Predicting the optimal rotation length of Teak plantations using a simulation model

L H P Gunaratne and T N Subramanium
Department of Agricultural Economics and Business Management,
University of Peradeniya, Sri Lanka.

The traditional problem in Forest Economics has been mainly dealt with the estimation of optimal rotation length for sustainable management. However, given the limitation of the availability of time series data on growth and management in forest plantations in Sri Lanka, such estimations are not feasible. Against this background, this study attempted to develop a simulation model and predict rotational interval of teak plantation under different management conditions.

A field survey was conducted to identify the plantation related parameters in the Kurunegala District. Meantime, a simulation model was developed with Microsoft Visual Basic and Microsoft Excel using the equations specified in the Teak Management Plan (1997) to supplement the field data. The past data obtained from the Forest Department was used to parameterize the model. Using the age and the height of a plantation at a particular time, the model was capable of predicting the plantation related parameters such as dbh and timber volume over the time.

According to the values predicted by the simulation model, four different categories were identified based on the site index, which represents the level of growth of a stand. Rotational interval was estimated using the Faustman rotational model at different discount rates. Thereby it was estimated that the rotational intervals for the four categories at discount rates 10%, 15% and 20% as 19, 17 and 15 years respectively. The internal rate of return obtained through the simulation was above the market rate of 12%. Though the model yielded shorter rotational intervals than the present field values, the approach could be used in future with more reliable field data.