Towards the sustainable management of thuya (Tetraclinis articulata (Vahl.) Mast.) forests in Tunisia: models for main tree attributes

Abstract

The thuya (Tetraclinis articulata (Vahl.) Mast.) forests are one of the most important ecosystems in semiarid environments in north-western Africa, providing important economic profit and social services to local populations. However, lack of tools aiding sustainable management of these forests is detected. In the present work models for the main tree attributes as total height, crown diameter, height to crown base and stem form are developed for the species, using data from a net of plots installed in JbelLattrech region, in the NE Tunisia. Presented models allow characterizing the actual state and timber production of forests by using variables measured in typical forest inventories and conform a preliminary step for the future development of dynamic growth models.Key words: thuya; stem curve; semiarid environments; tree-level models. ResumenHacia el manejo sostenible de los bosques de araar (Tetraclinis articulata (Vahl.) Mast.) en Túnez: modelos para las principales variables de árbolLos bosques de araar (Tetraclinis articulata (Vahl.) Mast.) constituyen uno de los ecosistemas más importantes de los ambientes semiáridos del noroeste de África, siendo además fuente de importantes beneficios económicos y servicios sociales a las poblaciones rurales. Pese a este interés, hasta el momento no se han desarrollado herramientas que faciliten la gesitón sostenible de estas masas forestales. En el presente trabajo se presentan modelos para los principales atributos de árbol individual: altura total, diámetro de copa, altura hasta la base de la copa y ecuación de perfil, desarrollados para la especie a partir de datos obtenidos en una red de parcelas permanentes instalada en la región de JbelLattrech, en el NE de Túnez. Los modelos presentados permiten caracterizar el estado y producción maderera actual de los bosques de thuya a partir de las variables medidas habitualmente en los inventarios forestales para la gestión, y constituyen además un paso preliminar para el desarrollo futuro de modelos dinámicos de crecimiento para la especie. Palabras

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

“…The models developed, along with the tree-level models proposed for the species by Calama et al (2012) and the diameter increment model proposed by Sghaier et al (2013), constitute the first set of basic, flexible tools for the classification and management of these ecologically and economically important forests, which in many arid areas represent the final serial stage of tree forests before shrublands. In this regard, the constructed tools support the forest manager's decision for making different management objectives (handicraft timber, fencing material, fuelwood, CO2 fixation).…”

“…These values were observed in sample trees and estimated for the rest of trees within the plot by using the models developed by Calama et al (2012). As regards crown bulk density, since no specific data for Tetraclinis articulata were found in the literature, we used the average value found for the species of the family Cupressaceae (Ricardi et al 2007), which is 0.06 lb ft -3 , or in metric units, 0.9612 kg m -3 .…”

“…The stem curve taper function and the height-diameter relationships developed by Calama et al (2012) were jointly used to estimate stem volume for all the trees within the plot. Total standing volume was thus computed as the sum of single tree volumes over the whole plot.…”

“…The nonlinear system of equations includes stand level attributes such as mean squared diameter, total stand volume, merchantable volume up to a flexible end-size diameter and aboveground biomass. In a previous study, tree-level attributes for the species such as total height, crown length, diameter and stem form were modeled (Calama et al 2012) and more recently, a distance independent diameter increment model has been constructed (Sghaier et al 2013). The aforementioned studies provide preliminary steps in the development of the present work.…”

“…Unfortunately, scientific literature on this species is scarce, and mainly focused on phytosociological and autoecological studies aimed at determining the potential distribution area of the species and habitat preferences on a local scale (Nabil 1989, Schoenenberger 1995, Nicolás et al 2004, Esteve-Selma et al 2010. However, in recent years a number of papers focusing on growth and yield modeling have been published (Calama et al 2012, Sghaier et al 2013.…”