Volume 10, June 2008

By Eli Zaady, Department of Natural Resources and Field Crops, Gilat Research Center, Agricultural Research Organization, Ministry of Agriculture, zaadye@volcani.agri.gov.il

The Negev highlands landscape is characterized by two patch types: shrubs, and open spaces covered with biological soil crusts. It has been shown that these crusts control water flow on the loess soils of the desert by regulating infiltration and evaporation. A proposed source-sink model of the functioning of dry-land ecosystems describes the landscape as one composed of two types of patches: shrubs and crusts. In this model, the crusts leak water, soil and nutrients to their surroundings, which then serve as a sink, which is a source of resources for the shrubs. Accumulated knowledge, gathered from studies in the northern Negev and from dry-lands worldwide, indicates the need for a detailed investigation of aspects of the source-sink model as they relate to the differences in soil traits between two patches.

To carry out the study, we selected eight shrub species commonly found in the Negev highlands and investigated the physical and biological traits of the soil below them and of the biological crusts adjacent to them. The study was carried out on the Zin Plains near Kibbutz Sde Boqer and on the eastern slope of the nearby Halukim Ridge. Four soil samples were collected to a depth of 10 cm from under each of the shrubs, and four samples were collected from soil crusts up to 1 m away from the shrubs. Seven variables were measured: 1) soil-surface compaction, 2) pH, 3) electrical conductivity (salinity), 4) soil saturation, 5) field capacity, 6) soil respiration and 7) organic carbon content. For all the plant species, we found that five of the seven variables tested, i.e., soil compaction, salinity, saturation, respiration and organic carbon content, exhibited significant differences between the soil under the shrubs and that in the adjacent crusts, thus contributing to verification of the source-sink model.

All of the variable measurements obtained were the outcome of resource redistribution. This study supports the source-sink model of the relationship between shrubs and biological crusts, and shows that relating to dry-lands as two-patch ecosystems can improve our understanding of dry-land productivity and biodiversity.

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By Nava Sever and Gidi Ne’eman (gneeman@research.haifa.ac.il), Biology School, Haifa University, Oranim, Israel

Massive leaf dehydration in the Israeli evergreen oak Quercus calliprinos in various places in Israel was previously reported. In the year 2000 drought seriously affected Q. calliprinos trees in locations from northern Galilee to the Judean Mountains, as well as in northern Jordan. Such sudden leaf dehydration can be caused by a succession of drought years, a temporary severe drought, a sharp decrease of water potential in the root space of the affected trees, by pests, pathogens, air pollution, or combination(s) of causes. This study followed the fate of oak trees that suffered severe leaf dehydration in Yagur on the northern slopes of Mt. Carmel and on Mt. Turan in eastern Lower Galilee in Israel: 25 affected and 25 control trees were monitored in each site. Death rates, lateral increment, leaf area index (LAI), pre-dawn water potential (PDWP) and chlorophyll fluorescence (Fv/Fm) of affected and control trees were monitored. Out of the 25 affected trees, 12 trees in Yagur and eight in Turan had died by 2002. The annual increments and LAIs of the affected trees were significantly lower than those of the control trees. However, no differences were detected in PDWP and Fv/Fm, between the affected and control trees, indicating that there were no differences in water availability in the root space of the trees and that there was full recovery of the photosynthesis (PSII) mechanism. No additional trees were affected by dehydration during the study years, which were rainy. Therefore, we conclude that the apparent cause of oak leaf dehydration was a sequence of drought years that affected only sensitive individuals. Such events were reported in the past in Israel and do not seem to have had any long-term effect on the oak population. However, if such sequences of drought years were to become more common because of global climate change, the whole Mediterranean forest ecosystem, especially oak populations, could be endangered.

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By Moses Getker, Shmuel Arbel (shmuela@moag.gov.il) and Ran Molcho, Soil Conservation and Drainage Division, Soil Erosion Research Station, Ministry of Agriculture, Bet Dagan, and by: Itshak Moshe, Moti Shriki and Arnon Ben-Dror, Forestry and Soil Conservation Division, Southern Region, KKL, Gilat, Israel

Testing Methods to Increase Annual Runoff
This work evaluated the quantities of runoff to be expected on slopes in the northern Negev. Runoff is collected and directed to the forest, adding to its water supply.

