Interior Douglas-fir Research Articles

Early field performance of three planted Inland Northwest conifer species: Effects of root growth potential, morphology, and environmental conditions

A common concern to planting for reforestation is seedling failure that is directly measurable by seedling early field performance of growth and survival. Root growth potential (RGP) is a commonly used metric of seedling quality and has been considered indicative of seedling field performance. The effect of RGP is thought to be dependent on planting site and underlining environmental conditions. Moisture stress often is considered the primary cause of seedling failure in addition to other environmental factors such as soil physicochemical properties in regions such as the Inland Northwest of the United States that is prone to growing season drought. In addition, it is interesting to test whether seedling early field performance is related to their morphological attributes and whether the morphological attributes are related to RGP. A comprehensive evaluation on early field performance of three planted conifer species of interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco), grand fir (Abies grandis (Douglas ex D. Don) Lindl.), and western larch (Larix occidentalis Nutt.) was conducted in this study. It was found that RGP did not show clear correlation with early field performance across species. RGP also was not significantly correlated with seedling morphological measures such as below- and above-ground biomass and root-to-shoot ratio (R:S, by mass). Early field performance of growth and survival varied greatly across individuals of seedlings. The most influential predictors of early seedling growth and survival were their initial size (indicative of energy reserve) and soil temperature that likely interacted with soil moisture. Our findings suggest that seed stock selection for reforestation probably should favor species and genotypes with greatest heat tolerance that may be better adapted to future conditions in the region.

Growth responses to thinning from below in uneven-aged interior Douglas-fir dominated stands

We assessed the impacts of three approaches to thinning from below with varying spatial patterns on several stand and individual tree variables for interior Douglas-fir ( Pseudotsuga menziesii var. glauca (Beissn.) Franco), interior spruce ( Picea glauca (Moench) Voss × Picea engelmannii Engelm.), and lodgepole pine ( Pinus contorta Dougl. Ex Loud. var. latifolia Englem.) in central British Columbia, Canada. The three thinning treatments were two experimental “clumped” treatments (3 m Clumped and 5 m Clumped) and the Standard (more uniform spacing) thinning treatment that was employed operationally at that time. We used long-term data from 24 plots measured five times over 21 years. Thinning increased stand basal area increment, with the plots that received the 5 m Clumped treatment having significantly higher periodic annual relative basal area increment than the unthinned Control plots. The responses for the two clumped treatments were not any lower than the Standard. The 3 m Clumped treatment was best if one is concerned about fast recovery of the growing space; however, the 5 m Clumped spacing treatment may be preferable if higher individual tree vigour is needed for resistance and resilience to fire, insects, and disease.

Partial cutting in a dry temperate forest ecosystem alleviates growth loss under drought

The increasing frequency of severe drought and heat events under climate change is a major cause for concern for forest productivity and survival. One potential solution to improve forest resilience to drought may involve tree removal to reduce competition. To quantify potential benefits of partial cutting systems under drought, we use tree-ring data from a long-term partial cutting experiment in a dry ecosystem in western Canada, composed primarily of mature interior Douglas-fir (Pseudotsuga menziesii var. glauca). We ask: (1) How does tree removal change growth responses to drought and (2) how persistent are effects across multiple drought events? We compare growth responses in 83 trees up to 400 years in age from eight treatment units in a randomized experimental design representing a logging treatment with 25% basal area retention and a control (100% basal area retention). Retention harvesting was conducted in winter of 2002/2003 after a moderate drought in the summer of 2002. The site experienced a more severe drought in 2009 and a drought-heat event in 2015. In 2020, we obtained tree height and diameter data as well as tree increment cores from canopy dominant Douglas-fir, which were used to derive basal area increments. Based on these growth increments, we calculated four indices of resilience to drought. Growth increments of remaining individuals substantially increased after tree removal. Relative to the control, the low retention treatment expressed significantly higher post-drought growth increments compared to growth increments after the drought years of 2002 and 2009, i.e., higher drought recovery. Growth increments in the low retention treatment also had a significantly higher ability to regain pre-drought growth levels after the 2002 and 2009 droughts, i.e., higher drought resilience. However, the treatment did not show higher resilience under a heat-drought event in 2015. Although the treatment effects on drought response indices diminished over time, the absolute growth increments of residual trees remained higher than the control 17 years after harvest, despite repeated droughts. These results suggest that partial cutting on moisture-limited sites provides immediate and medium term benefits for remaining trees in terms of drought resilience, which may help forests adapt to climate change.

