Stem and crown dimensions as predictors of thinning responses in a crowded tropical rainforest plantation of Flindersia brayleyana F. Muell.

A 67-year-old plantation of Flindersia brayleyana F. Muell. in the wet tropics of north-east Queensland had developed with minimal management. Before thinning, the stand had a canopy stem density of 770 stems ha^-1 of which 564 were F. brayleyana, a stand basal area of 78 m^2 ha^-1, a mean stem diameter at breast height (dbh) of 36 cm, and a mean dbh increment of 5.2 mm year^-1 over the life of the plantation and 0.5 mm year^-1 at the time of thinning. Sixty-three percent of the trees had crown ratios (crown diameter determined from foliage projected area: dbh) of less than 12. Thinning treatments removed 57% of the canopy stems and 45% of the stand basal area. Mean dbh increment over 2.5 years after thinning on basaltic soil was 5.8(plus-minus)0.3 mm year^-1, but for trees with crown ratio <12, it was not significantly different from trees in the unthinned stand with understorey removed (1.3 mm year^-1). Stem diameter, crown diameter and crown ratio at the time of thinning, and mean distance to nearest neighbours after thinning were imprecise predictors of post-thinning dbh increment. There were no consistent relationships between the various tree dimensions that would enable their inclusion in practicable tree selection rules. It is concluded that thinning in natural stands or in very crowded plantations should retain sufficient stems that a second thinning can be made when trees capable of resuming active growth can be identified. Flindersia brayleyana trees from an old, crowded plantation respond to thinning in a way that may allow the early development of a polycyclic silvicultural system, provided damage to smaller trees can be minimised during felling.