Plant Diversity Changes in Response to Environmental Drivers and Pressures at El Omayed “ROSELT/OSS” Observatory, Egypt

Abstract

The Observatory adopted a thematic procedure of evaluating and monitoring changes in natural resources. Data from previous studies were also reworked to fit into the themes being monitored. Temporal trends were evaluated using polynomial curve fitting, which were confirmed by statistical analyses. The extracted trends indicate a steady increase in air temperature, relative humidity and annual rainfall, while wind speed declined. The standardized seasonal rainfall shows an autumn trend that approximates the annual trend with amplitude of five years, while rainfall during the winter declines and inclines during above the long-term average during spring. Concurrently, sodium, sulfate and chloride soil concen trations increased rapidly in the late 1990s, together with increases in the very fine sand fraction, which reflects the active erosion and deposition processes associated with recent human interference. There is a general process of recharging plant spe cies diversity (long-term records; 122 perennials and 104 annuals) in the late 1990s following a sizeable decline; 26 perennials with declining density and spatial occu pation can be considered at threat. Some of these species are transient and show a three-year cycle of species replacement (turnover when related to added species). The change in the diversity of perennial species is allied to changes in rainfall, temperature and wind speed related to the climatic, salinity, bicarbonate, calcium, and sulfate of the edaphic variables. This also applies to endangered species, where especially air temperature and soil sulfates are the most determinant driving factors. Further, a shift of the rainfall above the long-term average from winter to spring elucidates the trend of change detected in the diversity. It is concluded that the diversity of biotops (spatial heterogeneity in habitats) in the area is the influential base for the biodiversity and is greatly affected by human impact. Concurrently, climatic changes and the associated environmental degradation of soil resources are more cyclic (recurring) phenomena, which reflect specific feedback effects on biodiversity in the region.