Sexual reproduction in two mixed stands of coastal and interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in Germany

Adult individuals and seeds of two mixed stands of coastal and interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were analysed for genetic differentiation between the two varieties and evidence of intervarietal pollination. Clear genetic discrimination between the two varieties was observed based on multilocus evaluation of nine microsatellite markers using other Douglas-fir stands of known variety composition for comparison. Analysis of pollination distances showed that 80% of pollinations took place within a distance of about 44–55 m. Analysis of stand structure showed clearly separated areas of mainly coastal or interior Douglas-fir within both stands. Together with short pollination distances this led to an apparent dominance of intravarietal pollinations. However, analysis of pollination partners of trees growing near the border of the variety specific areas, does not indicate the existence of reproductive barriers between trees of the two varieties growing in mixed stands. Therefore, commercial seed harvesting in mixed stands should be avoided if the production of seed lots of pure coastal or interior Douglas-fir is intended.

Temporal changes in tree spatial patterns in uneven-aged interior Douglas-fir dominated stands managed under different thinning treatments

Understanding the spatial patterns of trees and their interactions can reveal the ecological processes driving forest stand structure and stand development over time. We assessed temporal changes in tree spatial patterns in uneven-aged interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) dominated stands in central British Columbia, Canada. Data were available on 24 plots in three blocks over 21 years, 18 of which had received pre-commercial thinning (PCT) treatments of varying intensity. We first applied the Clark and Evans aggregation index and the L function, a transformation of Ripley’s K function, to describe the spatial pattern of live trees in thinned and unthinned plots over time. Second, we analysed the spatial correlations between live tree diameters using the mark correlation function and the mark variogram. Third, the spatial pattern of dead trees in the unthinned plots after 21 years was analysed. Lastly, we tested the spatial relationship between dead and surviving trees in the unthinned plots. In all three blocks, the spatial patterns of live trees in the unthinned plots were clustered through time. The moderate thinning treatments had random or regular spatial patterns that remained unchanged through time, because of reduced mortality rates and low levels of ingrowth. The heavier thinning initially retained a clustered pattern at small inter-tree distances; however, this changed to a random pattern with increasing distance 15 years post-thinning and remained as such until the end of the study period. Tree diameters were not spatially autocorrelated in the thinned plots, although there was positive spatial correlation of tree diameters in the unthinned plots, probably due to competitive growth inhibition among neighbouring trees. Dead trees were primarily smaller in size and were significantly clustered at all spatial scales. The lack of spatial relationship between dead and surviving trees indicated that mortality was a random process. Our study contributes to a better understanding of how spatial patterns of trees change over time in these stands, which could help in the design of silvicultural regimes that mimic natural processes.

Diffusion of indigenous fire management and carbon-credit programs: Opportunities and challenges for “scaling-up” to temperate ecosystems

