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Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750 kg N ha−1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of |$\sim$| 1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability. [ABSTRACT FROM AUTHOR]

The Elliott State Research Forest comprises 33,700 ha of temperate, Douglas-fir rainforest along North America's Pacific Coast (Oregon, United States). In 2015, naturally regenerated stands at least 92 years old covered 49% of the research area and sawtimber plantations younger than 68 years another 50%. During the winter of 2015–2016, a forest wide inventory sampled both naturally regenerated and plantation stands, recording 97,424 trees on 17,866 plots in 738 stands. The resulting dataset is atypical for the area as plot locations were not restricted to upland, commercially harvestable timber. Multiage stands and riparian areas were therefore documented along with plantations 2–61 years old and trees retained through clearcut harvests. This dataset constitutes the only open access, stand-based forest inventory currently available for a large area within the Oregon Coast Range. The dataset enables development of suites of models as well as many comparisons across stand ages and types, both at stand level and at the level of individual trees. DataSet: https://doi.org/10.7267/xp68kq79g DataSet License: CC-BY-NC-SA [ABSTRACT FROM AUTHOR]

The Elliott State Research Forest comprises 33,700 ha of temperate, Douglas-fir rainforest along North America’s Pacific Coast (Oregon, United States). In 2015, naturally regenerated stands at least 92 years old covered 49% of the research area and sawtimber plantations younger than 68 years another 50%. During the winter of 2015–2016, a forest wide inventory sampled both naturally regenerated and plantation stands, recording 97,424 trees on 17,866 plots in 738 stands. The resulting dataset is atypical for the area as plot locations were not restricted to upland, commercially harvestable timber. Multiage stands and riparian areas were therefore documented along with plantations 2–61 years old and trees retained through clearcut harvests. This dataset constitutes the only open access, stand-based forest inventory currently available for a large area within the Oregon Coast Range. The dataset enables development of suites of models as well as many comparisons across stand ages and types, both at stand level and at the level of individual trees.

Red alder (Alnus rubra Bong.) is an ecologically significant and important fast-growing commercial tree species native to western coastal and riparian regions of North America, having highly desirable wood, pigment, and medicinal properties. We have sequenced the genome of a rapidly growing clone. The assembly is nearly complete, containing the full complement of expected genes. This supports our objectives of identifying and studying genes and pathways involved in nitrogen-fixing symbiosis and those related to secondary metabolites that underlie red alder's many interesting defense, pigmentation, and wood quality traits. We established that this clone is most likely diploid and identified a set of SNPs that will have utility in future breeding and selection endeavors, as well as in ongoing population studies. We have added a well-characterized genome to others from the order Fagales. In particular, it improves significantly upon the only other published alder genome sequence, that of Alnus glutinosa. Our work initiated a detailed comparative analysis of members of the order Fagales and established some similarities with previous reports in this clade, suggesting a biased retention of certain gene functions in the vestiges of an ancient genome duplication when compared with more recent tandem duplications. [ABSTRACT FROM AUTHOR]

Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750 kg N ha-1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of $\sim$1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The alder bark beetle, Alniphagus aspericollis (LeConte), is known to overwinter as larvae and adults in the main stems of red alder, Alnus rubra (Bongard). Observations of adult alder bark beetles in the branch and bud nodes of planted saplings during the winter led to the hypothesis that these microhabitats represent alternative overwintering sites for the beetle in mature trees. To test this hypothesis, we surveyed crown branches at three coastal British Columbia locations, sampling three trees in 2003 and 2004 and three additional trees (nine branches per tree) in 2018–2019. Adult beetles were found overwintering inside sites excavated in the branch and bud nodes throughout the crowns of mature trees. Branch type, defined by growth class, and tree affected the overall distribution and likelihood of overwintering site occupancy among the three trees sampled intensively in 2018–2019, whereas overwintering site age (old versus new (current year)) affected the frequency of site occupancy across all six trees. We suggest that overwintering in tree crowns evolved from late-summer maturation feeding in new shoots and that the majority of beetles abandon terminal shoots as temperatures fall, moving deeper into the crown to overwinter preferentially in older branch tissues that offer greater thermal protection. [ABSTRACT FROM AUTHOR]

Watershed nutrient balance studies traditionally focus on annual fluxes. In areas with strongly seasonal, Mediterranean-type climate regimes, riverine nutrient export may be greater during wet seasons when hydrologic forcing overwhelms or bypasses retention mechanisms. By combining data on riverine export with spatially detailed nutrient inputs, we examine how nitrogen (N) supply, retention, and streamflow shape annual and seasonal riverine N export in Oregon's Willamette River Basin (WRB). The WRB has pronounced dry summers and wet winters, and the distribution of farmland, cities and forests create significant spatial variations in N inputs. Local data on N inputs were coupled with streamflow and chemistry to calculate fractional N export for 22 WRB sub-watersheds in the mid-2000s. For the entire WRB, 78% of the N inputs came from agricultural activities, mainly as synthetic fertilizer (69%); the next largest inputs were deposition (10%), alder fixation (5%) and point sources (5%). Crop-specific estimates of fertilizer agreed with county fertilizer sales rates at the high end of extension recommendations. Fractional riverine N export (annual riverine N export / net watershed N inputs) averaged 38% of net inputs in WRB tributaries, greater than other regions of North America. Fall and winter together accounted for 60–90% of the riverine N export across all watersheds. Summer export was small but was greatest in the watersheds that receive seasonal snowmelt. Large wet season losses, when biotic sinks are less active, result in a relatively high proportion of N inputs exported in this region with a Mediterranean climate and high runoff. [ABSTRACT FROM AUTHOR]

