Western Redcedar Trees Research Articles

First report of Truncatella angustata causing leaf blight on Thuja plicata Donn ex D. Don in Canada.

Western redcedar (Thuja plicata Donn ex D. Don) is one of the most important commercial tree species in British Columbia, generates more than $1 billion in economic activity annually and about 8-10 million trees are planted in reforestation efforts (Gregory et al. 2018). It has been selected as the provincial tree of British Columbia (BC) because of its tremendous economic, ecoogical and cultural value. However, foliar diseases such as leaf blights have serious impact on redcedar growth and may cause significant loss of tree volume (Russell, 2007). Our 2014 - 2015 surveys of western redcedar forests in coastal areas of BC indicated high incidence of a distinctive type of blight. We observed the incidence of this disease on more than 80% of western redcedar (approximately 493) trees from late May to early December. Early symptoms appeared as circular to oval, brownish to black spots (2-3 mm), 1-5 spots per branch tip, scattered at the tip margins. Sequentially, the spots enlarged and developed into necrotic lesions on both young and old leaves. More than 50 symptomatic leaves from 10 different trees were collected and rinsed in distilled water then surface-sterilized with three times washing in Tween 20 (%5 solution) for 2 minutes (each time) and %70 ethanol for 30 second (3 times repeat). Tissues from under lesions were placed on MEA (Malt Extract Agar; Phyto Tech® labs-Product ID: M498) and PDA (Potato Dextrose Agar; Phyto Tech® Labs-Product ID: P772). The plates were incubated at 21°C in the dark. They developed distinct dull white to brown, cottony colonies with each black acervuli approximately 450-500µm. The isolates produced fusiform conidia with four cells. They didn't have any distinct color. The conidiophore size was approximately 23-24 x 2-3 µm with mostly hyaline to light brown color, branched and conidiogenous was hyaline and not branched and simple. The spore size was approximately 15-20μm by 7-10μm with three transverse septa and endogenous papillae with hyaline apical appendages. Next, we collected spores and replated them on fresh MEA media culture and placed back in the incubator to produce pure cultures. We studied conidia from leaves of trees mentioned above using light and electron microscopy using Hitachi S-3500N Scanning Electron Microscope (Noshad et al. 2023). After morphological study, further identification to the species level conducted using Zambounis and Wenneker's approach (Zambounis 2019; Wenneker,2017). Genomic DNA from two single-spore isolates were isolated and sequenced. Sequences of ITS (Internal Transcribed Spacer) region amplified using primers ITS1/ITS4 and sequenced. Final sequences were deposited in Genbank and published (accession numbers OP086244 and OP086251). Blast analysis of these sequences showed 99% and 99% resemblances with T. angustata sequence (Sutton 1980). To verify its pathogenicity, we performed a comprehensive pathogenicity test to fulfill Koch's postulates. We collected their distinctive spores in an aseptic environment and standardized them (5000/ml) using a haemocytometer. Then we inoculated 100 western redcedar seedlings (three years old) by injecting standardized spore suspension solution (inoculum) using ultra-fine 0.3ml, 31G, 8mm syringes (approximately 0.1ml per inoculation site). Ten positive control seedlings were inoculated with distilled water and ten negative control seedlings were not inoculated at all. All inoculated (experimental) seedlings demonstrated same symptoms (black spots and characteristic spores) after eight weeks. None of the control seedlings showed any similar symptoms. In the next stage, we isolated and cultured spores from inoculated seedlings and studied them. The identity of reisolates confirmed using DNA sequencing. We used these spores for our next set of disease screening which was successful again. We identified Truncatella angustata (Pers.) Hughes as the causal agent for shoot-tip blight (STB) on western redcedar by examining morphological and molecular characteristics of the pathogen. This is the first report of T. angustata as a primary pathogen on western redcedar in British Columbia, Canada.

