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Ben-Gurion University of the

Jacob Blaustein Institutes for Desert Research

Albert Katz International School for Desert Studies

THE EDGE-EFFECT OF FARMING ON VEGETATION DENSITY AND RODENT ASSEMBLAGE OF A REMNANT SANDY PATCH IN A HYPER-ARID ENVIRONMENT (ARAVA VALLEY, )

Thesis submitted in partial fulfillment of the requirements for the degree of "Master of Science"

By Roy Talbi

Date: May 2009 2

Ben-Gurion University of the Negev

Jacob Blaustein Institutes for Desert Research Albert Katz International School for Desert Studies

THE EDGE-EFFECT OF FARMING ON VEGETATION DENSITY AND RODENT ASSEMBLAGE OF A REMNANT SANDY PATCH IN A HYPER-ARID ENVIRONMENT (ARAVA VALLEY, ISRAEL)

Thesis submitted in partial fulfillment of the requirements for the degree of "Master of Science"

By: Roy Talbi

Under the Supervision of Prof. Haim Tsoar and Dr. Amos Bouskila

Department of Desert Ecology

Author's Signature ………… Date 1/5/09

Approved by the Supervisor… . Date 4/5/09

Approved by the Supervisor………… Date 4/5/09

Approved by the Director of the School …………… Date ………..... 3

THE EDGE-EFFECT OF FARMING ON VEGETATION DENSITY AND RODENT ASSEMBLAGE OF A REMNANT SANDY PATCH IN A HYPER- ARID ENVIRONMENT (ARAVA VALLEY, ISRAEL)

ROY TALBI

ABSTRACT

Along with habitat destruction and fragmentation, agriculture in arid environments creates water- and nutrients-enriched terrestrial islands. Extensive agricultural practices have been implemented in hyper-arid deserts during the last decades, but the effect on the ecosystem remains vague. The present study examined the consequences of agricultural edge-effect on vegetation cover and rodent community structure, in a small and exclusive sandy patch. This patch, composed of several sand dunes, is adjacent to an irrigated date plantation in the hyper-arid southern Arava, Israel. I hypothesized that the dense vegetation characterizing the dunes is supported by the annual 2 million m3 of treated wastewater irrigating the plantations. At first, vegetation cover was measured in the field and by photogrammetry (GIS methods) of historical aerial photos from 1956-2003. In order to infer on the hydrologic condition of the patch, 19 boreholes (depth <6.5m) were drilled to locate the level of the underground water table and to identify anthropogenic indicators in the water. To follow ecological outcomes in the vegetation cover shift I examined the rodent assemblage using live-trapping and tracks identification. Field measurements and photogrammetry showed a significant increase in bush density during the last two decades along the habitat-farmland edge. The inter-dune boreholes revealed an unfamiliar groundwater table at a depth of 2-6m, and the water quality test indicated contamination by nitrates. Rodents assemblage in 'adjacent to farm' locations was dominated by the generalist species Gerbillus nanus and lacked the native specialist G. gerbillus. On the other hand, the community in the interior sand dunes, which was previously reported as purely inhabited by the native one, was disturbed by generalist invasion. The recent thriving of the local shrub Haloxylon persicum seemed to be related to leakage and sub-surface flow of irrigation water towards the sandy patch. This habitat modification negatively affects the psammophilic endangered gerbil G. gerbillus, and it 4 is expected to harm other habitat specialists inhabiting the last major sand dune within the Israeli Arava. Habitat management should be addressed, since the replacement of G. gerbillus at its primary resort (the Arava sandy patches), may finally lead to its extinction from the Israeli desert. Moreover, this study demonstrates an indirect effect of farming activity on a small and unique patch.

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ACKNOWLEDGMENT

This study was partially funded by the Faculty of Science and Science Education, University of Haifa, the Geography Dep. BGU and the Blaustein Institutes for Desert Research, BGU. In addition, I'm grateful to:  My supervisors, Haim Tsoar & Amos Bouskila, BGU  Uri Shanas (University of Haifa-Oranim) for many hours in the field and lab  Hanan Ginat (Samar) for touring and communications  Yehoshua and Rimon (BGU's Geography dep.) for great help with equipment  Bryan Medwed (may he rest in peace) for wind equipment and data (Samar)  Joe Nissim (Samar) for invaluable reviewing and field excavations  Miriam and the rest of the Arava Institute members  Larissa, Ya'akov and the Julia from Arava Research & Develop. Center (R&D)  Amnon Grinberg & Effi Tripler (R&D) for books & helpful communication  Rivka Amit and Yossi Yechieli (Israel Geological Survey)  Shanas's annual Biodiversity workshop associates  Ido Yzhaki for statistics (University of Haifa-Oranim)  Yael Olek, Boaz Idelevich, Idan Shapira and other Haifa-Oranim alumni  Tal Yasin for excavations and Yanai Shlomi (Samar) for communications  Dafna Carmeli & Yossi Avnat (Samar) for equipment support  Benny Shalmon (NPA) for good advices  Reuven Hepner (NPA) for moral support and advices  David Saltz & Ofer Ovadia (BGU) for great reviewing and advising  Bert Boeken (BIRD, BGU) for helpful reviewing and advising  Dorit Levine and other members of the AKIS, BGU  Aranne Library (BGU) and Ma'ale Shacharut School for books  Mori Chen for many communications and field tours  Aaron Yair for touring and advising, and Karin Ardon for great guiding  Herzel Naor and other members of Mekorot (National water company)  My "Gerbillus" Mika Talbi, Shiri Mor and the rest of my Family for supporting  My best friends Attila, Yossef, Raviv, Noach, Elad … for keeping me focus.

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TABLE OF CONTENT

1 INTRODUCTION...... 8

1.1 EDGE EFFECT AND PATCH SIZE ...... 8 1.2 FARMING AND BIODIVERSITY...... 9 1.3 THE SOUTHERN ARAVA VALLEY DESERT ...... 10 1.4 THE SANDY LANDSCAPE: STRUCTURAL, PHYSICAL AND ECOLOGICAL IMPLICATIONS ...... 12 1.5 INCENTIVES FOR RESEARCH: VEGETATION COVER AND RODENT ASSEMBLAGE ...... 16 1.6 RESEARCH AIMS & PREDICTIONS...... 18 2 METHODS ...... 18

2.1 STUDY SITE ...... 18 2.2 VEGETATION COVER ...... 20 2.3 UNDERGROUND WATER TABLE...... 22 2.4 RODENT COMMUNITY STRUCTURE...... 25 3 RESULTS ...... 26

3.1 VEGETATION COVER ...... 26 3.2 UNDERGROUND WATER TABLE...... 31 3.3 RODENT COMMUNITY STRUCTURE...... 35 4 DISCUSSION ...... 38

4.1 UNDERGROUND WATER TABLE AND ITS IMPLICATIONS ON VEGETATION COVER...... 38 4.2 RODENT COMMUNITY STRUCTURE...... 41 4.3 SYNTHESIS ...... 45 6 REFERENCES...... 49 6 APPENDICES ...... 57

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LIST OF TABLES

TABLE 1 RESULTS OF 19 BOREHOLES EXCAVATED IN THE STUDY SITE ...... 32

TABLE 2 SPSS OUTPUT OF PEARSON CORRELATION ANALYSIS OF ALL MONITORED FACTORS ...... 37

LIST OF FIGURES

FIGURE 1 TYPICAL VIEW ON THE SOUTHERN ARAVA, EAST FROM AYIT MOUNTAIN ...... 12

FIGURE 2 GEOLOGICAL MAP OF THE TIMNA REGION, SOUTHERN ARAVA...... 14

FIGURE 3 'SAND ROSE' FOR TIMNA DUNE DURING 2007...... 15

FIGURE 4 AERIAL PHOTO OF THE SOUTHERN ARAVA REGION INDICATING THE TWO SOLE SANDY PATCHES...... 19

FIGURE 5 SCHEME OF THE STUDY SITE AND ITS SURROUNDING ENVIRONMENT (GIS OUTPUT)...... 20

FIGURE 6 GENERALIZED STRATIGRAPHIC COLUMN AND THE MAIN AQUIFER UNITS IN THE ARAVA VALLEY ...... 23

FIGURE 7 AERIAL PHOTO OF THE STUDY SITE MARKED WITH 19 EXCAVATED BOREHOLES...... 24

FIGURE 8 THE EVOLUTION OF THE STUDY AREA ALONG 47 YEARS USING AERIAL PHOTOS...... 29

FIGURE 9 PERENNIAL BUSH COVER VALUES OF 7 AERIAL PHOTOS...... 30

FIGURE 10 MEAN (± SD) LENGTH OF PERIMETER AND BREADTH OF BUSHES IN 11 SAMPLING PLOTS...... 30

FIGURE 11 MEAN (± SD) BUSH DENSITY IN 11 SAMPLING PLOTS...... 31

FIGURE 12 MEAN (± SD) SAND STABILITY VALUES IN 11 SAMPLING PLOTS...... 31

FIGURE 13 UNDERGROUND WATER TABLE DEPTHS OF 17 DRILLED WELLS ...... 33

FIGURE 14 A TYPICAL GRADIENT OF MOISTURE CONTENT IN ONE OF THE CORES...... 33

FIGURE 15 TYPICAL GRADIENTS OF SOIL MOISTURE AND GRAIN SIZE RELATION...... 33

FIGURE 16 CONDUCTIVITY VALUES OF WATER SAMPLES FROM 17 BOREHOLES...... 34

FIGURE 17 BORON CONCENTRATIONS OF WATER SAMPLES...... 34 3 FIGURE 18 N‐NO CONCENTRATIONS OF WATER SAMPLES...... 35

FIGURE 19 DISTRIBUTION OF THE TWO SPECIES WITHIN THE STUDY SITE...... 36

FIGURE 20 REPEATED MEASURES ANOVA OUTPUT GRAPH OF THE TWO SPECIES...... 37

FIGURE 21 GRAPHIC RESULT OF THE RDA...... 37

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1 INTRODUCTION

Understanding of indirect effects of human activity on ecosystems is vital for conservation, particularly in small unique patches such as sand dunes in Israel. This singular and vulnerable ecosystem often experiences destruction and fragmentation due to high demand of sand for farming, quarrying etc. The present study engaged in the agricultural edge-effect on a small and isolated sandy patch in the hyper-arid Arava desert.

