PCWTHIN2.1 is a computer program which can be used to predict the growth and yield of thinned and unthinned old-field loblolly pine plantations and do financial analyses based on those predictions.      Inputs to the model are:           age           site index (base age 25)           stand density (trees and/or basal area per acre).      Outputs include (by 1-inch dbh classes):           surviving trees per acre           basal area           volumes (various units can be specified by the user).      PCWTHIN2.1 is based on numerous equations which predict and project whole stand and stand distribution characteristics. Data for the equations were from both Piedmont and Coastal Plain sites. Dbh distributions are obtained from stand-level characteristics by requiring the first two noncentral moments of a Weibull distribution match arithmetic mean dbh and quadratic mean dbh squared. All output is displayed on the monitor. The dbh distribution of the stand can be shown as a 3D bar graph. If a printer is available, the user can easily obtain printed copies of selected results. Output from the stand/stock table can be copied to the Windows clipboard and then pasted to other Windows applications for additional evaluation. Options are available to initialize a dbh distribution for a thinned or unthinned plantation, to thin a plantation according to one of several thinning algorithms, and to project a dbh distribution through time. With PCWTHIN2.1 a large number of plantations can be grown and studied within a short period of time. Further, numerous thinning strategies can be quickly compared, both from a biological and a financial basis, for a specific plantation.      Download a Demonstration Version (Windows only) 1. Click PCWTHIN to start downloading.(300k) 2. With Internet Explorer select "save this program to disk" , choose a directory or the desktop to save to. 3. Run the file saved in step 2 by double clicking it. The self extraction utility starts. 4. From the menu choose SelfExtract/Extract Files, choose a destination directory (directory must already exist). Click Execute. 5. Run the demo program in the destination directory of step 4. 6. The demonstration version site index is set to 60.      A detailed users manual is available at no charge and the software can be purchased for $50.00. For additional information, contact ralph@vt.edu. PCWTHIN user manual Need a PDF viewer? Try Adobe Systems' Acrobat Reader.