Savanna burning programs across northern Australia generate millions of dollars per year for Indigenous communities through carbon and other greenhouse gas (GHG) markets. In catalyzing Indigenous knowledge and workforce to mitigate destructive wildfires, these programs are considered a success story on a range of social, ecological and economic measures. Scaling-up to temperate ecosystems requires a focus on applying the architecture and governance of these programs, and accounting for fundamental differences in context. We examine the opportunities and challenges in applying the architecture of savanna burning to an Indigenous Fire Management (IFM) program in central British Columbia, Canada (the Chilcotin). The Chilcotin project involves Yunesit’in and Xeni Gwet’in First Nations, and we draw from eight key elements of the Australian savanna burning model to identify a project area that includes Aboriginal title and reserve lands. The area encompasses Interior Douglas Fir (IDF) and Sub-Boreal Pine—Spruce (SBPS) biogeoclimatic zones, or dry forest and grassland ecosystems where low intensity fires are applied by community members to remove forest fuels, with the goal of mitigating wildfires and associated GHG emissions. The multi-decadal intervals between contemporary fires in the Chilcotin region make it challenging to accurately document historical fire location, scale and intensity, and thus to establish an emissions baseline. If this issue can be resolved, the British Columbia Forest Carbon Offset Protocol version 2 (FCOPv2) offers promise for developing verified carbon credits for three reasons: first, carbon (CO2), nitrous oxide (N2O), and methane (CH4), the three main GHG emissions from Indigenous fire management, are included in the protocol; second, credits under FCOPv2 are eligible for either compliance or voluntary markets, offering diversification; and third, a range of activities are eligible under the standard, including fire management and timber harvesting, which offers flexibility in terms of management practices. The Chilcotin project is likely to generate substantial co-benefits related to cultural, health and wellbeing, and livelihood values among First Nations participants. The Australian experience suggests that getting governance right, and building community ownership through “bottom-up” governance, is critical to the success of these programs. From the Australian model, community-based planning, like the Healthy Country Planning approach, can be a positive step to take, engaging community in goal setting for the program to guide and take ownership of its direction.

Changes in size inequality and growth dominance in thinned and unthinned uneven-aged interior Douglas-fir dominated stands

This study sought to gain insight into the impact of thinning treatments on stand structure dynamics in uneven-aged interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) dominated stands in central British Columbia (BC), Canada. We applied the Gini coefficient (GC) and the growth dominance coefficient (GDc) to determine how size inequality and growth dominance changed through time in both pre-commercially thinned (PCT) and unthinned stands across a moisture gradient. We used data from 24 plots in three blocks of a long-term study on the response to PCT, comprising five measurements over a 21-year period. The stand structures of each of the thinned plots were not identical before thinning. Therefore, the GC of the post-thinning measurements was expressed as a ratio relative to the pre-thinning treatment GC, referred to as the Gini coefficient ratio (GCr), to compare changes in size inequality through time across the PCT treatments. Three PCT treatments were applied, which differed in intensity and spatial pattern. All PCT treatments were applied in such a way that size inequality was reduced immediately after thinning. Size inequality did not decrease with increasing thinning intensity. There was a non-constant decrease in GCr in the unthinned plots, but an increase in the more heavily thinned plots over time. GDc decreased with increasing thinning intensity, where smaller trees were relatively more productive as the thinning intensity increased. Over time, thinned plots on the site with limited soil moisture and the moistest site shifted from negative to zero to positive growth dominance, while the GDc in the thinned plots with moderate soil moisture remained negative. These results suggest that site characteristics impact the response to PCT in these stands, and consequently should be considered in the design of the thinning treatments.

Soil compaction and organic matter removal effects on soil properties and tree growth in the Interior Douglas-fir zone of southern British Columbia

Silviculture systems and associated forest harvesting practices that affect the level of soil compaction and organic matter retained on a site will cause changes to soil properties and processes that may affect the growth of planted trees. We present results for soil conditions and tree growth after 15 years for 6 Long-term Soil Productivity Study (LTSP) installations in 2 distinct regions of the Interior Douglas-fir (IDF) biogeoclimatic zone in southern British Columbia (BC). In a 3 × 3 factorial design, three levels of compaction and organic matter removal were replicated in two distinct IDF regions that varied in parent material, but with similar climates. Each treatment was then split and planted with two different species, Douglas-fir and lodgepole pine. In each region, three unique sites (block), all within a radius of 50 km from one other, were installed with the same combination of treatment and species for a total of six replicates, three in each of two regions. Across IDF regions, tree heights on calcareous soils in the Rocky Mountains of south-eastern BC were 36% lower for Douglas-fir and 23% lower for lodgepole pine than on more acidic soils on the Thompson Plateau. There were varying differences across treatments in soil and foliar nutrient concentrations between IDF regions, primarily from regional parent material differences. However, nutrient deficiencies were apparent in both regions and may have limited growth, especially on the more calcareous sites. Increases to soil bulk density (27%) 1 year after compaction did not impact tree survival, height at Year-15, or chemical properties in foliar tissue or soil. Fewer growing season frost events and increased soil water availability during the seedling establishment period was a likely reason for a 25% increase in Douglas-fir survival at Year-15 with the whole tree + forest floor removal (OM3) treatment. However, whole tree + forest floor removal (OM3) also produced a 13–19% reduction in soil N, S, K, and mineralizable N when compared to both stem-only (OM1) and whole tree (OM2) harvesting treatments that kept the forest floor intact. Effects on forest productivity from soil compaction after 15 years appear to be overshadowed by the more prominent effect of organic matter removal treatments during stand establishment and early growth. Future work at these installations focusing on nutrient budget, forest health, and ecosystem carbon stock differences across treatments will provide valuable insight into silviculture and harvesting practices for different species and regions in the dry forests of southern BC.

