Post-burn recovery in the flooding Pampa: impact of an invasive legume.

Abstract

Winter burning of Paspalum quadrifarium Lam. stands ("pajonales") promotes colonization of denuded spaces by several alien species. Lotus tenuis Waldst et Kit. ("lotus"), a recent invader of the region, is able to reach very high densities between the resprouting bunches of the dominant species. Results of a removal experiment performed to evaluate the impact of natural establishment of lotus on post-born colonization of pajonal stands are reported. Seedlings of lotus were removed shortly after their emergence between burned bunches of P. quadrifarium. Eighty days after burning, approximately 30% of the soil surface remained uncovered within removal plots, whereas canopy cover was complete within controls. Furthermore, final (137 days post-burn) total aboveground biomass was 2.7 times higher in control than in removal plots. Removal of lotus significantly (p<0.05) increased the cover of an annual native grass (Phalaris angusta Nees, ex Trin.) and the final biomass of an alien thistle (Carduus acanthoides L). A spatial association analysis provided additional evidence about the negative impact of lotus on colonization success of C. acanthoides. Weed colonization may be reduced, if not prevented, by managing the colonization processes of other new and useful invaders.