Ramat Bet Hakerem: Rock Type and Lichens
The aim of this chapter is to display selected sites which aided me in presenting many subjects to pupils, students and teachers on various occasions.
1. Ramat Bet Hakerem, Jerusalem
Ramat Bet HaKerem was selected as the first to be discussed for the following reasons:
- Before being turned into a densely built-up urban area, with ornamental plots planted with non-indigenous plants and irrigated, this area was a rocky hill very rich in natural history phenomena. In my childhood I spent many days in this place, learning to read nature in its special language – learning processes which continue even today.
- The rocky terrain in that area assisted me in teaching at the university and when giving special courses to school teachers. A geologist friend told me that the area is regarded as "the rock reserve." Visiting the area, I saw that, even with the best of intentions, there are people who harm the reserve in different ways. They are not aware of the additional natural treasures present there and harm the natural vegetation by planting ornamental plants and irrigating them.
- When you read the "book of nature" written in its various languages, you can only conclude that it is a "microcosmos," which justifies its selection as the first place to be dealt with.
1.1. The rock type of the reserve
Ramat BetHakerem is built on top of a layer of hard dolomite known as Vradim Formation or by its former name: Mizi yahudi. Under the Mediterranean climatic regime, this type of rock weathered into karstic landscape (Fig. 2.1.1), and was not used for cutting and building before the 19 century. For further information please read this article (Hebrew).
When the new suburbs of western Jerusalem were built and stones were cut from this rock, the Arab quarry workers and the stone cutters started to call it "The Rock of the Jews" = Mizi yahudi. When I began studying these rocks I talked with one of the famous Jewish stone cutters – Mordechai Ish-Shalom (former mayor of Jerusalem from 1959 through 1965), who lived in the Poalim (workers) suburb (HaBanai and HaSattat streets of today = "house builder" and "stone cutter" respectively). He worked in the quarries opened near his home (Fig. 2.1.2). The walls of the Bet HaKerem School and other houses in Jerusalem were built with stones taken from this rock formation. During recent decades the area has changed considerably; most of the rocky terrain has become flat ground, with no rock outcrops. Most large rock-blocks (geologists call them "boulders") were taken to other parts of the city or to the country, and the area was turned into built-up urban land (Figs. 2.1.3-2.1.5).
1.2. The lichens growing on the rock, inside it, and the derived micromorphology
The structure and activity of lichens were dealt with in detail in the website in "Plant Stories" chapter F, sections 6-8. The information brought here is partial and may be a local description of the specific situation dealt with here. I recommend reading the basic chapter first and then reading the following chapter.
Lichens are organisms composed of algae and fungi, living in symbiosis. The slightly inclined rock outcrops facing north are populated by epilithic ("on-rock") crustose lichens (Figs. 2.1.6/1 and 2.1.9). They form the white or black crust on the rock and when wetted with water or saliva and the crust is scratched with a finger-nail, the green color of the lichen's algae is revealed. The rock surface below these lichens is relatively smooth in the moist- and the semi-desert parts of the country (cf. "Plant Stories" chapter F section 6). The lichen crust on the rock prevents the direct contact of rain drops with the rock. Weak points, such as soft rock patches, joints, and fissures, are protected from weathering by the lichens. Thus, rain water reaches the actual rock only after wetting the 1-2 mm thick lichen crust. The entire rock surface weathers at the same rate and remains smooth (1 in Figs. 2.1.6, 2.1.7 and Fig. 2.1.9).
Rock parts facing south, sloping gently (Fig. 2.1.6/2), support endolithic lichens which look gray. Scratching the surface with a finger nail will do nothing; scratching with a knife will expose the green algae which are situated less than 2 mm deep. The fungi cells are situated inside the rock and their tips (microscopic in size) reach the surface. Influenced by solar radiation, the fungal cells produce dark pigments on the rock surface. Since they do not cover the entire surface but are situated among the minute white crystals, the entire rock looks gray in the area dominated by endolithic lichens. In addition to the color, the latter have a "jigsaw-puzzle" appearance (Fig. 2.1.6/2). Each area unit (a polygon) in this jigsaw is an individual thallus of lichen.
At the meeting zone of two lichens there is an elongated depression. In that area there are only fungal cells (well demonstrated in photos, in "Plant Stories" chapter F, section 8). However, fungi and algae are found together at the center of each lichen thallus. When the rock surface is wetted by rain water, the lichen returns to life after its drought dormancy and resumes its biological activity. When wetted at night the entire surface breathes, releasing CO2 into the water, which becomes a weak acid. When wetted during the day hours, the algae are active in photosynthesis and consume much of the CO2 available. Thus, weak acid remains near the rock surface near the lichen margin, for twice as long as it remains at the lichen center. Snails living in the rock habitat emerge from their hiding place to the rock surface and scrape the rock with the lichens inside. They prefer to scrape the area at the meeting zone of two lichens. As a result of these two processes small channel are formed. The process of the establishment and growth of the endilithic lichens and the formation of the jigsaw-puzzle like patterns continues for hundreds and thousands of years. If part of the rock is broken, the damage will be visible for a very long time. Many stone blocks which were quarried in the distant past are still without the jigsaw pattern of the rocks which "aged" without disturbance.
Climatic changes which took place tens of thousands years ago are marked in the rocks and shown in Figs. 2.1.7-2.1.9. As we saw in Fig. 2.1.7/1 the surface is relatively smooth whereas in Fig. 2.1.7/2 there are many pits. In our discussion of the biogenic weathering in the desert ("Plant Stories" chapter F, section 8 & section 14), areas with less than 200 mm mean annual rainfall are characterized by pitting. Micro-organisms establishing themselves in isolated places on the rock surface cause faster weathering near their microscopic body; the result is the formation of pits. As the years pass, the pits meet and create a micro-landscape typical of deserts. Various organisms there cause the pits' floor to appear perforated, like a sponge (under microscopic enlargement). However, in the Ramat Bet HaKerem rocks the pits' floor has endolithic lichens (jigsaw pattern). The conclusions of these findings are that these rocks faced desert conditions with 100-200 mm mean annual rainfall, when pitting took place. Later, when the climate became similar to that of the present, endolithic lichens covered the entire south-facing inclined surfaces. The former desert-induced pitted microtopography, with spongy floor of the pits changed now into pits with endolithic lichens in their floors. These findings turn the reserve area into a display of documentation showing considerable climatic changes.