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On the life cycle of Stipagrostis scoparia hillocks

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Abstract

Stipagrostis scoparia is a perennial grass which inhabits mobile sands in large parts of Sinai and adjacent areas of the Negev Desert. The species forms phytogenic hillocks which, according to the results of previous studies, are gradually taken over by later successional species during the course of succession. Based on information about this species from the literature, a conceptual model for the dynamics of establishment and ageing of Stipagrostis scoparia hillocks is proposed. We attempted to validate parts of the model using data collected in the Hallamish sands near Nizzana, north-western Negev. Eighty hillocks were sampled for parameters of hillock shape, vegetation cover and perennial species composition. We referred the age of hillocks as being positively correlated with perennial species richness. This assumption was found to be consistent with the proposed model. However, we conclude that further, more detailed research is needed in order to fully understand the temporal dynamics of Stipagrostis scoparia .

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... Tielbörger & Kadmon 1997; Holzapfel & Mahall 1999; El-Bana et al. 2003) so data are needed on the associated species of multiple host plants with diverging characteristics. Nebkha systems are highly suitable for this, given the variation in growth habits, life forms and rooting habits of nebkha building plants (Batanouny & Batanouny 1968; Bornkamm et al. 1999; Dougill & Thomas 2002). This variation apparently also gives rise to a range of nebkha sizes and shapes. ...
... In addition , they are representative of different successional stages on the coastal desert dunes. Succession on these dunes typically proceeds from chamaephytic grass (Stipagrostis scoparia), small shrubs and grass (Artemisia mono sperma, Moltkiopsis ciliata and Panicum turgidum ) to colonization by late successional, large shrubs including Calli gonum polygonoides and Retama raetam (Danin 1983; Tielbörger 1997; Bornkamm et al. 1999; El-Bana et al. 2002a ). These three life forms characterize the mobile, partially stabilized and stabilized dunes, respectively. ...
... Larger nebkhas have a larger seed bank (Brown & Porembski 2000) and are spatially more heterogeneous in microclimate and soil nutrients (Hesp & McLachlan 2000; El-Bana et al. 2002b ). The simultaneous presence of these abiotic and biotic resources creates niche differentiation, and promotes the recruitment of species with different life and growth forms on the nebkhas (Bornkamm et al. 1999 ). Moreover, the speciesarea relationships for different nebkha host species were consistent with the prediction of IBT, lending further support to the island like nature of nebkhas within sanddefl ated, sand-depleted and oil polluted areas in coastal and desert dunes (Brown & Porembski 2000; El-Bana et al. 2000b, 2003). ...
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Question: Phytogenic mounds (nebkhas) - the natural accumulation of wind-blown sediments within or around the canopies of plants - have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species-area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex? Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula. Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified - though to a limited degree - by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non-environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species. Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes.
... Tielbörger & Kadmon 1997; Holzapfel & Mahall 1999; El-Bana et al. 2003) so data are needed on the associated species of multiple host plants with diverging characteristics. Nebkha systems are highly suitable for this, given the variation in growth habits, life forms and rooting habits of nebkha building plants (Batanouny & Batanouny 1968; Bornkamm et al. 1999; Dougill & Thomas 2002). This variation apparently also gives rise to a range of nebkha sizes and shapes. ...
... In addition , they are representative of different successional stages on the coastal desert dunes. Succession on these dunes typically proceeds from chamaephytic grass (Stipagrostis scoparia), small shrubs and grass (Artemisia mono sperma, Moltkiopsis ciliata and Panicum turgidum ) to colonization by late successional, large shrubs including Calli gonum polygonoides and Retama raetam (Danin 1983; Tielbörger 1997; Bornkamm et al. 1999; El-Bana et al. 2002a ). These three life forms characterize the mobile, partially stabilized and stabilized dunes, respectively. ...
... Larger nebkhas have a larger seed bank (Brown & Porembski 2000) and are spatially more heterogeneous in microclimate and soil nutrients (Hesp & McLachlan 2000; El-Bana et al. 2002b ). The simultaneous presence of these abiotic and biotic resources creates niche differentiation, and promotes the recruitment of species with different life and growth forms on the nebkhas (Bornkamm et al. 1999 ). Moreover, the speciesarea relationships for different nebkha host species were consistent with the prediction of IBT, lending further support to the island like nature of nebkhas within sanddefl ated, sand-depleted and oil polluted areas in coastal and desert dunes (Brown & Porembski 2000; El-Bana et al. 2000b, 2003). ...
