogg Biological Station in south-western Michigan, U.S.A. using three different methods: direct germination, germination following cold-stratification, and washing using a modified elutriation system. A fourth method, flotation on a salt-density gradient was abandoned after preliminary trials showed it was inefficient and inaccurate. (2) Twenty soil cores (2 5 cm in diameter, 15 cm deep) were taken from each of twentyfive sampling points in the field. Cores were divided into three depth intervals (0-2 cm, 2-5 cm and 5-15 cm) and five cores from each quarter of a sampling quadrat were combined and randomly assigned to one of the four methods for estimating the seed bank. (3) A total of fifty species was detected in the seed bank of this community. Overall, more species were detected with cold-stratification (forty-two species) than with direct germination (thirty-seven) or elutriation (thirty-five). Plots of species-sampling-area curves showed that fifteen to twenty sampling locations were sufficient to determine the number of species present in the seed bank with any of these methods. (4) Seed-density estimates were significantly higher in the elutriated samples. This was due primarily to the inclusion of inviable seeds in the counts from the elutriated samples. (5) There were significant differences in seed viability among species recovered in the elutriated samples. Both Ambrosia artemisiifolia and Chenopodium album, seeds of which were common in the samples, had low viability (25% and 3%, respectively). (6) Germination methods (particularly when more than one pre-treatment method is used) provide a more complete listing of species present in the soil seed bank of a community than elutriation. However, elutriation methods may be more useful for documenting variation in seed distributions on a large spatial scale or in quantifying the distribution of species with unique, easily identifiable seeds. Elutriation seems particularly well-suited for quantifying the distribution of plants that are considered weeds in agricultural systems, because many of these species have seeds that are easily identified and retain viability when dried.

Abstract: SUMMARY (1) Micro-environmental conditions, vegetation structure and tree mortality in five forest edges ten months to twelve years old were studied in the tropical premontane wet forest of Panama. (2) Along transects from clearings to the interior of the forest, the greatest change in temperature and relative humidity occurred between 2 5 and 15 m into the forest. The forest canopy was most open at the clearing-forest border. At the most recently cleared site, this open canopy extended farther into the forest edge than at sites where clearing took place earlier. (3) Density and basal area of trees ( < 10 cm diameter at 1 3 m high) were twice as great at the forest edges compared with the interior of forests at the sites where the boundaries were created five to twelve years previously. (4) Floristic composition was unchanged along transects from the forest boundaries to the interior of forests and light-demanding species were not more abundant at forest edges compared with the forest interior. (5) The edge: interior ratio of trees that died after the edges were created was 14: 1. (6) Beyond 15-25 m into the forest, neither environmental conditions nor the forest structure and tree mortality were influenced by proximity to the forest boundary. Between 0 and 15 m, however, vegetation structure changed with both distance from the forest boundary and time elapsed since clearing. This study indicates the ecological significance of edge vegetation as a buffer protecting forest vegetation from conditions in adjacent clearings.

Abstract: This book reviews the biology of bryophytes and lichens in the polar tundra, where these plants may form a dominant component of the vegetation. It considers adaptation to severe environments in terms of growth form, physiology and reproduction. The role of bryophytes and lichens is discussed in vegetation processes such as colonisation and succession, and in energy flow, nutrient cycling and other functional aspects of polar ecosystems, both natural and as modified by man, The range of microclimates experience by polar cryptograms is described using an energy budget approach, and the environmental relationships of CO2 exchange, stress resistance, growth and other physiological responses are discussed against this background. Reproductive biology is also reviewed as an introduction to a consideration of population ecology, distribution patterns, dispersal potential and the origin and adaptation of polar cryptogamic floras. This book integrates the results of work in the Arctic and the Antarctic, and includes a classification of vegetation zones applicable to both polar regions. The study of plant ecology in these areas has advanced dramatically and the results synthesised here contribute to a general understanding both of polar ecosystems and of the environmental relationships of bryophytes and lichens.

