DROUGHT RESISTANT TREES AND SHRUBS FOR DRY PLANTING IN BAHRAIN ^{1 2}

by

C. Cossalter, Forestry Officer (Genetic Resources)
Forest Resources Development Branch, FAO
Rome, Italy

INTRODUCTION

The term dry planting is used in this paper in the sense of planting with an initial period of irrigation, in contrast to irrigated plantations, where water is supplied continuously during the whole lifetime of the tree (either permanently or intermittently). Due to harsh environmental conditions briefly described below, strict dry planting with no irrigation at all is not possible in Bahrain even if drought resistant species are used. Some form of initial irrigation to help trees to establish is essential.

The choice of potential species for different planting sites proposed below was obtained by analysing the information contained in reports and articles on tree planting in the Gulf and surrounding regions. This “desk screening” is, in its present form, still very preliminary and could be easily improved through a more intensive survey of all sources of information on the subject, published and unpublished.

A great deal of tree planting activities was and is still carried out in the region but is not adequately documented. A careful stocktaking of information presently available on species adaptability as well as on all other aspects of arid zone afforestation, holds a real potential for guidance and would help minimize errors.

In the context of Bahrain, characterized by very severe environmental constraints and no experience in dry planting, such a stocktaking exercise is an essential preliminary step.

The choice of planting material to use in afforestation is largely site specific in the sense that the planting material has to comply with a unique combination of environmental and socio-economic parameters.

Extrapolation of information from elsewhere, even if an essential first step, is inadequate since it cannot reveal the adaptability of a species/provenance to new ecological conditions and its ability to provide the expected goods and services. The best way to acquire such information is through trials in small plots set up at representative locations within the area proposed for afforestation.

ENVIRONMENTAL CONDITIONS

Location and Topography

Bahrain consists of a group of 33 islands situated in the Arabian Gulf, at latitude 26°N, longitude 21°E. The principal island, Bahrain, is linked by a causeway to the nearby major islands of Al Muharraq and Sitra. To the South lies the group of Hawar islands, which are sparsely populated.

The islands are low and flat or gently rolling. Bahrain Island has the highest summit: Jabal Al Dukhan (122 m). This rock outcrop, located at the centre of the island, is surrounded by an interior basin bounded by a rim about 50 m high.

Table 1. Climatic Matching with Neighbouring Countries of the Gulf Region where Experiences of Dry Planting Exist

Climate

The climate reflects Bahrain's location in the Arabian Gulf only a few hundred kilometers north of the Tropic of Cancer. It is a pronounced arid climate with dominant summer drought.

Annual rainfall is 74 mm (41 year average), of which about two-thirds falls in December–March, in about 7 days. The precipitation fluctuates greatly from year to year, sometimes dropping almost to zero, and in other years amounting to two or three times the annual mean. However, rainfall during the period of late May to the end of September is constantly close to zero.

Maximum daily temperatures reach above 38°C during the summer months, while the winter half of the year is characterized by fairly cool weather, with mid-day temperatures rarely exceeding 25°C. Due to the proximity of the sea in all directions, the difference between day and night temperatures is usually moderate. It should be noted, however, that the temperature during winter nights occasionally drops as low as 5° to 10°C, which may adversely affect some species.

As a result of its location and low topography, the island are windswept and, in particular, exposed to strong winds from between North and West, blowing all the year around. Winds blowing from other quadrants are predominantly light to moderate.

Relative humidity is higher than in many other parts of the sub-region, main daily maximum ranging from 79% in May and June to 89% in January, main daily minimum from 40% in May and June to 59% in January.

Geology and Soils

The interior of the islands consists of a series of carbonate formations, and the coastal plains of recent or quaternary marine deposits.

Soils have been briefly described by Mohammed S. Ali (1982) and a comprehensive study edited by Doornkamps, Brunsden and Jones 1980, included mapping at a scale of 1:10.000.

Most soils are coarse textured sand, sandy loams and occasionally sandy clay loams. The deeper soils are usually underlain by sand or a cemented gypsic or calcic horizon. The clay content ranges from 3–35% and permeability is high. The soils are of low natural fertility. Organic matter is low (less than 1%). Available phosphorus values are low and soluble nitrate ranges from 1–5ppm in the saturated extract of the top soil.

