Fuel-reduction and restoration treatments (“treatments”) are conducted extensively in dry and historically frequent-fire forests of interior western North America (“dry forests”) to reduce potential for uncharacteristically severe wildfire. However, limited understanding of treatment longevity and long-term treatment effects creates potential for inefficient treatment maintenance and inaccurate forecasting of wildfire behavior. In this perspectives paper, we briefly summarize current understanding of long-term effects of three common treatment types (burn-only, thin-only, and thin-plus-burn) in dry forests. We then propose six opportunities for future research: evaluate treatment longevity in the context of management goals and long-term treatment effects, reference departure from un-treated conditions and progress toward desired conditions, account for natural variance of dry forests and associated statistical challenges, explore within-treatment drivers of long-term responses, increase the frequency of post-treatment sampling, and incorporate spatial heterogeneity into long-term analyses. Integrating these opportunities into long-term treatment studies and adaptive management plans can improve treatment maintenance efficiency and wildfire modelling. Ultimately, improved understanding about long-term effects of treatment and treatment longevity can support climate-adaptive management that increases dry-forest resilience to wildfire.

Context Tasmania is the epicentre of the tallest and most massive angiosperms on Earth. Aims To survey Tasmania's tallest and most massive (large trunk volume) trees. Methods LiDAR and satellite imagery identified areas with very tall trees. Field surveys recorded the geolocation, height, diameter and condition of exceptionally large individuals, and effects of recent fires. Key results Giant trees occur in a band between dry forests and temperate rainforests, with the largest trees in areas with 1000-1500 mm rainfall and 8-12 degrees C mean annual temperature. We documented 18 trees taller than 90 m, and 32 trees with trunk volume of >250 m(3). Trunk volume was better correlated with diameter at 10-m height than at breast height, owing to irregularities near the base of large trees. The tallest tree was measured to be 99.6 m tall (now 96 m tall), and the most massive tree had a trunk volume of 460 m(3). Most of the largest and tallest trees in Tasmania were Eucalyptus regnans, but occasional individuals of Eucalyptus globulus, E. obliqua and E. tasmaniensis were also over 85 m tall or had a trunk volume of >280 m3. Post-fire surveys highlighted vulnerability of giant Eucalyptus trees to fire, with 60% of the largest known trees killed by fire since 2004. Conclusions The giant trees of Tasmania are of global significance, but vulnerable to a warming, drying climate and associated increase in fire activity. Implications We outline steps for the conservation of giant trees, a task made urgent by climate change.

This study of late-seral Douglas-fir forests in coastal Washington examined scales from 0.1 to 65-80 ha to quantify persistence of the Douglas-fir overstory and patterns of aboveground biomass (henceforth biomass) distribution. Plot-based biomass estimates were scaled from 0.1-1 ha via tree-level allometry in four forests with Douglas-fir 180-600 yr old. At the 0.1 ha scale, biomass ranged from 69-2905 Mg ha(-1) live and 12-792 Mg ha(-1) dead with magnitude and spatial variability increasing with dominant tree age. Some 0.1 ha areas had > 2000 Mg ha(-1) live Douglas-fir alone. Our 1-3 ha plots held 1100-1700 Mg ha(-1) biomass with Douglas-fir always accounting for > 70 % of live biomass and > 46 % of crown volume despite having only 23 trees ha(-1) when trees exceeded 500 yr old. Dead biomass in plots ranged from 10-25 % of the total with 50-85 % being Douglas-fir. A segmented canopy height model from airborne laser scanning (i.e., ALS segments) was mapped to 191 measured trees to create an allometric equation for predicting live biomass. This equation was applied to all ALS segments across 288 ha of forest with dominant trees ranging from 340-620 yr old. Within plot boundaries, ALS-predicted live tree biomass errors ranged from 10-23 %. At 65-80 ha spatial scales, patterns of biomass revealed a breakup of high-biomass forest into aggregations of < 1-ha patches. The largest trees (> 50 Mg) were associated with high-biomass areas when Douglas-fir were younger, but beyond 500 yr, such elite trees increasingly occurred in relatively low-biomass areas. Estimated live tree biomass ranged from 112-1600 Mg ha(-1) with median values decreasing with Douglas-fir age from similar to 900 Mg ha(-1) at 350 yr to similar to 600 Mg ha(-1) at 600 yr. In Douglas-fir-dominated rainforests, restoration management can promote long-lived high-biomass forests and arboreal biodiversity through actions that enhance development of elite trees across all overstory age cohorts, emulating patterns of biomass distribution observed here.

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 degrees latitudinal gradient of decreasing precipitation and summer fog frequency. Sequoia trees north of 40 degrees 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 degrees until the fourth consecutive year (2015), when growth efficiency dropped precipitously, recovering within two years. South of 40 degrees, Sequoia trees exhibited steadily declining growth efficiency during the multi-year drought followed by recovery, but recovery did not occur south of 37 degrees despite ample precipitation in 2017. Sequoia growth efficiency is currently highest in secondary forests north of 40 degrees, 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 degrees. 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.

