Long-term taper and growth reductions following pruning intensity treatments in giant sequoia (Sequoiadendron giganteum)

Abstract

A high degree of stem taper limits the potential value of giant sequoia (Sequoiadendron giganteum (Lindl.) J. Buchholz) when grown for timber. I measured the effects of pruning to different height targets (0, 2.0, 3.5, and 5.5 m), resulting in the removal of 25%–85% of crown length, on the growth of 360 S. giganteum trees over 17 years. Height growth and growth of diameter at breast height were both negatively related to pruning intensity to a similar degree. Within the 17 years following pruning, repeated measurements of stem growth at different heights above the ground revealed that radial stem growth reductions were localized on the stems from which branches were removed. The higher up that trees were pruned, the more that stem radial growth was reduced compared with control trees, with the greatest reductions occurring at stem bases. The effects of pruning decreased over time, but there were still significant differences after 17 years. Girard form class was only influenced by the most intense pruning at a stem height of 5.5 m. A benefit of pruning was reduced taper, but this came at the cost of reduced stem growth. Pruning in S. giganteum must be done carefully with respect to its timing, intensity, and interactions with other management treatments on young stands.