Hanan F. Kabiel

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.

Plant communities and reproductive phenology in mountainous regions of northern Libya

Within the semi-desert landscape of northern Libya, two sub-humid escarpments occur: Al-Akhdar in the east and Nafusa (Jabal Al-Gharbi) in the west. This study compares plant communities in the two regions, which are along an elevation gradient, in terms of species composition and diversity, frequency of different Raunkiaer life forms, and reproductive phenology. The two regions differed in species composition and life-form frequency between regions and between elevation zones within each region. Patterns were associated with the lower rainfall and lower moisture-holding capacity of soils at Nafusa, resulting in more xeric conditions. Only 13% of species were shared between the two regional landscapes. Species diversity, life-form frequency, and duration of the flowering–fruiting phenophase were all affected by elevation above sea level. The duration of flowering and fruiting in spring and fall was associated with environmental conditions, although there were different thresholds in the two regions. There was both a spring and fall episode of flowering at Nafusa, but only spring flowering at Al-Akhdar. It is anticipated that there will be a gradual shift of plant communities to higher elevations and loss of certain sensitive species in response to ongoing climate change.

Population ecology of some keystone tree species in the Jebel Marra region of Darfur

Populations of Albizia amara, Acacia senegal, Anogeissus leiocarpus, and Balanites aegyptiaca were monitored in five habitats in the Jebel Marra region: clay plains, sand plains, wadis, northern slopes, and southern slopes of the Jebel Marra (mountain) region. The plains and wadi habitat types had been regularly disturbed because of cycles of shifting cultivation. When land was prepared for cultivation, seedlings and juvenile plants were removed, leaving only larger adult plants, and, therefore, unstable tree populations, lacking juveniles, and growing in fallow lands. A. amara and A. senegal were more abundant than A. leiocarpus and B. aegyptiaca. The healthiest populations, with more juvenile recruits, were found in the grazing lands at higher elevations. However, A. amara and A. senegal showed stable size structure in both grazing and fallow lands. In general, in the four study species, we see a decline in growth and reproduction (with growth measured as tree height and number of branches, and reproduction assessed in terms of number of fruits per tree and dry weight of seeds) along a progression from fallow lands to the grazing lands, and, separately, from lower to higher altitudes. The resilience potential of each species in the fallow lands indicated two distinct population resilience strategies: (1) we saw faster rebound in the case of A. amara and A. senegal and (2) slow recovery from disturbance in the case of A. leiocarpus and B. aegyptiaca which showed low juvenile recruitment in fallow lands.

Variations of Plant Macronutrients and Secondary Metabolites Content in Response to Radionuclides Accumulation

Current knowledge on the basic radionuclide tolerance indicates that plants may develop mechanisms preventing the damaging effects of radionuclide stress. The radionuclides content was determined in the Mediterranean coastal black sand soil and in the edible portions of the four food crop plant species, viz., Eruca sativa, Lycopersicon esculentum, Pasidium guajava and Mangifera indica. Biochemical and nutritional constituents were assessed to elucidate the possible effect of radionuclides on the edible portions of the plants. The ability of the four study plant species to accumulate Uranium and Thorium in their edible portions from the coastal black sand soil is higher than that absorbed from the inland agricultural soils. The nutritional constituents were affected by the high concentrations of Uranium and Thorium in the plant tissues.