Western Red Cedar Seedlings 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.

Histological, chemical and gene expression differences between western redcedar seedlings resistant and susceptible to cedar leaf blight.

Western redcedar (Thuja plicata) is an important species in the Cupressaceae both at economic and cultural levels in the Pacific Northwest of North America. In adult trees, the species produces one of the most weathering-resistant heartwoods among conifers, making it one of the preferred species for outdoor applications. However, young T. plicata plants are susceptible to infection with cedar leaf blight (Didymascella thujina), an important foliar pathogen that can be devastating in nurseries and small-spaced plantations. Despite that, variability in the resistance against D. thujina in T. plicata has been documented, and such variability can be used to breed T. plicata for resistance against the pathogen. This investigation aimed to discern the phenotypic and gene expression differences between resistant and susceptible T. plicata seedlings to shed light on the potential constitutive resistance mechanisms against cedar leaf blight in western redcedar. The study consisted of two parts. First, the histological differences between four resistant and four susceptible families that were never infected with the pathogen were investigated. And second, the differences between one resistant and one susceptible family that were infected and not infected with the pathogen were analyzed at the chemical (C, N, mineral nutrients, lignin, fiber, starch, and terpenes) and gene expression (RNA-Seq) levels. The histological part showed that T. plicata seedlings resistant to D. thujina had constitutively thicker cuticles and lower stomatal densities than susceptible plants. The chemical analyses revealed that, regardless of their infection status, resistant plants had higher foliar concentrations of sabinene and α-thujene, and higher levels of expression of transcripts that code for leucine-rich repeat receptor-like protein kinases and for bark storage proteins. The data collected in this study shows that constitutive differences at the phenotypic (histological and chemical) and gene expression level exist between T. plicata seedlings susceptible and resistant to D. thujina. Such differences have potential use for marker-assisted selection and breeding for resistance against cedar leaf blight in western redcedar in the future.

Isolation and identification of diazotrophic bacteria from internal tissues ofPinus contortaandThuja plicata

Lodgepole pine ( Pinus contorta var. latifolia Engelm. ex S. Watson) and western red cedar ( Thuja plicata Donn ex D. Don) are capable of growing in soils that are severely nitrogen-limited. A rarely evaluated but possible nitrogen source for gymnosperms growing at nutrient poor sites is nitrogen fixation by endophytic bacteria. To investigate this possibility, we looked for nitrogen-fixing bacteria in surface-sterilized needle, stem, and root tissues of naturally regenerating lodgepole pine and western red cedar seedlings (2–4 years old) and trees (>20 years old) growing near Williams Lake, Chilliwack Lake, and Boston Bar, British Columbia, Canada. Ninety-nine bacterial isolates were obtained by plating surface-sterilized plant tissue extracts on tryptic soy agar (TSA) and combined carbon medium agar (CCMA), a nitrogen-free medium. Bacterial isolates were identified using gas chromatographic fatty acid methyl ester (GC-FAME) and 16S rRNA gene analyses and were evaluated for nitrogenase activity using an acetylene reduction assay. Representatives of the genera Bacillus and Paenibacillus dominated the culturable endophytic bacterial community in tissues of both tree species, with three Paenibacillus isolates and one Dyadobacter fermentans strain demonstrating consistently high acetylene-reduction activities. Our results raise the possibility that endophytic nitrogen fixation provides a supplementary nitrogen source for naturally regenerated lodgepole pine and western red cedar.

