Suivi de la régénération naturelle du Cèdre de l’Atlas dans les premiers stades de développement dans quelques stations du massif forestier de Chréa (Atlas blidéen, Algérie)

Abstract

Monitoring the early stages of Cedar natural regeneration in some stations of Chréa Forest (Blidean Atlas, Algeria). 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 anthropozoic 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 anthropozoic pressure.