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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 old-growth 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 ± 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.

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.

Key messageDendroclimatic sensitivity varies by axial position for Sequoiadendron giganteum: negative correlations with June temperature strengthen with height, while positive correlations with snow water are strongest in the lower trunk.Increment cores collected along trunks of mature Sequoiadendron giganteum provide new and updated ring-width chronologies ideal for assessing how height above ground affects sensitivity of radial growth to climatic variation. Chronologies from 61 living trees at nine locations across the geographic distribution span 1973 yr. Analyses of subsets of 18–44 trees reveal that correlations between radial increments and climate (temperature, water availability) vary with axial position. Negative correlations with maximum and minimum June temperature intensify with height and are strongest at the highest position analyzed (60 m above ground). Sensitivity to the hydroclimate variable of April-1 snow water equivalent is stronger at lower trunk positions (10 m) compared to breast height or the upper trunk, and a similar relationship is identified for the standardized precipitation evapotranspiration index using a 12-month window ending in September. Drought-induced low-growth years computed as radial increment relative to the mean of 10 yr before and after are more weakly expressed at breast height compared to higher on the trunk (10–60 m). Analysis of regional upper (maximum core height = 87 m) versus lower trunk (above buttress) chronologies corroborate differing inter-annual correlations with climate depending on height above ground. Accounting for axial variation in dendroclimatic sensitivity can maximize the quality of environmental reconstructions using tree rings and improve biophysical understanding of Sequoiadendron, especially in the context of an increasingly arid climate.

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.

Understanding biological invasions requires information on the history of spatial spread, as well as measures of landscape and biotic features that control habitat invasibility. Because invasive species often spread quickly over large areas, attaining these two sets of information simultaneously is uncommon. We studied the spread of a fatal nonnative root pathogen, Phytophthora lateralis, across a heterogeneous landscape of its host, Port Orford cedar (Chamaecyparis lawsoniana). Within our 37-km2 study area in southwestern Oregon and northwest California, Port Orford cedar populations are generally restricted to riparian zones along creeks. The pathogen is spread between watersheds in two ways: (1) by spore-infested material being dislodged from vehicles, and (2) by animals or people moving infested mud (i.e., via foot traffic). Using dendrochronological techniques, we determined the date of infection for dead cedars and reconstructed spread history across our study area from 1977 to 1999. Twenty-six of the 36 (72%) separate infection events we identified were caused by dispersal via vehicles along roads, and the remainder by foot traffic. Survival analysis demonstrated that cedar populations in creeks crossed by roads were more likely to be infected than those creeks that were not crossed by roads. Also, a comparison of minimum dispersal distances showed infections that moved via road moved significantly farther than those vectored by foot traffic, and the distance infection traveled declined significantly through time. We also coupled our spread history with measures of landscape and host features, including abundance of potential host trees, the distance from the road surface to the nearest potential host, length of road in immediate contact with the riparian zone, catchment area (a measure of stream flow), elevation, slope, and solar radiation. Our results show that catchment area, host abundance, and proximity to the nearest tree are significantly and positively associated with infection risk. Our study demonstrates that increased connectivity between invasible sites created by the presence of roads can increase invasion success of a plant pathogen. We also document that successful pathogen invasion can be governed by both physical landscape features and attributes of host plant populations.

Invasive pathogens are becoming increasingly important in forested ecosystems, yet they are often difficult to study because of their rapid transmission. The rate and extent of pathogen spread are thought to be partially controlled by variation in host characteristics, such as when host size and location influence susceptibility. Few host-pathogen systems, however, have been used to test this prediction. We used Port Orford cedar ( Chamaecyparis lawsoniana ), a foundation tree species in riparian areas of California and Oregon (USA), and the invasive oomycete Phytophthora lateralis to assess pathogen impacts and the role of host characteristics on invasion. Across three streams that had been infected for 13-18 years by P. lateralis , we mapped 2241 trees and determined whether they had been infected using dendrochronology. The infection probability of trees was governed by host size (diameter at breast height [DBH]) and geomorphic position (e.g., active channel, stream bank, floodplain, etc.) similarly across streams. For instance, only 23% of trees <20 cm DBH were infected, while 69% of trees ≥20 cm DBH were infected. Presumably, because spores of P. lateralis are transported downstream in water, they are more likely to encounter well-developed root systems of larger trees. Also because of this water-transport of spores, differences in infection probability were found across the geomorphic positions: 59% of cedar in the active channel and the stream bank (combined) were infected, while 23% of trees found on higher geomorphic types were infected. Overall, 32% of cedar had been infected across the three streams. However, 63% of the total cedar basal area had been killed, because the greatest number of trees, and the largest trees, were found in the most susceptible positions. In the active channel and stream bank, 91% of the basal area was infected, while 46% was infected across higher geomorphic positions. The invasion of Port Orford cedar populations by P. lateralis causes profound impacts to population structure and the invasion outcome will be governed by the heterogeneity found in host size and location. Models of disease invasion will require an understanding of how heterogeneity influences spread dynamics to adequately predict the outcome for host populations.

