Modeling taper and volume of Sal (Shorea robusta Gaertn. f.) trees in the western Terai region of Nepal

Abstract

Volume and taper equations are used for estimating timber volume and biomass of a tree. Despite their usefulness, precise and site specific equations are still lacking for commercially important tree species in Nepal. The study was carried out at Chandak Chatiya Mahila Community Forest in Bardia district and Lumbini Collaborative Forest of Saljhandi in Rupandehi district in western Terai of Nepal. A destructive sampling method was used and selected fifteen Sal trees (Shorea robusta Gaertn. f.) from Saljhandi (site 1) and eighteen trees from Bagnaha (site 2) randomly to calibrate an individual tree volume and a stem taper function. At first, a non-linear stem taper function was calibrated using stem diameters outside bark at different heights above ground as response variable and D (diameter at breast height), H (total height), h (height of interest) as predictors. Then, effect of crown characteristics on stem taper was evaluated. As stem HCB (height to crown base) was found to affect stem taper, its usefulness in existing stem volume equation was tested. Empirical relationships between V (stem volume) as a response variable and D, H, HCB and sites in Bardia and Rupandehi districts as predictors were established using a linear mixed modeling approach. Our result showed that, instead of H, use of HCB in stem volume equation increased model prediction accuracy and reduced prediction bias. Applicability of the suggested models for predicting individual S. robusta tree volume and stem taper is discussed.

Predicting the upper stem diameters and volume of a tropical dominant tree species

“…Taper functions for tree species of Nepal are limited. Only the taper function developed by Silwal et al (2018) is available for S. robusta which used 33 trees from two different sites of the Terai region. Our study has used a relatively larger number of sample trees (n = 54).…”

“…However, other studies have also reported that better performance of segmented taper functions over variable exponent taper functions (Crecente-Campo et al 2009;Özçelik and Crecente-Campo 2016;Shahzad et al 2021). Several studies have been carried out on tree tapers in different areas of the world (Candy 1989;Fang and Bailey 1999;Kozak 2004;Sharma and Patron 2009;Arias-Rodil et al 2015;Poudel et al 2018;Silwal et al 2018;Alkan and Özçelik 2020;Shahzad et al2021)…”

“…of studies have taken place in North America (Max and Burkhart 1976;Shaw et al 2003;Sharma and Patron 2009;Li and Weiskittel 2010;Poudel et al2018), in Europe (Arias-Rodil et al 2015Socha et al 2020), Asia (Fang and Bailey 1999;Tang et al 2016;Lumbres et al 2017;Silwal et al 2018;Shahzad et al 2021;Koirala et al 2021) and relatively a lower number in Australia (Gordon 1983;Bi and Turner 1994;Bi 2000), South America (Nunes and Görgens 2016;Beltran et al 2017) and Africa (Mabvurira and Eerikäinen 2002;Gomat et al 2011). To our knowledge, only two taper functions have been developed in Nepal and these were developed for S. robusta C.F.…”

“…However, studies in Nepal on the species are limited and mostly focused on volume models (Sharma and Pukkala 1990;Subedi 2017), biomass (Chapagain et al 2014;Bhandari and Chhetri 2020), form factors (Baral et al 2020;Chapagain and Sharma 2021;Subedi et al 2021), regeneration dynamics and diversity (Awasthi et al 2015(Awasthi et al , 2020. There is only one study by Silwal et al (2018) on predicting upper stem diameters of S. robusta. However, their function tested only one form of taper equation, did not consider the effect of stand density, and was based only on 33 individual trees.…”

Regularities in form of birch trees in Ukrainian Polissia

“…О. В. Поляков описав твірну стовбура рядом Фур'є за непарними багаточленами Чебишева першого роду (Polyakov, 2008), а А. З. Швиденко застосував показникову функцію, яка монотонно спадає й не має точок перегину. У закордонних працях опрацьовано чимало схожих моделей, які успішно апробовані на практиці (Fonweban et al, 2012;Rojo et al, 2005;Socha, 2002;Silwal et al, 2018).…”