Abstract: CONCEPTUAL ISSUES IN PLANT BREEDING SYSTEMS: J. and L. Lovett-Doust: Sociology of plants - an emerging synthesis Robert Bertin: Paternity in Plants David Haig and Mark Westoby: Inclusive fitness, seed resources, and maternal care Paul Cox: Monomorphic and dimorphic sexual strategies - a modular approach Spencer Barrett: The evolution, maintenance, and loss of self-incompatability systems Mark Schlessman: Gender diphasy ("sex choice") ECOLOGICAL FORCES: Michael Zimmerman: Nectar production, flowering phenology, and strategies for pollination Tom Lee: Patterns of fruit and seed production Don Waller: Plant morphology and reproduction Jacob Weiner: The influence of competition on plant reproduction Steve Hendrix: Herbivory and its impact on plant reproduction REPRODUCTIVE STRATEGIES OF NON-ANGIOSPERMS: Robert De Wreede and Terry Klinger: Reproductive strategies in algae Brent Mishler: Reproductive ecology of bryophytes Michael Cousens: Reproductive strategies of pteridophytes.

Abstract: SUMMARY (1) Two peat mounds have developed in the Lost River peatland of northern Minnesota. One has the chemical and physical properties of an extremely rich fen and the other has the properties of a raised bog. The two mounds are separated by a water track with poor-fen vegetation and chemistry. (2) The vegetation at Lost River can be divided into five noda that correspond to landform units: spring-fen channel, spring-fen forest, marginal swamp forest, water track, and raised bog. These vegetation types have well-defined ranges for pH and calcium concentration. (3) Ordinations of the vascular plant and bryophyte data indicate a close relationship between the vegetation and both moisture and chemical gradients. The link between vegetation and chemistry is also supported by plots of species richness vs. pH and calcium concentration in which the peak in species numbers occurs within the rich-fen range. (4) The chemistry of the surface waters at Lost River is largely determined by the mixing of alkaline groundwater with precipitation, because the entire peatland is located at least seasonally within a discharge zone for groundwater. Mixing models indicate that the amount of groundwater within the surface waters ranges from 50% in the spring-fen channels to 1 % on the raised bog. (5) The development of the two peat mounds was reconstructed from peat cores collected near the crests of the spring-fen mound and raised bog. The raised bog developed over a depression, which was first filled in with fen peat before minerotrophic sphagna invaded the site around 2625 B.P. By 2200 B.P. all fen indicator species had disappeared and the site was dominated by assemblages similar to those in the present raised bog. (6) The spring-fen mound, however, developed over a rise in the mineral substrate, which was not covered by peat until 3000 B.P. The mound was quickly colonized by Sphagnum and no fen indicators appeared until 1160 B.P. At this time the bog vegetation was replaced by a sedge fen containing assemblages similar to the present spring-fen channel. (7) This sharp reversal from bog to fen under the spring-fen mound can best be explained by the discharge of alkaline groundwater at the peat surface in sufficient quantities to convert the bog vegetation to a spring-fen channel.

Abstract: The natural history of Peyronie's disease was evaluated in 97 men by means of a questionnaire. Disease duration ranged from 3 months to 8 years. Questions addressed pain, bending, ability for intercourse, over-all effect of the disease, psychological effects, treatments received and degree of disease progression. Approximately 40% of the patients found pain, bending, ability for intercourse and over-all effects to be unchanged during the course of the disease. Bending and ability for relations worsened in 40% of the patients during the same interval, while only 6% had worsening of pain. Of the patients 77% reported psychological effects due to Peyronie's disease, which improved in 28%, did not change in 36% and worsened in 36%. Over-all, 13% of the patients believed the disease to be one of gradual resolution, 47% believed there had been little or no change and 40% believed that the disease pattern was one of gradual progression. We found no statistically significant association between disease duration and spontaneous improvement in penile bending. A similar lack of statistical significance was found when improvement in a variety of categories was compared in patients who received no therapy versus those who received a variety of conventional medical therapies.

