Relationship between health index (SI) and cork growth index (Iac) in two Algerian cork oak stands: M'Sila (W. Oran) and Zarieffet (W. Tlemcen)
Abstract: The health state of the crown top and the rate of cork growth are the two most commonly used parameters to describe the vitality of forest trees. These measures have been applied for the first time to silver fire (in Jura, France) to assess the relationship between crown top state, radial growth and stand state. Regarding the cork oak, this is the first time that the annual growth of the cork is directly related to defoliation (240 trees), by using two indices: corkgrowth (Iac) and health state of the stand (IS). At Zarieffet, a mountain cork oak forest, the slow cork growth induces stable oscillations of Iac around 1. The stability of growth goes with an annual fluctuation of the health index, the trees passing upon the respective states: “healthy”, “weak” and “decaying”. Multiple correlations showed a strong negative relationship (r = -0.85) between the two variables in the three Zarieffet stands. At M’Sila, a coastal oak forest, two different situations were highlighted. In stands (P1, P2, P3) of the Sheikh Khalifa canton characterized by a dominance (60%) of healthy trees (SI 2.1) (P4, P5, P6) dominated by trees of decline classes 3and 2, the relationship between IS and Iac is strongly negative(r =-0.74). This explains why the growth index significantly increases or decreases after any improvement or decline of the tree health index.