Timber durability is often assessed using small wood stakes exposed in direct soil contact, and the assessment generally emphasizes effects on wood rather than organisms involved. Understanding fungal colonization patterns can help identify key decay agents under varying conditions and use these patterns to improve wood protection strategies. Fungal colonization of red alder (Alnus rubra), Douglas-fir (Pseudotsuga menziesii) heartwood/sapwood, and western redcedar (Thuja plicata) field stakes was assessed over 2 y in western Oregon. Spatiotemporal fungal community variations were identified via culturing and DNA sequencing, where 814 isolates were identified from 84 stakes. Forty-six ascomycete genera were identified, with Phialophora, Trichoderma, and Epicoccum species occurring most frequently. Twenty-three basidiomycete genera were identified, with Trametes and Phanerochaete being the most common. Douglas-fir and western redcedar stakes contained the highest and lowest diversity levels, respectively, reflecting natural durability differences of these species. Fungal species abundance was higher below ground than in the above ground and groundline zones, likely reflecting more stable moisture regimes, proximity to soil-based fungi, and potential nutrient migration into wood beneath the soil surface. Ascomycetes were proportionally more abundant early in the exposure period, but basidiomycetes were also observed early in the process, and there appeared to be no consistent colonization pattern. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen (N)-fixing trees supply significant N inputs to forest ecosystems, leading to increased soil fertility, forest growth, and carbon storage. Rapid growth and stoichiometric constraints of N fixers also create high demands for rock-derived nutrients such as phosphorus (P), while excess fixed N can generate acidity and accelerate leaching of rock-derived nutrients such as calcium (Ca). This ability of N-fixing trees to accelerate cycles of Ca, P, and other rock-derived nutrients has fostered speculation of a direct link between N fixation and mineral weathering in terrestrial ecosystems. However, field evidence that N-fixing trees have enhanced access to rock-derived nutrients is lacking. Here we use strontium (Sr) isotopes as a tracer of nutrient sources in a mixedspecies temperate rainforest to showthat N-fixing trees accessmore rock-derived nutrients than nonfixing trees. The N-fixing tree red alder (Alnus rubra), on average, took up 8 to 18%more rock-derived Sr than five co-occurring nonfixing tree species, including two with high requirements for rock-derived nutrients. The increased access to rock-derived nutrients occurred despite spatial variation in community- wide Sr sources across the forest, and only N fixers had foliar Sr isotopes that differed significantly from soil exchangeable pools. We calculate that increased uptake of rock-derived nutrients by N-fixing alder requires a 64% increase in weathering supply of nutrients over nonfixing trees. These findings provide direct evidence that an N-fixing tree species can also accelerate nutrient inputs from rock weathering, thus increasing supplies of multiple nutrients that limit carbon uptake and storage in forest ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Wood is among the most decay-resistant cellulosic materials; however, all organics eventually succumb to decay. Understanding the degradation process is important when considering how products perform, but this knowledge can also be useful when determining how climates affect the organisms involved and the rates at which degradation occurs. Above ground wood decay tends to occur more slowly than decay in direct soil contact and is more dependent on climatic differences and wood species chemistries. While above ground wood deterioration is a subject of interest, most research has concentrated on the effects of the organisms on the wood. There are surprisingly few comprehensive studies of the fungi involved in the process and most have been performed under aggressive tropical conditions. Fungal colonization of red alder and Douglas-fir samples exposed above ground was evaluated over a 24-month period. Red alder is highly susceptible to fungal attack while Douglas-fir is moderately resistant. As such, they presented two differing selective media for fungal colonization. Red alder was more heavily colonized than Douglas-fir, reflecting the differing susceptibility of the two wood species to degradation. A similar number of Ascomycete and Basidiomycete species were isolated (11 vs 8 species, respectively), but Basidiomycetes were more frequently isolated. These results were similar to those found under more tropical conditions. The results illustrate the wide range of species that colonize wood exposed above ground. Highlights • Ascomycotina were more abundant than Basidiomycotina • White rot fungi were the predominant. • Alder was more heavily colonized than Douglas-fir. • Plant pathogens were among fungi in decaying wood. [ABSTRACT FROM AUTHOR]

Riparian ecosystems provide critical habitat and functions while being some of the most productive areas in forests. Both conifers and hardwoods contribute to maintenance of habitat and function. To determine the impact of water stress on growth of red alder (Alnus rubra Bong.) and western hemlock (Tsuga heterophylla [Raf.] Sarg.), we installed Nelder type 1a combined with replacement series plots on three Oregon Coast Range sites. Densities ranged from 988 to 85,400 trees/hectare, with ratios (hemlock:alder) of 100:0, 75:25, 50:50, 25:75, and 0:100. In the first 4 years after planting, alder used water in the growing season at greater depths earlier than western hemlock. Higher densities resulted in greater water stress later in the growing season in weeded areas (maintained by herbicide applications), but stress was similar across densities in unweeded areas. Water stress at early ages was correlated with decreased size 14 or 24 years after planting for both species, but these correlations were confounded with other effects of density. Increasing water availability in areas with low summer precipitation could enhance growth of red alder and western hemlock, even in highly productive riparian areas. [ABSTRACT FROM AUTHOR]

