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A correction model for estimating jack pine tree-level lumber recovery accurately using forest inventory data.

Article Excerpt
Abstract

This study proposes an approach to directly estimate lumber recovery from individual trees using forest inventory measurements. In this approach using tree measurements and taper equation, three-dimensional virtual stems were reconstructed for lumber recovery simulation, and simulated lumber recoveries from the virtual stems were compared with those from the real-shape stems to investigate the lumber recovery differences between the two types of stems. Lumber volume recoveries from jack pine real-shape stems were lower than those of the virtual stems due to stem deformations. There were no significant differences in the number of lumber pieces produced for each dimension (except for 1 by 3 board). The lumber volume recovery of the real-shape stems was linearly corrected with that of the virtual stems with an intercept coefficient not different from zero. As the linear models will allow for stem deformations to be taken into consideration when lumber recovery is estimated from the virtual stems reconstructed from forest inventory data, they will thus lead to a more accurate estimation of lumber recovery directly from forest inventory data.

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Forest inventory data are collected at different scales to estimate wood volume. For decades, the wood volume information estimated form forest inventory has been used to develop various forest management policies and decisions (e.g., annual allowable cut, silvicultural planning, harvesting target and schedules). It is well known to wood scientists that each [m.sup.3] of wood is not created equal in terms of product recovery (e.g., yield, mix, quality, value). For example, lumber recovery from one [m.sup.3] of sawlogs in a particular jack pine stand ranged from 157 to 278 BF (0.37 to 0.67 [m.sup.3]) in lumber volume, and from CND$51.41 to $130.39 in product value (Zhang et al. 2006). In order to make better-informed forest management decisions, it is necessary to estimate product recovery directly and accurately from forest inventory data.

Product recovery from a tree could be estimated accurately using a sawing simulator like Optitek (Goulet 2006) if three-dimensional (3-D) geometrical data could be acquired for the stem (Zhang and Tong 2005). For a number of reasons, however, forest inventory programs in Canada usually do not collect 3-D stem geometrical data. Forest inventory usually measures diameter at breast height (DBH), total tree height and selected stand characteristics (e.g., stand density and site quality). Using these measurements and a stem taper model, stem diameter profiles along the tree height can be established (Sharma and Zhang 2004) and thus a 3-D virtual stem can be reconstructed. However, the virtual stems reconstructed from a stem taper model, unlike the real-shape stems, contain no stem deformations (e.g., sweep and crook). On the other hand, stem deformations significantly reduce lumber volume recovery (e.g., Monserud et al. 2004), lumber properties and dimensional stability (Harris 1989, Taylor and Wagner 1996). Therefore, to accurately estimate lumber recovery directly from forest inventory, stem deformations should be taken into consideration.

Both forest scientists and wood scientists are fully aware of the negative effects of stem deformations on product recovery. Some studies have evaluated these negative effects (Brown and Miller 1975, Snellgrove et al. 1975, Dobie and Middleton 1980, Cown et al. 1984, Cahill and Cegelka 1989, Harris 1989, Oberg 1989, Todoroki and Ronnqvist 1998, Monserud et al. 2004). Due to the lack of required hardware and/or software together with some technical difficulties, insufficient effort has been made to develop such a lumber recovery correction model for stem deformations. Because of the irregular within-a-tree variation in stem geometry, it is impossible to describe stem deformations in 3-D using existing inventory measurements. Therefore, an alternative solution must be found to take stem deformations into consideration when product recovery is estimated directly from existing inventory measurements by means of virtual stem reconstruction. The purpose of this study is to develop a lumber recovery correction model to estimate the lumber recovery loss due to stem deformations. With such a lumber recovery correction model, then, the lumber recovery could be estimated accurately from forest inventory measurements. To develop such a lumber recovery correction model for stem deformations, lumber recoveries from virtual stems reconstructed from a stem taper model will be compared to those from corresponding real-shape stems to quantify differences in lumber recovery between the two types of stems. Then, the lumber recovery differences between the two types of stems in relation to various tree- and stand-level characteristics available from the forest inventory will be quantified to develop a descriptive mathematical model. This model will be used to estimate...

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