African sandalwood (Osyris lanceolata): resource assessment and quality variation among populations in Tanzania: research note

Abstract

African sandalwood (Osyris lanceolata) populations occurring in Tanzania were assessed to determine the current resource status and ascertain variation in quality existing among them. This will provide a guide in the selection of populations where conservation efforts and improvement programmes can be concentrated. The resource status was assessed through estimation of the species' density per unit area and measurements of tree dimensions. Quality variation was assessed by determining the amount of oil extracted from a given amount of wood and the proportion composition of santalol, a prime determinant of sandalwood oil quality. The study revealed that populations supporting O. lanceolata in Tanzania occur mostly in arid to semiarid areas with the majority being on stony and rocky soils. However, big sized trees are supported in humid climates, being favoured by relatively low soil pH and reasonable amounts of soil nitrogen. Tree density ranged from 38 individuals to 76 per hectare. The mean tree height was 3, 8 m (2, 1 to 6, 5 m) while the mean diameter was 5, 7 cm (3, 6 cm to 8, 6 cm). The best quality and quantity of oil came from populations of relatively arid climates compared to those of humid climates. Populations differed significantly in both yield and quality. The highest yield obtained was 8, 45 ± 0, 54% from Gubali population while the highest santalol content (32, 2 ± 1, 2%) was from Bereko populations. Within trees, quantity and quality of oil was higher in wood portions close to the ground in both the root and shoot system. The amount decreased toward the root and shoot tip. The root and the shoot system were similar in quality and quantity of oil. The observed harvesting selectivity is thus primarily influenced by quality differences among populations while the large dimension and density differences among populations seem to be secondary. Inclusion of the root systems during harvesting is also a matter of maximizing the raw material to be collected rather than differences between the two portions. The exact factors controlling wood quality in the species have however remained uncertain. Probably, genetic factors alone or in combination with the environmental factors play a significant role.


Keywords: African sandalwood, Osyris lanceolata, Oil yield, Santalol content, Resource status


Southern African Forestry Journal No.199 2003: 77-88