Ungulates and ecosystem services in Mediterranean woody systems: A semi-quantitative review

Ungulates are key elements that modulate the type and direction of ecosystem services in Mediterranean environments. Our main objective is to synthesize the provision of ecosystem services in forests, shrublands and woodlands dominated by ungulates (wildlife or livestock) in Mediterranean environments. To achieve this objective, we performed a systematic semi-quantitative review (n = 262 studies) across the Mediterranean climate area for the 1991-2018 period. Most studies focused on supporting services (80.35 % of all studies), with biodiversity (49.11 %) and plant recruitment (18.15 %) as the most studied services. A great number of studies addressed plant biodiversity preservation (63.40 % of studies on biodiversity). Surprisingly, we found a low number of studies on cultural (7.02 %) and regulatory (5.26 %) services. Regarding the direction of the relationship of ungulate effects on ecosystem services, 67 studies (25.57 %) showed positive effects and 86 studies (32.82 %) mentioned negative effects (disservices). Most studies that showed positive effects focused on biodiversity, mainly vegetation and birds, and wildfire prevention. However, most studies reporting negative effects were also based on biodiversity loss (mainly vegetation) and plant recruitment failure. Distribution of services remained similar across regions and species but positive effects of ungulates were reported mainly in shrublands and negative effects were reported primarily in forests and woodlands. Despite the fact that ungulate density is key to explain the direction of ungulate effects on ecosystem services, only 9.51 % of all studies considered different estimates of herbivore pressure and just 7.22 % of all studies considered different contrasted densities in the analysis. Overall, our analysis of services showed a decreasing tolerance to ungulate pressure from woodlands, through forests, to shrublands. Mean +/- SE ungulate densities (Livestock Units per ha) in studies that showed negative effects were 0.20 +/- 0.01 in shrublands, 0.22 +/- 0.01 in forests, and 1.98 +/- 1.70 in woodlands (including dehesas, montados and rangelands). Management in Mediterranean woody ecosystems should focus on neglected services (e.g. regulatory services) and try to adjust ungulate population densities to maximize positive effects and minimize negative effects on ecosystem services.