bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seed release without fire in Pinus halepensis, a Mediterranean serotinous wind‐dispersed tree
Authors: Nathan Ran , Safriel Uriel N. , Noy‐Meir Imanuel , Schiller Gabriel 
Published: March 2003

Summary 1 Although serotiny is frequently considered to have evolved under the selective pressure of fires, the drying conditions that induce cone opening are not necessarily associated with fire. We hypothesized that in Pinus halepensis, a Mediterranean serotinous wind‐dispersed tree, xeriscence (seed release induced primarily by drying conditions not generated by fire) bears intrinsic adaptive values, independent of those of pyriscence (fire‐induced seed release). 2 We used seed‐traps to quantify seed release in two scrubland pine stands in Israel. Contemporary meteorological data were used to seek correlations with climatic factors affecting seed release. 3 Substantial seed release, estimated to be about 60% of the annual crop, was observed in the absence of fire. Seed release was distinctly seasonal, with high rates in spring and autumn, and was strongly correlated with short, infrequent but temporally predictable Sharav events (dry and hot weather). In the most extensive Sharav‐induced seed release, seed density reached 117 seeds m–2 and 15% of the annual crop was released within 6 days. Stepwise multiple regression revealed that mean relative humidity (in both stands) and maximum temperature (in one stand) were significant predictors of seed release. 4 Vertical (upwards) wind velocity was significantly positively correlated with dry and hot weather. Seed counts in distant traps (> 20 m from the nearest tree) were significantly greater in periods in which Sharav events occurred than in other periods. Xeriscence may therefore have an adaptive value in promoting dispersal distance by wind. 5 Both xeriscence and pyriscence appear to be involved in determining serotiny in P. halepensis and provide means of exploiting establishment opportunities generated either by fire or by other factors.
Soil pathogenic fungi have the potential to affect the co‐existence of two tallgrass prairie species
Authors: Holah Jenny C. , Alexander Helen M. 
Published: March 2003

Summary 1 Negative feedback may exist between plant species and their biotic soil communities. Two co‐occurring native tallgrass species (Andropogon gerardii, a perennial grass, and Chamaecrista fasciculata, an annual legume) were reciprocally transplanted into pots containing soil from areas dominated by one of the species. Half of the soil derived from each area was microwaved to reduce soil fungi, resulting in four different ‘soil types’. 2 Chamaecrista fasciculata plants were smaller when grown in their native soil vs. that from under A. gerardii, but were unaffected by microwaving (i.e. fungal reduction). Andropogon gerardii plants were shorter with fewer inflorescences in non‐microwaved soil, with the poorest growth occurring in non‐microwaved C. fasciculata soil. 3 Fungi were isolated from roots of A. gerardii growing in the different soil types. We tested whether the fungi found differed between the four soil types and whether any species characteristic of C. fasciculata soil were responsible for the poor growth of A. gerardii in this medium. 4 Fungi unique to the non‐microwaved C. fasciculata soil type reduced tillering and caused an early reduction in growth of A. gerardii. These effects were partially ameliorated when potentially mycoparasitic fungi associated with A. gerardii were also included. By the end of the experiment, both fungal treatments increased above‐ground biomass but greatly reduced below‐ground biomass of A. gerardii compared with controls, suggesting that the exposure to potential fungal pathogens from C. fasciculata soil altered biomass allocation within plants. 5 There was no evidence of negative feedback between the prairie species and their own soils. However, fungi associated with Chamaecrista fasciculata were detrimental to A. gerardii, one of the dominant perennials in the surrounding area, and may facilitate the annual’s long‐term persistence. Arbuscular mycorrhizae did not ameliorate the pathogenic effects of these fungi as there was little colonization of A. gerardii roots in C. fasciculata soil.
Effect of light on the germination of forest trees in Ghana
Authors: Kyereh B. , Swaine M. D. , Thompson J. 
Published: March 2003

