Assessing the impact of post-fire restoration interventions using spectral vegetation indices: A case study in El Bruc, Spain

Sammanfattning: Ecological restoration has become an increasingly used practice to revert degraded land and mitigate the effects of extreme events in vulnerable biomes such as drylands. Methods to improve the assessment of these restoration interventions are essential to ensure their success, optimize resources and identify improvement aspects for future interventions. This study develops a method to assess the performance of post-fire restoration interventions on a pixel level when access to pre- and post- fire field data is limited, therefore depending on remote sensing data. The approach takes into account restoration intervention objectives, the state of the area before the intervention efforts began and key terrain variables. This method was applied to a restoration intervention made in a burnt forest in north-east Spain, where an agro-silvopastoral mosaic has been conceived under the frame of a Life 2020 program. To assess the restoration performance, different spectral vegetation indices (SVIs) linked to the objectives were used. By using the Before-After-Control-Impact (BACI) statistical method, the study isolates the impact of the interventions from temporal variability and natural regrowth. The study explored the effects of the interventions by comparing restoration types (active or passive), terrain variables and the post-fire recovery levels before the intervention efforts began. The study also showed that the sole use of one SVI to assess the impact of restoration interventions may lead to limited conclusions as the three selected indices were outputting different levels of performance for the comparisons undertaken. The pixel level analysis also allowed to map the detailed variation in performance across areas. The core of this method can be applied to other restoration intervention scenarios other than post-fire and its affordability could allow for its integration in monitoring protocols in large-scale endeavors such as the current UN Decade on Ecological Restoration program.