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Abstract: Current management practices encourage conversion of red alder (Alnus rubra) riparian forests to conifers in the Pacific Northwest U.S. Patches of young naturally regenerated conifers are commonly present in alder dominated riparian areas and an understanding of the soil processes in these patches will be helpful in guiding future riparian management. Study objectives were to: (1) determine decomposition rates of red alder leaves in riparian alder and conifer patches, (2) relate decomposition rates to environmental factors and litter chemistry, and (3) determine nutrient release from decomposing alder leaves in these patches. Study sites were riparian areas adjacent to Brown and Le Bar creeks in the Skokomish River basin, Olympic National Forest, Washington. Red alder leaves were placed in litterbags in red alder and conifer riparian patches along each stream in November 2000 and collected after 1 and 3 years. There was rapid mass loss of alder leaves in the first year in both patch types, but decomposition was significantly faster (p <0.05) in alder patches (43.2% mass remaining, k =0.855year−1) than in conifer patches (48.4% mass remaining, k =0.734year−1). There was little mass loss after the first year and no significant difference in decomposition rates. After 3 years mass remaining was 44.2% (k =0.283year−1) and 47.8% (k =0.48year−1) in alder and conifer patches, respectively. Decomposition rate differences were attributed more to the effects of the different litters in each patch and the influence on soil microbial and faunal communities than differences in soil temperature and moisture. The forest floor was deeper in conifer patches (3.7cm) than alder (1.8cm) patches. This was ascribed to slower decomposition rates in conifer patches, greater litterfall in conifer patches, and/or removal of alder surface litter by flooding. Alder patches were lower in elevation (0.8m above bankfull width) than conifer patches (2.2m). Forest floor and soil C and N concentrations and pHs were not significantly different in alder and conifer patches. Nutrient release from decomposing alder leaves was not significantly different in conifer and alder patches, although there was a trend for C, N, P, K, and Ca to be lost faster from leaves in alder patches than conifer patches in the first year. Red alder litter input to riparian conifer patches will initially decompose rapidly and provide nutrients, particularly N and P to conifers, as well as enhancing soil C since long-term decomposition rates are slow. [Copyright &y& Elsevier]

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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: Height growth equations for dominant trees are needed for growth and yield projections, to determine appropriate silvicultural regimes, and to estimate site index. Red alder [Alnus rubra Bong.] is a fast-growing hardwood species that is widely planted in the Pacific Northwest, USA. However, red alder dominant height growth equations used currently have been determined using stem analysis trees from natural stands rather than repeated measurements of stand-level top height from plantations, which may cause them to be biased. A regional dataset of red alder plantations was complied and used to construct a dynamic base-age invariant top height growth equation. Ten anamorphic and polymorphic Generalized Algebraic Difference Approach (GADA) forms were fit using the forward difference approach. The Chapman–Richards anamorphic and Schumacher anamorphic model forms were the only ones with statistically significant parameters that yielded biologically reasonable predictions across a full range of the available data. The Schumacher model form performed better on three independent datasets and, therefore, was selected as the final model. The resulting top height growth equations differed appreciably from tree-level dominant height growth equations developed using data from natural stands, particularly at the younger ages and on lower site indices. Both the rate and shape parameters of the Schumacher function were not influenced by initial planting density. However, this analysis indicates that the asymptote, which is related to site index, may be reduced for plantations with initial planting density below 500treesha−1. The final equation can be used for predictions of top height (and thus) site index for red alder plantations across a range of different growing conditions. [Copyright &y& Elsevier]

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: The composition and structure of riparian forests in the coast redwood region were analyzed in relation to the length of time since timber harvest, and the width of riparian buffer zone. Ten sites were sampled in the central range of the coast redwood forest type within a variety of post-harvest age groups and riparian buffer zone widths. Data was collected using randomly selected sample plots adjacent to perennial coastal steams. Correlation Fisher''s r to z tests and two-tailed t-test were used to examine the relationship between the sample variables and the experimental parameters “years since harvest”, and “width of buffer.” Results indicate that canopy cover was negatively correlated to “years since harvest” with the highest level of canopy cover found on the youngest sites and the lowest level found on the old-growth sites. The hardwood to conifer dominance ratio and the basal area of Alnus rubra (red alder) were correlated negatively to both “years since harvest” and “buffer width” indicating that timber harvest favored hardwood species. Late seral associates such as Oxalis oregana (redwood sorrel), Anthyrium filix-femina (lady fern), and Vaccinium parviflorum (billberry) were found preferentially in older forests and sites with wider buffer zones, while non-native species such as Hedera helix (English ivy), Pampas cortedaria (pampas grass), and Myosotis latifolia (forget-me-not) were found preferentially in younger forests and areas with smaller buffer zones. [Copyright &y& Elsevier]

