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Climate change is leading to increased drought intensity and fire frequency, creating early-successional landscapes with novel disturbance–recovery dynamics. In the Klamath Mountains of northwestern California and southwestern Oregon, early-successional interactions between nitrogen (N)-fixing shrubs (Ceanothus spp.) and long-lived conifers (Douglas-fir) are especially important determinants of forest development. We sampled post-fire vegetation and soil biogeochemistry in 57 plots along gradients of time since fire (7–28 years) and climatic water deficit (aridity). We found that Ceanothus biomass increased, and Douglas-fir biomass decreased with increasing aridity. High aridity and Ceanothus biomass interacted with lower soil C:N more than either factor alone. Ceanothus biomass was initially high after fire and declined with time, suggesting a large initial pulse of N-fixation that could enhance N availability for establishing Douglas-fir. We conclude that future increases in aridity and wildfire frequency will likely limit post-fire Douglas-fir establishment, though Ceanothus may ameliorate some of these impacts through benefits to microclimate and soils. Results from this study contribute to our understanding of the effects of climate change and wildfires on interspecific interactions and forest dynamics. Management seeking to accelerate forest recovery after high-severity fire should emphasize early-successional conifer establishment while maintaining N-fixing shrubs to enhance soil fertility.

Fire exclusion and a lengthening fire season has resulted in an era of megafires. Fuel reduction treatments in forested ecosystems are designed to guard against future extreme wildfire behavior. Treatments create a heterogenous landscape and facilitate ecosystem function and resilience in fire-adapted forests of the western United States. Despite widespread recognition that repeated fuel treatments are needed to maintain desired stand characteristics over time, few field studies have evaluated treatment longevity. The Blue Mountains Fire and Fire Surrogate site in northeastern Oregon presented an opportunity to investigate woody fuel loading 15–17 years after four treatments: mechanical thin, prescribed burn, both thin and burn, and no treatment control. The principal findings were: (1) fine fuel load 15 years post-burn remained slightly below pre-treatment values, (2) rotten coarse fuel load was reduced post-burn, but sound coarse fuel was not altered by any active treatment, and (3) total woody fuel load 15–17 years post-treatment was similar to pre-treatment values. Understanding surface fuel loading is essential for predicting fire behavior. Overall, the effects of fuel reduction treatments on woody surface fuels were transitory in dry mixed conifer forests. Frequent maintenance treatments are recommended to protect values at risk in areas with high fire hazards. Quantifying the persistence of changes in forest conditions aids in the planning and analysis of future fuel treatments, along with scheduling maintenance of existing treated areas.

The grading of wood veneers according to their true mechanical potential is an important issue in the peeling industry. Unlike in the sawmilling industry, this activity does not currently estimate the local properties of production. The potential of the tracheid effect, which enables local fiber orientation measurement, has been widely documented for sawn products. A measuring instrument exploiting this technology and implemented on a peeling line was developed, enabling us to obtain the fiber orientation locally which, together with global density, allowed us to model the local elastic properties of each veneer. A sorting method using this data was developed and is presented here. It was applied to 286 veneers from several logs of French Douglas fir, and was compared to a widely used sorting method based on veneer appearance defects. The effectiveness of both grading approaches was quantified according to mechanical criteria. This study shows that the sorting method used (based on local fiber orientation and average density) allows for better theorical quality discrimination according to the mechanical potential. This article is the first in a series, with the overall aim of enhancing the use of heterogeneous wood veneers in the manufacturing of maximized-performance LVL by veneer grading and optimized positioning as well as material mechanical property modelization.

