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Premise: Trees in wet forests often have features that prevent water films from covering stomata and inhibiting gas exchange, while many trees in drier environments use foliar water uptake to reduce water stress. In forests with both wet and dry seasons, evergreen trees would benefit from producing leaves capable of balancing rainy‐season photosynthesis with summertime water absorption. Methods: Using samples collected from across the vertical gradient in tall redwood (Sequoia sempervirens) crowns, we estimated tree‐level foliar water uptake and employed physics‐based causative modeling to identify key functional traits that determine uptake potential by setting hydraulic resistance. Results: We showed that Sequoia has two functionally distinct shoot morphotypes. While most shoots specialize in photosynthesis, the axial shoot type is capable of much greater foliar water uptake, and its within‐crown distribution varies with latitude. A suite of leaf surface traits cause hydraulic resistance, leading to variation in uptake capacity among samples. Conclusions: Shoot dimorphism gives tall Sequoia trees the capacity to absorb up to 48 kg H2O h−1 during the first hour of leaf wetting, ameliorating water stress while presumably maintaining high photosynthetic capacity year round. Geographic variation in shoot dimorphism suggests that plasticity in shoot‐type distribution and leaf surface traits helps Sequoia maintain a dominate presence in both wet and dry forests. [ABSTRACT FROM AUTHOR]

• New allometric equations for Sequoiadendron based on 60 trees of all sizes. • Old-growth forests have aboveground biomass up to 2683 Mg ha−1 and LAI up to 14.5. • Some forests lost more biomass to mortality than gained by growth during drought. • Distance to water and neighbor competition affect Sequoiadendron during drought. • Long-term analysis reveals relatively small effect of recent drought on Sequoiadendron. The largest tree species, Sequoiadendron giganteum has a small native range restricted to California's Sierra Nevada. Awe-inspiring stature contributed to its protection from logging, but anthropogenic climate change—particularly hotter drought—and over a century of fire suppression are possible threats. We measured 60 trees in seven forests to improve allometric equations for the species and installed five 1-ha plots to quantify biomass of Sequoiadendron and associated vegetation. Plots were re-measured after 5 yr to compute biomass increments and examine effects of management history as well as impacts of recent drought. Forests held up to 2683 Mg ha−1 aboveground biomass (1373 Mg C ha−1) and had leaf area index (LAI) up to 14.5 with Sequoiadendron accounting for the bulk of biomass but not LAI. Live trees of other species contributed up to 10.6 LAI and had biomass increments up to 6.1 Mg ha−1 yr−1, but drought contributed to tree mortality in three plots, where live biomass declined by 6.2–10.3 Mg ha−1 yr−1. Two plots had very little tree mortality and gained 5.5–7.9 Mg ha−1 yr−1. Sequoiadendron productivity was strongly correlated with tree-level photosynthetic capacity, but at the height of the drought, relative growth—expressed as the ratio of biomass produced during the driest and wettest recent years—correlated positively with site productivity and negatively with both vertical distance to water and presumed competition from neighboring trees. Prescribed fire in one plot caused a growth release in trees whose lower trunks were burnt and small neighboring Abies lowiana were killed. Effects of 21st century drought on Sequoiadendron productivity were greater in northern than southern locations but of lesser magnitude than many past events. No Sequoiadendron recruitment was observed. Planting can overcome the species' dependence on fire for regeneration, and Sequoiadendron has great potential for carbon sequestration in a variety of settings, including commercial forestry. [ABSTRACT FROM AUTHOR]