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.

The tallest species, Sequoia sempervirens, inhabits old-growth forests with global maximum biomass and leaf area. Here we determine if these forests also have maximum productivity. Intensive measurements of 114 trees 18-116 m tall and 115-2340 yr old were used to improve allometric equations for Sequoia. Applying the best available allometry to all vegetation in eleven 1-ha plots re-measured at 5-yr intervals yielded accurate estimates of aboveground biomass and growth increments. Plots initially held 1594-4341 Mg ha(-1) of biomass (805-2201 Mg C ha(-1)), which increased by 14.7-40.7 Mg ha(-1) yr(-1), including input of dead biomass from outside plots. Live biomass increments ranged from 1.2 to 19.2 Mg ha(-1) yr(-1) and were dominated by heartwood accumulation in Sequoia (up to 15.6 Mg ha(-1 )yr(-1)). Exceptional old-growth Sequoia forests thus produce more aboveground biomass annually-and sequester more carbon in decay-resistant heartwood-than forests dominated by any other species. However, live biomass increments are considerably higher in an exceptional second-growth Sequoia forest and a fully stocked Sequoia plantation. Old-growth forest productivity falls short of the maximum, because growth efficiency declines with increasing tree size such that much of an old forest's photosynthetic capacity resides in crowns of very large trees producing considerably less aboveground biomass per unit leaf mass than small trees. Decreasing Sequoia growth efficiency is strongly related to heartwood proportions of biomass increments, which increase as trees enlarge with age. With increasing tree size, more productivity may also be directed to roots supporting clonal regeneration, explaining why small Sequoia produce several times more aboveground biomass per unit leaf mass than co-occurring species. Since decay-resistant heartwood promotes tree longevity and supports biodiversity, silviculture that includes indefinite retention of Sequoia trees can sustain high productivity while also improving both the carbon sequestration potential and conservation value of managed forests.

Mature second-growth coast redwood (Sequoia sempervirens) forests-logged over 100 yr ago-are an important resource in the redwood region, but development of regenerating forests beyond rotation age (similar to 50 yr) is not well understood. Continuous long-term data are especially lacking, considering that the maximum possible age of second-growth stands is over 160 yr. Here we examine accumulation of tree biomass, leaf area, and canopy structure in three mature second-growth forests in California (Arcata, Big River, Oakland) that range in age from 133 to 159 yr since clearcut logging. Four fixed-area plots form the basis of this examination, including three 1-acre plots established in 1923 that together permit examination of Sequoia forest development over nearly a century. The four plots held 963 to 1476 Mg ha(-1) of aboveground tree biomass and 9M to 13.7 of tree leaf area index. From 1923 to 2017, the Big River plot exhibited rapid biomass accumulation (up to 23 Mg ha(-1) yr(-1)) as a densely stocked nearly pure Sequoia stand on an alluvial terrace. The two low-elevation plots near Arcata exhibited slower (up to 13 Mg ha(-1) yr(-1)) but consistent growth with an increasing dominance of Sequoia, as cooccurring conifers (Abies grandis, Picea sitchensis, Pseudotsuga menziesii) steadily declined in number despite rapid early growth. Increasing Sequoia dominance, substantial density-independent mortality in recent decades, and shifts in tree size distributions illustrate structural maturation as these forests approach an old-growth condition. The Oakland plot, which occurred similar to 300 m higher in elevation and received less than two-thirds as much annual rainfall, was a nearly pure Sequoia stand with canopy structure similar to, but shorter than, the Big River plot. Despite differences in elevation and rainfall, aboveground biomass of individual large trees in all four plots exceeded 15 Mg with Sequoia biomass increments averaging > 200 kg yr(-1) during the 21st century. Characteristics and developmental trajectories of these plots provide realistic benchmarks for management of alluvial, upland, and inland Sequoia forests.

Large trees are critically important for structuring ecosystems and providing habitat, and trees with complex crowns provide more of these services than comparably sized trees with simple crowns. Forest managers are increasingly emulating old-growth structure by retaining various densities of aggregated and dispersed trees. This study explores how individual within-crown complexity develops in a wide range of tree densities and interprets them in terms of management goals. Stratified LiDAR data were used to select 36 Picea sitchensis trees 55 to 91 m tall and from the complete range of tree densities in Olympic rainforests. These were climbed, three-dimensionally mapped-including the trunk and every appendage-to quantify tree allometry and habitat-related structures within their crowns. Sampled trees were then aged with crossdated increment cores to construct a chronosequence of crown development. The sample ranged from 70 to 250 cm diameter and 100 to 400 years old. Circular 30 m radius plots were installed around each tree to quantify neighborhood density. An additional 19 trees ranging from 10 to 94 m tall were added to the sample (N = 55) to describe baseline crown development and then compared to the 36-tree sample in which we modeled how this baseline is altered by neighborhood competition. After similar to 200 yr, crown mass increases faster than trunk mass due to accumulation and growth of large appendages. The largest neighbors within 25 m compete with Picea, reducing trunk and appendage diameters as well as crown volume by roughly 20% for each 25% increase in density for a given tree age. Reduced growth and higher mortality of lower-crown appendages in dense forests delays development of large (> 15 cm diameter) appendages for over 100 yr. Abundance of structures associated with reiterated trunks is unrelated to neighborhood density but increases with crown damage. These findings contribute to an empirically-based conceptual framework for crown development in Picea and interpretation of management guidelines. Picea is then compared to Pseudotsuga menziesii-another well-studied tall conifer of Olympic rainforests. Picea accumulates ecologically important crown structures much faster than Pseudotsuga yet has roughly half the longevity, indicating that these co-occurring species have complementary functions. Because of its shade tolerance and extremely rapid growth in rainforests, Picea can be used to accelerate development of complex crown structures in forests typically planted with Pseudotsuga after logging.

