Optimal Rotation Age of Pinus patula in Government Forest Plantations in Tanzania

Abstract

A study to determine the optimal rotation age of Pinus patula was conducted in five forest plantations in Tanzania, i.e., Kawetire, Kiwira, North Kilimanjaro, West Kilimanjaro and Meru. Growth and yield, and mechanical properties data were collected from compartments representing age from 5 to 25 years. In addition, revenues and management costs data were collected for the purpose of determining the economic rotation age. For the purpose of determining the optimal rotation age based on growth and yield, the following basic models were developed: 1) site index curves model, 2) height-D model, 3) Single tree volume model, 4) Basal area growth model 5) stand volume model, 6) mortality model, and 7) simulation of thinning. Analysis of Variance (ANOVA) was carried out to ascertain whether the wood properties vary across age classes. Economic analysis of rotation age data involved computation of Net Present Value (NPV). Growth and yield data revealed irrespective of site class, P. patula can be harvested at age of 18 years while mechanical wood properties show that harvesting ages range between 16 and 21 years. Based on NPV, the optimal age was 16 years. Therefore, it is recommended P. patula be harvested at age of 18 years irrespective of site class.