Improved allometry and heartwood development of Sequoia sempervirens in secondary forests

Heartwood is the majority of a tall tree’s biomass, and durability of this material is a major contributor to longevity. Toxins deposited during heartwood formation (extractives) are largely responsible for its durability and can be quantified by chemical extractions and well-replicated comparisons of sapwood and heartwood densities. Using the latter approach, we explore variation in heartwood attributes of the tallest species, Sequoia sempervirens, in secondary forests regenerating post logging in California. After climbing, measuring, and core-sampling 77 dominant trees (96–202 yr old, 56–87 m tall, 6–37 Mg biomass) in 18 locations distributed from northern rainforests to warmer, drier, and less foggy margins of the species range in California, we combine improved allometry with dendrochronology to reconstruct tree sizes for developmental analysis. Northern trees have the lowest wood densities, highest wood volume increment, fastest increase in the heartwood proportion of wood volume increment, highest growth efficiency (biomass produced per unit leaf mass), and lowest extractive proportion of heartwood increment, whereas marginal trees are at the opposite extreme and central trees are intermediate in all these metrics. In the climatically distinct and fire-prone canyons of the marginal range, higher density and extractive content of heartwood contribute to long-term carbon sequestration and persistence of Sequoia-dominated vegetation. Allowing Sequoia to reach great height may be the best way to improve carbon sequestration in the core range, where heartwood extractive content and decay resistance are lower in secondary forests than primary (old-growth) forests. Biophysical constraints on turgor pressure in lofty crowns may limit sapwood production and promote heartwood deposition throughout the trunk, explaining why tall trees in primary forests have higher heartwood extractive content than much shorter trees in nearby secondary forests. Understanding the causes of regional variation in heartwood attributes requires further study, including outside California where Sequoia is widely planted for its extraordinary values.