Native weed protects species that sustain cattle raising in semi-arid natural grasslands

Abstract

Facilitation may contribute to conserving natural systems disturbed by humans. We hypothesized that the unpalatable native weed, Baccharis ulicina (Baccharis) protects palatable plants from cattle grazing in central Argentina grasslands. We tested this hypothesis through observational and experimental studies. In the observational study, we compared consumption and performance of plants growing in Baccharis and Baccharis-free (open) microsites. We also recorded photosynthetically active radiation, soil moisture, and total soil nitrogen (N) in both microsites. In the experiment, we removed Baccharis aboveground biomass and compared herbivory and plant performance in Baccharis, Baccharis-removed, and open microsites. Palatable plants were less consumed when growing with than without Baccharis, and palatable grasses with the highest forage values were more abundant, taller, and fecund in Baccharis than open microsites in our observational study. Additionally, except for increased radiation in the open, there were no differences in abiotic variables between microsites. Results from the plant removal experiment were consistent with those from the observational study and did not offer evidence for direct facilitation. We conclude that protection from cattle is an important mechanism through which Baccharis benefits neighboring plants. Our work emphasizes the need to recognize the facilitative role of weeds in the management of semi-arid grasslands.