Using Traditional Ecological Knowledge to Understand the Diversity and Abundance of Culturally Important Trees

Combining Indigenous traditional ecological knowledge (TEK) with scientific research holds promise for more effectively meeting community objectives for the conservation of cultural forest resources. Our study focuses on predicting the abundance of western redcedar trees ( Thuja plicata) within the traditional territories of five Indigenous Nations that are part of the Nanwakolas Council in British Columbia, Canada. Indigenous people in this region use western redcedar extensively for cultural practices, such as carving dugout canoes, totem poles, and traditional buildings. However, after more than a century of industrial logging, the abundance of redcedar suitable for these types of practices is in decline and no longer reflects past baseline conditions. We assess how using TEK from interviews with Indigenous carvers refines predictions of resource abundance compared to using only conventional field surveys. Our findings reveal that western redcedar trees suitable for traditional carving are generally rare, and that some important growth forms, such as those associated with carving community canoes, are nearly extirpated from the landscape. We demonstrate a useful application of TEK in conservation planning and highlight concerns about the impact of industrial forestry on culturally important trees.

Identification of Three Monofunctional Diterpene Synthases with Specific Enzyme Activities Expressed during Heartwood Formation in Western Redcedar (Thuja plicata) Trees.

Upon harvest, Western redcedar (WRC; Thuja plicata) trees have a high incidence and extent of heartwood rot. While monoterpenoids and lignans have been linked to rot resistance in this species, other specialized metabolites, such as diterpenes, are likely to contribute to rot resistance. Here we report the cloning and functional assessment of three putative diterpene synthase (TpdiTPS) genes expressed during heartwood formation in WRC. The predicted proteins of the three genes lack either of the two catalytically independent active sites typical of most diTPS, indicating monofunctional rather than bifunctional activity. To identify potential catalytic activities of these proteins, we expressed them in genetically engineered Escherichia coli strains that produce four potential substrates, geranylgeranyl diphosphate (GGDP), ent, syn, and normal stereoisomers of copalyl diphosphate (CDP). We found that TpdiTPS3 used GGDP to produce CDP. TpdiTPS2 used normal CDP to produce levopimaradiene. TpdiTPS1 showed stereoselectivity as it used normal CDP to produce sandaracopimaradiene and syn-CDP to produce syn-stemod-13(17)-ene. These genes and protein enzymatic activities have not been previously reported in WRC and provide an opportunity to assess their potential roles in heartwood rot resistance in this economically important species.

Combining data from field surveys and archaeological records to predict the distribution of culturally important trees

AbstractAimIndigenous communities involved in conservation planning require spatial datasets depicting the distribution of culturally important species. However, accessing datasets on the location of these species can be challenging, particularly when the current distribution no longer reflects areas with the full range of suitable growing conditions because of past logging. We test whether using occurrence data from community‐based field surveys and archaeological records in species distribution models can help predict the distribution of monumental western redcedar trees (Thuja plicata)—large, high‐quality trees suitable for cultural purposes such as carving dug‐out canoes, totem poles and traditional houses. This species is critically important to indigenous people of the Pacific Northwest of North America, but trees suitable for traditional carving and building are diminishing in abundance due to logging.LocationOur analysis covers the spatial extent of the traditional territory of the Heiltsuk First Nation, which encompasses a portion of the Great Bear Rainforest in British Columbia, Canada.MethodsWe built and compared species distribution models using the machine learning program, Maxent, based on occurrence data from field surveys and archaeological records of culturally modified trees.ResultsOur findings highlight similarities and differences between the predictions from these species distribution models. When validating these models against occurrences from an independent dataset, the archaeological record model performs better than the field survey model. These findings may arise because the independent dataset was collected on an unlogged island—an environment that aligns more closely with the historic forest conditions revealed by the archaeological records than the current distribution revealed by the field surveys.Main conclusionsWe demonstrate and discuss the utility of using archaeological data in species distribution modelling and conservation planning when the target species is associated with shifting environmental baselines, data limitations and an important cultural resource.

Effect of Vegetation Management and Site Conditions on Volume, Biomass and Leaf Area Allometry of Four Coniferous Species in the Pacific Northwest United States