The influence of the root diseases Armillaria solidipes and Inonotus sulphurascens on the distribution of mule deer during winter

Abstract Armillaria (Armillaria solidipes) and laminated root diseases (Inonotus sulphurascens) are two wide-ranging fungal pathogens that occur in the southern half of British Columbia (BC), Canada, and can infect economically and biologically important tree species such as interior Douglas-fir (Pseudotsuga menziesii var. glauca). In northern, temperate locations, Douglas-fir forests serve as winter habitat for ungulates. When these fungal infections are in Douglas-fir forests, core components of winter ranges are altered, including canopy cover, snowpack and understory vegetation. In this study, we investigated how Rocky Mountain mule deer (Odocoileus hemionus hemionus) of central BC used winter range habitats that included root disease (A. solidipes and I. sulphurascens) centres. We used remote camera-traps to collect data from September 2017 to April 2019, and we assessed those habitats in which the cameras were located during the summer and winter of 2018. We used logistic regression and an information theoretic approach to test a series of factors hypothesised to influence the use of root disease centres by mule deer. Our results show that mule deer use root disease centres less than control forests as well as negatively respond to the deeper snow packs found in root disease centres, especially in late winter. Our cameras also detected higher vertebrate diversity in root disease centres. We suggest that forest policy-makers should acknowledge heterogeneous habitat features such as root disease centres within ungulate winter ranges and consider adjusting estimates of habitat capability for deer based on our findings.

Partial Retention of Legacy Trees Protect Mycorrhizal Inoculum Potential, Biodiversity, and Soil Resources While Promoting Natural Regeneration of Interior Douglas-Fir

Clearcutting reduces proximity to seed sources and mycorrhizal inoculum potential for regenerating seedlings. Partial retention of legacy trees and protection of refuge plants, as well as preservation of the forest floor, can maintain mycorrhizal networks that colonize germinants and improve nutrient supply. However, little is known of overstory retention levels that best protect mycorrhizal inoculum while also providing sufficient light and soil resources for seedling establishment. To quantify the effect of tree retention on seedling regeneration, refuge plants, and resource availability, we compared five harvesting methods with increasing retention of overstory trees (clearcutting (0% retention), seed tree (10% retention), 30% patch retention, 60% patch retention, and 100% retention in uncut controls) in an interior Douglas-fir-dominated forest in British Columbia. Regeneration increased with proximity to legacy trees in partially cut forests, with increasing densities of interior Douglas-fir, western redcedar, grand fir, and western hemlock seedlings with overstory tree retention. Clearcutting reduced cover of ectomycorrhizal refuge plants (from 80 to 5%) while promoting arbuscular mycorrhizal plants the year after harvest. Richness of shrubs, herbs, and mosses declined with increasing harvesting intensity, but tree richness remained at control levels. The presence of legacy trees in all partially cut treatments mitigated these losses. Light availability declined with increasing overstory cover and proximity to leave trees, but it still exceeded 1,000 W m−2 in the clearcut, seed tree and 30% retention treatments. Increasing harvesting intensity reduced aboveground and belowground C stocks, particularly in live trees and the forest floor, although forest floor losses were also substantial where thinning took place in the 60% retention treatment. The loss of forest floor carbon, along with understory plant richness with intense harvesting was likely associated with a loss of ectomycorrhizal inoculum potential. This study suggests that dispersed retention of overstory trees where seed trees are spaced ~10–20 m apart, and aggregated retention where openings are <60 m (2 tree-lengths) in width, will result in an optimal balance of seed source proximity, inoculum potential, and resource availability where seedling regeneration, plant biodiversity, and carbon stocks are protected.

