Abstract
Aim of study: The aim of the work was to develop an individual tree diameter-increment model for Thuya (Tetraclinis articulata) in Tunisia.Area of study: The natural Tetraclinis articulata stands at Jbel Lattrech in north-eastern of Tunisia.Material and methods: Data came from 200 trees located in 50 sample plots. The diameter at age t and the diameter increment for the last five years obtained from cores taken at breast height were measured for each tree. Four difference equations derived from the base functions of Richards, Lundqvist, Hossfeld IV and Weibull were tested using the age-independent formulations of the growth functions. Both numerical and graphical analyses were used to evaluate the performance of the candidate models.Main results: Based on the analysis, the age-independent difference equation derived from the base function Richards model was selected. Two of the three parameters (growth rate and shape parameter) of the retained model were related to site quality, represented by a Growth Index, stand density and the basal area in larger trees divided by diameter of the subject tree expressing the inter-tree competition.Research highlights: The proposed model can be useful for predicting the diameter growth of Tetraclinis articulata in Tunisia when age is not available or for trees growing in uneven-aged stands.Keywords: Age-independent growth model; difference equations; Tetraclinis articulata; Tunisia.
Highlights
Thuya [Tetraclinis articulata (Vahl.) Mast.] is endemic to the western Mediterranean region
Research highlights: The proposed model can be useful for predicting the diameter growth of Tetraclinis articulata in Tunisia when age is not available or for trees growing in uneven-aged stands
According to the obtained results (Tables 3 and 4) concerning the values of the various statistical criteria used to compare the models, it appeared that models using growth index (GI) as site quality measure give more precise results than those obtained by models using site index (S)
Summary
Thuya [Tetraclinis articulata (Vahl.) Mast.] is endemic to the western Mediterranean region. It is native to North-Western Africa in the Atlas Mountains of Morocco, Algeria and Tunisia, with two small outlying populations on Malta, and near Cartagena in SouthEast Spain (Blondel and Aronson, 1999). It grows at relatively low altitudes in a hot, dry subtropical Mediterranean climate (Farjon, 2005) and it can be trimmed as a hedge (Rushforth, 1999). The two main products of this species have been the resin and the wood. The wood is prized for cabinetry and was extensively used in construction by the Romans (Stevens, 2000)
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