This paper presents a new strategy in the use of wood of heterogeneous quality for composing LVL products. The idea is to consider veneers representative of the resource variability and retain local stiffness information to control panel manufacturing fully. The placement of veneers is also no longer random as in the first part of this group of papers but optimized for the quality of veneers according to the requirement of bending stresses along the beam. In a four-point bending test arrangement, this means the high-quality veneer is concentrated in the center of the beam in the area between the loading points where the bending moments are the most important, and the low quality is located at the extremities. This initiates the creation of variable stiffness beams. This is driven by an algorithm developed and tested on representative veneer samples from the resource. Four LVL panels were manufactured by positioning the veneers in the same positions as in an analytical calculation model, which allowed the calculation of beam mechanical properties in four-point bending. The proposed optimization of LVL manufacturing from variable quality veneers should help for more efficient usage of forest resources. This optimization strategy showed notable gains for modeled and experimental mechanical properties, whether in terms of stiffness or strength. The analytical calculation of the local modulus of elasticity from modelized beams was satisfactory compared to the tests of the manufactured beams test results, allowing the reliability of the model for this property to be confirmed.

In view of the increasing demand for forest resources in Europe, it is an option to foster the use of non-native tree species that can keep pace with the rapidly changing environmental conditions, such as Douglas-fir (Pseudotsuga menziesii). Thus, sufficient knowledge of how to manage such introduced species is highly required. In this study, we investigate theoretical silvicultural management options of Douglas-fir for forests in central Europe. We follow a three-step approach: (i) we collect the current central European management practices based on 434 Douglas-fir stands managed by 19 forest companies in Eastern Austria and Southern Germany using a survey. (ii) We calibrate and validate a Douglas-fir parameter set for the tree growth simulator MOSES so that we are able to (iii) simulate the silvicultural management options of Douglas-fir management. Our simulation results suggest: in mixed stands, Douglas-fir should be planted in mono-species patches. This leads to about six times higher productivity compared to a random arrangement. Natural regeneration is possible but requires active management at further development since the productivity might decrease up to 86% when growing in association with the highly competitive native tree species, Common beech (Fagus sylvatica). Intensive tending, as well as thinning, yields a surplus stem volume production of more than 30% in comparison with a moderate intervention. Even if our simulation results were not validated in the field, this analysis suggests that modeling as a heuristic tool is a useful instrument for forest managers in the decision-making process.

Patterns in foliar nitrogen (N) stable isotope ratios (δ15N) have been shown to reveal trends in terrestrial N cycles, including the identification of ecosystems where N deficiencies limit forest ecosystem productivity. However, there is a gap in our understanding of within-species variation and species-level response to environmental gradients or forest management. Our objective is to examine the relationship between site index, foliar %N, foliar δ15N and spectral reflectance for managed Douglas-fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) plantations across their geographic ranges in the Pacific Northwest and the southeastern United States, respectively. Foliage was measured at 28 sites for reflectance using a handheld spectroradiometer, and further analyzed for δ15N and N concentration. Unlike the prior work for grasslands and shrubland species, our results show that foliar δ15N and foliar %N are not well correlated for these tree species. However, multiple linear regression models suggest a strong predictive ability of spectroscopy data to quantify foliar δ15N, with some models explaining more than 65% of the variance in the δ15N. Additionally, moderate to strong explanations of variance were found between site index and foliar δ15N (R2 = 0.49) and reflectance and site index (R2 = 0.84) in the Douglas-fir data set. The development of relationships between foliar spectral reflectance, δ15N and measures of site productivity provides the first step toward mapping canopy δ15N for these managed forests with remote sensing. Published version

