Post-Fire Abiotic and Biotic Filters Limit Native Grassland Recovery in a Pinus pinaster Plantation

Fires are an ecological force that often mediates the balance between native and exotic plants in communities. We monitored post-fire vegetation dynamics in a Pinus pinaster plantation and adjacent grasslands 9, 15, and 18 months after the fire, evaluating structural and compositional changes through multivariate analyses. The invasive alien Acacia longifolia cover increased significantly in the plantation (p = 0.0006), while pine needle cover declined significantly (p = 0.0027), and P. pinaster cover did not change significantly over time (p = 0.063), although it showed an increasing trend towards the late stage. Both A. longifolia and pine needles were negatively associated with native species cover. Native cover remained consistently higher in continuous grasslands, with a significant Time × Site interaction. Post-fire succession in the plantation was associated with sequential abiotic and biotic filters, and the increase in A. longifolia may have contributed to reduced native recovery through competitive effects. These results suggest that fire alone may be insufficient to restore native grassland conditions within afforested systems and that early post-fire control of A. longifolia may be necessary to redirect succession.