Retention forestry in conifer plantations was studied to see how keeping some trees during harvesting affects productivity and cost. The researchers found that keeping broad-leaved trees increased felling and pre-hauling time, leading to higher costs for these operations. However, the overall cost to roadside only slightly increased because these operations made up a small portion of the total cost. This suggests that retaining trees during harvesting can be done without significantly raising the total cost, as long as trees are not kept on strip roads.