Degradation of the South Mediterranean forest ecosystem. A perspective on fire regime, land cover change and carbon stock dynamics: the case of Tlemcen, North-West Algeria

Abstract

Mediterranean-type vegetation is one of the world’s fire-prone biomes. Previous studies have reported the resilience of the Mediterranean ecosystem to fires. However, recent fire regime characteristics are known to set limits on vegetation resilience and determine vegetation dynamics. Fire recurrence halts the return to pre-fire conditions of the forest vegetation and transforms it into shrubland or grassland, irrespective of the pre-fire species composition. In the Mediterranean Basin, there is a lot of information about how fire affects land cover change, plant growth, and carbon dynamics in the European Mediterranean. However, this is not the case for the southern Mediterranean shore. Wildfire impacts on the vegetation in countries such as Algeria are therefore almost unknown despite their significant contribution to the general wildfire statistics in the Basin. To bridge the knowledge gap, this study aimed to assess the complexity of the South Mediterranean forest degradation in North-West Algeria in the contest of fire recurrence, which drives vegetation cover change and carbon stock dynamics. The study was conducted in Hafir-Zariffet forest, Tlemcen, North-West Algeria. The study used a combination of remote sensing data derived from Landsat images, fire records, and field measurements (carbon stock estimation) to assess land use and land cover (LULC) change, fire occurrence and variation, and carbon stock dynamics. The results show that sparse wooded maquis experienced a major decline (1989-2019) of 15.19%, whereas open matorral (+14.30), forest (+0.15%), and agriculture (+1.33%) increased. The simulation at a skill measure of > 0.50 showed that the open matorral could witness the highest loss of 29.13% while forest cover, sparse wooded maquis, settlement and bare lands, and agriculture could increase by 9.51%, 13.26%, 0.56%, and 5.79%, respectively, between 2019 and 2039 based on the change pattern between 1999 and 2009. The fire occurrence and LULC dynamics analyses show that fire activity was highly concentrated in the degraded areas (open matorral) than other LULC (sparse wooded maquis, forest, and agriculture). Tree species regeneration analysis revealed that all fire frequencies (B4-B13) affected tree species recovery. Furthermore, the results indicate a declining rate of tree species diversity and density with increasing fire frequencies. Carbon stock (aboveground and belowground) varied with fire frequency, with the lowest carbon stock found at the highest fire frequency site (B13). Overall, the results of the study show that frequent fires reduce tree density, alter tree regeneration, and promote the expansion of fire-tolerant shrubs and herbs. Tree regeneration can be improved by adopting integrated silvicultural practices. For example, areas with dense stands should be thinned to promote the growth of seedlings that are shade vi intolerant. Once the regeneration is established, grazing should be minimised to ensure the transition of seedlings to saplings. Keywords: Land use and land cover, Mediterranean Basin, Fire recurrence, Biodiversity, Carbon stock, Tlemcen, Algeria