Effects of ungulates on oak regeneration in Mediterranean woodlands: A meta-analysis

Abstract

Mediterranean-climate oak woodlands, including those in North America and in the Mediterranean basin, are human-shaped ecosystems with high biodiversity value, which generate different ecosystem services, including grazing resources for livestock production. Low oak recruitment rates, however, are affecting the ecological sustainability of these ecosystems. Understanding the factors affecting recruitment dynamics in Mediterranean oak woodlands is crucial for adequately managing these ecosystems. We used a meta-analysis approach to evaluate the direct effects of ungulates on Mediterranean oak woodlands at various stages of recruitment, analysing publications based on ungulate exclusion experiments. The relationship between ungulates and recruitment is complex, involving multiple interacting factors, but, with very few exceptions, studies reported substantial negative direct impacts. Our meta-analyses show that the odds of an acorn surviving are much lower when ungulates are present and that the impact of wild ungulates on acorn survival was more marked than that of domestic animals. Ungulates also reduce the recruitment rates of oak seedlings and saplings as well as their growth rates. Ungulate management is crucial to achieve adequate oak recruitment in Mediterranean oak woodlands. We suggest management practices that may contribute to reduce the effects of ungulates in oak recruitment and to ecologically sustainable Mediterranean oak woodlands.