Abstract
Ancient valley agriculture in the northern Negev highlands was based on the principle of directed collection of water and eroded material from the slopes and their consequent flow towards the valleys. The stones on these slopes were therefore removed and/or collected into piles known as โgrape moundsโ. The aim of this study was to understand the contribution of stone cover and slopeโfacing to biological activity in soil. Soil samples from a depth of 0โ5โmm from the soil surface were collected during the study period (December 1994โMarch 1996) from northern and southern hill slopes, from under limestones and between stones. Soil moisture, organic matter, chlorophyllโa and soil respiration were determined. The results obtained in field and laboratory studies demonstrated differences between the northern and southern slopes. The stone cover on the northern slope made up 33 per cent and in the southern slope 23 per cent, stone size ranging from 15โ50โcm^2^ and 15โ35โcm^2^, respectively. Soil moisture content varied from 12 per cent in December 1994 on both slopes to oneโquarter of the initial value during the dry period. Organic matter content reached a maximal level of 14 per cent and 16 per cent on the northern and southern slopes, respectively. Values of chlorophyllโa on both the northern and southern slopes were 0.38โฮผgโg^โ1^ dry soil during the wet season, decreasing to 0.05โฮผgโg^โ1^ dry soil during the dry period. Soil samples from under the stones on both slopes produced high levels of CO~2~, ranging between 50 and 100โฮผg CO~2~โg;^โ1^ dry soil h^โ1^, whereas in the control samples the levels ranged between 30 and 70โฮผg CO~2~โg^โ1^ dry soil h^โ1^. In conclusion, the stone cover apparently plays an important role in the maintenance of biological activity through its contribution to slope biotope stability. Copyright ยฉ 2001 John Wiley & Sons, Ltd.