Effect of Aleppo Pine (Pinus halepensis Mill.) Leaf Litter Decomposition on Mass Loss, Nitrogen Concentration Changes, and Soil Properties in the Al Jabal Al Akhdar Region, Libya

Abstract

The objective of this study was to trace the dynamic changes of nitrogen during the process of mass loss throughout the decomposition stages of brown needle litter from Aleppo pine (Pinus halepensis Mill.) growing in the Green Mountain region of Libya. To achieve this goal, the litter bag technique was applied at three sites located at elevations of 800 m (Sidi Al-Hamri Forest), 600 m (Ain Al-Hafra Forest), and 400 m (Al-Mansoura “Al-Masaha”) above sea level. The experiment began in autumn and continued until spring. The results revealed two successive phases of nitrogen dynamics. The first phase was characterized by the rapid leaching of soluble nitrogen compounds caused by early autumn rainfall, followed by a phase of accumulation (immobilization) in which microorganisms colonizing the decomposing needles increased the total nitrogen content compared to the initial levels. The highest nitrogen accumulation was recorded at the 800 m site, where cooler and more humid climatic conditions enhanced microbial activity, while changes were less pronounced at the drier, lower-elevation sites. The mass loss rates varied among the three sites, showing similar general trends but differences in actual values, which led to fluctuations in nitrogen concentrations. The study identified an initial leaching phase of nitrogen, followed by an accumulation phase, confirming that the initial nutrient content of the litter, site fertility, and local climatic conditions interact to regulate both decomposition rates and nutrient cycling. These findings highlight the ecological importance of the forest litter layer as a natural reservoir of nitrogen, emphasizing the need to preserve it to sustain soil fertility and maintain the productivity of Aleppo pine forests in the Mediterranean environment.