Allometric equations are useful tools for calculating tree and stand-level attributes, such as above-ground biomass or stem volume, using simple measurements that can be obtained from stand inventory data. These equations tend to be species-specific and can be affected by site conditions and silvicultural treatments. Forest vegetation management treatments (VM) are an important component of reforestation programs in the Pacific Northwest of the United States; however, no study has investigated the impact of these treatments on crop tree allometry. In this study we assessed the long-term effects of two contrasting VM treatments on the allometry of sixteen-year-old Douglas-fir, western hemlock, western redcedar, and grand fir trees growing in Oregon’s central Coast Range (CR) and fifteen-year-old Douglas-fir and western redcedar trees growing in Oregon’s Cascade foothills (CF). The VM treatments included a control which received only a pre-planting herbicide application and a VM treatment consisting of five consecutive years of vegetation control after planting. The equations developed in this study were species-specific and were not affected by VM with the exception of western redcedar foliage biomass. For western redcedar, tress of similar diameter had more foliage biomass when growing on plots without VM after planting. The allometry of Douglas-fir and western redcedar was also found to be affected by site, such that trees of similar diameter and height had larger stem volume when growing at the CR site than the CF site. This difference in stem volume was found to be the result of differences in stem tapering. There was a strong relationship between stand basal area and leaf area index that was the same for all species tested and was unaffected by site. The equations presented in this study are useful for calculating stem volume, leaf area and individual tree and component biomass for stands of the studied species that are of similar age.

The effect of stump removal and tree admixture on butt decay incidence, damage and wood density in western redcedar

Western redcedar (WRC) trees of 48–49 years in age grown in monoculture and in admixtures with birch, Douglas-fir and pine in the interior of British Columbia were sampled for wood density and the presence and level of damage from butt decay initiated by Armillaria ostoyae in stumped and unstumped plots. Stump removal reduced butt decay incidence in WRC from 18% to 2% and damage from 3.5% of the diameter at base to 0.3% compared to when stumps remained. External lesions on tree bases caused by Armillaria root disease increased the probability of WRC stems having butt decay by 1.25 times for an average-sized lesion. The incidence of butt decay and the level of internal damage to WRC in sampled plots was not related to admixture, tree size or site index. Stump removal controlled the inoculum of Armillaria root disease, thereby reducing incidence and size of WRC basal lesions that probably act as infection courts for other fungi causing butt decay. WRC trees grown in monoculture or with birch had the highest wood densities of all planting mixes tested. Wood density in WRC was lowest at the outer edges of individual WRC trees, in larger trees, and in plots where stumps had not been removed. The lower density WRC wood is thought to occur by overtopping from fast-growing species in admixture and depletion of soil moisture affecting latewood formation. This is a first report of stump removal affecting butt decay and admixture affecting wood density in WRC.

Application of Western red cedar (Thuja plicata) tree bark as a functional filler in pMDI wood adhesives

In this study, Western red cedar (Thuja plicata) tree bark was used as a reactive functional filler (oven-dry particles, <0.1 mm) in polymeric diphenylmethane diisocynate (pMDI) wood adhesives at four different loading levels (5, 10, 15 and 20 wt.%) to improve the bondline formation at the adhesive-substrate interface. Adhesion performance and curing behavior of the bark containing pMDI (B-pMDI) were investigated. B-pMDI adhesive had a higher viscosity than pMDI control and the viscosity value varied according to the bark/pMDI weight ratio. Compared to the pMDI control wood adhesive without bark, B-pMDI showed comparable dry bonding strength and enhanced wet bonding strength for wood substrates. SEM images indicated that B-pMDI formed a thicker and more consistent bondline than the pMDI control due to bark particles effectively bridging the gap between the wood substrates. Based on both Kissinger and isoconversional model-free methods, cure kinetics revealed that oven-dry bark particles chemically reacted with pMDI. Moreover, it was found that a lower activation energy and a higher reaction rate were observed for pMDI curing with moist bark than with oven-dry bark. FTIR characterization suggested the existence of urethane and urea linkages in the cured adhesives.

Ecological legacies of anthropogenic burning in a British Columbia coastal temperate rain forest

