Do the invasive trees, Ailanthus altissima and Robinia pseudoacacia, alter litterfall dynamics and soil properties of riparian ecosystems in Central Spain?

AIMS: To assess the impacts of Ailanthus altissima and Robinia pseudoacacia on the whole litterfall process and on soil properties of riparian ecosystems of Central Spain by comparing invaded and non-invaded forests. METHODS: We selected 3–4 plots of four different types of forests: invaded by A. altissima or R. pseudoacacia, or dominated by the native Fraxinus angustifolia or Populus alba. In each plot we collected the litter monthly over 2 years and separated the litter from different plant organs. We calculated annual inputs of litter, nitrogen (N) and phosphorus (P) to soil. We also analyzed soil pH, organic matter (OM), N and P. RESULTS: Most litter fractions from the two invasive trees contained over twice as much N as those from the native P. alba. Although not significantly different, the annual inputs of N in invaded forests were 1.7–2.2 times higher than in native forests. In the invaded forests, extra litterfall peaks were found in summer and/or late-spring (June), corresponding to reproductive and/or leaf litter fractions. The percentage of annual litter represented by these peaks was over twice those in native forests. Soil OM, N and P were higher in invaded than in P. alba forests. In addition, forests invaded by R. pseudoacacia had higher soil OM and N than F. angustifolia forests. CONCLUSIONS: This study showed the capability of A. altissima and R. pseudoacacia to alter soil properties and litterfall dynamics in riparian ecosystems.