Summary 1  Seed germination in light and dark, and responses to irradiance and light quality, were tested in shadehouse experiments for 19 West African tropical forest tree species representing a wide range of ecological types. Germination in forest gaps of different size was tested for 11 species. 2
Percentage germination was reduced in the dark only for three small‐seeded species that are common in forest soil seed banks: Musanga cecropioides, Nauclea diderrichii and Milicia excelsa. Percentage germination of the other 16 species, including four widely regarded as ‘pioneers’, was unaffected. 3  Effects of different irradiances in shadehouses, where the seeds were watered, were significant for some species, but there was no consistent pattern. Irradiance effects in forest gaps, where the seeds received only natural wet season rainfall, were more widespread and substantial, and were most commonly shown as a depression of percentage germination at high irradiance. 4
Effects of light quality (neutral vs. green shade; red : far‐red = 0.43) were insignificant at 5% irradiance in shadehouses for all species except Nauclea diderrichii. In growth chamber experiments, the low energy response was only evident at 1.0 µmol m–2 s–1 (< 1% of unshaded forest irradiance) in Musanga and Nauclea. 5  The speed of germination was affected by irradiance in many species, but the effect was small compared with differences between species, in which time to complete germination varied between 3 weeks and over 6 months. 6
Seeds of Ceiba pentandra and Pericopsis elata planted in deep forest shade (2% irradiance) and in a small gap (30% irradiance) germinated well in both sites, showed exponential biomass growth in the gap but a linear decline in mean seedling biomass and subsequent death in deep shade. 7  Light‐mediated germination is relatively rare among these forest trees, even among pioneers, so that the working definition of a pioneer should be seen to depend more on a species’ ability to survive in forest shade. The effects of canopy opening on seed germination are small except in the largest openings, which severely depress germination in a number of species, including some species with strongly light‐demanding seedlings.
Fire, resprouting and variability: a recipe for grass–tree coexistence in savanna
Authors: Higgins Steven I. , Bond William J. , Trollope Winston S. W. 
Published: March 2003

Summary 1 Savanna ecosystems are characterized by the codominance of two different life forms: grasses and trees. An operational understanding of how these two different life forms coexist is essential for understanding savanna function and for predicting its response to future environmental change. 2 The existing model, which proposes that grasses and trees coexist by a separation of rooting niches, is not supported by recent empirical investigations. Our aim was to define an alternative mechanism of grass–tree coexistence in savanna ecosystems. The model we have built concentrates on life history–disturbance interactions between grasses and trees. 3 The model demonstrates coexistence for a wide range of environmental conditions, and exhibits long periods of slow decline in adult tree numbers interspersed with relatively infrequent recruitment events. Recruitment is controlled by rainfall, which limits seedling establishment, and fire, which prevents recruitment into adult size classes. Decline in adult tree numbers is the result of continuing, but low levels, of adult mortality. Both aspects of the dynamics are consistent with an established non‐equilibrium mechanism of coexistence (the storage effect). 4 A sensitivity analysis indicated that data on tree resprouting ability, stem growth rates and the relationship between seedling establishment and wet season drought are essential for predicting both the range of conditions for which coexistence is possible and the response of savanna ecosystems to environmental change. 5 Our analysis suggests that understanding grass–tree interactions in savanna requires consideration of the long‐term effects of life history–disturbance interactions on demography, rather than the fine‐scale effects of resource competition on physiological performance.
The effect of initial density on interactions between bryophytes at individual and community levels
Authors: Zamfir Manuela , Goldberg Deborah E. 
Published: March 2003

Summary 1 A glasshouse experiment was conducted with seven bryophyte species to determine the effects of competition. We tested whether competitive hierarchies varied with initial abundance (density and biomass) and between two different experimental approaches. 2 Relative competition intensities were calculated based on proportional growth (G) and relative biomass (R). The standards for comparison (i.e. no interactions) were species’ performance in monocultures at one of two sowing abundances (the combined monocultures method; CM) and in a low‐density mixture of equal proportions of all species (the community density series method; CDS). 3 Proportional growth decreased with increasing initial abundance for all species. Community effects (relative biomass of each species) were generally weaker and more variable than individual effects. R increased linearly with abundance for only one species, while three species showed a quadratic response (of which two were negative). 4 Competitive hierarchies derived by the CM method differed with abundance, and we argue that the CDS method is likely to provide a more reliable comparison. 5 With CDS, competitive hierarchies were similar along the community abundance gradient, implying that non‐linear competitive effects are not likely to be a mechanism of coexistence in this community. 6 There were significant competitive effects on community composition, but not on diversity as measured by evenness. At the community level individual species tended to show either competitive or positive effects throughout the gradient of initial community abundance, with decreasing values for most species at high initial community abundance, as were the effects of interactions on community composition.
Recruitment dynamics of a fleshy‐fruited plant (Olea europaea): connecting patterns of seed dispersal to seedling establishment
Authors: Rey Pedro J. , Alcántara Julio M. 
Published: March 2003

