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

One of the most obvious features on the foredunes and strands of coasts and lakes is recurrent burial in sand. Burial levels vary in different coastal sand dune systems and influence the physical a...

Adaptations of plants to burial in coastal sand dunes

Studies on the survival and establishment of seedlings in coastal and lacustrine sand dune systems suggest that nutrient deficiency, lack of moisture, sand accretion, salt spray and predation are probably the most important limiting factors. Seedlings employ both avoidance and tolerance strategies to with-stand the different stresses. For example, seedling recruitment of dune species coincided with periods of high moisture availability and occurred in years with high well distributed rainfall. The seedlings exhibited rapid vertical elongation of roots, avoided moisture stress by leaf rolling, dense hair on leaves, fleshy cotyledonary leaves, and by growing in the shade of nurse plants. A certain proportion of seedlings of all species survived partial burial and showed stimulation of leaf growth, total leaf area, number of tillers and total dry matter. Seedlings of most species could not survive complete burial, however, some species did grow through the sand deposit by an increase in the number of nodes and length of internodes. Plants responded to salt spray by inhibition of seed germination, developing resistance, increase in leaf thickness and reduced uptake of Na and Cl ions. Several characters such as higher vigour of seedlings, larger seed size and seed polymorphism were also of adaptive significance to the species.

Adaptations enhancing survival and establishment of seedlings on coastal dune systems

Vegetation and soil properties were described across a well-dated sand-dune chronosequence bordering northern Lake Michigan to document patterns and rates of primary succession and forest ecosystem development, and to determine environmental constraints that potentially drive succession and regulate species diversity. The site experienced frequent and continuing formation of 72 shore-parallel dune ridges over the past 2375 yr. Across the chro- nosequence represented by the youngest 13 dune ridges aged 25-440 yr, there were clear patterns of species turnover and community convergence as well as successional changes in species diversity, aboveground biomass, aboveground litter production, net ecosystem produc- tion, nutrient pools, and nutrient cycling. Dune-building species were replaced by evergreen shrubs and bunchgrass within 100 yr, which in turn, were replaced by mixed pine forest within 345 yr. Plant-species richness increased to a peak in developing forest at 285 yr but thereafter decreased as early-successional species disappeared from the communities. Rates of species addition peaked between 95 and 145 yr as forest species invaded, whereas rates of species loss peaked between 345 and 440 yr as early-successional species were lost from the developing forest. Development of the forest ecosystem required ;300 yr (i.e., 145-440 years). Total eco- system carbon increased in a logistic manner to 128 Mg C/ha, with net ecosystem production peaking at 30 g C·m 22 ·yr 21 in developing forest. Aboveground biomass and O horizon mass increased to ;137 Mg/ha and ;79 Mg/ha, respectively, whereas aboveground litter production increased to 3.5 Mg·ha 21 ·yr 21 at 440 yr, but thereafter varied between 175 and 350 Mg·ha 21 ·yr 21 . Total carbon and total nitrogen in the upper 15 cm of mineral soil and O horizon accumulated to ;42 Mg/ha and ;1.36 Mg/ha, respectively. Estimated average rates of carbon and nitrogen accumulation over 440 yr of ecosystem aggradation were 23.2 g·m 22 ·yr 21 for carbon and 0.38 g·m 22 ·yr 21 for nitrogen. Because nitrogen-fixing plants are rare on the upland dune ridges, ecosystem aggradation depends largely on atmospheric nitrogen inputs. Following colonization by conifers, soil acidification resulted in rapid leaching losses of calcium and magnesium, whereas phosphorus and potassium were cycled more tightly. The dune chronosequence represents a complex gradient of changing environmental con- straints that differentially reduce the survival, growth, and reproduction of plant species. Young dune ridges near the lake shore are characterized by strong winds, sand burial and erosion, high insolation, high rates of evaporation, and low availability of nitrogen and phosphorus. These conditions ameliorate with increasing dune age as wind velocities and sand movement diminish with distance from the lake, as accumulating organic matter improves the moisture- holding capacity and nitrogen availability of the soil, and as mineral weathering mobilizes soil phosphorus. However, in developing forest, light and cationic nutrients may become limiting, and decreased light availability, cool soil temperatures, and accumulation of a thick forest floor may limit recruitment from seed for many species. These numerous potential environmental constraints suggest a considerable complexity in this ostensibly simple ecosystem.

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Primary succession and forest development oncoastal lake michigan sand dunes

The Ecology of Seeds: Seedling establishment

Studies were conducted to determine the effects of sand burial on seed germination, seedling emergence, survival, and growth of Agropyron psammophilum In the field, seedlings of A psammophilum em

M. A. Maun

Papers

Effects of sand burial on seed germination, seedling emergence, survival, and growth of Agropyron psammophilum