Evaluating the role of fire over a decade in a tropical mountainous forest-grassland mosaic

Forest-grassland mosaics comprise a major component of tropical landscapes, hosting invaluable biodiversity and providing essential ecosystem services to hundreds of millions of people worldwide. While open biomes often benefit from disturbance, forests can particularly be susceptible to structural changes resulting from such disruptions. Here we evaluate the influence of fire on the structure and landscape properties within natural forest islands immersed in a matrix of megadiverse montane grasslands. We conducted this study in 15 forest islands located in southeastern Brazil, assessing its fire frequency, intensity, and post-fire time over an eleven-year period from January 2012 to December 2022. Our results show that fire frequency is linked to soil characteristics and the percentage of herbaceous cover within the forest islands. We also found that the post-fire time is related to the percentage cover of the forest islands' associated herbs and shrubs. However, neither fire frequency, intensity, nor post-fire time was connected to significant changes in plant species richness, abundance, or in the upper vegetation strata (tree species richness and abundance, and canopy cover) in the interior of the forest islands. Furthermore, these fire-related variables did not result in temporal changes in the forest island's canopy variation or landscape metrics. Our results underscore a low fire frequency and intensity within our study area, potentially explaining the limited fire-associated impact, and primarily on the lower vegetation strata. Despite acknowledging the relative stability of these forest islands under current fire regimes, we suggest further studies that can experimentally manipulate not only fire but also other anthropic disturbances for understanding the temporal dynamics of the forest islands and, consequently, their preservation. This perspective is indispensable for comprehensively understanding the ecological consequences of anthropogenic disturbances in natural forest islands.