Tree-ring data from Chamaecyparis lawsoniana (A. Murr.) Parl. (Port Orford cedar; Cupressaceae) were used to create a standardized chronology, assess the local, limiting factors on radial growth, and investigate the extent of a unique climatic event. We produced a 580-year tree-ring chronology (A.D. 1420 to 2000) from a large number of cedars (n = 1537) sampled in one 37 km2 area in the Siskiyou Mountains of southwestern Oregon and northern California. This chronology represents an area with few long-term climatic studies and a species with no dendrochronological data. We found radial growth to be positively correlated with year-round soil moisture conditions, specifically with cool, wet conditions in summer and warm, wet conditions in winter. The year 1739 stood out as a climatic pointer year with the smallest ring width index for the entire chronology and anatomically distinctive damage to the latewood of 1738 and earlywood of 1739. This pointer year was consistently identified across watersheds, topographic position (e.g., streamside, hillslope), and the range of the cedar, corresponding to an extreme, single-year drought occurring throughout the Pacific Northwest.

Understanding biological invasions requires information on the history of spatial spread, as well as measures of landscape and biotic features that control habitat invasibility. Because invasive species often spread quickly over large areas, attaining these two sets of information simultaneously is uncommon. We studied the spread of a fatal nonnative root pathogen, Phytophthora lateralis, across a heterogeneous landscape of its host, Port Orford cedar (Chamaecyparis lawsoniana). Within our 37-km2 study area in southwestern Oregon and northwest California, Port Orford cedar populations are generally restricted to riparian zones along creeks. The pathogen is spread between watersheds in two ways: (1) by spore-infested material being dislodged from vehicles, and (2) by animals or people moving infested mud (i.e., via foot traffic). Using dendrochronological techniques, we determined the date of infection for dead cedars and reconstructed spread history across our study area from 1977 to 1999. Twenty-six of the 36 (72%) separate infection events we identified were caused by dispersal via vehicles along roads, and the remainder by foot traffic. Survival analysis demonstrated that cedar populations in creeks crossed by roads were more likely to be infected than those creeks that were not crossed by roads. Also, a comparison of minimum dispersal distances showed infections that moved via road moved significantly farther than those vectored by foot traffic, and the distance infection traveled declined significantly through time. We also coupled our spread history with measures of landscape and host features, including abundance of potential host trees, the distance from the road surface to the nearest potential host, length of road in immediate contact with the riparian zone, catchment area (a measure of stream flow), elevation, slope, and solar radiation. Our results show that catchment area, host abundance, and proximity to the nearest tree are significantly and positively associated with infection risk. Our study demonstrates that increased connectivity between invasible sites created by the presence of roads can increase invasion success of a plant pathogen. We also document that successful pathogen invasion can be governed by both physical landscape features and attributes of host plant populations.

We present the discovery of KELT-21b, a hot Jupiter transiting the \\(V=10.5\\) A8V star HD 332124. The planet has an orbital period of \\(P=3.6127647\\pm0.0000033\\) days and a radius of \\(1.586_{-0.040}^{+0.039}\\) \\(R_J\\). We set an upper limit on the planetary mass of \\(M_P<3.91\\) \\(M_J\\) at \\(3\\sigma\\) confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin-orbit misalignment of \\(\\lambda=-5.6_{-1.9}^{+1.7 \\circ}\\). The star has \\(T_{\\mathrm{eff}}=7598_{-84}^{+81}\\) K, \\(M_*=1.458_{-0.028}^{+0.029}\\) \\(M_{\\odot}\\), \\(R_*=1.638\\pm0.034\\) \\(R_{\\odot}\\), and \\(v\\sin I_*=146\\) km s\\(^{-1}\\), the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal-poor and \\(\\alpha\\)-enhanced, with [Fe/H]\\(=-0.405_{-0.033}^{+0.032}\\) and [\\(\\alpha\\)/Fe]\\(=0.145 \\pm 0.053\\); these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1.2\" and with a combined contrast of \\(\\Delta K_S=6.39 \\pm 0.06\\) with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of \\(\\sim0.12\\) \\(M_{\\odot}\\), a projected mutual separation of \\(\\sim20\\) AU, and a projected separation of \\(\\sim500\\) AU from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.