1.1 Edge Effect and Patch Size

Edge effect was defined as the modification of ecological patterns as it occurs around the edge of two adjacent ecosystems (Fonseca & Joner, 2007). Such patterns may be either natural and beneficial to wildlife (Leopold, 1933), or detrimental (Murcia, 1995), as presented here. Many studies regarding fragmented habitats have emphasized the significance of edge effects and patch size on species diversity (Saunders et al., 1991; Shafer, 1995). For instance, Bender (1998) predicted that patch size will substantially affect population size of native (interior) species, but will be negligible for generalist species. In general, the smaller the patch and the core area is, the greater the impact external factors (e.g. farmland edge-effect) have on the patch (Saunders et al., 1991). Implementing this principle in conservation strategies is essential for species conservation, although some may argue that small reserves are not justifiable due to predicted low species diversity or relatively high management costs (Shafer, 1995). Anthropogenic related edge effects often result in increased prevalence of generalist species, corresponding with a decrease in specialized ones (Butler et al., 2007; Connell, 1978; de la Pena et al., 2003; Denslow, 1985; Hansson, 1991; Webala et al., 2006). In this frame, any possible species replacement is expected to be intensified by the proximity to agriculture and by the small size of the studied patch.

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1.2 Farming and Biodiversity

About 37% of the world’s land is agricultural, while world food demand is expected to more than double by 2050 (Benton, 2007; Green et al., 2005). In addition to human population growth, agricultural activity is likely to increase because of rising standards of living (Darkoh, 2003). Farming was specified amongst the predominant factors leading to current global alteration of natural ecosystems (Matson et al., 1997), and as one of the greatest threats to wild species (Donald & Evans, 2006; Hole et al., 2005; Holloway, 1991). For instance, rodent species diversity was shown to have been modified in intensively agricultural areas (de la Pena et al., 2003), as well as in abandoned farmlands (Giraudoux et al., 1994). Moreover, it has been recently recognized that farming poses the greatest extinction threat to birds (Green et al., 2005). In arid lands, farming is known as the main cause of desertification (Agnew & Warren, 1990). Some of the prominent outcomes of this phenomenon include: reduction in water quantities, increase in soil salinity, intensified soil erosion and a consequent reduction in vegetation (Agnew & Warren, 1990). Darkoh (2003) reported that agricultural practices, such as over-cultivation, overgrazing, bush fires, mechanization and the widespread use of chemicals, have intensified degradation of soil and vegetation in Africa, and led to a rapid biodiversity decline. Agricultural expansion has also altered the global water flows, by changing the level and quality of water tables and vegetation patchiness in adjacent locations (Gordon et al., 2008). In addition to the on-site outcomes, the adverse ecological effects of agriculture on the nearby nonagricultural environment are well established (Benton, 2007; Donald & Evans, 2006; Matson et al., 1997; Meffe & Carroll, 1997; Tilman, 1999; Vandermeer & Perfecto, 2005). Working on sand dune desert lizards, Barrows et al. (2006) have found that anthropogenic related edge effects can be found up to 150m from the affecting factor. Similarly, Khoury & Al-Shamlih (2006) have found altered structure of a sand dune bird community up to 1km from desert farming projects, while Hawlena & Bouskila (2006) have recorded deterioration in reptile community structure in natural habitats due to forestation activity in adjacent arid landscapes. Unsurprisingly, Israel’s extensive agricultural activity (over 19% of total area, CBS, 2007) has significantly reduced vertebrate populations (Yom-Tov & Mendelssohn, 1988). In the extreme desert of the southern Arava intensive and extensive farming has been introduced as well. Such an ecosystem (where food and water are scarce) offers a 10 suitable ground for isolating and researching different effects of the recently introduced farmlands on wild populations and their natural habitats.

1.3 The Southern Arava Valley Desert

The southern Arava Valley (Wadi 'Araba) is part of the Dead Sea transform that stretches from the northern tip of the to northern Syria. This rift is an outcome of tectonic movements involving the Arabian and the African plates (Ginat, 1993), creating a low and flat strip between south-west Jordan (the Edom mountain range) and southern Israel (the Negev mountains). A diverse geomorphological landscape characterizes this region, including wadi beds, regs, alluvial fans, playas (referred here as 'Sabkha' or 'salt flat'), sand dunes and sandy plains (Ginat, 1995; Ron, 1967b). The climate in the southern Arava region is immoderate and characterized by strong irradiation, high air temperatures (annual average > 23c°; summer average > 31c°) and a scant amount of rainfall (< 25mm/yr) as well as high potential evaporation (~ 3,500mm/yr; Goldreich & Karni, 2001; Yotvata Meteorological Station). These extreme rates specify the climate of the southern Arava region as hyper-arid (Goldreich & Karni, 2001; Noy-Meir, 1973; Whitford, 2002). An acceptable indication of dryness extent is the aridity index (AI, Eq. 1), calculating precipitation (P) and potential evaporation (PET), with hyper-arid climate defined as having AI < 0.05 (UNEP, 1992): P (1) AI  PET

A calculation of the aridity index for the studied region leads to AIu = 0.007, and reflects the extreme aridity of this region. Furthermore, a dramatic decline in annual precipitation has been documented over the past decade (~15mm/yr on average; Shlomi & Ginat, unpublished data; see also Appendix 1).

From an ecological viewpoint, the southern Arava exhibits a meeting point of zoogeographic and geobotanic elements (such as Saharo-Sindian, Irano-Turanian and tropical) from surrounding regions (Werner, 1988; Zohary, 1945; Zohary, 1962). Whereas still considered as one of the least populated and relatively intact areas in Israel, the Arava's rapid farming development (Khoury & Al-Shamlih, 2006; Shanas et al., 2006; Shapira, 2006; Trigger Foresight & Daroma, 2007), poses many risks for this unique biota. 11

Farming practices on both sides of the political border (although much modest in Jordan, see Fig. 1) intensively exploit the underground water reserves, and routinely use fertilizers and pesticides (Khoury & Al-Shamlih, 2006; personal observation). Crops on the Israeli side include varied vegetables (31% of total water) and fruit plantations, especially dates (43% of total water consumption in District) mostly due to the high market value of the Medjoul cultivar. Considering the notably wet conditions required by palms (each tree receives > 1,000L/day), the high evapotranspiration rates and the varied soil conditions (e.g. salts that should be washed off by over irrigation) in the region, farmers (not including cowsheds) excessively irrigate using 17.3 million m³/year. These massive quantities of water used by the Arava's farmers originate from underground pumping and treated wastewater (sewage of the city of ). Such irrigated agrosystems (rich with water, food, shade and shelter; see Appendix 12) are presumed to stipulate changes in local wild populations, and may support species invasion. The hyper-arid southern Arava has barely been studied in an ecological perspective, and information (essential for a suitable management) regarding the direct and mostly indirect effects of farming on this ecosystem is scarce (including: Khoury & Al-Shamlih, 2006; Shanas et al., 2006; Shapira et al., 2007). Due to cultivation preferences of the Arava farmers, most farmlands were placed on sandy soils (Fig. 1), leaving only a few remnant sandy patches on the Israeli side of the border (Shapira, 2006).

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T h e E d o m m o u n t a i n r a n g e

Massive sandstone exposures

S p a c i o u s s a n d d u n e s Jordan Lotan field crops Israel Lotan & dates

Figure 1 Typical view on the southern Arava, east from Ayit Mountain. Note the extensive farming on the Israeli side of the political border. Dashed line represents the political border.

1.4 The Sandy landscape: Structural, Physical and Ecological Implications

Unlike the northern Negev, the Arava sands have originated from a regional source and possess a unique history (Evenari et al., 1982). The southern Arava exhibits diversified magmatic, metamorphic and sedimentary rock formations (Marko, 1995). One example of a continental sedimentary rock is the Nubian sandstone of the lower Cretacious period (Yom-Tov & Mendelssohn, 1988). This sandstone was formed by erosion and deposition of primary igneous rocks during the last 550-100 million years (Ginat, 1995; Marko, 1995; Segev et al., 1992). Exposures of this sandstone are infrequent but conspicuous in the region, and play a major role in sand dune formation (Ginat, 1995). The process begins (~5mya) with fluvial erosion of the Nubian layers presented in Fig. 2. These exposures are forming the Timna cirque and its south and north extensions (see Appendix 2). The outwash products are being carried to the Arava's peneplain, following gradual alluvial deposition of varied sediments on a west-to-east gradient (Ginat et al., 1999; Zohary, 1980). Gradual sedimentation is clearly influenced by rain intensity and slope degree, but grain size classification is the key reason. This distribution of diverse particles brought about (1) the formation of coarse-grain alluvial fans, (2) large accumulations of sand (quartz being hardly erodable), and (3) the settling of the clay and silt particles in the deep Sabkha (over 1km of highly saline clay layers; 13

H. Ginat, personal communication). After sand (mostly free of pebbles) is being accumulated around the Sabkha basin, it finally mobilized by wind, forming sand dunes (Ginat, 1995) and varied structures such as nebkhas around shrubs (see photo in Appendix 3). Interestingly, alluvial sand deposition took place on both sides of the Sabkha (the main basin in the southern Arava), establishing extensive sand dunes in the north, and the small Timna sand dune (also known as Samar dunes) in the south. The formation of sand dunes on the northern and southern sides of the regional basin (i.e.Yotvata Sabkha) is not accidentally, and can be explained by the fluvial history of the region (H. Ginat, personal communication). One fundamental feature of sand is its high porosity and its increased hydraulic conductivity (Bagnold, 1935; Danin, 1991; Danin, 1996; Orev, 1984; Tsoar, 1997; Yair et al., 1997). Due to inconstant fluvial stratigraphy, underground sand accumulations generally overlay clay and silt lenses (Evans et al., 1991; Ibe & Sowa, 2002; Oren et al., 2004). Assuming that rainfall and percolation occurs, such impermeable layers (aquiclude) establish shallow underground water tables, and facilitates the development of relatively dense vegetation (Orev, 1984; Tsoar, 1997; Yair et al., 1997; Zohary, 1962). Appendix 4 illustrates the typical structure of a non-sandy desert aquifer, indicating the relevant clay lens (adapted from: Oren et al., 2004).

