Thinning

Abstract

Thinning involves the removal of trees from a plantation from time to time during its life. Despite the loss of leaves from the trees removed at thinning, the remaining trees are able to increase their photosynthetic rates so there is no loss of growth overall. Over 2–3 years, the crowns and root systems of the remaining trees expand to replace what was lost at the thinning. After thinning, new growth is distributed amongst the fewer trees that remain; their stem diameter growth rates accelerate and they produce large-diameter logs at earlier ages than would have occurred without thinning. Thus, thinning speeds production of larger, commercially more valuable logs to be used for sawn wood production. A thinning regime for a plantation requires consideration of how many times and at what ages it should be thinned and how many and which trees should be removed at each thinning. These should be chosen to achieve the best possible financial outcome for the plantation enterprise. Modern thinning regimes commonly involve two or three thinnings before 15–20 years of age, with 100–300 trees per hectare left after the final thinning. The final harvest then occurs at 25–30 years of age.