Two comparable sites with uneven-aged mixed forest stands with more than 20% Douglas-fir in the growing stock at an altitude of 650 m a.s.l. were selected. The physiological response of young trees to different light intensities was measured during the main growing season in three consecutive years, and four different light categories, which were determined from hemispherical photographs. The four light intensity categories were defined according to Indirect Site Factor (ISF%): in the open (A-ISF &gt, 35%), at the outer forest edge (B-25% &lt, ISF &lt, 35%), at the inner forest edge (C-15% &lt, 25%), and under complete canopy under mature forest stand (D-ISF &lt, 15%). Climate data were obtained from the Royal Netherlands Meteorological Institute ‘Climate Explorer’ website. For the intensive micrometeorological observations, four monitoring sites were established along the elevation gradient at each site during summer and late fall to record relative humidity (RH%) and temperature (°C) with a 30 min recording interval sequence. Measured assimilation responses (A) and light use efficiency (Φ) at one site followed the expected pattern, while humidity combined with microsite conditions proved significant in explaining the specific response of young Douglas-fir to the different light intensity at the other site. For higher survival and optimal future development of Douglas-fir in the changing environment, microsites with higher capacity for storage moisture and favorable microclimate should generally be preferred to exposed and dry sites.

Research Highlights: (1) Optimizing mid-rotation thinning increased modeled land expectation values by as much as 5.1–10.1% over a representative reference prescription on plots planted at 2.7 and 3.7 m square spacings. (2) Eight heuristics, five of which were newly applied to selecting individual trees for thinning, produced thinning prescriptions of near identical quality. (3) Based on heuristic sampling properties, we introduced a variant of the hero heuristic with a 5.3–20% greater computational efficiency. Background and Objectives: Thinning, which is arguably the most subjective human intervention in the life of a stand, is commonly executed with limited decision support in tree selection. This study evaluated heuristics’ ability to support tree selection in a factorial experiment that considered the thinning method, tree density, thinning age, and rotation length. Materials and Methods: The Organon growth model was used for the financial optimization of even age Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) harvest rotations consisting of a single thinning followed by clearcutting on a high-productivity site. We evaluated two versions of the hero heuristic, four Monte Carlo heuristics (simulated annealing, record-to-record travel, threshold accepting, and great deluge), a genetic algorithm, and tabu search for their efficiency in maximizing land expectation value. Results: With 50–75 years rotations and a 4% discount rate, heuristic tree selection always increased land expectation values over other thinning methods. The two hero heuristics were the most computationally efficient methods. The four Monte Carlo heuristics required 2.8–3.4 times more computation than hero. The genetic algorithm and the tabu search required 4.2–8.4 and 21–52 times, respectively, more computation than hero. Conclusions: The accuracy of the resulting thinning prescriptions was limited by the quality of stand measurement, and the accuracy of the growth and yield models was linked to the heuristics rather than to the choice of heuristic. However, heuristic performance may be sensitive to the chosen models.

Douglas-fir (Pseudotsuga menziesiivar. menziesii (Mirbel) Franco) plantation forests of the coastal Pacific Northwest have been intensively managed to improve the yield of forest products. However, the long-term effects of these management techniques have received limited research attention in this region. Three affiliate Long-Term Soil Productivity study sites were installed in Douglas-fir forests to understand the impacts of organic matter removals and vegetation control on soil productivity over time. Matlock and Fall River are located in Washington, USA and Molalla is located in Oregon. Organic matter removal treatments included traditional bole-only harvest (BO), whole tree removals (WT), and a whole tree plus coarse woody debris removal (WT+) (Fall River only). Five years of annual vegetation control (AVC) was compared with a conventional initial vegetation control (IVC) treatment at all sites. Douglas-fir biomass allocation to foliage, branch, and stem components was modeled using 15- to 20-year-old trees from this study along with 5- to 47-year-old trees from previous studies on these sites. Across all sites, model predictions indicated that the WT treatment had 7.1 to 9.7 Mg ha&minus, 1 less Douglas-fir biomass than the BO treatment. There was 1.5 to 20.5 Mg ha&minus, 1 greater Douglas-fir biomass in the AVC treatment than in the IVC treatment at all sites. Douglas-fir carbon and nitrogen biomass were consistently lower in the WT treatment, but there were no significant changes in overall site nutrient pools. The AVC treatment resulted in greater Douglas-fir nutrient pools yet there was a net loss in site calcium, magnesium, and potassium due to lower forest floor and soil base cation pools. While WT removals did not significantly affect site nutrition, the decrease in Douglas-fir biomass at all sites and increase in invasive Scotch broom (Cytisus scoparius (L.) Link) biomass at Matlock suggests that the standard practice of retaining harvest residuals is beneficial. The use of intensive vegetation control to improve Douglas-fir biomass and nutrition must be balanced with retaining soil base cations.