Article
Question: Phytogenic mounds (nebkhas) – the natural accumulation of wind-blown sediments within or around the canopies of plants – have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species-area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex? Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula. Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified – though to a limited degree – by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non-environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species. Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes.
... On the other hand, Stipagrostis pungens is regarded as a pioneering species in the succession of vegetation on mobile sand dunes (Bendali et al., 1990;Bornkamm et al., 1999). Because of the ecology of this fibrous rhizomatous grass, its local presence is fugacious. ...
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Apart from a decrease in total perennial plant cover, degradation of North-African arid lands is not easy to qualify. Yet, simple and comprehensive yardsticks are necessary to assess degradation. We assigned components of competitive ability (C), stress tolerance (S) and ruderality (R) to 15 common perennials of Presaharian Tunisia. We used for that purpose phyto-ecological studies, data about life-form, grazing value and demography and circumstantial data. Assigning CRS-strategies to these species improves understanding of vegetation change under increased anthropic influence, helps to conceive experiments to confirm underlying hypotheses and sheds another light on the controversy about restoring arid lands.
... An exception is Stipagrostis scoparia as a perennial grass which colonizes mobile sands in Sinai by forming phytogenic hillocks. The stabilized sand is overtaken later on by successor species (Bornkamm et al., 1999). The plant permits a continuous root cover by sand sheath. ...
... Previous studies have emphasized the morphological diversity and sediment retention characteristics of nebkhas (Wang et al. 2006(Wang et al. , 2008 Electronic supplementary material The online version of this article (doi:10.1007/s11284-015-1277-z) contains supplementary material, which is available to authorized users. 2013) but studies concentrating on floristic composition and ecological processes are lacking (Bornkamm et al. 1999). Natural trapping of wind-borne sediments within or around the body of shrubs plays a major role in species diversity and the succession of plant communities in desert ecosystems (El-Bana et al. 2003;Biederman and Whisenant 2011;Simmons et al. 2011). ...
Article
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Nebkhas (phytogenic miniature dunes) are mounds composed of wind-borne sediment within or around shrub canopies and often develop under plants, creating microenvironments that affect the distribution of vegetation. In our study we investigated the vegetation of 397 nebkhas populated with the shrub Nitraria tangutorum in Yanchi County, in the northwest of China. We measured nebkha size (height, width and length) and soil moisture (from 0 to 100 cm). Distinct microsites of each nebkha (crest, mid-slope, bottom, edge and internebkha space) were identified and plant species diversity was also measured. Four vegetation groups (N. tangutorum-Chloris virgata + Eragrostis pilosa, N. tangutorum-Artemisia scoparia, N. tangutorum-Salsola collina + Bassia dasyphylla, N. tangutorum-Agriophyllum squarrosum) were described by two way indicator species analysis (TWINSPAN) on the basis of classification and, concomitantly, the relationships between species composition and environmental gradients were explained by canonical correspondence analysis (CCA). Regression analysis indicated that as height and area of the nebkhas increased, species richness increased linearly, while the other species diversity indices (Simpson index, Pielou index and Shannon-Wiener evenness index) increased logarithmically. The response of species richness to heterogeneity of the microenvironment resulted from the four aspects (east, south, north and west) of the nebkhas, and varied among the different microsites of the nebkhas. Species composition was correlated with spatial variability in soil moisture along the gradient from the nebkha crest to the internebkha space. It appeared that the microheterogeneity of the nebkhas promoted the abundance of plant species.
... Geomorphological characteristics of nabkhas and their significance to plant diversity, wind erosion and land degradation in arid ecosystems have been studied by several authors (e.g. Batanouny and Batanouny, 1968;Bornkamm et al., 1999;Dougill and Thomas, 2002;Wang et al., 2006;El-Bana et al., 2007). ...
