Status and prospects for the conservation of remnant semi-natural carob Ceratonia siliqua L. populations in Lebanon

Abstract

The carob tree (Ceratonia siliqua) has been included in a national list of priority forest genetic resources as a target for conservation and management in Lebanon, a country bordering the eastern Mediterranean shores. To provide baseline information for the development of a conservation strategy for the species, the current status of remaining semi-natural carob populations in Lebanon was assessed through an ecogeographic survey, a bio-climatic distribution study, and a genetic analysis. Field explorations were carried out throughout the reported natural distribution range of the target taxon (≤750 m altitude) and all areas where carob was found, were mapped. Data including land use, main associated vegetation, major threats, percentage of grafted trees, and landform were recorded for each population. Climate data were interpolated as functions of geographic parameters to create maps for mean minimum temperature of the coldest month (m), mean maximum temperature of the warmest month, and annual precipitation. These were then used to calculate the pluviometric quotient (pmq) as a measure of aridity. The largest populations encountered in the study were targeted for molecular analysis. Polymorphic amplification products of RAPD were analyzed for 10–15 trees from each population. The ecogeographic survey revealed that most remaining populations are very small consisting of low numbers of individuals. Anthropomorphic activities such as coppicing, grafting and/or grazing were evident in all populations, however, it was clear that these populations were abandoned and had become part of the Mediterranean maquis vegetation. Overlays of soil maps and carob distribution data indicated that the species occurs preferentially on Terra Rossa soils, which have typically poor agricultural capability. An examination of the climatic conditions in which carob could be found showed that the distribution of carob is limited by (m) of less than 1 °C and a pmq below 60. Analysis of RAPD products indicated that the populations did not cluster based on geographic proximity and revealed a significant difference between and within populations suggesting that the remaining populations constitute a valuable germplasm. The prospects for conservation of carob in the Lebanese context are discussed.