Positive adjacency effects mediated by seed disperser birds in pine plantations

Abstract

This study examines the consequences of adjacent elements for a given patch, through their effects on zoochorous dispersion by frugivorous birds. The case study consists of pine plantations (the focal patch) adjacent to other patches of native vegetation (mixed patches of native forest and shrublands), and/or pine plantations. Our hypothesis is that input of native woody species propagules generated by frugivorous birds within plantations strongly depends on the nature of the surrounding vegetation. To test this hypothesis, we studied frugivorous-bird abundance, seed dispersion, and seedling establishment in nine pine plantation plots in contact with patches of native vegetation. To quantify adjacency arrangement effects, we used the percentage of common border between a patch and each of its adjacent elements. Frugivorous bird occurrence in pine plantations is influenced by the adjacent vegetation: the greater the contact with native vegetation patches, the more abundant were the frugivorous birds within pine plantations. Furthermore, frugivorous birds introduce into plantations the seeds of a large sample of native fleshy-fruited species. The results confirm the hypothesis that zoochorous seed rain is strongly determined by the kind of vegetation surrounding a given plantation. This finding underlines the importance of the composition of the mosaic surrounding plantations and the availability of mobile link species as key landscape features conditioning passive restoration processes.