Société nationale de protection de la nature et d'acclimatation de France, Paris (FRA)
Abstract
L’objectif de cette étude est d’analyser le comportement in situ de semis naturels de Cèdre dans les premières phases de la régénération, connues comme étant les plus vulnérables et tenter de définir la niche de régénération du Cèdre dans un contexte actuel contraignant. L’étude est menée au niveau de deux stations représentatives de l’hétérogénéité structurale de la cédraie de Chréa (Atlas blidéen). Une analyse statistique comparative de différents niveaux d’observation a permis de mettre en évidence l’impact important du climat, l’effet de versant et de l’altitude, sur la germination, la croissance et le potentiel de survie des semis, mais également celui, aggravant, de l’action anthropozoogène, par comparaison à une situation témoin. Sont également soulignés au niveau local, le rôle déterminant de la structure du peuplement qui influerait par son degré d’ouverture, l’effet facilitateur du sous-étage arbustif ou compétitif de la strate herbacée, ainsi que la réceptivité de la surface du sol.The Cedar (Cedrus atlantica (Endl.) Carrière), endemic species in North Africa, is currently experiencing a regression of its range due first to the decline and second to the lack of regeneration over much of its range. These problems of regeneration seem exacerbated over recent decades, in relation to climate changes that knows the Mediterranean region and to intensification of human action. In Algeria, this issue is more pronounced at low altitude and hot exposures characterized by deficient water. The aim of this study is (i) to analyse in situ behaviour (survival, growth) of cedar seedlings in the early stages of regeneration which are known as the most vulnerable ones and (ii) to attempt to define the niche of cedar regeneration in this restrictive context. The study was conducted at two stations in the cedar forest of Chréa (Blidean Atlas), representing various situations of cedar development. Within these stations, five plots (400 m²) and fourteen elementary quadrats (1 m²), representative of the structural heterogeneity of the cedar forest and diversity of potential host microsites for cedar seeds, have been followed during two years (2013 and 2014). A measure of the respective lengths of underground and aboveground parts was performed on 256 seedlings. A comparative statistical analysis of these different levels of observation was made to highlight the important role of climate on the germination and seedling survival potential relative to the daily, seasonal and interannual variation of climatic parameters (P, Tmin, Tmax) as well as the side effect and the altitude. This comparison showed also the aggravating or moreover deciding role of anthropozoïc action including trampling of seedlings and soil compaction by livestock, silvicultural measures (pruning, cutting, etc.), as well as ploughing boars digging up seedlings, compared to control conditions (exclosure). In fact, average survival rates in this case are considerably higher (54-76 %) compared to situations excluding deferred grazing (9-21 %). Regeneration requires a combination of many factors like adequate availability of seeds, receptive soil, climatic conditions favouring of the emergence of seedlings and not penalizing their survival, but these conditions need a decreased anthropozoïc pressure
