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The effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986.In comparison with the adjacent unburned forest, total nitrogen decreased by 25% but available forms of nitrogen were much higher. In burned and unburned soils there was a similar trend to increase and decrease in NH~--N, However, while (NO~-+ NO3 )-N decreased in the unburned soil it rose rapidly in the burned ash soil. Total phosphorus increased by 300% after the fire but decreased again 2 months later. Also water-soluble P increased up to November and then decreased to the levels of the unburned soils. The same was true for electrical conductivity and pH, increasing immediately after the fire and then leveling off again.This increase in nutrient levels in the "ash soil" was reflected in the striking increase in shoot and root biomass and in the content of N, P, Mg, K, Ca, Zn and Fe in wheat and clover plants grown in pots in these soils. These nutrient levels were much higher in the wheat plants, which also produced 12 times more seeds in the "ash soil."It seems that fire in these pine forests causes a short-term flush of the mineral elements in the upper "ash soil" layer which is reverted gradually via the herbaceous post-fire to the ecosystem.

This study has investigated the effect of south-and north-facing hillslopes (SFS and NFS, respectively) on soil and vegetation properties along a climatic transect that covers four climatic zones: Mediterranean, semiarid, arid, and extreme-arid. The results indicate that differences between NFS and SFS in organic matter and soil moisture contents were significantly higher in the Mediterranean zone than in any other site along the climatic transect, particularly at the end of the rainy season. Both soil properties were higher on NFS than on SFS. Similarly, differences between the opposite hillslopes in species richness along the climatic transect were found significant only in the Mediterranean zone, where species richness was higher on the SFS than on the NFS. However, species diversity on SFS was significantly higher than that on NFS at all sites, except for the semiarid zone, where no significant difference between aspects was found. Species diversity on SFS changed along the climatic transect at an almost linear rate, while on NFS there was a sharp increase from the extreme-arid zone to the semiarid zone, followed by a decline moving towards the Mediterranean zone. Vegetation cover along the climatic transect was higher on NFS than on SFS, except for the extreme-arid zone, where no significant difference was found. The general conclusions are: (a) The most significant differences in soil and vegetation properties between NFS and SFS are found in the Mediterranean zone, mainly at the end of the rainy season; in the semiarid, arid, and extreme-arid zones the differences are small and generally negligible. (b) The spatial and seasonal differences on SFS are smaller than those on NFS.

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