public static double Calculate_Establishment(ISpecies Species, float PAR, float PressureHead)
        {
            double frad = Math.Pow(SubCanopyLayer.CumputeFrad(PAR, Species.HalfSat()), Species.EstRad());
            double fwater = Math.Pow(SubCanopyLayer.GetFWater(Species, PressureHead), Species.EstMoist());

            return frad * fwater;
        }