Abstract: We examined the effects of competition from red alder (Alnus rubra Bong.) and paper birch (Betula papyrifera Marsh.) on the growth of western redcedar (Thuja plicata Donn), western hemlock (Tsuga heterophylla Sarg.), and Douglas-fir (Pseudotsuga menziesii Franco) at a site near Maple Ridge, British Columbia, Canada. At this site, the three coniferous species and two broadleaf species had been planted in 1999 as part of a long-term experiment examining effects of broadleaf density on conifer growth. Red alder and paper birch were planted alone and as a 50:50 mixture at four densities (0, 277, 556, and 1150stemsha−1). Red alder density was positively correlated with total available nitrogen in soil measured using ion-exchange membranes whereas density of paper birch was not. For Douglas-fir only, foliar N concentration was positively related to red alder density. Relationships between stem volume increment and competition indices varied between the three conifer species: (1) For Douglas-fir the highest correlations were obtained using a distance-independent competition index based on broadleaf crown surface area and diffuse transmittance (DIFN) measured using LAI-2000 plant canopy analyzers had the lowest R 2 of the competition measures tested; (2) for western redcedar the highest correlations were with DIFN and the second best competition measures were distance-dependent indices; (3) for western hemlock broadleaf competition did not have significant effects on growth. Height of each species at the time of measurement and crown surface area appear to be more important than shade tolerance in affecting conifer growth. At this site, significant reductions in stem volume (30%) of Douglas-fir and western redcedar occurred when red alder density exceeded 500stemsha−1 while paper birch was not detrimental to western redcedar growth until densities exceeded 1000stemsha−1 and birch density did not significantly affect Douglas-fir. The influence of red alder on soil N and foliar N of Douglas-fir may be leading to a weaker relationship between growth and DIFN for Douglas-fir compared to that for western redcedar. [Copyright &y& Elsevier]

Ten-year data on growth and survival of two red alder provenance-progeny test trials located in the southern and northern coastal regions in British Columbia, Canada, were analysed and their implications for the genetic improvement of this species were discussed. A total of 42 and 41 provenances, each represented by two to five open pollinated families were evaluated at each site, respectively. Results indicate that red alder provenances responded differently to the environmental conditions of the two sites. At age 10, red alder provenances tended to perform better at sites near their origin. The results support earlier work that two breeding zones should be delineated with the boundary at approximately 52° N. One may expect an average of about 5% decrease in stem volume and 6% increase in mortality, respectively, for each degree of southward and northward transfer of seed sources from their origins. Individual, family, and within-family heritabilities for height, diameter, stem volume were moderately high (0.22-0.42), for the southern zone, implying good potential for genetic improvement. Heritabilities were somewhat lower (0.12-0.39) for the northern zone because of greater environmental heterogeneity of the test site. Selecting the top 20 unrelated individuals for seed orchard establishment would result in 29% and 23% gain in stem volume at a rotation age of 40 years in the southern and northern zones, respectively. Correlation between ranks of the predicted breeding values for height at different ages and stem volume at age 10 increased rapidly when plantation was young and became relatively stable after 6 years of out planting. Stem volume had much stronger correlation with diameter (⩾0.84) than with height (⩽0.67). Early selection at age 6 based on stem volume is therefore recommended. [ABSTRACT FROM AUTHOR]

Litterfall and its subsequent decomposition are important feedback mechanisms in the intrasystem cycling of nutrients in forest ecosystems. The amount of litterfall and the rate of decomposition are expected to vary with stand age and climate. Over a 2-year period, decomposition of five litter types were measured in two second-growth forest stands and one old-growth stand in the Cascade Mountains of southern Washington state, USA. Both second-growth stands were dominated by Douglas-fir [ Pseudotsuga menziesii (Mirb.,) Franco] but one had a significant proportion of red alder ( Alnus rubra Bong.), a nitrogen (N) fixer. The old-growth stand was dominated by Douglas-fir and western hemlock [ Tsuga heterophylla (Raf.) Sarg.]. All stands had a relatively shallow layer of forest floor mass. The five litter types were placed in each stand to evaluate decomposition patterns. Despite significant differences in stand age, microclimate and mean residence times for carbon (C) and N, the rates of litter mass loss varied only slightly between sites. The relative order of species litter mass loss was: vine maple ≫ salal = western hemlock > Douglas-fir (from the youngest stand) > Douglas-fir (from the N rich stand with red alder). The initial litter lignin concentration, not lignin:N, was the primary determinant of decomposition rates, although the initial N concentration was the predictor for mass loss after 2 years in the N rich Douglas-fir-alder stand. All litter types showed immobilization of N for nearly 2 years. Data for Douglas-fir litter suggest that higher levels of N may retard decomposition of tissues with greater amounts of lignified material. The retention of N by the litter appeared influenced by the nutrient capital of the stands as well as the forest floor C:N ratio. Decomposition was minimal during the cold winter months, but displayed a definitive peak period during early Fall with wet weather, warm soils, and fungal activity. Thus, long-term climatic change effects on forest floor C storage may depend more on changes in seasonality of precipitation changes than just temperature changes. [ABSTRACT FROM AUTHOR]

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: Simulating the influence of intensive management and annual weather fluctuations on tree growth requires a shorter time step than currently employed by most regional growth models. High-quality data sets are available for several plantation species in the Pacific Northwest region of the United States, but the growth periods ranged from 2 to 12 years in length. Measurement periods of varying length complicate efforts to fit growth models because observed growth rates must be interpolated to a common length growth period or those growth periods longer or shorter than the desired model time step must be discarded. A variation of the iterative technique suggested by Cao [Cao, Q.V., 2000. Prediction of annual diameter growth and survival for individual trees from periodic measurements. Forest Sci. 46, 127–131] was applied to estimate annualized diameter and height growth equations for pure plantations of Douglas-fir, western hemlock, and red alder. Using this technique, fits were significantly improved for all three species by embedding a multi-level nonlinear mixed-effects framework (likelihood ratio test: p <0.0001). The final models were consistent with expected biological behavior of diameter and height growth over tree, stand, and site variables. The random effects showed some correlation with key physiographic variables such as slope and aspect for Douglas-fir and red alder, but these relationships were not observed for western hemlock. Further, the random effects were more correlated with physiographic variables than actual climate or soils information. Long-term simulations (12–16 years) on an independent dataset using these annualized equations showed that the multi-level mixed effects models were more accurate and precise than those fitted without random effects as mean square error (MSE) was reduced by 13 and 21% for diameter and height growth prediction, respectively. The level of prediction error was also smaller than an existing similar growth model with a longer time step (ORGANON v8) as the annualized equations reduced MSE by 17 and 38% for diameter and height growth prediction, respectively. These models will prove to be quite useful for understanding the interaction of weather and silviculture in the Pacific Northwest and refining the precision of future growth model projections. [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]

