Post-dispersive losses of acorns from Mediterranean savannah-like forests and shrublands

Abstract

We studied post-dispersive losses of holm-oak acorns ( Quercus ilex subsp. ballota) due to wild and domestic ungulates and to small mammals in two types of Mediterranean ecosystems in south-western Spain, savannah-like forests, locally named dehesa, and shrublands. Savannah-like forests which are used for sheep and cattle grazing and for acorn fattening of Iberian pig show a lack of oak regeneration. However, these ecosystems are considered as a model of sustainable resource use in all the fragile area of the Mediterranean region. During the 2 years, 1999 and 2000, we carried out a field experiment in three savannah-like forest and three shrubland sites. At each site, we added marked acorns and studied their loss from plots that were either accessible to any animal (no exclosure), protected against ungulates but accessible to small mammals (partial exclosure), or protected against big and small mammals and other vertebrates (complete exclosure). Results indicated that in the no exclosure treatment (i.e., the normal environment) acorn recovery was very low at any site (0–2.4%) without significant differences between savannah-like forests and shrublands. In the partial exclosure treatment, with small mammals having access to the plots only, acorn recovery varied from 0 to 42%. In this treatment, acorn recovery tended to be higher in the savannah-like forests (0.5–42%) when compared to the shrubland sites (0–2.5%). However, the three savannah-like forest sites, in different years, experienced >92% of acorn loss due to small mammals. In addition, many complete exclosures were disrupted, presumably by rodents, and lost 60% of the acorns. These results indicate that loss of acorns due to small mammals is very important in the two type of ecosystems, suggesting that proper management of oak self-regeneration in Mediterranean savannah-like forests should take into account the effect of small mammals, as well as livestock, especially during the seeding stage.