Post-fire soil hydrology, water erosion and restoration strategies in Andosols: a review of evidence from the Canary Islands (Spain)

Andosols are the most characteristic soils of volcanic regions such as the forested, fire-prone, hillslopes of the mountainous Canary Islands (Spain). Due to their volcanic nature, these soils have traditionally been considered highly resistant to water erosion processes in undisturbed conditions, but are also highly susceptible to environmental disturbances. In addition, volcanic terrains often underlie heavily-populated, steep areas where torrential rains are frequent, increasing the threat to the population and infrastructures down-slope. Numerous hydrological and erosional catastrophic events in disturbed Andosols in the Canary Islands and worldwide, leading to major losses to lives and properties, have been historically and recently reported. The impact of environmental alterations such as land use change on hydrological and erosional response of Andosols has been widely studied in the Canary Islands and worldwide. However, the effect on this soil type of wildfires, generally considered one of the main geomorphological agents, and historically connected to the forested fire-prone Andosols of the islands, has had scant attention to date. This review seeks to redress this knowledge gap by: (i) evaluating the factors affecting the susceptibility of Andosols to catastrophic hydrological and erosional events; (ii) summarizing the published studies on the impact of fire and the post-fire response of this soil type and the specific restoration measures developed to date; and (iii) identifying research gaps and suggesting new lines of investigation in order to reduce the hydrological and erosional risks in these particular terrains