Sequoia Sempervirens Research Articles

Performance and genetic analysis of coast redwood cultivars for afforestation of converted grassland in California

Afforestation of pasture sites results in a net reduction in atmospheric CO2. Coast redwood (Sequoia sempervirens) is well suited to carbon forestry due to its rapid growth and long-lived decay-resistant heartwood. We sought to identify redwood cultivars (clones) suitable for afforestation and rapid growth on pasture sites. Our common garden experiment replicated at three sites tested performance of 32 cultivars and a commercial seedlot. After four growing seasons, the tallest cultivar on the two more productive sites measured 6.1 m and 5.2 m and average heights were 3- and twofold that of the least productive site. Seedling heights ranked intermediate, being outperformed by ≥ 50% of the cultivars. Height growth differed significantly among cultivars. Compared to the seedlings, the top three cultivars averaged 15–18% greater height after four growing seasons at each site. This translated to stemwood volume gains of 106% at the best site and 68% at the second best site. There was relatively low—yet statistically significant—G × E interaction, indicating that redwood cultivars can be expected to rank consistently for growth across a range of different pasture sites. However, there may be minor benefits to specific cultivar-site matching especially under suboptimal conditions such as under partial shade on poorer sites. Overall, our results demonstrate the potential of elite cultivars for rapid afforestation of pasture sites.

Shade, light, and stream temperature responses to riparian thinning in second-growth redwood forests of northern California.

Resource managers in the Pacific Northwest (USA) actively thin second-growth forests to accelerate the development of late-successional conditions and seek to expand these restoration thinning treatments into riparian zones. Riparian forest thinning, however, may impact stream temperatures–a key water quality parameter often regulated to protect stream habitat and aquatic organisms. To better understand the effects of riparian thinning on shade, light, and stream temperature, we employed a manipulative field experiment following a replicated Before-After-Control-Impact (BACI) design in three watersheds in the redwood forests of northern California, USA. Thinning treatments were intended to reduce canopy closure or basal area within the riparian zone by up to 50% on both sides of the stream channel along a 100–200 m stream reach. We found that responses to thinning ranged widely depending on the intensity of thinning treatments. In the watersheds with more intensive treatments, thinning reduced shade, increased light, and altered stream thermal regimes in thinned and downstream reaches. Thinning shifted thermal regimes by increasing maximum temperatures, thermal variability, and the frequency and duration of elevated temperatures. These thermal responses occurred primarily during summer but also extended into spring and fall. Longitudinal profiles indicated that increases in temperature associated with thinning frequently persisted downstream, but downstream effects depended on the magnitude of upstream temperature increases. Model selection analyses indicated that local changes in shade as well as upstream thermal conditions and proximity to upstream treatments explained variation in stream temperature responses to thinning. In contrast, in the study watershed with less intensive thinning, smaller changes in shade and light resulted in minimal stream temperature responses. Collectively, our data shed new light on the stream thermal responses to riparian thinning. These results provide relevant information for managers considering thinning as a viable restoration strategy for second-growth riparian forests.

Optimization of the micropropagation of elite adult trees of Sequoia sempervirens: forest species of interest in the Basque Country, Spain

