The protection of ecological environments and conservation of natural resources are current
trends would wide. Therefore, the ban of natural forest cutting is still a continuing tendency. Under
these circumstances, sustainable and intensive management of forest plantations through silvicultural
practices should render them the main provider of forest products. Chamaecyparis formosensis
(red false cypress) is a native species to Taiwan and has good wood properties which can serve
as an excellent timber for furniture. The stand we investigated underwent serious self-thinning at 8
yr of age, and stand densities of treatment plots were while that of the control plot was 8606 trees
ha-1 were adjusted to 5000, 2500, 1660, and 1110 trees ha-1, while Chamaecyparis obtusa var. formosana
(yellow false cypress) sites were located at compartment no. 94 of Ta-Shi and no. 32 of the
Tai-Ping-Shan working circle at Chi-lan Mt. in northern Taiwan. The former site was a naturally
regenerated stand after site preparation. Stand density reached 11,200 trees ha-1 at 15 yr of age, due
to serious competition. The stand densities for the treatment plots were adjusted to 5000, 3300,
and 2000 trees ha-1. At the latter site, stand densities were 1500~2000 trees ha-1 at 32 yr old for
non-thinned plots. However, the above different stand densities, while reaching maximum densities
for both species, should decrease with increasing stand growth, and then are expected to level
off to a constant trajectory. In this report, the mortality ratio reached 5%, and served as the fulldensity
or self-thinning threshold. The relationship between the mean stem volume (ν) and stand
density (ρ) for red cypress was: ν = 4.73544×104 ρ-1.67604; anf for yellow false cypress was:
ν = 4.12392×105ρ-2.12166. When reaching the maximum density, the quadratic mean diameter (QMD)
and stand density (ρ) equations were: red false cypress QMD = 2.393×103ρ-0.662, and yellow false
cypress QMD = 4.667×103ρ-0.801. Results of this study can serve as a useful reference for thinning
practices of Chamaecyparis plantations at difference stand growing stages or ages.