Recruitment and survival of seedlings of a perennial Hieracium species in a patchy environment

Abstract

Observations on a population of Hieracium piloselloides Vill. in an old-field habitat revealed two distinct microsites on which seeds might land, bare soil and moss-covered areas. Regular monitoring of newly emerged seedlings on both microsites revealed that the seeds could germinate as soon as they are shed and that emergence of the seedlings coincided with rainfall, forming distinct emergence flushes. The number of emergences and losses recorded on the bare soil sites always exceeded those which occurred on the moss-covered microsites. The greatest losses of seedlings from the population occurred in periods of low rainfall. The mortality in six seedling cohorts was also followed on these plots. Similar patterns of survival were shared by most of the bare soil cohorts and by all cohorts of moss-covered soil, but the decline in the bare soil cohorts was always more rapid. The number of seeds available in the natural seed rain is estimated to be 40 190 seeds/m2. To this, a total of 120 000 seeds/m2 were added artificially in marked plots, and from the recorded emergences, the establishment success of seedlings was estimated at less than 1%. It is suggested that in terms of monthly microclimatic variation, both types of microsite may be of value in contributing to the apparent stability of the population.