Forest trees are renewable sources of timber and other valuable non-timber products. Nowadays, the increase in population and demand for forestry products results in overexploitation of forestry. Therefore, there is an urgent need to produce elite plants with higher productivity under stress derived from climate change to have available to afforestation. For this reason, propagation methods should be improved to be more efficient in terms of quality and productivity. The main species planted in the Basque Country is Pinus radiata; during the last three years, Pinus radiata plantations have suffered a fungus attack affecting mainly needles until the tree's death. This crisis is caused by the combined action of two fungi of the genus Dothistroma and Lecanosticta acicola, whose expansion seems to have been enhanced by weather-related factors, such as humid and hot summers. Although we have evidence of this disease's presence in our mountains since 1942, the disease has had a speedy expansion with an aggressive effect for reasons that are not scientifically known today. For the above, Basque Country forestry sector is looking for alternative species to be used in its plantations. Part of the forestry sector considers that Sequoia sempervirens could be a good choice for plantations. Besides, its high-quality wood and its tolerance to the attack of several pathogens and other diseases derived from climate change are characteristics that could confer some advantage over other forest species. The main goal of this study was to optimize the micropropagation of adult elite trees of Sequoia sempervirens. The effect of 6-benzylaminopurine, meta-Topolin and Kinetin, and 4 types of explant in the multiplication stage were analyzed to carry out this objective. Furthermore, the effect of two types of auxins: 1-naphthalene acetic acid, indole-3-butyric acid, and a mixture of both, were evaluated on the induction of roots and their subsequent effect on the acclimatization process. The best multiplication index was obtained when 4.4 µM 6-benzylaminopurine and apical explants longer than 1.5 cm of length were used. The root induction percentage was 75% in the most responsive genotype analyzed when 4.4 µM 6-benzylaminopurine was used on the induction stage, and 50 µM of 1-naphthalene acetic acid was used for rooting. Finally, after 3 months in the greenhouse, the explants cultured with Kinetin and rooted in a culture medium with indole-3-butyric acid showed the highest acclimatization success (94%).

Haplotype-resolved de novo assembly using phased assembly graphs with hifiasm.

Haplotype-resolved de novo assembly is the ultimate solution to the study of sequence variations in a genome. However, existing algorithms either collapse heterozygous alleles into one consensus copy or fail to cleanly separate the haplotypes to produce high-quality phased assemblies. Here we describe hifiasm, a de novo assembler that takes advantage of long high-fidelity sequence reads to faithfully represent the haplotype information in a phased assembly graph. Unlike other graph-based assemblers that only aim to maintain the contiguity of one haplotype, hifiasm strives to preserve the contiguity of all haplotypes. This feature enables the development of a graph trio binning algorithm that greatly advances over standard trio binning. On three human and five nonhuman datasets, including California redwood with a ~30-Gb hexaploid genome, we show that hifiasm frequently delivers better assemblies than existing tools and consistently outperforms others on haplotype-resolved assembly.

Impacts of Timber Harvest on Communities of Small Mammals, Ticks, and Tick-Borne Pathogens in a High-Risk Landscape in Northern California.

Timber harvest may impact tick-borne disease by affecting small mammal and tick community structures. We assessed tick and small mammal populations in older second-growth redwood (Sequoia sempervirens (D. Don) Endl) habitat at two harvested sites in Santa Cruz County, California, where local risk of tick-borne disease is high and determined the prevalence of tick-borne pathogens in ticks. After single-tree removal harvest in 2014, there was a modest reduction in canopy, primarily toward the end of the study. Harvested sites showed strong reductions in California mouse (Peromyscus californicus, (Gambel)) captures 2-yr after harvest, resolving such that treatments and controls were comparable by the end of the study. Following harvest, treated sites experienced a transient decreased tick infestation while control plots experienced an increase. Ixodes angustus (Neumann) infestation probability on harvested plots decreased immediately after harvest, increasing with time but remaining lower than control plots, whereas I. pacificus (Cooley and Kohls) prevalence was higher shortly after the harvest on harvested plots, and continued to increase. Mean abundance of ticks on vegetation increased on control plots. We detected Borrelia burgdorferi ((Johnson et al.) Baranton) and Anaplasma phagocytophilum ((Foggie 1949) Dumler) in 3.8 and 3.1% of ticks on rodents, but no differences were associated with harvest. Impacts of forest harvest on tick-borne disease depend on removal practice and intensity, whether or not hosts are habitat specialists, and whether or not ticks are host specialists.