Factors (riparian stand condition, management regimes, and channel properties) affecting distributions of wood, detritus (leaves and branches), and sediment were examined in headwater streams draining young-growth red alder (Alnus rubra Bong.) – conifer riparian forests (< 40 years old) in southeast Alaska. More riparian red alder were found along streams affected by both timber harvesting and mass movement than in streams affected by timber harvesting alone. Young-growth stands produced little large wood material (diameter ≥10 cm) and had little effect on altering the size distribution of functional large wood in channels, although more alder wood pieces were found in streams with greater numbers of riparian alder trees. Legacy wood pieces (>40 years old) remained in channels and provided sites for sediment and organic matter storage. Despite various alder–conifer mixtures and past harvesting effects, the abundance of large wood, fine wood, and detritus accumulations significantly decreased with increasing channel bank-full width ( 0.5–3.5 m) along relatively short channel distances (up to 700 m). Changes in wood, detritus, and sediment accumulations together with changes in riparian stand characteristics create spatial and temporal variability of in-channel conditions in headwater systems. A component of alder within young-growth riparian forests may benefit both wood production and biological recovery in disturbed headwater stream channels. [ABSTRACT FROM AUTHOR]

Interest in mixed red alder (Alnus rubra Bong.) – conifer young-growth stands has grown in southeast Alaska, USA, because they appear to provide much more productive understory vegetation and wildlife habitat than do similar-aged pure conifer stands. We studied understory vegetation in nine even-aged young-growth stands (38–42 years old) comprising a gradient of red alder – conifer overstory composition, with red alder ranging from 0% to 86% of stand basal area. Conifers were Sitka spruce (Picea sitchensis (Bong.) Carr.), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn ex D. Don). We measured understory biomass and net production (current annual growth) in each stand by species and plant part and estimated carrying capacity for black-tailed deer (Odocoileus hemionus sitkensis Cowan) with a food-based habitat model. Highly significant positive relations (P < 0.002) were found between red alder basal area and all of the following: total understory biomass (r2 = 0.743), net production of shrubs (r2 = 0.758) and herbs (r2 = 0.855), and summer carrying capacity for deer (r2 = 0.846). The high correlation between red alder and herbaceous production is especially important, because herbs are least abundant and most difficult to maintain in young-growth conifer forests of this region. Red alder offers prospects for increasing understory vegetation biomass and its food value for deer and other wildlife when included as a hardwood overstory species in mixed hardwood–conifer young-growth forests. [ABSTRACT FROM AUTHOR]

In the Pacific Northwest, a mixture of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) often results when red alder regenerates naturally in planted conifer stands. The relationships among stand structure, tree mortality, tree size, and understory development in the two species mixtures were explored at two sites for the first 16 years after planting. Treatments included a range of species proportions, and red alder was either planted simultaneously with Douglas-fir or planting was delayed for 5 years. Red alder was also removed from some simultaneously planted proportions. Both replacement effects (total stand density held constant) and additive effects (stand density doubled) of the interaction were considered. Red alder grew relatively better at Cascade Head Experimental Forest in the Coast Range, while Douglas-fir grew better at H.J. Andrews Experimental Forest in the less temperate Cascade Mountains. Possible production benefits from mixed plantings were examined using two methods of calculation. Potential production benefits from certain planted proportions of the two species occurred at H.J. Andrews Experimental Forest. No planting time or species proportion resulted in yield improvements over monoculture stands at Cascade Head Experimental Forest. Understory species also varied because of differences in site and stand characteristics that resulted from the differences in planting times and species proportions. [ABSTRACT FROM AUTHOR]

To assess the effects of timber harvesting on headwater streams in upland forests, benthic community structure was contrasted among four dominant forest management types (old growth, red alder-dominated young growth, conifer-dominated young growth, clearcut) and instream habitats (woody debris, cobble, gravel) in southeastern Alaska. Benthos in streams of previously harvested areas resulted in increased richness, densities and biomass relative to old growth types, particularly in young growth stands with a red alder-dominated riparian canopy. Woody debris and gravel habitats supported a combination of higher densities and biomass of invertebrates than cobble habitats. In addition, woody debris also supported a richer and more diverse invertebrate fauna than either cobble or gravel substrates. Maintaining both a woody debris source and a red alder component in regenerating riparian forests following timber harvesting should support greater invertebrate densities and diversity following clearcutting. [ABSTRACT FROM AUTHOR]

