5. Discussion
The world is currently facing serious and very rapid land degradation. Indeed deforestation and desertification two types of closely related threats are taking on an unprecedented scale on forests. Land clearing, fires, overuse of land, overgrazing, deforestation are causing the destruction of land cover and land. The demand for fuel wood is one of the main causes of deforestation, especially in dry highlands where trees grow slowly. Fires are mainly caused by negligence: uncontrolled discharges, rarely by malicious acts. In addition, it promotes the leaching of organic matter from soils that were part of the forest carbon sink. After the fire, the forest canopy and organic matter in the soil surface horizon (litter and humus) were completely burnt down and destroyed by fire, reducing the protection of the soil (siband, 1972; roose 1980). Unfortunately, our study area has undergone an intense degradation of woodlands, which the maquis is increasing. This degradation of the natural environment leads to the reduction of biological potential and by the disruption of the ecological balance and socio-economic. The forest of Tenira is distinguished by a semi-arid bioclimatic and is generally this vegetation comes in the form of maquis indicating the nature of a local bio-climate (Benaouada, 1997). The high percentages of maquis observed during the study periods is due to the continuing degradation of this dense forest. This decline of the surface of dense forest is the result of an anthropogenic exploitation and frequent fires. This effect adds bioclimatic and soil heterogeneity that has fostered the development and installation of vulnerable species. Fires of shrubs in regions of the Mediterranean climate generally burn with considerable intensity. Average fire return times range from 20 to 30 years to more than a century, and fuel combustion during individual fire events ranges from 1 to 5 kg/m2 (Olson, 1981). Spatial variation in fire response is widely a result of differences in fuel mass before fire, fuel moisture content, fire weather conditions and site topography. The frequency of fires (both regional frequency and return time) is regulated by the frequency and timing of ignition events, fuel accumulation rates and landscape configuration. The importance of this latter factor has received considerable attention (Minnich, 1983 and 1988; Turner, 1987; Malanson, 1984). The relative impact of topography and space variation of fuels depends on weather conditions and fuel moisture. At moderate to high of this latter, variations in vegetation structure and localized landscape fragmentation (due to past fire history) may determine burning patterns. However, when fuel moisture drops below threshold levels and weather conditions are extreme (such as hot, dry winds), fire may be regulated primarily by wide-scale topographic features such as major rivers or divides (Turner and Romme, 1994). There is general agreement that the above factors regulate Mediterranean climate fire systems, but quantitative estimates of their relative importance are difficult, if not impossible. This is due in part to limited data available, but is also a consequence of the stochastic nature of several of these factors. Thus, it is incorrect to view Mediterranean ecosystem fire regimes as being under finely tuned feedback control. Indeed, the variability in fire regimes resulting from these largely (Christensen, 1987; Christensen and Muller, 1975 a and b). The importance of bushy stratum is a remarkable sign of degradation of vegetation often reaching the irreversible stage. Furthermore, fires are a major disruption of Mediterranean landscapes. They are linked to intense human pressures but also to the character of pyrophytique and xerophytic vegetation (Delabraze and Vallette, 1974; Houérou 1980; Tatoni and Barbero, 1995). The current situation of this forest stands as one of the most critical in the Oran region. According to Benabdeli (1996), urgent, effective and radical solutions must be found immediately if we do not want to attend a total disappearance of natural woody vegetation. The main consequences will result in an amplification of the desertification process, that is gaining more and more space through the regression of woodlands and rangelands, erosion, disruption of water systems, the deterioration of the environment and especially by a decline in economic and social productivity of natural resources (Benabdeli, 1996). This increase in forest area is mainly due to the efforts of the forest service in the field of watershed protection by various techniques including reforestation of Pinus halepensis , which constitutes the main essence. Similarly, these improvements are insufficient to protect the forest; we estimate that after 31 years, only 9% of reforestation work has been done to protect the forest of Tenira. In general, and despite the reforestation campaigns conducted annually since independence, the reforestation rate in Algeria is between 10% and 12% only. The reforestation rate remains insufficient to ensure both the physical and biological balance and does not cover the needs of field of forest products, nor the economic revenues for the