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During the last two decades, the Costa Rican government has promoted the
establishment of Tectona grandis plantations for sawn timber. However, there is a
lack of knowledge on optimum spacing and on thinning regimes, in contrast to high
expectations of final mean diameter at breast height (DBH) between 35 and 40 cm
and stand volumes between 200 and 300 m3 ha-1. The aim of this study was to
establish guidelines for plantation management in terms of appropriate intensity and
timing of the first thinning (from approximately 4 thinnings recommended in 20–25
year-old rotation management systems). A thinning trial was established in a 4-year
old T. grandis plantation that was originally established with initial spacing of 1600
trees ha-1. The experimental design consisted of randomized complete blocks,
with eight treatments and three replicates. Each treatment consisted of 80 trees in
square blocks of 500 m2. The treatments were of different thinning intensities (from
25% to 60% removal of standing trees, and the unthinned control) applied at two
timings (at the ages of 4 and 6 years, and one treatment applied at the ages of 4
and 5 years) and an unthinned control in each replicate. The trees in each
treatment were measured annually between age 4 and 8 years. At the age of 8
years, the average DBH for all treatments was 17.5 cm (15.2–20.1 cm) and the total
height averaged 18.8 m (17.7–19.5 m). The total volume (Vo) varied from 90 to 200
m3 ha-1, at corresponding BA between 12 and 28 m2 ha-1.The 60% thinning
intensity applied at the age of 4 years, and the two consecutive 25% thinnings at
the ages of 4 and 5 years gave the highest individual tree growth, while the control
was the lowest. The current annual increment (CAI) of DBH was highest in the 40
and 60% thinned treatments. The CAI of DBH and BA decreased rapidly with
increasing age in every treatment. The values of CAI of Vo varied between 9 and 39
m3 ha-1 year-1. The high values of CAI of Vo were obtained at BA between 18 and
20 m2 ha-1. At BA of 18 m2 ha-1, Vo was between 120 and 150 m3 ha-1 on a
stand conformed by trees with an average DBH between 17 and 20 cm. The
recovery of BA and Vo was faster in the treatments carried out at the age of 4 years
than at 6 years, when measured 2 years after the thinning. In terms of the remaining
stand volume (after thinning), tree size and rate of recovery, the best thinning was at
the age of 4 years removing 40–60% of the trees, or consecutively at the ages of 4
and 5 years removing 25% of standing trees in each year. Results of this thinning trial
indicate that T. grandis plantations can be managed towards the production of high
individual tree growth or towards the production of high stand growth, by means of
varying the intensity and timing of the thinning interventions through rotation.