We investigated the influence of red alder (Alnus rubra) stand density in upland, riparian forests on invertebrate and detritus transport from fishless headwater streams to downstream, salmonid habitats in southeastern Alaska. Red alder commonly regenerates after soil disturbance (such as from natural landsliding or timber harvesting), and is common along streams in varying densities, but its effect on food delivery from headwater channels to downstream salmonid habitats is not clear. Fluvial transport of invertebrates and detritus was measured at 13 sites in spring, summer and fall during two years (2000–2001). The 13 streams encompassed a riparian red alder density gradient (1–82% canopy cover or 0–53% basal area) growing amongst young-growth conifer (45-yr-old stands that regenerated after forest clearcutting). Sites with more riparian red alder exported significantly more invertebrates than did sites with little alder (mean range across 1–82% alder gradient was about 1–4 invertebrates m-3 water, and 0.1–1 mg invertebrates m-3 water, respectively). Three-quarters of the invertebrates were of aquatic origin; the remainder was of terrestrial origin. Aquatic taxa were positively related to the alder density gradient, while terrestrially-derived taxa were not. Streams with more riparian alder also exported significantly more detritus than streams with less alder (mean range across 1–82% alder gradient was 0.01–0.06 g detritus m-3 water). Based on these data, we predict that headwater streams with more riparian alder will provide more invertebrates and support more downstream fish biomass than those basins with little or no riparian alder, provided these downstream food webs fully utilize this resource subsidy. [ABSTRACT FROM AUTHOR]

1 We used repeated measurements of tree growth and population-level and neighbour- hood conditions from three mixed Alnus rubral Pseudotsuga menziesii forests in the Pacific Northwest, USA to investigate why previous results regarding the importance of neighbourhood competition as a determinant of plant growth were inconsistent 2 We propose that relative dominance ot a particular species determines the importance of neighbourhood interactions, and tested whether growth performance of both species at various stand ages agrees with this relative dominance hypothesis. 3 Neighbourhood and relative dominance interaction indices were modified to accommodate two-species mixtures and were incorporated into a growth model predicting relative diameter growth rates. The corrected Akaike Information Criterion (A/Cc) was used to identify the optimum interaction measures and model forms for each species and measurement period. 4 Interaction indices reflecting the sue of a tree relative to the population were the best predictors of growth of the dominant (i e taller) species and neighbourhood interaction indices of the subordinate species 5 Performance of interaction measures as predictors of relative growth rates in our study varied in agreement with the relative dominance hypothesis for both species and on all sites. Results from other studies suggest that the hypothesis may explain growth performances on a species and individual plant level and for a variety of' life forms. 6 These findings suggest that the spatial scale of plant interactions is influenced by the sue structure of plant populations. The relative dominance hypothesis offers a framework to provide insight into the mechanism of' competition, based on the relative performance of competition indices. [ABSTRACT FROM AUTHOR]

The relationships among stand structure, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) branch characteristics, and red alder (Alnus rubra (Bong.)) stem form attributes were explored for 10- to 15-year-old trees growing in mixed Douglas-fir – red alder plantations. Treatments included a range of species proportions, and red alder was either planted simultaneously with Douglas-fir or after 5 years. Both replacement effects (total stand density held constant) and additive effects (stand density doubled) of competition were considered. When the two species were planted simultaneously and red alder proportion was low, red alder trees had low crown bases and much stem defect (lean, sweep, and multiple stems). Douglas-fir grew slowly when the two species were planted simultaneously. When red alder planting was delayed, species proportion did not affect red alder stem form, and height to the base of the Douglas-fir live crown decreased with increasing red alder proportion. Doubling Douglas-fir density increased the height to the base of the Douglas-fir live crown; however, doubling stand density by adding red alder did not affect Douglas-fir crown height. Douglas-fir lumber coming from mixed stands may be inferior because of the changes in knot characteristics associated with these different patterns of crown recession. In stands with a low proportion of red alder, red alder product recovery may be compromised because of the stem defects described above. [ABSTRACT FROM AUTHOR]

Stand structure and dynamics were evaluated in mixed red alder (Alnus rubra Bong.) – conifer forests of southeast Alaska. We assessed stand development, tree density, total basal area, diameter distribution of live and dead trees, height distribution of live trees, and mean diameter of all and largest conifers in 40-year-old red alder – conifer stands that developed following logging. Forty-five plots were established in nine stands sampled across a com po si tional range of 0%–86% alder. Alder height growth was initially rapid then slowed considerably, whereas conifer height growth was initially slow then rapidly increased with conifers now being 4–9 m taller than associated alders. Most alder diameters were 20–30 cm and conifer diameters were more variable with numerous small (3–10 cm) and a few large (>25 cm) trees. Total stand basal area significantly decreased (p = 0.013) with increasing proportions of alder, but density of live and dead trees was not closely associated with alder composition. More than 60% of all dead trees died standing regardless of size or species. Overall, these mixed red alder – conifer stands provided more heterogeneous structures than pure conifer stands, with more even diameter distributions, multiple canopy layers, and similar numbers of large diameter conifers. [ABSTRACT FROM AUTHOR]

