Nahal Secher

Published: February 18th, 2013 | Updated: 14/01/15

6. The sands of Nahal Secher (precipitation 150 mm)

When looking from Har Tsavoa northwards (Fig. 9.1.29) the sand “tongue” of Nahal Secher (No. 5) stands out. The chalk hills between Beer Sheva (Fig. 9.1.30, No. 4) and Tsomet HaNegev (No. 6) are continuously covered by these sands. These sands look prominent also in satellite images (Figs. 9.1.30, 9.1.31). The sand cover improves water penetration which leads to an increase in vegetation cover. Sand also covers the channels of wadis which are clearly seen in units 4 and 6. The wadis draining water out of the area disappeared from the sandy area covering the chalk hills. Until the 1970s the sands of Nahal Secher were mobile. Visitors, including botanists, could stop their vehicles and see and point out the vegetation of desert dunes. Afforestation of the sands west of the asphalt road arrested the sands. Plants and landscapes associated with the sand disappeared. At present one has to drive several dozen kilometers in order to learn about such sands and plants. The process of sand stabilization is accompanied by changes in the development of several unique plant communities. Since we cannot show them here, we shall present only a limited number of important sand plants (known in literature as psamophytes).

Stipagrostis scoparia is the plant best adapted to live in mobile sand at the precipitation range of 100-150 mm (Figs. 9.1.32, 9.1.33). When sand covers its stems, roots develop from the buried nodes, new shoots sprout from the buried buds, grow above the sand which covered them, and gradually form a hillock (which is known in professional literature as “nebka”). After blooming, each diaspore (dispersal unit) contains one seed and three hairy awns equal in length (Fig. 9.1.32, bottom right). The awns function as a parachute. If the paratrooper does not disconnect himself from the parachute after landing he may be dragged on the soil in the direction of the wind. The Stipagrostis diaspore is dragged on the sand surface until it passes the tip of the dune. It lands on the slip-face of the dune where wind velocity is zero. It becomes covered by sand grains arriving in saltation. As the years pass the S. scoparia population becomes denser and changes the wind velocity at the dune surface.

Artemisia monosperma germinates in the area, increases vegetation density, and stabilizes sand more efficiently. Airborne dust becomes trapped in the sand surface and filamentous cyanobacteria develop and glue themselves to sand and dust particles (Fig. 9.1.34). The decreasing wind velocity enables additional dust trapping and amelioration of the sand’s water regime. Dark colored vegetation develops (Fig. 9.1.35), partially covered by the mobile longitudinal dunes of light colored sand.

Fig.9.1.29: Horizontal view from Har Tsavoa towards Beer Sheva (No. 4, houses close to the picture’s horizon). Beyond loessial plains and hills (No. 6) the dark growth on the eastern tongue of Haluza sands stands out – Nahal Secher sands (No. 5)

Fig.9.1.30: A vertical satellite view of Nahal Secher area; numbers as in Fig. 9.1.29

Fig.9.1.31: A vertical satellite view of Nahal Secher area; numbers as in Fig. 9.1.29. Resulting from full infiltration of water into the sandy soil, there is no run-off and wadi channels are missing in unit 5

Fig.9.1.32: Sand mounds (nebkas) built by Stipagrostis scoparia which grow above the sand burying them. Lower right corner shows a section of about six dispersal units ready to be moved by winds along the sand dunes

Fig.9.1.33: Longitudinal dune with nebkas of Stipagrostis scoparia

Fig.9.1.34: Stable dune surface with sand grains attached to the filamentous cyanobacteria

Fig.9.1.35: Sands in the western Negev. Longitudinal dune covered with nebkas of Stipagrostis scoparia with light sand between them. Sand in the area between the mobile dunes is dark colored and has no nebkas

Following the renovation of highway No. 40, the only place where one may stop safely to view Nahal Secher sands is the gasoline station going southward. Most of the area is disturbed by being frequently driven over by all-terrain vehicles. However, these people have not succeeded in destroying everything in that area. The basic situation where sand covers the limestone hills (Fig. 9.1.36) may still be seen there. The top of the limestone hills may be recognized by its loessial soil rich in stones, surrounded by sandy soil patches with no stones. Large shrubs of Noaea mucronata (Fig. 9.1.13) accompanied by Thymelaea hirsuta populate the sandy soil. Some 200-300 m west of the gas station there are remnants of the British asphalt road. In the spring of a rainy year, west of the road, one can see plants of Iris mariae blooming (Fig. 9.1.37). Plantago crypsoides, among others, typically grows on the limestone rich in patches of loess soil (Fig. 9.1.38). In the neighboring sandy soil a new species of Plantago was recently discovered and published (2011).

Plantago sabulosa, the new species (Fig. 9.1.39) differs from P. crypsoides by having 1 mm thick peduncles (not 2-3 mm) and inflorescences longer than the leaves (not inflorescences shorter than the leaves). As far as we know the new Plantago is endemic to the Halutsa sands (including Shunra sands and sand near Nitzana). Its primary adaptation to sands is the ability to remain alive even when a considerable part of its body is buried in the sand (Figs. 9.1.40, 9.1.41). Plantago crypsoides (Fig. 9.1.42, right) and P. sabulosa (Fig. 9.1.42, left), that were raised in adjacent pots from seeds collected near Mash’abbe Sade, differ significantly in the ratio of leaves/inflorescences. P. sabulosa is adapted to occasional burial by mobile sand. I hope that future genetic research will find the relationship and distance between the two species.

Fig.9.1.36: A schematic presentation of the area in Ramat Beqa sandy area. Plantago crypsoides grows on the limestone patch; the nearby sand supports Plantago sabulosa

Fig.9.1.37: Iris mariae, an endemic plant, is confined to the Western Negev sands and grows on stable sand west of the gasoline station of Ramat Beka

Fig.9.1.38: Plantago crypsoides from the top of a limestone hill (cf. Fig. 9.1.36), a blackish plant of the previous year with a green and blooming plant of the present year

Fig.9.1.39: Plantago sabulosa which was growing several meters away from the plant of Fig. 9.1.38

Fig.9.1.40: P. sabulosa buried by mobile sand; the tips of the inflorescences keep developing

Fig.9.1.41: P. sabulosa buried by sand after ripening two inflorescences. It continues to develop by leaf tips and inflorescences that are above the sand

Fig.9.1.42: Plantago plants whose parents grew close to each other near Mashabbe Sade and were raised in the same pot in Jerusalem. On the left two individuals of P. sabulosa with inflorescences longer than leaves and on the right two individuals of P. crypsoides with much shorter inflorescences