AbstractAimFew long‐term fire histories have been reconstructed in coastal temperate rain forests, and little is known regarding the spatial and temporal characteristics of lightning and human ignitions. We use a multidisciplinary approach to assess the impact, scale and ecological legacies of historic fires.LocationWe focus on perhumid temperate rain forests located on the central coast of British Columbia, Canada.MethodsWe reconstructed 700 years of temporal and spatial aspects of fire activity with 30 plots on Hecate Island using fire scars and forest‐stand establishment. We then conducted a paired study of 20 former indigenous habitation and control sites on 15 islands to relate fire activity to patterns of human settlement. We mapped 15 years of lightning strike densities and use mixed‐effects modelling to assess whether fire activity predicted the distribution and abundance of traditional plants.ResultsSixteen low‐ and mixed‐severity fires were recorded from 1376 to 1893. The abundance of traditional plants and the density of western redcedar trees were best predicted by the location of former habitation sites and shorter mean fire intervals. Lightning is too rare to explain the pattern of fire activity in the study area. No fire activity was detected after 1893, coinciding with the relocation of indigenous groups from the study area.Main conclusionsFire was strongly associated with former indigenous habitation sites during the periods of occupation. People likely utilized fire as a tool for resource management to influence the densities of specific plants by creating mosaics of vegetation in different stages of succession. By assessing the ecological impacts of historic fire events, we gain a better understanding of the abrupt changes that occurred in the 20th century. Our ability to understand present‐day temperate rain forest ecosystems may be compromised if we underestimate the role of humans in driving historic fire activity.

A solvent-based extraction fails to remove mobile nitrogen from western redcedar (Thuja plicata)

The ability to accurately measure interannual variability of the stable isotope of nitrogen, 15N, in tree rings could greatly improve understanding of marine-derived nitrogen delivery to terrestrial ecosystems, soil nitrogen dynamics, and the influences of climate on nitrogen cycles. It could also provide a tool for reconstructing past salmon abundances. However, the mobility of nitrogen throughout the entire tree including between rings has confounded attempts to make full use of 15N in dendrochemistry. We report that despite solvent-based extraction pretreatment to remove nonstructural, mobile nitrogen from increment core samples, an elevated 15N signal is detected in rings formed up to about ten years prior to application of a 15N-enriched tracer in four western redcedar trees. We conclude that the interpretation of the heavy nitrogen signal in tree rings via this pretreatment extraction method is confounded. These findings corroborate work already done in the field.

Effects of wounding and fungal infection with Armillaria ostoyae in three conifer species. II. Host response to the pathogen

SummaryStructural responses in the bark and wood were described following penetration by Armillaria ostoyae in the roots of 20‐ to 30‐year‐old Douglas‐fir, western hemlock and western redcedar trees. Tissue necrosis presumably caused by fungal exudates was commonly observed at inoculum contact. In Douglas‐fir and western hemlock, A. ostoyae interfered with the initiation of active defence mechanisms involving the development of a lignified zone of impervious tissue (IT), necrophylactic periderm (NP) formation and compartmentalization of infected woody tissue. Breaching of IT and NP barriers was frequent, particularly around the clusters of sclereid cells in western hemlock. In western redcedar, the IT zone was inconspicuous. Induced rhytidome formation occurred in western redcedar either simultaneously with or after completion of NP development. The formation of this tissue facilitated en masse sloughing of infected tissue from the surface of roots. In western redcedar, traumatic phloem resin ducts formed in tangential bands surrounding the margin of expanded lesions. Effective compartmentalization in western redcedar was achieved by a barrier zone comprised of a higher‐than‐average number of axial parenchyma that accumulated polyphenolic deposits. A combination of host‐mediated defence mechanisms in western redcedar resulted in a significantly higher frequency of effective resistance reactions than in western hemlock or Douglas‐fir.

Vegetation Response to Prescribed Fire in Douglas-Fir Forests, Olympic National Park

Abstract Fire exclusion for more than a century in Olympic National Park changed old-growth Douglas-fir forest stand structure and species composition from an open structure of fire-adapted species to a more crowded, complex structure formed by fire-avoiding species. A previous study identified an historical mean fire return interval of 21 yr for these forests in the eastern Olympics prior to fire exclusion, with frequent, small surface fires maintaining an open forest. We tested whether Douglas-fir/salal forests would support low intensity prescribed fires, and monitored community responses for 3 yr post-fire in a randomized complete block ANOVA. Compared to pre-fire values, total fuels, 1000-hr fuels, 1-hr fuels, duff depth, total tree density, tree species density, sapling density, understory cover, and understory frequency of five prominent species were significantly lower one month post-fire. Differences in tree basal area, Douglas-fir sapling density, and western redcedar tree density were not signi...

New Method to Isolate Gamma-Thujaplicin from Western Red Cedar (Thuja plicata Donn.)