In the Pacific Northwest, Alnus rubra Bong. (red alder) is a common deciduous tree species especially prevalent in riparian corridors and disturbed sites, including metropolitan areas undergoing land use changes and development. Importantly, red alder is also considered a bioindicator for ozone pollution and, like all plants, harbors a diverse endophyte community that may interact with aerial pollutants. In this study, we surveyed foliar fungal endophyte communities (microfungi) in red alder leaves from the metropolitan area of Portland, Oregon, USA, using culture-based techniques, and found that communities differed significantly by site. Our results suggest that the fungal endophyte community composition in red alder leaves may be influenced in part by local air pollution sources, likely in conjunction with other site characteristics. As urban areas expand, more studies should focus on how the urban environment affects plant–microbe community ecology and endophyte–host interactions, as well as on the long-term consequences for other ecosystem processes such as leaf litter decomposition. [ABSTRACT FROM AUTHOR]

• Red alder shows promise to aid in soil health post-fire. • Mixed stands with red alder demonstrated increased site index. • Douglas-fir site index continued to increase after alders died out. • Airborne lidar can be used to compare tree height when updated field data unavailable. A forester set up a large-scale, 1600-m fire-break trial with red alder (Alnus rubra Bong.) inter-planted between Douglas-fir (Pseudotsuga menziesii Mirb Franco) , after the extensive 1927 Yacolt Burn in the Columbia Gorge. This now 90-year-old trial demonstrates dramatic effects of alder on soils and growth of Douglas-fir; it also provides a timely lesson for foresters deciding what to do after recent similar fires in western Oregon and Washington. We used 2015 airborne lidar to re-examine the trial effects. Douglas-fir trees in stands mixed with alder (Strip) continue to grow taller than those in adjacent pure stands (Controls), even though almost all alder died out 30–40 years ago. Site index in Strip stand continues to increase relative to Controls, now averaging 30–40 % higher than Controls. Basal area ha−1 is 2.1, and stem biomass is 2.8 times higher in Strip than Control stands. Implications and future studies are discussed. Before planting wall-to-wall Douglas-fir, foresters responding to new fires in this region might contemplate alder interplanting and crop rotation for their likely positive effect on future revenue, wildlife, and carbon sequestration rates and storage above and belowground. [ABSTRACT FROM AUTHOR]

Carbon allocation demands from root-nodulating nitrogen-fixing bacteria (NFB) can modulate the host plant's chemical phenotype, with strong bottom-up effects on herbivores. In contrast to well-studied rhizobia, the effects of other important NFB on plant chemistry and herbivory are much less understood. Here, combining field surveys in the Oregon Coast Range, USA with laboratory experiments, we analyzed how N-fixing Frankia bacteria influenced plant growth, chemistry, and herbivory on Alnus rubra (red alder) seedlings. In the field, we quantified Frankia nodulation, herbivore damage, and plant size. In the laboratory, we grew seedlings with Frankia (F+), Frankia-free but nitrogen-fertilized (N+), or both uncolonized and unfertilized (F−N−) and assessed growth and leaf chemistry. We further conducted choice trials with black slugs, Arion rufus, a natural red alder herbivore. In the field, Frankia nodulation was significantly positively correlated with herbivory and negatively with seedling height. In contrast, in the lab, F+ as well as N+ seedlings were significantly taller than the F−N− controls. Seedlings from both treatments also had significantly increased leaf protein concentration compared to controls, whereas carbon-based nutritive compounds (carbohydrates) as well as leaf palatability-decreasing condensed tannins, lignin, and fiber were decreased in F+ but not in N+ treatments. In the choice assays, slugs preferred leaf material from F+ seedlings, but the effects were only significant in young leaves. Our study indicates that colonization by Frankia causes short-term ecological costs in terms of susceptibility to herbivory. However, the ubiquity of this symbiosis in natural settings suggests that these costs are outweighed by benefits beyond the seedling stage. [ABSTRACT FROM AUTHOR]

Highlights • Red alder density of up to 400 tph may be acceptable on nitrogen deficient sites. • Douglas-fir growth may be enhanced when red alder density is relatively low at age 15. • Competitive effects of red alder were lower than that of conifers in this study. • The effectiveness of competition indices varies with tree species. Abstract Red alder (Alnus rubra [Bong.]), is the most common broadleaf species in the Pacific Northwest, and is widely distributed as a component of mixed stands with conifers. It rapidly overtops associated juvenile conifers and is a strong competitor. However, red alder is also a symbiotic nitrogen fixer and can contribute to improvement in soil nitrogen, as well as serving other roles such as improving biodiversity and forest health. We examined data collected in mixed red alder-conifer plantations established between 1992 and 1999 to examine the effects of red alder on the growth of Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco, Fd) and western redcedar (Thuja plicata Donn., Cw). Results suggest that densities of up to 400 alder trees per hectare may be acceptable and possibly desirable on nitrogen deficient sites. The growth of Fd may be enhanced when red alder density is relatively low at older ages. We found that the competitive effects of red alder on conifer growth were consistently lower than that of the conifers (Fd and Cw) while alder had stronger effects on light availability. The relationship between volume growth and competition indices varied between the two conifer species: (1) for Fd the highest correlations were obtained using a distance-dependent competition index based on the height differences, and (2) for Cw the highest correlations were with distance-independent Lorimer's index. As also expected due to Cw's greater shade tolerance, its volume growth showed less sensitivity to the presence of red alder than Fd. [ABSTRACT FROM AUTHOR]