Summary 1
Little is known about the consequences of seed‐disperser activity for plant demography. We compared the spatial patterns of seed dispersal generated by frugivorous birds with those of seedling survival for the shrub Olea europaea. We examined the relative importance of dispersal in determining plant recruitment and tested whether the initial dispersal pattern persisted throughout recruitment. 2  We quantified the processes affecting each stage of regeneration (seed within a ripe fruit, dispersed seed, seedling and sapling) in different microhabitats, and evaluated transition probabilities between stages. We could then determine the overall probability of a seed in a ripe fruit becoming a sapling, and compare the probability of such an event occurring in different microhabitats. 3  Only 9.3% of the emerged seedlings reached the sapling stage, whereas 35.3% of the seeds were dispersed; 27.0% of dispersed seeds produced seedlings and 62.9% of saplings survived for 2 years. Seedling survival was therefore the critical link in regeneration. Water stress was responsible for more than 70% of seedling losses, which suggests that abiotic factors (mainly rainfall) may account for most of the fluctuation in recruitment in this species. 4  Neither post‐dispersal seed predation nor germination caused changes in the initial spatial distribution of seeds, but differences in the requirements of seeds and seedlings then caused spatial uncoupling. The most favourable places for seeds were the worst for seedlings, and consequently frugivore‐generated dispersal patterns differed from the final spatial pattern of recruitment. 5  Recruitment under conspecifics was nearly zero and dispersers are therefore crucial if recruitment is to occur. Their effect on the amount of recruitment was, however, overwhelmed by processes acting on the seedling stage. 6
For Olea europaea, the pattern generated by short‐term recruitment dynamics persists in the long‐term spatial distribution of saplings.
Quantitative aspects of community structure examined in a semi‐arid grassland
Authors: Wilson J. Bastow , Steel John B. , Newman James E. , King Warren MCG. 
Published: March 2003

Summary 1 Community structure was examined by analysing the spatial distribution of species' biomass–abundance, as well as species' occurrences, in two semi‐arid grassland sites in New Zealand. This is the first attempt to search for a range of assembly rules (variance in species occurrence, guild proportionality and intrinsic guilds) using quantitative data. 2 One site, with a greater proportion of native species, had a larger species pool, greater species richness and greater biomass. At this site, variance in richness was generally greater than expected at random, but variance in biomass tended to be less than expected at random, probably indicating competition. Microsites which had lower biomass and fewer species tended to be dominated by exotic species; it is suggested that these are more recently disturbed microsites. 3 At a second site, dominated by exotic species, there was no significant evidence for community structure, i.e. no non‐random patterns in richness or biomass, i.e. no assembly rules. 4 Guild proportionality was not seen in a priori guilds: dicots, monocots, cryptogams, native species and exotic species. 5 Searches for intrinsic guilds produced no evidence of guild structure, in the Pianka sense of groups of species that use similar resources, compete strongly with each other, and thus are especially subject to mutual competitive exclusion. 6 It is concluded that interspecific competition limits the biomass of each species in these grasslands, but there is no evidence from the community structure that it causes local competitive exclusion. There was no indication at either site that the communities were structured by guilds. It is concluded that, at least at the scale examined and at the time examined, Pianka‐type guilds do not exist in this vegetation.
Climatic control of blanket mire development at Kentra Moss, north‐west Scotland
Authors: Ellis Christopher J. , Tallis John H. 
Published: March 2003

Summary 1 Four peat cores were collected from Kentra Moss, north‐west Scotland, and analysed for botanical macrofossils and peat humification. The pollen record was used as a template for the identification of synchronous levels between cores. 2 A non‐random pattern of change in bryophyte macrofossils and humification was simultaneous between all four cores. Stratigraphic changes occurred independently of human land‐use and were best interpreted as palaeoclimatic events. Remains of Racomitrium lanuginosum and Sphagnum papillosum, in conjunction with changes in peat humification, provided the clearest indication of past increases in climatic wetness (‘wetshifts’) to impact upon mire hydrology and ecology. 3 Eight wetshifts were identified and radiocarbon‐dated, beginning at c. 3250, 2550, 2150, 1400, 1150, 875, 600 and 325 calibrated years BP (cal. BP). Seven of these wetshifts match closely with palaeoclimatic events from a range of mires previously examined in Britain and Ireland. We suggest that blanket mires may provide the best source of decade‐ to century‐scale palaeoclimatic information in oceanic north‐west Europe. 4 The proxy‐climatic evidence indicates that: (i) the extinction of Sphagnum imbricatum at Kentra Moss (at c. 1400 cal. BP) was caused by an increase in climatic and mire surface wetness, when it was replaced first by Racomitrium lanuginosum and then by Sphagnum papillosum; and (ii) that increased climatic wetness and human land‐use were responsible for the shift from an early minerotrophic peatland to ombrotrophic blanket mire at c. 4070 cal. BP. 5 Given the evidence for a prevailing climatic effect on the development of Kentra Moss, the effect of human‐induced global warming on Britain's blanket mire resource will probably be significant. British blanket mires have international conservation status, and future changes in their ecology will challenge conservationists, academics and politicians.
Post‐dispersal fate of seeds in the Monte desert of Argentina: patterns of germination in successive wet and dry years
Authors: Marone Luis , Horno Manuel E. , Solar Rafael González Del 
Published: March 2003

