Seed dispersal and colonization ability of plants - Assessment and implications for conservation

Seed dispersal is one of the least understood phases in plant life-cycles, despite bring recognized as fundamentally important for understanding species distribution, abundance, population dynamics and life-history variation. For species living in fragmented habitats, dispersal may be crucial for regional persistence. This paper synthesizes studies performed in Swedish semi-natural grasslands and deciduous forests. The main objective was to develop a simple method to assess the dispersal and colonization ability of plants. Dispersal and colonization were considered as a series of steps: seed production, seed transport and seedling recruitment. With the use of verified assumptions on (i) a trade-off between seed production and seed size, (ii) a relatively small predictive power of seed transport for species actual dispersal and colonization, (iii) a positive effect of seed size on recruitment, and (iv) a general prevalence of recruitment limitations by seed availability, a prediction is made that dispersal and colonization ability will be highest among species with intermediate seed sizes in a given community. This prediction is supported by field data. Based on estimated dispersal and colonization ability, and the ability of local populations to persist, a scheme is suggested with four basic categories of plants. Some implications are suggested for conservation, in a landscape scale, of plants belonging to each of these four categories.