Most old fields in the Queers Valley of Olympic National Park, USA, remain dominated by exotic herbs 60 y after abandonment although the fields are surrounded by temperate rain forest. However, areas of some fields have been invaded by Picea sitchensis, one of three dominant forest species (with Alnus rubra and Tsuga heterophylla). This provided an opportunity to examine local variation of factors (competition, facilitation, cervid herbivory, soils) that influence tree colonization within a set of old fields, an approach rare in previous studies. Picea sapling invasion of field edges was negatively correlated with percent cover of Agrostis gigantea and positively correlated with Anthoxanthum odoratum. Potential indicators of competition (sod thickness, thatch thickness, percent ground cover) were correlated with Agrostis cover, Picea edge invasion was also correlated with soil organic matter. In experiments, seedlings of Picea and Tsuga emerged as readily in Agrostis as in Anthoxanthum or Pteridium aquilinum, but suffered higher mortality in Agrostis. Experimental seedling establishment was low and required reduction of competing vegetation. In experiments with transplanted seedlings, cervid herbivory suppressed growth of Tsuga and Alnus, but not Picea. Growth of Picea seedlings was facilitated by Pteridium. Differential tree colonization of the fields resulted from: (1) differential competition by invaded cover types against seedling establishment, (2) selective herbivory on tree species of established seedlings and (3) facilitation by fern cover of seedlings of an unbrowsed species. [ABSTRACT FROM AUTHOR]

To evaluate the distance over which red alder patches influence adjacent conifer stands, we measured light transmission and nutrient contents of soil and litterfall along transects crossing the boundary between alder and conifer stands at three sites (10–15, 20–25, and >= 40 years old) in coastal British Columbia. Light levels were higher in the understory of alder stands than in adjacent conifer stands. In simulated openings, light levels rapidly increased with distance from the alder edge, reaching 60% of full sunlight at south-facing edges, 5 m from north-facing edges, and 2–3 m from east- and west-facing edges. Soil N, NH4-N, NO3-N, and mineralizable N remained elevated for about 10 m from the alder boundary. Nitrogen contents of Douglas-fir seedlings grown in soil from the alder stand were elevated and correlated to soil N concentrations. Nutrient inputs in alder litterfall were positively related to concentrations of total C; total, extractable, and mineralizable N in soils; and the N, P, and B concentrations of seedlings. Alder litterfall drift extended 8–18 m into adjacent conifer stands. The optimal arrangement for alder–conifer mixtures would be alder patches or strips at least 10 m wide and about 20 m apart oriented north to south. [ABSTRACT FROM AUTHOR]

Variations in plant community composition across the landscape can influence nutrient retention and loss at the watershed scale. A striking example of plant species importance is the influence of N2- fixing red alder (Alnus rubra) on nutrient cycling in the forests of the Pacific Northwest. To understand the influence of red alder on watershed nutrient export, we studied the chemistry of 26 small watershed streams within the Salmon River basin of the Oregon Coast Range. Nitrate and dissolved organic nitrogen (DON) concentrations were positively related to broadleaf cover (dominated by red alder: 94% of basal area), particularly when near-coastal sites were excluded (r² = 0.65 and 0.68 for nitrate-N and DON, respectively). Nitrate and DON concentrations were more strongly related to broadleaf cover within entire watersheds than broadleaf cover within the riparian area alone, which indicates that leaching from upland alder stands plays an important role in watershed nitrogen (N) export. Nitrate dominated over DON in hydrologic export (92% of total dissolved N), and nitrate and DON concentrations were strongly correlated. Annual N export was highly variable among watersheds (2.4- 30.8 kg N ha-1 y-1), described by a multiple linear regression combining broadleaf and mixed broad- leaf-conifer cover (r² = 0.74). Base cation concentrations were positively related to nitrate concentrations, which suggests that nitrate leaching increases cation losses. Our findings provide evidence for strong control of ecosystem function by a single plant species, where leaching from N saturated red alder stands is a major control on N export from these coastal watersheds. [ABSTRACT FROM AUTHOR]

In southern coastal British Columbia, red alder (Alnus rubra Bong.) is recommended for reforestation on some low-elevation, fertile, and moist sites (e.g., alluvial sites). Correlative data indicate that P deficiencies limit the growth of alder in low-pH soils; deficiencies of P and other elements may also develop in the presence of an alder stand. Because alder may be grown in repeated rotations on alluvial sites, we sought to determine whether elemental deficiencies were likely in soils from mature stands. We examined the effects of P additions (as triple super phosphate) and liming (as dolomitic limestone) on potted red alder seedlings grown in soils from mature alluvial alder stands. Four soils were "low-pH" (mean = 4.5) and two were "high-pH" (mean = 5.5); all were classified as very rich. Growth of unfertilized seedlings was greatest in the soil with the highest soil Bray-P levels. Growth rates increased with P supply, but the response decreased with increasing Bray-P and was less in the high-pH soils. Liming increased soil pH and uptake of Mg, but did not increase growth. Phosphorus additions increased growth mainly by increasing P uptake, leaf size, and biomass allocation to branches. Photosynthetic rates were highest in the intermediate P treatment, but instantaneous water use efficiency increased with P rate. Phosphorus deficiencies may limit the growth of alder seedlings in alluvial soils previously containing mature alder stands. [ABSTRACT FROM AUTHOR]

