Early Precommercial Thinning of Redwood Sprout Clumps: Evaluation of Four Techniques

摘要

Redwood (Sequoia sempervirens (D. Don) Endl.) responds favorably to sprout clump thinning in clearcut environments, but appropriate silvicultural techniques for this practice have not been developed. Four power tools for this unique application were evaluated: standard mid-sized chainsaw (long saw), small arborist chainsaw (short saw), power hedge trimmer, and a customized power brushcutter. Linear mixed effects model analysis was conducted to determine tool differences in clump processing speed, transit time, cycle time, and worker difficulty (peak heart rate). Machine costs and unit production costs were calculated separately for each tool, and perceived ease-of-use by workers was noted. Clump difficulty (sprout clump size) was a strong determinant of processing time and affected the performance of each tool differently. The long saw performed well across the range of clump difficulties but forced the highest heart rates in operators and was the most costly. The short saw was especially proficient on easy to moderate clumps, was among the least difficult, and was the least costly; it was the clear favorite for easy clumps. The hedge trimmer was among the fastest and least difficult, but its capability was constrained by sprout caliper. The brushcutter’s lackluster performance and several inadequacies prevent its recommendation. Regardless of tool selection, the condition of the sprout clump is a factor that must be taken into consideration since it strongly affects average production rates (clumps processed per productive machine hour) and area costs. Sprout age and clump size should guide tool selection, but should also be considered by operators in selectively choosing a subset of crop stumps for sprout clump thinning.