Livestock exclusion boosts regeneration and ecosystem complexity in an endangered palm savanna

Butia yatay (Mart.) Becc. is a vulnerable palm species endemic to southeastern South America, forming palm savannas characterized by dense herbaceous layers and tall palms. These ecosystems are undergoing degradation, partly due to widespread livestock grazing, which limits juvenile palm survival and threatens population viability. To assess how grazing regime influences the recovery of a Yatay palm savanna in Uruguay, we conducted a long-term comparative field study contrasting continuously grazed and non-grazed zones (old exclusions: from 1996 and recent exclusion: from 2016). We used a multi-scale sampling design combining repeated measurements of palm population structure (20 × 20 m plots surveyed in 2017, 2021 and 2025), vegetation structure (20 m Canfield transects), landscape-level canopy cover (100 × 100 m quadrats from aerial photographs and satellite imagery), and bird and mammal communities (fixed-radius point counts and camera traps). To evaluate treatment effects, we fitted generalized linear mixed models (GLMMs) including grazing regime as a fixed effect and zone or plot as random factors. In long-term (29 years) exclusion zones, we found enhanced juvenile palm survival and growth, a healthier population structure (i.e. balanced distribution of stages), increased vegetation complexity and canopy cover, and differentiated bird and mammal communities. However, the density of palm seedlings was high in the grazed plots, but 60% of them showed browsing damage, and their mean height was only half of that observed in the exclusions. Livestock grazing does not limit palm seedling emergence, but it strongly reduces seedling survival, growth and transition probability to advanced stages, while decreasing vegetation complexity and canopy cover, affecting vertebrate assemblages. Implementing livestock management strategies that include temporary exclusions is essential to sustain B. yatay regeneration, maintain viable populations and restore the ecological integrity of Yatay palm savannas.