VEGETATION COMPOSITION CHANGES IN EX-ARABLE FIELDS FOLLOWING GLYPHOSATE APPLICATION: THE ROLE OF SOIL SEED BANK AND TIMING OF SEED PRODUCTION

In Hungary, common milkweed (Asclepias syriaca L.) has invaded large areas of semiarid sandy ex-arable fields. Elimination of this species is required since it hinders secondary succession. In June 2006 broadcast-applied glyphosate was sprayed to three oldfileds. Broadcast application of glyphosate affects both target and non-target species in the plant community. In June 2006 and 2007, percentage cover of vascular plant species was estimated in 1 m(2) plots. Relative abundance of categories of seed bank types and time of seed production were used to explore the effects of herbicide treatment on the resident vegetation. The revealed changes showed that non-target vegetation was significantly affected by the extensive herbicide application in the study sites. The time of seed production has more predictive value on the nature of vegetation changes than does soil seed bank type. Species producing seeds before glyphosate application gained advantage in contrast with species of usual seed production after the glyphosate treatment. The abundance of species with different seed bank types changed according to the time of seed production.