Field monitoring focused on Sayeret Shaked Park, south of Ofakim: rainfall and runoff data were collected from 16 sloping plots, each of 60 square meters. Four treatment methods were applied, to assess their influence on runoff: compaction, scraping, spraying, and mowing.

Rainfall and runoff data collected between 1991/2 and 2000/1 were processed and analyzed. It was found that the mowing and compaction treatments yielded 35% more runoff than the control plots. A strong correlation was found between the annual runoff and the rainfall quantities in the control plots. This correlation enables us to compute the annual runoff, based on annual rainfall data.

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A Quantitative Analysis of Storm Runoff for Planning Water Harvesting Terraces
This aim of this study is to provide tools to calculate runoff quantities, to aid the planning of terraces in southern Israel. Between 1991/2 and 2000/1, storm rainfall-runoff relationships were surveyed on slopes within the Sayeret Shaked Park, and a strong correlation was found between storm rainfall and runoff depth. Perennial (over a 50-year period) surveys of storm rain depth at all meteorological stations were analyzed. Based on the short-period rainfall-runoff correlation and the statistical analysis of the results from longer periods, high-probability runoff quantities were calculated for southern Israel. The results enable planning of the ideal terrace by calculating the appropriate volume to catch runoff efficiently.

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By Meni Ben-Hur, Institute of Soil, Water and Environmental Sciences, Volcani Center, Bet-Dagan, Israel, meni@volcani.agri.gov.il

The objective was to study the effects of physical properties of various rocks and water regimes in Ramat Hanadiv on development of natural vegetation. The rocks in Ramat Hanadiv comprised three general types: (i) hard rock, (ii) porous rock, and (iii) soft rock. Samples were taken from the internal volume of rocks of each type, and the physical properties and root contents were determined for each sample. The bulk densities of the hard, porous and soft rock were 2.24, 1.43, and 1.27g/cm3, respectively, and the total porosities were 17, 47.1, and 52.9%, respectively. The infiltration rate, water capacity and water availability to plants were highest for the soft rock, and lowest for the hard rock. The pores in the various rocks could be divided into two groups: (i) macro-pores, which are small cracks developed by gentle weathering; and (ii) micro-pores, formed during the crystallization of the rock. The development of roots in rocks could occur in two ways: (i) development of the roots within the bulk of the rock, which is typical of soft rocks; and (ii) development of roots in wide cracks or karstic sinkholes, which is typical of hard rocks.

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By Yoram Goldring (yoramg@kkl.org.il) and Ami Zehavi, Forest Department, KKL, Eshtaol, Israel

The susceptibility of stone pine, Pinus pinea L. to calcareous soils, high pH and drought conditions limits the potential sites in which this species can be used. Grafting of stone pine on rootstock of Aleppo pine, Pinus halepensis Mill., can widen the range and the possible use of this species in afforestation, because of the high tolerance of the latter species to the soil conditions prevailing in most parts of Israel.

Seedling grafting of stone pine on Aleppo pine seedlings yielded 14 saplings that grew well; six of them were planted in 2002 and eight in 2004.

Controls, non-grafted stone pine saplings of the same age, were also planted in 2002. The experimental site is situated in Eshtaol Forest, on highly calcareous white rendzina soil.

In spite of the development of "bottle neck" at the grafting location, the grafted plants grow very well: their average height today (213.3 cm) is twice that of the non-grafted controls (126.6 cm). The grafted plants that were planted 2 years later are now almost at the height of the control plants which are 2 years older (111.3 cm).

The coming years will reveal whether the "bottle neck" is a serious problem, and whether the grafting provides the stone pines with the required tolerance of calcareous soils and drought conditions.

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By Zohar Litmanovich, Alex Fradkin, Tamara Khtema and Michal Katzenelson, KKL Forest Department, Kiryat Bialik, Israel

For many years Israel’s forest authorities, ignoring soil temperature conditions, have planted seedlings in winter, to ensure enough moisture for their survival, despite the suggestion of fall planting that was published as early as 1947. Seedlings planted in the autumn may benefit from favorable soil temperature and an entire season of rain.