Strong seasonal increases in aquatic (stream, ground and hyporheic water) nitrate have been observed in a variety of ecosystems. In most cases, changes in hydrological and vegetative activity occur contemporaneously, making it difficult to determine whether soil leaching is being driven by increases in the availability of leachable N or is simply due to flushing of N that has accumulated over longer periods. Three studies were conducted to better determine controls on soil nitrate leaching in a near-pristine temperate floodplain ecosystem receiving large N inputs via N-fixation by red alder: 1) an artificial rainfall experiment was conducted to estimate N-leaching potential during the summer, when plant uptake is high and new inputs of organic matter are low; 2) soil solution, groundwater and surface water were sampled during a major autumn storm to document exchanges at the seasonal transition, when plant uptake is low and inputs of senescent organic matter are high; and 3) monthly samples of soil and aquatic nitrogen were collected in 1997 and 1998 to document seasonal patterns of N exchanges. Collectively, these studies demonstrate the importance of hydrologic factors in controlling N flux. Nitrate was rapidly leached from soils during actual and simulated rainstorms. Two pathways of nitrate leaching were identified. Localized flooding and direct leaching of streamside soils into surface waters contributed to high solute concentrations in peak flows. Nitrate that leached into interstitial waters was subject to various factors that could delay or reduce its delivery to surface waters. Greater residence time may increase the influence of this component of stormflow on ecosystem productivity. While soil nitrate pools were rapidly depleted during rainstorms, accumulation of soil nitrate occurred over summer dry periods. Large differences in soil and aquatic nitrate concentrations between two years with contrasting rainfall highlight the potential for inter-annual hydrologic variability to affect ecosystem nutrient cycling. [ABSTRACT FROM AUTHOR]

Examines growth and biomass allocation of individual Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) seedlings grown under contrasting combinations of light and water. Alder growth that was always greater than Douglas-fir; Full sunlight and soil moisture at field capacity that caused large differences in size between the two species; Differences that were smaller with limited light and water; Douglas-fir that allocated a high portion of its biomass to roots under full light and limited water; Red alder that allocated a high percentage to aboveground biomass components under full light and limited water; Red alder growth that responded negatively to water limitation; Red alder that exhibited greater foliage plasticity to light; Species differences in size and allocation in response to resource availability that may determine pathways by which Douglas-fir and red alder interact in a mixed community; Findings that support the hypothesis that the potential of species to use growth-limiting resources is an indicator of competitive ability; Suggestion that red alder and Douglas-fir can co-exist under conditions of full light and limiting soil moisture availability; Douglas-fir's relatively greater tolerances to low light that allow it to better persist in the understory; Red alder's rapid early growth and competitive ability that will be superior under full light and nonlimiting soil moisture conditions.

Examines soil carbon and nitrogen changes under Douglas fir with and without red alder. Influence of red alder on soil carbon and nitrogen pools; Temporal plot pairing.

Presents a study that examined the variation in seed production in catkins from red alder Alnus rubra. Determination of the total number of seed produced; Analysis of the number of viable seed produced; Relationship between seed number and percent viability.

The genetic structure of 19 red alder (Alnus rubra Bong.) populations representing the natural range of the species in British Columbia was investigated at 19 allozyme loci. The estimated average number of alleles per locus (1.79), percentage of polymorphic loci (52.6), and total expected genetic diversity (0.113) were all lower than those reported for most long-lived woody species but comparable to early successional species. About 8% of the total genetic variation was attributable to among-population differentiation, the majority being detected at the Aat-2 locus between the Mainland and the Islands regions. Phylogenetic analysis grouped the 19 populations into two distinct clusters that perfectly coincided with their geographical arrangement. Genetic differentiation between populations within both the Mainland and the Islands regions was very weak, accounting for about 3% of the total genetic variation within each region. Red alder is predominantly an outcrossing species with an average outcrossing rate of 0.85. The rate of outcrossing also varied widely among populations, ranging from 0.56 to 0.98. Practical implications of these findings with respect to tree improvement and in situ gene conservation are discussed. [ABSTRACT FROM AUTHOR]

Examines the influence of the density and rectangularity of plantation on the growth and development of red alder in Oregon. Patterns of tree growth and stand development; Comparisons of the growth of trees with other plantations; Analysis of the diameter-density relationships in spacing.

During the last two decades, the value of red alder wood products has substantially increased and several initiatives have been launched in the United States to use red alder for reforestation. Nonetheless, red alder is a largely neglected resource in British Columbia. This review paper examines the reasons behind the under-utilization of red alder in British Columbia and investigates whether changes in red alder management practices could improve the value of the resource. Red alder's potential for plantation forestry and genetic tree improvement are discussed, and possible breeding objectives were evaluated with consideration for the species biology, growth, product value and market demand. Seed transfer rules and the possibility of gains from selection are summarized in the light of new research results in genecology and quantitative genetics for red alder populations in British Columbia. [ABSTRACT FROM AUTHOR]

Describes long-term nutrient cycling patterns in Douglas-fir and red alder stands. Simulation of regrowing stands using the nutrient cycling model; Differences in nutrient cycling between Douglas fir and red alder; Temporal patterns in nitrogen fixation in the regrowing stands; Canada Decline in biomass production due to lower base cation availability under red alder.

Reports on the measured rates of decomposition at three sites representing the major mixedwood forest types of British Columbia: (i) boreal forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.), (ii) coastal forests of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.), and (iii) a wet interior forest of Douglas-fir, paper birch (Betula papyrifera Marsh.), and lodgepole pine (Pinus contorta Doug. ex Loud.). Mass loss of litter of each species (both pure and in combination with the other species) that was measured in forests of each species to determine (i) if broadleaf litter decomposed faster than needle litter, (ii) if litter decomposed faster in broadleaf or mixedwood forests than in coniferous forests, and (iii) if mixing with broadleaf hastened decomposition of needle litter; Broadleaf litters that decomposed faster than needles during the first year but, thereafter, decomposed more slowly; Litter that tended to decompose faster in the broadleaf forests than in the coniferous forests; No evidence to indicate that the addition of broadleaf litter hastened decomposition of needle litter; Results that indicate that the mixing of needle litter with broadleaf litter is unlikely to hasten decomposition in mixedwood forests of British Columbia.