Article
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Phytogenic mounds, nabkas, or hillocks are stabilized dunes formed around many perennial plants growing in desert and salt marsh, sabkha, habitats. The present study aims to analyze the vegetation structure and soil conditions of phytogenic mounds formed around two dominant perennial plants; Haloxylon salicornicum representing desert Nabkas and Nitraria retusa representing sabkha nabkas. Twenty sites were randomly chosen in the study area for vegetation measurements, soil sampling, and human activities description. Fifty surface soil samples were taken from the phytogenic mounds and interspaces for physical and chemical analysis. Signs of human impacts in the study area were also considered. Nabkas play crucial roles in soil fixation and limiting dunes migration. They are considered islands of fertile soil that are richer in organic matter, and silt and clay contents than soils of the interspaces. In addition, phytogenic mounds provide important niches for many types of animals and birds. Climatic conditions, soil salinity, and soil fine fractions are the main environmental gradients controlling the distribution of Haloxylon salicornicum and Nitraria retusa. Human impacts are the main threats affecting the health and abundance of phytogenic mounds causing land degradation and species loss. Management and conservation plan for phytogenic mounds should rely on the understanding of the potential and status of the vegetation structure and soil conditions.
... Several nebkha fields mentioned in peer reviewed articles were screened for use in this study. Grouped by country, these articles are: Burkina Faso (Dhief et al., 2009), China (Tengberg and Chen, 1998), Egypt (Wang et al., 2008), Israel (El-Bana et al., 2003), Iceland (Ardon et al., 2009;Bornkamm et al., 1999), Kuwait (Mountney and Russell, 2006), Mali (Brown and Porembski, 1997;Khalaf et al., 1995), New Mexico (Nickling and Wolfe, 1994), South-Africa (Gibbens et al., 2005;Langford, 2000;Parsons et al., 2003), Tunisia (Dougill and Thomas, 2002;Hesp and McLachlan, 2000) and U.S. (Tengberg and Chen, 1998). This study withheld only nebkha fields of which (i) exact locations were known, (ii) high resolution imagery was available, and (iii) species were identified. ...
... The species is highly tolerant of alkaline and saline soils and contributes to sand dune and saline soils reclamation (Ecocrop, 2011;Orwa et al., 2009). Hesp and McLachlan (2000), Khalaf (1989), Tengberg and Chen (1998) and other authors investigated the geomorphological or pedological characteristics of nebkhas, while the floristic composition of the associating species and their ecological processes were studied, e.g., by Bornkamm et al. (1999) and Brown and Porembski (1997). The formation of nebkhas by leguminous woody shrubs was investigated by Danin, (1996), El-Bana et al. (2002), and Tielbörger (1997). ...
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Few studies were published on the effect of nebkhas (phytogenic mounds) on species diversity and soil resources, but no detailed study has been conducted yet on possible specific influence of nebkhas on growth and survival of the plants associated with them. We studied the nebkhas of Salvadora persica and their effect on growth and survival of three woody species (Prosopis cineraria, Tamarix aphylla, and Capparis decidua) in the Ommanian coast of Hormozgan Province in the south of Iran. The results showed that mean height and mean canopy diameter of P. cineraria and T. aphylla trees and shrubs inhabiting nebkhas of Salvadora persica were considerably higher than those of plants of these species growing outside nebkhas. The reverse occurred in the case of C. decidua. Generally, the percentages of stems with dead parts were significantly lower in plants inhabiting the nebkha sites in comparison to comparable ones growing outside the nebkhas. Salvadora persica nebkhas are enriched with more soil nutrients in comparison to inter-nebkha sites. Soil accumulated per each hectare in the nebkhas of the study area dominated by trees of Salvadora persica amounted to 237.6 m3. This indicates the great importance of nebkhas in the protection of soil and the associating species.
... An exception is Stipagrostis scoparia as a perennial grass which colonizes mobile sands in Sinai by forming phytogenic hillocks. The stabilized sand is overtaken later on by successor species (Bornkamm et al., 1999). The plant permits a continuous root cover by sand sheath. ...
