Caesarea Sands from Above; Kurkar and Hamrah Soils; Soil Texture; Conclusions
10. Caesarea Sands as Seen from Above
The experts who made the satellite image on the left (Fig. 4.1.58) assigned the red color for the infra-red radiation returning to the camera in space from the green areas on earth. In the image on the right, produced by another laboratory, the experts tried to assign colors that are similar to the actual colors of the land. In the area marked 2 in Fig. 4.1.58, we see the “tongue” of active sand near Caesarea. This sand tongue developed in the distant past and owes its existence to the strong winds passing regularly through the opening in the coastal hills between Nahal Hadera (4.1.58/1) and Sdot Yam.
In this sand tongue there are considerable areas of mobile sand populated by Artemisia monosperma – Polygonum palaestinum (Fig. 4.1.59). In the aerial photograph (Fig. 4.1.60) it is evident that the tongue is composed of many small tongues. When starting to examine sand stabilization (Figs. 4.1.15-4.1.18) we saw how such tongues are formed. Two generations of sand tongues dominated by A. monosperma and P. palaestina are marked by 1 (the younger) and 2 (the older) in Fig. 4.1.64. They cover an old sand sheath (No. 3) older than both of them and populated with H. stipulatum – R. raetam association. In Fig. 4.1.65 we are looking from the H. stipulatum – R. raetam association (1) towards the covering A. monosperma and P. palaestina association (2).
Before the penetration of the sands into the Kurkar (= calcareous sandstone) hills near Caesarea, this area was covered by woodlands of Pistacia lentiscus – Ceratonia siliqua association. Such woodland has survived near the junction of highway 2 and highway 65 (Fig. 4.1.62/4). In Fig. 4.1.62 it is clear that the mobile sand killed all the trees in its way by covering them with a deep sand layer. Sand tongues that covered considerable areas of the P. lentiscus – C. siliqua association (Fig. 4.1.63/3) are at present populated by the H. stipulatum –R. raetam association (Fig. 4.1.63/1; Fig. 4.1.64/3). In Fig. 4.1.63, the A. monosperma and P. palaestina sand tongue, marked 4, is seen from afar.
11. Changes in the Soil Texture
The sand that comes from the sea contains a mixture of grains of varying sizes. The quantitative relationships among these grains (soil texture) typify each of the succession stages. The most important components are silt and clay (Fig. 4.1.66). The relationship between vegetation cover and the percentage of the fine grained particles is presented in Fig. 4.1.67.
It shows the dependence of the one on the other, which can be explained in the following way: an increase in the percentage of fine grains has the effect of improving the moisture regime; an improved moisture regime allows for the growth of denser vegetation, which traps dust more efficiently. At the beginning of the process, when the sand is mobile, winds remove the fine grains from the system. At the soil surface of samples 1 and 2 (Fig. 4.1.66), 1-2% of fine grains are contributed by silt alone. We shall consider such texture in the following profiles as belonging to “dune sand.”
The soil surface of a dense Artemisia monosperma association (No. 3 in Fig. 4.1.66) already traps a considerable amount of silt and clay, whereas at a depth 15-17 cm the dune sand is poor in fine-grained particles. The most prominent changes during the succession take place at the soil surface (the top left row of columns in Fig. 4.1.66). There, a gradual increase in the percentage of silt and clay is prominent. In the last stages of the succession the fine particles contribute 12-18% of the soil surface. The efficiency of dust trapping increases with the increasing density of vegetation (Fig. 4.1.67). Studies of the deposition of dust originating from the desert reveal that there is a constant annual deposition of ca. 0.1 mm across the whole country.
From the time sand becomes stable and vegetation becomes dense, there is a constant addition of dust and the amount of dust in the soil surface may be used as a chronometer for comparing the relative age of soil samples. When comparing the texture at a depth of 1 meter, profile 8 (in Fig. 4.1.66) looks unusual in having 14% of silt and clay. We may now use our findings, presented in Fig. 4.1.66, to interpret the significance of this deviation. Profile 8 was dug below dense vegetation of Pistacia lentiscus and Calicotome villosa. The texture deviation indicates that before the sand covered this area there was similar vegetation here, which efficiently trapped dust and raised its percentage to 14%. The mobile sand did not kill the plants of the ancient site 8 and the survivors continue to trap dust as seen in depths of 0-2 cm and 15-17 cm. Dune sand which did not change significantly is seen at a depth of 50-52 cm.
