Seasonal Variation in Above-Ground Annual and Perennial Phytomass of an Arid Rangeland in Libya

Abstract

An Aristida pungens-Retama r&m rangeland in the rrid Jefhra plain in Libya produced 2,000 and 950 kg (dry matter) ha-’ of net above-ground phytomass with 200 mm and 171 mm of rainfall during the 1977178 and 78179 growing seasons, reavly. Annual plants contributed 460 and 300 kg (dry matter ha ) in the 2 seasons, respectively. Perennial shrubs lost their 1978 winterspring aerial production during the long 1978 summer and dry winter when graxable forage was most needed. In contrast, spring production of annual plants remained available and graxable until late summer. Settlement of shepherds’ families on site is not advised as the dead standing phytomass (270 kg dry wood ha-‘) may be rapidly exhausted for fuel consumption, leading to wind erosion problems on presently fixed sand dunes. Libya has embarked on a large rangeland development programme involving 2 million ha (Gintzburger and Bayoumi 1977) of its estimated 12.5 M ha of nonagricultural lands located above the 50 mm isohyet (Le Houerou 1965). Most rangeland development projects are located between the 100 and 200 mm year-’ isohyets on what is considered as marginal, yet sometimes valuable, cropping land by local farmers. In the northwestern zones of Libya, approximately 500,000 ha were surveyed to provide Libyan authorities with vegetation maps as well as estimates of rangeland carrying capacities (GEFLI 1974) based upon research work in a similar environment in Tunisia (Le Houerou 1969, Floret et al. 1983). To provide their rural population with modern facilities, including schooling, medical care, and technical assistance in agriculture, the Libyan authorities have planned to allocate one set piece of rangeland to each shepherd’s family. It was anticipated that each shepherd should derive an adequate minimum and sustained income from proper management of his land and flock of sheep and goats. Conflicting estimates of long-term carrying capacity (1.5 to 3 ha sheep-‘) reported by different advisory teams rendered rangeland management and planning difficult. Problems were compounded by desertification hazards in this region. Suggested long-term carrying capacities resulted largely from guesses or one-time measurement, usually at the supposed peak standing phytomass in a similar environment. The relationship between average annual rainfall and net consumable rangeland production proposed by Le Houerou and Hoste (1977) for the Mediterranean Basin, though useful, appeared to be optimistic and needing refinement. None of these estimates took into account the yearly distribution of the rangeland production or considered the contribution and availability of ephemerals (annuals and ephemeroids). This situation prompted the author to measure the seasonal variation of above-ground phytomass of a rangeland type representative of some lOO,OOO-200,000 ha of the Libyan Jeffara Plain. The information gathered was aimed at providing range managers with an improved knowledge of above-ground phytomass dynamics and forage availability throughout seasons, hence to assist in planAt the time of the research, the author was working as an FAO range ecologist with the Agricultural Research Centrc (Tripoli, Libya). The research was financed through a Libyan funded FAO project (TF/LIBO6). Present address of the author: Instltut National de la Recherche Agronomique (LECSA), Place Viala, 34060 Montpellier, France. The field assistance of Hedi H’Diden and Muamar A’Sid, the support of FAO of The United Nations, the Libyan Agricultural Research Centre, and friends of the Grazing Projects are acknowledged as well as constructive criticism from M. D’Antuono, B. Wroth, A. Payne, and C. Trotman (Western Australian Department of Agriculture), and G. Long, C. Floret, and E. Le Floch (CEPE/CNRS, France). Manuscript accepted 21 October 19X5. 348 ning rational long-term utilization of Libyan rangelands by livestock.