Settler colonialism and the violent geographies of tourism in the California redwoods

Hidden from view, underneath the tourism landscape of the California redwoods, is a genocidal settler colonial history of warfare, massacres, and forced removal of Native Americans from their ancestral lands. This history has been ignored in the touristic narrative of people and place presented by a redwoods attraction in northern California, which are rife with unacknowledged histories and geographies of violence. Framed by scholarship on violent geographies in tourism development, this study shows how redwoods tourism has erased Indigenous people and history from the landscape, and how new ‘power-laden’ tourism imaginaries have been created in their place. The new tourism narrative is found in the spatial layout, interpretive signage, exhibits, website, museum of Native American artifacts, and interpretive trails in a roadside attraction called Trees of Mystery. Secondary historical literature and maps of local Yurok ancestral territory and land ownership construct a counter-narrative of the site's geography and history. Findings reveal a fanciful settler colonial history highlighting heroic male loggers on the ‘frontier’, and representations of ingenious Native Americans as historic people who produced beautiful tools, clothing and artwork but are now defeated, dead, and exotic. In fact, white settlers, backed by the U.S. Army and local militias, appropriated and logged Native American redwood lands, and in doing so massacred resident Yurok People and forced the survivors from their traditional territories. Conversely, the Yurok People have been reclaiming ancestral lands, reviving cultural practices, and resisting settler colonialism from the early 1800s to the present-day. Across the Americas, countless other settler colonial tourism sites like these sit upon violent geographies. Unearthing the hidden geography of this particular site shows how decolonizing research might be undertaken at other tourism sites situated on stolen Indigenous lands in the U.S. and beyond.

Genetic structure of coast redwood (Sequoia sempervirens [D. Don] Endl.) populations in and outside of the natural distribution range based on nuclear and chloroplast microsatellite markers.

Coast redwood (Sequoia sempervirens) naturally growing in southern Oregon and northern California is one of the few conifer tree species that are polyploid. Despite its unique ecological and economic importance, its population genetic structure is still insufficiently studied. To obtain additional data on its population genetic structure we genotyped 317 samples collected from populations in California (data set C) and 144 trees growing in a provenance trial in France (data set F) using 12 nuclear (five random nuclear genomic nSSRs and seven expressed sequence tag EST-SSRs) and six chloroplast (cpSSRs) microsatellite or simple sequence repeat (SSR) markers, respectively. These data sets were also used as reference to infer the origin of 147 coast redwood trees growing in Germany (data set G). Coast redwood was introduced to Europe, including Germany as an ornamental species, decades ago. Due to its fast growth and high timber quality, it could be considered as a potential commercial timber species, especially in perspective to climate warming that makes more regions in Germany suitable for its growing. The well performing trees in colder Germany could be potential frost resistant genotypes, but their genetic properties and origin are mostly unknown. Within the natural range in southern Oregon and northern California, only two relatively weak clusters were identified, one northern and one southern, separated by the San Francisco Bay. High genetic diversity, but low differentiation was found based on the 12 nuclear SSR markers for all three data sets F, C and G. We found that investigated 147 German trees represented only 37 different genotypes. They showed genetic diversity at the level less than diversity observed within the natural range in the northern or southern cluster, but more similar to the diversity observed in the southern cluster. It was difficult to assign German trees to the original single native populations using the six cpSSR markers, but rather to either the northern or southern cluster. The high number of haplotypes found in the data sets based on six cpSSR markers and low genetic differentiation based on 12 nuclear SSRs found in this study helps us study and better understand population genetic structure of this complex polyploid tree and supports the selection of potential genotypes for German forestry.

