Developing a stand-based growth and yield model for Thuya (Tetraclinis articulata (Vahl) Mast) in Tunisia

Abstract

(2) Thuya (Tetraclinis articulata (Vahl) Mast) is a Mediterranean forest species mainly occupying semiarid environments in North African countries, where it provides important ecological and economical services, such as biodiversity conservation, soil protection against erosion, fuelwood, timber for fencing, construction and handicraft, resins, etc. Despite the importance of the species, there is a severe lack of scientific knowledge as regards the management of these forests or modeling tools to support multifunctional forest management decision making. In the present work, we developed a stand-level integrated model for the management of Thuya forests in Tunisia. The model comprises a family of site index curves, built using the Generalized Algebraic Difference Approach (GADA) method, which provides predictions for stand growth, aboveground biomass, total and merchantable volumes, along with a non-linear system of stand level equations presented as stand density management diagrams (SDMD). The developed model has been used to define, characterize and compare four different management specific schedules for different site qualities and multifunctional objectives.

Modelling diameter distribution of Tetraclinis articulata in Tunisia using normal and Weibull distributions with parameters depending on stand variables

“…The developed model, used in conjunction with the previously developed models for tree level attributes (Calama et al 2012), the distance-independent individual tree diameter-increment model (Sghaier et al 2013) and the stand based growth and yield model presented in Sghaier et al (2015), constitutes a useful tool for the sustainable management of Tetraclinis articulata forests in north-east Tunisia.…”

“…The sum includes all diameter classes in the i-th plot. In this error index, we can multiply the absolute difference between the observed and predicted number of trees per diameter class by the volume, using an equation developed by Sghaier et al (2015) This index can also be expressed relatively as a percentage by dividing it by the total volume of the observed distribution in the plot (Lejeune 1994 -eqn. 19).…”

“…The example which is provided here uses information from the yield table elaborated as part of this study for modeling the growth and production associated with the management and conservation of Tetraclinis articulata forests in Tunisia (Sghaier et al 2015). Tab.…”

“…The diameter-growth dynamics of the trees was studied by developing a distance-independent individual tree diameter increment model (Sghaier et al 2013). A stand-level growth and yield model has recently been developed consisting of a site index sub-model and a system of compatible stand attribute equations present-ed in the form of a stand density management diagram (Sghaier et al 2015). The next step would be to characterize the stand diameter structure.…”

Should the silviculture of Aleppo pine (Pinus halepensis Mill.) stands in northern Africa be oriented towards wood or seed and cone production? Diagnosis and current potentiality

“…Sites on calcareous brown soil and rendzine correspond to fertility class 2, with a site index of 10.5 to 13.5 m for 50-year-old trees. Sghaier et al (2001) identified four classes of fertility, with a reference height of 45 years in descending order: class 1, with a reference height of 13.5 m; class 2, with a reference height of 10.5 m; class 3, with a reference height of 7.5 m; and class 4, with a reference height of 4.5 m. The authors concluded that about 49% of Aleppo pine stands in Tunisia belong to fertility class 3. Akrimi (1984) and Garchi (1991) studied the production of Aleppo pine in northwestern Tunisia (Sakiet region), showing that the most important production was between 0.4 and 4 m 3 ha -1 yr -1 for a dominant height (9.7-22.8 m).…”