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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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Coastal sand dunes are considered to be amongst the most fragile natural systems, however they may be subject to high-intensity recreational stresses. The aim of this study was to assess the response of soil and annual plants of stabilized Mediterranean coastal dunes in Israel to various short-duration pedestrian and motorcycle traffic intensities. A standard experimental procedure was used comprising of 0, 50, 100, 300 and 500 pedestrian passes, and 0, 20, 50, 100, 200 straight and 150 turn motorcycle passes. The response of annual plants was assessed by determining ground cover, height, species richness and diversity, and soil penetrable depth, organic matter and moisture content. The pedestrian traffic did not affect the cover of annual plants, however; mean annual height, species richness and species diversity were significantly but temporarily affected by 500 passes. Conversely, motorcycle passage had an immediate significant impact on annual plants at all traffic intensities. The maximum effect on plants was observed in the wheel tracks and in the turn lanes. The mean annual ground cover and height were less sensitive measures than species richness and diversity for determining the overall impact of motorcycles on the area. Impact of pedestrian and motorcycle traffic on soil was detected only as an increase in penetrable depth, which was significant at 300 and 500 pedestrian passes, and at 100, 200 straight and 150 turn motorcycle passes. The soil and herbaceous vegetation of Mediterranean stabilized coastal dunes is relatively resistant and shows recovery potential to recreational impacts.

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