Forest shifts induced by fire and management legacies in a Pinus pinaster woodland

World forests are undergoing contrasted trends. While in some areas pressures continue, in others these are decreasing, setting forests into a trajectory of recovery. However, disturbances can interact with this process, inducing shifts toward alternative states. Here we investigated the post-fire recovery of an ancient Pinus pinaster forest with Quercus pyrenaica in the understory in Central Spain, in which intensive management had decreased. Post-fire forest recovery was sampled and stand history was characterized using forest planning records. Stand history, structure and other geophysical data, including fire severity, were utilized as predictors, as appropriate, of pre-fire stand structure and of the post-fire forest using boosted regression trees. We found that pre-fire Quercus stem density tended to be higher in stands without recent management plans, although overall stand structure was poorly predictable. The post-fire forest was dominated by Pinus, Quercus, or a mixture of both. Pinus density was mostly unpredictable, while Quercus abundance was highly dependent on its pre-fire stem density: In stands with over 200 Quercus stems per hectare, the post-fire forest was dominated by Quercus. Therefore, fire mediated a forest shift from Pinus to Quercus, driven by the pre-fire colonization of Quercus in the understory in areas with a longer time without management plans. Arguably, in case of recurrent fire, shifts will continue occurring where Pinus is still dominant. However, in the longer term, Quercus persistence in the area is threatened by climate change, since the climate space will be drastically reduced for Quercus, not for Pinus.