Discusses the use of multiple provenance trials of red alder to demonstrate how geostatistical method can be applied to develop better seed-transfer guidelines and seed-procurement zones for forestry. Evaluation of the environmental basis of local adaptations; Impact of geographic and climatic variation on height of plants.

We sought to determine whether changes in chemical composition could be a factor in increased utilization of red alder ( Alnus rubra) by the two cervids, the Columbian black-tailed deer ( Odocoileus hemionus columbianus) and Roosevelt elk ( Cervus elaphus roosevelti), during the fall in parts of the Douglas fir region of the Pacific Northwest. We found that concentrations and astringency of phenolic compounds decreased from spring through fall, while crude protein content remained high. We conclude that red alder leaves provide a significant source of digestible protein for cervids during fall, when availability of nutrients in most forage species is generally declining. [ABSTRACT FROM AUTHOR]

Interest in managing red alder (Alnus rubra Bong.) for pulp, lumber and improving site quality is increasing. Proper management of this species requires growth and yield information. Height-age and years to breast height models developed for western Washington and northwestern Oregon are being used in British Columbia. It is unknown whether these models are suitable for British Columbia's conditions. Therefore, new models were developed from thirty stem analysis plots established in red alder stands in coastal areas of British Columbia. The sample trees in the plots were intensively sampled by taking sections out of the tree stems and counting the annual growth rings on each section. This led to height-age data for each tree, which was then averaged by age to get plot height-age data. Years to breast height and height-age models were developed from these data and are summarized in this paper. The height-age model was anamorphic, which contrasts with the model previously used in British Columbia. The new years to breast height model provides more resolution than the previous model. [ABSTRACT FROM AUTHOR]

Midday stomatal closure is mediated by the availability of water in the soil, leaf and atmosphere, but the response to these environmental and internal variables is highly species specific. We tested the hypothesis that species differences in stomatal response to humidity and soil water availability can be explained by two parameters: leaf-specific hydraulic conductance (KL) and a threshold leaf water potential (Ψthreshold). We used a combination of original and published data to estimate characteristic values of KL and Ψthreshold for four common tree species that have distinctly different stomatal behaviors: black cottonwood (Populus trichocarpa Torr. & Gray.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), red alder (Alnus rubra Bong.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). We used the values to parameterize a simple, nonelastic model that predicts stomatal conductance by linking hydraulic flux to transpirational flux and maintaining Ψleaf above Ψthreshold. The model successfully predicted fundamental features of stomatal behavior that have been reported in the literature for these species. We conclude that much of the variation among the species in stomatal response to soil and atmospheric water deficits can be explained by KL and Ψthreshold. The relationship between Ψthreshold and xylem vulnerability to cavitation differed among these species. [ABSTRACT FROM PUBLISHER]

Examines phosphorus forms, distribution and cycling in adjacent stands of Douglas-fir and nitrogen-fixing red alder. Long-term impact of red alder growth on soil phosphorus forms; Use of Chang-Jackson phosphorus fractionation; Soil biogeochemistry; Ecosystem phosphorus distribution and fluxes.

The acetylene reducing activity of Alnus rubra nodules is maximal in 15 to 30% oxygen. Within the nodule, the large number and size of many of the intercellular spaces between the uninfected cells in the outer cortex facilitates the diffusion of air through the lenticels to the infected cells in the mid-cortex. Access of air to the infected cells, which are arranged in longitudinal bundles separated by one or more lines of starch-containing uninfected cells and which run at an angle away from the stele towards the nodule apex, is restricted by the reduced number and size of air spaces in this region. The cytoplasm of the infected cells shows high activity of peroxidase and o-diphenol oxidase, but the lack of correlation between the activity of these enzymes and nitrogenase activity suggests that they are not involved in the control of access of oxygen to the endophyte. It is suggested that one role of nodule peroxidase is the ignification of the infected cells associated with cellular senescence. [ABSTRACT FROM AUTHOR]

This article presents information on the fungal disease Aureobasidium pullulans. It is an associate of Alnus rubra and Lactarius obscuratus mycorrhizae. A studied was carried by researchers in which mycorrhizae was collected in a mixed 40-years old red alders at a scientific laboratory near Corvallis, Oregon. Researchers isolated A. pullulans from the 50% of Alnus rubra and Lactarius obscuratus mycorrhizae. Colonies in pure culture was found to be yeasty white, which turned black later.

Experiments well conducted on 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and 2- to 3-month-old alder [Alnzus rubra (Bong)] seedlings growing in drying soils to determine the relative influence of root and leaf water status on stomatal conductance (gc). The water status of shoots was manipulated independently of that of the roots using a pressure chamber that enclosed the root system. Pressurizing the chamber increases the turgor of cells in the shoot but not in the roots. Seedling shoots were enclosed in a whole-plant cuvette and transpiration and net photosynthesis rates measured continuously. In both specks, stomatal closure in response to soil drying was progressively reversed with increasing pressurization. Responses occurred Within minutes of pressurization and measurements almost immediately returned to pre-pressurization levels When the pressure was released. Even in wet soils there was a significant increase in gc with pressurization. In Douglas fir, the stomatal response to pressurization was the same for seedlings grown in dry soils for up to 120d as tot those subjected to drought stress ever 40 to 60 d. The Stomatal conductance it both Douglas fir and alder seedling was less sensitive to root chamber pressure at higher vapour pressure deficits (D), and stomatal closure In response to increasing D from 1.04 to 2.06 kPa was only partially reversed by pressurization. Out results are in contrast to those of other studies on. herbaceous species, even though we followed the same experimental approach. They suggest that it is not always appropriate to invoke a 'feedforward' model of short-term stomata! response to soil drying, whereby chemical messengers from the roots hung about stomatal closure. [ABSTRACT FROM AUTHOR]

