Is there an effect of storage depth on the persistence of silver birch (Betula pendula Roth) and rowan (Sorbus aucuparia L.) seeds? A seed burial experiment

Abstract

Sorbus aucuparia L. (rowan) and Betula spp. (birch) are the most common of the early successional pioneer tree species in central Europe with the ability to form a soil seed bank. Little is known about the reasons for the high variations observed in the persistence in the soil of rowan and birch seeds. The objective of this study was to assess the ability of buried birch and rowan seeds to form short-term persistent soil seed banks and to analyse the influence of burial depth on seed persistence. An artificial seed burial experiment was initiated to study the persistence of birch seeds and rowan seeds, with and without pulp, stored at depths of 2, 5 and 10 cm in mineral soil over 2.5 years. The predicted maximum storability periods for buried birch seeds was 13 years, compared to 4.5 years for rowan seeds with pulp and 3.5 years without pulp. The lower storage capacity of rowan seeds was demonstrated by germinations in the darkness within soil of 3-22% of seeds without pulp and 4-48% of seeds with pulp. Germination percentages of birch and rowan with and without pulp did not differ between depths. Only burial duration had an effect for either tree species. Birch and rowan seeds are able to form short-term persistent soil seed banks. Birch accumulates a seed reserve in the soil over time, until a change in conditions conducive to germination occurs, while rowan seeds germinate promptly after overcoming seed dormancy. The pulp provides no benefits in relation to the persistence of rowan seeds; rather, it appears to act as a physical inhibitor of germination. Therefore, annual input of fresh seeds is required for the success of rowan. Seed input every few years seems sufficient to guarantee a minimum number of viable birch seeds.