Although Acacias are ecologically and culturally significant in arid environments, their mortality, recruitment and long-term change are poorly known. This study aims to quantify population change of the Acacia tortilis subsp. raddiana in South Sinai of Egypt in the period between 1968 and 2004. Remote sensing (RS) and geographic information systems (GIS) analyses of aerial photographs (1968) and high-resolution IKONOS images (2004) in combination with topographic maps (1987) and field data were used to estimate changes in abundance, density, and canopy area of A. tortilis. Changes were statistically significant and the overall trend in population size was negative. At some sites this negative trend is alarming because the reduction in mature trees was substantial (about 40-50%) and the recruitment was nearly absent. The continuity of this trend over time will endanger tree populations in the study area. Due to increasing the growth of Acacia trees, changes in canopy area of Acacia trees were positive in most of the study area. Absence of juveniles and clear reduction in small categories suggest that A. tortilis are suffering population decline. Aridity conditions may explain some of the observed pattern of mortality, however our results indicate that human disturbances, particularly over-cutting and over-grazing, are considered the main driving forces of these negative changes in South Sinai. Understanding trend of long-term changes, awareness and engagement of Bedouins are crucial to establish effective conservation and sustainable use strategy for A. tortilis in South Sinai.