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Efforts are made to record biodiversity of microflora and diazotrophs associated with the plant cover of the major agricultural development areas in north Sinai, around the El-Salam canal, a newly-constructed canal that brings Nile water westward across the Suez canal. Natural plant communities were collected from three major areas. Ectorhizosphere, endorhizosphere and phyllosphere samples were examined for total microbial population and diazotrophs. The vegetation of South Qantara (area I) is characterized by the dominance of Stipagrostis scoparia followed by Nitraria retusa, Convolvulus lanatus, Cornulaca monacantha and Filago desertorum. Rabaa-Bir El Abd (area II) is dominated by Artemisia monosperma, Panicum turgidum and Zygophyllum album. Euphorbia terracina, Oligomeris linifolia, Astragalus kahiricus, Hyoscyamus muticus and Thymelea hirsuta represent the major plants of El Ser and Al Quarir (area III). Microorganisms colonized root surfaces of all tested plants ranging from > 10 to 10 cfu g. Diazotrophs were common residents (10 cfu g), invaded the root tissue and established endophytically (10 – 10 cfu g). Fifty-one N2-fixing isolates were obtained. Among the 32 bacilli isolates, Bacillus polymyxa and Bacillus circulans were more common compared to Bacillus macerans. BNF Gram-negative isolates belonged to Enterobacter agglomerans, Enterobacter gergoviae, Enterobacter amnigenus, Klebsiella pneumoniae, Pseudomonas luteola, Pseudomonas cepacia, Agrobacterium radiobacter and Azospirillum spp.
... This improvement in soil condition and local differences in microtopography reflected a greater species diversity including many glycophytes and some annuals around nebkha. Nebkha systems are highly suitable for this, given the variation in growth habits, life forms and rooting habits of nebakha building plans [48], [49]. On other hand, groups in site I, II and III are less well and separated, this is because to be a mixed community of shrubs and grasses this is consistent with [30]. ...
Article
Salt marshes are widely distributed in the eastern province of Saudi Arabia with their own distinct vegetation. The objective of this study were to study the effect of soil properties on characteristics of Halopeplis perfoliata community and plant response to environmental conditions of the eastern coast of Saudi Arabia. The study area is located at five sites: Ras Tanura, Syhat, Dammam, Al-Uqair and Salwah of the Arabian Gulf Coastal salt marshes in eastern province of Saudi Arabia where the plants grows under the natural environmental condition. Plant samples and soil of H. perfoliata succulent (halophyte) collected from the five sites. Several soil concentrations were determined such as electric conductivity (EC), organic carbon (O.C.), Na+, Cl−, So4, K+, Ca2+, and Mg2+. The highest concentrations of the ions of Na+, K+, Ca2+, Mg2+ in soil samples were found in Dammam site compared with the other sites, where Cl− is the major ion followed by Na+, Ca2+, K+, Mg2+. The involvement of photosynthetic pigments, and proline investigated. Values of TWC and RWC and photosynthetic pigment fractions content (chl. a, chl. b and carotenoids) from the plants obtained from Dammam were higher. In this study proline contents increased significantly in the leaves of H. perfoliata as the salt concentration increased. A total of 57 plants species were identified in all the five study site. The life forms of the studied plant spices exhibit a wide variation, perennial shrub (PSH) were the dominate growth form (63.16 %). This research suggests that H. perfoliata could remove salt from soil.
... On the other hand, Stipagrostis pungens is regarded as a pioneering species in the succession of vegetation on mobile sand dunes (Bendali et al., 1990;Bornkamm et al., 1999). Because of the ecology of this fibrous rhizomatous grass, its local presence is fugacious. ...
... These changes lead to complex local interaction between vegetation and soil (Batanouny & Batanouny 1968; Bendali et al. 1990; Danin 1996 ). The mounds are termed phytogenic hillocks or nebkhas (Batanouny & Batanouny 1968; Danin 1996; Bornkamm et al. 1999) because they are composed of wind-borne sediments that accumulate within or around the canopies of plants (Vasek & Lund 1980; Tengberg & Chen 1998; Batanouny 2001). Recent work has emphasized the role of nebkhas in combating land degradation through stabilizing soil surfaces and, by preventing soil erosion, in facilitating plant recruitment and survivorship (Brown & Porembski 1997; Blank et al. 1998; El-Bana et al. 2002b). ...
