Growth & Yield Projection System - Forest Management

The Alberta government is responsible for managing provincial Crown forest lands within the Green Area. As part of that responsibility, forest managers assess the growth rate of forests.

Alberta Agriculture and Forestry (AF) has developed a whole-stand growth prediction model named Growth and Yield Projection System (GYPSY). GYPSY is used to forecast the growth and yield of stands of trees on a per hectare basis.

The Government of Alberta acknowledges the substantial support for GYPSY development provided by the Forest Resource Improvement Association of Alberta (FRIAA) and by the ten Forest Management Agreement (FMA) holders who supported the provision of FRIAA funding.

System Versions

The first version of GYPSY was released in 2001. The forecasting capability of this version was limited to pure lodgepole pine stands.

The 2009 version has been updated to include modeling capability for multiple species in pure and mixed species stands. It also enables forest managers to predict future growth based on reforestation survey results.

GYPSY Tree Species Groups

GYPSY can forecast the growth of four tree species groups:



Aspen group

balsam poplar (Populus balsamifera)
trembling aspen (Populus tremuloides)

Black spruce group

black spruce (Picea mariana)

Pine group

jack pine (Pinus banksiana)
lodgepole pine (Pinus contorta v. latifolia)
tamarack/larch (Larix laricina)

White spruce group

alpine fir (Abies lasiocarpa)
balsam fir (Abies balsamea)
Douglas-fir (Pseudotsuga menziesii)
Engelmann spruce (Picea engelmannii)
white spruce (Picea glauca)

GYPSY Sub-models

GYPSY is composed of a number of sub-models:


Prediction Area

Top height

Predicts the average height of the 100 largest diameter at breast height (DBH) trees per hectare

Percent stocking

Predicts the level of stocking in a stand, provides a direct linkage between regeneration survey standards and yield forecasts

Non-spatial density

Predicts stand density changes over time without using percent stocking as an input

Non-spatial basal area increment

Predicts the annual basal area increment without using percent stocking as an input

Spatial density

Predicts stand density changes over time using percent stocking as an input

Spatial basal area increment

Predicts the annual basal area increment using percent stocking as an input

Gross total and merchantable volume

Predicts the species group-specific gross total volume of a stand at 0/0 or any other user-defined utilization standard

Merchantable density

Predicts the species group-specific density of a stand at any user-defined utilization standard

Where stocking information is available, the model can use either the spatial or the non-spatial sub-models for forecasting.

Model Documentation

GYPSY Software Tools

The GYPSY sub-models were initially compiled into a fully functional growth-and-yield model using the Statistical Analysis System (SAS). GYPSY SAS code is available upon request. There are two Microsoft Excel implementations of GYPSY 2009: the GYPSY Yield Table Generator Tool, and the Performance Age Silvicultural Scenario (PASS) Tool. Excel GYPSY is more flexible and produces yield tables and other key outputs from starting conditions at any age. The PASS Tool is simpler to use and provides graphical and summary output specifically in support of reforestation performance surveys for stands aged 12-14. The following sections provide installation information for these tools, user licenses, and manuals.

Both the Microsoft Excel GYPSY Yield Table Generator and the PASS Tool requires the installation of the GYPSY 2009 COM DLL, which needs to be registered properly on your system.

The COM DLL is a library of the GYPSY functions in compiled computer code that can be called from other programs or programming languages. Once registered, the DLL components can be freely accessed by any program without having to explicitly reference it again.

System Requirements

Excel GYPSY Yield Table Generator:
  • Operating System: MS Windows 95; MS Windows XP; MS Vista; MS Windows 7/8/10
  • Compatible with MS Office 2002 and newer, 32-bit software only
Excel PASS Tool:
  • Operating System: MS Vista; MS Windows 7/8/10
  • Compatible with MS Office 2007 and newer, 32-bit software only

Initial Setup to Use the Excel GYPSY Tools

1. Download the Excel GYPSY Yield Table Generator ZIP file or the Excel GYPSY Pass Tool ZIP file. These contain:

Excel GYPSY Yield Table Generator ZIP:
  • GYPSY 2009 COM DLL File
  • DLL Interface Manual
  • DLL Troubleshooting Memo
  • Excel GYPSY License Agreement
  • Excel GYPSY Yield Table Generator Tool
  • Excel GYPSY Yield Table Generator Tool User's Manual

  • GYPSY 2009 COM DLL File
  • DLL Interface Manual
  • DLL Troubleshooting Memo
  • PASS Tool License Agreement
  • PASS Tool
  • PASS Tool User's Manual
2. Extract the files from the ZIP file by using MS WINZIP or a similar application.

3. Register the GYPSY 2009 COM DLL file (GYPSY_2009.dll) on your system by following the steps in the GYPSY 2009 DLL Interface Manual. Newer versions of Windows will require use of the DLL Troubleshooting Memo.

4. Open the Excel GYPSY Yield Table Generator Tool (GYPSY_YTG_2009v2.xls), or open the Excel PASS Tool (PASS_Tool_2014.xlsm) (no installation is required once these are unzipped, however, you will need to enable macros in Excel) and follow the instructions. Detailed instructions are provided in the user manuals for these packages.

Copyright and Licence Agreement

All proprietary rights, including copyright in the GYPSY software, its documentation and data, are owned by and shall remain the property of the Government of Alberta (the "Crown"). All rights reserved.

The Crown makes no warranty or representations of any kind with respect to the GYPSY software, its use, suitability or application for any purpose. The Crown, its officials, Ministers, employees and contractors shall have no liability or responsibility for any loss or damage whatsoever arising from or as a result of the use of this software.


By downloading the following program files, you have agreed to the terms and conditions of the detailed Licence Agreement for this software. To view the GYPSY Copyright and Licence Agreements, see: Contacts

For answers to technical questions regarding GYPSY and its associated tools, contact:
For more information about the content of this document, contact Wendy Machan.
This information published to the web on February 25, 2016.
Last Reviewed/Revised on March 9, 2018.