Évolution des proportions d’aubier et de duramen du cèdre de l’Atlas, Cedrus atlantica Manetti, en Algérie

This study was conducted in the cedar forests of the Belezma (Aures), Djurdjura (Kabylia) and Theniet El Had (Orania) ranges, which vary widely in altitude as well as bioclimatically. The study was undertaken as part of an overall project on the functioning of Algeria’s cedar forests. The problem addressed was the lack of data on the process of heartwood formation in Atlas cedars, which provides very useful information to improve knowledge on the typology of cedar forests. The aim was firstly to identify changes in heartwood formation over space and time. A total of 485 tree sections and cores from the three cedar forests were analysed. The results shows little variation in the proportions of heartwood from different stations in the same forest. Overall, age has a positive influence on heartwood formation and a negative influence on the proportion of sapwood. Heartwood formation appears to begin earlier in the Theniet El Had and Djurdjura forests (at 14 to 17 years of age) and later in the Aures forests (at 20 to 30 years). Cedar trees in the latter char- acteristically have a lower proportion of sapwood, ranging from 45% to 50%. In every case, the Djurdjura forest, which has the most humid bioclimate, differs from the two others in having a lower pro- portion of heartwood (44%) and a higher proportion of sapwood (55%). The highest proportion of sapwood, 78%, was found in the Talla Guillef cedar forest, and the lowest in the Belezma forest, where the average was 68%. This suggests a tendency for sapwood proportions to vary in accor- dance with a per-humid to semi-arid bio- climatic gradient. Our study also high- lighted the very low proportion of sapwood in trees affected by dieback, where the average proportion was 46%.