Article
Abstract Natural accumulation of wind-borne sediments within or around the canopies of plants plays an important role in the ecological and evolutionary dynamics of many coastal and desert ecosystems. The formation of such phytogenic mounds (nebkhas) creates patches that can strongly influence the spatial distribution of plant and soil resources. In land restoration of arid and semiarid environments it is important to study the potential role of such biological patchiness that may provide sites for coexistence of species with different life and growth forms. Our main objective was to test whether the nebkhas of a leguminous shrub, Retama raetam (white broom), promote restoration of herbaceous vegetation and soil in the degraded rangelands of northern Sinai. Vegetation and microclimatic and edaphic characteristics within the nebkhas, as well as within internebkha spaces, were compared for ungrazed and grazed sites. Abundance and richness of herbaceous plants were positively related to nebkha area, which explained more of the variance of abundance and richness in the grazed site than in the ungrazed one. Protection from grazing, especially on nebkhas, was associated with an increase in abundance and richness of herbaceous plants, improved soil microclimate, and increased soil fine particles and nutrient concentrations. The results suggest that management (in casu protection from grazing) of nebkhas of woody perennial shrubs changes rangeland conditions and improves the resource regulatory processes. Furthermore, nebkhas of unpalatable plants have the potential to preserve plant diversity in overgrazed plant communities, because they are effective in capturing and retaining water, soil materials, and propagules within and from nearby areas, resources that would otherwise be lost.
... of the western non-calcareous islands, re- spectively. Zahran et al. (1990) found that Asparagus stipularis is the characteristic species for the stabilized dunes along the Mediterranean deltaic coast. Stipagrostis scoparia is a perennial grass which dominates mobile sands of both coastal and desert dunes (Gibali 1988; Danin 1996; Tielbörger 1997). Bornkamm et al. (1999) argued that Stipagrostis scoparia is the pioneering species in the succession of vegetation on sand dunes of north-western Negev. Calligonum polygonoides has been classified as resistant to deep sand cover or removal (Danin 1996). The findings of the present study confirm this classification , as the species dominates the windward side ...
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Lake Bardawil is the only oligotrophic hypersaline lagoon along theMediterranean coast of Egypt. Its ecological significance is increasing due tothe progressive degradation of comparable wetlands in the region. The aim ofthis study is to analyse the structure and life forms of the vegetation alongthe lake before the execution of the North Sinai Agricultural DevelopmentProject (NSADP) which will threaten the ecosystem of the lake. A data set of150 stands was analysed using multivariate procedures(TWINSPAN, DCA and CCA), to classify the lake's vegetation, and to determinetherelationship between the plant community structure and the environmentalfactors. The classification and ordination resulted in a clear demonstration ofnine vegetation groups associated with four habitat types: submerged seagrasses, salt marshes and sabkhahs, eastern and middle calcareous dunes, andwestern non-calcareous dunes. The first axis of the CCA-ordination separatesthe salt marshes andsabkhahs species from those of the sand dunes along the soil salinity, watertable depth, cations, and pH gradients. CaCO3 and soil textureshowedhighly significant correlation with the second axis of CCA which was animportant predictor for the psammophytic species distribution. The life formsranged from hydrophytes (sea grasses) to phanerophyteswith the dominance of therophytes and chamaephytes. Geophytes and chamaephytesdominate the saline habitats, while therophytes and hemicryptophytes dominatedthe sandy dunes. Eventhough the eastern section of the lake (Lake Zaraniq) wasdeclared as a RAMSAR site, Lake Bardawil needs urgent management to prevent itspollution by the new land use system.
... This spatial variation in vegetational pattern was most clearly illustrated by the DCA ordination of the vegetation of nebkha and internebkha microsites. This microscale heterogeneity is one of the most conspicuous sources for variation of plant communities in the deserts of the Middle East (Batanouny, 2001; Boeken and Shachak, 1998) and one of the major promoters of the high species diversity found in habitats with low productivity (Bornkamm et al., 1999; Brown and Porembski, 1997 ). Our data support that the nebkhas comprise vegetation structures that are totally different from those of internebkha spaces (Danin, 1996). ...
