Quantifying and Predicting Stand Diameter Structure with the Logistic Distribution

The possibility of applying the Logistic distribution: F(x) =1/1+exp[-(x-a)/b] to quantify and predict diameter distributions for even-aged pure stands was discussed from the distribution point of view. Results of analyses show that the relationship between parameter a,b and stand quadratic mean diameter Dg could be expressed as linear forms as following: a=a0+a1Dg,b=b0+b1Dg and then the predicting model for stand diameter distribution was constructed: F(x)=1/1+ exp -[x-(a0+a1Dg)]/b=b0+b1Dg (note: a,b,a′,b′,a0,a1,b0,b1 are parameters, F(x) is the cumulative frequency corresponding to diameter x).