The White-footed Vole ( Arborimus albipes) is one of the least-studied small mammals in North America. Most reported occurrence data come from incidental captures from larger trapping efforts and have demonstrated a strong affinity for Red Alder ( Alnus rubra) trees. Recent research represented a range expansion in western Oregon, but little is known about the species at the southern end of its range in California. We developed a distribution model for the species to identify areas best targeted for additional White-footed Vole research. We used this model to survey by trapping in Humboldt and Del Norte Counties, California, and documented 3 new occurrences for the species. These 3 occurrences were incorporated into a final distribution model. This model suggests the possibility of White-footed Vole occurrence in southern Humboldt and northern Mendocino Counties, which would represent a southern expansion of their range. White-footed Voles were captured in areas with smaller alders than non-capture areas, supporting work from Oregon that suggests the species may not be tied to older stands as had been previously reported. Targeted trapping and physiological studies could clarify the environmental niche of this vole. [ABSTRACT FROM AUTHOR]

• Similar total stand volumes were found in 20-year-old mixtures and pure stands of western redcedar and red alder. • Soil N increased with increasing red alder proportion with increases in exchangeable cations (K, Ca, and Mg) and C in the soil under pure red alder. • Western redcedar height and diameter growth were found to surpassed alder growth performance in the last 7 years. A replacement series designed trial containing mixed and pure stands of western redcedar and red alder (cedar: alder; 100:0, 75:25, 50:50, 0:100) was monitored over a 20-year period. Tree and stand growth performance across the pure and mixed species treatments were inconclusive. Inherent site variation in soils and microclimate resulted in a range of survival and productivity responses. After twenty years since planting, total stand volumes were similar across the treatments, ranging between 145 and 165 m3/ha. Average cedar height and diameter growth performance surpassed alder growth performance in the last 7 years. Soil C, N and exchangeable cations (K, Ca, and Mg) trended towards greater accumulation with increasing red alder proportion. These observations indicate cedar in combination with alder may further benefit from enhanced soil fertility over the next decades as stands continue to develop. [ABSTRACT FROM AUTHOR]

The phenology of many species is shifting in response to climatic changes, and these shifts are occurring at varying rates across species. This can potentially affect species' interactions and individual fitness. However, few studies have experimentally tested the influence of warming on the timing of species interactions. This is an important gap in the literature given the potential for different direct and indirect effects of temperature via phenological change., Our aim was to test the effects of warming on the western tent caterpillar ( Malacosoma californicum pluviale). In addition to the direct effects of warming, we considered the two primary indirect effects mediated by warming-driven changes in its host plant, red alder ( Alnus rubra): changes in resource availability due to phenological mismatch (i.e. changes in the relative timing of the interaction), and changes in resource quality associated with leaf maturation., We experimentally warmed egg masses and larvae of the western tent caterpillar placed on branches of red alder in the field., Warming advanced the timing of larval but not leaf emergence. This led to varying degrees of phenological mismatch, with larvae emerging as much as 25 days before to 10 days after the emergence of leaves. Even the earliest-emerging larvae, however, had high survival in the absence of leaves for up to 3 weeks, and they were surprisingly resistant to starvation. In addition, although warming created phenological mismatch that initially slowed the development of larvae that emerged before leaf emergence, it accelerated larval development once leaves were available. Therefore, warming had no net effect on our measures of insect performance., Our results demonstrate that the indirect effects of warming, in creating phenological mismatch, are as important to consider as the direct effects on insect performance. Although future climatic warming might influence plants and insects in different ways, some insects may be well adapted to variation in the timing of their interactions. [ABSTRACT FROM AUTHOR]

Red alder ( Alnus rubra), a nitrogen(N)-fixing deciduous broadleaf tree, can strongly influence N concentrations in western Oregon and Washington. We compiled a database of stream N and GIS-derived landscape characteristics in order to examine geographic variation in N across the Oregon Coast Range. Basal area of alder, expressed as a percent of watershed area, accounted for 37% and 38% of the variation in summer nitrate and total N (TN) concentrations, respectively. Relationships between alder and nitrate were strongest in winter when streamflow and landscape connections are highest. Distance to the coast and latitude, potential surrogates for sea salt inputs, and watershed area were also related to nitrate concentrations in an all-subsets regression analysis, which accounted for 46% of the variation in summer nitrate concentrations. The model with the lowest Akaike's Information Criterion did not include developed or agricultural land cover, probably because few watersheds in our database had substantial levels of these land cover classes. Our results provide evidence, at a regional scale, that background sources and processes cause many Coast Range streams to exceed proposed nutrient criteria, and that the prevalence of a single tree species (N-fixing red alder) exerts a dominant control over stream N concentrations across this region. [ABSTRACT FROM AUTHOR]

Soil exchanges of greenhouse and other gases are poorly known for Pacific Northwest forests where gradients in nutrient availability and soil moisture may contribute to large variations in fluxes. Here we report fluxes of methane (CH4), nitrous oxide (N2O), and nitric oxide (NO) over multiple seasons from three naturally N-rich, aggrading forests of coastal Oregon, USA. Mean methane uptake rates (3.2 mg CH4 m−2 d−1) were high compared with forests globally, negatively related to water-filled pore space (WFPS), but unrelated to N availability or temperature. Emissions of NO (6.0 μg NO-N m−2 h−1) exceeded N2O (1.4 μg N2O-N m−2 h−1), except when WFPS surpassed 55%. Spatial variation in NO fluxes correlated positively with soil nitrate concentrations (which generally exceeded ammonium concentrations, indicating the overall high N status for the sites) and negatively with soil pH, and at one site increased with basal area of N2-fixing red alder. Combined NO and N2O emissions were greatest from the site with highest annual net N mineralization and lowest needle litterfall C/N. Our findings of high CH4 uptake and NO/N2O ratios generally >1 most likely reflect the high porosity of the andic soils underlying the widespread regenerating forests in this seasonally wet region. [ABSTRACT FROM AUTHOR]

