where \(l_{1}\) is the first shape coefficient, \(l_{2}\) is the second shape coefficient, \(\text{fr}_{PHU,1}\) is the fraction of the growing season corresponding to the 1st point on the optimal leaf area development curve, \(\text{fr}_{LAI,1}\) is the fraction of the maximum plant LAI corresponding to the 1st point on the optimal leaf area development curve, \(\text{fr}_{PHU,2}\) is the fraction of the growing season corresponding to the 2nd point on the optimal leaf area development curve, and \(\text{fr}_{LAI,2}\) is the fraction of the maximum plant LAI corresponding to the 2nd point on the optimal leaf area development curve.
For tree stands, the canopy height varies from year to year rather than from day to day: