Effects of the Invasion of Honey Locust (Gleditsia triacanthos L.) on Macrophytes and Algae of Pampean Streams (Argentina)

Abstract

Invasion by Gleditsia triacanthos L. (honey locust) along the banks of Pampean streams and rivers appears to induce profound changes in species richness, macrophyte cover, and producer biomass. Seasonal effects of the invasion on macrophytes cover and biomass of seston, periphyton, and benthos were studied at three low order streams from the Pampas region (name them here), in sections with and without invasion of honey locust. We hypothesized that light reduction by honey locusts reduces macrophyte coverage and algal biomass, thereby modifying the structure of the stream communities. Incident light and nutrient concentrations showed differences between invaded and not invaded reaches. Stream sections with tree canopy showed a negative correlation with the percentage of macrophyte cover (R = -0.41, p < 0.05). In the three streams, the biomass of seston, periphyton and benthos was reduced in summer, when canopy cover was most developed. This study demonstrates that a high degree of honey locust invasion modifies the structure of aquatic communities of Pampean streams therefore urgent action is needed. Options for honey locust management are suggested.