Abstract
Naturally regenerated yellow cypress (Chamaecyparis obtusa var. formosana) stands were
located at Chilan Mountain, northern Taiwan, on Hwy. 100 near the 14.5-km marker. Thinning and
pruning treatments were carried out in 1993 when the stands were 32 yr old. This study reports
the results of diameter at breast height (DBH) and tree height growth 7, 12, 17, and 20 yr after
thinning and pruning. Data of DBH and net height growth of yellow cypress showed a significant
increase 12 yr or longer periods after thinning compared to the no-thinning stand. However, the
basal area and timber volume showed no difference among thinning treatments. Pruning treatment
showed a trend of net height growth, i.e., pruning 1/2 of tree height > 2/3 of tree height > no pruning
(control), but tree growth traits such as DBH, tree height, and volume showed no differences
at 20 yr after pruning. Tree mortality percentages of yellow cypress with medium thinning, light
thinning, and control treatments were 3.1, 6.3, and 9.6%, respectively, at 20 yr after thinning. Since
yellow cypress trees grow very slowly, the average annual growth increments of DBH 20 yr after
treatment for medium thinning, light thinning, and control treatments were 0.31, 0.30, and 0.26 cm,
respectively, and of volume were 5.80, 6.46, and 6.09 m3 ha-1, respectively. We used the Weibull
probability density function with thinning, pruning, and age as parameters to estimate the diameter
distribution. Results showed the goodness of fit was p = 0.01 by the Kolmogorov-Smirnov test.
Furthermore, the parameters and elements of stand structure had significant relationships. These results
can explain the dynamics of stand growth based on the diameter distribution and can be used
to estimate the structure of the stand and carbon sequestration in the future.