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Alternative Biome States theory (ABS) helps to explain the presence of open biomes (grasslands, shrublands) in environments sufficiently warm and humid for the development of forest biomes. In these environments it is possible to find areas dominated by open biomes that, according to this theory, respond mainly to fire and herbivory. The aims of this work are to identify whether there are different types of forest biome-open biome ecotones based on woody composition, describe them and explore their relationship with livestock management and environmental variables, using a protected area in Uruguay as a case study. We sampled woody vegetation and other environmental variables in transects (delimited in 200m) in 10 sites across four livestock management systems. We identified two types of forest biome-open biome ecotones, one dominated by shrubland and the other dominated by grassland. Our results agree with the ABS theory and suggest the mechanisms determining the woody composition and the structure of the ecotone vegetation are cattle and use of fire and/or rotary cutter. The changes in vegetation structure and woody richness were partly abrupt, which is consistent with what is proposed by the ABS theory. However, the composition also interacted with site factors such as rockiness and distance to the watercourse, suggesting that site-level environmental variables are acting synergistically with vegetation removal to determine vegetation composition. We found that these ecotones are sensitive to management and environmental variables; so, it is necessary to incorporate this landscape and site heterogeneity to articulate productive activity with nature conservation. [ABSTRACT FROM AUTHOR]