Terpene production and growth of three Pacific Northwest conifers in response to simulated browse and nutrient availability

Natural variation in ungulate browsing behavior interferes with the understanding of plant morphological and biochemical responses to herbivory. To investigate mechanisms for recovery from herbivory, we examined growth patterns and biosynthesis of terpenoids under simulated browse (three clipping intensities) and supplemental mineral nutrition (four levels of controlled-release fertilization) for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock (Tsuga heterophylla Raf. Sarg.), and western red-cedar (Thuja plicata Donn ex D. Don) seedlings on a reforestation site in Northwestern Oregon, USA, that was fenced to exclude ungulates. Higher clipping intensities increased relative height growth (at cost of diameter growth) for all the species. Only western red-cedar showed a decline in monoterpene concentrations with increasing clipping severity, suggesting prioritization in biosynthesis of terpenoids for this species. Douglas-fir and western hemlock responded to fertilization mostly through increased growth. Western red-cedar growth responses to fertilization were less pronounced, but monoterpene concentrations were 2–3 times higher compared to non-fertilized trees. Douglas-fir and western hemlock browse recovery and responses to fertilization consisted primarily of increased growth, while western red-cedar balanced growth promotion with production of chemical defense compounds. Our data suggests the evolution of species-dependent resource allocation strategies in response to both browse and soil nutrient availability.

Ungulate herbivory of regenerating conifers in relation to foliar nutrition and terpenoid production

Ungulate browsing greatly influences regeneration dynamics of some forest ecosystems, yet the relationship between browse susceptibility and foliar chemistry of forest tree seedlings is not well understood. We applied field fertilization (15N-9P-10K controlled-release fertilizer at 0, 20, 40, and 60 g per seedling) and investigated how subsequent changes in terpenoid production and foliar nutrition influence ungulate browse preference for Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), western hemlock ( Tsuga heterophylla Raf. Sarg.), and western redcedar ( Thuja plicata Donn ex D. Don) seedlings across four sites in northwestern Oregon, USA. Fertilization increased foliar N concentration of all three species, but above-ground growth of only Douglas-fir and western hemlock. Foliar monoterpene concentrations for western hemlock and western redcedar also increased at higher fertilization rates, while Douglas-fir monoterpene production was not affected by fertilization. Regardless of monoterpene levels, ungulate browse preference was greater for fertilized western hemlock seedlings. The opposite response, however, was observed for western redcedar at two of the four study sites where the likelihood of browse was greater for non-fertilized than fertilized seedlings. Differences in browse preference among species may depend on the type and amount of individual monoterpenes manufactured in response to fertilization. Western redcedar produce α- and β-thujone, oxygenated monoterpenes known to promote gastroenteritis and possibly inhibit microbial rumen activity, which were absent from Douglas-fir or western hemlock. Higher concentrations of α- and β-thujone associated with increasing fertilizer rate provide a plausible explanation as to why ungulates preferred non-fertilized western redcedar. Our results illustrate species-specific adaptation in browse avoidance and selective ungulate browsing behavior of individual trees as linked to foliar chemistry.

Evaluating new protein sources for development of a deer repellent product

Several protein sources were tested as deer repellents with captive deer. Black-tailed deer were offered Western redcedar seedlings treated with corn gluten meal, feather meal, poultry blood, hydrolyzed casein, or a control (latex sticker used for treatment proteins). After 37 days, feather meal and hydrolyzed casein provided equivalent protection against browse damage (only 23% of seedlings significantly browsed). Poultry blood provided less browse protection (44% browsed), while browse damage to seedlings treated with corn gluten meal (73% browsed) was not statistically different than the control (100% browsed). Based on the efficacy of feather meal and its low material cost, this protein hydrolysate should be investigated for use in commercial deer repellent formulations.

Influence of sulfometuron methyl on conifer seedling root development

On three sites in coastal northwestern Oregon, USA, seedling root and shoot development were assessed for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western red-cedar (Thuja plicata Donn ex D. Don) container seedlings under varying sulfometuron methyl (Oust XP®) herbicide application treatments. Treatments consisted of application of 0.16 kg active ingredient (ai) ha−1 as a site preparation in fall 2003, a release application in fall 2004, or a control treatment with no application. Seedlings were planted in winter 2004 and measurements recorded in summer 2004, winter 2005, and summer 2005. During first season growth, western red-cedar seedlings showed the greatest negative impact to site preparation compared to the control with overall average new root length outside the root plug reduced by 67%. Significant reductions in root length also occurred for western hemlock (47%) and Douglas-fir (40%) seedlings. About 9 months after the release treatment, and 21 months after the site preparation application, there were no significant differences between treatments for any measured parameter. These findings suggest that seedlings under the site preparation treatment recovered from initial damage incurred to the root system. Lack of seedling response under the release treatment may be the result of opposing influences from the herbicide application associated with seedling phytotoxicity and enhanced seedling development resulting from effective vegetation control. Although our study was limited to 21 months following planting, reduced vegetation cover in the site preparation and release treatments suggests that these treatments may benefit future seedling growth.