Altering Neighborhood Relatedness and Species Composition Affects Interior Douglas-Fir Size and Morphological Traits With Context-Dependent Responses

Trees often exist in a complex ecological system with many biological interactions. Here we examine kin interactions of Pseudotsuga menziesii var. glauca (interior Douglas-fir) both in the context of pure kin stands, in accordance with established plant kin selection and recognition studies, but also in combination with inter and intraspecific neighbors in order to observe how interactions may differ in a more complex system. Seedlings grown with kin neighbors (i.e. in stands that contained only kin) were significantly larger (biomass, height and root length) than those grown with any type of unrelated neighbor. However, of those with an unrelated neighbor, performance was better if that neighbor was interspecific (lodgepole pine rather than a stranger, or non-kin, Douglas-fir neighbor). Interestingly when Douglas-fir was grown in mixed stands, the four growth and four morphological traits of the seedlings examined paralleled neither pure stranger nor pure kin stands. This suggests that a mixed stand environment yielded cues that were uniquely different than either type of pure stand and that these seedlings are able to integrate that information and respond in a different way; for example, with increased early mycorrhizal fungal colonization. The morphological traits fine: coarse root allocation and slenderness (height relative to diameter) closely paralleled the seeding-size results, with the greatest values in pure kin stands. Whereas, fine root: needle allocation showed a kin response of less fine root allocation relative to needle mass compared to strangers, but kin seedlings had more fine root allocation when grown with a pine compared to a stranger Douglas-fir neighbor. We have demonstrated that the kin response in Douglas-fir is influenced by the complexity of the environment in which it grows, and this has significant effects on growth, morphology and mycorrhizal fungal colonization that may affect the success and resiliency of regeneration.

Growth and mortality of planted interior Douglas-fir and western larch seedlings during the establishment phase in Idaho, USA

Planting for reforestation is increasingly important for the establishment of forests for future timber production and enhanced carbon sequestration. Planting also requires significant investment to ensure successful seedling establishment. However, initial seedling growth and survival is a common missing link in forest growth and yield models as they are predominantly designed to project established trees often post canopy closure. The multitude of both biotic and abiotic factors that influence growth and mortality of planted seedlings during the establishment phase is less examined. This is likely due to the high variability and complexity of this type of analysis, as well as the general lack of available data. The current study utilized annual measurements of 13,701 seedlings beginning immediately after planting to evaluate growth and mortality of planted interior Douglas-fir (Pseudotsuga menziesii var. glauca [Mirb.] Franco) and western larch (Larix occidentalis Nutt.) seedlings across multiple contrasting sites in northern Idaho and eastern Oregon for the first two years. Our results indicate that growth and mortality of seedlings were strongly influenced by their initial diameter and height such that slimmer and taller seedlings had higher mortality, while diameter and height growth was positively related to initial diameter and height, respectively. Weather conditions, especially measures of temperature and precipitation, had a similarly important role on seedling growth and mortality. The effects of root growth potential and competing vegetation were generally insignificant as pre-planting chemical preparation was applied to all sites. Improved western larch seedlings from seed orchards had higher growth rates with small increases in mortality compared to wild collected sources, but improved Douglas-fir had minimal gains in growth and much higher mortality. The developed seedling models readily fit into the architecture of current individual tree growth and yield models, which extend these models' ability to forecast seedlings during and after establishment. The identified influential factors and specific differences in seedling growth and mortality during the establishment phase provide critical information and guidance to the increasingly important reforestation practice of planting, and the overall analytical framework presented in this analysis is generally applicable to species beyond Douglas-fir and western larch.

