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.

Rainfall in the Algerian highlands is experiencing a significant decrease, prompting the state to exploit surface water, namely the establishment and operation of dams in the supply of drinking water and irrigation. To this end, our work focuses on the study of the water quality of the BOUGARA dam, supplied mainly with treated wastewater, and its effects on the quality and yield of barley, because this dam, with a capacity of 11 million m3, is located in an agricultural perimeter with an area of approximately 1000 ha. To obtain valid results, we proceeded with the installation of 14 rectangular plots with an area of 100 m2 each around the dam. These plots were the subject of identification of the type of soil and the sowing of barley (Hordeum vulgare), where 7 plots were irrigated from the dam while the other 7 were not subject to any irrigation. Will this be the subject of a witness? In addition, seven bottles of 250 ml each at a depth of 10 cm were taken from the points closest to the plots to define the quality of the water in the dam. Harvested barley was measured qualitatively and quantitatively for all plots, followed by a comparison between irrigated and non-irrigated plots using one-factor ANOVA. The water quality of the dams has been studied through principal component analysis (PCA) by comparing it to the quality recommended by the Algerian standard. The soil in this study area is light, sandy to sandy clay loam, with a pH of 7.39 to 8.17 and high levels of organic matter. These results indicate an excellent soil for growing barley. Algerian irrigation standards for dam water do not meet Algerian irrigation standards. Analysis of variance at the 95% significance level suggests that a lack of water during the development cycle of barley has a significant effect on germination, grain yield, and straw. The salinity of the water in the dam causes the quality of the barley to be inferior on the irrigated plot, measured by the length of the ears, the length of the beard, and the weight of a thousand grains. These results indicate a failure in the treatment of treated wastewater discharged into the dam and require a revision of the method used.