Reducing biotic and abiotic land-use legacies to restore invaded, abandoned citrus groves.

Land-use legacies associated with agriculture, such as increased soil fertility and elevated soil pH, promote invasions by non-native plant species on former agricultural lands. Restoring natural soil conditions (i.e. low fertility and low pH) may be an effective, long-term method to control and reduce the abundance of non-native and ruderal species that invade abandoned agricultural lands. In this study, we examined how soil manipulation treatments of lowering soil fertility with carbon additions and lowering soil pH by applying sulfur affect non-native and ruderal native plant species abundance in two former citrus groves in central Florida. Non-native plant biomass was removed by one of two methods (tilling or topsoil removal), and was combined with a soil amendment of sulfur, carbon, sulfur + carbon, or none. The biomass removal treatments significantly decreased non-native abundance, with topsoil removal as the most effective. Carbon additions did not affect soil fertility or vegetation. Sulfur and sulfur + carbon additions significantly decreased soil pH in both groves for at least 1 year post-treatment; however, we did not see a significant vegetation response. Overall, our results suggest that removing vegetation by tilling and topsoil removal is an effective method for reducing non-target species cover. Although we did not see a response of vegetation to our treatments, we were able to restore the initial soil characteristics, which can be a first step toward complete restoration.