Study area
The Tandilia Mountains extend along a 350 km long diagonal in the Province of Buenos Aires (Argentina), covering the districts of Azul, Balcarce, Benito Juárez, General Pueyrredón, Lobería, Necochea, Olavarría and Tandil (figure 1). The maximum width is in its central part and reaches an extension of 63 km, and the maximum height is 525 m (Cerro la Juanita, Benito Juárez district). The whole region occupies an area of approximately 1.231.400 ha, including scattered hills separated by valleys and plains (Herrera et al., 2019). The agricultural expansion and other anthropogenic activities (such as mining), added to the lack of natural protected areas (Nanni et al., 2020), produce changes in grassland species richness, composition, and abundance, and the increase of exotic species (Filloy & Bellocq, 2007). Of a total of 505 plant species that have been found in the Highland grassland of the Pampa, 139 are exotic (27%) (Sánchez & Núñez, 2004; D’Alfonso et al., 2014). Despite the significant impact, the Tandilia Mountains continue to be considered one of the last refuges of Pampa grassland and one of the most biodiverse sites in the Province of Buenos Aires (Chebez, 2005; Pedrana et al., 2008).
Due to the fragmentation of this habitat, the Pampa grassland has been relegated to remnants of different sizes, mainly on hills where the presence of rock and shallow soils makes it impossible to use plows to cultivate annual crops (Herrera & Laterra, 2007). However, other activities, such as quarrying and forestry, remain as important threats.