• 235 trees across 6° latitude climbed, measured, and core-sampled. • Recovery from multi-year hotter drought slowest south of 37°. • Heartwood investment and nocturnal summer fog affect growth efficiency. • Carbon sequestration and biodiversity higher in primary than secondary forests. • Managing for Potential Elder Trees can maximize non-timber values. Heavily exploited for its reddish, decay-resistant heartwood, the tallest conifer, Sequoia sempervirens , is a major component of coastal forests from extreme southwestern Oregon to California's Santa Lucia Mountains. Primary Sequoia forests are now restricted to < 5 % of their former distribution, and mature secondary forests with trees over 60 m tall are even scarcer due to repeated logging. Leveraging allometric equations recently derived from intensive work in both forest types, we climbed, measured, and core-sampled 235 trees in 45 locations distributed across the species range to examine growth trends and understand how tall Sequoia are responding to recent environmental changes. Paired samples of sapwood and heartwood collected along the height gradient were used to quantify Sequoia investment in decay resistance. During the 20th century, trees in most locations began producing more wood than expected for their size with this growth surge becoming pronounced after 1970 and ending around 2000. Radial increments—ring widths—correlate with climatic variables related to water availability, and these relationships are strengthening as temperatures rise. Sensitivity to drought increased from north to south along a 6° latitudinal gradient of decreasing precipitation and summer fog frequency. Sequoia trees north of 40° were least sensitive to drought, producing similar biomass annually during dry and wet years, whereas trees farther south produced less biomass during individual drought years. Hotter 21st century drought barely affected Sequoia growth efficiency (biomass increment per unit leaf mass) north of 40° until the fourth consecutive year (2015), when growth efficiency dropped precipitously, recovering within two years. South of 40°, Sequoia trees exhibited steadily declining growth efficiency during the multi-year drought followed by recovery, but recovery did not occur south of 37° despite ample precipitation in 2017. Sequoia growth efficiency is currently highest in secondary forests north of 40°, where trees produce relatively small amounts of heartwood with the lowest decay resistance (least fungicide) while receiving the most nocturnal summer fog. Increasing sink limitations, whereby rising temperatures, drier air at night, and extreme tree height collectively lower turgor pressure to inhibit cambial activity, may reduce Sequoia growth efficiency while contributing to more durable biomass production. Heartwood and fungicide increments are higher in primary than secondary forests across the species range. Crown structural complexity promotes development of vascular epiphytes and arboreal soil habitats in Sequoia forests with sufficient moisture availability. These habitats are lacking in secondary forests and rare in primary forests south of 40°. After logging, restoration of tall Sequoia forests can be achieved via silviculture that maximizes height increments during early stand development and then retains some dominant trees in perpetuity, allowing them to gain full stature, produce increasingly decay-resistant heartwood, and support significant arboreal biodiversity. [ABSTRACT FROM AUTHOR]

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 m3/yr), aboveground biomass growth (up to 0.77 vs. 0.45 Mg/yr), and aboveground growth efficiency (0.55 ± 0.04 vs. 0.22 ± 0.01 kg annual growth per kg leaves, mean ± 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. [ABSTRACT FROM AUTHOR]

Extremely decay-resistant wood and fire-resistant bark allow California’s redwoods to accumulate millennia of annual growth rings that can be useful in biological research. Whereas tree rings of Sequoiadendron giganteum (SEGI) helped formalize the study of dendrochronology and the principle of crossdating, those of Sequoia sempervirens (SESE) have proven much more difficult to decipher, greatly limiting dendroclimatic and other investigations of this species. We overcame these problems by climbing standing trees and coring trunks at multiple heights in 14 old-growth forest locations across California. Overall, we sampled 1,466 series with 483,712 annual rings from 120 trees and were able to crossdate 83% of SESE compared to 99% of SEGI rings. Standard and residual tree-ring chronologies spanning up to 1,685 years for SESE and 1,538 years for SEGI were created for each location to evaluate crossdating and to examine correlations between annual growth and climate. We used monthly values of temperature, precipitation, and drought severity as well as summer cloudiness to quantify potential drivers of inter-annual growth variation over century-long time series at each location. SESE chronologies exhibited a latitudinal gradient of climate sensitivities, contrasting cooler northern rainforests and warmer, drier southern forests. Radial growth increased with decreasing summer cloudiness in northern rainforests and a central SESE location. The strongest dendroclimatic relationship occurred in our southernmost SESE location, where radial growth correlated negatively with dry summer conditions and exhibited responses to historic fires. SEGI chronologies showed negative correlations with June temperature and positive correlations with previous October precipitation. More work is needed to understand quantitative relationships between SEGI radial growth and moisture availability, particularly snowmelt. Tree-ring chronologies developed here for both redwood species have numerous scientific applications, including determination of tree ages, accurate dating of fire-return intervals, archaeology, analyses of stable isotopes, long-term climate reconstructions, and quantifying rates of carbon sequestration. [ABSTRACT FROM AUTHOR]

Redwood branches provide all the carbohydrates for the most carbon-heavy forests on Earth, and recent whole-tree measurements have quantified trunk growth rates associated with complete branch inventories. Providing all of a tree's photosynthetic capacity, branches represent an increasing proportion of total aboveground wood production as trees enlarge. To examine branch development and its effects on wood volume growth, we dissected 31 branches from eight Sequoia sempervirens (D. Don) Endl. and seven Sequoiadendron giganteum Lindl. trees. The cambium-area-to-leaf-area ratio was maintained with size and age but increased with light availability, whereas the heartwood-deposition-area-to-leaf-area ratio increased with size and age but was insensitive to light availability. The proportion of foliage mass arrayed in <1-cm-diameter epicormic shoots increased with decreasing light and was higher in Sequoia (20–60%) than in Sequoiadendron (3–16%). Well-illuminated branches concentrated leaves higher and distally, while shaded branches distributed leaves lower and proximally. In similar light environments, older branches distributed leaves lower and more proximally than younger branches. Branch size, light, species, heartwood area, a heartwood-area–species interaction, and ovulate cone mass predicted 87.5% of the variability in wood volume growth of branches. After accounting for the positive effects of size and light, wood volume growth declined with heartwood area and age. The effect of age was trivial compared to the effect of heartwood area, suggesting that heartwood expansion caused the age-related decline in wood volume growth. Additionally, Sequoiadendron branches of similar size and light environment with more ovulate cones produced less wood, even though these cones were long-lived and photosynthetic, reflecting the energetic cost of seed production. These results contributed to a conceptual model of branch development in which light availability, injury, heartwood content, gravity, and time interact to produce the high degree of branch structural variation evident within redwood crowns. [ABSTRACT FROM AUTHOR]

