See http://heurekaslu.org/wiki/ControlTable_Production_Model

The example below shows how to active natural ingrowth of new trees (which is inactivated by default in the API). This feature should be activated if simulering continous cover forrestry, if longer planning horizons are used (say more than 10 years).

var ct = gc.GetControlTable<ProductionModelControlTable>();
ct.IngrowthModel = IngrowthModelType.Deterministic;