Variation of seedling recruitment in wet meadow species over six years: positive effects of mowing and negative effects of fertilization

Germination and seedling recruitment are stages of the plant life cycle
that are highly sensitive to biotic and abiotic filtering. Simultaneously,
seedling regeneration is considered crucial for biodiversity maintenance
in grasslands and is strongly affected by grassland management. The
response of seedling regeneration to management and its interannual
variability remains understudied. We studied the effects of mowing,
fertilization, dominant removal, and their combinations on the seedling
composition in a species-rich wet meadow community in Central Europe. We
also measured litter and moss cover and analyzed their effect on
seedlings. Firstly, we analyzed the total seedling numbers and species
composition across six consecutive years. Secondly, we tested the spatial
relationship between conspecific seedling–adult pairs and their strength,
by comparing it against that of heterospecific seedling–adult pairs, and
explained the observed pattern with species traits, namely the dispersal
mode. Total seedling numbers were significantly decreased by
fertilization, and significantly increased by mowing. Increased litter
cover was an important mechanism causing the extremely low numbers of
seedlings in fertilized plots. The association between conspecific
seedling–adult pairs was always significantly positive and higher than for
heterospecifics. The tightness of the relationship was determined by the
individual species’ dispersal mode. We found that a key process of the
plant species' life cycle, seedling regeneration, was overwhelmingly
negatively affected by fertilization in experimental plots. Mowing is
efficient in preserving species’ successful regeneration, but only in
unfertilized plots. Large differences in both total seedling numbers and
species proportions between individual years suggested that different
species probably establish themselves in different years, which is a
co-existence maintaining mechanism suggested by Grubb’s regeneration niche
theory. Such high spatio-temporal variability in seedling recruitment
forms the basis for niche partitioning and storage effects as mechanisms
of biodiversity maintenance in wet meadow communities.