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2km

Figure 2 Geological map of the Timna region, southern Arava. Sandstone exposures are in purple; magmatic formations are in red. Arrows indicate water flow direction (Geological Map of the Southern Negev, Israel Geological Survey).

Desert sands form a distinct geomorphological and ecological unit (Danin, 1996; Fet et al., 1998). The relatively large grain size facilitates high permeability (as well as low field capacity and poor nutrient content), and similarly, causes low soil cohesiveness (Bagnold, 1935; Tsoar, 1997). This latter trait promotes aeolian erosion that is increased as (1) wind drift potential (DP) increases, (2) soil moisture decreases (i.e. hyper-arid climates), and (3) vegetation cover decreases (Tsoar, 2005). Obviously, these factors interact and work as a system. For instance, increased wind power may facilitate dune formation, while reduced wind encourages vegetation growth (Tsoar, 1997) and weakens sand mobility (Bendali et al., 1990; Buckley, 1987; Kutiel et al., 2000; Tsoar, 2005). Lancaster (1988) developed a simple equation (Eq. 2) for a mobility index (M) that is based on AI (Eq. 1) and the degree of windiness (W – average annual % of time experiencing winds above the threshold velocity for sand movement):

W (2) M  AI 15

He also defined that if M > 200, the sand dune is expected to be mobile and devoid of vegetation. In spite of the low averaged wind velocity that characterizes the study site (< 4m/sec, personal measurements), the extreme dryness gives rise to an exceptional mobility index (M = 1,857; whereas W = 13% and P/PET = 0.007). This exceptional M index is apparently not applicable in this case, since the Timna sand dune isn't highly mobile and it is relatively vegetated. While Lancaster's index is focusing on water dynamics (P/PET), a better index for sand dynamics is the drift potential (DP) which is based on the sand erosion (q) equation (Tsoar, 2005):

U 2 )U-(U (3) qDP  t t  100 This measure of potential wind power includes:

(1) The site's wind velocity (U); (2) The threshold wind velocity (Ut) which represent velocities that are capable of moving the sand (> 12knots = 6.2m/sec); (3) The percent of time (t) the wind is above Ut; (4) And q that is calculated separately for each wind

(Ut) direction. Fig. 3 shows the 'sand rose' and specific measurements from the study site. Corresponding to rather low values of DP (Drift Potential), t and RDP (the resultant of all drift potential directions), the directional variability of the wind (RDP/DP) is quite low as well (RDP/DP = 0.6, indicates relatively unidirectional wind) and is mostly characterized by northern winds (the resultant drift direction, RDD = 17.3°). Unlike the Mobility index, the low value accepted by the sand erosion equation (DP) seems to better explain the low mobility of sand in the studied habitat.

Figure 3 'Sand rose' for Timna dune during 2007 (measured at a height of 10m using wind explorer data logger, NRG Systems). The DP vectors (in blue) are proportional in length to the potential sand transport (the interior scale signifies knots). The net potential trend of all DP vectors (RDP) is indicated by the red arrow in the direction of the resultant drift direction (RDD). Sand rose by MATLAB.

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In spite of the great challenges posed for living organisms (Bowers, 1996; Seely & Louw, 1980; Tsoar, 1997), the sandy landscape bears a rich fauna (Fet et al., 1998). Such an environment promotes remarkable ecomorphological adaptations and enables the evolution of habitat specialists (Fet et al., 1998). Some of the Arava's native and singular psammophile species include the scorpion Buthacus yotvatensis, the gecko Stenodactylus doriae, and the rodent Gerbillus gerbillus. Unfortunately, recent exploitation and other human-related effects of sandy landscapes all over Israel have led to a deterioration of these exclusive environments (Yom-Tov & Mendelssohn, 1988), and caused a tremendous population reduction in many habitat specialists. Amongst the issues conservationists are now facing is the negative consequences of sand dune stabilization (Danin, 1996; Kutiel et al., 2000; Perevolotsky & Pollak, 2001), which will be explained in the next chapter. The present study deals with the fundamental role sand mobility has on the conservation of native fauna and flora.

1.5 Incentives for Research: Vegetation Cover and Rodent Assemblage

One of the most evidential features of the studied patch is its high vegetation cover dominated by Haloxylon persicum Bunge, an Irano-Turanian tall shrub (Danin, 1996; Zohary, 1980). In Central Asia, H. persicum (also known as 'white saxaul'; Zohary, 1980) covers spacious sandy deserts; there it relies mainly on rainfall and condensing moisture (Orlovsky & Birnbaum, 2002; Sveshnikova, 1972). Orlovsky & Birnbaum (2002) and others (Anon, 1980; Gintzburger et al., 2003) emphasized its outstanding adaptation to extreme ambient conditions, e.g. aridity, wide temperature range, shifting sands, nutrient scarcity, and high water salinity. In Israel, it is widespread throughout the Arava, inhabiting vast sandy areas (Zohary, 1945), and functions as the major producer within those habitats. The puzzling occurrence H. persicum in the dry Arava cannot be explained other than by the assumption that a fair amount of moisture in the soil in deep layers, is feeding the shrubs (Zohary & Orshan, 1956).

Two rodent species of the genus Gerbillus (Mammalia: Rodentia: Gerbillidae) are found in the Arava's sandy landscape: G. gerbillus and G. nanus (see Appendix 5). The psammophile Lesser Egyptian Gerbil, G. gerbillus (Olivier, 1801), is essentially a Saharan species, but is found also in southwest Asia and Arabia (Harrison & Bates, 1991; Mendelssohn & Yom-Tov, 1999). Within the Israeli desert it is distributed mainly 17 in the Arava sand dunes surrounding the Yotvata Sabkha (Abramsky et al., 1985; Harrison & Bates, 1991; Shalmon, 2004; Shanas et al., 2006; Sinai et al., 2003; Zahavi & Wahrman, 1957). This nocturnal sand-dweller rodent (weighting 22g on average, Brand & Abramsky, 1987), is equipped with hairy soles, facilitating its movement on the sandy surface (Harrison & Bates, 1991; Mendelssohn & Yom-Tov, 1988). According to Zahavi & Wahrman (1957) and more recent studies (Abramsky et al., 1985; Bar & Brand, 1984; Mendelssohn & Yom-Tov, 1988; Shanas et al., 2006), G. gerbillus mainly inhabits the most sparsely vegetated and mobile dunes, i.e. the poorest habitat. In the same context, it is suspected to be extinct from the northern Negev sand dunes due to intensified vegetation cover caused by lack of grazing (Shalmon, 2004). Since the remnant sandy patches in the southern Arava serve as its last major resort in Israel, Shalmon (the red list of Israel's threatened vertebrates, 2002) has specified it as 'vulnerable'. Unlike G. gerbillus, the Baluchistan gerbil G. nanus (Blanford, 1875) is a widespread generalist rodent that inhabits salt-flats and wadi-beds throughout the Arava (Harrison & Bates, 1991; Zahavi & Wahrman, 1957). Although it was also found to inhabit stabilized sands and margins of sand dunes, it is yet to be found in the core of a sandy area, dominated by G. gerbillus (Brand, 1983; Shanas et al., 2006; Zahavi & Wahrman, 1957). Zahavi & Wahrman (1957) suggest that G. nanus, though capable of existing on sand dunes, is being impeded by the better adapted true psammophile G. gerbillus. In view of a possible ecological deterioration due to a change in bush density or other agricultural effect, I assayed the present assemblage of these two gerbils in the major sandy patch within the Israeli Arava.

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1.6 Research Aims & Predictions

The aims of the present study were: 1. To examine whether vegetation cover in the Timna sand dunes correspond with development of the nearby agricultural practices. 2. To examine the correlation of the adjacent farming activity to the distribution of endangered psammophilic rodent (G. gerbillus).

Respectively, I predict that: 1. Perennial cover close to farming will be higher and will correspond to intensity of farming. 2. Sand stability will increase proportionally to the proximity of farming. 3. There is a shallow underground water table in the sand dune that can sustain rich vegetation. 4. Analysis of the underground water will reveal high concentrations of irrigation water indicators, evidencing leakage of polluted wastewater and underground flow from nearby farming towards the sandy patch. 5. Ordination of gerbil species will reveal that in plots with high perennial cover the native psammophile G. gerbillus is being excluded by the generalist G. nanus.

2 METHODS

2.1 Study Site

The study was conducted in a sandy patch situated near Samar (30km north of Eilat), within the rectangle between longitudes 35°2.150’E and 35°3.058’E and latitudes 29°47.379’N and 29°49.835’N, from January 2006 until January 2008. Although the Timna sand dune area (originally covering 15km2; Ron, 1967b) has been reduced by human activity to 2.3 km2, it is still considered the largest sandy patch remaining in the Israeli side of the Arava valley. This patch is quite isolated from a larger sandy patch (80 km2), the latter stretching mostly on the Jordanian side with only several sand dunes and sand plains within the Israeli territory (Fig. 4). 19

Figure 4 Aerial photo of the southern Arava region indicating the two sole sandy patches. The studied patch is the small one (2.3Km2), located in the Israeli territory.

The surrounding structure of the Timna sand dune (Fig. 5) includes the Yotvata Sabkha ('Sabkha a-Taba') on the east and north, and the irrigated farmland to the west. Both practices located west of the study site are based on extensive date plantations, and massive use of water and fertilizers. The major plantation (7,000 date palms) belongs to Kibbutz Samar and it is farmed in accordance with certified organic practices, i.e. no chemicals but large quantities of compost. During the last 3 decades, all wadis, except one gully in the north brink of the sand dune, were gradually dammed in order to prevent flooding of the agricultural lands (Fig. 5). Considering the limited surface water that flows into the dune (especially in light of the present drought), groundwater seems to be the main possible source for life in the patch. Unfortunately, the literature dealing with such a system is poor and data about the shallow hydrology was mostly obtained by communication with local experts and geohydrologists from the national water company (“Mekorot”). Total of 12 sampling plots (20,000m2 each) were chosen in order to examine the vegetation, soil and rodent assemblage. Six plots were located in the west edge of the 20 sand dune, as close as possible to well-established farmland, i.e. plantations and open fields older than 20 years. Four of the above 'close to farm' plots were located north-east of the farmland, adjacent to date plantations that are over 30 years old (see Fig. 5). The 6 'far from farm' plots were located at a relatively uniform distance from the parallel 'close to farm' plots, with respect to the habitat size and structure (inter-dune valleys). Due to these geographic limitations, one of the remote plots was placed in Jordanian territory, and studied only via remote sensing.

