Growth and yield of 5years old teak and flueggea in single and mixed species forestry systems in the Solomon Islands

Abstract

Mixed species plantings of teak (Tectona grandis) and flueggea (Flueggea flexuosa) were introduced as a method for overcoming the reluctance of local growers to thin their teak. Flueggea is a well-used local species and removal of the flueggea for personal use would effectively thin the entire stand over time. Stocking rates and tree species composition are two important factors affecting tree growth and yield when a mixed species plantation is established. This study aimed to investigate the effects of stocking rates on early teak growth in a mixed species system in a humid tropical region of Western Province, Solomon Islands. The experimental design included: teak planted as a monoculture at standard stocking of 833 stems per hectare (sph) (Treatment 1); teak planted in rows alternating with 2 rows of flueggea at 833 sph; 625 sph; and 416 sph (Treatments 2,3 and 4 respectively); and teak planted in alternating rows with a single row of flueggea at 833 sph (Treatment 5). Teak basal area was optimum at the lowest stocking rates of 412 and 625 sph for both species. However, teak yield (volume per hectare) was greater in the higher stocking rate treatments. Teak basal area mean annual increment (BA MAI) decreased in higher stocking rates between the age of 4 and 5 years indicating the onset of suppression and the need for progressive thinning. Under correct silvicultural maintenance, the 833 sph planting density offers the benefits of higher stocking and lower maintenance. As the present investigation was confined to the establishment phase for teak, more studies are needed to understand the system development to maturity.