ARID LANDS

activity adaptation Africa agricultural amount animals annual areas arid lands arid regions arid zone Australia barchans become breeding cattle central changes Chapter climate communities considerable countries course cover crop cultivation cultural depend depth desert dunes East economic effects environment evaporation example existing extensive extreme factors farming grazing ground growth heat human humid important improvement increase influence irrigation less limited live major material means measure methods moisture natural nomadic occur particularly periods plant Pleistocene population possible practices present problems production rain rainfall range reduced regions relation Research river rocks Sahara saline salt sand season selection semi-arid sheep social soil South species stream structure summer supply surface temperature tion types United usually valley various vegetation wind winter