The Algerian forest, the last bulwark against desertification coming from Sahel, is particularly vulnerable to global change and must be protected from deforestation, which is constantly advancing. Aleppo pine, which covers 880,000 ha, is the predominant species of forests in semi-arid and arid regions. The soils of these regions are generally fragile and vulnerable due to climatic aridity; their degradation today has accentuated the phenomenon of desertification.The objective of this work was to compare the physicochemical and microbiological characteristics of the coniferous forest soils of the semi-arid and arid zones of the Algerian west. In addition to characterization of climates, 16 physical, chemical and microbiological properties were analyzed on soils collected from forest areas characteristic of the two zones: Jebel Sid Ahmed Zeggai forest massif (Saida province) located in the semi-arid zone and the forest massif of jebel Antar (Naama province) located in the arid zone. Our results showed very different soil qualities between the two zones: moisture content, water retention capacity, permeability, porosity and organic carbon content, total nitrogen and organic matter are higher in the semi-arid zone compared with the arid zone, which is characterized by the large presence of total limestone. Biomass and microbial basal respiration are higher in the semi-arid zone. Our results are discussed with regard to the vulnerability of soils to the respective climate of each of the zones and agro-silvo practices potentially involved in the degradation of these soils.

Natural disturbances, such as forest fires, cause significant changes in the structure and functioning of semi-arid ecosystems. After such disturbances, the impact on the soil ecosystem in its entirety is misunderstood. In this study, two years after the last fire, changes in the physicochemical and biological properties of Aleppo pine forest soils in the semi-arid zone were observed. Among all physical properties analysed, only the soil moisture remained significantly lower in the burnt zone in contrast to control zone. Considering the chemical properties, the only negatively affected parameter is the rate of organic matter. In terms of biological properties, results showed that the fire caused a significant decrease in soil microorganisms by decreasing basal respiration and microbial biomass. Conversely, the metabolic quotient recorded higher values in the fire zone than in the control zone. These results indicate that microbial communities in semi-arid soils, already stressed by climatic hazards, are very sensitive to the passage of even low-intensity fires.

The research work was conducted on eroded soil in the Keroua forest of Saida, Algeria, whose objective is to know the changes in the physicochemical and biological properties of forest soils subjected to the effect of water erosion. The samples were taken to a depth between 0-10 cm in each zone (eroded zone and control zone). Our results show that the biological properties are the most affected by water erosion where there was a significant decrease in basal respiration and microbial biomass, which had a negative influence on the metabolic quotient (higher values in the eroded area). For chemical properties, there was an increase in organic matter and total limestone, while the pHWater decreased in the eroded zone. For the physical properties. We raised a slight difference between the two areas, but which was not statistically significant.

Arid zones are very harsh environments characterized by binding edaphic and climatic factors, their rainfall is low and irregular accentuated by high temperatures and their soils are fragile and vulnerable. In recent years, it has been noted that vegetation is regressing and that the majority of reforestation has been a failure. Our study aims to know the physico-chemical and microbiological characteristics of forest soils in the pinewoods of an area of the highlands of western Algeria (Naama). For this we analyzed several soil samples spread over five sampling stations in a forest of Aleppo pine. The results show that the forest soils of our study area are characterized by a generally sandy texture and an orange color for all the selected stations. They are characterized by: a very high C/N ratio that indicates a slow evolution of organic matter and a nitrogen deficiency that is necessary for carbon decomposition. The conductivity shows that the soil contains some salinity, its permeability is strong and its humidity fairly low with an alkaline pH (> 8) due to the increase in the limestone level in the area. Basal respiration is low compared to microbial biomass due to poor physico-chemical quality of soils and the effect of water stresses that slow down microbial activities. Soils in this arid forest are generally characterized by soil homogeneity sensitive to the influence of environmental factors mainly poverty into elements necessary for its proper functioning such as nitrogen and water that accentuate soil degradation of these forest formations, which results in the risk of degradation being triggered.

The development of agriculture to the detriment of the forest is one of the strongest pressures, essentially anthropogenic. The particularity of this study was that the traditional agricultural practice used was low intensity agriculture (fallow period) since the first conversion. The experiment was conducted in the Keroua forest, Saïda Province, north-western Algeria. Soil samples from two experimental areas were collected at depths ranging from 0 to 10 cm. The findings came from the statistical analysis of the data, some of which revealed the sensitivity of this ecosystem. The conversion of the forest soil to agricultural land increased the alkalinity of the soil (pH H2O increased by 0.16 units), and the acidification of the soil with a significant decrease in pH KCl values (by 0.24 units). Moreover, the organic matter content in the converted soil decreased by more than 50%, while the physical characteristics changed slightly with a decrease in moisture content and water holding capacity and an increase in bulk and real density. Meanwhile, the permeability and total porosity did not change in the two areas. For biological properties, basal respiration and microbial biomass decreased by more than 45% in the converted soil compared to the forest soil.