Erosion in Sands and the Impact of Sea Water Spray

Published: October 19th 2011 | Updated: 14/01/15

1. Vegetation of sand under wind erosion conditions

Most of the area protected from human activity reveals processes of sand stabilization. Vegetation cover increases during plant succession processes. However, there are small patches of soil, randomly distributed, where excessive sand erosion took place, leading to the development of retarded vegetation with special plant composition. Studies in coastal areas in Europe revealed that there are local events of whirl-wind, where air moves in circles and sucks large quantities of small particles from the soil.

This process resembles tornado storms where air-bodies are much larger and destructing forces are much higher. There are patches as that seen in Fig. 5.1.1, where a group of Artemisia monosperma with exposed roots develops on poor soil without the companions expected in an area with stable sand and dominated by A. monosperma. Such a situation is a result of local erosion caused by whirl-wind. Such climatological events are not common but their impact extends to a long time. Two species which passed evolutionary adaptation to the processes of wind erosion grow in the coastal- and the desert sands. These are Echiochilon fruticosum and Moltkiopsis ciliata (both of the Boraginaceae). In the desert sands there are additional two species which have a similar life cycle and adaptation to sand mobility.

All these four species have the ability to produce stems carrying leaves from exposed roots (Figs. 5.1.2, 5.1.3). Thus, when a root is exposed by whirl wind activity, twigs develop from the roots. The leafy twigs locally reduce wind velocity and lead to sand accumulation around the root-borne shoots. I liked to explain it to my students as a “self service” restoration of a natural damage. Lateral roots with such shoots that become disconnected from the mother plants are in fact a product of vegetative reproduction.

Fig.5.1.1: Sandy area after erosion by strong wind. Shrubs of Artemisia monosperma remained with exposed roots which became black and were unharmed due to their cork layer protecting them from drought

Fig.5.1.2: Moltkiopsis ciliata in an area where sand erosion exposed its roots. New stems sprout from the exposed roots.

Fig.5.1.3: Moltkiopsis ciliata – new stems sprout from the exposed roots.

Fig.5.1.4: Aerial photograph of the Sharon coastal area: 1. Nahal Alexander, 2. The sand tongue of the Artemisia monosperma – Polygonum palaestinum assoc., 3. Remnants of ancient agriculture between the gasoline station and the sea, 4. Ceratonia siliqua – Pistacia lentiscus assoc. covered by sand.

2. Areas of ancient agriculture

A large area north of Nahal Hadera and south of kibbutz Sdot Yam functioned, according to the archaeologists (No. 3 in figs. 5.1.4 and 5.1.5) as intensive agricultural plots. The rectangles are seen in the aerial photographs due to the existence of light-colored boundaries among the dark colored squares center. The look of these squares resembles the agricultural areas between Rafah and El-‘Arish, locally known as “mawasi”. Sand ramparts separate large agriculture beds which are irrigated by shallow wells reaching the high underground water.

The rectangles seen in figs. 5.1.4 and 5.1.5, north of the electric power station Orot Rabin, are assumed to have been similar mawasi. The agricultures 1500-2000 years ago did not dig in the sand and their ramparts were made of the refuse soil of the town Caesarea of the past. The soil of the ramparts contain a high proportion of dust, it is dark colored when compared to the sand arriving to the area at present. It contains pottery fragments and stones of Italian marble. The latter are not original Israeli stones and are good indicators for their origin as refuse of the old city. In my early life I was use to visit my cousin Oded, who was one of the founders of Kibbutz Sdot Yam. I was use to go to these ancient refuse hills and search for ancient coins. I did not find many coins because my “teacher” in this profession, Aaron Wegman, a friend of my cousin, already collected the big ones which are saved in the kibbutz’ museum.

I was use to call the soil of the refuse ramparts “pottery soil” and used them for an introduction to the sand accumulation processes. Ammophila arenaria plants which germinate and establish themselves on hills of the pottery soil trap and fix airborne sand grains and grow above it. When making a profile in such a sand covered hill one can see the sharp transit between the white newly arrived sand and the dark colored pottery soil. When I started to teach in this location in the 1970s the low areas among the ramparts were covered with shrubs of Retama raetam and Artemisia monosperma and their companions.

