Spatiotemporal dynamics of vegetation dieback in the Talassemtane fir forest (western Rif, Morocco)

Abstract

Forest dieback is becoming an increasingly serious concern worldwide. Its causes are multiple, complex and often difficult to disentangle. The primary reports of dieback in the Moroccan fir forest go back to the beginning of the 21st century, but there are no studies dedicated to dieback in this forest documenting those earlier observations. In this study, we quantify the spatiotemporal evolution of dieback in the Talassemtane fir forest through remote-sensing- and field-based assessments between 2009 and 2019. We analysed the inter-annual and seasonal variations in the Normalised Difference Vegetation Index (NDVI) and the effect of precipitation and temperature on forest cover. We found evidence of earlier and recent dieback symptoms, though their extent has declined over time from 369.27 ha in 2009 to 100.08 ha in 2019. During this period, NDVI values increased significantly, mean precipitation increased slightly but not significantly, and mean temperature decreased significantly. NDVI was positively influenced by precipitation and negatively affected by temperature. Overall, spring temperature and precipitation had a strong impact on vegetation cover during the subsequent summer. The highest NDVI values were concentrated on north- and west-facing slopes, within an altitudinal range of 1229 to 1800 m. These findings provide valuable initial insights to aid forest managers in identifying locations of dieback for the planning of a monitoring strategy and highlight the need for further research to better understand the drivers of Moroccan fir forest dieback.