Long lasting human impact on the natural Mediterranean vegetation is the reason for its degradation. Uncontrolled felling of trees, fire and overgrazing are the most important ecological causes of this process.
Geobotanical investigations made in the area of Algiers facilitated the characterization of degradation changes in the structure of vegetation and in the floristic composition in all the degradation stages.
Under the influence of the degradation factors, mentioned above, the oak forests, growing on different, more or less calcareous substrates, are transformed into various shrub formations, mainly into many types of 'maquis' and 'garrigue'. The floristic composition of these communities is given in Table 2.
Further degradation leads to widespread Cistus-formations and then to 'palmitto', a formation created by the dwarf palm (Chamaerops humilis).
When the anthropopressure becomes stronger even this dwarf palm retreats. Loose swards, replacing the 'palmitto' formation, often cannot stop the subsequent degradation. Bare rock is the extreme, relatively rare stage of forest degradation in this area.
The most common form of natural regeneration is the invasion of Pinus halepensis, observed in all degradation stages identified. This pine is also one of trees, most commonly planted on mountain slopes to prevent their erosion.