Small seed bank in grasslands and tree plantations in former grassland sites in the South Brazilian highlands

The soil seed bank can be an important source for vegetation regeneration,
and data on the similarity between aboveground vegetation and the seed
bank can provide information about successional pathways after
disturbances or land-use change. We conducted this study in natural
grasslands in the subtropical highland region in southern Brazil. We
evaluated the effect of silviculture on richness, density, and composition
of the seed bank at former grassland sites converted to pine plantations
25 years ago. We worked at six grassland sites and three pine plantation
sites and used the seedling emergence method. Seed bank density and
richness in grasslands was lower than those reported in similar
environments in other regions. Species richness and density varied
considerably within each vegetation type therefore, richness and density
were not statistically significant, while composition varied among
vegetation types. In terms of species, the pine plantation seed bank was a
small subset of the grassland seed bank. Seeds of typical grassland
species were missing in the pine plantation, but also had only low
abundances in the grassland, and similarity of seed bank and vegetation
was low (less than 20%). The low seed density found in this study,
including in grasslands areas, indicates that regeneration of species from
the soil seed bank likely is of a limited role for the maintenance of
plant populations after disturbances in this system. Our data further
suggest that natural regeneration after tree planting in grasslands is
reduced due to seed limitation.