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Tracheid buckling may protect leaves in the dynamic environments of forest canopies, where rapid intensifications of evaporative demand, such as those brought on by changes in light availability, can result in sudden increases in transpiration rate. While treetop leaves function in reliably direct light, leaves below the upper crown must tolerate rapid, thermally driven increases in evaporative demand. Using synchrotron‐based X‐ray microtomography, we visualized impacts of experimentally induced water stress and subsequent fogging on living cells in redwood leaves, adding ecological and functional context through crown‐wide explorations of variation in leaf physiology and microclimate. Under drought, leaf transfusion tracheids buckle, releasing water that supplies sufficient temporal reserves for leaves to reduce stomatal conductance safely while stopping the further rise of tension. Tracheid buckling fraction decreases with height and is closely coordinated with transfusion tissue capacity and stomatal conductance to provide temporal reserves optimized for local variation in microclimate. Foliar water uptake fully restores collapsed and air‐filled transfusion tracheids in leaves on excised shoots, suggesting that trees may use aerial water sources for recovery. In the intensely variable deep‐crown environment, foliar water uptake can allow for repetitive cycles of tracheid buckling and unbuckling, protecting the tree from damaging levels of hydraulic tension and supporting leaf survival. If sudden changes in microclimate increase transpirational demand, tracheid buckling in the water‐filled transfusion tissue of Sequoia sempervirens leaves can release a quantity of water sufficient to briefly sustain increased transpiration, thereby providing time for stomatal adjustment. The temporal reserves supplied by tracheid buckling can be replenished through foliar water uptake, which allows collapsed tracheids to refill to their former volumes. [ABSTRACT FROM AUTHOR]

Context: Western Olympic valley bottoms, disturbed by alluvial processes, are dominated by Picea sitchensis and isolated cohorts of Pseudotsuga menziesii, while upland contexts, disturbed by wind and fire, are dominated by P. menziesii. These forests have distinct structure and produce large trees with habitat for endangered birds. Objectives: Describe how disturbance and forest development create landscape forest patterns and distribution of large trees in valley bottom and upland forests. Methods: LiDAR data of ~ 9700 ha within Olympic National Park, USA was classified based on vegetation height and percent cover to contrast valley bottom and upland forests. Within-crown structure from 36 P. sitchensis and 12 P. menziesii was then used to predict locations of the largest and most complex trees. Results: Valley bottoms comprise small patches of dense tall (11%), medium-height trees (19%), and gaps (7%) embedded in open-canopy forest with scattered tall trees (63%). Upland forests comprise larger patches of tall (16%), medium (58%), and open-canopy forest (25%) with few gaps (1%). The largest trees are more abundant in valley bottoms (0.05 tree ha−1) than upland (0.02 tree ha−1) due to small patches of tall trees within open-canopy forest. Conclusions: Alluvial disturbance, fungi-wind interaction, and dominance of late-successional fast-growing P. sitchensis create open-canopy forest with more large trees, while severe fire and wind interacting with P. menziesii create patchy closed-canopy forest with fewer large trees. Management for large habitat trees should use aggregated retention with P. menziesii, multi-aged selection techniques with P. sitchensis, and indefinitely retain a low density of large trees. [ABSTRACT FROM AUTHOR]

