Biophysical environmental factors influencing the distribution and yield of Osyris lanceolata (hochst&steud). Case study of Gachuthi and Kibwezi forest, Kenya.

Abstract

East African Sandalwood (Osyris lanceolata) is a dioecious shrub growing to 1-7 m tall depending on environmental factors and genetic variation. Sandalwood is widely exploited for extraction of oil, which is used in the fragrance, perfumery and pharmaceutical industries. Efforts are being made to domesticate the species in order to reduce pressure from its natural habitat. However, little is known in regard to its ecological factors, range of oil yields and quality across its distribution in highlands and lowlands areas in Kenya. Therefore, the broad objective of this study was to determine biophysical environmental factors influencing the distribution and oil yield of Osyris lanceolata in highland and lowland forests in Kenya. The study employed experimental and ecological survey design where Gachuthi highland forest and Kibwezi lowland dry forest were selected as the study areas. Line transects were laid in areas where O. lanceolata was naturally growing and also in areas where it was not found in both forests. Subsequently, nested intensity plots were established along transects where vegetation habit and species data collected, soils and O. lanceolata trees sampled. Then, vegetation data was transformed into a species occurrence/ absence matrix for all plots; soils’ physical and nutrients properties determined in the soils laboratory; and oil yield and quality in roots, stems and barks determined through chromatography. Indicative species for predicting O. lanceolata occurrence and the soil variables where it grows naturally were simultaneously determined through canonical correspondence analysis using CANOCO for windows version 4.15. Variation of soil variables, difference in oil yield and quality among tree components and between sites were analyzed using SPSS version 20.0. Indicative species for O. lanceolata occurrence and soil variables influencing its occurrence differed between Gachuthi highland and Kibwezi drylands forests. However, Rhus natalensis was a common indicator species in both forests, suggesting its indisputable predictive capacity for O. lanceolata occurrence. Soil physical and nutrient variables differed significantly with Kibwezi nutrient levels of nitrogen, phosphorus and potassium higher than Gachuthi forest. Extracted oil yield in roots, stem and bark from both sites showed a significant difference at (p<0.05) with highest yield found in Kibwezi roots (2.26%). Quality of oil in reference to concentration of α and β santalol showed that Gachuthi root samples had traces of α santalol, stems were ranging from (0-3.1%) and barks (0-0.06%) when compared to Kibwezi with a range of (10.80-35.21%) in roots, (0.01-5.82%) in stem and (2.30-14.24%) in the bark. In conclusion these findings show that Sandalwood plantations could preferably be established in Kibwezi lowland dry forest.