Abstract: (1) Leaf fall and reproductive phenology of Avicennia marina assessed during 1982-83 using litter fall collections from twenty-five sites in Australia, Papua New Guinea and New Zealand revealed major trends with latitude. Flowering shifted from November- December in northern tropical sites, to May-June in southern temperate sites. Periods between flowering and fruiting increased from two to three months in tropical sites to ten months in southernmost sites. Leaf fall was more variable with unimodal annual peaks in temperate sites and often multimodal patterns in the tropics. (2) Correlative evaluation of simple models suggested that initiation of the reproductive cycle occurred when daylength exceeded 12 h, followed by rates of development to flowering and fruit maturation given by a linear function of mean daily air temperature. This explained up to 92% of variance in total cycle duration and timing. Temperature affected reproductive development by increasing growth rates by a factor of two or three for each 10 'C rise. The model was tested using independent data to predict timing of reproductive events in respective sites. (3) Appearance of new leaves on canopy shoots in situ near Townsville, northern Queensland, had seasonal highs followed by peak falls a month later, and leaf longevity was estimated to be around thirteen months. Timing of new leaf appearance and leaf fall were comparable with observations from other studies and sites, geographically overlapping with the present litter-fall sites in Australasia. These had seasonal peaks, chiefly related to either the reproductive cycle during initiation of inflorescence development or independent growth. Respective heights of these peaks for particular sites appeared to depend on environmental factors of temperature and moisture. Thus, inflorescence leaf appearance was predominant in low-moisture and low-temperature sites during early summer, and independent leaves appeared mostly in wetter tropical sites during winter months. (4) Distributional limits of A. marina in higher latitudes coincide with trends towards zero reproductive success (notably seen in flowering). This was apparently brought about by a convergence of phenological events within the shorter growth period of summer in these latitudes.

Abstract: By assessing productivity and ecosystem nutrient distribution, this work extends the early classic studies of the influence of N 2 fixers and conifers on soil development and nitrogen accumulation in a primary succession chronosequence at Glacier Bay, Alaska, U.S.A. The nitrogen-fixing shrub Alnus sinuata (Sitka alder) dominates recently deglaciated sites along Glacier bay but is replaced by Picea sitchensis (Sitka spruce) after about 80 years. While Alnus dominated, soil organic matter and nitrogen (N) increased very rapidly (...)

Abstract: (1) The effect of disturbance on diversity patterns of cryptogams has received little attention. We compared bryophyte diversity in thirty-seven patches formed by uprooting with that of the undisturbed forest floor in a north Swedish Picea abies forest. (2) Bryophyte diversity and species richness were significantly higher in patches with soil disturbance compared with undisturbed forest floor. Species richness and diversity were highest at intermediate patch ages, but disturbed patches had an altered vegetation composition for at least 100 years. (3) Four causes of high bryophyte diversity in disturbed patches are proposed: (i) uprooting creates space for bryophyte colonization that is free from potential competitors; (ii) disturbed patches have high habitat heterogeneity; (iii) within-patch disturbance continues long after patch formation through erosion from the tip-up mound; and (iv) the small patch size implies a short distance to potential sources of bryophyte diaspores which should increase the chance of establishment. (4) Both early and late successional bryophytes establish shortly after an uprooting has occurred. This suggests that no facilitation by early species is necessary before late successional species invade. (5) Results show that treefall disturbances are important for both the persistence of colonists and the maintenance of high bryophyte diversity in boreal-forest ecosystems. Consequently, the studied system has clear parallels with the gap-phase systems widely recognized in temperate and tropical forests.

Abstract: (...) Before settlement, Fagus grandifolia (beech) and Tsuga canadensis (hemlock) dominated the moister segments of the Plateau. Outliers of the more southern Appalachian oak forest occupied the more xerophytic sites, e.g. upper slopes, stonier soils, and soils with a fragipan. The disturbance regime of the pre-settlement period, creating small canopy gaps, favoured the ascendancy of the slower growing shade-tolerant beech and hemlock in the understorey and eventually the overstorey. (...)

