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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Dominant height growth modelling and fertility of Aleppo pine (Pinus halepensis Mill.) stands in Tunisia
Auteurs :	T. Sghaier, Auteur ; S. Garchi, Auteur
Type de document :	Article
Dans :	Ecologia Mediterranea (35(1) 2009)
Article en page(s) :	49-63
Résumé :	The Aleppo pine (Pinus halepensis Mill.) is a rustic species, very present in Mediterranean regions (Parde J. 1957; Quezel P. 1986; Mezali M. 2003). Representing more than 56% of the total forest area (Sghaier 2005), this species is of a great economical, ecological and social values in Tunisia. The development of management models for various area of this species is currently one of the first priorities of the forest administration in the country. It is within this framework that an integrated study on Aleppo pine was undertaken in Tunisia by installing 348 temporary plots with a circular of 400 m(2) each. These plots were set in such a way to cover the whole distribution area of the species in the country, from the arid to sub-humid bioclimates.To choose a model which describes the dominant height growth according to the age and to identify the sites quality relating to this species, varied mathematical models with common asymptote, based on the difference equations method (Table 1), were adjusted and compared. The difference equations method supposes that the observations on a given plot should belong to the same site index curve. The dominant height H-2 measured at the age t(2) is expressed as a function of t(2), the height H-1 measured at the age t(1), and t(1). The expression is obtained by the substitution of one parameter in the growth model height-age (Elfving and Kiviste 1997). The data, which were used for the different adjustments, come from the stem analyses.To estimate the parameters of the various tested models, we performed a non-linear regression using the NLIN procedure of SAS software. A certain number of criteria were used to compare these models (Table 2). These criteria are based on the value and the distribution of the residues and the relation between the observed and estimated values. After analysis, it appeared that the polymorphic difference equation derived from the Lundqvist-Korf function resulted in the best compromise between biological and statistical aspects, producing the most adequate site index curves. This equation is as follows:where H-1 is the height (m) at age t(1) (years), H-2 is the height (m) at age t(2) (years). Thanks to this model, the various Aleppo pine stands in Tunisia were divided into 4 classes of quality or productivity. These classes are characterized by average dominant heights obtained at 50 years age of 13,5 m; 10,5 m; 7,5 m and 4,5 m, respectively for the first, second, third and fourth class of quality.

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