Compressions of Sequoia (Cupressaceae sensu lato) from the Middle Jurassic of Daohugou, Ningcheng, Inner Mongolia, China

The specimens (two pairs of part and counterpart) of coniferalean branched leafy shoots were collected from the Jiulongshan Formation (Middle Jurassic) at the village of Daohugou, Ningcheng, Inner Mongolia, China. The fossil material displays helical phyllotaxy, dorsiventrally flattened linear, sessile leaves with decurrent base and prominent and single mid-vein. The foliate shoots are assigned to Sequoia jeholensis by comparing those of the genera Yanliaoa, Sequoia, Metasequoia, Taxodium, and Glyptostrobus, the basal members of the Cupressaceae sensu lato. Sequoia jeholensis is the oldest Sequoia species to date. It has coriaceous, dimorphic, helically arranged linear and scale leaves, with entire margins, attached obliquely to the axis by their decurrent bases. The leaf cuticle of S. jeholensis is described here for the first time. Leaves are hypostomatic, with stomata only on the abaxial surface. Anticlinal walls are straight, with single or more often paired pits. The epidermal structures of Sequoia are one of the key characters to distinguish it from similar genera, but they usually could not be used to distinguish the species within Sequoia. The Middle Jurassic of Daohugou represents a lacustrine environment with a warm and humid climate reflected by the species assemblage. So, the extinct Sequoia probably had similar climatic requirements to those of extant Sequoia sempervirens.

Development of Redwood Regeneration after Conifer Partial Harvest and Hardwood Management

Abstract Harvesting of commercial conifer species from conifer-hardwood mixtures can leave residual stands dominated by hardwoods. Removing unwanted hardwoods by cutting or herbicide makes growing space available to residual trees and regeneration and can restore conifer dominance. Forest managers of north coastal California need guidance on how such treatments affect subsequent growth of planted redwoods (Sequoia sempervirens [D. Don.] Endl.) or natural regeneration, as well as proliferation of undesirable species. Our observational study reconstructed growth of 108 regenerating redwoods in 26 treated stands. Residual stand density was the main driver of height and diameter growth in the new cohort of redwoods, irrespective of whether hardwoods were cut or received herbicide frill treatment (prevents resprouting). At lower residual stand densities, there were higher densities of natural regeneration (ingrowth) of conifers and hardwoods, which affected diameter at breast height (dbh) growth of regenerating redwoods. After heavier cutting of hardwoods, this ingrowth comprised a greater proportion of unwanted hardwood regeneration. Therefore, frill treatment is recommended when the objective of management is to reduce hardwood stocking and regeneration. Combining partial harvesting of conifers with cutting or frill treatment of hardwood is another option that reduces stand density to promote height and dbh growth of regenerating redwoods.

The generalizability of water-deficit on bacterial community composition; Site-specific water-availability predicts the bacterial community associated with coast redwood roots.

Experimental drought has been shown to delay the development of the root microbiome and increase the relative abundance of Actinobacteria, however, the generalizability of these findings to natural systems or other diverse plant hosts remains unknown. Bacterial cell wall thickness and growth morphology (e.g., filamentous or unicellular) have been proposed as traits that may mediate bacterial responses to environmental drivers. Leveraging a natural gradient of water-availability across the coast redwood (Sequoia sempervirens) range, we tested three hypotheses: (a) that site-specific water-availability is an important predictor of bacterial community composition for redwood roots and rhizosphere soils; (b) that there is relative enrichment of Actinobacteria and other monoderm bacterial groups within the redwood microbiome in response to drier conditions; and (c) that bacterial growth morphology is an important predictor of bacteria response to water-availability, where filamentous taxa will become more dominant at drier sites compared to unicellular bacteria. We find that both α- and β-diversity of redwood bacterial communities is partially explained by water-availability and that Actinobacterial enrichment is a conserved response of land plants to water-deficit. Further, we highlight how the trend of Actinobacterial enrichment in the redwood system is largely driven by the Actinomycetales. We propose bacterial growth morphology (filamentous vs. unicellular) as an additional mechanism behind the increase in Actinomycetales with increasing aridity. A trait-based approach including cell-wall thickness and growth morphology may explain the distribution of bacterial taxa across environmental gradients and help to predict patterns of bacterial community composition for a wide range of host plants.

Comparative development of the four tallest conifer species

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.

