Growth and form of giant sequoia (Sequoiadendron giganteum) in a plantation spacing trial after 28 years

Abstract Giant sequoia is a famously massive and long-lived tree endemic to the Sierra Nevada of California, whose persistence is threatened by a changing climate and an altered disturbance regime. One approach for protecting threatened species is to incorporate them into working landscapes. In a forestry context, the objectives of a working landscape include the production of timber and the storage of carbon. Given its potential for rapid growth, an understanding of the growth-density relationships for giant sequoia is a necessity for planning future management for these common management objectives. To investigate the effect of initial planting density on both individual tree and stand level characteristics, we used repeated measures data from a 28-year-old giant sequoia spacing trial. After 28 years, survival among all spacing treatments was high (>98%). Individual bole volume increased with greater growing space allocated per tree. Although initial relative growth rates based on bole volume differed among spacing treatments, relative growth rates were similar after 21 years. At the stand level, total stand volume was similar across all spacing treatments after 28 years. However, wider spacing treatments exhibited higher amounts of merchantable volume. After 28 years, stands of giant sequoia sequestered approximately 92.2 Mg ha−1 across all spacing treatments. Our results show that giant sequoias are able to produce merchantable timber at a young age and sequester large amounts of carbon in a relatively short amount of time, supporting that giant sequoia is a promising candidate species for planting for timber production as well as carbon sequestration.