Influence of maintenance practices on hydraulic functions of ditches: A trait‐based approach

Maintenance practices in agricultural ditches influence their abiotic and biotic functioning in the short and medium terms, leading to modifications of plant communities. These modifications might in turn affect the water transport regulation and seed retention functions of ditches. The effects of maintenance practices on ditch plant communities have been poorly studied in terms of (i) functional response traits to maintenance practices and (ii) functional effect traits driving ecosystem functioning. We designed an experiment to compare the effects of different maintenance practices (mowing, burning, chemical weeding and dredging) in an agricultural Mediterranean ditch. We measured the plant species richness (i.e. alpha diversity or number of species), stem densities and plant traits/community functional parameters affecting water transport and seed retention (height, blockage factor and surface vegetation ratio), every year during 2 years before and after applying contrasting maintenance practices. All the plants growing in the bottom and on the banks of the studied ditch were identified. We characterised the differences between treatments using linear mixed‐effects models. Maintenance practices differently affected plant communities and resulting ecosystem functions. After 2 years, burning was the poorest practice regarding seed retention and the best practice regarding hydraulic transport capacity, on the basis of a water depth of 60 cm in the ditch. Mowing was the poorest practice regarding water transport and was an averaged practice for seed retention. Mowing was also the practice favouring the highest richness. Chemical weeding did not really differ from the control in terms of studied traits and parameters, although a slight decrease in water conveyance ability and increase in seed retention were assessed after 2 years. The results pave the way to developing easy to implement maintenance solutions with the potential to optimise ecosystem functions, relying both on historical agricultural practices for farmers (involving no new know‐how) and on non‐introduced plant species.