Woody encroachment threatens several ecosystems around the world. In general, management of grasslands includes regulation of fire and grazing regimes. Changes in these two types of disturbances are potential drivers of woody encroachment. Here we assessed how the traditional management carried out by local landholders affects a highland grassland ecosystem in southern Brazil. We hypothesized that grasslands converted to protected areas undergo fast woody encroachment. To reconstruct changes in vegetation, we interviewed former and current landholders and coupled their knowledge with an analysis of aerial and satellite images. During the first 11 years without fire and cattle, woody encroachment in grasslands increased exponentially. Woody encroachment occurred mostly by the replacement of grasslands by shrublands. Meanwhile, grasslands under traditional management remained almost unchanged for the last 40 years. The management of fire by local landholders has been part of their traditional practices for decades. Such management prevents largescale wildfires and maintains natural highland grasslands. The quick pace of shrub encroachment in such grasslands threatens its exclusive diversity, human well-being and regional cultural heritage. Thus, conservation policies are needed to regulate and instruct about the use of fire as a management tool in highland grasslands of southern Brazil. Extensive vegetation change can have important consequences in ecosystem functioning and economy 1. For instance, woody encroachment (or woody plant encroachment), which is the increase in density, cover and biomass of shrubs or woody vegetation in grasslands 2 , has been reported around the world 3. Woody encroachment is caused by several factors such as shifts in climate and biogeochemical cycles, changes in disturbance regimes (e.g. fire and grazing), or modification in ecological succession by introduction of non-native species or predator removal 2-5. Woody encroachment alters fundamental ecological processes of ecosystems, including global carbon balances, reduction of water flow or groundwater recharge and the loss of biodiversity 4,6,7. Because woody encroachment tends to negatively affect herbaceous vegetation, it constitutes a major threat to savanna and grassland ecosystems. Control of woody encroachment is a key concern in rangelands. Woody encroachment reduces forage production, creates habitat for ectoparasites, and hampers animal handling 4. Woody encroachment concerns land managers and methods for control and eradication include either fire, cutting trees, grazing, or a combination of these three methods 8,9. Woody encroachment has been reported all over the world, e.g., southern Ethiopian savanna 8 , North American savanna, shrub-steppe and grasslands ecosystems 10 , southeastern South American savanna 11 ('Campos' 6), and Brazilian savanna ('Cerrado' 12). In highland grasslands of southern Brazil, extensive cattle grazing is part of the traditional management employed for centuries 13. In addition, local ranchers c...