Figure 5 Scheme of the study site and its surrounding environment (GIS output). The arrows indicate the direction of surface and subsurface ground water flow (H. Ginat, pers. comm.).

2.2 Vegetation Cover

2.2.1 General Vegetation is the most common and consistent stabilizer of sand (Bendali et al., 1990; Duran & Herrmann, 2006), while erosion of sand by wind is the major limiting factor of vegetation cover (Tsoar, 1997). Plants decrease wind velocity around them (Bullard, 1997), and act as a sand barrier (Danin, 1996; Wood et al., 1978). In case of over- vegetation, such sand traps may cause general stabilization (Tengberg & Chen, 1998; Tsoar, 1997), leading to habitat deterioration. Concerning conservation, vegetation 21 cover should be assessed in order to infer on possible negative trends among psammophilic species. The resistance of soil surface (i.e. sand stability) is usually measured (in units of kg/cm2) using soil penetrometer (Zaady & Bouskila, 2002). Vegetation cover can be assessed either by traditional field methods (Ardon, 2006; e.g. Wiggs et al., 1995) or by GIS methods (e.g. Ardon, 2006; Ouma & Tateishi, 2008). The GIS procedure is based on remote sensing for surveying, classifying and mapping aerial photographs. The performed classification (named 'supervised classification') is based on selection of spectral classes that best represent land cover patterns (Lathrop, 2005). The spectral signature outputted by supervised classification (non-parametrically) defines clusters in a feature space (i.e. by pixel classification). After adapting the software to distinguish between land-cover categories, a classification is made. Eventually, the analyst should assess the resulting classification accuracy by comparison to field observations data.

2.2.2 Materials and Methods a. Vegetation cover by photogrammetry: Seven aerial photographs of the study site, from the last 50 years, were used for classification. Based on characteristic objects in the old photographs, I geometrically referenced those to the coordinated orthophoto from 2003 (to maximize classification accuracy) using ERDAS 8.6 software. The same software was used to execute supervised classification and to calculate the percentages of perennial bush cover vs. bare sand. ArcGIS 9.1 software was used in order to edit and present maps and aerial photos. During statistical analysis of the classification results (% of pixels of each category), values of bush cover from 'close to farm' plots were compared on a time scale with the 'far from farm' plots, by paired t-Test (using SPSS software). b. Vegetation cover in the field: I randomly selected 20 bushes (randomization was performed by GIS software and GPS device), within each one of the 11 sampling plots and monitored those using a measuring wheel (± 0.1m). Vegetation variables included bush perimeter, bush breadth (from the western to the eastern margins of the foliage) and inter-bush distance ('nearest bush'). A t-Test was used to examine the difference in mean values of bush perimeter and breadth, and inter-bush distances between 'close' and 'far' plots. 22 c. Sand stability rate: I measured the soil cohesiveness rate (in pressure units, ± 0.02kg/cm2) in spots between the same bushes using Pocket Penetrometer (Forestry Suppliers, Inc.), and used t-Tests to examine the difference in values of sand stability between 'close' and 'far' plots.

2.3 Underground Water Table

2.3.1 General Underground water in the Arava valley is found in several levels of aquifers which vary mostly by their depth, rock formation, and chemical properties of the water (Naor & Granit, 1999). As described in Fig. 6, the alluvial aquifer is the uppermost sub-basin. It is composed of pebbles and small-sized particles (sand and clay), and may reach a few hundreds of meters in its thickness (Ginat, 1993; Naor & Granit, 1999; Ron, 1967a). The water of the alluvial unit originates from flooding in the drainage basin (Ron, 1967a), and it serves as an important water source for the Arava settlements and farmlands. During strong rain, water percolates via the relatively poriferous alluvium, and a subsurface flow towards the Sabkha occurs (Ginat, 1993; Naor & Granit, 1999; Ron, 1967a). Today, the continuous drought and the farmland's dam both minimize natural percolation into the sand dune aquifer. Moreover, the sand porosity increases optional aquifer pollution from the adjacent farmland. Oren et al., (2004) has found that intensive irrigation and fertilization in the middle Arava, affected the quantity and quality of the underground water table. Moreover, two wells pumping from the same alluvial aquifer have been shut down during 1998 for high levels of salinity and nitrate (NO3) due to irrigation leakage (Naor & Granit, 1999). My observation was aimed at studying the effect of intensive irrigated farming on the shallow hydrological system of the dune. 23

Figure 6 Generalized stratigraphic column and the main aquifer units in the Arava valley (after Ginat et al. in prep.)

2.3.2 Materials and Methods I drilled a total of 19 boreholes (see Fig. 7) down to a depth of up to 6.5m in the sand dunes. The drilling locations were fixed in the inter-dune surfaces in order to reach the underground water table in the shortest way (see Appendix 6). Eighteen of them were drilled using a portable auger (Dormer Engineering) with a drill suited for removing a core from clay-sandy sediment. One additional borehole was drilled using an excavator tractor on disturbed soil near the dune. Values of water table depths were linearly regressed on distance from the farming land. To examine the moisture column of the sand, samples of sediment were taken intermittently every 30cm during the vertical drilling (Yair et al., 1997). Each sample was documented and placed immediately into a sealed plastic box to avoid evaporation. In case of reaching a shallow water table, 2-3 water samples from each borehole were documented, preserved in sealed plastic boxes, and placed in a relatively cool location until reaching the lab. In the lab, sediment samples were weighed (±0.001g) and oven- dried in 105◦C for 24-48 hours (Dekker et al., 2001). After weighing the dried samples, several samples were sieved and sorted to three rough categories of grain-size (i.e. sand, silt and clay). This procedure was done in order to achieve a better understanding of soil 24 structure and its dynamics with moisture content. Relations of water and sand percentages (in each soil sample) were tested vs. depth using linear regression. Underground-water samples from each drill were sent to the Hevel-Eilot regional "Research & Development" laboratory for chemical (boron and nitrate-nitrogen) and physical (electrical conductivity) analysis. The purpose of the laboratory tests was to learn about the water quality supporting the dunes and to suggest their source (E. Tripler, personal comm.; O. Oren, personal comm.). The conductivity, boron and N-

NO3, were linearly regressed on distance from the irrigated farmland.

Figure 7 Aerial photo of the study site marked with 19 excavated boreholes.

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2.4 Rodent Community Structure

2.4.1 General Traditional rodent sampling is usually obtained by placing live-traps in transects within the studied habitat (e.g. Abramsky et al., 1985; Sinai et al., 2003). The disadvantage of this technique, particularly throughout the Arava valley, is the threat from trapped rodent predation, mostly by foxes (personal observations). In recent years, as the red fox (Vulpes vulpes) population increases (B. Shalmon & R. Hepner, personal comm.) it became almost impossible to perform rodent trapping without losing animals and traps (personal observations, Shanas et al., unpublished data, Shapira, 2006).

2.4.2 Materials and Methods In an attempt to learn the gerbil assemblage in various stages of habitat modification, I sampled the rodents along several replicated transects. Trapping was executed in all seasons (though less in the winter) during 2006-2007, for 1-4 nights each month (total of 2,500 trap-nights). Non random transects from the farmland's edge towards east were set according to the topographic structure. Eighty Sherman live traps were placed (10- 20m intervals) in late afternoon, baited with mixed bird seeds, and checked in early morning. All captured gerbils were released immediately after identification (and sometimes measurement) at the exact trapping location. Soon after initiating the trapping, I faced high rate of trapped gerbil predation by foxes. One solution to minimize the risk for gerbils was to check the traps in the middle of each trapping night, in addition to the early morning checking. The release of gerbils from traps at midnight indeed diminished gerbil predation, but did not eliminate the risk completely. Another attempt to minimize predation was the coating of traps with a concentrated Capsaicin solution (the active compound found in red pepper). A similar application has been previously tried by farmers to keep mammalian predators away from irrigation equipment (B. Shalmon, personal comm.). Such implementation may be effective against pipe damage, but failed to prevent trapped gerbil predation; in a very short time, the foxes ignored the deterring taste when a gerbil was present in the trap. After one year of attempts to monitor the populations via trapping, an alternative method was developed, relying on identification of G. gerbillus and G. nanus footprints. An evaluation of the method was achieved by trapping the animals at the footprint location. Track-counts courses were similar to the trapping transects, and conducted 26 monthly, from May 2007 until Jan 2008. In general, the tracks count method was very practical and tremendously expanded the rodents' data set from 193 (by trapping) to 1,017 observations. ArcGIS was used to present the distribution of the species throughout the sand dune. In order to correlate the gerbil distribution to the obtained environmental data (bush and soil parameters), I monitored gerbil assemblage within each plot using 40 traps along four transects in each of them. Random track-counts data were added to reinforce information from plots characterized by low capture rate. For data collected within the investigated plots: Pearson correlation analysis was carried out to explore possible correlations among all environmental variables and locations of gerbils. In addition, I linearly regressed G. nanus and G. gerbillus abundances (dependent variables) with environmental data (independent variables). In order to explore the relationship between the two species and the most dominant factor determining their distribution, a repeated measures ANOVA was used (since I observed both species within the same plots). Redundancy analysis (RDA) ordination and Monte Carlo permutation test were performed using CANOCO 4.5, to explore the relations between the dependent variables (gerbil data) and the independent variables on a multidimensional scaling. An experimental attempt to trap juvenile gerbils was based on drift fences and 20 pitfalls in 2 he plot for 3 consecutive nights (see also Shanas et al., 2006). This method found to be ineffective in trapping gerbils. A different try to learn about the domicile habits of the psammophile G. gerbillus and G. nanus was performed by recording burrow locations (using GPS), and excavating a few burrows in distant from farmland locations. The latter procedure was not replicated due to technical difficulties.

