Effects of early respacing on physico-mechanical properties of naturally regenerated Picea sitchensis in Great Britain

Natural regeneration can reduce costs compared with replanting. However, its use requires knowledge about how either active or passive management will affect the balance between quality and quantity in the timber supply. This study aimed to quantify the effects of respacing on volume recovery and wood properties. Two British forest experiments using Picea sitchensis with various respacing distances and an un-respaced control were assessed 21-22 years after the treatments were applied. Tree dimensions were measured and used to quantify slenderness, merchantable volume and sawlog-volume. Wood properties were assessed on a sub-sample using mechanical testing. Generalised linear mixed models were used to examine differences between treatments and sites. Respacing decreased slenderness and increased relative sawlog volume and branch size. Wider respacing reduced wood strength and the widest respacing reduced wood stiffness. Respacing did not affect wood density. However, at the relatively low productivity sites considered here, respacing to 2.1m represented the best compromise for current markets. In summary, not respacing improved some wood properties, but reduced tree stability and the proportion and volume of sawlogs, which will negatively affect forest value.