How do tree structure and old age affect growth potential of California redwoods?

Abstract

As the only species exceeding 90 m in height and 2000 years of age, Sequoia sempervirens and Sequoiadendron giganteum provide the optimal platform upon which to examine interactions among tree structure, age, and growth. We climbed 140 trees in oldgrowth redwood forests across California, USA, spanning a broad range of sizes and including the tallest, largest, and oldest known living individuals (i.e., 115.86 vs. 96.29 m tall, 424 vs. 582 Mg aboveground dry mass, and 2510 vs. 3240 years old for Sequoia and Sequoiadendron, respectively). We used a combination of direct measurements, hierarchical sampling, and dendrochronology to quantify tree structure and annual growth increments through old age. We also developed equations to predict aboveground attributes of standing redwoods via ground-based measurements. Compared to Sequoia, Sequoiadendron develops thicker bark on lower trunks, provisions leaves with more sapwood, and delays heartwood production throughout the crown. Main trunk wood volume growth (up to 1.6 vs. 0.9 m 3 /yr), aboveground biomass growth (up to 0.77 vs. 0.45 Mg/yr), and aboveground growth efficiency (0.55 6 0.04 vs. 0.22 6 0.01 kg annual growth per kg leaves, mean 6 SE) are all higher in Sequoia. Two independent dimensions of structure-size and aboveground vigor-are the strongest predictors of tree-level productivity in both species. A third dimension, relative trunk size, is a significant predictor of growth in Sequoia such that trees with relatively large main trunks compared to their crowns produce more wood annually. Similar-size trees grow at similar rates regardless of latitude or elevation in tall forests of each species. Recent annual growth increments are higher than in the past for the majority of trees, and old trees are just as responsive to environmental changes as young trees. Negative growth-age relationships in previous centuries and positive growth-age relationships in recent decades reflect sampling bias and shifting disturbance regimes. Overall, we find little (if any) evidence for negative effects of old age on tree-level productivity in either species. Except for recovery periods following temporary reductions in crown size, annual increments of wood volume and biomass growth increase as redwoods enlarge with age until extrinsic forces cause tree death.

Crown dynamics and wood production of Douglas-fir trees in an old-growth forest

“…In large trees of Sequoia sempervirens D. Don and Sequoiadendron giganteum (Lindl.) Buchh., for example, trunk growth is depressed during recovery periods following fire damage, presumably as trees rebuild crowns to recover leaf area (Sillett et al, 2015a).…”

“…Among 140 S. sempervirens and S. giganteum trees up to 116 m tall and 3240 years of age that were climbed and intensively measured, there was little or no evidence for negative effects of old age on tree-level mass increments, and old trees were just as responsive to environmental changes as young trees (Sillett et al, 2015a). Because tree growth is a cumulative process, increasing leaf area and cambium area lead to increasing mass increments as trees gain size, regardless of age (Enquist et al, 1999).…”

“…of two quantities derived from core samples: (1) ring width of the lowest core and (2) the ring-width: wood radius ratio at the lowest core height multiplied by the wood radius at that height. This procedure maintained a consistent rate of taper change and accounted for wood investment in buttress formation (Sillett et al, 2015a). After determining wood radii of the trunk of each tree at all heights for all cross-dated years, we generated time series of two annual growth increments-ring width (radial) and wood volume-using equations for conic frusta.…”

“…Because of their size, estimates of biomass and growth rates of large trees are often based on ground-level measurements, such as diameter at breast height (DBH) scaled to the tree level using empirically derived allometric equations (e.g., Jenkins et al, 2003;Stephenson et al, 2014). Only a handful of studies utilize multiple measurements made at various heights within the living crown (e.g., Gilmore and Seymour, 1996;Inoue et al, 2008;Sumida et al, 2013;Sillett et al, 2015a) and/or repeated measurements of crown growth and dynamics (e.g., Ishii and Kadotani, 2006;Sillett et al, 2015b). As trees age, the lower trunk becomes a platform upon which new trunks and branches are produced by reiteration, the production of repeating architectural units within a tree (Barthelemy et al, 1989;Ishii and Kadotani, 2006;Sillett and Van Pelt, 2007).…”

Contrasting Impacts of Climate and Competition on Large Sugar Pine Growth and Defense in a Fire-Excluded Forest of the Central Sierra Nevada

“…For all sampled sugar pine, we recorded DBH (cm) and bark thickness (cm) and extracted one large diameter (12 mm) core to measure the annual growth and resin duct defense for each tree. The bark thickness (cm) was estimated by finding the cambium inside the hole from the extracted core, using the increment borer spoon to demark the length to the outside of the bark, and measuring the distance using digital calipers [45].…”