Summary 1 Patterns of seed germination of grass and forb species were studied in open Prosopis woodland of the central Monte desert (Argentina) during several years, to test the hypotheses that (i) seed germination is positively affected by both rainfall and protection afforded by vegetation cover (a facilitative effect), (ii) the number of surviving plants is positively influenced by rainfall but negatively affected by established vegetation (a competitive effect), and (iii) seed loss from soil banks owing to germination is lower than that caused by granivorous animals. 2 Forb species germinated during restricted periods, either in early autumn or in spring. Grasses, however, germinated throughout the growing season, but because seedlings could not be identified to species level, it was impossible to discern whether different species germinated in particular seasons, or if all grasses germinated in all seasons. Grass and forb germination were generally of similar magnitude, but grass germination increased by an order of magnitude during a summer of unusually abundant rainfall related to an El Niño Southern Oscillation (ENSO) event. 3 Overall, the spatial distribution of neither germinating seeds nor surviving plants could be explained by interactions with established vegetation (facilitation and competition effects, respectively). An alternative explanation may be provided by the distribution of forb and grass seeds in the soil. 4 Seed loss owing to germination was low in both dry and rainy years. For forbs, such loss totalled < 1% of soil‐seed reserves, and no forb species suffered losses > 4%. Total grass‐seed loss to germination was usually < 0.5%, and the 5% reached in 1997–98 corresponded to an interruption of a prolonged drought by unusually abundant rainfall associated with a reduced seed bank. 5 Grass‐seed loss caused by germination was one to two orders of magnitude lower than that reported due to autumn‐winter granivory in the central Monte desert.
Seedling emergence, survival and size in relation to light and water availability in two bottomland hardwood species
Authors: Battaglia L. L. , Foré S. A. , Sharitz R. R. 
Published: March 2003

Summary 1 Windstorm disturbances create a wide range of microsites which can have complex effects on forest regeneration patterns. We investigated the combined effects of light and microtopography on emergence, mortality and size of seedlings of two bottomland hardwood canopy tree species, Quercus michauxii and Liquidambar styraciflua, over a 2‐year period. A split‐plot design in experimental tanks represented the range of light levels and the pits and mounds found in a disturbed floodplain forest. 2 Emergence was always higher on mounds than in pits, except for L. styraciflua in full sunlight. For both species, mortality was consistently lower, and seedlings of both species grew better in both years on mounds. Light levels did not affect the two later stages. 3 There were species‐specific interactions between the effects of two factors on seedling emergence. Lower emergence of L. styraciflua on mounds in full sunlight suggested that full sunlight at this stage can eliminate the advantage to later stages of being on a mound. The combined stresses of low light and a high water table significantly reduced emergence of Q. michauxii in pits at low light. 4 Microsites optimal for one regeneration component of a species were not always optimal for others as seen for L. styraciflua. The relative significance of environmental factors also varied with regeneration stages, such that neither light nor a light‐water interaction influenced regeneration after emergence. 5 Environmental factors may have independent or interacting effects on regeneration, and the nature or presence of these effects can vary among demographic stages. Within each environmental combination, effects may be consistently positive or negative across stages; alternatively, demographic conflicts may develop.
Effects of global change on a sub‐Arctic heath: effects of enhanced UV‐B radiation and increased summer precipitation
Authors: Phoenix Gareth K. , Gwynn‐Jones Dylan , Callaghan Terry V. , Sleep Darren , Lee John A. 
Published: March 2003

Summary

The responses of sub‐Arctic heathland vegetation to enhanced UV‐B radiation and increased summer precipitation over 7 years were investigated in a field experiment in northern Sweden.
Growth, phenology and reproduction of the dominant dwarf shrubs Vaccinium myrtillus, V. uliginosum, V. vitis‐idaea and Empetrum hermaphroditum were studied after 5–7 years of manipulation and retrospective analyses were used to assess growth responses in earlier years. Leaf tissue N and P and 13C natural abundances were determined for V. myrtillus and E. hermaphroditum. Growth responses were also assessed for the moss Hylocomium splendens.
The deciduous V. myrtillus showed reduced growth, increased leaf thickness and increased flowering and berry production under enhanced UV‐B in some years. V. uliginosum, V. vitis‐idaea, E. hermaphroditum and H. splendens were, in general, tolerant of UV‐B.
Increased precipitation affected growth only in the evergreen species: stem length and branching were sometimes stimulated in E. hermaphroditum, whereas V. vitis‐idaea showed reduced branching.
Precipitation also increased leaf thickness in V. uliginosum and reduced flowering and berry production in V. myrtillus.
In the interactions that occurred between enhanced UV‐B radiation and increased summer precipitation, combining the two treatments often negated any effect that either may have had separately. The effect of concurrent increases on this ecosystem is therefore likely to be much less than if either occurred singly.
Enhanced UV‐B and increased summer precipitation appeared not to effect dwarf shrub abundances during the first 5 years of the experiment, suggesting that overall this heath may be more tolerant of these environmental changes than previously thought.