<i>Broussonetia papyrifera</i>controls nutrient return to soil to facilitate its invasion in a tropical forest of Ghana

Abstract

Non-native invasive plants can alter soil chemistry through litter production and decomposition to facilitate their invasion. However, the important roles of these underlying processes in plant invasion remain poorly understood, particularly in tropical forest ecosystems. Here, we compared litter production, quality and decomposition of two invasive species (Broussonetia papyrifera and Cedrela odorata) and two co-occurring native species (Celtismildbraedii and Funtumia elastica), and soil properties under them to elucidate their roles in the invasion of a tropical forest in Ghana. Leaf litter production rates were determined using 36 mesh traps installed in the study area, while litter quality and soil physicochemical properties were determined using standard protocols. A 6-month decomposition experiment using the litterbag technique was conducted to compare the decomposition rates of the species. Litter production varied among the species and over time, with B. papyrifera producing 0.35–4.27 tons ha−1 y−1 from October to January; the other species produced 0.03–1.74 tons ha−1 y−1 over the same period. In the litterbag experiment, B. papyrifera recorded the lowest mass remaining (11–36%), followed by C. odorata (17–51%), F. elastica (31–55%) and C. mildbraedii (48–62%) in that order. Broussonetia papyrifera had the highest nitrogen (3.91%) and phosphorus (0.24%) but lowest lignin (12.20%) concentrations and the lowest C:N (10.87) ratio, indicating higher litter quality compared to the other species. Soil under B. paprifera was richest in phosphorus and nitrogen compared to the other species. Overall, our results indicate that the production of more nutrient-rich and rapidly decomposing leaf litter by B. papyrifera may constitute an important positive feedback mechanism driving its invasion and impacts in this tropical forest.