A general form for expressing gross volume increment in terms of stand density is derived and tested with data from spacing trials in red alder ( Alnus rubra Bong.), eastern white pine ( Pinus strobus L.), longleaf pine ( Pinus palustris Mill.), and loblolly pine ( Pinus taeda L.). The equation relates the stand sum of individual-tree volume increment per metre height increment to a power function of quadratic mean diameter times tree density. The proposed equation fit the data best when the model included an intercept. Within each species, the fits were unbiased with respect to the independent variables, plantation age, and site height, and with the exception of the youngest ages for red alder and loblolly pine, they were unbiased with respect to the plot sums of individual-tree volume increment divided by individual height increment. Exponents estimated for quadratic mean diameter for each species ranged from 1.58 to 1.80. The resulting equations indicate a linear relationship between the stand sum of individual-tree volume increment per metre height increment and stand density. Scattergrams of gross-volume increment per hectare per year and stand density can be recovered by multiplying the predicted values of the regressions by Lorey's height. The regressions support the hypothesis that each metre of height growth produces consistent changes in stem size, regardless of initial tree size, age, or site quality, and implies that the change in stem size is a predictable power function of stem diameter for an individual tree or quadratic mean diameter for a stand. [ABSTRACT FROM AUTHOR]

Biomass estimates are required for reporting carbon, assessing feedstock availability, and assessing forest fire threat. We developed diameter- and height-based biomass equations for Western hemlock (Tsuga heterophylla (Raf.) Sarg.) and red alder (Alnus rubra Bong.) trees inWestern Oregon. A system of component biomass equations was fitted simultaneously with a constrained seemingly unrelated regression. Additionally, a linear model that predicts total aboveground biomass as a function of DBH and height was also fitted. The predicted total biomass was then apportioned to different components according to the predicted proportions from beta, Dirichlet, and multinomial log-linear regressions. Accuracy of these methods differed between species with higher root mean squared error (RMSE) being produced in red alder trees. Within species, the accuracy of the equation for bole biomass was better than the equations for other components. None of these methods stood out as a clear winner, but the multinomial log-linear regression produced marginally better results compared to other methods in terms of RMSE, except for Western hemlock bark biomass and red alder bole and branch biomass. The equations based on a seemingly unrelated regression provided lower RMSEs for those species-component combinations. [ABSTRACT FROM AUTHOR]

Riparian-zone vegetation can influence terrestrial and aquatic food webs through variation in the amount, timing, and nutritional content of leaf and other litter inputs. We investigated how riparian- forest community composition, understory density, and lateral slope shaped vertical and lateral litter inputs to 16 streams in the Oregon Coast Range. Riparian forests dominated by deciduous red alder delivered greater annual vertical litter inputs to streams (504 g m-2 y-1) than did riparian forests dominated by coniferous Douglas-fir (394 g m-2y-1). Deciduous forests also contributed greater lateral litter inputs per meter of stream bank on one side (109 g m-1y-1) than did coniferous forests (63 g m-1y-1). Total litter inputs from deciduous forests exceeded those from coniferous forests most strongly in November, coincident with an autumn peak in litter inputs. Lateral litter inputs contributed most to total inputs during winter in both forest types. Annual lateral litter movement increased with slope at deciduous sites, but only in spring/ summer months at coniferous sites. Neither experimental removal of understory vegetation nor installation of mesh fences to block downslope litter movement affected lateral litter inputs to streams, suggesting that ground litter moves <5 m downslope annually. N concentrations of several litter fractions were higher at deciduous sites and, when combined with greater litter amounts, yielded twice as much total litter N flux to streams in deciduous than coniferous sites. The presence of red alder in riparian forests along many small streams of the deeply incised and highly dendritic basins of the Oregon Coast Range enhances total fluxes and seasonality of litter delivery to both terrestrial and aquatic food webs in this region and complements the shade and large woody debris provided by large coniferous trees. [ABSTRACT FROM AUTHOR]