Highlights • New allometric equations for Sequoia sempervirens in second-growth forest. • Evaluation of bias in allometric equations derived from forests of different ages. • Complete structural analysis of 159-year-old forest in Fritz Wonder Plot. • Estimating aboveground biomass and carbon stock in mature and old-growth forests. • Comparison of long-term tree performance and canopy structure in alluvial forests. Abstract Mature second-growth forests dominated by Sequoia sempervirens occupy only two percent of the species' current distribution yet represent an important benchmark for restoration management. Here we develop new allometric equations for these forests based on 44 trees 23–84 m tall, which can be used to estimate leaf, bark, cambium, sapwood, and heartwood quantities, including biomass and carbon content, from ground-based measurements of trunk diameter, height, and crown size. New equations complement those already available for S. sempervirens in young and old-growth forests and should be applied judiciously. We use fixed area plots in a 159-year-old second-growth forest (0.5 ha) and a primary forest with trees >1100 years old (1.0 ha) to compare three sets of equations. Whereas equations from young forests underestimate biomass in older forests, new equations underestimate trunk and overestimate branch quantities in the old-growth forest, and equations from old-growth forests do the opposite in the mature second-growth forest. Despite the great age difference, canopy structure of these low-elevation, alluvial forests is similar with S. sempervirens stratified into dominant and subordinate crown classes towering above a diminutive understory. Dendrochronological reconstruction of heights and wood radii for nine individuals reveal that both forests have trees producing >300 kg yr−1 with tall trees in the old-growth forest producing up to 800 kg yr−1 in recent decades. Sequoia sempervirens represents nearly 100% of biomass and 83 to –92% of leaf area in the second-growth (total LAI = 15.0) and old-growth (total LAI = 19.3) forests, respectively. The best allometric equations estimate that the second-growth forest holds 1667 Mg ha−1 of aboveground biomass (837 Mg C ha−1), 56% of which is heartwood, whereas the old-growth forest holds 4595 Mg ha−1 of aboveground biomass (2332 Mg C ha−1), 76% of which is heartwood. Restoration management has potential to harness the carbon sequestration potential of S. sempervirens by promoting heartwood accumulation through silviculture. [ABSTRACT FROM AUTHOR]

In old-growth Sequoia sempervirens forests, reiterated trunks and limbs provide required habitat elements for specialized arboreal species, including an endangered seabird, Brachyramphus marmoratus . The oldest second-growth redwood forests—established after 19th century logging—lack species dependent on complex structure, presumably because redwoods maintain simple, model-conforming crowns for centuries unless damaged by wind or fire. We imposed a factorial experiment on 24 redwoods 59–75 m tall in six second-growth forests to determine if trunk reiteration and limb formation can be induced by removing treetops (topping) and branch tips (tipping) to disrupt apical control. We also increased light availability in the upper crown by pruning branches. After intensively mapping trunks and branches and imposing treatments, we re-mapped trees three years later to quantify growth increments. Topping stimulated trunk reiteration from the cut, and reiterated tops gained height more rapidly than controls. Tipping also stimulated trunk reiteration from branches, especially when combined with topping, resulting in formation of limbs (i.e., branches giving rise to reiterated trunks). Pruning had consistently negative effects on trunk and branch growth increments even after accounting for post-treatment variation in leaf area and light availability, suggesting that photosynthate was diverted to compartmentalization of wounds. Strategic injury of trees may have long-term conservation value in second-growth redwood forests if limbs can be initiated high enough in the crown to persist as trees approach maximum height. Topping and tipping treatments should be combined with silvicultural thinning of neighboring trees to increase light availability far more than can be achieved by pruning. [ABSTRACT FROM AUTHOR]

Organic soils up to 1 m thick cover tree surfaces within the canopies of old-growth redwood [Sequoia sempervirens (D. Don) Endl.] forests 50 m or more above the ground. Very little is known about litter quality and litter decomposition processes within these canopies. A combination of solid-state cross-polarization magic-angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy, natural 13C and 15N isotopic analyses, and proximate analyses were used to gain insight into soil organic matter accumulation and decay processes within two arboreal soils. Arboreal soil, redwood, and fern (Polypodium scouleri Hook. & Grey.) litter as well as epiphyte roots were analyzed. Proximate analyses showed that the arboreal soil parent materials contained a high concentration of the acid residue fraction (i.e., Klason lignin), from 379 g kg-1 for fern rhizomes up to 652 g k-1 for redwood bark litter. This high concentration of acid residue fraction in the soil parent materials probably promotes organic matter accumulation within the tree crown. Results from 13C NMR spectroscopy analyses indicated a preferential decomposition of carbohydrates and an accumulation of alkyl structures from the redwood and fern litter to the < 2-mm soil materials and from the Oi to the Oa horizons in both soils. On the other hand, there was no consistent variation in terms of C/N ratios and stable isotope composition along the depth gradient, suggesting that organic matter in these soils has undergone limited microbial processing but instead reflects the selective preservation of recalcitrant litter moieties. [ABSTRACT FROM AUTHOR]