Post-fire salvage logging reduces snowshoe hare and red squirrel densities in early seral stages

Wildfire is an important natural disturbance in western North American forests and has been increasing in prevalence and severity in recent decades. Post-fire salvage logging is a common practice, however, the impacts of salvage logging on wildlife are poorly understood. We studied populations of snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus) in a post-fire and salvage-logged interior Douglas fir (Pseudotsuga menziesii) forest on the Chilcotin Plateau, British Columbia, Canada. Snowshoe hare densities were low, but densities were highest in 8–9-year-old regenerating post-fire forests. Hares were mostly absent from 1 to 2-year-old post-fire forests. Salvage-logged areas were not used by snowshoe hares. Red squirrel detections were highest in mature forests, and squirrels were not present in post-fire salvage-logged habitat. Post-fire salvage logging removed live canopy trees required by both snowshoe hares and red squirrels. The large scale and intensity of post-fire salvage logging removes important regenerating post-fire habitat and has detrimental impacts on these important prey species, likely leading to consequences for avian and mammalian predators.

Multidecadal Growth of Western White Pine and Interior Douglas-Fir Following Site Preparation

Site preparation is used to favor seedling regeneration and establishment by enhancing growing conditions and increasing resource availability, yet few studies have compared different site preparation techniques on growth and yield of trees over multiple decades. We destructively sampled 34-year old trees of western white pine (Pinus monticola Douglas ex D. Don) and Interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco planted at two sites using a replicated experiment to test the effectiveness of different site preparation treatments: (1) no site preparation, (2) scalping, (3) bedding, and (4) bedding plus three years of competition control with herbicide. Growth and yield were compared among the treatments, and models of growth were developed for each species and treatment combination. The herbicide treatment was the only treatment that consistently improved growth and yield of both species resulting in 19%–30% gains in height, 43%–63% gains in diameter, and 31%–109% gains in stem volume by age 34. Height growth response to herbicide was sustained until age 14 for white pine and age 12 for Douglas-fir, while the diameter response was sustained until age 23 for white pine and 20 for Douglas-fir. The later peak in growth for white pine suggests a better response to treatment and that the species was able to maintain higher growth following crown closure. Both species exhibited a Type 2 growth response to herbicide, suggesting competition control resulted in sustained gains over time with associated age shifts of 8.5 and 9.7 years for white pine and 7.1 and 10.2 years for Douglas-fir, height and diameter, respectively. This compares to scalping and bedding which produced no detectable difference in growth compared to the control, and in some instances, reduced growth. In the Northern Rocky Mountains, moisture is most limiting. This is likely why trees showed the greatest response to competition control. Interestingly, this growth was sustained well beyond seedling establishment.

Assessing Differences in Competitive Effects Among Tree Species in Central British Columbia, Canada

Research Highlights: We investigated the competitive interactions among three tree species (interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), interior spruce (Picea glauca [Moench] Voss × Picea engelmannii Engelm.), and lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Englem.)) in multi-aged stands in central British Columbia, Canada. Background and Objectives: Understanding competitive interactions among tree species in mixed-species stands is fundamental to supporting silvicultural decision-making in such stands. Using the periodic annual basal area increment for single trees as our dependent variable, we investigated whether neighboring trees competed with subject trees independently of species identity. We also examined the differences in single-tree basal area growth among the three conifer species over time under different levels of competition. Materials and Methods: We developed several spatially explicit, single-tree basal area growth models for interior Douglas-fir, interior spruce, and lodgepole pine using data from 16 plots in two blocks of a long-term study (five measurements over a 21-year period) on the response to pre-commercial thinning. We compared these equations to assess whether intraspecific or interspecific competition predominated. We also examined the differences in basal area growth among the three conifer species over time under different levels of competition. Results: We found asymmetrical relationships between the conifer trees and their neighbors for all species, indicating that the main driver limiting growth in these stands is aboveground competition for light. There was evidence of higher intraspecific competition for small (<10.0 cm DBH) interior Douglas-fir in one block. However, there was no general pattern among larger subject trees with respect to the identity of neighborhood competitive effects and the equivalence of neighbors. We observed a higher level of basal area growth over time for interior Douglas-fir than for lodgepole pine and interior spruce, irrespective of the competition intensity and, not surprisingly, the growth rate declined with increasing competition levels for the three species. Conclusions: Our results provide an understanding of how interior Douglas-fir stands will develop over time and information on species interactions that could help forest managers explore different silvicultural options and their effects on individual tree growth in these complex stands.