3 RESULTS

3.1 Vegetation Cover

GIS analysis of vegetation cover produced adequate results thanks to coloration simplicity and high contrast of the photographs. Fig. 8 presents farming intensification and accelerated sand dune vegetation growth, mostly after the foundation of Kibbutz Samar and Kibbutz Elifaz (during the 70-80's). As shown in Fig. 9, percent cover of 27 vegetation and sand calculate by the supervised classification method produced significant differences between 'close' and 'far' plots in photographs from 1993 (paired t- Test, t = 2.604, d.f. = 5, P <0.05) and 2003 (t = 3.07, d.f. = 5, P < 0.05). Perennial cover, as indicated by the bush perimeter (Fig. 10; t-Test, t = 2.204, d.f. = 9, P = 0.055), bush breadth (Fig. 10; t = 2.665, d.f. = 9, P < 0.05) and distance to the nearest bush (Fig. 11; t = -5.373, d.f. = 9, P < 0.001), showed distinct differences between 'close' and 'far' locations at the same years. Values of sand stability between bushes showed significant difference between 'close' and 'far' locations (Fig. 12; t-Test, t = 2.886, d.f. = 9, P < 0.05). For visual impression of the response of perennial vegetation see Appendix 7-8.

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Figure 8 The evolution of the study area along 47 years using aerial photos indicating the experimental classification plots (2ha each). The 1956 photo serves as index of classification plots names. Note that except for the 1970 photo, all photographs were sampled in 12 identical plots during photogrammetry. Six plots represent the 'close to farm' environment, and 6 represent the 'distant from farm' environment. Due to technical problems, during classification of the 1970 photo (limited photograph area and inaccurate georeferencing), it was necessary to discard the "Far-5" plot from this classification, and to slightly relocate the "Far-4" and "Far-6" plots during the classification.

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Figure 9 Perennial bush cover values of 7 aerial photos, using photogrammetric tools, in 12 sample plots, close to and distant from the farming (1956-2003). There were significant differences in photos from 1993 and 2003 (paired t-Test).

Figure 10 Mean (± SD) length of perimeter and breadth of bushes in 11 sampling plots, 6 close to and 5 distant from the farmland. A significant difference was not found for the bush perimeter index, but was found for the bush breadth (t-Test).

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Figure 11 Mean (± SD) bush density (calculated as 1/inter-bush distance) in 11 sampling plots, 6 close to and 5 distant from the farmland. A significant difference was found (t-Test).

Figure 12 Mean (± SD) sand stability values in 11 sampling plots, 6 close to and 5 distant from the farmland. A significant difference (t-Test) was found.

3.2 Underground Water Table

Free underground water was discovered in 17 boreholes, while two additional boreholes (#18-19) located in the center and edge of the Sabkha, showed high saturation values but lacked free water (Table 1). Water table depth measurements (from the surface) (Fig. 13) were positively correlated with distance from irrigated farmland (linear regression, r2 = 0.784, P < 0.001, N = 17). Repeated measurements of water level in several boreholes revealed no meaningful differences throughout the seasons. Fig. 14 illustrates a typical soil moisure column (> 20% moisure equals max saturation, i.e. water table), and Fig. 15 illustrates water content vs. grain size in borehole #11 (linear regression, n.s.). Conductivity (in units of deci-Siemens/metre) 32 was positively correlated with distance from irrigated farmland (linear regression, r2 = 0.462, P < 0.005, N = 17; Fig. 16). Boron concentrations in water samples showed no meaningful correlation on a 'distance from irrigated farmland' gradient (linear regression, r2 = 0.064, N = 14, Fig. 17), while nitrate-nitrogen concentrations did show a negative correlation (linear regression, r2 = 0.446, P < 0.05, N = 11, Fig. 18). For visual impression of the discovered aquifer see Appendix 9.

Table 1 Results of 19 boreholes excavated in the study site. For boreholes locations see Fig. 7. Abbreviations: UWT – underground water table; Lon. – Israel longitude; Lat. – Israel latitude; ND – no data.

Borehole Lon. Lat. Meters from UWT Conductivity Boron N-NO3 farmland depth dS/m mg/l mg/l 1 203740 414300 300 -5.5 10.91 5.84 ND 2 203777 414234 337 -5.4 14.17 8.99 ND 3 203871 414243 431 -4.6 20.2 ND ND 4 203905 414241 465 -5.4 28.1 14.46 53.8 5 203969 414184 529 -5 23.8 8.29 266 6 203992 414496 552 -3.6 10.59 3.77 164.9 7 204023 415185 583 -4 18.6 ND 1.1 8 204038 414629 598 -3.6 22.3 8.22 53.6 9 204043 414134 603 -4 12.45 4.37 ND 10 204081 415267 641 -3 29.8 7.15 0.3 11 204085 414210 645 -4 ND ND 22.7 12 204092 414516 652 -3.3 14.09 5.94 36.4 13 204191 414750 751 -3 18.4 6.88 17.1 14 204206 414543 766 -3 31.9 ND 1.9 15 204244 413800 804 -3.3 26.8 13.58 2.5 16 204258 414546 818 -2 30.8 9.9 0.6 17 204274 413302 834 -3.3 20.7 6.08 12.8 18 204480 415750 1350 ND ND ND ND 19 204511 415109 1100 ND 43.6 1.18 ND

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Figure 13 Underground water table depths (dependent variable) of 17 drilled wells on a 'distance from irrigated farm' gradient (independent variable). A significant correlation was found (linear regression).

Figure 14 A typical gradient of moisture content in one of the cores (borehole #9).

Figure 15 Typical gradients of soil moisture and grain size relation (borehole #11). There was no significant correlation (linear regression).

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Figure 16 Conductivity values (dependent variable, in deci-Siemens/metre) of water samples from 17 boreholes on a distance from farmland gradient (independent variable). The uppermost dot (43.6 dS/m) refers to a soil sample taken from the Sabkha's sterile zone (while seawater is 55 dS/m). A significant correlation was found (linear regression).

Figure 17 Boron concentrations (dependent variable) of water samples from 14 boreholes on a distance from farmland gradient (independent variable). There was no significant correlation (linear regression).

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Figure 18 N-NO3 concentrations (dependent variable) of water samples from 11 boreholes on a distance from farmland gradient (independent variable). A significant correlation was found (linear regression).

3.3 Rodent Community Structure

Out of 1,017 observations (193 trapped gerbils + 824 track identifications), 564 were specified as G. nanus and 453 as G. gerbillus. Spatial structure of the two species, as indicated by trapping and tracks count locations, seems to be substantially affected by the proximity to farming (Fig. 19). The interior dunes were mostly inhabited by G. gerbillus but also by G. nanus, while the affected edge was almost purely inhabited by the generalist G. nanus. Correlation analysis of all environmental variables (nearest bush, bush perimeter, soil density, distance from farmland and bush cover by photogrammetry) and gerbil observations within the sampled plots showed significant Pearson values in most of the combinations, while the nearest bush, soil density and distance from farmland variables presented the strongest correlation of all (Table 2). Additionally, a linear regression analysis was performed on gerbil observations vs. the environmental data, and showed a similar result (G. nanus, r2 = 0.88 and G. gerbillus, r2 = 0.91), while reemphasizing that distance from farming is the most meaningful factor in both species. A similar strong significance was found (repeated measures ANOVA, F = 143.927, P < 0.001) when comparing the two species distributions within the close and far plots. As shown in Fig. 20, G. nanus was again identified with 'close to farm' plots, while G. gerbillus with 'far from farm' plots. Moreover, G. nanus showed stronger connection to close locations, than G. gerbillus to 'far' locations. Finally, a redundancy analysis (RDA) was done to seek the combinations of explanatory variables that best explain the gerbil abundance variation. The first RDA (using CANOCO software) analyzed the two gerbil abundances vs. the seven environmental variables. The results 36 of the Monte Carlo permutation test were significant for both axes (eigenvalue = 0.895, P = 0.01 and trace = 0.909, P < 0.05). The second RDA (Fig. 21) referred to the most effective factors derived from the first ordination. All canonical axes were significant (eigenvalue = 0.878, P < 0.01 and trace = 0.882, P < 0.01).

Figure 19 Distribution of the two species within the study site (aerial photo, 2003).

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Table 2 Pearson correlation analysis of all monitored factors.

Nearest

bush Pearson -0.679* Perimeter Sig. 0.022 Perimeter Pearson -0.757** 0.838** Soil density Soil density (Kg/cm^2) Sig. 0.007 0.001 (Kg/cm^2) Pearson 0.884** -0.626* -0.673* From farm From (m) Sig. 0.000 0.039 0.023 farm (m) Pearson -0.675* 0.924** 0.699* -0.674* Veg. Cover Vegetation (%) Sig. 0.023 0.000 0.017 0.023 cover (%) Pearson -0.825** 0.556 0.623* -0.913** 0.659* G.n. Sig. 0.002 0.075 0.040 0.000 0.027 G.n. Pearson 0.854** -0.557 -0.641* 0.877** -0.685* -0.853** G.g. Sig. 0.001 0.075 0.034 0.000 0.020 0.001

N = 11 in all cases; significant values are in bold while * indicates P < 0.05 and ** indicates P < 0.01.

G. nanus

G. gerbillus

Figure 20 Repeated measures ANOVA output graph of spatial distribution of the two species.

Figure 21 Graphic result of the RDA of the two species vs. four environmental variables (proximity to farmland, nearest bush, cover by photogrammetry) using CANOCO software.

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4 DISCUSSION

4.1 Underground Water Table and its Implications on Vegetation Cover

The edaphic factor plays a prominent role in arid zones, modifying the water regime and shaping the fauna and flora community structures. Noy-Meir (1973) points out that in an extreme desert like the Arava, receiving less than 60mm/yr of rain on average, water is limited and vegetation is restricted to favorable locations only (e.g. wadis etc.). Examples for such favorable locations include areas with sandy soils, thanks to rapid deep percolation that is likely to feed the shallow aquifer. This type of aquifer sustains relatively high species diversity (Fet et al., 1998), and enables the thriving of deep- rooted perennials (Orev, 1984). Such water tables are being filled following and between significant rain events (Noy-Meir, 1973). In the southern Arava, these extremely infrequent floods are initiated only by brief and strong rains (> 10-20mm, personal observations). In this region (graded as one of the harshest deserts in the world, Whitford, 2002) the stochastic rain regime (Noy-Meir, 1973) is being greatly influenced by a prolonged drought that tremendously affects most desert dwellers (personal observations). Here I shall refer to the abiotic conditions supporting the observed vegetation, in spite of the drought.