country (Alexandrian and al., 1999). In the province of Sidi Bel’Abbes, the pastoral activity care is higher and the animals are forced to graze off, especially in state forests. The size of the herd necessarily led to the degradation of the forest and damaging the young plantations (Benabdeli, 1996). Our forests are often solicited by pastors as an auxiliary source for livestock feed (Benabdeli, 1996). The cattle farming remains the most practical at the level of forest areas in high altitudes. More than 1 200 000 head of cattle are found in the mountainous forest areas (Benabeli, 1998). The permanent increase in herds imposed a destructive pressure especially on forest areas (Benabeli, 1998). According Bedrani, 1993, if the number of herds is high it easily destroys the protective vegetation cover in forestry. The trampling of the powdery surface of soil causes a reduction in permeability therefore, its water reserves increase by favoring runoff. The clearings leave a strong imprint on the physiognomy of this forest, where large areas have been converted into pasturage and cereal field. The extension of agriculture on the plains of Tenira led at the inhibition on the foothills on the edge of forests. Currently, private populations of farmland on the mountains continue to carry out plowing in different levels of the forest edges, clearings, mountain tops (Benabdeli, 1993). According to the results obtained, the installation of annual crops is very important. Indeed, deforestation and land clearing for agriculture have accelerated soil erosion. By the intensification of crops requires an increase in inputs (fertilizers, mechanization, irrigation, chemical control of parasites and weeds) which can lead to a certain imbalance in the soil, but that the resulting degradation depends on clearing, plant cover, and the cropping system in place. Clearing new lands which are more and more fragile, the biomass of a dense forest (> 800 t / ha: might believe that the soils are extremely fertile. The rock is so deeply altered that all that remains in the soil cover is quartz, kaolinite, a little iron and aluminum, and some traces of incompletely altered minerals. The roots are concentrated in the surface horizons where organic matter and available nutrients are found. Brutal clearing or poorly adapted cultivation techniques, the humus horizons are stripped there remains only a crusted, compact, inert, almost sterile mineral mass. Biogeochemical assessments show that under natural vegetation (forest or undegraded savannah) the inputs of nutrients by rain, dust and biological returns (roots and meso-fauna) exceed the losses by erosion and by deep drainage. The balance being positive, the forest fallow accumulates on the surface (in the litter and the humus) organic matter capable of storing water and nutrients, and the nutrients that the roots have recovered in depth (Roose, 1980; Beirnaert, 1941; Fauck and al., 1969-77; Godefroy, I974; Roose 1972-82; Lal, 1982). This population exerts continuous pressure on the forest types by clearing and overgrazing this disrupts forest protection and development. However, any clearing interrupts this chain of potential fertilization accumulation. The contributions decrease (reduction of the meso-fauna and the efficiency of the root network to capture the nutritive elements under most cultures) and especially the losses increase. Exporting crops reduces the stock of easily tradable items; 50% of organic matter is mineralized after 4 years and part of the nutrients released are leached (Fauck and al., 1969; Kang and Juo, 1982). Quezel and al.,1992; argue that in 50 years without a total change of socio-economic and of forest policy, it should theoretically remain less than half of the current area covered by forests. The regeneration after 2007 fire was very low especially for the formation of thuya and lentisc. However, regeneration between 2007 and 2010 was significant for groupings of aleppo pine. The progressive destruction of the soil in the root systems of these types of forests prevents optimal recovery of some species, and the trees are close to their ecological limits (sauvages, 1961). According Trabaud, 1992 a; five years are sufficient for the burned resumed woody vegetation. The passage of a fire resulting in the alteration more or less pushed vital organs of the plant, to the foliage, trunk, and roots, it follows a loss of tree vigor that could cause its death. In almost all cases, after the fire, the vegetation quickly returns to its original state without human interference. Heat can destroy underground organs or seeds of survival, and thus greatly limits the regeneration of vegetation, resulting in a floristic impoverishment. The repeated fires result in a marked floristic impoverishment. Thus, many plants do not have time to reach sexual maturity before the passage of a new fire. In these semi-arid areas, in normal circumstances out fires, the vegetation is in continual struggle against the harsh climate, its poor soil nutrient, and organic matter. The passage of a fire even in low intensity translates directly by impairing the vital organs of the plant; at tree, vigor may cause their death (Benabdeli, 1996).