Performance of Quercus ilex saplings planted in abandoned Mediterranean cropland after long-term interruption of their management

Quercus ilex is a slow-growing, sclerophyllous evergreen oak that is a major structural component of the natural forests and woodlands in western European and northern African Mediterranean regions, and thus a valuable species for revegetation of abandoned cropland. In a field experiment consisting in four combinations of summer irrigation (presence–absence) and artificial shading (presence–absence), we managed 12 plots planted with 50 seedlings each for 3 years, and four plots remained as unmanaged, control plots. Then these treatments were interrupted for 6 years. We measured survival, above-ground growth, and reproductive capability to test the hypothesis that the manipulation of the environment during Q. ilex establishment improves its performance and to suggest adequate forestation practices. Sapling mortality did not differ among treatment plots during the post-treatment period. Previous artificial shading decreased sapling annual growth rate in height, crown projected area, and volume, but not in stem diameter, after it was interrupted. Some evidence points to both abiotic and competition effects as responsible for the growth pattern. Plot cover by the saplings was only marginally affected by the treatments after the treatment plus post-treatment period. Previous summer irrigation and artificial shading increased the percentage of reproductive saplings among treatment plots, and this effect was independent of sapling size. There was a tradeoff between growth and reproductive capability. Management of plantations during the first year only would likely provide a better investment/benefit ratio. Artificial shading provided more benefits than summer irrigation during the treatment period but, in the long run, these benefits were approximately equal. We do not advise applying both treatments simultaneously and the technique to be chosen would depend on the relative costs of irrigation and artificial shading. Long experiments under field conditions like the one presented here are scarce in the scientific literature but very valuable to optimize active restoration of Mediterranean abandoned cropland and other ecosystems of the world.