New 3D measurements of large redwood trees for biomass and structure

Large trees are disproportionately important in terms of their above ground biomass (AGB) and carbon storage, as well as their wider impact on ecosystem structure. They are also very hard to measure and so tend to be underrepresented in measurements and models of AGB. We show the first detailed 3D terrestrial laser scanning (TLS) estimates of the volume and AGB of large coastal redwood Sequoia sempervirens trees from three sites in Northern California, representing some of the highest biomass ecosystems on Earth. Our TLS estimates agree to within 2% AGB with a species-specific model based on detailed manual crown mapping of 3D tree structure. However TLS-derived AGB was more than 30% higher compared to widely-used general (non species-specific) allometries. We derive an allometry from TLS that spans a much greater range of tree size than previous models and so is potentially better-suited for use with new Earth Observation data for these exceptionally high biomass areas. We suggest that where possible, TLS and crown mapping should be used to provide complementary, independent 3D structure measurements of these very large trees.

Anisotropic electrical conductivity of green timber within $$20-90^{\circ }\hbox {C}$$ temperature range

Electrical conductivity (EC) of the unseasoned timber of three softwood species (Pinus radiata, Pseudotsuga menziesii, and Sequoia sempervirens) and one hardwood species (Eucalyptus globoidea) was studied over the temperature range of $$20-90^\circ \hbox {C}$$ . EC was measured in sapwood, transitional wood, and heartwood in the three principle grain directions. All species exhibited similar behaviour: (1) heartwood EC was lower than that of sapwood and (2) EC increased with temperature. P. radiata samples from two regions of New Zealand’s South Island showed variation of EC by a factor of two in the longitudinal direction; however, in the radial and tangential directions, the EC variation was less pronounced. This work seeks to provide possible explanations for EC variation in green wood and to propose suggestions for future research.

Ágar e carvão ativado influenciam no desenvolvimento in vitro da parte aérea e radicular de sequoia

Plantios experimentais com Sequoia sempervirens (Lamb), espécie conhecida mundialmente pelo grande porte, longevidade e qualidade madeireira, estão iniciando no Brasil, tornando necessário a disponibilidade de mudas de qualidade. Assim, a técnica de cultura de tecidos, via micropropagação, se torna uma grande aliada pela garantia de superioridade genética, produção em grande escala e tempo reduzido de propagação. Atualmente há inúmeros protocolos para diversas espécies, porém, é necessário verificar todos os agentes influentes no sucesso do desenvolvimento in vitro. O objetivo deste trabalho foi determinar a influência do carvão ativado e de concentrações de ágar no desenvolvimento in vitro aéreo e de raízes de S. sempervirens. Os tratamentos realizados envolveram a presença/ausência do carvão ativado (1 g L-1), combinados com concentrações de ágar (4, 5 e 6 g L-1) em meio MS 50%. Para o número e comprimento de brotos e de raízes, apenas o carvão ativado foi significativo, sendo que a presença beneficiou o desenvolvimento dos explantes. Para porcentagem de calo, houve interação dos fatores, sendo que maiores concentrações de ágar (5 e 6 g L-1) na presença do carvão foram prejudiciais, pois apresentaram maior calosidade, o que minimiza as taxas de enraizamento. Indica-se a adição de carvão ativado (1 g L-1) e de menor concentração de ágar (4 g L-1) em meio de cultura MS 50% para um melhor desenvolvimento in vitro de sequoia.

De novo transcriptome assembly of cold stressed clones of the hexaploid Sequoia sempervirens (D. Don) Endl.

