Construction of site index equations for even aged stands of Tectona grandis (teak) from permanent plot data in India Anoop Upadhyay, Tron Eid * , Prem L. Sankhayan Department of Ecology and Natural Resource Management, Agricultural University of Norway, P.O. Box 5003, NO-1432 Aas, Norway Received 7 November 2003; received in revised form 5 November 2004; accepted 21 February 2005 Abstract A quantitative measure of the timber production potential of a given site may be provided by site index equations, which predict site index at a reference age from height and age information of a forest stand. Data from permanent sample plots laid down in even aged stands of Tectona grandis in six states of India were used to develop site index equations. Eleven growth functions were estimated from height–age data using the guide curve method and difference equation method with anamorphic and polymorphic formulations. The applied methods and estimated functions were compared with respect to residual variation, i.e., root mean square error (RMSE) from original data. The difference equation method gave lower RMSE than the guide curve method. A special solution of the difference equation derived from one of the growth functions, where a hyperbolic relationship between site index and a parameter was assumed, gave the best fit to the data. Site index curves with dominant heights in the 11– 28 m range at a reference age of 25 years are presented. # 2005 Elsevier B.V. All rights reserved. Keywords: Difference equation method; Guide curve method; India; Site index; Tectona grandis 1. Introduction Tectona grandis (family Verbenaceae) or teak is a predominantly tropical or sub-tropical tree. The natural distribution of the genus Tectona is in South and South- East Asia. India is one of the major teak producing countries where the genus is known only by T. grandis and has great genetic variability with distribution over 8.9 million hectares. Its natural zone of distribution is confined mostly to the peninsular region below 248 latitude (Tewari, 1992). Teak is a strong light demander, frost sensitive and a vigorous coppicer. It is capable of thriving on a variety of soils and geological formations, but requires good sub-soil drainage. Teak is the most important and general-purpose timber in India, suitable for several end uses. It is used for construction and making of furniture, railway sleepers, doors, windows, electric poles, etc., and is the best Indian timber in dimensional stability with very low fibre saturation point and shrinkage. In order to classify and group www.elsevier.com/locate/foreco Forest Ecology and Management 212 (2005) 14–22 * Corresponding author. Tel.: +47 64 94 8901; fax: +47 64 94 8890. E-mail address: tron.eid@umb.no (T. Eid). 0378-1127/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2005.02.058