<span>Trees grow below or above the timberline, or tree line, depending on the environmental conditions present. Alpine tree lines are common near or on mountains and mountain ranges. The weather above the timberline is too cold and possibly too dry for trees to grow and take root. Desert tree lines are common in and near deserts. The soil is too dry for the trees to take root and get the water and nutrients they require. Desert-Alpine tree lines are environments where the elevation is too high and the soil too dry to foster tree growth.</span>
In 1970 when the Aswan High Dam was completed, the annual Nile floods and sediment stopped for most of Egypt's civilisation which lived downstream. In addition to creating electricity, the dam allowed Egyptians to control the flow of water and build upon the Nile's banks with certainty that it wouldn't be flooded.
