Forestry owners are increasingly deciding not to prune their trees as their value relative to unpruned trees drops.
The Ministry for Primary Industries' forestry report for 2012 shows more than 1.7 million hectares of land is planted with production forests.
In the year to March about 23 million cubic metres of logs were harvested.
The report says 58%, or 900,000 hectares, of the forest planted in radiata pine was pruned.
That's a 9% reduction from 10 years ago.
The ministry's forestry and plant sector manager Lisa Winthrop says several factors are contributing to fewer trees being pruned.
She says there is a long term trend of less pruning of New Zealand forests due to the relative value of pruned and unpruned logs.
"Pruning costs more because of the labour, but it does produce wood with fewer knots and that looks better."
She says anecdotally one reason given for less pruning is the fact that technology means wood processors can do more with knotty timber.