Uncovering mechanisms of bird seed dispersal in semiarid environments to help to restore them

Abstract

Mediterranean semiarid areas are suffering a growing process of agricultural abandonment that represents a challenge for restoration. Limited seed arrival, drought, and scarce suitable microhabitats in oldfields make plant colonization difficult. Restoration through ecological succession can take advantage of increased seed dispersal through animal vectors, but precise knowledge of the factors involved (e.g., seed disperser behavior, rate of effective recruitment of dispersed seeds, and effectiveness of the applied restoration structures) is critical. Otherwise, efforts to foster the processes of interest may be misdirected. We propose and test a methodological approach based on the combination of ecological (bird censuses and camera trapping) and genetic tools (DNA barcoding), to assess seed dispersal of fleshy-fruited shrub species by birds toward oldfields in one of the driest areas of southeastern Spain. We assisted natural restoration with artificial bird attractors (perches and water troughs) in two abandoned areas with different ages. Furthermore, we provided microenvironments (rocks) and prevented herbivory (by fencing) to enhance plant recruitment. Results revealed strong differences among assessment techniques in the characterization of dispersal interactions. While bird censuses only informed about frugivores occurrence, camera trapping and barcoding enabled the quantification of species responses. Attractors proved to be effective in triggering a quantifiable seed arrival, but no subsequent plant establishment occurred. We highlight the importance of implementing different techniques to characterize and assess avian seed disperser performance. Water provision increased seed arrival, but our design failed to enhance plant recruitment. The next logical step in the restoration of Mediterranean oldfields is the optimization of conditions for seed germination and successful plant establishment.