Abstract: On the mountains in humid East and South Asia, arboreal life-forms at the forest limit depend on their latitude relative to c. 20 o N: to the north there are mostly evergreen needle-leaved trees with some deciduous broad-leaved trees, while to the south, evergreen broad-leaved trees prevail. These contrasting patterns relate to temperature conditions both at the forest limit and at the upper limit of evergreen broad-leaved forests. (...)

Abstract: In this study, the structural and chemical properties of fynbos and forest vegetation across the boundary between the two communities were examined in order to establish differences in their fuel properties.

Abstract: (...) Relationships of leaf area to sapwood area, stem respiration to sapwood volume and vigour to growth efficiency provide equations for tree growth, leaf-area dynamics and canopy structure. The model simulates mixed-age, mixed-species populations of trees on a 1000-m 2 patch. The test site, Fiby urskog (central Sweden), has been unmanaged since a catastrophic storm in 1795. (...)

Abstract: SUMMARY (1) The probabilty of germination, the length of seed dormancy, and the temporal pattern of germination of five bird-dispersed plant species of an eastern Mediterranean scrubland community varied depending on the plant species, on which of seven bird species they were experimentally fed to, on whether or not they remained covered by pulp, and on whether or not the pulp was experimentally removed before sowing. (2) It is proposed that, in order to withstand the passage through the gut, seeds are protected in a way that may delay their germination after defecation and alter the inherent dormancy, depending on the amount of wear the seeds go through while in the gut. The experimental results suggest that frugivory modifies the length of this dormancy so that the evenness of seedling emergence over time increases as more dispersers, each of which treats the seed in its gut differently, ingest the fruit. This may help to spread the risks encountered during germination, as an adaptation to a relatively mesic environment with an unpredictable rain pattern. (3) Rhamnus palaestinus seeds are encased in a sheath with unique features. It fully protects the seeds during passage through the gut of a disperser, and is shed immediately after defecation. Thus protection does not wear out in the gut, yet germination is not impaired and remains totally independent of gut characteristics of the various dispersers.

Abstract: Many concepts in ecology are imprecise because ecosystems are large, loosely organized objects. Fuzzy-set theory provides a mathematical approach that is able to cope with imprecision. The aim of this paper is to demonstrate that fuzzy sets are a suitable description of ecological communities, using Calluna vulgaris moorland data from the North York Moors National Park as an example. (...)

Abstract: (1) Seedling development under nutrient-deficient conditions was investigated for five bradysporous members of the Proteaceae to test the hypothesis that large seed size and high embryo nutritional quality reflect the outcome of selection favouring propagules suited for establishment in infertile soils characteristic of those natural environments dominated by members of the Proteaceae. (2) Seeds of Protea lorifolia, Protea cynaroides, Leucadendron laureolum, Hakea sericea and Banksia laricina were germinated and grown on nutrient-deficient sand for 200 days. Every forty days ten seedlings of each species were harvested to determine growth, allocation patterns and nutrient use. Seedling parts were dried, weighed and analysed for N, P, K, Ca and Mg. . (3) Seedlings of all Proteaceae species were able to survive prolonged periods of nutrient scarcity irrespective of seed size. (4) Rapid germination of Proteaceae seeds does not appear to be a significant means of increasing seedling fitness. (5) Seed mass was positively correlated with seedling size. (6) No correlation between relative growth rates and seed size was found. (7) Seeds of members of the Proteaceae show selective storage of specific nutrients (N and P) such that seed chemical composition is unbalanced for optimum seedling growth. These elements complement the rich sources of cations Ca,Mg and K found in soils of post-fire environments when maximal recruitment of proteoid species occurs.

