Mechanisms for the successful biological restoration of the threatened African pencilcedar (Juniperus procera Hochst. ex. Endl., Cupressaceae) in a degraded landscape

Juniperus procera Hochst. ex. Endl. (Cupressaceae) is world's largest juniper, but is currently threatened owing to multiple anthropogenic factors. This paper describes mechanisms for the successful biological restoration of African pencilcedar in a degraded landscape that had been depleted of organic matter and essential nutrient elements as a consequence of relentless deforestation, soil erosion, unsustainable farming and overgrazing. We used stecklings (= planting materials derived from rooted cuttings) of J. procera, and deployed Acacia abyssinica Hochst. ex Benth. (Fabaceae) to serve as a putative foster tree. The study was conducted for a period of 7 years, with major soil fertility indicators determined at years 0, 3 and 7. We found that mean height, crown length, crown diameter, branch length, and branch numbers of J. procera trees grown in association with A. abyssinica were significantly (p = 0.001) higher than those grown without the putative foster tree. Mean plant-available P (15 ± 2.1 ppm) and soil N-content (0.42 ± 0.04%) were approximately 3- and 2-fold higher, respectively, in the A. abyssinica-treated plots than in the non-treated ones. Similarly, the levels of exchangeable cations and soil organic carbon were twice higher in the A. abyssinica-treated plots than in the non-treated ones. Cation exchange capacity improved with restoration time, both in the 0-15 and 15-30 cm soil profiles, but the extent of improvement was significantly (p = 0.001) higher in the 0-15 cm soil profile of the A. abyssinica-treated plots than in the non-treated ones. We conclude that successful restoration of Juniperus procera in degraded landscapes and across the species' range of habitats is feasible provided that strong and well-fortified stecklings are established along with the N2-fixing, fast-growing and drought-tolerant Acacia abyssinica.