GML Yield and Update ver. 1.2.9 is a synthesis of several contemporary growth and yield models for loblolly, slash, and longleaf pine plantations and southern hardwoods developed by southern research organizations. GML was developed to generate yield tables for multiple thinning and fertilization treatments and to update inventory records (stand-level only in this version). The first objective is accomplished by specifying a range of first and second thins (thinning windows), with or without mid-rotation fertilization, for one to many stands. Inventory updating is accomplished by using grow-to dates. In both cases, yields are written to an Access database. The generated yields can be filtered and reviewed as a quality control measure and then reformatted as Woodstock yield tables within the same program.
Data for single stands are entered by using a Windows interface, while data for multiple stands are entered by using an Excel workbook. Current stand inputs for pine include plantation age, trees/acre, base site index or observed dominant height, and basal area (ft2/acre) if known. If base site index in not known, then it is estimated iteratively from observed dominant height, silvicultural treatments, and genetic improvement. If initial pine product weights are known, an interpolation procedure can be used to match these with the predicted product volumes.
GML can simulate various levels of genetic selection and silvicultural treatments, including chemical site preparation, bedding or tillage, herbaceous and woody competition control, and time-of-planting and juvenile fertilization. Mid-rotation thinning limits can be specified in terms of residual basal area or residual TPA, and mid-rotation fertilizer rates can be entered in terms of product or elements. A thinning “window” can be defined in which a thin is simulated, with or without fertilization, for each increment of age.
The user interface for GML Yield and Update ver. 1.2.8 has 8 tabs for specifying inputs and outputs: Options; {Stand Info}; {Stand Data}; {Silviculture}; {Thinning}; Product Specs; Run GML; QC Setup/Results. Tab names enclosed with ellipses ”{Stand Info}, {Stand Data}, {Silviculture}, and {Thinning}”correspond to worksheets in the Excel workbook for multiple stands (see description of Batch Processing).