Abstract: Distributions of several variables of above-ground growth form, including plant height, vertical distribution of leaf area and vertical distribution of primary and secondary branch length, were compared for crowded (naturally occurring) and uncrowded (naturally occurring and experimentally thinned) populations of Impatiens pallida in south-eastern Pennsylvania. Growth form was examined at the population, individual plant and sub-individual levels. (...)

Abstract: The influence of climatic factors on the growth of Pinus sylvestris was evaluated by comparing annual ring-widths from seven sites along an altitudinal gradient in Scotland with monthly climatic data. Temperature was found to be more important than rainfall in influencing growth. Both late-winter (January-February) and summer (July-August) temperatures were significantly and positively correlated with ring-width. Winter browing or frost drought is a possible cause of the winter temperature correlation (...)

Abstract: (1) The composition of bulk precipitation (rainfall plus dry deposition as collected by funnels) and throughfall water was studied during one year on a weekly basis in two epiphyte-rich Andean rain forests (Cordillera Central, Colombia, 2550 and 3370 m a.s.l.) (2) Nutrient input to the forest by bulk precipitation was higher at 2550 m because of larger precipitation volumes; rainfall was 2115 mm at 2550 m and 1453 mm at 3370 m. Losses of nutrients from the canopy, both total amounts and amounts per unit of precipitation, were also higher at 2550 m. (3) Net fluxes (throughfall flux minus bulk precipitation flux) and deposition ratios (ratio of throughfall flux to bulk prec;pitation flux) were generally within the range reported for other montane tropical rain forests. Differences between forests appear to be related to climate (mainly precipitation amounts), geographical situation (e.g. maritime influences) and the availability of nutrients in the soil. The patterns described in the present study are in accordance with other studies that show reduced cycling rates and limited availability of nitrogen and phosphorus in high-altitude rain forests. (4) Volcanic activity in the proximity of the forests (continuous SO2 emission and incidental ash-falls) was shown to affect precipitation chemistry. Inputs of S04-S were high (26 2 and 16 8 kg ha-' year' at 2550 and 3370 m, respectively) and correlated with rainfall acidity. As a consequence of an ash-fall, concentrations of Ca, Mg and S04-S in bulk precipitation were far above average on one occasion. Throughfall concentrations fell to normal within two to three weeks in spite of low rainfall.

Abstract: (1) The age and size structures of peatland populations of Pinus sylvestris were studied at eight different sites along a latitudinal gradient from central to northernmost Sweden (6 1-67N). (2) Three of the northern populations had age structures with two or several peaks representing periods of successful pine regeneration. The five remaining populations had unimodal age distributions. The youngest age class was the modal class in only three populations. (3) Stem diameter and height were significantly correlated with age, but the variation in size for any given age was large in all populations. (4) Size distributions were skewed towards larger size classes in all populations. (5) The age structures of most populations suggest a wave-like regeneration pattern. Only the age distributions of the two southernmost populations may reflect a more-or-less constant rate of pine recruitment. No signs of major disturbances could be found at the study sites, and it is suggested that the periodic increases of successful regeneration may be the result of interactions between different age and size classes of pine. (6) Periods of abundant regeneration showed a striking coincidence in the three studied populations which had several peaks in their age structures. These periods also coincide with periods of successful regeneration documented by studies in high-altitude pine populations on mineral soil in the same region of northern Sweden. This suggests that a common external factor, like the fluctuating climate, has played an important role in synchronizing these patterns.

Abstract: (1) The pollen and plant macrofossils in sediments from three high-altitude lakes in the Sierra Nevada, California, document vegetation changes that have occurred over the last 12500 years. (2) Trees became established around the lakes by c. 10 000 years ago. Early Holocene forests were structurally different from those of today; they were more open than at present, with more montane chaparral shrubs. Several tree species characteristic of modern subalpine forests were rare and restricted to mesic habitats. Significantly drier conditions are inferred. (3) By c. 6000 B.P., effective precipitation had increased, as shown by an increase in subalpine conifers, principally Tsuga mertensiana (mountain hemlock) and Abies magnifica (red fir). (4) The upper altitudinal limits of many subalpine conifers began to fall c. 2500 B.P., coincident with the beginning of Neoglacial cooling. (5) The climatic interpretations are consistent with those previously described for the Pacific North-west region of North America, but not consistent with those for the American South-west.

