Functional Guilds Mediate the Effects of Woody Encroachment on the Ground Layer in the Brazilian Cerrado

Aims Woody encroachment is happening in open ecosystems around the world, with a general trend for biodiversity loss. Little attention has been paid, however, to the dynamics of ground‐layer vegetation as trees increase. We explored temporal changes in the ground‐layer community of tropical savannas along after fire suppresion and undergoing woody encroachment, to check for plant‐diversity loss and to understand whether functional guilds might be driving the community dynamics. Location Cerrado (Brazilian Savanna), Southeastern Brazil. Methods We sampled (2016 and 2022) all plant species in the ground layer of 20 permanent plots (0.1 ha each) within a continuous Cerrado remnant. Plots represent two different encroachment stages—open and dense savanna, categorized by their tree basal area in 2016 (below or above 15 m 2 ha −1 , respectively). Species were grouped in functional guilds by habitat preference, growth form, and dispersal syndrome. We assessed changes over time in richness per guild in open and dense savanna and verified which guilds were more or less frequent than expected after 6 years among gained or lost species. Results Richness decreased by about 10 species per year in the whole area. Losers were small plants (graminoids, forbs, and subshrubs, mostly perennials), mostly savanna specialists and heliophytes. Winners were trees and climbers from shaded environments (generalist or forest species). Regarding dispersal agents, losers were associated with non‐flying mammals or autochory, and winners with bats. Bird‐dispersed species were dominant, with stable frequency, despite the high species turnover. Conclusion The dynamics of the ground layer in tropical savannas long after fire suppression is driven by increasing shade and seed dispersal filters, which are typical forest drivers of community assembly, not related to response to fire, evidencing the biome shift from savanna to forest. These transformed ecosystems will no longer contribute to the conservation of savanna plant diversity in the near future.