The soil seed bank in abandoned tropical pastures: source of regeneration or invasion?

Resumen

We assessed the availability of both pioneer and non-native species in the soil seed bank of old-growth
forest and recently abandoned pasture, to evaluate whether the soil seed bank in these pastures represents a source of
regeneration of species from adjacent old-growth forest or of invasion by non-native species. Our study was conducted
at Selva Lacandona, Chiapas, Mexico. Soil samples were randomly collected from 6 sites in old-growth forest, and 6
sites in abandoned pastures. Seedlings from soil samples were identified and classified into pioneer, non-native (weeds/
graminoids), and other forest species. Pioneer species seeds were virtually absent in pastures, but represented ~30%
of seeds in the forest. Non-native species comprised ~99% of the soil seed bank in pastures. In the forest, soil seed
bank density of weeds and graminoids decreased with increasing distance (up to 4 km) from agricultural fields, and
comprised up to 25% (Mean ± 1SE= 16 ± 7) of the seed bank. Our results show a near total elimination of pioneer
species from the soil seed bank in pastures, and considerable invasion of the borders of the Montes Azules reserve by
seeds of non-native species. Thus, in the region studied, the soil seed bank in abandoned pastures represents a source of
invasion by non-native species into old-growth forest rather than a potential source of forest regeneration.