Abstract: (1) In a permanent pasture, fine and field-scale heterogeneity were monitored at different intervals of time. For a period of two years, rooted frequency was recorded in March, May, July and October in permanent field plots at scales of 1 cm and 1 m. This gave a measure of spatial heterogeneity at those scales and simultaneously a measure of seasonal, annual and biennial temporal heterogeneity. On the larger scale of the whole pasture, changes in the cover patterns of six of the most common species were assessed over a seven-year period. (2) On the 1-cm scale, significant and consistent deviations from randomness were found, both in the spatial arrangement of species and in the patterns by which they replaced each other. Certain species, primarily the stoloniferous ones, continually colonized and left gaps in the sward more often than predicted from their abundance in the field. (3) Most species which were spatially associated also showed significant interactions in time. It is suggested that the common grasses may be divided into two guilds, depending on whether or not they are associated with Trifolium repens. (4) The probability that the same species would still occupy the same 1-cm space after one year was highly species specific. Viewed on a scale of 1 m over a one or two-year period, some species had a static, but others a highly dynamic pattern. It is concluded that the concept of a static or dynamic community pattern has no meaning unless referred to a particular species and viewed from a particular scale. Evidence for cyclic regeneration as postulated by Watt was not found. (5) While seasonal patterns of species replacements were significantly non-random, deviations from randomness were not detected on the time-scale of one or two years. This indicates that the outcome of interactions between plants is decided within each growing season and not on a time-scale of years. (6) With one exception, the small-scale distribution of plants in March and May was random but, as the growing season progressed, increasing deviations from randomness were detected. The repeated creation of the same patterns excludes the possibility that the patterns were the results of historical chance events. It is concluded that the patterns were generated and maintained by the plants themselves through species-specific interactions.

Abstract: This paper reports the results of an investigation of spatial, temporal and individual variability of survivorship, growth rates and reproductive behaviour of a dioecious palm, Chamaedorea tepejilote, in a high evergreen tropical forest in Mexico. Mortality, number of leaves, stem height increment, number of inflorescences and probability of reproduction were observed for 810 individuals over four years on three permanent plots, each 20 m × 30 m in area (...)

Abstract: (1) The incidence of disease caused by host-specific systemic fungal pathogens was compared in populations of three host plants, Valeriana sambucifolia, Trientalis europaea and Silene dioica. (2) The study was conducted in an archipelago area in the Gulf of Bothnia, Sweden, subject to isostatic readjustment (land uplift). In this area primary succession is in strikingly different phases on different islands. The height above sea level of an island is correlated with island age and the time since it was first colonized by plants. Approximate ages of host-plant populations could thus be estimated. (3) In all three systems, disease incidence peaks during an early-intermediate phase of population development. In V. sambucifolia maximum disease (84%/,) occurs in forty to forty-five-year-old populations, in T. europaea in fifty to 100-year-old populations (-45%), and in S. dioica in fifty to 120-year-old populations (-600%0). Populations with an estimated age of greater than fifty years for V. sambucifolia, > 400 years for T. europaea and > 300 years for S. dioica show low disease incidences (< 10%). (4) A significant positive correlation between disease incidence and mean host population density was detected only for the Valeriana-Uromyces system, where the pathogen has an annual cycle, in contrast to the other two pathogens, which are perennial. (5) Three hypotheses could account for the observed population age-disease incidence pattern: (i) host population size and density effects, (ii) founder effects and selection for resistance, and (iii) changes in the environment during primary succession.

Abstract: Spore dispersal and disease incidence in the S. alba-U. violacea system were examined in natural and experimental populations in Virginia, U.S.A.