Comparative ecology of seedling recruitment in an oligotrophic wet meadow

Abstract

Abstract. For the regeneration niche to contribute to the maintenance of species diversity interspecific differences in sensitivity of seedling recruitment to environmental conditions is assumed. We experimentally tested differences between meadow species for the response of seed germination to chilling, and sensitivity of seedling recruitment to microscale heterogeneity. We also compared the dynamics of seedling recruitment in gaps. Seed germination was tested in standard laboratory germination tests, comparing control seeds with seeds chilled at +4 °C, and at –14°C for one month. Species responses varied from significant increases in germinability after chilling (e.g. Cirsium palustre, Betonica officinalis, Angelica sylvestris) to significant decreases (e.g. Hieracium umbellatum, Succisa pratensis, Selinum carvifolia). In some species, chilling at + 4 °C has a similar effect to chilling at –14 °C, in others the effect of chilling at + 4°C was intermediate, and in some, there was no effect of chilling at + 4°C, but an effect of chilling at –14°C. Different chilling temperatures also affect timing and speed of seed germination under greenhouse conditions.The dynamics of seed germination under field conditions was studied by sowing seeds into artificially created gaps and following their germination, both where the seedlings were removed after emergence and where they were not removed. Species differ in their germination dynamics: they all start late April, but then differentiate from an abrupt maximum and early finish of germination (in the second half of May), to prolonged germination without a marked maximum. Seedling removal increased the total number of germinated seeds, with a marked density dependence at this stage. Seeds were also sown into plots with treatments (1) gaps, sod stripped, above‐ground vegetation removed; (2) mown, moss layer removed; (3) mown; (4) untouched control. Seedling emergence was monitored for 3 yr. Seedling recruitment decreased from treatments (1) to (4), but sensitivity differed between species. With increasing seed weight, the difference between gaps and other treatments decreased. The results show that there are considerable differences in seedling recruitment sensitivity between species.