Western red cedar (WRC) (Thuja plicata Donn.) is one of the most durable softwoods in North America, and this durability has largely been attributed to its tropolone content. Further studies on factors contributing to the durability of this species require isolation of substantial quantities of the active components. Wood meal from the heartwood butt of a WRC tree was extracted with hexane for 24 hours. The thujaplicin mixture was obtained by chloroform extraction of the alkali solution adjusted to a pH of 6.5. With chemical conversion and regeneration, the selected compound, “gamma-thujaplicin,” was isolated from the thujaplicin mixture and characterized by Fourier transform infra-red (FTIR) spectroscopy, High Performance Liquid Chromatography (HPLC), Mass Spectroscopy (MS), 1H-nuclear magnetic resonance (NMR), Gas Chromatography–Mass Spectroscopy (GC–MS), a color test, and comparison with standard gamma-thujaplicin. Relative purity reached up to 99%. Additionally, a by-product, nezukone, could be also isolated from the hexane extractives.

Nested patterns of community assembly in the colonisation of artificial canopy habitats by oribatid mites

An observed species–area relationship (SAR) in assemblages of oribatid mites inhabiting natural canopy habitats (suspended soils) led to an experimental investigation of how patch size, height in canopy and moisture influence the species richness, abundance and community composition of arboreal oribatid mites. Colonisation by oribatid mites on 90 artificial canopy habitats (ACHs) of three sizes placed at each of three heights on the trunks of ten western redcedar trees was recorded over a 1‐year period. Fifty‐nine oribatid mite species colonised the ACHs, and richness increased with the moisture content and size of the habitat patch. Oribatid mite species richness and abundance, and ACH moisture content decreased with increasing ACH height in the canopy. Patterns in the species richness and community composition of ACHs were non‐random and demonstrated a significant nested pattern. Correlations of patch size, canopy height and moisture content with community nestedness suggest that species‐specific environmental tolerances combined with the differential dispersal abilities of species contributed to the non‐random patterns of composition in these habitats. In line with the prediction that niche‐selection filters out species from the regional pool that cannot tolerate environmental harshness, moisture‐stressed ACHs in the high canopy had lower community variability than ACHs in the lower canopy. Colonising source pools to ACHs were almost exclusively naturally‐occurring canopy sources, but low levels of colonisation from the forest floor were apparent at low heights within the ACH system. We conclude that stochastic dispersal dynamics within the canopy are crucial to understanding oribatid mite community structure in suspended soils, but that the relative importance of stochastic dispersal assembly may be dependent on a strong deterministic element to the environmental tolerances of individual species which drives non‐random patterns of community assembly.

Diversity and Distribution of Oribatid Mites (Acari: Oribatida) Associated with Arboreal and Terrestrial Habitats in Interior Cedar-Hemlock Forests, British Columbia, Canada

We assessed oribatid mite abundance, species richness and community composition in arboreal and terrestrial habitats associated with 12 western redcedar trees in the Interior Cedar-Hemlock biogeoclimactic zone of British Columbia, Canada. We extracted microarthropods from 36 canopy litter samples, 36 epiphytic lichen samples from three different lichen functional groups, and 36 soil core samples of the forest floor litter layer. Oribatid mites dominated microarthropod assemblages in all habitats. Total microarthropod and oribatid mite abundances were significantly greater in forest floors and foliose (leaf-like) lichens compared to canopy litter accumulations, and alectorioid (hair-like) and cyanolichen (lobed) groups. Sixty-one species of oribatid mites were identified from the study area. The ten species collected from canopy litter and 14 species collected from epiphytic lichens shared five species in common, whereas only three of the 45 species collected from the forest floor also were found within the canopy system. Principal components analysis and discriminant function analysis differentiated three distinct assemblages of oribatid mites corresponding to the canopy litter accumulations, epiphytic lichens and forest floor habitats. Low abundance of oribatid mites in canopy litter accumulations is attributed to low microhabitat structural complexity, low food resources and low desiccation resistance in these habitats compared to canopy lichen habitats and the forest floor. Epiphytic lichens are the domi nant habitat for arboreal oribatid mites in the ICH forest zone, and contribute to the overall biodiversity of the forest system by containing distinct oribatid mite assemblages.