Symbiotic N-fixing tree species can accelerate ecosystem N dynamics through decomposition feedbacks via both direct and indirect pathways. Direct pathways include the production of readily decomposed leaf litter and increased N supply to decomposers, whereas indirect pathways include increased tissue N and altered detrital dynamics of non-fixing vegetation. To evaluate the relative importance of direct and indirect pathways, we compared 3-year decomposition and N dynamics of N-fixing red alder leaf litter (2.34% N) to both low-N (0.68% N) and high-N (1.21% N) litter of non-fixing Douglas-fir, and decomposed each litter source in four forests dominated by either red alder or Douglas-fir. We also used experimental N fertilization of decomposition plots to assess elevated N availability as a potential mechanism of N-fixer effects on litter mass loss and N dynamics. Direct effects of N-fixing red alder on decomposition occurred primarily as faster N release from red alder than Douglas-fir litter. Direct increases in N supply to decomposers via experimental N fertilization did not stimulate decomposition of either species litter. Fixed N indirectly influenced detrital dynamics by increasing Douglas-fir tissue and litter N concentrations, which accelerated litter N release without accelerating mass loss. By increasing soil N, tissue N, and the rate of N release from litter of non-fixers, we conclude that N-fixing vegetation can indirectly foster plant-soil feedbacks that contribute to the persistence of elevated N availability in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims: General theory of forest floor dynamics indicates convergence of properties during detrital decomposition. This study examined the hypothesis that nutrient stoichiometry, i.e. the relative amounts of nutrients, converges during litter decomposition. Methods: Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) and red alder ( Alnus rubra Bong.) foliar litters that decomposed in their respective forests were analyzed for N, P, Ca, Mg, K, S, Mn, Fe, Zn, and Cu. A novel approach quantified the stoichiometric difference as the angle between nutrient vectors. The approach was also used to synthesize data from 11 previously published studies representing a broad array of litter types and locations. Results: The stoichiometries of the Douglas-fir and red alder litters converged during the first 2 years of decomposition, but diverged in the subsequent 4 years. This temporal trajectory was explained by two competing sets of processes: stoichiometric convergence occurs when different litters decompose in the same environment, and divergence occurs when the same litter decomposes in different environments. Manganese, Fe, and Ca were important contributors to stoichiometric differences. Conclusions: Stoichiometric convergence processes often dominate over divergence processes. Consideration of multi-nutrient stoichiometries may enhance the understanding of the functions of litter, including rates of decomposition and relative rates at which nutrients are released. [ABSTRACT FROM AUTHOR]

While aboveground biomass and forest productivity can vary over abiotic gradients (e.g., temperature and moisture gradients), biotic factors such as biodiversity and tree species stand dominance can also strongly influence biomass accumulation. In this study we use a permanent plot network to assess variability in aboveground carbon (C) flux in forest tree annual aboveground biomass increment (ABI), tree aboveground net primary productivity (ANPPtree), and net soil CO2 efflux in relation to diversity of coniferous, deciduous, and a nitrogen (N)-fixing tree species (Alnus rubra). Four major findings arose: (1) overstory species richness and indices of diversity explained between one third and half of all variation in measured aboveground C flux, and diversity indices were the most robust models predicting measured aboveground C flux; (2) trends suggested decreases in annual tree biomass increment C with increasing stand dominance for four of the five most abundant tree species; (3) the presence of an N-fixing tree species (A. rubra) was not related to changes in aboveground C flux, was negatively related to soil CO2 efflux, and showed only a weak negative relationship with aboveground C pools; and (4) stands with higher overstory richness and diversity typically had higher soil CO2 efflux. Interestingly, presence of the N-fixing species was not correlated with soil inorganic N pools, and inorganic N pools were not correlated with any C flux or pool measure. We also did not detect any strong patterns between forest tree diversity and C pools, suggesting potential balancing of increased C flux both into and out of diverse forest stands. These data highlight variability in second-growth forests that may have implications for overstory community drivers of C dynamics. [ABSTRACT FROM AUTHOR]

Hood Canal, Washington, USA, is a poorly ventilated fjord-like sub-basin of Puget Sound that commonly experiences hypoxia. This study examined the influence of watershed soils, vegetation, physical features, and population density on nitrogen (N) export to Hood Canal from 43 tributaries. We also linked our watershed study to the estuary using a salinity mass balance model that calculated the relative magnitude of N loading to Hood Canal from watershed, direct precipitation, and marine sources. The overall flow-weighted total dissolved N (TDN) and particulate N input concentrations to Hood Canal were 152 and 49 μg l, respectively. Nitrate and dissolved organic N comprised 64 and 29% of TDN, respectively. The optimal regression models for TDN concentration and areal yield included a land cover term suggesting an effect of N-fixing red alder ( Alnus rubra) and a human population density term (suggesting onsite septic system (OSS) discharges). There was pronounced seasonality in stream water TDN concentrations, particularly for catchments with a high prevalence of red alder, with the lowest concentrations occurring in the summer and the highest occurring in November-December. Due to strong seasonality in TDN concentrations and in particular stream flow, over 60% of the TDN export from this watershed occurred during the 3 month period of November-January. Entrainment of marine water into the surface layer of Hood Canal accounted for ≈98% of N loading to the euphotic zone of this estuary, and in a worst case scenario OSS N inputs contribute ≈0.5% of total N loading. Domestic wastewater discharges and red alders appear to be a very important N source for many streams, but a minor nutrient source for the estuary as a whole. [ABSTRACT FROM AUTHOR]

This study examined the effect of host species identity on the structure of Alnus-associated Frankia bacterial assemblages in the Pacific Northwest, United States, using two approaches. First, Frankia in nodules were sampled from six stands of Alnus rubra or Alnus viridis. Second, a bioassay was conducted where A. rubra and A. viridis seedlings were grown in different soils collected from these two hosts. Frankia genotypes were characterized with nifH sequences and bacterial assemblages were compared using taxon- and divergence-based analyses. Strong host associations were evident in the field; the dominant Frankia genotypes showed significant associations with either A. rubra or A. viridis, and there were host-associated groupings at the assemblage level as well. In the bioassay, host associations among Frankia genotypes were evident but less pronounced, reflecting an interaction between host species and other factors. Although nodule abundance varied among bioassay treatments, seedling dry mass was not strongly correlated with either nodule quantity or soil chemistry. Collectively, our observation and experimental results indicate that host identity is a major factor influencing the genotype composition and abundance of Alnus-associated Frankia assemblages. [ABSTRACT FROM AUTHOR]

