This article summaries the main uses of the I300 growth model within YTGen.

In summary the 300 Index model is a New Zealand national growth model for Pinus radiata. The Plantation Management Co-operative initiated its development before 2005; later Future Forests Research has been involved. Development is ongoing, and the model has been developed in stages and refined over time. The 300 Index growth model (GM:I300) has been available within YTGen since September 2008 for members of the Future Forests Research.   It becomes available within YTGEN through your licensing codes provided.

The 300 Index growth model offers YTGen users several options related to user variables that modify behaviour of the growth model. As a consequence of YTGen dealing with plots the modified behaviour are implemented at plot level and hereafter applied at the population or yield request level.

Available user variables that modify behaviour are:

  • Planted stocking
  • I300 stocking event
  • I300 Pruning Event
  • Altitude
  • Latitude
  • I300 Drift Factor
  • I300 Step Length
  • I300 Allow Backward Growth Through Thin
  • I300 Print Index
  • I300 History Writer Thin Age
  • I300 Compatibility Mode

These variables can be used to forecast silviculture regimes, hereby enabling YTGen to simulate growth scenarios from early age to maturity.

The following is an example of the syntax entered into YTGEN for nominating the 300 index as a growth model and providing parameters to constrain the model.   In this case for a site; at altitude of 180m, latitude of 40 degrees south, specifying a regional drift factor for Northland Coastal Sand of -0.3, planted at 1111 SPH, with two thinnings at age 5 and 12, and 3 lift pruning at ages 5 (1.8m lift 500SPH), 6 (3.8m lift 400 SPH) and 8.5 (6.2m lift 250 SPH).  Also specified is a flag to print the 300 Index value to the information log window in YTGEN during processing which is useful for understanding, but not required.

User Variables
GM:I300 ALTITUDE=180 LATITUDE=40 I300_DRIFT_FACTOR=-0.30 PLANTED_STOCKING=1111 I300_STOCKING_EVENTS:(7,0,550),(12,0,250) I300_PRUNING_EVENTS:(5,1.8,500),(6,3.8,400),(8.5,6.2,250) I300_PRINT_INDEX=1


We will continue to publish more about these in later posts, or feel free to contact Interpine or Silmetra for more information.

Using the I300 and applying these variables to define your growth parameters enhances its application. When including spatial location (Latitude, Altitude) and I300 Drift Factor it provides an alternative to previous regional growth models such as: NapiRad, CANT, PPM88, Sands, Clays etc.

Figure 1 displays several examples of using I300 with some of these other common models.   The influence of the model will always depend on its constraints, input data, and start point so do not use these for generic assumptions about growth.



Figure 1: Yield prediction using regional and national I300 Index.


The industry is turning towards using the national I300 Index.   Please feel free to contact us if you have comments or questions related to this article and I will post more about the syntax to use in YTGEN for constraining the 300 Index in further articles.