4.12. Changes in soil color
During our study of plant succession in Caesarea sands (Danin & Yaalon, 1982) we saw changes in the soil color from the pioneer- to the climax vegetation. We used a simple tool for teaching in the field, developed by the late Gideon Halevy (the Acacias researcher who was killed in action in the Yom Kippur War); we shall use it here as well (Fig. 4.1.68). A transparent bottle is filled with a sand layer 2-3 cm high, of each plant community visited and each layer is marked with an appropriate number. Sand that comes from the sea is white and is trapped in this color by the Ammophila association (Fig. 4.1.68/1). It is still white in the first nebkas of Artemisia monosperma (Fig. 4.1.68/2), but in places with an increasing cover of A. monosperma, where sand movement ceases, black flakes of humus start to develop in the soil.
A. monosperma stands with Retama raetam shrubs show additional changes, mainly under the Retama shrubs. Stands of the Helianthemum stipulatum – Retama raetam association in the sites where Trifolium palaestinum and Aegilops sharonensis grow have considerably darker soil under the R. raetam shrubs (Fig. 4.1.68/5a). The soil at a depth of 20-30 cm in the same profile (Fig. 4.1.68/5b) is light colored. These spots of dark soil support Mediterranean plants that are not considered as “sand plants” (psammophytes), such as: Umbilicus intermedius (Fig. 4.1.57), Cyclamen persicum, Sedum species, and typical Mediterranean vines. A big jump in the gradual color changes take place in the shade of P. lentiscus bushes that have germinated in the shade of R. raetam shrubs. The effective, denser shade of the pistachio induces the rapid development of humus. At these sites, at a depth of 50 cm there is white dune sand. In the shade of remaining carob trees, left from the Pistacia – Ceratonia association that covered the sandstone (Kurkar) hills, the entire soil profile, to a depth of 65 cm, is almost black from the great quantity of humus.
4.13. Changes in the amount of calcium carbonate in the soil
The percentage of calcite (CaCO3) in the soil is presented in the column diagrams of Fig. 4.1.69. Sand deriving from the sea may be rich in calcite, originating from broken sea shells and limestone rocks; air-borne dust may contain up to 40% calcite. The most important factor for de-calcification is the leaching of the soil by rain water. In addition, the humus formed in the shade of plants is washed by the rain water, and small quantities of calcite are absorbed by plants and become fixed in their lignified skeleton. Thus, the gradual decrease in the quantity of calcite in the soil is seen throughout all the profiles from left to right in Fig. 4.1.69. The lowest values of calcite content are seen in the soil surface of site 7, dug in the P. lentiscus – C. villosa association. A similarly low level is found in site 8 at a depth of 1 m, conforming with the findings in soil texture (chapter 4.11). It proves that the layer of No. 8 at 1 m was functioning as the soil surface of vegetation, resembling that of No. 7. The high quantity of humus in the P. lentiscus association prior to being covered by a sand dune, assisted in the efficient dissolution of the soil’s calcite. The sand cover above that layer contains high quantities of calcite as expected from young dune sand, whereas the top layer is de-calcified underneath the dense vegetation. Profile 9 (Fig. 4.1.69) was dug above deteriorating calcareous sandstone; therefore the amount of calcite at a depth of 50 to 65 cm is much greater than that in the upper soil layer (0 to 22cm).
14. Kurkar and Hamrah Soils
The decisive statement of my geologist colleagues, that the source from which the Kurkar (calcareous sandstone) sands developed was different from that of the Hamra (red loam) sands, made me feel bad. In order to resolve my disagreement with their hypothesis, I followed Charles Darwin’s famous statement: “The present is the key to the past.” In the study I carried out with Prof. Dan Yaalon (1982), we learnt that sand from the same geological period changes in one kind of plant succession from rich in calcite and poor in clays, to poor in calcite and rich in clays. Under different environmental conditions the sand remains rich in calcite and poor in clays. The succession in Caesarea causes the soil surface sand to change from having 23% calcite and 1% silt in the Ammophila arenaria association, to sand with 1-2% calcite, 8% clay and 4% silt in the P. lentiscus and C. villosa association. This process functioned for a period of 1500-2000 years, as can be determined by the remains of archaeological sites in various places in the country. The product of the plant succession processes in Caesarea is parent material that after additional changes will become a Hamra type of soil provided that the process continues for another few thousand years. Plant succession on sands in the southern coastal plain does not bring about the development of vegetation with large quantities of humus. Calcite dissolution is not so efficient in this environment and nor is dust trapping. The sand retains its original chemical and textural composition throughout the process of sand stabilization in dry lands. This material may become Kurkar.
