Bulletin 13 - March 1981: ENHG Field Trip - Suweihan Road



ENHG Field Trip - Suweihan Road

The first ENHG Field Trip of 1981 took place on 9th January. Some two dozen members turned up at a pre-arranged spot about 36 km east of the new Abu Dhabi Airport Roundabout. Overnight dew had largely dried out and the sun was well up when the group plus children assembled near an artificial pond on the north side of the road. There was a northerly breeze that increased during the morning, but it was noticed from the lie of the sand and dunes that the predominant wind of the region was from the opposite direction.

The pool was gouged out in the late seventies to facilitate road-building operations, and has never to our knowledge dried out, even during the hottest part of summer. In spite of its very high salt content (parts of the bed were encrusted with dirty white salt), it has been used by local animals in the past. On this occasion the amount of tracks surrounding the pool was much reduced, which may imply an unacceptable increase in salinity or a decrease in the number of animals locally. Though never more than a few centimeters deep, the pool contained thousands of microscopic larvae, all apparently in good health judging from their activity. Their identity was not established, but there were a number of dragonflies flying in the immediate vicinity.

The group split into three teams and moved off southwards on diverging routes over the low dunes. The idea was to fan out over a distance of about a kilometer and then link up. Several natural history interests were represented, including fauna, flora, geography and geology. The primary objective was to record the status of the local environment in early January.

The commonest plant around the pool was Hamada elegans (= Haloxylon salicornicum), a straggling sand-stabilizing bush that was mostly in seed. There were no flowers. Some plants were old and large, creating huge sand hummocks up to three meters high and broad in dune hollows. These hillocks were frequently dotted with beetle and lizard holes, especially under and around roots. The sand of the hillocks was firm and in places slowly cementing, perhaps due to the continual nocturnal dampness caused by dewfall from leaves and branches. Binding roots also contribute to this effect. Early in 1980 much an activity had been recorded around this species, when large columns of the insects could be seem transporting the characteristic winged seed to their nests. On this occasion, however, such activity was nil. Younger bushes were plentiful, especially close to the road, but apparently too small to flower; most energy seemed to have gone into producing growth shoots. These younger plants were greener and fresher looking, with waxy-white segmented stems.



A much less common plant was Dipterigium glaucum, a smaller species up to half a meter high here. Isolated specimens were recorded in dune hollows where the sand has lower salinity content. None of the plants looked overgrazed, and all were healthy looking; one or two were in full flower and seed. The tiny yellow flowers and green scaly fruits covered the slender branches up to the tip. Leaves on some plants were almost absent or greatly reduced in size, whereas other plants bore only leaves. The species is easy to recognize at a distance by its usually isolated position and its intricate tracery of stiff interlocking branches. D. glaucum seems to flower on and off throughout most of the year, with local variations. On Abu Dhabi Island, it can be seen in much more saline conditions than usually found inland. It is spreading particularly fast on the northwest slopes of the higher dunes on Sadiyat.

Another common species all along this stretch of the Suweihan road is Zygophyllum album, recognizable by its generally compact bush-like shape and bright green succulent leaves. Just two plants were recorded in flower, the minute white heads originating from between leaf and branch joints. All appeared to be the same Zygophyllum species, though Z. coccincum (yellow flowers) may have been represented. Individual plants had much larger leaves, but in all other aspects were identical. This plant is salt-tolerant and generally ignored by herbivores because of its purgative effects. However, camels have been known to nibble at it. Its compact density creates a high level of dewfall immediately beneath, often seen later in the morning as sandy pockmarks. This species is widely distributed through the desert regions of the Emirate, at least into the Liwa and possibly beyond.

A much rarer plant recorded was Cynomorium coccineum, specimens of which were found in only one spot, and may have been attached to the same host plant (= H. elegans). This dark reddish-brown parasite has a phallus-like head up to 10cms long on a fleshy tubular stem that extends a long way into the sand where it is eventually attached to the host plant via a long thin thread. The two specimens recorded here had head-lengths of 3.5 and 6 cm respectively. Several specimens had not yet broken through the surface. C. coccineum is the rarer of the two parasite plants usually found in this area. Cistanche phelypaea, the commoner, was not represented here though an isolated example was recorded near Al Hair on the Dubai to Al Ain road on 30th December 1980. This latter species is commonly associated with coastal habitats, though it has been recorded in the Liwa. Its bright yellow hyacinth-type flowers are a sharp contrast to its usually muddy-gray and calcareous environment.



A few examples of Heliotropium (crispum?) (=H. bacciferum?) were also found in the pool area. Characterized by its short but erect stance, dark green stiff hairy leaves and white flowers borne in backwards curving inflorescences, this shrub has been found in various locations along this road during December. There were smaller versions too of what could have been the same plant with less hairy leaves and no flowers.

Of the grasses and sedges in this area, Panicum turgidum and Pennisetum divisum were by far the most common. The former appears mostly dead at this time of the year in this area, consisting of dry clumps of flowerless or broken stalks intertwined and more or less stiffly erect. The basal tufts are attached directly to a mass of roots forming a combined stable clump. Thread-like root extensions can often be seen spreading taut across the sandy surface up to two meters around each plant. On the same date, several very healthy specimens of the same grass were noted in full flower and seed near the new Abu Dhabi Airport.