An Axiom SNP genotyping array for Douglas-fir

BackgroundIn forest trees, genetic markers have been used to understand the genetic architecture of natural populations, identify quantitative trait loci, infer gene function, and enhance tree breeding. Recently, new, efficient technologies for genotyping thousands to millions of single nucleotide polymorphisms (SNPs) have finally made large-scale use of genetic markers widely available. These methods will be exceedingly valuable for improving tree breeding and understanding the ecological genetics of Douglas-fir, one of the most economically and ecologically important trees in the world.ResultsWe designed SNP assays for 55,766 potential SNPs that were discovered from previous transcriptome sequencing projects. We tested the array on ~ 2300 related and unrelated coastal Douglas-fir trees (Pseudotsuga menziesii var. menziesii) from Oregon and Washington, and 13 trees of interior Douglas-fir (P. menziesii var. glauca). As many as ~ 28 K SNPs were reliably genotyped and polymorphic, depending on the selected SNP call rate. To increase the number of SNPs and improve genome coverage, we developed protocols to ‘rescue’ SNPs that did not pass the default Affymetrix quality control criteria (e.g., 97% SNP call rate). Lowering the SNP call rate threshold from 97 to 60% increased the number of successful SNPs from 20,669 to 28,094. We used a subset of 395 unrelated trees to calculate SNP population genetic statistics for coastal Douglas-fir. Over a range of call rate thresholds (97 to 60%), the median call rate for SNPs in Hardy-Weinberg equilibrium ranged from 99.2 to 99.7%, and the median minor allele frequency ranged from 0.198 to 0.233. The successful SNPs also worked well on interior Douglas-fir.ConclusionsBased on the original transcriptome assemblies and comparisons to version 1.0 of the Douglas-fir reference genome, we conclude that these SNPs can be used to genotype about 10 K to 15 K loci. The Axiom genotyping array will serve as an excellent foundation for studying the population genomics of Douglas-fir and for implementing genomic selection. We are currently using the array to construct a linkage map and test genomic selection in a three-generation breeding program for coastal Douglas-fir.

Stand growth responses after fertilization for thinned lodgepole pine, Douglas-fir, and spruce in forests of interior British Columbia, Canada

This study was conducted to quantify growth responses of three major commercial conifer species (lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson), interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco), and spruce (white spruce (Picea glauca (Moench) Voss) and hybrid spruce (Picea engelmannii Parry ex. Engelm. × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carrière))) to various fertilizer blends in interior British Columbia, Canada. Over 25 years, growth-response data were repeatedly collected across 46 installations. The fertilizer blends were classified into three groups: nitrogen only; nitrogen and sulfur combined; and nitrogen, sulfur, and boron combined. The growth responses for stand volume, basal area, and top height were calculated through absolute and relative growth rate ratios relative to a controlled group. Fertilizer blend, inverse years since fertilization, site index, stand density at fertilization, and their interactions with the fertilizer blend were used as explanatory variables. The magnitude and significance of volume and basal area growth responses to fertilization differed by species, fertilizer-blend groups, and stand-condition variables (i.e., site index and stand density). In contrast, the response in top height growth did not differ among fertilization blends, with the exception of the nitrogen and sulfur fertilizer subgroup for lodgepole pine. The models developed in this study will be incorporated into the current growth and yield fertilization module (i.e., Table Interpolation Program for Stand Yields (TIPSY)), thereby supporting guidance of fertilization applications in interior forests in British Columbia.

