Assessment of current and previous dieback of Atlas cedars in Algeria's Theniet El Had National Park

Dieback of Atlas cedars is a complex phenomenon that has been affecting the cedar forests of the Aures mountains and Theniet El Had since the 1980s. Its causes are still unknown. This study focused on the cedar forest of Theniet El Had in order to gain a better understanding of the way Atlas cedar dieback is evolving over time and space and to establish whether it has any relationship with environmental factors. Two approaches were applied. In the first, a spatial approach, the distribution of affected trees was mapped out according to altitude, slope, exposure, dendrometric parameters (diameter and height) and state of health (percentage of defoliation). In the temporal approach, radial growth rates were compared between affected and healthy trees in six ecological stations that were representative of Atlas cedar stands in the study zone. The results show that dieback is more severe in the Theniet El Had forest towards its lower limits in steeply sloping low-altitude stations exposed to sunlight and heat. Dieback is advanced and affects adult and/or aging trees. The trees affected stand out for their poor growth and very high average sensitivity to climatic factors. The prolonged drought in the region from 1980 to 2002 has exacerbated the effects of aging, which has affected and worsened the state of health of the Atlas cedars. These results point to the urgency of undertaking sylvicultural work to improve the health of these stands and to establish sampling plots.