Fire and torrential rainfall: effects on seedling establishment in Mediterranean gorse shrublands

Soil degradation and desertification are key problems facing Mediterranean ecosystems and these have worsened recently with the increasing frequency of fires. Moreover, rainfall in western Mediterranean areas is characterized by high intensity, and extreme rainfall events after fire strongly affect the equilibrium between soil erosion and vegetation recovery. These facts led us to carry out experimental fires in a fire-prone vegetation community ( dominated by Mediterranean gorse, Ulex parviflorus Pourr.) to study the effect of a torrential rainfall event ( through rainfall simulation) on the short-term vegetation regeneration process ( seedling emergence and survival). The results indicate that, in Mediterranean gorse shrublands after fire, an extreme precipitation event does not affect seedling emergence ( either through seed loss or from seed germination). In contrast, it has a significant effect on the reduction of seedling survival both from direct impact ( seedlings buried by sediment or seedlings totally or partially unearthed) and indirectly as a result of soil and litter losses. As a consequence, the combination of fire and torrential rainfall has an important and persistent effect on vegetation recovery, and may cause further degradation, which eventually becomes irreversible.