Is Small-Scale Species Richness Limited by Seed Availability or Microsite Availability?

Abstract

To evaluate the relative roles of seed availability and competitive interactions in creating within-community patterns of species richness in unproductive grassland, we conducted a sowing experiment in a dry calcareous (alvar) grassland, where both the number of arriving seeds and the number of arriving species were approximately doubled compared to the natural seed rain. Also, in half of the plots, 36% of the vegetation and bryophyte cover was removed to simulate disturbance. Sowing significantly increased species richness and the number of seedlings in plots. Disturbance increased the number of seedlings but had no significant effect on species richness. In the first year, the highest number of seedlings was found in disturbed and sown plots. The dynamics of seedling numbers differed among species. Of the 15 sown species, seedlings of nine species were found in some plots. The number of seedlings of two species were not dependent on treatments, those of three species depended only on sowing, and for four species there was a significant positive interaction between sowing and disturbance. The establishment of sown species was not dependent on initial species richness or number of adult ramets in experimental plots. It was concluded that, though the behavior of individual species may differ, the local deficiency of seeds may be an important force generating small-scale community patterns of calcareous grasslands.

Changes in plant species composition in abandoned and restored limestone grassiands - the effects of tree and shrub cutting

“…Various experiments have shown that the limited availability of seeds is the principal reason for the weak regeneration of grasslands. The dispersal of most grassland species is limited to several metres or even to several dozen centimetres (Verkaar et al 1983;Stampfli and Zeiter 1999;Kalamees and Zobel 2002 and Fernández-Palacios 1995;Stampfli and Zeiter 1999;Kupferschmid et al 2000;Zobel et al 2000). Our results agree with earlier studies implying that in contrast to the initial colonisation of new sites, where stochastic processes are more important and species life-history traits are of little importance, later spread of species in developing grasslands strongly depend upon their life-history traits and becomes a function of time and management (cf.…”

The ecology of restoration: historical links, emerging issues and unexplored realms

“…However, sowing additional seeds on even undisturbed sites frequently does increase the number of established individuals of seeded species, indicating that there are more safe sites than seeds to fill them for some species in many communities (e.g. Tilman 1997;Turnbull et al 2000;Zobel et al 2000;Foster & Tilman 2003). These results suggest that likelihood of seed arrival does influence community structure in some communities, and more specifically support lottery-type models of species coexistence (McEuen & Curran 2004).…”

Plants are least suppressed by their frequent neighbours: the relationship between competitive ability and spatial aggregation patterns

“…Numerically, the vast majority of individuals in temperate grasslands are a result of clonal propagation, with only a small percentage of individuals originating from seeds (Rusch & van der Maarel 1992;Zobel et al 2000;Benson & Hartnett 2006). Clonally propagated offspring (ramets) are placed at a widely varying, species-specific distance from the mother plant, and this distance has been shown to explain betweenspecies variation in the degree of conspecific aggregation (Turkington & Harper 1979;Lovett Doust 1981;McLellan et al 1997;Benot et al 2013).…”