Screening Hydrolyzed Casein as a Deer Repellent for Reforestation Applications

Abstract Three independent experiments were conducted to evaluate hydrolyzed casein deer repellent to minimize browse damage in reforestation efforts. In the first experiment, western redcedar seedlings were treated with 12% hydrolyzed casein and a latex sticker or one of two commercial deer repellents in the nursery prior to a 45-day cold storage period. Treated and control (sticker only) seedlings were then offered to captive deer, and browse activity was monitored for 20 days. Whereas all control trees were severely browsed by day 4, the three repellents offered browse protection (17 to 33% survivability at day 20). The second experiment was a field evaluation of 12% hydrolyzed casein, a commercial repellent, and a control. Western redcedar seedlings in nine reforested units were treated and monitored periodically for browse damage by free-ranging deer. After 17 weeks, browse damage to the repellent-treated seedlings (93 and 89% survivability) was significantly lower than the control trees (85%). In the final experiment, three different products were used to affix hydrolyzed casein powder to western redcedar seedlings prior to a 45-day cold storage period. Treated seedlings were offered to captive deer, and browse activity was monitored for 28 days. Hydrolyzed casein–treated seedlings sustained significantly less browse damage (more than 70% survivability at 28 days) versus the controls (all trees browsed by day 28). Nursery treatment with hydrolyzed casein may provide significant protection for conifer seedlings in reforestation operations.

Variation in cedar leaf blight (Didymascella thujina) resistance of western redcedar (Thuja plicata)

Western redcedar ( Thuja plicata Donn ex D. Don) seedlings from a population study with family structure were planted at four sites across coastal British Columbia. All seedlings at the time of planting were infected with cedar leaf blight (CLB) ( Didymascella thujina (E.J. Durand) Maire). CLB severity and tree heights were measured at various ages from 2 to 12 years. There were significant site differences in CLB severity with the coastal hypermaritime site showing the most and with the submaritime site showing the least. Population differences in disease severity were evident with British Columbia coastal, low-elevation populations exhibiting the most resistance and with British Columbia high-elevation and California sources showing the least. Population resistance was consistent across all four sites (all r > 0.90, p < 0.001). Coefficients of additive genetic variation in CLB severity at all four sites varied from 13.2% to 20.1% with narrow-sense heritabilities from 0.21 to 0.66. Type B genetic correlations in CLB severity across sites averaged 0.59. Type A genetic correlations between 6 year CLB severity and height at the Jordan River site on western Vanvouver Island and at the site on the Queen Charlotte Islands were –0.96 and –0.86 (p < 0.001), respectively. Results are discussed with respect to climatic influences and prior exposure to CLB on among- and within-population variation in western redcedar natural populations and impact on gene resource management.

Five-year growth responses of Douglas-fir, western hemlock, and western redcedar seedlings to manipulated levels of overstory and understory competition

