Thinning and spacing research in Sitka spruce and lodgepole pine.

Thinning and spacing experimentation began in Ireland in the late 1950's. Some meaningful results are now available from these experiments. If spacing at planting is increased from 1.8 to 2.4m square in Sitka spruce a loss in production of about 4% is incurred. A loss of the same magnitude results from a thinning intensity which removes 80% of volume increment. Wider initial spacings or heavier thinning intensities than those conventionally practised give greater quantities of sawlog timber. A first thinning in spruce which removes alternate lines of trees does not depress increment. Rethinning after line thinning comprises a certain amount of unattractive material. There are implications for timber quality where wide spacing and heavy thinning are employed.