The long-term effectiveness of dry-forest fuels treatments (restoration thinning and prescribed burning) depends, in part, on the pace at which trees regenerate and recruit into the overstory. Knowledge of the factors that shape post-treatment regeneration and growth is limited by the short timeframes and simple disturbance histories of past research. Here, we present results of a 15-year fuels-reduction experiment in central Washington, including responses to planned and unplanned disturbances. We explore the changing patterns of Douglas-fir regeneration in 72 permanent plots (0.1 ha) varying in overstory abundance (a function of density and basal area) and disturbance history&mdash, the latter including thinning, prescribed burning, and/or wildfire. Plots were measured before treatment (2000/2001), soon afterwards (2004/2005), and more than a decade later (2015). Thinning combined with burning enhanced sapling recruitment (ingrowth) into the overstory, although rates of ingrowth were consistently low and greatly exceeded by mortality. Relationships between seedling frequency (proportion of quadrats within a plot) and overstory abundance shifted from weakly negative before treatment to positive after thinning, to neutral in the longer term. However, these relationships were overshadowed by more recent, higher-severity prescribed fire and wildfire that stimulated seedling establishment while killing advanced regeneration and overstory trees. Our results highlight the dependence of regeneration responses on the history of, and time since, fuels treatment and subsequent disturbance. Managers must be aware of this spatial and temporal complexity and plan for future disturbances that are inevitable but unpredictable in timing and severity.

Nitrogen (N) fertilization is a commonly applied silvicultural treatment in intensively managed coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations. Field trials were established in a randomized complete block design by Stimson Lumber Company (Gaston, Oregon), to test the economic viability of N fertilization on their ownership and to better understand Douglas-fir growth responses. The 23 stands comprising the trials were Douglas-fir dominated, had a total age of 16&ndash, 24 years, had been precommercially thinned, and had a density of 386&ndash, 1021 trees ha&minus, 1. Fertilizer was applied aerially at a rate of 224 kg N ha&minus, 1 as urea during the 2009&ndash, 2010 dormant season. In the dormant season of 2016&ndash, 2017, seven growing seasons following application, 40 trees were felled and measured with the objective of assessing crown attributes and aboveground allometrics. Branch-level foliage mass equations were developed from 267 subsampled branches and were applied to the 40 felled sample trees on which the basal diameter and height of all live branches were measured, allowing estimation of both the total amount of foliage and its vertical distribution. A right-truncated Weibull distribution was fitted to data, with the truncation point specified as the base of live tree crown. The resulting tree-level parameter estimates were modeled as functions of tree-level variables. Stand-level factors not explicitly measured were captured through the use of linear and nonlinear mixed-effects models with random stand effects. Fertilization resulted in more total crown foliage mass in the middle crown-third and caused a downward shift in the vertical distribution of foliage, with implications for feedback responses in crown development and photosynthetic capacity. Defining the morphological responses of Douglas-fir crowns to nitrogen fertilization provides a framework for studying influences on stand dynamics and should ultimately facilitate improved site-specific predictions of stem-volume growth.