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The nebkhas of woody plants represent distinct habitats in arid and semiarid ecosystems. Nebkhas are mounds composed of wind-borne sediment within or around shrub canopies. We studied the effects of widely spaced nebkhas of Retama raetam shrub on their micro-environment and associated herbaceous vegetation in the Mediterranean coast of Sinai Peninsula. Our measurements included nebkha size (height and width) and shrub size (canopy height and diameter). We identified four distinct microsites at each nebkha: crest, mid-slope, edge, and internebkha space. We measured soil temperature and moisture, photosynthetically active radiation (PAR), and soil properties. The plant species grown at each microsite were identified and their densities were measured. Average soil temperature and PAR were highest at inter-nebkha space and lowest at nebkha crest. The maximum diurnal temperature and PAR of inter-nebkhas exceeded that of nebkhas. Soil moisture and nutrient concentrations showed a gradient of spatial heterogeneity and were highest at the nebkha edge. Regression analysis indicated that total herbaceous plant density was significantly related to nebkha size, and to shrub canopy diameter and area. Detrended correspondence analysis indicated that patterns of species composition were correlated with the spatial variability in soil moisture and nutrient content along the gradient of increasing distance from the nebkha crest. It is assumed that shrub canopy and its nebkha interact in governing ecosystem functioning in this environment.
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Chapter
The study of the vegetation of the Northern Negev has a long history (see Danin and Orshan 1999 and references cited therein). For example, previous phytosociological studies (Eig 1938; Zohary 1944; Eig 1946; Orshan and Zohary 1963; Danin 1978, Danin 1983; Zohary 1982) have characterized the vegetation of the large northern Sinai and northern Negev sandy areas as one association dominated by Stipagrostis scoparia and Artemisia monosperma. More recently, Danin and Solomeshch (1999) have presented a comprehensive work on the coastal and desert vegetation of Israel, which covers the Nizzana area. While the vegetation of the Nizzana research site has been previously mapped and described in detail (Tielbörger 1993, 1997), no attempt has yet been made to integrate the findings into a larger syntaxonomic system. One aim of this study was to fill that gap and search for ties to the more recent work of Danin and Solomeshch (1999).
Chapter
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Recent research suggests that, under unconstrained human circumstances, pastoral nomads within arid environments have at their disposal means of evading ecological stress that could impel them to cause damage to their grazing and land resources. The Israeli-Egyptian border has imposed a severe constraint upon the range management strategy of the Bedouin whose traditional territory it bisects. The border forced them to exert an increased pressure upon local resources. Considerable damage was thus caused to the perennial vegetation cover (both macrophytes and microphytes) and to the structure of sand dunes on the Egyptian side of the border, with opposite effects on the Israeli side to which the Bedouin had no access. This case study adds a further dimension to the discussion of range management by pastoral nomads in arid and semi-arid areas.
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Several natural and anthropogenic phenomena in the northern Sinai sand sea and the northern Negev desert were caused by desiccation of the area during most of the 17th and the 18th century. The dry phase had been preceded by a wet period. It appears that the combination of several wet decades followed by a long period of desiccation was the cause of desertification processes in the area which then triggered the destruction of vegetation. There is some congruity between the wet period and the period of maximum sunspot activity, known as theMedieval Maximum, while the desiccation of the area which followed coincided approximately with the period of minimum solar activity, known as theMaunder Minimum.
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Plant species diversity was measured in a sandy area, 15 km south of Beer Sheva, with a mean annual rainfall of ca. 150 mm, and mean annual temperature ca. 20 °C. Species diversity and production of phytomass was found to increase with and stability, owing to the increase of available water with increasing amounts of silt and clay in more stable sands. Supply of nutrients and the influence of a crust of blue-green algae and mosses may also play a role.
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In 1992 the flora and vegetation of an area of linear sand dunes at Nizzana, western Negev desert, Israel, was investigated. Seven different plant communities were found and a vegetation map of the research area was produced. The plant communities were distinguished by only the dominating perennial species. Nevertheless, the results of the study indicate, that also annual species may be suitable as a tool to distinguish between desert plant communities. The results suggest, that the most important environmental factor determining patterns of plant distribution in the Nizzana research site is the structure and dynamics of the soil-surface. Vegetation cover was lowest in highly stable areas with hard surface crust or a high amount of fines in the soil (playas) and on the mobile dune tops. Highest plant cover was found at the dune bases and in areas which had been used for cultivation in former times. Mean species richness per unit area was lowest on the dune tops and highest in the interdune areas with more or less stable surface crust. Absolute number of species found was highest for the playas and lowest on the dune-tops. As most of the plant communities described for the research site are restricted to areas which are characterized by a certain surface stability it is discussed to regard some of the vegetation units as succession stages in a process of continuing stabilization of the dunes.