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn ex D. Don) seedlings were planted in March 2001 within three clearcut-harvested, shelterwood, or thinned stands of mature Douglas-fir near Olympia, Washington. From 2002 to 2005, areas of vegetation control of 0, 4.5, or 9 m2were maintained with herbicides around a total 162 seedlings per species. Photosynthetically active radiation (PAR) was 34%, 62%, and 100% of full sunlight in thinned stands, shelterwoods, and clearcuts, respectively. Effects of overstory level and vegetation control on seedling growth and resource availability generally were additive. Seedling stem volume index in clearcuts averaged four to eight times that observed in thinned stands, and with vegetation control, it averaged two to four times that observed without it. In thinned stands, relative growth rate of seedling stem volume index had a positive linear relationship with PAR (R2 = 0.38). Foliar nitrogen content of Douglas-fir explained 71% of the variation in relative growth rate. Factors explaining the most variation in foliar nitrogen content differed between thinned stands (PAR, R2 = 0.34) and clearcuts or shelterwoods (midday water potential, R2 = 0.63), suggesting that light and root competition, respectively, were the primary growth-limiting factors for these overstory levels.

Boomer or Bust: Managing a Pacific Northwest Pest Species

Mountain beaver are a primitive rodent species endemic to the Pacific Northwest and California. In Oregon and Washington, mountain beaver are managed as a pest species due to the damage they inflict to Douglas-fir seedlings as well as 10- to 15-year-old trees. Available biological information on the mountain beaver is limited, thus hampering the ability of managers to develop new tools and techniques to reduce damage. We conducted a series of studies to increase our knowledge of mountain beaver biology and the influence of environmental attributes and stand management practices on demographics. Although mountain beaver damage Douglas-fir and western red cedar seedlings, observations suggest that these tree species are not preferred forage. In one pen study, pens void of preferred vegetation (i.e., salal and sword fern) had significantly more damage than pens with additional forage. Damage did not occur when animals were allowed access to pens with preferred forage, even with increased population pressure. In addition to pen trials, we radio-collared 62 mountain beaver in 3 different harvest units, which varied in vegetation management and stand age, to assess movements and seedling damage. Home ranges were larger on the chemically prepared site with reduced forage than on the non-treated site. Although mountain beaver can inhabit older timber stands, home ranges were relatively large in such stands because of the reduced preferred forage in closed-canopy habitats (3.66 ± 1.49 ha). Once units were harvested, population size increased and home range size decreased (0.88 ± 0.27 ha). Seedling damage and reproductive success were only slightly related to available forage, which was in turn affected by site preparation. Information on home range use, habitat requirements, and the difference in carrying capacity for mountain beaver under varying site preparations, can assist managers in manipulating habitats in order to minimize colonization and reduce seedling damage. We suggest several integrated pest management strategies to minimize seedling damage by mountain beaver.

Responses of gas exchange to reversible changes in whole-plant transpiration rate in two conifer species.

This study examined the autonomy of branches with respect to the control of transpiration (E) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn) seedlings. Experiments were conducted on whole seedlings in a gas exchange system with a dual-cuvette that permitted independent manipulation and measurement of E in the upper and lower cuvettes. The value of E in one cuvette was manipulated by varying vapor pressure deficit (D) between 2.2 and 0.2 kPa, whereas D in the other cuvette was held at 2.2 kPa. Reducing D, while increasing stomatal conductance (gs), resulted in an overall decrease in E. In western red cedar, this decrease was almost threefold, and in Douglas-fir, approximately fourfold. In well-watered western red cedar, a reduction of whole-plant E by 46% (brought about by reducing D in the upper cuvette) resulted in a 12% increase in gs, a 12% increase in E and a 7% increase in net assimilation (A) of untreated foliage in the lower cuvette. Responses of gs, E and A of untreated foliage were similar irrespective of whether foliage was at the top or bottom of the seedling. When D in the treatment cuvette was restored to 2.2 kPa, gs, E and A of foliage in the untreated cuvette returned to pretreatment values. In contrast, in well-watered Douglas-fir, there was almost no change in gs, E or A of untreated foliage in one cuvette when D in the other cuvette was reduced, causing a 52% reduction in whole-plant E. However, similar manipulations on drought-stressed Douglas-fir led to 7-19% increases in gs, E and A of untreated foliage. In well-watered western red cedar, daytime leaf water potential (Psil) was maintained near -0.9 MPa over a wide range of D, whereas Psil of Douglas-fir decreased from -1.2 to -1.5 MPa as D increased. The tighter (isohydric) regulation of Psil in western red cedar may partly explain its greater stomatal response to D and variation in whole-plant E compared with Douglas-fir. In response to a reduction in E, measured increases in Psil and gs of unmanipulated foliage were less than predicted by a model assuming complete hydraulic connectivity of foliage. Our results suggest the foliage of both species is partially autonomous with respect to water.

