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Al Jabal al Akhdar, Locally known as the Green Mountain, located in Cyrenaica on the north east coast of Libya. It is a limestone plateau with maximum altitudes of about 900 meters, holds the highest plant density and species diversity within the country. Among these plants is the Juniperus phoenicea (JP) which covers about 70% of this mountain. It has been sharply deteriorated by unidentified causes over large scales. In this work, we have used remote sensing and GIS data to monitor vegetation vigor variations and study the drought related issues to forest and JP decline in the this area. The analysis of the collected data involved Topological, Geological and Geographical (TGG) data modelling over the selected area and within a period of eight years from 2006 to 2013. We have included two main data sets among few sets of satellite images that were employed in this study. The first data set was from the updated version of Shuttle Radar Topography Mission (SRTM) DEM of ~90 m spatial resolution and the second data set from Landsat 7 and Landsat 8 Level 1T images of 30 m spatial resolution. The collected data were used to construct the images and figures, to monitor and map the forest and JP decline through the normalized difference vegetation index (NDVI) and, then to illustrate the expected reasons and attributes for this decline. The study attributes the decline due to several specific indicators related to TGG inter-related factors including; altitude, slope, aspect, drainage pattern, topographic curvature, seawater intrusion, wind and soil erosions. The results were consistent and in a good agreement with several published data on the effect of topography, geology and geography on vegetation covers of similar terrain regions.