STUDY OF THE REGENERATION DENSITY IN EAST MEDITERRANEAN PINE FORESTS {Pinus brutia Ten.) OF DIFFERENT SUCCESSION STAGE DEFINED BY LAST FIRE EVENT

摘要

Global changes are expected to have major impacts upon ecosystem processes and to intensify the occurrence of extreme environmental events, changing, for example, the fire frequency and intensity in fire-prone Mediterranean ecosystems.This paper reports the findings of a synchronic study of the regeneration density in East Mediterranean Pine forests (Pinus brutia). Ten forest sites located in Lesbos Island were categorized in five classes based on the time since the last fire event occurred (0-10,10-20, 20-30, 30-40, 40-50 years). Regeneration density (number of individuals) of dominant woody plant species was recorded in ten plots of 10m x 10m within each forest site (total number of plots=100). The recorded individuals of all species were categorized to three maturity classes based on their height: seedlings (1-10cm), small saplings (11-50cm), and saplings (51-100 cm). In each plot, diameter at breast height and maximum height of pines with a height greater than 137 cm were measured. Altitude, slope, orientation and soil depth of each forest plot were taking into account. Light availability was calculated taking and analyzing two hemispherical photographs at the centre of each plot. Forest plots were also categorized based on the heterogeneity in their vegetation structure, thai probably indicates the occurrence of ground fire (i.e. fire that burn just above the ground surface) in time period less than of those since the last crown fire occurred (i.e. fire that burn in the canopies of trees). Mean basal area of pine trees increased with the time from last fire occurrence in both homogeneous and heterogeneous forest plots. Pinus brutia s population density maximised on time period between 10 and 20 years after the last fire in homogeneous forests, while no significant differences were observed in heterogeneous ones. Canopy openness of each plot, was a decreasing function of the time since the last occurrence of the fire in both homogeneous and heterogeneous forests. Time since las! fire occurrence affected the recruitment density of P. brutia. An analogous pattern could not be identified for the regeneration of shrubs. Heterogeneity in vegetation structure significantly affected P. brutia only at the small sapling and saplings size class, by increasing the variability in the light regime. The presence of shrubs affected the recruitment density of pines mainly in heterogeneous forest stands. Our results confirm the importance of fire in regeneration of East Mediterranean Pine forests. Regeneration patterns differ among stands characterized by different species composition, probably due to competitive interactions. In addition, different fire regimes controls pine regeneration density by diversifying the light environment and/or excluding competitive shrub species.