Abstract
Vegetation’s increased vulnerability to extrinsic disturbances is an important but less studied effect of natural habitat fragmentation. Fire is part of the evolutionary history of grassland ecosystems, but fragmentation by forest plantations can alter the fire regime and influence their resilience. This study compares the successional trajectories after fire in continuous and fragmented grassland in terms of composition and abundance of plant species. Grassland fragments of varying sizes (0.1 to 2.5 ha) surrounded by a forest matrix and grassland controls of an equivalent area in adjacent, non-fragmented sites were selected. Fire was associated with an increase in the abundance of exotic plants in the fragmented grassland whereas the continuous grasslands were much more resistant to invasion. These differences in the species composition between fragments and continuous areas, which were limited to the smaller areas before the fire, were observed one year after the fire throughout the range of sizes analyzed. These results show the impact of fragmentation on grassland resilience and how the effects of this process become evident even months after a disturbance, highlighting the synergistic effect of habitat fragmentation and biological invasions, two factors identified as the main forces of biodiversity erosion.
Highlights
Vegetation’s increased vulnerability to extrinsic disturbances is an important but less studied effect of natural habitat fragmentation
The after-fire successional trajectories of the grassland fragments surrounded by pine plantations and of the continuous grassland controls were qualitatively similar with respect to the cover of the native and exotic plants and of bare ground, regardless of the size of the plots
The vegetation gave way to bare ground following the fire, reversing this trend fifteen months later. While these changes were barely significant in the continuous grassland, they were much more noticeable in the fragments surrounded by the forest plantations, in the smaller areas, which at least shows a delay in the recovery of the vegetation cover in response to fragmentation
Summary
Vegetation’s increased vulnerability to extrinsic disturbances is an important but less studied effect of natural habitat fragmentation. Fire was associated with an increase in the abundance of exotic plants in the fragmented grassland whereas the continuous grasslands were much more resistant to invasion These differences in the species composition between fragments and continuous areas, which were limited to the smaller areas before the fire, were observed one year after the fire throughout the range of sizes analyzed. These results show the impact of fragmentation on grassland resilience and how the effects of this process become evident even months after a disturbance, highlighting the synergistic effect of habitat fragmentation and biological invasions, two factors identified as the main forces of biodiversity erosion. We propose that fragmentation will affect the successional trajectory of the burnt habitats, with increases in the abundance of exotic species in the fragments immersed in the forest matrix with respect to the continuous grassland, and that this difference will be more significant in the smaller fragments
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