Coast redwood is a very important endemic conifer timber species in Southern Oregon and Northern California in the USA. Due to its good wood properties and fast growth rate it can be considered as a prospective timber species also in other countries with similar or changing toward similar climatic conditions due to global climate warming, such as Germany. In general, it is frost sensitive and suffers from freezing temperatures. To study genetic mechanisms of frost resistance in this species and to select the most frost tolerant trees we tested 17 clones in climate control chamber experiments and generated two de novo assemblies of the coast redwood transcriptome from a pooled RNA sample using Trinity and CLC Genomic Workbench software, respectively. The hexaploid nature of the coast redwood genome makes it very challenging to successfully assemble and annotate the coast redwood transcriptome. The de novo transcriptome assembly generated by Trinity and CLC considering only reads with a minimum length of 180 bp and contigs no less than 200 bp long resulted in 634,772 and 788,464 unigenes (unique contigs), respectively.

Induction of tolerance by chlorocholine chloride in Sequoia sempervirens seedlings under natural cooling and drought

Two-years-old Sequoia sempervirens seedlings were foliar sprayed once and twice with chlorocholine chloride (CCC) at 0, 100, 500, 1 000, 1 500 and 2 000 mg·l<sup>–1</sup>. The purpose was to investigate the effect of CCC on the growth and photosynthetic activity of S. sempervirens seedlings under natural cooling and drought in autumn and winter. The findings showed that the increments of plant height and crown diameter were significantly decreased with the increase of chlorocholine chloride concentration, and the increment of root collar diameter, net photosynthetic rate, actual photochemical quantum yield and photosynthetic electron transport rate showed the trend of increasing first and then decreasing, and reached the maximum at concentrations of 1 000~2 000 mg·l<sup>–1</sup>. There was not a significant difference between two applications and single application. It suggests that 1 000~2 000 mg·l<sup>–1</sup> chlorocholine chloride can protect the photosynthetic activity of S. sempervirens seedlings and alleviate the stress induced by low temperatures and drought in autumn and winter.

Landscape scale variation in the hydrologic niche of California coast redwood

Topoclimatic diversity within forest landscapes can underlie variation in water availability, which may correspond to patterns in habitat suitability of tree species with differing hydrologic niches. However, the trade‐off between the collection of data at a fine grain size over large spatial extents has limited comprehensive analyses of landscape scale variation in habitat suitability. We present a fine scale analysis of the roles of topographic gradients in moisture availability, soil water storage and fog frequency in the spatial pattern of habitat suitability for coast redwood Sequoia sempervirens, at 10 m resolution across 34 800 ha and three landscapes spanning approximately one‐third of redwood's latitudinal range. A new 10 m resolution presence‐absence map derived from airborne imaging spectroscopy was used to characterize current redwood distributions in three landscapes. Access to belowground moisture was assessed through four measures calculated from a high‐resolution LiDAR digital elevation model, soil water storage was mapped from the USDA Soil Survey Geographic Database, and fog frequency was calculated from MODIS cloud cover data. Access to belowground moisture and fog predicted variation in suitability as redwood habitat from 22–75% and predicted redwood presence and absence at 10 m resolution with 63–74% accuracy. Across all three landscapes, redwood density consistently decreased with increasing interpolated height above a stream (IHAS), but the role of other predictors varied among the sites. Our results challenge previous assumptions that redwood habitat suitability within much coarser resolutions (800 m × 800 m) can be described by a single value. The elevated habitat suitability of sites close to streams suggests that these sites should be evaluated for their potential to become microrefugia within landscapes that may become climatically‐unsuitable for redwoods at a regional scale.

Bark Thickness in Coast Redwood (Sequoia sempervirens (D.Don) Endl.) Varies According to Tree- and Crown Size, Stand Structure, Latitude and Genotype