The aquifer monitoring (Table 1 and Fig. 13) revealed that water was abundant throughout the sand dune in depths of 2-5m and appeared to be easily accessed by the 8m vertical roots of H. persicum (Orlovsky & Birnbaum, 2002). In fact, most boreholes comprised root pieces within the soaked area of the soil, and abandoned boreholes became clogged due to root intrusion. Soil-moisture samples from each drill (Fig. 14) repeatedly presented a minor peak in a depth of 1.5-2m, a steep increase at around 2.5- 3m, and field capacity of the loamy soil (~ 20%) at around 3-5m below the surface. Grain size classification of sieved samples from each drill matched the above trend (Fig. 15 – soil moisture content in relation to soil composition), and exemplified the dune stratigraphy at shallow depths. Both the clay's strong adhesion forces (due to high 'surface area to volume' ratio) and the specific soil layering, play a major role in aquifer formation. After the dominant clay lens has been soaked and sealed (i.e. aquiclude), the sandy layers above form a water table and thus increase water availability. Before 39 discussing the possible refilling of this water table by nearby farming, I shall examine the botanical response to the existence of a shallow water table in the dune. The studied 'white saxaul' (H. persicum) is recognized as a deep sand shrub (Orlovsky & Birnbaum, 2002) that thrives without rain as long as the subsurface soil is soggy. In the present study, shrub cover was analyzed via remote sensing and field observations, and found to be significantly higher in 'close to farm' plots (> 40%). Habitat modification is clearly visible from aerial images (Fig. 8) and onsite observations. In some parts of the dune bush cover was close to 100%, and bush height exceeded 4m, forming an inaccessible Haloxylon persicum forest-like environment. As a result, the loose sand stabilized and settled amongst shrubs (forming sand mounds around shrubs, i.e. 'nebkha', Ardon, 2006) thus causing a general surface stabilization (see also Fig. 12). These processes are accompanied by organic material enrichment (wood, foliage, seeds etc.). These improved conditions apparently facilitate the development of a friendly environment for psammophile and non-psammophile dwellers, by providing exceptional quantities of food, shelter, shade etc. As was mentioned in the introduction, one of the scientific indices (M index; Lancaster, 1988) specifies these extreme-arid dunes as mobile and barren. In fact, examination of historical images revealed that vegetation cover was relatively high (1- 5% shrub cover) and was distinguishable even before the introduction of farming (see photo year 1956 in Fig. 8; and Fig. 9). Studies conducted in the Timna dunes after farming was established have indicated a similar perennial bush cover (Abramsky et al., 1985, respectively; 6% and 8%; Brand, 1983). Wind is the main ecological limiting factor characterizing this ecosystem, but local hydrology prior to farming should be regarded as well. Due to the west to east slope of the soil layers, irrigation water (mainly treated wastewater) is presumed to flow towards the Yotvata Sabkha, over and under the ground. Past percolation of occasional floods (that used to be much more abundant and not diverted by damming) through the porous sandy layers to the shallow aquiclude (clay lens) seems to have refilled the aquifer that supported life on the dune. Supposing that massive irrigation resembles flood activity, wastewater percolation follows the same track and refills the aquifer nowadays. This indeed improves plant life in a long term, but what actually triggered the first exceptional proliferation of shrubs two decades ago? It is assumed that the establishment of H. persicum seedlings may have been a result of an occasional wetting by small floods or even leakage in irrigation 40 piping (Samar farmers, personal communication; see photo, App. 2). Once the deepening root approaches the enriched water table, shrub proliferation accelerated.

In spite of the rise in the aquifer level towards the east side of the dune, bush biomass seemed to be decreasing. The high salinity found in the Sabkha soil and around it (conductivity increased towards the center; Fig. 16), is caused by continuous evaporation of saline water, mainly from the sterile zone soil (Gillespie et al., 2006; Ron, 1967a). Consequently, this impedes any vegetation growth in the sterile zone, and defines the ecological belts surrounding it. The inverse process (dilution of soil salts) may occur within the farmland edges, while > 3 million m³ of wastewater are being used annually by the two adjacent farmlands. Wastewater samples taken from irrigation pipes, combined with data from the farmer's monthly wastewater reports (performed by 'Eco-Stream'), have shown low salt content (conductivity = 1.8 dS/m) relative to the much saltier water found in most boreholes (conductivity = 22.1 dS/m on average). Accordingly, it is presumed that the significant flourishing of shrubs around the farmland edge was accelerated not only by water abundance, but also by salt rinsing and the following soil improvement for plants. In an attempt to further characterize the possible hydrological shift, boron concentrations were monitored in most boreholes. It was presumed that boron, as an irrigation water indicator (Hudak, 2004; Rowe, 1999; Shouse et al., 2006) and particularly wastewater indicator will demonstrate relatively high concentrations in 'close to farm' plots. In natural habitats, it is likely to be accumulated in desert soil and vegetation, due to low solubility (E. Tripler, personal comm.). This plant micronutrient, which is essential at small concentrations but may be toxic for plants at high concentrations (E. Tripler, personal comm.), was found in boreholes in high values (7.5mg/L on average) (Fig. 17). The mean value is within the range 6-10mg/L, which is considered very toxic to most crops (Shouse et al., 2006). The reason for high boron concentrations throughout the Timna dunes (see Fig. 17) is probably due to the decrease in salt rinsing following the diminishing annual rainfall, and the large drainage of wastewater (domestic-boron enriched). An additional six leaf samples (of H. persicum and two accompanying shrub species), taken from close to and distant from farmland, have revealed extreme boron concentrations (60-100mg/L). It seems that its natural abundance in desert soils (mostly due to low mineral rinsing) dwarfs the amount of its leakage from farming irrigation sources to the shallow aquifer. Boron sources and its 41 spatial distribution remains unclear. In order to learn about the possible effects of boron on the desert ecosystems, additional research is needed.

Finally, most of the tests for nitrates (N-NO3: a prominent indicator for water pollution by irrigation drainage, Shouse et al., 2006), revealed high concentrations (Table 1), notably concentrations above 10 mg/l, which no doubt indicate anthropogenic pollution (H. Naor, personal comm.). Increased levels of N-NO3 were correlated with farmland proximity (Fig.18), while two boreholes, located adjacent to farmland, showed extreme values (> 150mg/L) emphasizing the significance of over-irrigation. Although nitrogen may enter the system via natural processes, its accumulation in desert soil is usually negligible due to low rainfall and resultant reduced biomass. Therefore, the main possible source for nitrogen in the soil is likely to be agriculture. It penetrates the soil either via infiltration of raw manure from cowsheds (Kibbutz Samar and Elifaz both own cowsheds), or via flushing of fertilizers and compost in farmed lands. I presume that in addition to the above, treated wastewater used by Samar and Elifaz farmlands probably increases the amount of nitrogen and additional elements in the groundwater below.

Gordon et al. (2008) have remarked that agricultural modifications of hydrological flows may create ecological surprises. In this study, I have described a rise in groundwater levels due to irrigation, resulting in significant increase in bush density. Regarding the drop in water levels around the Sabkha's sterile zone recorded by Gillespie et al. (2006), it may be explained by the remoteness of their studied area (less affected by irrigation sources). Our understanding of changes in groundwater characteristics is incomplete, and additional hydrological research is necessary for future management of this resource. Special attention should be directed to groundwater pollution (especially contamination of usable aquifers), salt leaching in soils around farmlands, and their ecological consequences.

4.2 Rodent Community Structure

Rodents may function as reliable indicator of ecosystem integrity (Manor et al., 2008). Human disturbance often causes a replacement of a specialist by a generalist species in rodents and other taxons as well (Hawlena & Bouskila, 2006; e.g. Khoury & Al- 42