We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood ( Sequoia sempervirens) and giant sequoia ( Sequoiadendron giganteum) trees of different sizes. Leaf-specific hydraulic conductivity ( kL) increased with height in S. sempervirens but not in S. giganteum, while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios ( δ13C) increased, and maximum mass-based stomatal conductance ( gmass) and photosynthesis ( Amass) decreased with height in both species. As a result, both Amass and gmass were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum. In addition, Amass and gmass were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO2 conductance ( gi). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat. [ABSTRACT FROM AUTHOR]

We studied changes in morphological and physiological characteristics of leaves and shoots along a height gradient in Sequoia sempervirens, the tallest tree species on Earth, to investigate whether morphological and physiological acclimation to the vertical light gradient was constrained by hydrostatic limitation in the upper crown. Bulk leaf water potential (Ψ) decreased linearly and light availability increased exponentially with increasing height in the crown. During the wet season, Ψ was lower in the outer than inner crown. C isotope composition of leaves (δ13C) increased with increasing height indicating greater photosynthetic water use efficiency in the upper crown. Leaf and shoot morphology changed continuously with height. In contrast, their relationships with light availability were discontinuous: morphological characteristics did not correspond to increasing light availability above 55–85 m. Mass-based chlorophyll concentration (chl) decreased with increasing height and increasing light availability. In contrast, area-based chl remained constant or increased with increasing height. Mass-based maximum rate of net photosynthesis ( P max) decreased with increasing height, whereas area-based P max reached maximum at 78.4 m and decreased with increasing height thereafter. Mass-based P max increased with increasing shoot mass per area (SMA), whereas area-based P max was not correlated with SMA in the upper crown. Our results suggest that hydrostatic limitation of morphological development constrains exploitation of light in the upper crown and contributes to reduced photosynthetic rates and, ultimately, reduced height growth at the tops of tall S. sempervirens trees. [ABSTRACT FROM AUTHOR]

• 169 trees of 4 tallest conifers climbed, measured, and core-sampled. • Species investing most in leaves and least in defense grows fastest. • Evidence for tree senescence diminishes with species longevity. • Tall forests have unrealized potential to provide ecosystem services. The tallest conifers— Picea sitchensis , Pseudotsuga menziesii , Sequoia sempervirens , Sequoiadendron giganteum —are widely distributed in western North America, forming forests > 90 m tall with aboveground biomass ≥ 2000 Mg ha−1. Here we combine intensive measurements of 169 trees with dendrochronology and allometry to examine tree and stand development. The species investing least in bark protection and heartwood defense— P. sitchensis —has more leaves, denser wood, larger appendages, and produces more aboveground biomass during its relatively brief lifespan than other conifers at equivalent ages. The species investing most in bark protection and heartwood defense— S. giganteum —has the least dense wood, largest appendages, and greatest longevity. Evidence for senescence diminishes with longevity; only P. sitchensis exhibits a post-maturity decline in tree productivity after accounting for leaf mass. Growth efficiency declines with age in all species, falling most rapidly in P. sitchensis followed by P. menziesii , S. sempervirens , and S. giganteum in the same sequence as longevity. Centuries-long time series of age, size, and growth increments identify years when trees first reach a given height as well as biomass and growth rates at that height, providing snapshots of performance useful for simulating development. Stands dominated by P. sitchensis and P. menziesii gain height at similar rates, but P. sitchensis accumulates biomass more rapidly until senescence curtails tree productivity, which takes centuries longer in P. menziesii. Whereas S. sempervirens in primary forest grows more slowly than P. sitchensis and P. menziesii until ~70 m tall, S. sempervirens in secondary forest outpaces other conifers with biomass increments approaching global maxima within a few centuries. Beyond ~70 m, S. giganteum gains height more slowly than other conifers, but it sustains relatively high biomass increments for millennia. Both within and beyond their native ranges, the four tallest conifers have unrealized potential to provide ecosystem services. [ABSTRACT FROM AUTHOR]