Density effect on decline of Cedrus atlantica Manetti Ex Carriere in national park of Theniet El Had, Algeria

Abstract

This study focuses on the study of the causal factors of Atlas cedar decline in the Theniet el Had national park, once classified as the first park in Algeria and the most beautiful cedar forest in northern Africa. Although severalstudies have been done on the causative agent of decline, none of them have confirmed the predisposing factors, thus weakening its vigor. Therefore, in this study, the search for possible relationship between dieback and ecological, dendrometric characteristics as well as the spatial distribution of trees were taken into consideration. 40 concentric circular plots of 200, 400, 500 and 1,000 m² were installed in the northern part of the park for dendrometric and edaphic surveys, in addition to rectangular plots of 200 m2 installed in the center of the concentric plots were measured of distance between trees and of the four radii of the crown. The results obtained showed that the circumference in the reduced areas (the circular plots of 200m²) declined significantly. The spatial distribution of the trees, schematized by the AutoCAD software, was chaotic and the crowns showed deterioration influenced by their overlapping. In 76% of the rectangular plots, the maximum area of the crowns had an overlap of more than 90%. The application of Schütz's inter-individual competition index also indicated that competition between trees was very important. This situation only explains the chaotic distribution of the trees, due to the lack of forestry work, imposes a competition between the trees causing, thus, the weakening of their vigor. Therefore, the establishment of a short- and longterm Atlas cedar decline management plan is of high recommended importance, in which adjusting the spatial distribution can promote the future strength and vitality of Atlas cedars.