Assessing the extent of decling in Juniperus phoenicea trees and its relationship to environmental factors at several locations in Al-jabal Al-akhdar, Libya

Abstract

This study was conducted on the Juniperus phoenicea L. in the Al-Jabal Al-Akhdar region in two phases. In the first phase, a field survey was carried out in 2016 across several juniper forests located in the central part of the Al-Jabal Al-Akhdar. The study included various sites at different elevations, such as Soussa, Ras Al Hilal, Al-Hamamah, Al-Wasita, Qasr Al-Muqaddam, Bel-Hadid, Belghrai, Wadi Al-Kouf, and Al-Bayda. The results revealed a variation in infection rates among the sites. When calculating the infection percentages, it became evident that most locations showed high rates exceeding 90%, with the exception of Qasr Al-Muqaddam and Al-Bayda, which recorded lower rates of 46.8% and 68.0%, respectively. The highest severity of infection was noted in Wadi Al-Kouf and Belghrai, with 60.9% and 64.0%, respectively. Moderate infection severity ranging from 47% to 55% was observed in Ras Al Hilal, Al-Wasita, and Bel-Hadid, while the remaining areas recorded lower severity levels below 35%. The second phase focused on monitoring the decline of Juniperus trees across three terraces located at different elevations throughout the four seasons of 2017. These terraces were Al-Hamamah, situated at approximately 40 meters above sea level; Al-Wasita, at about 290 meters; and Wadi Al-Kouf, located around 600 meters above sea level. Environmental and climatic factors, including temperature, relative humidity, and physical and chemical soil properties, were measured at each site to identify the causes of juniper mortality. The results indicated a seasonal variation in infection rates across the three locations. The highest infection rate was recorded in summer at Wadi Al-Kouf, reaching 89.83%, whereas the lowest was observed in spring at Al-Hamamah, at 49.03%. Infection severity followed a similar pattern, with the highest values also occurring in summer: 78.47% in Wadi Al-Kouf, 65.70% in Al-Hamamah, and 63.07% in Al-Wasita. In contrast, spring recorded the lowest severity, particularly in Al-Wasita, where it did not exceed 30.80%. The study concluded that unfavorable climatic conditions, especially high temperatures in summer, played a significant role in the accelerated decline of juniper trees. Wadi Al-Kouf was identified as the most affected site during the summer season. Furthermore, analysis of disease progression showed a clear relationship between juniper mortality and environmental factors. Pearson’s correlation coefficient (r) revealed a moderate relationship between infection rate and severity with temperature in 2016, a moderate correlation between infection rate and seasonal changes, a moderate correlation between infection rate and temperature, and a strong correlation between infection severity and temperature in 2017.