What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

Seed size, dormancy, and dispersal share three population-dynamic functions in temporally and spatially varying environments: risk reduction or bet hedging, escape from crowding, and escape from sib competition. Here we developed a model to explore the ways they may interact to reduce risk. We have shown that the risk-reducing properties of these three seed traits evolve only in response to global temporal variance. Thus, to understand how selection impinges on the seed traits, creating fitness interactions, we must understand the factors contributing to global temporal variance and how they are mitigated by the various seed traits. Since the traits interact to reduce variance, arbitrarily fixing any one trait at different values alters the fitness-maximizing values of the others, resulting in trade-offs among traits. We explore how changes in the number of independent environmental patches, the probability of favorable conditions, the radius of dispersal, and spatial and temporal autocorrelation of envir...

The Selective Interactions of Dispersal, Dormancy, and Seed Size as Adaptations for Reducing Risk in Variable Environments

An understanding of seed persistence in the soil is important to vegetation management and weed control, but experimental collection of seed bank data is tedious and expensive. We report a rapid, simple method for predicting seed persistence in the soil. The method is tested on a range of British, mostly herbaceous, species. Diaspore (seed or fruit) weight is plotted against variance of the three linear dimensions of the diaspore. All diaspores within an area of the graph defined by a maximum weight and variance are persistent in the soil. The critical weight is the same for fruits and seeds, but the critical variance of diaspore dimensions appears slightly higher for fruits. The great majority of diaspores outside this region are short lived, and the relatively few ambiguous cases can be resolved by reference to habitat (...)

https://www.jstor.org/stable/info/2389893

Seed size and shape predict persistence in soil

In landscapes subject to intensive agriculture, both soil fertility and vegetation disturbance are capable of impacting strongly, evenly and simultaneously on the herbaceous plant cover and each tends to impose uniformity on the traits of constituent species. In more natural and ancient grasslands greater spatial and temporal variation in both productivity and disturbance occurs and both factors have been implicated in the maintenance of species-richness in herbaceous communities. However, empirical data suggest that disturbance is the more potent driver of trait differentiation and species co-existence at a local scale. This may arise from the great diversity in opportunities for establishment, growth or reproduction that arise when the intensity of competition is reduced by damage to the vegetation. In contrast to the diversifying effects of local disturbances, productivity-related plant traits (growth rate, leaf longevity, leaf chemistry, leaf toughness, decomposition rate) appear to be less v...

Trait convergence and trait divergence in herbaceous plant communities: Mechanisms and consequences

Restoration ecology deals with the scientific and ecological background of nature management practices aiming at the re-establishment of plant species which have disappeared. As we focus on semi-natural landscapes, these disappearances can be caused by intensification of agricultural practices or cessation of human interference. Nature management practices attempt to re-establish the often species-rich original plant communities by the removal of nutrients (sod cutting, hay-making, grazing) after eutrophication (Schiefer 1984; Bobbink & Willems 1991; Oomes 1992; Bakker & OUT 1995), rewetting after severe drainage (Grootjans & Van Diggelen 1995; Koerselman & Verhoeven 1995), scrub and woodland removal (clear cutting, grazing) after bush encroachment (Willems 1988; Poschlod & Jordan 1992). The re-appearance of plant species may depend on their persistence in the soil seed bank as a ‘memory’ of the original plant community. If the species has been lost from the persistent soil seed bank, it has to be transported to the site of re-appearance by some vector, e.g. wind, water, animals, man, and incorporated into the fresh seed bank. The site of re-appearance after emerging either from the old seed bank or from the fresh seed bank has to be proven to be a safe site from the point of view of abiotic and biotic conditions (Harper 1977). Without the presence or arrival of seeds no re-appearance in the established vegetation will be possible. For this reason we focus on seed bank dynamics and seed dispersal in restoration ecology. We will present (i) a review of current methods of seed bank analysis including estimations of longevity and density, and (ii) the state of the art on methods and results of seed dispersal.

/pdf/seed-banks-and-seed-dispersal-important-topics-in-1ihzjqcngm.pdf

Seed banks and seed dispersal: important topics in restoration ecology

SUMMARY (1) Measurements have been made of seasonal variation in the density and composition of the reservoir of germinable seeds present in surface (0-3 cm) soil samples collected at 6-weekly intervals from ten ecologically-contrasted sites in the Sheffield region. (2) The procedure was not designed to provide a complete assessment of the seed flora, and the methods were found to be ineffective in recovering germinable seeds of those species (e.g. Endymion non-scriptus, Viola riviniana, several Umbelliferae) in which there is only a brief interval between fulfilment of a chilling requirement and the onset of germination. (3) The techniques adopted were particularly suitable for the detection of persistent seed banks (i.e. those in which some of the component seeds are at least 1 year old), and also allowed recognition of species in which there is a transient accumulation of detached germinable seeds during the summer. (4) Comparison of the results obtained for populations of the same species in different types of habitat suggests that seasonal variation in seed number is a function of the species rather than of the environment. (5) It is concluded that the major evolutionary force determining the nature of the seed bank is the selective advantage derived from mechanisms of seed dormancy and germination which allow seedlings to evade the potentially-dominating effects of established plants. (6) From the data collected in this study, four types of seed bank (Types I-IV) have been recognized, and an attempt has been made to assess their ecological significance. (7) The transient seed banks (Types I and II) are adapted to exploit the gaps created by seasonally-predictable damage and mortality in the vegetation, whilst the persistent seed bank (Type IV) confers the potential for regeneration in circumstances where disturbance of the established vegetation is temporally and/or spatially unpredictable. A second type of persistent seed bank (Type III) has characteristics intermediate between those of Types I and IV, and contains some seeds which germinate soon after release and others which are more persistent in the soil. (8) A feature of the results was the lack of a general correspondence between the species-composition of the seed flora and that of the associated vegetation. At certain sites, substantial persistent seed banks were detected for species which were either extremely scarce or did not occur at all in the established vegetation. (9) Both transient and persistent types of seed banks were represented at each of the ten sites; this is consistent with the hypothesis that complementary mechanisms of regeneration are involved in the maintenance of floristic diversity.

http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2745/homepage/SeasonalVariation.pdf

K. Thompson

Papers

Seasonal variation in the seed banks of herbaceous species in ten contrasting habitats