Sequoia sempervirens (redwood) is a long-lived, shade-tolerant tree capable of regeneration without disturbances and thus often present in all sizes within a single forest. In order to evaluate functional linkages among structures, plant distribution, and biodiversity in the canopy, we quantified all vascular plants from ground level to the treetops in an old-growth redwood forest (Prairie Creek Redwoods State Park, California, USA). This involved mapping terrestrial and epiphytic trees, shrubs, and ferns as well as climbing 27 trees up to 101 m tall within a 1-ha plot. We monitored canopy microclimates using sensor arrays that collected hourly data for up to 30 months. The plot held 4283 Mg/ha of aboveground dry mass in living plants, 95.4% of which was contributed by redwood. A high degree of structural complexity and individuality was evident in the crowns of the 14 largest trees in the form of reiterated trunks arising from main trunks, other trunks, and limbs. Thirteen species of vascular plants occurred as epiphytes in the plot, and all but one of these were restricted to the 14 largest trees. The evergreen shrub Vaccinium ovatum had the highest biomass of any epiphyte (212 kg/ha) followed by the evergreen fern Polypodium scouleri (196 kg/ha). The spatial aggregation of reiterated trunks was highly coincident with epiphyte masses, explaining 92% of the variation in fern and 75% of the variation in woody plant distribution along the vertical gradient. In addition to epiphyte biomass, there were 2366 kg/ha of soil in the canopy. Soils in crotches held 2-4 times as much water as soils on branches or limbs, and deeper layers held more water than shallower layers. During two years of monitoring, the volume of water stored in dead wood and soils in the canopy fluctuated between 24.7 m³ and 53.4 m³/ha. The vast majority of the plot's structure and arboreal habitats was held in the crowns of the 14 largest trees. Reiterated trunks and limbs on a small number of trees have important ecological functions in old-growth redwood forests, and it may be feasible to accelerate the development of structural complexity and biodiversity in maturing redwood stands. [ABSTRACT FROM AUTHOR]

Within the canopy of old-growth redwood (Sequoia sempervirens [D. Don] Endl.) forests, accumulations of plant debris in crotches and on massive limbs serve as parent materials for ‘arboreal soils’ up to 1 m thick and over 50 m above the forest floor. These soils are important habitats and water sources for desiccation-sensitive organisms in the forest canopy ecosystem. We investigated two of these arboreal soils to better understand how they form and function. The primary vascular epiphyte growing in these soils is leather-leaf fern (Polypodium scouleri). Fern biomass and redwood leaves and bark are the main parent materials of the soils, which are entirely organic. The soils have distinct horizons and soil structure, and have been changed from their initial parent materials as a result of additions, losses, and transformations of organic matter. They are classified as Typic Udifolists. The soils become more decomposed with depth as fibrous components transition to sapric materials. They have low bulk densities (0.07–0.16 g cm-3) and lose most of their water at relatively high matric potentials. Field water contents and potentials of the arboreal soil materials taken near the end of the dry season indicate that water remains available for uptake by ferns. High base saturation values (>55%) suggest that nutrients are available for plant uptake. The soils are extremely acidic, with pH values around 3.0 in 0.01 M CaCI2. Decomposition may be hindered by the low soil pH and by relatively low soil moisture contents in surface horizons during the dry season. [ABSTRACT FROM AUTHOR]