Western spruce budworm (WSBW) is a common defoliating insect that has caused extensive damage and mortality to a number of tree species across the western United States (US). Past studies have linked outbreaks of WSBW to increased moisture stress of host trees in the Northwest and decreased moisture stress in the Southwest. Our study analyzed seasonal drought stress metrics with WSBW outbreaks within Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in the western US during 1997&ndash, 2015. Superposed epoch analysis and defoliation area growth rates (representing insect population growth rates) were assessed to quantify the drought conditions associated with the initiation and continuation of outbreaks, respectively. We found that multiple years of drought occurred prior to and during outbreak initiation in the Northwest, and that outbreak initiation in the Southwest was associated with only weak drought or neutral conditions. During the outbreak continuation stage, there was a weak positive correlation between May moisture availability and defoliation area growth rates in the Southwest (R2 = 0.12), but no clear relationship was identified in the Northwest. Increased frequency of summer droughts such as these expected from climate change may increase WSBW outbreaks and promote tree dieoff. Improved understanding of the role of different influences of drought and moisture availability across landscapes will lead to improved predictions and management of future outbreaks of WSBW.

Forest fertilization is common in coastal British Columbia as a means to increase wood production and potentially enhance carbon sequestration. Generally, the effects of fertilization are determined by measuring sample plots pre- and post-treatment, resulting in fertilization effects being determined for a limited portion of the treatment area. Applications of remote sensing-based enhanced forest inventories have allowed for estimations to expand to the wider forested area. However, these applications have not focused on monitoring the effects of silvicultural treatments. The objective of this research was to examine if a multi-temporal application of the LiDAR area-based method can be used to detect the fertilization effects on volume, biomass, and height in a second-growth Douglas-fir (Pseudotsuga menziesii) stand. The study area on Vancouver Island was fertilized in January 2007, and sample plots were established in 2011. LiDAR acquisitions were made in 2004, prior to fertilization, and in 2008, 2011, and 2016, covering both treated and untreated areas. A total of 29 paired LiDAR blocks, comprised of four 20 m resolution raster cells, were selected on either side of the fertilization boundary for analysis of the effects across several different stand types differing in the percentage of Douglas-fir, site index, and age. Random forest (RF) plot-level models were developed to estimate total stem volume and total stem biomass for each year of LiDAR acquisition using an area-based approach. Plot level results showed an increase in stem volume by 13% fertilized over control from 2005 to 2011, which was similar to a 14% increase in above-ground carbon stocks estimated using a tree-ring stand reconstruction approach. Plot-level RF models showed R2 values of 0.86 (volume) and 0.92 (biomass) with relative cross-validated root mean square errors of 12.5% (volume) and 11.9% (biomass). For both the sample plots and LiDAR blocks, statistical results indicated no significant differences in volume or biomass between treatments. However, significant differences in height increments were detected between treatments in LiDAR blocks. The results from this research highlight the promising potential for the use of enhanced forest inventory methods to rapidly expand the assessment of treatment effects beyond sample plots to the stand, block, or landscape level.

Douglas-fir, the most important timber species in the Pacific Northwest, US (PNW), has high stiffness and strength. Growing it in plantations on short rotations since the 1980s has led to concerns about the impact of juvenile/mature wood proportion on wood properties. Lumber recovered from four sites in a thinning trial in the PNW was analyzed for relationships between thinning regime and lumber grade yield. Linear mixed-effects models were developed for understanding how rotation age and thinning affect the lumber grade yield. Log small-end diameter was overall the most important for describing the presence of an appearance grade, generally exhibiting an indirect relationship with the lower quality grades. Stand Quadratic Mean Diameter (QMD) was found to be the next most uniformly important predictor, its influence (positive or negative) depending on the lumber grade. For quantity within a grade, as log small-end diameter increased, the quantity of the highest grade increased, while decreasing the quantity of the lower grades differentially. Other tree and stand attributes were of varying importance among grades, including stand density, tree height, and stand slope, but logically depicted the tradeoffs or rebalancing among the grades as the tree and stand characteristics change. Structural lumber grade presence was described best by acoustic wave flight time, log position (decreasing presence in upper logs), and an increasing presence with rotation age. A smaller set of variables proved useful for describing quantity within a structural grade. Forest managers can use these results in planning to best capture value in harvesting, allowing them to direct raw materials (logs) to appropriate manufacturing facilities given market demand.