From 2000 to 2006, the KKL Forest Department conducted field experiments to study the influence of autumn planting, with an initial irrigation, on survival and growth of forest tree seedlings. Eight species were examined: Brutia pine (Pinus brutia), Aleppo pine (Pinus halepensis), Italian cypress (Cupressus sempervirens), carob (Ceratonia siliqua), Mt. Tabor oak (Quercus ithaburensis), Eucalyptus stricklandii, Eucalyptus spathulata and Eucalyptus torquata.

Seedling height was measured throughout the year after planting, and the total annual growth data are presented here. After one year a significant difference in survival was observed between the autumn and winter plantings. A significant difference was also found between the total yearly growth in the respective plantings, except in the case of brutia pine. Finally, we found that autumn-planted seedlings were more developed. In conclusion, the results of the experiment indicate that autumn planting of forest tree seedlings is more successful than winter planting. In addition, this technique saves irrigation of the plants over the first summer season in the Southern Region.

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By Zion Madar, Forest Department, KKL, Kiryat Bialik, Israel, zionm@kkl.org.il

Significant mortality of cedar trees (Cedrus libani, C. atlantica, C. deodara) has been observed in recent years, in the forest and, in some cases, also in irrigated gardens. Two types of disorders have been observed: a) a slow decline accompanied by yellowing of the canopy and reduction of the needle length; and b) a sudden mortality of young or mature trees. The slow decline of cedars has been observed mainly on a light rendzina soil, but in some cases also on brown rendzina. The causes of the decline are not clear but appear to be related to the high calcium content in the rendzina soils, which prevents the uptake of microelements. No connection has been found to known diseases or pests. The sudden mortality of cedars occurs mainly on shallow soils and, therefore, may be related to drought stress. It is recommended to use cedar species in afforestation on less calcareous soils (terra-rossa, basaltic grumusols, sandy soils and brown rendzina) at high elevations above 500 m with annual mean rainfall of more than 500 mm.

By Anat Madmony (madmony@agri.huji.ac.il) and Yosef Riov, Faculty of Agriculture, the Hebrew University, Rehovot

The wild flora sanctuary in north Jerusalem (a semi-arid area) was established in 2001. It was created by a joint effort of the local community, the Society for Protection of Nature in Israel, the KKL Forest Department, and other organizations, in order to rehabilitate and restore the natural vegetation of northern Jerusalem. The main aim was to establish safe haven for local rare and endangered species which would also serve as an educational center for the community.

Published information about restoration and rehabilitation of Mediterranean ecosystems is limited. One of the main problems is the wide variability of the natural vegetation within small areas. In Israel only a few projects are dealing with utilization of wild flowers for landscaping, and none of them is scientific. Biotic and abiotic data have been collected in the sanctuary since 2006.

We tend to "blame" the British Forest Department for introducing into Israel Acacia saligna, Ailanthus altissima and other invasive tree species during the time of their Mandate rule (1917 – 1948). But, reading the 1st Report of the Department of Agriculture & Fisheries – A Review of the Agricultural Situation in Palestine (March 1922) reveals a list of exotic species now sub-spontaneous which includes: Melia azedarach, Acacia saligna, Parkinsonia aculeate, Robinia pseudoacacia, Acacia farnesiana, Ailanthus glandulosa and Cupressus sempervirens (Appendix XVII: The Forest Flora).
Oppenheimer (1959) discussed the contribution of Aaron Aaronsohn to forestry in Israel mentioning that he brought to his experimental station in Atlith (probably ca. 1910), among many other species, the now invasive Acacia saligna (=cyanophilla) and the less invasive Prosopis juliflora and Melia azedarach.

I present here a photograph from 1888 which I encountered lately, titled "a citrus grove in Jaffa", in which A. altissima and M. azedarach trees are clearly seen. By this, their presence in this country significantly precedes that attributed to the British and Aaronsohn.

Due to lack of awareness to ecological questions in those days, gardeners and foresters continued to plant these successful trees for many years.

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