Abstract
The importance of biological crusts in arid and semiarid ecosystems has been widely recognized in the last decades, but their function is still not fully known, much less so in our country (Argentina) and region, where they have often gone unnoticed. Biological crusts appear in sites with a low level of disturbance and have a fundamental role in maintaining the soil surface structure. In the Monte ecoregion of Rio Negro province, Argentina, this layer is dominated by moss, and it is present in diverse physiognomic-floristic types of vegetation, but it tends to disappear in sites disturbed by grazing and by severe fires, and at sites where clearing methods were used to remove the soil surface. The multiple benefits that these crusts can provide to ecosystems justify the need to intensify the knowledge of their structure and functioning, to understand the particular role that they fulfill and to be able to manage these systems by taking this component into account.