Oribatid mite communities and foliar litter decomposition in canopy suspended soils and forest floor habitats of western redcedar forests, Vancouver Island, Canada

Litter decomposition and changes in oribatid mite community composition were studied for 2 years in litterbags collected from arboreal organic matter accumulations (canopy suspended soils) and forest floors associated with western redcedar trees on Vancouver Island, British Columbia. We tested the hypotheses that lower rates of mass loss, higher nutrient levels, and different patterns of oribatid mite richness and abundance in decomposing western redcedar litter would be observed in litterbags associated with canopy suspended soils compared to forest floors. Decomposition, measured by mass loss of cedar litter in litterbags, was not significantly different in canopy and forest floor habitats, although reduced in the canopy. Abundance and richness of oribatid mites inhabiting litterbags were significantly greater on the forest floor compared to the canopy suspended soils. Canopy suspended soils had higher levels of total nitrogen, available phosphorus and potassium than the forest floor, but moisture content was significantly lower in the suspended soils. Higher nutrient levels in the canopy system are attributed to differences in coarse woody debris input (but not foliar litter), combined with reduced nutrient uptake by roots and lower mobilisation rates of nutrients by detritivorous and fungivorous microarthropods. Moisture limitation in the canopy system possibly contributed to lower mass loss in litterbags, and lower abundance and richness of oribatid mites in litterbags placed on canopy suspended soils. Patterns of oribatid mite community composition were related to mite communities associated with the underlying substrate (forest floor or canopy suspended soil) which act as source pools for individuals colonising litterbags. Successional and seasonal trends in oribatid mite communities were confounded by moisture limitation at 24 months, particularly within the canopy habitat.

Resident corticolous oribatid mites (Acari: Oribatida): Decay in community similarity with vertical distance from the ground

The decrease in community similarity was examined in corticolous oribatid mites (Acari: Oribatida) sampled along a 36-m vertical profile of 5 western redcedar trees in a temperate rainforest on Vancouver Island, Canada. Samples were collected every 2 m, and all adult oribatid mites were identified to species. When compared to species recorded from previous ground/canopy sampling efforts in the same trees, the 62 corticolous species unequivocally support the separation of these 2 communities at 4 m. All sampling heights contained canopy oribatid species, but only 0–4 m communities contained ground-dwelling oribatids. There was significant overall spatial autocorrelation and decay in community similarity with distance originating from species turnover at 4 m, suggesting limited range expansion of ground species into corticolous habitats. Community similarity, richness, and abundance of corticolous oribatid mite assemblages were not autocorrelated after 4 m above ground. Observed patterns at 4 m likely represent an environmental transition zone for ground-dwelling species, such as changes in moisture availability, rather than a physical dispersal barrier for individuals. We conclude that the trunk is not a dispersal corridor for ground species to colonize tree crowns and suggest that low similarity between nearest neighbouring sampling points, combined with the presence of immature and gravid oribatids, supports the assumption that corticolous oribatid mite assemblages are likely dispersal-limited residents.

Local–regional boundary shifts in oribatid mite (Acari: Oribatida) communities: species–area relationships in arboreal habitat islands of a coastal temperate rain forest, Vancouver Island, Canada

AbstractAim This study investigates the species–area relationship (SAR) for oribatid mite communities of isolated suspended soil habitats, and compares the shape and slope of the SAR with a nested data set collected over three spatial scales (core, patch and tree level). We investigate whether scale dependence is exhibited in the nested sampling design, use multivariate regression models to elucidate factors affecting richness and abundance patterns, and ask whether the community composition of oribatid mites changes in suspended soil patches of different sizes.Location Walbran Valley, Vancouver Island, Canada.Methods A total of 216 core samples were collected from 72 small, medium and large isolated suspended soil habitats in six western redcedar trees in June 2005. The relationship between oribatid species richness and habitat volume was modelled for suspended soil habitat isolates (type 3) and a nested sampling design (type 1) over multiple spatial scales. Nonlinear estimation parameterized linear, power and Weibull function regression models for both SAR designs, and these were assessed for best fit using R2 and Akaike's information criteria (ΔAIC) values. Factors affecting oribatid mite species richness and standardized abundance (number per g dry weight) were analysed by anova and linear regression models.Results Sixty‐seven species of oribatid mites were identified from 9064 adult specimens. Surface area and moisture content of suspended soils contributed to the variation in species richness, while overall oribatid mite abundance was explained by moisture and depth. A power‐law function best described the isolate SAR (S = 3.97 × A0.12, R2 = 0.247, F1,70 = 22.450, P &lt; 0.001), although linear and Weibull functions were also valid models. Oribatid mite species richness in nested samples closely fitted a power‐law model (S = 1.96 × A0.39, R2 = 0.854, F1,18 = 2693.6, P &lt; 0.001). The nested SAR constructed over spatial scales of core, patch and tree levels proved to be scale‐independent.Main conclusions Unique microhabitats provided by well developed suspended soil accumulations are a habitat template responsible for the diversity of canopy oribatid mites. Species–area relationships of isolate vs. nested species richness data differed in the rate of accumulation of species with increased area. We suggest that colonization history, stability of suspended soil environments, and structural habitat complexity at local and regional scales are major determinants of arboreal oribatid mite species richness.

