Scientific basis for sustainable management of barbary sheep (Ammotragus lervia) populations in protected areas of semiarid environments

Resumen

Ungulate preferences for woody species and its implications for plant regeneration are key aspects to determine sustainability thresholds of ungulate populations and to define adequate management and conservation measures. This research aims to improve our understanding on Barbary sheep (Ammotragus lervia) interactions with vegetation in a protected area of a semiarid environment to provide new insights in the ecology and management of ungulate-dominated systems. The thesis is structured in four studies that provide valuable science-based data on the ecology and management of both the Barbary sheep populations and their habitat in SE Spain. First, we analyzed plant preferences on widespread woody species. We found that browsing intensity on widespread woody species was low in broadleaved trees and negligible in conifers. Highly preferred and sparse shrub species were the most vulnerable and might be severely affected by medium to high Barbary sheep densities. Second, we compared the herbivore impact on widespread vs. threatened (rare) species and found that, contrary to our hypothesis, the herbivore impact on threatened woody species was significantly higher than on widespread woody plants, probably due to their overall higher payability. The use of threatened woody plants revealed to be very useful as a warning signal of unsustainable densities of large herbivores. Third, we analyzed the effects of regeneration silviculture treatments on the Barbary sheep use, woody plant diversity and plant regeneration in pine (Pirtus spp.) forests. We found that recruitment levels were significantly higher in regeneration silvicultural plots as compared to intact (control) plots only for saplings and juveniles (>130 cm high). We did not find any clear patterns indicating that treated areas suffered heavier browsing damage across all woody plant species. Ungulates caused significantly greater rubbing damage in treated areas but did not use the treated areas more often than the control plots, indicating that small-scale treatments (< 0.75 ha) are compatible with low to moderate ungulate densities. Fourth, we examined the use of man-made structures (supply points and firebreaks) by Barbary sheep and analyzed the derived effects on vegetation (diversity, regeneration and fuel load). We found that ungulate habitat use decreased with longer distances to structures. Areas close to the structures (<50 m) showed greater plant damage (browsing, trampling and rubbing) and lower fuel load than areas located farther away (100 m). Firebreaks were less susceptible to ungulate damage as compared to supply points and, thus, an appropriate combination of both structures can help distribute more efficiently the ungulate effects throughout the system according to our management goals. The integrative approach of these four studies provides researchers and managers with a scientific basis towards sustainability, conservation and management of ungulate-dominated environments in a Mediterranean context where biodiversity enhancement, fire prevention and overall sustainability represent nowadays strong priorities.