Forest management choices offer significant potential to mitigate global climate change and biodiversity loss. To illuminate tradeoffs relevant to policymakers, forest sector stakeholders, and consumers of forest products, we utilize three Key Performance Indicators&mdash, average carbon storage in the forest and wood products, cumulative timber output, and discounted cash flow&mdash, to compare four alternative management scenarios for Douglas-fir forests on 64 parcels across western Oregon and Washington. These scenarios are designed to meet one of two alternative management objectives: (i) maximize Net Present Value, or (ii) maximize sustained timber yield, according to one of two alternative sets of forest practice constraints: (i) compliance with minimum Oregon/Washington Forest Practices Act (FPA) rules, or (ii) two key requirements (increased green tree retention and wider riparian buffers) of Forest Stewardship Council (FSC) certification. Improved performance in terms of carbon storage for these alternatives generally also corresponded with reduced Net Present Value and timber yields. The gap between FSC and FPA performance indicators was wider in Oregon than Washington, which is primarily attributed to the higher level of stream protection required under Washington versus Oregon FPA rules. We observed consistently higher average carbon storage per cumulative timber output among FSC scenarios relative to business-as-usual, indicating FSC-certified wood carries an embedded carbon benefit. Our findings highlight options for targeted policies to incentivize management that increases carbon storage and minimizes disruptions in timber output, as well as for narrowing the financial gap (or opportunity cost) that would be involved in a transition away from contemporary common practice on industrial timberlands in the coastal Douglas-fir forests of the Pacific Northwest.

Douglas-fir (Pseudotsuga menziesii) seedlings are periodically challenged by biotic and abiotic stresses. The ability of endophytes to colonize the interior of plants could confer benefits to host plants that may play an important role in plant adaptation to environmental changes. In this greenhouse study, nursery-grown Douglas-fir seedlings were inoculated with diazotrophic endophytes previously isolated from poplar and willow trees and grown for fifteen months in nutrient-poor conditions. Inoculated seedlings had significant increases in biomass (48%), root length (13%) and shoot height (16%) compared to the control seedlings. Characterization of these endophytes for symbiotic traits in addition to nitrogen fixation revealed that they can also solubilize phosphate and produce siderophores. Colonization was observed through fluorescent microscopy in seedlings inoculated with gfp- and mkate-tagged strains. Inoculation with beneficial endophytes could prove to be valuable for increasing the production of planting stocks in forest nurseries.

The forest stand structure class “old-growth” has previously been qualitatively described as having several distinct “sub-structures.” Species composition, diameter distribution, and other structural features commonly associated with old-growth in the Pacific Northwest are quite variable. We determined which quantitative stand structure variables are commonly found together using the Spearman correlation and non-metric multidimensional analysis. Some features were more commonly found together than others, indicating different old-growth stand types, or sub-structures. Cluster analysis classified the old-growth forests into four groups: Douglas-fir dominance, shade tolerant species dominance, and intermediate groups. The intermediate groups were split by the density of large logs and large shade tolerant trees. The old-growth sub-structures appear to change from one to another as the old forest develops.

Douglas-fir is the most commercially important timber species in the US Pacific Northwest due to its ecological prevalence and its superior wood attributes, especially strength and stiffness properties that make it highly prized for structural applications. Its economic significance has led to extensive establishment and management of plantations over the last few decades. Cultural treatments and genetic improvement designed to increase production of utilizable wood volume also impact tree morphology and wood properties. Many of these impacts are mediated by crown development, particularly the amount and distribution of foliage and size and geometry of branches. Natural selection for branch architecture that optimizes reproductive fitness may not necessarily be optimal for stem volume growth rate or for wood properties controlling the quality of manufactured solid wood products. Furthermore, Douglas-fir does not self-prune within the rotation lengths currently practiced. This paper synthesizes extensive Douglas-fir research in the Pacific Northwest addressing: (1) the effects of silviculture and genetics on branch structure and associated consequences for wood quality and the product value chain; and (2) methods to measure, monitor, modify, and model branch attributes to assist managers in selecting appropriate silvicultural techniques to achieve wood quality objectives and improve the value of their Douglas-fir resource.