Responses of transpiration and photosynthesis to reversible changes in photosynthetic foliage area in western red cedar (Thuja plicata) seedlings.

Experiments were conducted on 1-year-old western red cedar (Thuja plicata Donn.) seedlings to determine the response of illuminated foliage to reversible changes in total photosynthetic foliage area (L(A)). Reductions in L(A) were brought about by either shading the lower foliage or by reducing the ambient CO2 concentration (c(a)) of the air surrounding the lower part of the seedling. In the latter case, the vapor pressure was also changed so that transpiration rates (E) could be manipulated independently of photosynthetic rates (A). We hypothesized that following such treatments, short-term compensatory changes would occur in stomatal conductance (g(s)) and A of the remaining foliage. These changes would occur in response to hydraulic signals generated by changes in the water potential gradient rather than changes in the distribution of sources and sinks of carbon within the seedling. When a portion of the foliage was shaded, there was an immediate reduction in whole-seedling E and a concomitant increase in g(s), A and E in the remaining illuminated foliage. However, the intercellular CO2 concentration did not change. These compensatory effects were fully reversed after the shade was removed. When the lower foliage A was reduced to < 0 micromol m-2 s-1, by shading or lowering c(a), and E was either unchanged or increased (by adjusting the vapor pressure deficit), there was no significant increase in g(s) and A in the remaining foliage. We conclude that compensatory responses in illuminated foliage occur only when reductions in L(A) are accompanied by a reduction in whole-plant E. The relationship between the reduction in whole-seedling E and the increase in A is highly linear (r2 = 0.68) and confirms our hypothesis of the strong regulation of g(s) by hydraulic signals generated within the seedling. We suggest that the mechanism of the compensatory effects is a combination of both increased CO2 supply, resulting from increased g(s), and a response of the rate of carboxylation, possibly related to the activity of Rubisco.

Biotic injuries on conifer seedlings planted in forest understory environments

We investigated how partial overstory retention, understory vegetationmanagement, and protective Vexar® tubing affected the frequency andseverityof biotic injuries in a two-storied stand underplanted with western redcedar(Thuja plicata Donn ex D. Don), Douglas-fir(Pseudotsuga menziesii (Mirb.) Franco, grand fir(Abies grandis (Dougl.) Lindl), and western hemlock(Tsuga heterophylla (Raf.) Sarg.). The most prevalentsource of damage was browsing by black-tailed deer (Odocoileushemionis columbiana); deer browsed over 74% of Douglas-fir and over36% of western redcedar seedlings one or more times over the four years of thisstudy. Neither the spatial pattern of thinning (even or uneven) nor the densityof residual overstory affected browsing frequency. Spraying subplots may haveslightly increased browsing frequency, but the resulting reduction of theadjacent understory vegetation increased the volume of all seedlings by 13%,whether or not they were browsed. Vexar® tubing did not substantiallyaffectseedling survival, browsing damage frequency, or fourth-year volume. Greaterlevels of overstory retention reduced frequency of second flushing. Chafing bydeer and girdling by rodents and other small mammals began once seedlingssurpassed 1 m in height. Essentially all grand fir seedlingsexhibited a foliar fungus infection.

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.