A comparison of microarthropod assemblages with emphasis on oribatid mites in canopy suspended soils and forest floors associated with ancient western redcedar trees

Microarthropod abundance, oribatid mite species richness and community composition were assessed in the high canopy (ca. 35 m) of an ancient temperate rainforest and compared with microarthropod communities of the forest floor. Microarthropods were extracted from 72 core samples of suspended soils and 72 core samples from forest floors associated with six western redcedar trees in the Walbran Valley on the southwest coast of Vancouver Island, Canada. Total microarthropod abundances, mesostigmatid and astigmatid mites, Collembola and other microarthropod abundances were significantly greater in forest floors compared to canopy habitats. Oribatid and prostigmatid mite abundance were not significantly different between habitats. The relative abundances of all microarthropod groups considered in this study differed significantly between habitats. Eighty-eight species of oribatid mites were identified from the study area. Eighteen of the 53 species observed in suspended soils were unique to the canopy. Cluster analysis indicates that the arboreal oribatid mite community is distinct and not a taxonomic subset of the forest floor assemblage, however, canopy oribatid mite communities are more heterogeneous in species composition than in the forest floor.

Thujone in soil under Thuja plicata

Thujone is a toxic monoterpene produced in needles of western red cedar (Thuja plicata Donn) and transferred to the soil with defoliation. Thujone is toxic at relatively low levels to a wide range of organisms. This study was conducted to determine whether thujone could be detected in the soil in a western red cedar stand in Denmark. Western red cedar needles and soil samples from the organic and mineral soil underneath were collected in Lille Bøgeskov forest near Sorø in Denmark. Thujone was extracted from the samples by steam distillation, followed by liquid–liquid extraction into hexane, and determined by gas chromatography. Needles sampled from a western red cedar tree at four heights between 1.9 and 17.8 m had concentrations of thujone in the range 2220–6550 mg kg−1 dry weight. The thujone content in the organic soil layer was in the range 170–1200 mg kg−1 dry weight, whereas only 1.2–3.0 μg kg−1 was found in the upper 2 cm of the mineral soil. The high amounts of thujone present in the forest floor may therefore have a significant effect on organisms in soils and fresh water streams in a western red cedar forest.

Ionic balance and organic acids in western redcedar, western hemlock, and Douglas-fir seedlings grown in low- and high-N soils

Seedlings of western redcedar (Thuja plicata Donn ex. D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were transplanted into soils with low and high levels of available NO3-(and total N). Current-year foliage was sampled after 10 weeks to determine the effect of N availability on foliar cation-anion balance (C-A) and the concentrations of low molecular weight organic acids of the three species. Carboxylate concentrations were estimated by using the difference between sums of cations and anions (C-A): 750 mequiv.·kg-1for western redcedar, 351 mequiv.·kg-1for western hemlock, and 266 mequiv.·kg-1for Douglas-fir. Quinic acid was a primary constituent, accounting for 40% of the total for western redcedar and 75% for western hemlock and Douglas-fir. Oxalic acid was present in greatest concentration in the foliage of western redcedar (65 mequiv.·kg-1) but was a minor constituent in western hemlock and Douglas-fir. The quantified acids accounted for only 15% of the C-A of western redcedar but &gt;80% of the C-A of western hemlock and Douglas-fir. A considerable portion of the C-A balance not accounted for in redcedar may be associated with the accumulation of CaCO3. Litterfall deposition of CaCO3may lead to the consumption of H+ions and enrichment of exchangeable soil Ca in the rooting zone of long-lived western redcedar trees. No statistically significant differences among the soils were detected with regard to C-A or the concentration of organic acids.