We sought to answer the question: How do we restore characteristics of old-growth evergreen mixed-conifer forests in young even-aged stands on upland terrain at Headwaters Forest Reserve (HFR)? We described the old-growth reference condition for three stands at HFR. In each old-growth stand, trees within a 1-ha plot were inventoried. We found coast Douglas-fir (Pseudotsuga menziesii var. menziesii) and tanoak (Notholithocarpus densiflorus) well represented while coast redwood (Sequoia sempervirens) dominated in terms of size. Numbers of understory and overstory trees ha−1 and average tree sizes were similar among sites, suggesting these were useful goals for restoration. Adjacent to each old-growth stand, we measured recent growth rates of second-growth trees and remnant old trees across a range of tree sizes, stand structures, and densities. The resultant growth models of redwood and Douglas-fir enabled us to project the development of precommercially thinned young stands at HFR forward in time under two silvicultural prescriptions: (i) no further management; and (ii) partial harvesting simulated before trees attained 30 cm dbh. The partial-harvesting prescription reduced stand density and set the young stand on a more rapid trajectory towards the reference condition found at HFR.

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&rsquo, s central Coast Range (CR) and fifteen-year-old Douglas-fir and western redcedar trees growing in Oregon&rsquo, 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.

In plantation forests, competition from unwanted vegetation may reduce survival and negatively impact tree growth. The goal of this study was to examine the influence of vegetation management treatments on plant water relations and wood properties. Control trees (no treatment) were compared to trees subjected to post-planting competing vegetation control for five consecutive years after planting. Four conifer species (Douglas-fir, western hemlock, western redcedar, and grand fir) were studied on two different sites in western Oregon, USA. Carbon isotope (13C) analysis was used to study intrinsic water use efficiency (iWUE) and X-ray densitometry was used to measure specific gravity, ring width, and latewood percent. We found a significant interaction between vegetation management treatment and wood ring (growing season) in iWUE for Douglas-fir. There was little effect of vegetation management treatment on ring specific gravity for all species. Only western redcedar growing at a central Coast Range site showed increased ring specific gravity under sustained competing vegetation control. When growing under conditions of sustained control of competing vegetation, western redcedar at a central Coast Range site had a significant increase in earlywood specific gravity, while Douglas-fir at a Cascade Foothills site had a significant decrease in latewood specific gravity. Western redcedar and grand fir had a significant interaction-effect on its latewood percentage, with treatment trees having a higher latewood percentage than control trees after ring 8. Further, Douglas-fir and western hemlock had a significant increase in ring, earlywood, and latewood area with treatment, and grand fir had a significant interaction-effect of treatment &times, ring for ring, earlywood, and latewood area. This study indicates that, for conifer trees growing under sustained vegetation control, growth gains could be achieved without compromising wood properties. However, if harvested at a target diameter, these trees will have a larger proportion of low quality corewood compared to trees from conventionally managed stands.

Within the Analytic Hierarchy Process (AHP) framework, a hierarchical model was created considering anthropogenic, genetic and ecological criteria and sub-criteria that directly affect Douglas-fir (Pseudotsuga menziesii (Mirb.)) risk of extinction in central Mexico. The sub-criteria values were standardized, weighted, and ordered by importance in a pairwise comparison matrix, the model was mathematically integrated to quantify the degree of extinction risk for each of the 29 populations present in the study area. The results indicate diverse levels of risk for the populations, ranging from very low to very high. Estanzuela, Presa Jaramillo, Peñas Cargadas and Plan del Baile populations have very low risk, with values less than 0.25. On the other hand, Vicente Guerrero, Morán, Minatitlán, La Garita and Tonalapa populations have very high risk (&gt, 0.35) because they are heavily influenced by anthropogenic (close to roads and towns), ecological (presence of exotic species and little or no natural regeneration) and genetic (presence of mature to overmature trees and geographic isolation) factors. In situ conservation activities, prioritizing their implementation in populations at most risk is highly recommended, in addition, germplasm collection for use of assisted gene flow and migration approaches, including artificial reforestation, should be considered in these locations.

