Quantifying aboveground components of Picea sitchensis for allometric comparisons among tall conifers in North American rainforests

Tree biomass is one of the most important variables for studying and managing forest ecosystems. With emphasis shifting from young forests grown for timber production to forests with old-growth characteristics, the need to quantify various components of individual trees in natural settings is increasing. Destructive methods are inherently limited by what is feasible to cut down, dissect, and measure. In contrast, crown mapping is a minimally invasive technique for quantifying aboveground tree components such as wood, cambium, bark, and leaves. Despite being applied mostly to large trees, it is generalizable to any woody plant and can be adapted to answer diverse questions about biology, ecology, and ecosystem functions. We present a generalized approach for non-destructively quantifying the three-dimensional structure and aboveground components of whole trees along with a new programmatic tool for error-checking, visualizing, and interacting with tree-level data. Crown-mapping data from 60 lowland rainforest Picea sitchensis trees are presented to demonstrate the utility of this method for deriving allometric equations of tree components based on ground measurements. The 60 trees range from 14 to 495 cm trunk diameter at breast height, 10 to 94 m tall, and include simple to structurally complex individuals in dominant to suppressed positions within forests varying widely in density. Final allometric equations explain > 90% of the variability in volumes and masses of bark, wood, and leaves; are applicable to P. sitchensis throughout much of its geographic range; and are conservative relative to equations based on smaller dissected trees. Dendrochronology and allometric equations demonstrate that Picea sitchensis radically out-paces both Pseudotsuga menziesii and Sequoia sempervirens in accumulation of aboveground biomass and leaves, becoming heavier (155 ± 9 Mg) than any living P. menziesii and almost half as heavy as any living S. sempervirens in <500 years.