Red alder (Alnus rubra Bong.) and sitka alder (A. viridis ssp. sinuata [Regel] Löve & Löve) are nitrogen-fixing woody species that grow sympatrically along the Pacific coast of North America. Red alder is found in poorly drained lowlands, as well as in soils of moist upland slopes, whereas sitka alder generally colonizes well-drained soils. To identify factors that contribute to flood tolerance, we conducted greenhouse experiments subjecting both species to a 20-day flood and 10-day recovery and red alder to a 50-day flood and 20-day recovery. We determined the effect of this stress on nitrogenase activity, root and nodule alcohol dehydrogenase (ADH) activity, lenticel and adventitious root development, relative growth rate (RGR), and leaf gas exchange. After 24 h of flooding, nitrogenase activity could not be detected in either species. Limited nitrogenase activity did return in red alder at the end of a 10-day recovery following the 20-day flood, but sitka alder showed no recovery of nitrogenase activity. After 50 days of continuous flooding, red alder nitrogenase activity returned to pretreatment levels. Red alder root and nodule ADH activity was more than twice that of sitka alder under flooded conditions. Sitka alder showed extensive root mortality and leaf abscission over the same 20-day flooding period. Flooded red alder exhibited an initial decline in root RGR, but recovered between days 10 and 20 with the formation of adventitious roots. Furthermore, initiation of adventitious roots in red alder coincided with an increase in stomatal conductance without a similar recovery of carbon dioxide exchange rate. Sitka alder formed few adventitious roots, lost much of its root and leaf biomass, and showed no restoration of growth during flooding or recovery. Different responses of red and sitka alder to flooding serve as a partial explanation for the different patterns of distribution of these species and suggest some adaptations of red alder that permit flood tolerance. [ABSTRACT FROM AUTHOR]

Nitrogen-fixing root nodules are formed by Frankia spp. (Actinomycetales) on dicotyledonous hosts such as alders (Alnus spp.). Flavonoid-containing preparations from seed washes of red alder (Alnus rubra Bong.), and individual compounds isolated from such preparations, influenced nodulation of A. rubra by Frankia. Nodulation was enhanced by one flavonoid-like compound. and apparently inhibited by two other such compounds. Four flavonoid-like compounds had no significant effect on nodulation. The seven individual compounds purified from the seed washes were characterized spectrally as possible flavanones and isoflavones. Both the enhancer and the inhibitors appeared to be possible flavanones. [ABSTRACT FROM AUTHOR]

The influence of short day and low temperature on cold acclimation of A. crispa (Ait.) Pursh., A. glutinosa (L.) Gaertn, and A. rubra Bong, was investigated. Two clones of each species originating from in vitro propagation were exposed to three daylength/temperature treatments. Periodically plantlets were exposed to controlled freezing temperature in order to evaluate their level of frost hardiness. Short day (SD) and cold temperature (CT) and long day (LD) and cold temperature (CT) were the most effective treatments for the development of frost hardiness in shoots and roots of the three species tested. Short day (SD) and warm temperature (WT) induced a significant increase in hardiness in shoots of all three species. However, this treatment did not trigger root hardening. A. crispa was found to be the hardiest species followed by A. glutinosa and A. rubra. Intraspecific variation was observed between the two A. glutinosa clones. A. glutinosa clone AG8, a Russian provenance, showed a greater freezing resistance than A. glutinosa clone AG2, a German provenance. [ABSTRACT FROM AUTHOR]

The effectivity of nodulation of Alnus rubra Bong. by Frankia isolates from A. rubra and Alnus glutinosa (L) Gaertn. in Northern Britain was compared with strains from The Netherlands and North America, using plants grown in combined nitrogen-free conditions. All strains gave rise to spore (-) nodules, even when isolated from nodules from sites known to contain spore (+) nodules. Nodules of all plants evolved little hydrogen, probably due to the presence of an efficient uptake hydrogenase in the microsymbionts. Nodule weight as a percentage of whole plant weight was higher for nodules of low specific activity (N fixed per unit weight nodules), attaining a maximum of 5.1% of plant dry weight in the least effective of the heterologous associations of A. glutinosa Frankia with A. rubra. The range of variation in nodule specific activity was much greater in heterologous than homologous associations, but nodules of high specific activity were found in both associations. However, plants that fixed most N during the growth period were not those with nodules of highest specific activity. The most effective associations were homologous symbioses, which combined good nodule growth per plant with satisfactory specific activity, fixing N at rates which would support superior plant growth under the prevailing growth conditions. Preliminary field experiments suggest that the most effective of the A. rubra isolates is suitable for use as an inoculant in nurseries. Strains isolated from A. glutinosa were more effective and showed a different order of effectivity in homologous symbioses compared with their association with A. rubra. An A. glutinosa strain was isolated, which stimulated satisfactory nodule growth and gave good nodule specific activity in both A. rubra and A. glutinosa. [ABSTRACT FROM AUTHOR]