Mixed forest of Douglas-fir and beech has been suggested as one of the possible future forest types in Northwest Europe but the effects of this mixed forest on soil properties relative to monoculture stands are unknown. In a transboundary investigation of adjacent common garden Douglas-fir and beech stands, we determined the effects on topsoil properties. However, responses of C and N stocks, the C/N ratio and pH were site- and soil layer-specific and were mainly single-sided and without synergistic effects. Beech reduced the soil C and N stocks in Douglas-fir at the nutrient-poor site, caused an increase in the C/N ratio in the forest floor and mineral soil at both nutrient-poor and -rich sites, and reduced the acidifying effect of Douglas-fir at the nutrient-poor site. These results do not support the hypothesis that mixture effects would be consistent across sites and soil layers. The lack of synergistic effects may be attributed to the relatively similar litter quality or rooting depth that prevented any larger niche differentiation and complementarity. The results indicate that the transboundary approach within a mature common garden proved useful as a platform to test tree species interactions, and this approach could be explored in soil studies until dedicated mixed-species common gardens reach maturity.

A large research effort was initiated in the 1990s in western United States and Canada to investigate how the development of old-growth structures can be accelerated in young even-aged stands that regenerated following clearcut harvests, while also providing income and ecosystem services. Large-scale experiments were established to compare effects of thinning arrangements (e.g., spatial variability) and residual densities (including leave islands and gaps of various sizes). Treatment effects were context dependent, varying with initial conditions and spatial and temporal scales of measurement. The general trends were highly predictable, but most responses were spatially variable. Thus, accounting for initial conditions at neighborhood scales appears to be critical for efficient restoration. Different components of stand structure and composition responded uniquely to restoration thinnings. Achieving a wide range of structures and composition therefore requires the full suite of silvicultural treatments, from leave islands to variable density thinnings and creation of large gaps. Trade-offs among ecosystem services occurred as result of these contrasting responses, suggesting that foresters set priorities where and when different vegetation structures are most desirable within a stand or landscape. Finally, the results suggested that foresters should develop restoration approaches that include multiple treatments.

Three large-scale, experimental, dispersed residual tree sites established in coastal British Columbia, Canada were measured for planted Douglas-fir tree growth and survival five to six years after planting. The dispersed trees were predominantly large diameter (60 cm+) Douglas-fir left with a range of 0% to 30% of the original forest stand basal area (0 m2 ha-1 to 14 m2 ha-1). Two sites had 0%, 5% and 15% retention, while one site had 0%, 5%, 10% and 30% retention. The trees were measured in sector plots established to randomly sample the range of microsites in each treatment. There was no detectable difference between height and basal diameter growth or mortality rates between the retention treatments over the measurement period, except for a reduction of basal diameter growth at the 30% retention level (p < 0.05). Thus a statistically significant impact on growth was demonstrated for the 30% retention compared to the 0% retention level. We expected intermediate growth rates between the 0% and the other lower retention levels but were unable to demonstrate this due to the low statistical power of the test (10 observations) and high site variability for these very young trees. This is an electronic version of an article published as: Smith, N.J. & Beese W.J. (2012). "Effects of low levels of dispersed retention on the growth and survival of young, planted Douglas-fir." Forests, 3(2), 230-243. Forests is available online at: http://www.mdpi.com/journal/forests and this article is available at: http://www.mdpi.com/1999-4907/3/2/230. https://viuspace.viu.ca/bitstream/handle/10613/2717/Beese.Forests.pdf?sequence=3