Ecological assessment of populations of Juniperus phoenicea L. in the Al-Akhdar mountainous landscape of Libya

Abstract

The Phoenician juniper (Juniperus phoenicea L.) has long been common in the Al-Akhdar mountain range in NE Libya. Juniper trees in the region are showing signs of dieback, and minimal successful seedling recruitment has occurred. We investigate this effect at the level of individual trees, tree size classes, and populations. At ten sites, population size, growth and reproductive traits, and percentage dieback in different size classes were evaluated. Elevation, distance from the sea, and the interaction between these factors had a significant effect on tree volume, and number of branches, number of female cones per branch and number of female cones per tree. Two groups of populations were recognized: the first (Sites 2, 3, and 4) were near the coast. They appeared to be more recently established, with no individuals in the largest size class, and, at this point, less severe dieback. In contrast, in the rest of the sites there were no individuals (Sites 1, 5, 6, and 9) or very few individuals (Sites 7, 8, and 10) in the smallest size class, indicating widespread failure of recruitment in recent years. Mature female cones containing seeds were abundant at these sites (except for Site 8); therefore, this was not attributable to failure of sexual reproduction, but rather was associated with higher levels of intra- and inter-specific competition, combined with more variable rainfall in recent years. Smaller trees are particularly susceptible to dieback throughout the region. Conservation initiatives should include restrictions on clearing these natural forests for conversion to agriculture and, where harvesting is necessary, preferential harvesting of larger individuals.