Application of a naturalness index for the hills of the Tandilia System. The low hills in the Tandilia system are considered important sites for biodiversity conservation. Since they are immersed in the agricultural matrix, the hills depend on farmers' management decisions. A simple tool to assess their degree of intervention could be useful for territorial planning. We developed a naturalness index for these hills that includes the main plant communities and current productive management and applied it to thirteen hills. This index is based on eight variables: dominant native species, dominant endemic species, exotic woody species for commercial purposes, grazing, overgrazing, soil and rock extraction, crops, and intentional fire. The following five degrees of naturalness were established: Natural, Sub-Natural, Semi-intervened, Sub-intervened, and Intervened. More than half of the hills (53.84%) were linked to the Semi-intervened degree, followed by the Sub-natural (38.46%) and the Sub-intervened (7.69%) degrees. The Natural and Intervened degrees were not represented in this sample. The agricultural intensification of the region can lead farmers to intensify their management to maximize their income. Thus, the hills representing the Semi-intervened and Sub-intervened degrees would easily move to the Sub-Intervened and Intervened categories, respectively. This index is a valuable resource to know the hill' state of intervention and guide not only the farmers toward pro-sustainability decision-making but also the social actors involved in comprehensive land management.