Pennisetum divisum, on the other hand, was in a far better condition in the region of the field trip. Many plants had fresh flower-spikes up to 10 cm long on the end of tall (up to 1.25 m) stems. The flower head is completely different to that of P. turgidum which has loose panicles, not spikes. Both grasses have stems that are angled at the nodes, and both are usually heavily grazed. One grass of a possible Stipagrostis species in flower was also recorded on a north-facing dune.



Of the sedges, only Cyperus species were encountered, and all were small plants with young growth. There were no flower heads. In all probability, this was C. conglomerates, a plant that was recorded in flower in this area in the summers of 1979 and 1980. It is common throughout the Emirate, while the rarer C. rotundus is very localized; it has been recorded at the sewage farm outfall on Abu Dhabi Island.

Beyond the first two hundred meters of low dunes, moving south, was a long but relatively narrow gravel plain running east-west. The gravel and small stones were all smooth and sandblasted, and included basalt and chert. Beneath the two or three centimeters, the soil consisted mostly of chalky "Katch". A trial hole 50 cm deep failed to reach water though the sub-soil ("katch", gravel and sand) was slightly damp.

Several dozen fossils of Nummulites species (Foraminiferae) were found on the surface. These tiny fossils, wafer-thin yellow discs a few millimeters in diameter with whorls on one side, are normally associated with limestone outcrops (nummulitic limestone) and belong to the Eocene and more recent epochs.

The dominant plant species of the plain was Limonium axillare, or Sea Lavender, currently not in flower, though the old 1980 flower heads in their dried-out dirty gray form were still on the majority of the plants ("Everlasting flowers"). This species prefers a saline habitat and is abundant along the coast north of Abu Dhabi and in desert depressions. Some plants along the coast have been noted in flower as late as October, but it flowers en masse from March to June and the purple inflorescences attract a large number of insects.

Just beyond the plain dunes rose again in higher east-west ranks, from the tops of which the southern vista was a series of plains and sand hills. On the edge of the first plain a few low limestone hillocks were prominent by their gray color but they contained little or no vegetation beyond a few scraggy grasses. A long-legged gray-white spider escaped capture by dodging among broken stones atop one of these bluffs.

Among the higher dunes was the very occasional stunted Calligonum comosum tree. This is one of the larger desert plants and is indicative of 'sweeter' i.e. less saline, conditions. Normally found deeper into the desert, where the sand is redder, this species has nevertheless been recorded even closer to the coast, but in poor condition. Here, the broken examples were sometimes three-quarters buried in the shifting sands, yet new leaf growth was pushing through the surface of the dune. The branches and stem out of the ground appeared mostly dead, a feature that had been noticed on the majority of C. comosum trees observed on a visit to the desert south of Al Ain two weeks earlier. This plant flowers in February and its distinctly large hairy fruits can be seen from March onwards; these fruits are either whitish-yellow or reddish-brown.



No large animals were encountered during the trip but tracks of both hare and fox were not uncommon. Hares have been flushed here previously. Several lizards were seen, though not as many as on previous visits, and one collected. An Eremias species it measured 14 cm.

One large yellow scorpion was caught which measured some 9 cm to the sting. Such creatures are not rare in this area and have been recorded on top of large, open dunes. In May 1980 one such was caught closer to Suweihan. It was frantically running in circles and appeared lost, but became very threatening when approached.

Several ground mantises were seen and one collected. These insects are common in gravelly and stony areas but are at a disadvantage on sand. Colors were variable from light gray to dark brown. All moved very quickly over rough terrain and were not easy to capture without injury.

The tracks of a viper were also measured. Snakes are fairly common - one was captured on a previous visit to the same location (see Bulletin 11) - but not often seen.

Two female wasps of Bembix species were noted. This wasp is usually a solitary by nature but lives in small groups.

Termite mounds up to 5cm high were fairly numerous. These insects have been recorded in the Liwa and appear to thrive in the desert given organize material. They particularly seem to prefer dead logs and stumps; date palm (Phaenix dactilifera) and Calligonum comosum wood tends to be a favorite, though these are the desert plant species with thickest stems and branches, anyway.

Disappointingly, there were very few birds to record. Ten plus desert larks in flight, one great-gray shrike, one desert wheatear and a hoopoe lark were the only observations. Ravens have previously been noted in the area. However, the total vegetation cover is sparse. Apart from the concentration of L. axillare shrubs on the plain, plants were generally well spaced and the dominant visual aspect was of a vast area of rolling sand sparsely dotted with clumps of plants.

Back at the starting point, the morning's collected was sorted and observations checked. The usefulness of the trip for recording purposes is not questioned, but it is recommended that an area such as this be monitored on a regular basis throughout 1981. Meanwhile, other ENHG trips are planned for the Al Ain area and the coast this year.

-- Editor


 


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