Shamlih, 2006; Manor et al., 2008; Manor & Saltz, 2008; Shanas et al., 2006). The Timna dune is characterized by unique species that are well adapted to life in extreme arid sand dunes. Such species are, therefore, more vulnerable to extrinsic impacts, such as invasion by generalist species. In this study I investigated an endangered rodent in and the results may illuminate its conservational status and to improve its habitat management. Bush cover, sand stability and distance from farmland, significantly correlated with the rodent species abundance (Table 2 and Figs. 20-21). Therefore, I suggest that disturbances in habitat structure (in the form of bush growth accompanied by sand dune stabilization) negatively affect the psammophilic species arrangement; in particular by increasing the population of G. nanus at the expense of the G. gerbillus population (Fig.21). Unlike Zahavi & Wahrman report (1957) and later studies (Abramsky et al., 1985; e.g. Brand, 1983), G. gerbillus is not dominating the Timna dune anymore, and extensive land is now purely inhabited by the generalist G. nanus, while the dunes distant from farmland are mixed with both gerbils species. The only additional rodent observed in one of the remote and less affected dunes was the Greater Egyptian Jerboa (Jaculus orientalis). Despite the fact that this species has never been found in the Arava, I trapped one subadult male using a Sherman trap (October 12, 2006), and recorded footprints on two other occasions; all from the southern tip of the Timna dune. Its relative, the Lesser Egyptian Jerboa (Jaculus jaculus) has never been recorded in the Timna dunes, but commonly observed in alluvial soils surrounding the southern Arava sand dunes. Interestingly, J. jaculus was found to coexist with G. gerbillus in the remnant sand dunes, east of Kibbutz Yotvata's farmland (personal observation), but possible interaction has never been examined. In vicinity to farmland, populations of G. gerbillus and G. nanus were occasionally accompanied by Mus musculus, Crocidura russula (insectivore), and Meriones crassus (the two latter species were caught using pitfalls during a small-scale experimental attempt); but due to low numbers of these generalist species, I predict that encounters and competition with G. gerbillus and G. nanus are negligible. The clear habitat selection presented here is likely to be a result of competition interaction between the two gerbils. In fact, Brand (1983) indicated on a high competition coefficient for the negative effect of G. nanus on G. gerbillus, and Shapira (2006) reported on significant changes in foraging behavior of G. gerbillus due to competition with G. nanus. Some interaction between the two species was observed via footprints and trapping. When I removed several specimens of the more abundant G. 43 nanus from a moderately-vegetated sand dune, an immediate re-occupation by G. gerbillus was observed at the same trapping locations during the following trapping night. Interestingly, gerbil trapping and handling have revealed great aggression by G. nanus accompanied by screaming and biting. That may indicate an aggressive interaction, and may serve the latter during invasion and competition with its relatively docile rival G. gerbillus. Though interesting, no solid conclusion can be made regarding the mechanism causing this species replacement. Brand (1983) has found that in Hetzeva, G. nanus was the sole gerbil to inhabit all sandy habitats. In Timna it mostly inhabited less mobile sandy habitats (i.e. shallow sand fields), as G. gerbillus significantly preferred sand dunes but may be found on sand fields as well (Brand, 1983). The latter finding is interesting since it contradicts the general consensus that G. gerbillus dwells only mobile sand dunes, with not a single specimen caught outside them (Harrison & Bates, 1991). Trapping in stabilized sandfields throughout the southern Arava revealed that G. gerbillus is not limited to mobile sand, as it dwells neighboring habitat as well (personal observations; see Appendix 16). G. gerbillus was constantly reported as the sole rodent to survive the harshest sand dune conditions (with the least vegetation cover). The same distinct adaptation (to life in extreme habitat) may interpret its existence on relatively barren sandfields in vicinity to sand dune. In other words, G. gerbillus is the dominant rodent in the harshest conditions of mobile sand dunes and barren sandfields. Oppositely, G. nanus is the dominant rodent in relatively vegetated alluvial plains and Sabkhas (Zahavi & Wahrman, 1957). Verily, Harrison & Bates (1991) have specified G. nanus as a widespread species (in Asia and North Africa), especially in Arabia, where it is one of the most widespread gerbils. Moreover, its existence in farmlands and their disturbed surroundings throughout the Arava implies on its ability to invade habitats characterized by more common generalists such as Mus musculus and Acomys cahirinus, typical of a generalist (personal observations in the middle and southern Arava). Although considered as extinct from the semi-desert of the northern Negev (Shalmon, 2004), historic observations on G. gerbillus have indicated similar habitat preference, as it found to inhabit the most loose and barren sand dunes (T, Magen, personal communication). The moderate conditions in this region are being intensified by recent dunes stabilization (vegetation increase due to lack- of grazing), and therefore, are likely to benefit the more common psammophile G. pyramidum and endanger the specialist G. gerbillus. In order to clarify the status of G. gerbillus in the Negev, a wide 44 survey should be conducted referring to its distribution in relation to vegetation cover and possible competitors. As indicated by the monthly observations, seasonality seems to have no meaningful effect on the gerbil community structure in the Timna dune. One seasonal factor that may change gerbil configuration in the field is the vegetation burst (of annuals) following the extremely infrequent rain events. However it was not studied here. Regarding body size, it was found that G. gerbillus from southern populations (i.e. the southern Arava) were significantly larger than specimens from the north-western Negev (23.7 and 20.5g, respectively; Brand & Abramsky, 1987). The above observation is contrary to 'Bergmann's rule'. Therefore, it has been suggested that mass differences are caused due to 'ecological release' of the Arava's G. gerbillus from possible competing rivals (Brand & Abramsky, 1987), while gerbils from the northern populations 'lost mass' as a result of competition pressure. Since the Arava's gerbils are supposed to exhibit spatial partitioning, (Brand & Abramsky, 1987; naturally sharing discrete habitats; Zahavi & Wahrman, 1957), this incompatibility may also explain the similarity in size of G. gerbillus and G. nanus (size ratio of the two species equals 1.06, Brand, 1983; Brand & Abramsky, 1987).

The fact that both G. gerbillus and G. nanus are mainly granivores (but also feed on vegetation, Bar et al., 1984; Zaime & Gautier, 1989), adds an additional factor to the competition interaction. Krasnov et al. (2000) have indicated that olfaction is the main mechanism facilitating seed search in G. gerbillus. This important trait enables it to find seeds at relatively deep locations in the sand dune, and may give the species an advantage in its competition with its rival when available seed abundance is low. Intensified bush cover decreases drift potential by wind, and thus, reduces sand mobility and seed burial in sandy habitats (Ben-Natan et al., 2004). Consequently, the stable and seed-enriched habitat probably promotes the invasion by G. nanus, while the strong olfaction ability of G. gerbillus to detect seeds in un-stabilized surfaces (Krasnov et al., 2000) will not confer an advantage in these conditions. Regarding food handling, Shapira (2006) has indicated caching behavior by G. gerbillus during lab experiments, and I located seed banks in deep sand of two excavated burrows in the field. Shapira suggests that this trait may results from intraspecific competition on scattered food source in the dunes' edges, where both species coexisted before agriculture development. Namely, hoarding by G. gerbillus maximizes its seed collection ability in 45 such a mobile substrate, and additionally reduces its risk from predation by decreasing handling and eating time out in the open (decreasing the 'giving up density'). Alternatively, G. nanus was reported as a 'slow' seed sorter that spends more time foraging in cases of co-occurrence with G. gerbillus (Shapira, 2006). Hoarding in deep and humid sand is also likely to elevate the water content of seeds (e.g. Hatough- Bouran, 1990; Reichman et al., 1986; Vander Wall, 1993), advantaging the extreme habitat dweller. An additional factor that affects habitat selection is the domicile habits of the two species. Locations of gerbil burrows were recorded occasionally during work in the field, and revealed a clear preference of G. gerbillus to dwell in large open sand sheets (free of shrubs, mainly in distant from farmland locations), rather than burrowing in the relatively comfortable nebkhas surrounding it. On the other hand, it seems that G. nanus, which has been described as preferring vegetated and stable surfaces (Zahavi & Wahrman, 1957), is likely to burrow in nebkhas around vegetation. Gerbils inhabiting vegetated areas use bushes as a refuge from predators, and thereby decreasing their apprehension while foraging (Kotler et al., 2002). Unlike the latter, Shapira (2007) has found that gerbils in 'close to farm' locations in the Arava increased their apprehension due to high fox aactivity. It is also accepted that living in the open reduces apprehension due to wider visual range, thus, G. gerbillus may be more vigilant to foraging foxes. Several occasional attempts to (partially) excavate G. gerbillus burrows revealed deep (> 1m) and mazy tunnels while burrows of G. nanus were shallower and confined to shrubs (mainly in close to farmland locations). Such deep labyrinths may play as additional factor reducing the potential predation risk in sparsely vegetated dunes. Harrison & Bates (1991) have strongly correlated its sand dwelling habits to the hairy conditions of its soles (feet and toes). This may be complemented with the strong olfaction ability to detect seeds in deep sand, its fast locomotion on loose sand and its potential to reduce predation by digging complex burrows in barren sheets within the sand dune.

4.3 Synthesis

In recent years, the Arava Valley has gone a great changes due to human activities, including mining, settlement development, infrastructures of local and national scale, and presumably climate change (see Appendix 1 for a multi-year rainfall graph); but the 46 predominant influence on the fragile ecosystem is definitely agricultural activity. In addition to direct landscape modification, agricultural activity has indirectly caused to substantial changes in wild populations throughout the Arava (Shapira et al., 2007). Such changes may lead to population decline, and sometimes local extinction of species (e.g. sand fox Vulpes rueppelli and sand cat Felis margarita, Shalmon, 2004). The ecosystem of the Timna sand dune is composed of several endangered species and regarded as highly important in the list of conservation priorities. During the last decades the adjacent farmland has affected the natural sandy ecosystem, leaving the psammophile diversity under a great risk of local extinction. In other parts of the Israeli sandy desert, the effects of human activities have also led to significant reduction in distribution and abundance of psammophile species, and to an increase in more generalist species. The first indication was the unusual shrub density along the edge of farmland (prediction 1). As high density of shrubs usually decreases sand transport, sand dune stabilization processes intensified (prediction 2). Considering the prolonged drought and the dislocation of wadis surrounding the dunes, the most probable source of water supporting the thriving of perennial vegetation on the sands is the substantial farmland expansion and increase in intensive irrigation by the settlements Samar and Elifaz during the last 40-50 years. Observations have verified that the process causing the ecological modification is mainly hydrological and it relates to the nearby agriculture activity (prediction 3). Ground drilling in the sand dune has revealed a shallow water table that is likely to be a result of irrigation leakage and subsurface flow east towards the interior dunes and the Yotvata Sabkha. The same water source apparently supports the observed vegetation growth, as roots remains of Haloxylon persicum were found in depths over 5m. Conductivity and boron tests (of the aquifer water) did not indicate irrigation leakage in particular, apparently due to the general high salinity of the Sabkha surroundings.

Nitrate concentrations did indicate anthropogenic pollution. Enrichment of N-NO3 is presumed to be initiated by rinsing of compost and other additives by the massive wastewater irrigation, and percolation to the shallow aquifer levels (prediction 4). Oren et al. (2004) reported a similar phenomenon taking place about 100 km north from the Timna sand dune, in the Central Arava. They indicated that low irrigation efficiency of about 50%, contributes approximately 3.5-4 million m3/year to the hydrological system. The above corresponds to massive recharge in the irrigated area and is suggested to be 47 the most significant recharge mechanism in the area (Oren et al., 2004). Both farmlands in proximity to the Timna dune, irrigate over 3 million m3/year, while similarly to the Central Arava data, irrigation is inefficient (> 30%, E. Trippler, R&D Arava, personal communication). Moreover, the organic methods used by Samar's farmland do not necessarily reduce the above effect. While the use of chemical fertilizers in conventional practices degrades aquifers, the use of irrigated compost in organic systems also leads to infiltration of organic compounds to underground water tables. The clear relation between the thriving of Haloxylon persicum adjacent to irrigated areas (i.e. agricultural edge effect) is the first major conclusion to be deduced. Luckily, the H. persicum dominating the habitat is a native species; however, monitoring in the future will be necessary to prevent the occupation by invasive species.

