The importance of recruitment limitation in forest plant species colonization: a seed sowing experiment

Abstract

Summary Flora and vegetation of ancient forests differ from that of new forests. Former agricultural use is still detectable in the composition of the flora centuries after new forests are established. The reason for the very slow migration of some forest species has been discussed and it has been suggested that establishment of ancient forest species in new forests may be hampered by altered soil conditions and competitive species in new forests. In the present paper we tested whether ancient and other forest species are able to germinate and establish in new or ancient forest after seed addition. Eight herb species were sown in 5 ancient forests and 4 recent forests in Eastern Denmark in 1998. Four of the species had been shown in previous investigations to occur more often in ancient forests (Vicia sepium, Roegneria canina, Impatiens noli-tangere, Rumex sanguineus); whereas the remaining four occurred equally in ancient and recent forests (Galium odoratum, Milium effusum, Impatiens parviflora, Circaea lutetiana). Two of four ancient forest species (Impatiens noli-tangere and Rumex sanguineus) seemed unable to germinate in the experiment wherever they were sown. The two other ancient forest species and the four forest species with no preference for ancient forests all increased their abundance after seed addition in both forest types, but most in new forests. Though soil variables were important for the distribution of most species, germination seemed less affected except for one ancient forest species. The general picture was that soil variables did not influence the germination and establishment of new plants, and did not inhibit establishment more in new forests than in ancient, but this experiment only recorded the effect for two years after sowing and the soil variables may prove to be important over a longer period of time series. Seed size was not related to germination of species.