Since then the invader Heterotheca subaxillaris (Fig. 5.1.8) out-competed many plants of these depressions. H. subaxillaris was introduced from western USA by Dr. Tsuriel who constructed an experimental station for sand fixation in Acco Plain. The plant which became invader did not obey the intentions of the introducer and expanded by its own means. It covers at present considerable sandy areas along the coastal plain. The ramparts of the pottery soil support also Artemisia monosperma shrubs which trap and fix mobile sand. Many soil profiles displaying this activity of sand trapping and fixation along the path between the gasoline station and the beach.

Plants which accompany A. monosperma along the sequence of associations of the plant succession grow also on the pottery soil. They use the amelioration of soil conditions which took place by human activity hundreds of years ago. One of these plants is Cyperus capitatus (Fig. 5.1.9). It occurs on the eastern ramparts, close to the gasoline station. It inhabits a layer of shallow sand, less than 10 cm deep. It has thin horizontal rhizome, all the leaves have a similar width; its inflorescences are carried on peduncles 10-30 cm long.

Closer to the beach, some 50 to 100 m east of the beach line is the site where the holotype of Cyperus sharonensis (Fig. 5.1.10) was collected. This plant, which was described as new to science in 1995, has thick rhizomes growing obliquely. Its lower leaves are wide (Fig. 5.1.10, right) and those accompanying the inflorescence are narrower. The inflorescence may be 50 cm tall and resist cover of the entire plant by sand.

Fig.5.1.5: Aerial view of Caesarea area in 1945: 1. Nahal Hadera, 2. the sand tongue of Artemisia monosperma – Polygonum palaestinum, 3. agricultural plots, 4. Ceratonia – Pistacia lentiscus association.

Fig.5.1.6: A view from the bottom of an ancient agricultural plot towards its wall. Most stones are fragments of ancient pottery among the Retama raetam shrubs.

Fig.5.1.7: Surface of “pottery soil”.

Fig.5.1.8: Heterothecca subaxillaris – an invasive adventive plant of North American origin out-competing local plants. It was brought to Israel as a sand stabilizer and spread to many sandy areas.

Fig.5.1.9: Cyperus capitatus. A dwarf plant with one type of leaf that is slightly longer than the peduncles.

Fig.5.1.10: Cyperus sharonensis. The lower leaves in the rosette are wide; upper leaves are narrow. The transition between the two types is sharp and therefore many plants are seen with two leaf types. Inflorescences are carried on peduncles much longer than the leaves.

Fig.5.1.11: Cyperus sharonensis. Growing in deep sand and having long, thick oblique rhizomes.

3. Vegetation of the sea-water spray zone along the beach

When I was a student in the 1960s there was a prevailing opinion among botanists that one of the most important factors affecting vegetation poverty of the coastal plain is the sea water spray. When studying the distribution of plants in the coastal plain, I found that plants adapted to sea-spray hazards occur in a strip of a few dozens of meters. Chemical investigations of rain water showed that a minute quantity of sea salts is carried by the rain water dozens of kilometers east of the sea, but the impact of sea-water spray as a factor causing ecological stress is of a limited extent.

Every shrub of Artemisia monosperma growing in the sea-spray belt along the Mediterranean has cauterized leaves in their western side or seaward side and almost regular growth in their eastward side. A. monosperma shrubs growing more than 50 m away from the beach look symmetrical and develop similarly in all directions. In my first teaching years I was use to get summary reports from many students claiming the high importance of the sea-spray factor.

I stopped showing the sea-spray belt in my excursions to Caesarea and restricted the field lessons to sand stabilization processes. Students who did not pay enough attention to the field lessons copied to their reports from old literature or from reports of students from previous years the “spray” ideas. Thus the battle of sand against salt-spray continued. In order to deal with the sea-spray properly I postpone the discussion for an independent chapter where plant communities of this zone on various soil types will be discussed in detail.