Moss cover and browsing scores as sustainability indicators of mountain ungulate populations in Mediterranean environments

Abstract

Here, we aimed to define ecological indicators of environmental change for monitoring the effect of a reintroduced species, the Iberian ibex (Capra pyrenaica), over the vegetation of a natural protected area with contrasting habitats. This species was reintroduced 30 years ago in the Sierra de Guadarrama National Park, Spain, and its population has since grown exponentially, reaching high densities in some areas. We tested the suitability of two complementary indicators: browsing damage on woody species and the percentage of moss cover loss on rocky outcrops. For this purpose, we used a mathematical approach to zone the natural protected area according to the historical presence of the species and established five different Iberian ibex pressure classes (Classes I–V). Our results showed a direct link between Iberian ibex pressure and vegetation status. Model predictions suggested 10% moss loss in the areas with low pressure (Class I) but 64% loss in the areas with high pressure (Class III), mostly due to ungulate trampling on rocks. Similarly, browsing damage increased with increasing pressure classes for different woody species. Low palatable plant species such as Pinus spp. showed little change in browsing damage for increasing ungulate pressure whereas more palatable plants (e.g., Erica arborea) showed significantly greater browsing damage variation across pressure classes (i.e., high sensitive to herbivory pressure). Both, moss cover on rocks and widely distributed palatable woody plants proved useful ecological indicators for monitoring ungulate populations in mountainous areas with a diverse array of habitats (e.g., rocky vs. woody). This methodology may help select the most suitable indicators for each type of ecosystem or dominant habitat in ungulate-dominated ecosystems.