Seed-bank convergence under different tree species during forest development

Abstract

Abstract Seed banks are of vital importance for local plant persistence and recruitment, for maintaining both plant and genetic diversity and for habitat restoration. Yet, seed-bank dynamics, particularly on the long term and in deciduous forests, remain poorly understood. Additionally, information on compositional seed-bank differences under contrasting tree canopies remains scarce. This study aims at quantifying long-term seed-bank dynamics by sampling vegetation and seed banks along a four-stage successional chronosequence (40, 80, 120 and 250 years) using 12 10 m×10 m plots per forest stand age–class under fully developed oak–hornbeam and beech canopies. Seed banks were remarkably abundant and diverse. Species richness and seed density declined steeply with forest stand age, regardless of canopy species. Seed-bank composition differed significantly with stand age, yet also with tree species. Most likely, tree species-dependent ecosystem engineer effects on light availability and possibly also litter quality affect the seed bank through the vegetation. Compositional differences between seed banks from stands with a different canopy diminished with increasing stand age, possibly due to a gradual loss of species with a less persistent seed bank. Long-term seed-bank dynamics in deciduous forests seem to consist predominantly of a unidirectional and predictable depletion of the seed bank as long as large disturbances, which would allow seed-bank replenishment of early-successional species, are lacking. Furthermore, forest seed-banks appear to converge upon a characteristic seed bank in the later stages of forest development, irrespective of canopy composition, driven by seed-bank depletion and limited input from the herb layer.