Structure, floristic composition, and dynamics of Pistacia atlantica subsp. atlantica communities in the north-west of Algeria

The forest species in arid and semi-arid Mediterranean ecosystems already under threat from human and animal activities are now facing heightened vulnerability. This is evident with Pistacia atlantica in the extreme northwest of Algeria, which now occupies a smaller territory than previously. Our study aims to identify and describe P . atlantica communities based on floristic, physiognomic, and dynamic aspects, using a phytoecological approach at the ecological station scale. In this study, the sigmatist phytosociological method was used, based on floristic surveys that integrate all the ecological factors (climatic, edaphic, biotic and anthropic) responsible for the distribution of the vegetation. The climatic conditions in the far northwest of Algeria, from ancient times to the present day, are still favorable for the rehabilitation and maintenance of P . atlantica . Results revealed four distinct P . atlantica groups, varying geographically and floristically. Transitions between groups trigger regressive phenomena, leading to environmental disturbance and a high degree of therophytisation (68%). In conclusion, P . atlantica is experiencing dual-directional evolution, with regressive changes due to human pressures, leading to spiny/toxic species proliferation, and progressive changes within these clusters, promoting P . atlantica seed germination.