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

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

Efficacy of selected repellents to deter deer browsing on conifer seedlings

Foraging deer can negatively impact agricultural resources. Repellents offer a plausible approach to inhibit browsing. The efficacy of Big Game Repellent-Powder (BGR), Deer Stopper (DST), Plantskydd (PLA) and ECX95BY (ECX) to deter black-tailed deer ( Odocoileus hemionus columbianus) browsing of ponderosa pine ( Pinus ponderosa), Douglas-fir ( Pseudotsugamenziesii) and western red cedar ( Thuja plicata) seedlings was assessed during the winter. Extent of damage was expressed as number of seedlings damaged, number of terminal buds damaged, number of lateral bites taken and the number of seedlings with severe damage. BGR, DST and PLA significantly reduced deer damage relative to controls for at least 14 weeks. After 1 week, damage to seedlings treated with ECX was similar to that inflicted on control seedlings. Aversive agents contained in BGR, DST and PLA probably produce sulfurous odors, while ECX contained denatonium benzoate, a bittering agent.

Rates of stomatal opening in conifer seedlings in relation to air temperature and daily carbon gain

ABSTRACTExperiments were conducted on well watered 1‐year‐old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western redcedar (Thuja plicata Donn) seedlings to determine the effects of temperature on whole‐plant photosynthetic and stomatal responses to short‐term fluctuations in irradiance (Q). Following a step change in Q, time constants (τ, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar τA decreased from 30 ± 4 min at 5 °C to 10 ± 1 min at 25 °C. In all cases, τA was within 10–15% of τgs. There was considerable variation in τ among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for τ accounted for 99% of the diurnal variability in A and gs for seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of daily A were within 2% of those measured. Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3–4 episodes (≥1 h) of shade (200 or 500 μmol m−2 s−1) or complete darkness during the day. In such cases, daily A was overestimated by up to 4 and 21%, respectively, if a function for τ was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in τ could lead to increases in daily carbon gains of almost 5% depending on the frequency and degree of shading. If these daily gains were translated into increased dry matter production and compounded, seasonal gains would be even larger.

Frost hardiness of Thujaplicata and Pseudotsugamenziesii seedlings when nutrient supply varies with season

Seedlings of coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and western redcedar (Thujaplicata Donn ex D. Don) were subject to three nutrient treatments varying the rate of application of nitrogen (N) and phosphorus (P) over the growing season. A control treatment provided seedlings with a constant supply of N and P. A high–low treatment reduced the rate of N and P supply after mid-July. A low–high treatment initially supplied seedlings with low amounts of N and P, and then increased the rate of supply after mid-July. Foliar nutrient concentration of seedlings of each species from each nutrient treatment was measured in September and the following April. Cold tolerance of seedlings was assessed five times over the winter season by freeze-induced electrolyte leakage and twice by differential scanning calorimetry (DSC). Nutrient treatment did not significantly affect foliar nutrient concentration in either species. Height of Douglas-fir seedlings was also unaffected by nutrient treatment, but western redcedar seedlings in the control treatment were 6.3 cm taller than those in the high–low treatment. Interpolated damage at −13 °C from freeze-induced electrolyte leakage indicated that Douglas-fir seedlings from the control treatment had 19.8% less damage than high–low seedlings in October, 18% less damage in November, and 1.6% less damage in December. The same trend was evident, although not always significant, in western redcedar. Differential scanning calorimetry analyses of Douglas-fir in October and November showed freezing and melting curve onset and peak temperatures to be, on average, 2.3 °C and 0.4 °C warmer, respectively, in control seedlings than in high–low plants.

Influence of cavity size, seedling growing density and fungicide applications on Keithia blight of western redcedar seedling growth and field performance

To determine the influence of cavity size, seedling density and fungicide application on severity of Keithia blight caused by the fungus Didymascella thujina (Durand) Maire, western redcedar (Thuja plicata Donn) seedlings were grown in styroblocks of 3 cavity sizes, thinned to 3 growing densities and sprayed several times monthly with mancozeb fungicide. After two growing seasons cavity size, seedling growing density and number of fungicide applications all significantly (p≤0.05) affected blight severity. Blight severity was inversely related to the number of mancozeb fungicide applications. The only significant two-way interaction was for cavity size and seedling growing density.