Ne'eman, G., Department of Biology, University of Haifa at Oranim, Tivon 36006, Israel
 

Israel's largest natural Pinus halepensis Mill. forest is on the Mt. Carmel range and belongs to the distinct East Mediterranean genetic group. Most of this forest is the result of invasion of abandoned fields and grazing lands, resulting in a heterogeneous pine forest with an understory of broad-leaf shrubs and trees. Species composition, vegetation cover, pine-stand structure, and pine genetic diversity of plots in sites of known fire history, burned 5, 11, and 20 years ago, were studied with adjacent unburned sites forming a chronosequence. Except for annual species, no species replacement took place during post-fire succession. The main observed changes were in the cover of species and of plant life forms. The ratio of tree/dwarf-shrub cover was found to be linearly related to the number of years elapsed since the last fire. Therefore, this ratio could serve as an index to determine the successional stage of Aleppo pine stands with unknown fire history. It is estimated that 30-40 years are needed for full recovery of Aleppo pine stands after fire, depending upon site quality. The stands of post-fire regeneration are of uniform age and are less variable in their structure than unburned stands. The genetic distance among the various Pinus halepensis subpopulations was found to be very small; most of the genetic variability was due to within-subpopulations variability, with almost no variability among subpopulations. Alleles that are typical of West Mediterranean P. halepensis populations or of P. brutia, were found in two post-fire subpopulations (stands), indicating pre-fire cross pollination between native Pinus halepensis trees and trees in adjacent pine plantations of foreign origin. The conclusion is that fire has little effect on species composition and on vegetation structure, but that it alters the Aleppo pine stand structure.