The SOHARC Model System for Growth and Yield of Southern Hardwoods John Paul McTague, David O’Loughlin, Joseph P. Roise, Daniel J. Robison, and Robert C. Kellison A system of stand level and individual tree growth-and-yield models are presented for southern hardwoods. These models were developed from numerous permanent growth-and-yield plots established across 13 states in the US South on 9 site types, in even-aged (age classes from 20 to 60 years), fully stocked, naturally regenerated mixed hardwood and mixed hardwood-pine stands. Nested plots ( 1 /5 and 1 /10 ac) were remeasured at 5-year intervals. The system of permanent plots was established and maintained by private and public members in the North Carolina State University Hardwood Research Cooperative. Stand level models are presented for dominant height, survival, basal area prediction and projection, and the ingrowth component. Individual tree diameter growth and tree height models were constructed for the most common species: sweetgum, tupelo, yellow-poplar, blackgum, and red maple. All other species were grouped according to growth dynamics into four species groups using cluster analysis. A ranking variable was incorporated into the individual tree growth models to account for competition. Keywords: natural stands, repeated measured fixed plots, species projections, basal area projections, stand- and tree-level projections, general G ood decisionmaking regarding the marketing of timber- land and timber for optimum value can not be made until there is an inventory of standing volume and grade. Long- term management of the forest asset is governed by financial matu- rity and stewardship values, which are influenced by species compo- sition, growth rate, site, quality changes, and interest rates. The development of stand, stock, and growth-and-yield tables, together with a current inventory, are essential to making optimal forest management decisions. Growth-and-yield systems are reasonably well documented for species that occupy pure natural stands and plantations. Multiple growth-and-yield systems have been developed for southern pines, especially loblolly pine (Pinus taeda L.) and slash pine (Pinus elliotii Engelm.) (Clutter 1963, Burkhart and Strub 1974, Clutter and Jones 1980, Hafley and Buford 1985). Growth and yield in mixed stands are much more difficult to model because the species have different growth rates and timber quality. Of the 214 million ac of forestland in the South, hardwoods occupy about 120 million ac (Forest Inventory Analysis [FIA] 2002). The gamut runs from high timber value, such as cherrybark oak (Quercus pagoda R.) and green ash (Fraxinus pennsylvanica Marsh.) to species of lower timber value such as sweetgum (Liqui- dambar styraciflua L.) and red maple (Acer rubra L.). Our objective was to develop a system of models to predict the growth and yield of mixed species hardwood and hardwood-pine stands in the southern United States. This system represents 41 years of collective effort by the members and partners of the North Carolina State University Hardwood Research Cooperative (HRC). We call this system, “SOHARC,” for the Southern Hardwood Research Cooperative. Data and Methods In 1967, the HRC at North Carolina State University initiated a project, known as Region-Wide Study 55, to develop growth-and- yield tables for southern hardwoods. The first effort was to recognize the forest site types that were of sufficient size to be identified as separate operating units. Nine such units were identified (Table 1), six in the Coastal Plain (muck swamps, peat swamps, wet flats, red river bottoms, black river bottoms, and branch bottoms) and three in the Piedmont/mountains (bottomlands; coves, gulfs, and lower slopes; upland slopes and ridges; Kellison et al. 1982). To develop growth-and-yield tables for the southern hardwood resource a large amount of data were needed. Over 600 plots were established by members of the HRC, across the South [1]. About 1 /5 of the plots (187) were maintained for repeated measurements on a 5-year cycle. Of the 187 established plots, 146 were observed more than once, and 92 were measured on three or more occasions. Over the years, some plots were lost to harvest and changes in landownership. Received October 25, 2007; accepted August 20, 2008. John McTague (johnpaul.mctague@rayonier.com), Rayonier, 1901 Island Walkway, Fernandina Beach, FL 32035, and Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695. David O’Loughlin (oloughlind@bellsouth.net), Joseph Roise (joe_roise@ncsu.edu), Daniel Robison (dan_robison@ncsu.edu), and Robert Kellison (bkelliso@bellsouth.net), Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695. This work is the culmination of decades of collective effort by many research and field foresters and technicians associated with 48 different organizations from across the US South. Among the many deserving formal recognition, are, from North Carolina State University—Carol Beam, Peter Birks, Robert Chu, Doug Frederick, William Gardner, Karin Hess, Martha Holland, Robin Hughes, John William Johnson, Russ Lea, Chien Lu, P. Marsh, Robert McElwee, Dennis Mengel, Heather Moberly, James Roberds, Ken Roeder, Jamie Schuler, Tom Tew, Carmen Thomas, Roman Tseng, Michael Young, and Bruce Zobel, and from various members of the North Carolina State Hardwood Research Cooperative (NC State HRC), most recently—Warren Boyette, Leonard Breeman, Bruce Brenneman, Steve Coleman, Joe Cox, Eddie Drayton, Dick Fisher, Thomas Fox, Gerald Hansen, Joseph Hughes, Marshall Jacobson, Matthew Lowe, Martha Loyd, John Martin, Joe Mills, Hank Page, Robert Purnell, Harry Quicke and Kurt Zweizig. There were many others from the NC State HRC membership whose names could be listed. Funding for this work came from the NC State HRC members, in-kind contributions from many, and support from the NC State University Department of Forestry and Environmental Resources through department heads T. Ewald Maki, Charles Davey, John William Johnson, Arthur Cooper, Fred Cubbage, and Barry Goldfarb. Copyright © 2008 by the Society of American Foresters. SOUTH. J. APPL.FOR. 32(4) 2008 173 ABSTRACT Downloaded from https://academic.oup.com/sjaf/article/32/4/173/4774750 by guest on 28 February 2021