The Forestry Source - December 2010 - (Page 14)
Here’s How to
Build a Local Weight Table for Loblolly Pine
Office Procedure The data for each sample tree were compiled in a database with fields as shown in Table 1. For ease of use, the data were sorted first by one-inch class, then by dbh, and finally by total height. Avery and Burkhart note that this method “is dependent on a well-established height-diameter relationship.” They also state that there is a straight-line relationship between the reciprocal of dbh (dbh-1) and the natural logarithm of total height (ln h). The scatter diagram and regression line for these two variables are shown in Figure 1. The formula for the regression line was calculated as: ln h = 4.8217 – (6.1471 x dbh-1)
Figure 1. Scatter diagram and regression line for the sample tree data.
By Michael C. Thompson his article describes the construction of a singleentry weight table for managed stands of loblolly pine (Pinus taeda L.) for Montgomery County, North Carolina, using a multiple-entry weight equation for loblolly pines in North Carolina and Virginia. Instructions for the procedure were provided by Avery and Burkhart (2002). Using a single-entry local weight table eliminates the need to measure or estimate height for each tallied tree on a timber cruise. “In” trees are tallied by diameter at breastheight (dbh) only, and a stand table is developed. Total tract weights or weights per acre are derived by multiplying the number of trees in each dbh class by weight per tree. Cruise fieldwork can be completed more quickly. This procedure is useful when broad regional values are appropriate (such as in the preparation of management plans or cutting budgets) and stock/stand tables must be developed. Caution, good judgment, and experience must be exercised when using it for specific timber sales where accuracy is paramount. The procedures described here may be useful for foresters working in the southern Piedmont loblolly pine region, because it gives tons per tree by dbh class. Scaling in tons for both pulpwood and sawtimber is fast becoming the normal, if not exclusive, practice here in central North Carolina. These procedures also may be used to create single-entry local weight tables for other regions and other species. Montgomery County lies in the Piedmont in the geographic center of North Carolina. The western part of the county contains the remnants of the Uwharrie Mountains,
Coefficient of determination (r2) = 0.760. Average heights for each one-inch class were predicted by substituting into the formula above. For example, the predicted total height of an eight-inch dbh tree is 58 feet. Weights of trees in pounds were derived from a formula developed by the USDA Forest Service (1984): W = -64.22742 + (0.14439 x h x dbh2) Where: W = green weight of the main stem (wood and bark) to a four-inch top, in pounds; h = total height in feet; and dbh2 = dbh squared. Example: For a loblolly pine that is eight inches dbh and 58 feet total height, the weight to a four-inch merchantable top is: -64.22742 + (.14439 x 58 x 82) = 472 pounds The tree weights provided by the USDA formula above compare very favorably, usually within .01 ton per tree, with results obtained by the Research Division of the Georgia Forestry Commission (1990) for planted loblolly pines in the Piedmont. The completed single-entry local weight table is shown in Table 2. While it is specific to Montgomery County, NC, it could possibly be used elsewhere in North Carolina and Virginia if the local diameterheight relationship is the same as that revealed by this study. It should be emphasized that complete utilization to a four-inch merchantable top is assumed for all stems regardless of dbh. Therefore, using the table to predict total weights of stands with a high sawtimber component and where topwood is not utilized will probably result in estimates that are higher than those actually realized from a harvesting operation. Michael C. Thompson is a registered forester in North Carolina. He is senior instructor of forest management technology at Montgomery Community College in Troy, NC. Contact him
The Forestry Source
at firstname.lastname@example.org or at (910) 576-6222, ext. 233. For those who are interested, the original field data from this study is available upon request. Literature Cited Avery, T. E., and Burkhart, H. E. 2002. Forest Measurements. 5th Ed. McGraw-Hill Higher Education, New York. 456 pp. Section 8-12. Research Division, Georgia Forestry Commission. Georgia Forest Research Paper 79. Alexander Clark III and Joseph R. Saucier. “Tables for Estimating Total-Tree Weights, Stem Weights, and Volumes of Planted and Natural Southern Pines in the Southeast.” September 1990. Table 29—Predicted green weight of stem wood and bark to 4-inch dob (diameter outside bark) top for planted loblolly pine in the Piedmont, based on dbh and total height. US Department of Agriculture, Forest Service. General Technical Report WO-42. “Tables of Whole-Tree Weight for Selected U. S. Tree Species.” July 1984. Table 128—main stem, wood and bark, green weight (pounds). Pinus taeda–loblolly pine, North Carolina, Virginia. Have an idea for a “How to,” let us know. Send your idea to email@example.com.
Table 1. Sample-tree database structure.
where clay soils predominate, while the southeastern part lies in the Sandhills region and could be considered the beginning of the upper coastal plain. Elevations range from about 200 feet above sea level in the Pee Dee River bottom to more than 900 feet in the Uwharrie Mountains. Forest types include loblolly, longleaf, and shortleaf pine; and mixed hardwoods, with oak, hickory, and yellowpoplar prevailing. The natural range of loblolly pine ends in the northwest corner of the county. Field Procedure From May through November 2009, measurements of diameter at breast height and total height were taken from 110 loblolly pines growing in managed stands in Montgomery County. For the purpose of this study, “managed stands” includes pine plantations, both thinned and unthinned, and natural stands that have been thinned. Of the 110 trees included in the study, 106 were measured in plantations and four in natural stands. An attempt was made to find trees growing on a variety of sites throughout the county on different ownerships, which included forest industry, national forest, community college, and private land. The dbh of each tree was measured with a diameter tape and placed in a one-inch diameter class. For example, class boundaries for a 10-inch class tree were 9.5 inches to 10.4 inches, with 10.0 inches considered the midpoint. Boundaries for an 11-inch-class tree were 10.5 inches to 11.4 inches, with 11.0 inches considered the midpoint. Ten trees in each one-inch diameter class from five inches through 15 inches were measured. Total heights were measured to the nearest foot for each sample tree using a clinometer at known horizontal distances of 33 to 75 feet, depending on the height of the target tree.
Table 2. Height-diameter equation: ln h = 4.8217 - 6.1471dbh-1. Weight is pounds of the main stem, wood and bark, green weight, to a four-inch merchantable top for loblolly pines in North Carolina and Virginia. Multiple-entry weight equation (W = -64.22742 + 0.14439*h*dbh2) taken from US Forest Service General Technical Report WO-42.
Table of Contents for the Digital Edition of The Forestry Source - December 2010
The Forestry Source - December 2010
2010 National Convention Recap
An Overview of Forestry and Natural Resources Master’s Degree Programs in the United States
Field Tech: A Forester’s Wish List
Here’s How to Build a Weight Table for Loblolly Pine
People in the News
Continuing Ed. Calendar
Bcap Is Back: Usda Revises Rules for Biomass Crop Assistance Program
The Forestry Source - December 2010