In South Africa, near Port Elizabeth, is a large river that brings vast quantities of sand to the coast. A visit to this coastal area added another dimension to the theory I constructed. The quantity of sand and the rate of its transportation are much greater than the rate of change of the substratum by vegetation through plant succession. Hence, such sands may also turn into Kurkar.
15. Conclusions and summary
Sand reaching the Mediterranean Sea from neighboring desert areas becomes transported by sea currents and is deposited on the beach. After drying out, the sand is transported inland by strong winds and accumulates in sand dunes. Seeds of Ammophila arenaria transported by wind and trapped in the moving sand germinate in the rainy season. They grow despite and with the aid of the sand that partially covers them.
They expand by the branching of their stems and by rhizomes, and form mounds (nebkas). The efficiency of sand trapping increases with the increasing density of leaves and branches. Sites suitable for the germination of Artemisia monosperma are formed on the leeward sides of the Ammophila nebkas. Decreasing wind velocity, influenced by the denser crown of A. monosperma, stops the sand movement more efficiently. Humus is formed in the shade of the dense plants and together with fine-grained particles trapped below the plants, the moisture regime is improved. In the areas of stable sand occupied by A. monosperma part of the area becomes populated by Helianthemum stipulatum and Retama raetam. Thin, dry branches, falling seasonally, accumulate in the shade of the Retama shrubs. When rotting, they become a nutrient-rich microhabitat populated by mosses. The mosses trap dust efficiently and thus contribute toward upgrading the moisture regime in their close vicinity. At this stage of the plant succession sand mobility ceases and air-borne dust, derived from the surrounding deserts, becomes trapped and added to the system at a constant rate.
The Retama raetam shade becomes a site of dramatic change, where plants that are not sand plants (not psammophytes) establish themselves. Shrubs and vines confined to the maquis are brought to these sites by birds consuming the fruits in the maquis. In a few sites where Pistacia lentiscus germinated and developed, the humus production becomes more efficient. The soil becomes darker and the list of maquis plants increases in the formerly bare sand dunes. As the number of P. lentiscus shrubs on the former dune increases, shrubs of Calicotome villosa establish themselves among the pistachios and close off the area for annuals by shading it. This soil, rich in humus and clay, may become a habitat in which carob seedlings can become established and pass their first critical years. A few of these carobs may reach adult size. The soil in each of the stages described above has a typical texture. According to the soil-forming (pedogenetic) trends dealt with above, that have taken place during the last 1000-2000 years, we may surmise that after another 10,000 years of such plant succession, typical Hamra will develop in these areas.
No area exists in Israel in which dunes that were covered with plants have survived for 10,000 years and we may only hypothesize. The sand that arrived at Israel’s beaches was rich in calcite and poor in clays, and changed during the plant succession to become a soil poor in calcite and rich in clays. These latter properties characterize the Hamra soil. When sand stabilization takes place in areas where annual rainfall is less than 300 mm, or in places where the rate of sand input to the land is higher than that of Caesarea, different results may be expected. The biological-physical systems that decrease the calcite quantity and increase the amount of clays in the soil do not approach the level of the processes in Caesarea. Sand stabilized in the second mode develops into soil that resembles that of the parent material, which is rich in calcite and poor in clays. Such parent material developed during the Pleistocene into calcareous sandstone also known as Kurkar.
Danin, A. 2005. The sandy areas of Caesarea, a rare situation of alpha and beta diversity linked by plant succession. Israel J. Pl. Sci. 53: 247-252.
Danin, A. 1997. Shootborne roots – an adaptive organ in sand dunes. In: A. Altman & Y. Waisel (eds.) Biology of Root Formation and Development. Plenum, New York, pp. 221-226.
Danin, A. and Orshan, G. (eds.) 1999. Vegetation of Israel. I. Desert and coastal vegetation. Backhuys, Leiden, 341 pp.
Danin, A. and Yaalon, D.H. 1982. Silt plus clay sedimentation and decalcification during plant succession in sands of the Mediterranean coastal area of Israel. Israel J. Earth Sci. 31: 101 109.