Restoration of Juniperus excelsa Bieb. and Olea europaea L. subsp. africana (Mill.) P.S. Green woodlands in Eritrea

Abstract

The research aim was to assess the vegetation and soils of the Rora /' Habab plateau, Eritrea and to develop methods of propagating the native tree species, juniper and olive. The research consisted of vegetation and soil surveys, interviews with local people, archival research, and experiments on propagation of olive and juniper. Junipers are now confined to the north of the plateau. Olives are more abundant in the north but have very few individuals in the centre, where there are many dead trees, or south. Soil erosion was ubiquitous and often severe. Soil morphology and nutrient status were related to vegetation, topography, land use, and erosion status, and varied greatly over short distances. Soil texture was coarser and most chemical factors (except total Ca and exchangeable Na) were lower in the south. Organic C, total N, exchangeable Ca, percent day, CEC and the sum of bases were higher in soils from grazed land than in cultivated fields. Germination of olive seeds was 92% when the endocarp was removed; stratification had little effect. Rooting of olive stem cuttings attained 76% under mist when parent plants were fertilised and cuttings were treated with rooting hormone. Germination for juniper was 56% after stratification at 5°C for 30 to 60 days. Juniper stem cuttings rooted in only one of three experiments, where rooting was 78% in a well ventilated, cool, low-mist environment. Olive seedlings which were fertilised and watered every 7, 14, or 21 days for two months, were taller, had lower root:shoot ratios and soil moisture than unfertilised plants. Fertilised seedlings watered every 28 days died. Root volume was less for plants watered every 21 days but watering interval had little effect on other variables in unfertilised seedlings. Ecological restoration is urgently required to rehabilitate the Rora plateau, which has Africa's most northerly remnant juniper / olive woodlands.