Research Highlights: Bark thickness (BT) in coastal redwood (Sequoia sempervirens (D.Don) Endl.) varies in accordance with tree size, crown ratio, position within the canopy, height along the tree stem, genetic identity and latitude. However, current BT predictive equations do not account for such variability, leading to inaccurate BT estimations. We present improved BT models to increase the accuracy of BT estimates for coastal redwood in northern California. Background and Objectives: BT is an important metric that has many practical applications in forest management. However, BT varies substantially across species and environments, as well as across individuals and populations. Our objectives were to investigate BT along various gradients of change, with factors accounting for genetics, tapering of BT along the tree bole, differences in BT according to tree crown position within the stand, and the latitude. Materials and Methods: We collected BT data throughout most of redwood’s natural range along a north–south latitudinal gradient. Subsets of these data were used to examine the influence of particular variables on BT while holding the other variables constant. Results: Regionally, the bark was thicker among more xeric southern redwoods and thinner among more mesic northern redwoods. We found that the BT of codominant, intermediate and suppressed trees was around 8%, 14%, and 18% thicker, respectively, than bark of the same size dominant tree. Redwood trees growing in the partial shade of an overstory had thicker bark than trees growing in even-aged stands and incorporating genetic identity yielded major improvements in the BT model estimates, suggesting that BT is under genetic control. Bark thickness decreased with increasing height along the tree stem, with notable differences in the BT above and below breast height. Conclusions: We recommend utilizing the best available BT equations (over standard ‘bark factors’) in forest science, modeling and management applications. We also recommend the adoption of our drilling method for BT measurement on larger trees due to the potential for error associated with traditional bark gauge measurements.

Physiology and Growth of Douglas-Fir and Redwood Seedlings Planted After Partial Harvesting

Reforestation following timber harvests and natural disturbances is an essential component of sustainable forest management. As disturbances such as drought-induced mortality and wildland fires spread across many forests of the western U.S., a better understanding of the influences of stand structure on seedling physiology can foster more effective reforestation efforts. Moreover, as climate throughout the West is projected to become hotter and drier, it is important to investigate regeneration under xeric conditions, particularly for species restricted to mesic habitats. To study the influences of stand structure and climate on regeneration success, we monitored physiology (water potential [Ψ] and stomatal conductance [gs]), growth (change in basal diameter and biomass accumulation), and mortality rate of planted Douglas-fir (Pseudotsuga menziesii) and coast redwood (Sequoia sempervirens) seedlings for two growing seasons after partial harvesting in inland northern California. Compared to seedlings in the no-cut and moderate-retention treatments, seedlings in the gap (100% cut) treatment had the highest Ψ and gs, greatest growth, and lowest mortality. We also found that compared to Douglas-fir, redwood had higher Ψ and gs, greater growth, and lower mortality. Overall, our study indicates that low-retention silvicultural treatments can minimize water stress and maximize gas exchange, growth, and survival in regenerating seedlings. Our results also demonstrate that redwood, a species generally restricted to mesic coastal habitats, can successfully establish in xeric inland sites when planted after partial harvesting, even during drought conditions.

MINI-CUTTINGS ROOTING OF Sequoia sempervirens AT DIFFERENT IBA CONCENTRATIONS AND CLONES

Sequoia is a species that provides large volumes of wood, is resistant to decomposition and has seedling production by mini-cutting as a viable alternative. The aim of this work was to evaluate the rooting of mini-cuttings of different clones of Sequoia sempervirens and subsequent use of different concentrations of IBA in clones with low adventitious rooting. Mini-cuttings of different clones were used, from clonal mini-garden. In the experiment with the growth regulator, different concentrations of IBA (from 0 mg L -1 to 3000 mg L -1 ) were used. The material was placed to be rooted in a mini-tunnels and evaluate at 90 days. All experiments were installed in a completely randomized design, with a subsequent evaluation of survival (%), mini-cuttings with calluses (%), mini-cuttings rooted (%) and number of roots (only in the experiment with different concentrations of IBA). In the first experiment, the survival of mini-cuttings was high (close to 95%) and rooting showed great variation among the clones (22.8 to 100%). In the second experiment, using clones that previously presented rooting less than 50%, submitted to IBA application, high survival (88.1 to 99.4%) was observed. The clones presented different responses among themselves, but with improve in the rooting using growth regulator.