In contrast to the acknowledged outcomes of desertification processes caused by farming (Agnew & Warren, 1990), the Timna dune and other sandy patches in proximity to farmlands in the Arava are being modified in a way leading to an opposite trend. The significant addition of water and nutrients promote vegetation thriving, bringing about remarkable changes in habitat structure. One of the outcomes of this is that the distribution of the psammophile G. gerbillus is being reduced due to a replacement by the generalist G. nanus (prediction 5). In contrast to previous reports (> 2 decades ago), the interior dune is dominated by G. gerbillus mixed with G. nanus, and the vegetated edge of the dune is dominated solely by G. nanus. This finding was lately implied by Sinai et al. (2003) in the Timna dunes during 1998-2001, and has assumed to become more established with time. The mechanism facilitating exclusion of one species and co-occurrence of two species in some areas has not been studied, but it is assumed to involve competitive interactions over food and space availability, especially in highly vegetated locations. The main point of my discussion is the significance of the high specialization of G. gerbillus in extremely harsh conditions, and its exclusiveness in the less-affected remote dunes of the southern Arava. Further observations are needed to define the extent of vegetation density and sand stability that triggers species replacement and endangers a habitat specialist. G. gerbillus has been declared only as vulnerable in the red list of Israel's threatened vertebrates (Shalmon, 2004), but since the remnant sandy patches of the Arava is its last main resort it's status should be revised.

48

As agricultural practice is expanding throughout the valley, its unstudied direct and indirect effects are assumed to be great, and the risk for small and unique patches is substantial. The reported extensive agricultural edge effect in the small studied patch, emphasizes the concept of patch size and its impact on the intensity of edge effect processes. Beside limited size, additional key reason for promoting conservation of the Timna dune is the general scarcity of sandy patches within the Israeli Arava. Up to date, a small portion (0.6km2) of the total Timna sand dune area (2.3km2) is protected by law under the definition of a formal nature reserve, while 1km2 was originally predesignated for farming, but is now scheduled to be included within the reserve. The southern part of the dune (0.7km2) has been previously designated as sand mining area (see Appendix 17), and a recently declared intention of the Israel Ministry of National Infrastructures to renew mining has drawn great public and legal attention. Fortunately, these acts have managed to postpone the beginning of mining, but the actual risk for the last major dune in the Israeli Arava remains relevant.

49

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6 APPENDICES

Appendix 1. Annual rainfall values since 1939 in the southern Arava (Yotvata and Eilat meteorological stations). Grey line = 10-year averages; Black arrow = drought (< 15mm in average).

Appendix 2. Lookout from Mt. Berech on the northern side of the Timna Valley, and east towards the Timna dunes in the Arava Valley.

T h e E d o m m o u n t a i n r a n g e

Sasgon Valley Timna Mt. (sandstone) Timna Dunes (granite)

Flow direction

S a n d s t o n e r e m n a n t s

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Appendix 3. Small Nebkha mound around Haloxylon persicum. It comprised of sand, silt, roots, seeds and other organic elements carried by wind. North wind direction is indicated by the vertical ripples.

Appendix 4. Schematic geohydrological cross-section near Wadi Arava (En-Yahav) in the central part of the valley. Loaned from Oren et al., 2004.

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Appendix 5. Photos of the two gerbils, indicating the great difference in feet furriness.

(23g~) גרביל דרומי 23g) G. gerbillus~) גרביל ערבה G. nanus A widespread generalist that inhabits salt- Restricted to mobile sand dunes with little flats and wadi-beds throughout the Arava, vegetation. Its hairy feet may be useful during including the edges of sandy patches (Zahavi movement on sand. and Wahrman, 1957). Was found to inhabit Apparently extinct from the Negev (Sinai et al., disturbed habitat (cultivated land). 2003). Shalmon (2004) defined it as “vulnerable”

Appendix 6. Drilling location in fixed loamy soil amongst sand dunes. The auger composed of a knob, several tubes (1m each) and hollow drill designed to remove core from depth > 10m.

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Appendix 7. The study site from the irrigated farm towards north. Note the high density of Haloxylon persicum in close sand dunes, and the low density characterizes the remote dunes.

Yotvata Sabkha

Appendix 8. The study site east from the farm. Note that shrub cover in proximity to farmland > 50%.

Yotvata Sabkha

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Appendix 9. Photograph of the borehole excavated by a tractor, indicating the underground water level at 5.5m.

Water table

Appendix 10. The remote southern dunes of the Timna sands, towards north. Photograph by Ariel Immerman.

F a r m l a n d s Yotvata Sabkha

Appendix 11. North-Eastern lookout from the interior part of the dune. Vegetation cover is much lower in these interior and less affected dunes.

Edom Mountains

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Appendix 12. Kibbutz Samar's organic date plantation. Each Palm is irrigated by > 1,000 m3 of water daily.

Appendix 13. Photograph showing the vegetation burst after a severe leakage in irrigation pipes.

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Appendix 14. Photograph of a fox pathway near the highly vegetated area. Many predatory species (such as fox, jackal and wolf) dwell these forest-like surroundings and thrive due to the proximity of the refuge to the nearby agrosystem. The fox and jackal photos by Mori Chen and Benny Shalmon, respectively.

Appendix 15. Observations in desert hedgehog Paraechinus aethiopicus within the Timna dunes were concentrated mostly along the extended edge. While Paraechinus aethiopicus is being replaced by the more generalist hedgehog Erinaceus concolor in the central Negev (Bouskila, personal communication), its populations are increased in farmlands and their surroundings. Hedgehog photo by Benny Shalmon.

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Appendix 16. A sandfield located in the fringe of the southern Timna dune (Timna Mountain is seen on the east). This poor environment bears < 1% cover of Haloxylon persicum, and despite the solid surface conditions it found to support population of the psammophile G. gerbillus.

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Appendix 17. Aerial photo of the Timna sand dune indicating the different statutory cases (SD = sand dune).

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אפקט-שוליים חקלאי נסתר והשלכותיו על צפיפות הצומח ומבנה חברת המכרסמים בכתם חולי במדבר קיצוני, ערבה דרומית, ישראל רועי טלבי המחלקה לאקולוגיה מדברית, המכונים לחקר המדבר, אוניברסיטת בן-גוריון בנגב

התפתחות החקלאות והתפשטותה על-פני כדור הארץ הינם בין הגורמים העיקריים להכחדת מינים. מלבד הרס של בתי - גידול וקיטוע שטחים טבעיים, שטחי חקלאות יוצרים בסביבה צחיחה איים עתירי מים ונוטריינטים העשויים לשנות באופן מהותי את המערכת המדברית. בערבה הדרומית, מואצים בעשורים האחרונים יישומי חקלאות שהשלכותיהם על הסביבה לא נחקרו דיין . בעבודה זו . בדקתי תמורות באקולוגיה של צמחים ומכרסמים אשר התרחשו בכתם חולי קטן בערבה הדרומית בהשפעת חקלאות אינטנסיבית סמוכה. המחקר התבצע בחולות סמר, גוש החולות המשמעותי (2.3 קמ"ר) היחיד בגבולות הערבה הישראלית. האתר גובל במטעי תמרים ושדות בני 30 שנה המושקים ומדושנים באופן אינטנסיבי במיוחד (סה "כ > 3 מליון מטר מעוקב מי-קולחין בשנה). לצורך אפיון השפעת החקלאות על הכיסוי הצמחי בחולות, ניתחתי מספר צילומי אויר (משנת 1956 עד 2003) בתכנת עיבוד תמונה, וכן ערכתי חתכי צומח ומדידות לבדיקת התייצבות החולות. במטרה למדוד את עומק מי - התהום קדחתי 19 קידוחים <( 6.5 מטר) בבסיסי הדיונות. את מבנה חברת המכרסמים בדקתי על ידי לכידה במלכודות וזיהוי המינים על - פי דגם העקבות בחול. אנליזות של צילומי אויר מתקופה טרום-חקלאית בהשוואה לצילומים עדכניים הציגו עלייה מובהקת בצפיפות הצומח הטבעי בשולי שטח המחקר. מדידות השדה חיזקו תוצאות אלו, ואף הדגישו את התייצבות הדיונות באזורים הסמוכים לגידולים המושקים. הקידוחים חשפו שכבת מי- תהום לא מוכרת בעומקים של 2-6 מטרים מתחת לפני השטח, ונמצא כי הצמחים המקומיים מנצלים משאב זה. מדיגום המכרסמים הובהר כי אוכלוסיית המין הגנרליסט, גרביל ערבה (Gerbillus nanus), מרחיבה את תפוצתה בשולי בית - הגידול החולי הגובל בחקלאות. במקביל, חלה נסיגה ברורה של אוכלוסיית המין המתמחה, גרביל דרומי (G. gerbillus), מבית-גידולו הטבעי בדיונות. עבודה זו מצביעה על ירידה בטיב בית - הגידול החולי בערבה הדרומית בהשפעת החקלאות. התפשטות הצמחייה המקומית (פרקרק פרסי Haloxylon persicum), מתבססת לכאורה על מי - השקיה המחלחלים וזורמים מזרחה, מן המטעים לכיוון אגן ההיקוות (מלחת יטבתה). כתוצאה מכך, חלה התייצבות של חוליות בגבול שטח המחקר. סביר כי שינויים אלו מהווים יתרון למין 'חובב חקלאות' כגרביל ערבה, ומתגלים כחסרון למין 'חובב חולות נודדים' כגרביל דרומי. להחלפת מיני המכרסמים באתר זה השלכה מהותית מאחר ותהליך הדחיקה של גרביל דרומי מחולות הערבה עשוי להוביל להכחדתו מישראל. כפועל יוצא מכך, יש ליישם ממשק מתאים ולמנוע התייצבות הדיונות ופגיעה במגוון המינים.

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אוניברסיטת בן-גוריון בנגב המכונים לחקר המדבר ע"ש יעקב בלאושטיין ביה"ס ללימודי מדבר ע"ש אלברט כץ

אפקט-שוליים חקלאי והשלכותיו על צפיפות הצומח ומבנה חברת המכרסמים בכתם חולי בתנאי מדבר קיצוני (ערבה דרומית, ישראל)

חיבור זה מהווה חלק מהדרישות לקבלת תואר מוסמך בלימודי מדבר (.M.Sc)

מאת: רועי טלבי

אייר, התשס"ט מאי 2009, 2009,