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Plants growing in a sandy habitat are adapted to specific stresses that differ from one habitat to another. The establishment of grasses that easily produce adventitious roots and rhizomes and develop new stems when covered by sand leads to a local decrease in wind velocity. Consequently, fine-grained particles are deposited, the amount of available water increases, and filamentous cyanobacteria became established. Aggregation of clay- and silt-sized particles by cyanobacterial filaments, and gelatinous polysaccharides excreted by their trichomes lead to trapping of these particles and to the formation of a microphytic crust. Consequent improvement of the soil moisture regime and increasing soil stability and fertility, through development of nitrogen-fixing cyanobacteria, lead to the development of different higher plant communities in the processes of plant succession. -from Author
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Germination of achenes of Artemisia monosperma is absolutely dependent on light, irrespective of temperature. Full saturation by light was obtained with 24 meter-candle seconds and more than half with 0.1 meter-candle second. Nevertheless, even with saturating irradiation, action of light was cumulative, requiring repeated short irradiation, the number depending on temperature, separated by a minimal interval. Responsiveness to light increased with progress of incubation. The cumula-tiveness and the increase in responsiveness are discussed. A gradual achievement of an equilibrium between an inactive precursor and a substance which participates in the light-induced reactions, is postulated. The stage of equilibrium, as well as the rate at which it is reached are temperature-dependent. Light-independent reactions which are triggered by irradiation may be reversed by incubation at supra-optimal temperatures, or by desiccation, and full promotion may be restored after re-imbibition or after return to optimal temperatures, by an additional irradiation. The ecological significance of the germination responses is also discussed.
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1. We report laboratory studies that aim to characterize the microphyte community composition and metabolic features of crusts covering dunes in the Negev. 2. The crusts are formed by at least one moss, four blue-green (Cyanobacteria) and two green (Chlorophyta) algal species with Microcoleus sociatus being dominant. The sheaths of the latter procaryotic alga, together with a contribution by moss rhizoides and protonemata, are responsible for stability of the topsoil crusts. 3. Following moistening of the dry crust, CO<sub>2</sub> release took place, even in the light, until positive net photosynthesis was achieved. This delay was mainly due to the high CO<sub>2</sub> buffer capacity of the soil solution. In moist crusts, growth of the microphytes soon took place, and CO<sub>2</sub> assimilation increased continuously. Net photosynthesis seemed to be adapted to relatively low light and temperature conditions. 4. Maximal photosynthesis was still possible with a crust water content equivalent to precipitation of 0.2-0.3 mm, but was suppressed at less than 0.1 mm. Dew and fog inhibition would be expected to allow photosynthetic activity and growth. Chlorophyll-related maximal rates of carbon gain were of similar magnitude to leaves of arido-active phanerogamous Negev plants. Area-related maximal rates reach more than 20% of desert shrubs. Thus, in the short term, carbon input into the ecosystem through the soil crusts can become substantial.
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A dune area of 2 km2 in the Negev (Israel) with an annual precipitation of 90 mm was mapped. The soils developed from eolic and fluviatile sediments were Arenosols, Calcisols, Solonchaks, Regosols and Fluvisols. The Arenosols of the dunes are more homogeneous in texture and salt content than the soils of the interdunal corridors: Besides the Fluvisols, also the Calcisols, Solonchaks and Regosols are stratified due to episodic flooding by a wadi, and are rich in salts and lime. The soils are of minor development. Aggregation and enrichment of lime, enrichment and movement of salts, and the enrichment of organic substances are indications of soil formation. The distribution of salts within the profiles was calculated by their solubility. High and low soluble salts appear together in thin layers of Calcisols, Solonchaks and Fluvisols, while the most-soluble salts appear in deeper layers. The salts, therefore, must have accumulated by lateral movement, precipitation and temporal flooding. Influence of groundwater can therefore be excluded. The Arenosols also show the same sequence of salt types, indicating the accumulation due to precipitation and eolic mass movement. Abandoned arable land sites did not show any different soil characteristics from the unused soils. On the basis of the distribution of salts in the profiles and soil types genesis and classification of the soils is discussed.