Cross-boundary flows of energy and nutrients link biodiversity and functioning in adjacent ecosystems. The composition of forest tree species can affect the structure and functioning of stream ecosystems due to physical and chemical attributes, as well as changes in terrestrial resource subsidies. We examined how variation in riparian canopy composition (coniferous, deciduous, mixed) affects adjacent trophic levels (invertebrate and microbial consumers) and decomposition of organic matter in small, coastal rainforest streams in southwestern British Columbia. Breakdown rates of higher-quality red alder (Alnus rubra) litter were faster in streams with a greater percentage of deciduous than coniferous riparian canopy, whereas breakdown rates of lower-quality western hemlock (Tsuga heterophylIa) litter were independent of riparian forest composition. When invertebrates were excluded using fine mesh, breakdown rates of both litter species were an order of magnitude less and were not significantly affected by riparian forest composition. Stream invertebrate and microbial communities were similar among riparian forest composition, with most variation attributed to leaf litter species. Invertebrate taxa richness and shredder biomass were higher in A. rubra litter; however, taxa evenness was greatest for T. heerophylla litter and both litter species in coniferous streams. Microbial community diversity (determined from terminal restriction fragment length polymorphisms) was unaffected by riparian forest or litter species. Fungal allele richness was higher than bacterial allele richness, and microbial communities associated with lower-quality T. heterophylla litter had higher diversity (allele uniqueness and richness) than those associated with higher-quality A. rubra litter. Percent variation in breakdown rates was mostly attributed to riparian forest composition in the presence of invertebrates and microbes; however, stream consumer biodiversity at adjacent trophic levels did not explain these patterns. Riparian and stream ecosystems and their biotic communities are linked through exchange and decomposition of detrital resources, and we provide evidence that riparian forest composition affects stream ecosystem catabolism despite similarities in microbial and invertebrate communities. [ABSTRACT FROM AUTHOR]

To quantify the genetic diversity of Frankia bacteria associated with Alnus rubra in natural settings and to examine the relative importance of site age, management, and geographic location in structuring Frankia assemblages in A. rubra forests, root nodules from four A. rubra sites in the Pacific Northwest, USA were sampled. Frankia genetic diversity at each site was compared using sequence-based analyses of a 606 bp fragment of the nifH gene. At a 3% sequence similarity cutoff, a total of 5 Frankia genotypes were identified from 317 successfully sequenced nodules. Sites varied in the total number of genotypes present, but were typically dominated by only one or two genotypes. Phylogenetic analyses showed that all of the A. rubra-Frankia genotypes grouped with other Alnus-infective Frankia. Analysis of similarity (ANOSIM) and chi-square analyses indicated that Frankia assemblages were more strongly influenced by site age/management than geographic location. This study demonstrates that the Frankia assemblages in A. rubra forests have low genotype diversity, but that genotype abundance can differ significantly in forests of different age/management history. [ABSTRACT FROM AUTHOR]

1. After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (‘flexible’ red alder leaves and three ‘stiff’ particle types – Douglas-fir needles, red cedar fronds and Douglas-fir branch pieces). 2. Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas-fir needles and red cedar fronds, which all reached constant still-water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3. We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ‘riffle’ than a slow, deep ‘pool’. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4. These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second-order coastal stream. 5. When the experimental channel and in-stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams. [ABSTRACT FROM AUTHOR]

In recent decades, red alder (Alnus rubra Bong.) has become an important Pacific Northwest hardwood in appearance-grade lumber markets, such as exports, furniture, and cabinets. However, red alder generally is a short-lived pioneer species, and small logs can result in proportionally large volumes of lower grade lumber containing numerous visual defects, such as knots, often referred to as character marks. Given that markets for character-marked wood could provide an income stream for management of red alder, it becomes important to understand consumer and retailer response to character-marked red alder products. In the current study, we used a policy capturing approach (the lens model) to assess the cues used by furniture consumers and retailers to evaluate several furniture pieces constructed from character-marked red alder lumber. The cues used by consumers and retailers to form willingness-to-pay judgments were found to be different. Character marks, design, and naturalness were important to consumers. None of the investigated cues were significant to retailers, suggesting they were using an entirely different model. Such divergence creates challenges in the forestry supply chain for development of new forest products. [ABSTRACT FROM AUTHOR]

Abstract: River flow regulation by dams for hydroelectric generation has been a common practice worldwide for centuries, with diverse ecological impacts. We studied upstream and downstream reaches of three British Columbia Hydro reservoirs on the Allouette, Coquitlam, and Cheakamus Rivers to determine if riparian plant communities were affected by the dams. We determined cover of all plants in consecutive 1m2 quadrats along five to six 14m-long belt transects in each 300m upstream and downstream sections of these rivers. We encountered 166 plant species in a total of 448 quadrats. Differences in plant communities (abundance, species richness, diversity) amongst rivers were larger than that between the upstream versus downstream of the rivers. This suggests that any difference caused by reservoir management was within the natural range of variation found across the rivers. We found significant reductions in the occurrences of red alder and western red cedar downstream of reservoirs. The lack of regeneration of these two species may be attributable to the reduction in extremes of flow variation and lack of sediment transport due to the reservoirs. Coordinated flow management can help mitigate these downstream impacts. [Copyright &y& Elsevier]