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.

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.

One of the five tallest tree species, Pseudotsuga menziesii has enormous economic and ecological importance, but rainforests dominated by this species are not as well understood as their drier montane counterparts. We climbed and measured 30 trees up to 97 m tall growing in coastal forests of the Olympic Peninsula and northern California to quantify structural attributes-leaves, bark, cambium, sapwood, heartwood, deadwood, biomass, growth increments, and age-and combined these with an equal number of trees up to 85 m tall growing in forests of the Cascade Mountains to develop allometric equations based on ground-level predictors. After comparing new equations to those previously published, we applied the best available equations for tall forests to predict aboveground quantities of all vascular plant species in 12 ha of Olympic and Cascade forests. The largest (117 Mg) and one of the oldest (615 years) trees we studied had the highest biomass increment (305 kg yr(-1)), but age had a negative effect on current and long-term growth increments. After accounting for variation in tree size and aboveground vigor, older trees produced less wood annually and grew less efficiently than younger trees. Size of P. menziesii trees increased more rapidly, and the proportion of biomass and leaf area in P. menziesii decreased more slowly, in Olympic than Cascade forests over six centuries following stand-replacing fire. Maximum aboveground biomass (1999 Mg ha(-1)) and carbon density (994 Mg ha(-1)) occurred in a Cascade forest with high abundance of three conifer species (P. menziesii, Tsuga heterophylla, Thuja plicata), but maximum P. menziesii biomass (1289 Mg ha(-1)) occurred in an Olympic forest with 50 trees ha(-1) up to 90 m tall. Vulnerability to wood decay fungi and dependence on fire for stand dominance limit P. menziesii biomass accumulation in 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. sempetvirens in < 500 years.

Fires that burn through forests cause changes in wood anatomy and growth that can be used to reconstruct fire histories. Fire is important in Sequoia sempervirens (D. Don) Endl. (coast redwood) forests, but fire histories are limited due to difficulties crossdating annual rings of this species. Here we investigated three fires (1985, 1999, 2008) in two old-growth forests (Montgomery Woods State Natural Reserve and Landels-Hill Big Creek Reserve, California, USA) to quantify these responses via crossdated increment cores from lower trunks of 53 trees, including 10 that were climbed and cored at 10 m height intervals. Redwoods frequently responded to fire by producing anomalous growth during the fire year; 100 of 240 lower trunk cores recorded at least one anatomical indicator (i.e., intra-annual density fluctuation, faint latewood, resin, or scar). Following fire, radial growth decreased by 29% to 43% compared to the fire year. After accounting for climatic influences, radial growth was 27% to 32% lower than expected in the post-fire year and declined to as low as 46 % after three years. Growth suppression persisted for up to seven years after fire, followed by up to 40% higher than expected radial growth. Several of the climbed trees expressed disruption of incremental growth along the height gradient following fire. The 1985 event consistently generated stronger growth and anatomical responses than the 1999 and 2008 events, and showed a co-occurrence between faint latewood during the fire year and subsequent narrow or missing rings. We used post-fire low growth relative to drought combined with anatomical indicators to detect past fires, identifying five additional events at Landels-Hill Big Creek Reserve dating back to 1634. Although other disturbances could have initiated these responses, our detection method enhances current capabilities for the spatiotemporal resolution of redwood fire histories via non-scar indicators on increment cores from living redwoods.

The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of Sagole Big tree, a giant African baobab from Limpopo, South Africa.Several wood samples were collected from the walls of its inner cavity and dated by radiocarbon.The age values along the cavity samples increase with the distance into the wood.This anomaly shows that the cavity is a false one.The oldest sample segment had a radiocarbon date of 781 ± 29 BP, which corresponds to a calibrated age of 740 ± 15 yr.We estimate that the oldest part of the Sagole baobab has an age of 800-900 yr.We determined that the tree has a closed ring-shaped structure, which consists of a large unit with six fused stems and of two additional leaning stems.

Three-dimensional models of Sequoia sempervirens.

A table showing the years, scale, type, and sources of the photo series used in the GIS analysis.

Variation in crown-level leaf density with tree age in two species.

Aboveground structural attributes of 140 trees.