Plant succession and its optimization on tar-polluted coasts in the Arabian Gulf region

Coastal ecosystems in the Arabian Gulf region are under increasing pressures from hostilities and other developmental activities; the region has a long history of crude-oil pollution. Because of the high ambient temperature, oil deposited along the coastline or inland evaporates, leaving a semi-solid tar. In Qatar, to clean up the polluted sites, the deposited tar is stripped off and dumped in the coastal marshes as confluent dome-shaped piles. Flowering plant colonization of tar-piles is described here as a chrono-sequence, ranging in age from 2 to 14 years. The successional patterns in vegetation, seed bank, species diversity and plant growth were predicted from tar-pile disturbances with different ages and tar content. The success of natural plant colonization and the establishment of plant communities on the tar-pile disturbances depend upon: (1) age of the tar-pile disturbances, (2) tar content of the piles and soil physico-chemical properties, (3) soil moisture content, (4) structure of plant communities in the surrounding landscape, (5) size of the disposal sites and the method of dumping, and (6) prevailing environmental conditions. A management and restoration framework is proposed to optimize the natural recolonization of tar-piles. To retain these ecosystems in a self-sustaining state, some native plant species might be used including: Aeloropus lagopoides, Aizoon canariense, Anabasis setifera, Fagonia indica, Mesembryanthemum nodiflorum, Reichardia tingitana, Salsola imbricata, Suaeda aegyptiaca, Senecio glaucus, Sporobolus arabicus, Zygophyllum quatarense, and Zygophyllum simplex. To clarify the biological and chemical aspects of the problem, further research on the chemistry of tar-polluted soil and its vegetation in relation to the food web is needed.