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In the arid sand dune ecosystem of Nizzana, northwestern Negev, Israel, three perennial species were investigated far concentrations of the elements C, N, S, P, Ca, Mg, K, Na and Cl. From the dune tops (crests) to the dune valleys six different ecotopes (habitats) were discerned where the sampling took place. The soil conditions are known due to previous investigations of H.-P. Blume and his coworkers. The species Anabasis articulata and Cornulaca monacantha (both Chenopodiaceae) showed considerable variation of element contents;according to the ecotopes. In some ecotopes of the dune valleys they showed higher contents of sodium and chloride than in the ecotopes of the proper dune, and by Na/K ratios of > 1 they indicated slightly halophytic character. The glycophyte Thymelaea hirsuta (Thymelaeaceae) exhibited very low element concentrations which practically did not change between the ecotopes. The conclusion was drawn that Thymelaea is characterized by a higher selectivity of ion uptake than,the two other species.
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Four ecomorphological types are recognised in the ‘Old World’ genusStipagrostis: (1) species confined to areas of high sand mobility, which require accumulating sand cover for survival; (2) species of sandy areas which may be covered with sand or the sand may be removed; (3) species confined to stable or slightly eroding sand sheets; and (4) annual species of areas with less than 50 mm rainfall annually. Most species have a plumose diaspore which glides easily over long distances. Diaspores of a few species have a pappose awn, and are dragged on the dune surface to a leeward slope where they are covered by sand.
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This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.
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The water regime in the sandy dunal area of Nizzana, north-westem Negev Desert, Israel, is highly dependent on a fragile cryptogamic crust only several millimetres thick. This crust develops due to the presence of Cyanobacteria which agglomerate the sand grains and trap aeolian dust particles. Not only does this semi-permeable crust increase runoff but the water which does infiltrate the soil is protected from excessive evaporation. This study presents quantitative measurements of the physical properties of the crust which are important to the water regime in desert dunal areas—the granulometry, porosity and water retention capacity.The grain size distribution shows a concentration of silt and clay in the crustcompared to the sands just beneath the crust. The microporosity (measured using a mercury pore sizer) shows that approximately 40% of the access pores can be blocked by the swelling of Cyanobacteria trichomes as they absorb water, which limits rainwater infiltration. These observations concur with rain simulation experiments made in the field. An evaporation phase was simulated in the laboratory in order to quantify the water retention capacity of the crust and compare it with that of other sediments, in which the algal mat is not intact, or absent. At the end of the cycle, the crust was found to contain approximately ten times more water than the other samples.
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Dwarf shrubs play a predominant role in the natural vegetation cover of Kuwait, with the chenopod Haloxylon salicornicum widespread in northern parts of the country. A number of influences, largely anthropogenic in nature, have led to serious land degradation in many areas. The present study deals with species diversity and other floristic attributes of the ephemeral vegetation in a sand-depleted Haloxylon salicornicum community, contrasting the situation of miniature dunes formed at the base of shrubs with that of the interdune space. The importance of such dunes and their associated shrub cover as a protection against further land deterioration is examined.
Outline of vegetation of the northern Negev
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Zohary, M. & Feinbrun, N. (1951). Outline of vegetation of the northern Negev. Palestine Journal of Botany, Jerusalem Series, V: 96–114.
Studies on the flora of northern Sinai
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Gibali, M. (1988). Studies on the flora of northern Sinai. M.Sc. thesis, Cairo University. 403 pp.
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Danin, A. & Nukrian, R. (1991). Dynamics of dune vegetation in the southern coastal area of Israel since 1945. Documents phytosociologiques, N.S.XIII: 281–295.
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Berkowicz, S.M., Blume, H.P. & Yair, A. (1995). The Arid Ecosystem Research Centre of the Hebrew University of Jerusalem. Advances in GeoEcology, 28: 1–11.
The Arid Ecosystem Research Centre of the Hebrew University of Jerusalem
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Dynamics of dune vegetation in the southern coastal area of Israel since 1945
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Vegetation of Israel and adjacent areas
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