Soils are generally saline to extremely saline, 4–120 mmhos/cm for the top soil and 7–64 mmhos/cm for subsoil. Sodium chloride is the dominant salt. The soil salinity is usually considerably modified by the irrigation water used, which is itself saline.

Water

With the exception of the north and west coasts most of the Bahrain island has no available ground water for agricultural production and tree growth. Where available, ground water is always brackish. Analysis made on 18 well waters of the West coast have given the following results:

• Electrical conductivity ranging from 3370 to 8980 in mmhos/cm at 25° C;
• parts per million total dissolved salt ranging from 2170 to 5330 ppm TDS;
• Ph ranging from 7.23 to 7.53;
• total alkalinity ranging from 164 to 179 in ppm CaCo₃,
• chloride ranging from 782 to 2740 in ppm Cl;
• sulphates ranging from 421 to 900 in ppm SO₄.

The salinity of the ground water is presently increasing drastically in some areas in response to excessive demands on acquifiers, which is the consequence of increasing urbanisation, increased standards of living and increasing industrial activity. This tendency is particularly noticeable in the extreme west and north of Bahrain Island, and in Sitra and Muharraq islands.

The Government has increased supplies of water by the establishment of desalination plants and a sewage treatment plant at Tubli, however water consumption is still close to potential production and surplus of water cannot be foreseen in the near future. Therefore, any extra use of water must be carefully considered and any tree planting programme can only rely on a minimum quantity of low grade water.

Figure 1.  Main Features of the Most Widely Represented Potential Sites for Arid Zone Tree Planting

SPECIES BY SITE MATCHING FOR DRY PLANTING OF TREES AND SHRUBS

Species combining salt tolerance, drought resistance and wind tolerance (priority species for “dry planting”)

Ranking according to tolerance to maximum electrical conductivity of soil solution (expressed in relative values termed E.C × 10³)

Ranking in alphabetical order for those species whose tolerance to maximum electrical conductivity is potentially good but needs to be further documented.

Species with excellent to good resistance to drought, good to fair tolerance to salinity and good tolerance to wind (species whose capacity to withstand high salinity should be further investigated)

Ranking according to tolerance to maximum electrical conductivity of soil solution (expressed in relative values termed E.C. × 10³)

Ranking in alphabetical order for those species whose tolerance to maximum electrical conductivity is potentially good but needs to be further documented.

Species with excellent to good tolerance to salinity, good to fair drought resistance and good tolerance to wind (species whose capacity to withstand dry planting in the Bahrain conditions needs further investigation)

Ranking according to tolerance to maximum electrical conductivity of soil solution (expressed in relative values termed E.C. × 10³)

Ranking in alphabetical order for those species whose tolerance to maximum electrical conductivity is potentially good but needs to be further documented.

REFERENCES

BOOTH, F.E.H. and WICKENS, G.E. (1988). Non timber uses of selected arid zone trees and shrubs in Africa. FAO Conservation Guide No. 19, Rome. 176 pp.

FAO (1971). Report to the Government of Kuwait - Afforestation based on the work of R. Firmin. FAO/KU/TF 46.

KHAN, I.R. (1981). Afforestation and Agricultural Development in the Western region of Abu Dhabi (January 81); 4–11.

KHAN, I.R. (1981). Natural Vegetation of Abu Dhabi Emirate. The Pakistan Journal of Forestry (April 81): 45–50.

SHEIKH, M.I., KHAN, S.M. and KHAN, S.R. (1985). A Report on the Study Tour to United Arab Emirates. Pakistan Forest Institute, Peshawar. 41 pp.

VON MAYDELL, H.J. (1983). Arbres et arbustes du Sahel - Leurs caractéristiques et leurs utilisations. GTZ Eschborn. 531 pp.

WOOD, P.J., WILLENS, A.F. and WILLENS, G.A. (1974). An irrigated plantations project in Abu Dhabi. Commonw. For. Rev. 54.2:139–146.

¹ Manuscript prepared June 1989

² Paper prepared within the framework of FAO/UNDP project BAH/87/001/01/12, “Youth Participation in Environmental Preservation”.