Long-term changes in size and composition of seed bank during succession: from meadow to forest

Abstract

Studies of the relation between the size and floristic composition of the seed bank and the vegetation during succession were conducted in the years 1976-1996. The results of the research did not confirm the hypothesis of directional changes in the density of seeds as the observed changes were of fluctuating nature. At the start of succession the seed bank was small (2970 seeds/m²), and in subsequent years the density of seeds increased successively to reach the highest level after 15 years (9170/m² ), then dropped again. After 20 years the density of seeds reached the value recorded at the initial stage (2468/m²). Successional changes in floristic richness of seed bank were directional with the number of species falling from 52 to 24. All data indicate that the floristic composition of the seed bank is not a mirror reflection of the vegetation structure, but rather a record of a long-term turnover of species and many different events which in various periods of time influenced the inflow of seeds to the soil (spatial dynamics of the necromass, perennial herb and willow canopy structure, seed migration).