A Height-Diameter Curve for Longleaf Pine Plantations in the Gulf Coastal Plain

An important component of a growth-and-yield model is the relationship between dbh (4.5 ft above ground) and the total height of individual trees. The US Forest Service laboratory at Pineville, Louisiana, has collected over 65 years of longleaf pine .plantation growth information from seven studies within the Gulf Coastal plain. The primary purpose of this collection is to develop a regional growth-and-yield model for thinned and unthinned plantations of longleaf pine (Pinuspalustris Mill.). An important component of a regional growth-anti-yield model is the ability to supply heights for trees where orly diameter is known. T&al heig 'h't -is 6oih an'important des- criptiv&individual tree variable and also is'neces'sary to calculate tree volume or other product yields. Heightpiedictions can be used both in this regional model and in other situations where only diameters were measured. Model development is frequently not as orderly as one would like baue the 'rue mathematical relationship is seldom known, and there are infinite possible approximations for the true model. Curtis ( 1967 ) examined many forms of height—diameter equations and ultimately suggested that "any reasonable and moderately flexible curve" will give similar results. Complex mathematical functions are much easier to fit now than in 1967, so a current evaluation of many model form's that were formerly used by other researchers was conducted The necessary assumptions for valid regression models and