Modifying soil properties promote diversity in native plant and arthropod communities following plant invasion and drought

Background/Question/Methods

Plant invasions are a threat to biodiversity, given that changes in characteristics of plant and soil communities resulting from invasion can affect other organisms, such as arthropods. However, plant invasion may be only one of many disturbances affecting native plant and arthropod communities, and multiple disturbances may create novel situations that alter the efficacy of restoration. Modifying properties of the soil to favor native plant and arthropod communities may provide alternatives to traditional management strategies. We conducted a field experiment to measure the efficacy of soil modification techniques at restoring native arthropod communities following invasion by nonnative Kleberg bluestem grasses (Dichanthium annulatum) in southern Texas. An extreme drought event occurred during the study, which provided us with the opportunity to test the efficacy of soil treatments under varying weather conditions. We applied 10 treatments (simple soil disturbance, pH decrease, pH increase, carbon addition, mycorrhizal fungi, and each of the previous in combination with native seed) to 50 plots in June 2011 and compared treated plots to monocultures of Kleberg. We sampled plants and arthropods June-August 2011-2013, quantified richness and canopy cover classes of plants, and abundance and richness of arthropod functional groups (herbivores, decomposers, predators, and ants). 

Results/Conclusions

Although changes in soil chemistry in treated plots were short-lived, we observed reduced dominance of Kleberg bluestem in all treated plots. Overall, treated plots had more species and cover of native plants as drought conditions subsided, which was associated with an increased diversity of herbivore, decomposer, and predator communities, compared to Kleberg plots. Although invasive arthropods were present in all plots, treated plots had fewer invasive arthropods than Kleberg communities. In particular, the abundance of an invasive leafhopper was associated with Kleberg bluestem and may use the plant as refugia in the leafhopper’s introduced range. Seeded plots also had more litter cover and more decomposer arthropods; diverse plant litter may provide higher quality habitat for detritivores than monocultures of invasive plants. Some arthropods, such as ants and isopods, may have inhibited some treatments, such as seeding, and a thorough understanding of the arthropod community prior to treatment may help determine which restoration tools may be most effective. Soil disturbance and seeding with native propagules increased diversity of native plants and arthropods and reduced Kleberg dominance in the short term, but long-term monitoring after soil modification may reveal additional benefits to native communities.