Intraspecific Fine-Root Trait-Environment Relationships across Interior Douglas-Fir Forests of Western Canada.

Variation in resource acquisition strategies enables plants to adapt to different environments and may partly determine their responses to climate change. However, little is known about how belowground plant traits vary across climate and soil gradients. Focusing on interior Douglas-fir (Pseudotsuga menziesii var. glauca) in western Canada, we tested whether fine-root traits relate to the environment at the intraspecific level. We quantified the variation in commonly measured functional root traits (morphological, chemical, and architectural traits) among the first three fine-root orders (i.e., absorptive fine roots) and across biogeographic gradients in climate and soil factors. Moderate but consistent trait-environment linkages occurred across populations of Douglas-fir, despite high levels of within-site variation. Shifts in morphological traits across regions were decoupled from those in chemical traits. Fine roots in colder/drier climates were characterized by a lower tissue density, higher specific area, larger diameter, and lower carbon-to-nitrogen ratio than those in warmer/wetter climates. Our results showed that Douglas-fir fine roots do not rely on adjustments in architectural traits to adapt rooting strategies in different environments. Intraspecific fine-root adjustments at the regional scale do not fit along a single axis of root economic strategy and are concordant with an increase in root acquisitive potential in colder/drier environments.

New insights on the behaviour of alternative types of individual-based tree models for natural forests

Agent/individual-based models (A/IBM) help to explain in a mechanistic way how spatial plant patterns evolve through time. In the past, seemingly different and independent types of A/IBMs were developed for modelling the dynamics of tree populations, e.g. growth interaction (GI) and shot noise (SN) models. In this paper, we present a new, advanced methodology of pattern-oriented modelling (POM) for the comparative, synoptic analysis of the behaviour of different types of A/IBMs by using recombinations of model components, validation and sensitivity analysis. We analysed model behaviour for spatio-temporal data from natural forests of interior Douglas fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) and Scots pine (Pinus sylvestris L.) populations from Canada and the UK, respectively. Our detailed analysis clarified that both models, GI and SN along with their recombinations performed similarly and belong to the same group of A/IBMs. From the application of our new methodology we learnt that SN models were able to describe interactions more accurately than GI models and additionally produce interaction fields that can be used for other modelling purposes. On the other hand the GI model was more robust when using observed data that did not include sufficient information on tree interactions. Maximum-likelihood estimations were more reliable in spatial regression analysis than least-squares methods and should be preferred in spatial A/IBM parametrisation.

Shifts in Ectomycorrhizal Fungal Communities and Exploration Types Relate to the Environment and Fine-Root Traits Across Interior Douglas-Fir Forests of Western Canada.

Large-scale studies that examine the responses of ectomycorrhizal fungi across biogeographic gradients are necessary to assess their role in mediating current and predicted future alterations in forest ecosystem processes. We assessed the extent of environmental filtering on interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) ectomycorrhizal fungal communities across regional gradients in precipitation, temperature, and soil fertility in interior Douglas-fir dominated forests of western Canada. We also examined relationships between fine-root traits and mycorrhizal fungal exploration types by combining root and fungal trait measurements with next-generation sequencing. Temperature, precipitation, and soil C:N ratio affected fungal community dissimilarity and exploration type abundance but had no effect on α-diversity. Fungi with rhizomorphs (e.g., Piloderma sp.) or proteolytic abilities (e.g., Cortinarius sp.) dominated communities in warmer and less fertile environments. Ascomycetes (e.g., Cenococcum geophilum) or shorter distance explorers, which potentially cost the plant less C, were favored in colder/drier climates where soils were richer in total nitrogen. Environmental filtering of ectomycorrhizal fungal communities is potentially related to co-evolutionary history between Douglas-fir populations and fungal symbionts, suggesting success of interior Douglas-fir as climate changes may be dependent on maintaining strong associations with local communities of mycorrhizal fungi. No evidence for a link between root and fungal resource foraging strategies was found at the regional scale. This lack of evidence further supports the need for a mycorrhizal symbiosis framework that is independent of root trait frameworks, to aid in understanding belowground plant uptake strategies across environments.