Abstract: Canopy-held organic matter develops into a distinct soil system separate from the forest floor in wet temperate coniferous forests, creating a natural microcosm. We distinguished between fungal and bacterial components of the decomposer community in one site with Maple (Acer macrophyllum) and one site with Alder (Alnus rubra) by using direct measurements of growth; acetate incorporation into ergosterol, and leucine incorporation for fungi and bacteria, respectively. The higher organic matter content of the canopy soils correlated with higher fungal growth. The relative importance of fungi, indicated by fungal:bacterial growth ratio, was higher in the canopy soil of the Maple site, while there was no difference in the Alder site. The high C:N ratio of the Maple canopy soil likely contributed to this difference. These results demonstrate a divergence between canopy and forest floor that should be explored to gain insights in decomposer ecology using the natural microcosms that the canopy soils provide. [Copyright &y& Elsevier]

Abstract: A study was conducted at two experimental tree plantations in the Pacific Northwest to assess the roles of bacteria and fungi in nitrogen (N) cycling. Soils from red alder (Alnus rubra) and Douglas-fir (Pseudotsuga menziesii) plots in low- (H.J. Andrews) and high- (Cascade Head) productivity stands were sampled in 2005 and 2006. Fungal:bacterial ratios were determined using phospholipid fatty acid (PLFA) profiles and quantitative (Q)-PCR. Ratios from these two molecular methods were highly correlated and showed that microbial biomass varied significantly between the two experimental sites and to a lesser extent between tree types with fungal:bacterial biomass ratios lower in more N-rich plots. 15N isotope dilution experiments, with ammonium (NH4 +) and nitrate (NO3 −), were paired with antibiotics that blocked bacterial (bronopol) and fungal (cycloheximide) protein synthesis. This modified isotope dilution technique was used to determine the relative contribution of bacteria and fungi to net N mineralization and gross rates of ammonification and nitrification. When bacterial protein synthesis was blocked NH4 + consumption and nitrification rates decreased in all treatments except for NH4 + consumption in the Douglas-fir plots at H.J. Andrews, suggesting that prokaryotic nitrifiers are a major sink for mineral NH4 + in forest soils with higher N availability. Cycloheximide consistently increased NH4 + consumption, however the trend was not statistically significant. Both antibiotics additions also significantly increased gross ammonification, which may have been due to continued activity of extra- and intracellular enzymes involved in producing NH4 + combined with the inhibition of NH4 + assimilation into proteins. The implication of this result is that microorganisms are likely a major sink for soil dissolved organic N (DON) in soils. [Copyright &y& Elsevier]

Abstract  Studies on Alnus rubra Bong. (red alder) were carried out to assess its potential for use as a component of a silvopastoral system. Comparison was between two treatments: red alder at 400 stems ha−1 (silvopasture) and red alder at 2,500 stems ha−1 (forestry control). δ15N values close to zero were recorded in all red alder plant parts except for root nodules, indicating that a large proportion of N in red alder was fixed from the atmosphere. Overall, it was estimated that there was 63.45 kg N ha−1 fixed N accumulated in red alder trees, and the rate of N fixation was estimated at 30.95 kg ha−1 year−1 in the silvopasture treatment. The total amount of N that could potentially be added to the soil in the silvopasture treatment as a result of decomposition of senescent leaves, roots, and dead nodules was estimated at 40.56 kg ha−1 year−1. Of the total N added to the soil, 27.1 kg ha−1 year−1 was due to N fixation from the atmosphere. These results show that red alder has a potential to improve and maintain soil fertility in a silvopastoral system. [ABSTRACT FROM AUTHOR]

Coastal rainforests of southeast Alaska have relatively simple species composition but complex structures with high diversity of tree ages, sizes and forest canopy layers, and an abundant understory plant community. Wildlife and fisheries resources also play an important role in the ecological functioning of forest and aquatic systems. Clearcutting has greatly altered these forest ecosystems with significant decreases in structural diversity of forest stands and greatly reduced wildlife habitat. This paper synthesizes information on management options in older forests that have never been actively managed, and in younger forests to increase diversity of stand structures and their associated effects on biodiversity. Light to moderate levels of partial cutting in old-growth forests can maintain the original diversity of overstory stand structures and understory plant communities. In younger forests that develop after clearcutting, mixed alder-conifer stands provide more heterogeneous structures and significantly higher understory biomass than in pure conifer forests. Research has shown that red alder increases diversity and abundance of understory plants, and provides forage for deer and small mammals. Results also show a clear linkage between alder and improved invertebrate diversity in aquatic systems. A combination of light partial cutting in older forests along with inclusion of red alder in conifer-dominated forests could provide the greatest amount of diversity and maintain the complex stand structures that are an important component of these forest ecosystems. [Copyright &y& Elsevier]

Studies on red alder (Alnus rubra Bong.) and sycamore (Acer pseudoplatanus L.) were carried out to assess their timber and wood-fuel properties when grown at wide spacing as in a silvopastoral system. Initial tree-planting density had significant effects on the modulus of elasticity (MOE) in red alder and compression strength in sycamore. Wood samples taken from red alder in high-density plots of 2500 stems·ha–1 had a significantly higher MOE than those from trees in low-density plots of 400 stems·ha–1 (silvopastoral system). Sycamore wood from the high-density plots had significantly higher compression strength than that from the low-density plots. However, there was no significant effect of planting density on the modulus of rupture in either species. On average, red alder had lower wood density, modulus of rupture, and compression strength than sycamore, but there was no significant difference in MOE between the two species. Planting density did not have any effect on the wood-fuel higher heating value of either red alder or sycamore, nor was there a significant difference in wood-fuel higher heating value between the two species. However, red alder wood had a significantly higher fuel-value index than sycamore, owing to its lower ash content. [ABSTRACT FROM AUTHOR]