Determination of site class in uneven-aged pine stands for forest management in Mexico.

In a 16 ha large uneven-aged (17 to 72 years) natural stand of Pinus teocote of the Sierra Madre Oriental in the north east of Mexico, with different sites (yield classes 1.5 to 11.5) a simplified method for estimation of age and site class for forest management is developed. Hereto, a partial age-diameter (dbh) function with 40 sample trees from an interval around the d(g) (20 cm to 30 cm dbh) was established (Fig. 1). Smoothing by a simple linear function has proved suitable. 95% confidence intervals for mean age increase according to decreasing of sample size (Fig. 2, Tab. 1). The half width of the confidence interval for mean age at the d(g) (d(1.3)=25 cm) for a sample size of n = 10 is only +/-3.3 years. Beside the mean age the mean height (h(g)) is necessary in order to estimate the site class of the stand. Using the same sample trees a simple linear height-diameter-model is established. This function gives about the same results as the MICHAILOV-height-curve (Fig. 3). With decreasing sample size (N = 37 --> N = 10) the half width of confidence intervals for mean height increases from 0.30 m to 0.50 m (Tab. 2). Measurement of 10 representative sample trees from an interval around d(g) seems to be sufficient to estimate mean age and mean height of an uneven-aged pine stand. Further investigations are recommended.