Size Structure of Cupressus sempervirens L. and Pistacia lentiscus L. Popula- tions in Wadi Alkuf, East of Libya

Wadi Alkuf is one of the richest of all the phytogeographical regions of Al-Jabal Al- Akhder. The present work aims to study the size structure of Cupressus sempervirens L. and Pista- cia lentiscus L. populations in relation to their physiographic and soil conditions in Wadi Alkuf, northeast of Libya. Eighteen terraces (25 m × 25 m) were selected at Wadi Alkuf of Al-Jabal Al- Akhder at three different levels (six downstream, midstream, and upstream). The number of indi- viduals of each species was counted while the height (H) and mean crown diameter (D) were meas- ured. The size index of each individual was calculated and then used to classify the population into 7 size classes: 1 m to 7 m. The height, mean diameter, height to diameter ratio, size index, and vol- ume per individual in each size class were determined. Generally, the height to diameter ratio was more than unity for C. sempervirens L., this means that the diameter of these species tend to expand vertically rather than horizontally, while the height to diameter ratio was less than unity for P. len- tiscus L, this means that the diameter of these species tends to expand horizontally rather than verti- cally. The total size structure of C. sempervirens L. in the study area is characterized by the prepon- derance of the young individuals comparing with the old ones, while that of P. lentiscus L. showed a reverse pattern (i.e., preponderance of mature individual compared with the young ones). Five forms of size distributions along the different elevations were recognized: more or less inverse J- shaped distribution, positively skewed distribution, bell-shaped distribution, more or less J-shaped distribution, and more or less stationary size distribution biased to large size. The study’s results show that density histograms of size distributions are good indicators of future trends in population numbers for the studied species. The field observations were consistent with the results of the inves- tigation of soil properties. The soil downstream has the highest values of pH, EC, HCO-3, SO4-2, Cl- and Na+, while that of the upstream has the lowest values except for K+.