Growth Of Alder Research Articles

Establishment of Nitrogen-Fixing Frankia, Arbuscular Mycorrhizal Fungi, and Their Effects on Alder (Alnus glutinosa L.) Growth in Post-Mining Heap Soils

Planting nitrogen-fixing plants in post-mining sites and similar degraded areas is a common approach to speed up soil development and buildup of the nitrogen pool in soil organic matter. The aim of this study was to explore if slower growth of alder seedlings in initial post-mining sites results from adverse soil conditions or lack of microbial symbionts. To address this question, we sampled young soil (age 15 years) and more developed soil (age 70 years) from heaps after coal mining near Sokolov (Czech Republic). Soil samples were sterilized and not inoculated or inoculated with arbuscular mycorrhizal fungi (AMF) or AMF + Frankia, followed by planting with alder (Alnus glutinosa) seedlings germinated and precultured under sterile conditions. The effect of soil age on alder growth appeared to be non-significant. The only significant growth effect was seen with Frankia inoculation, implicating this inoculum as a key factor in later succession in post-mining soils. When the soil was fully inoculated, alder biomass was higher in developed soil supplied with iron (Fe) and phosphorus (P), indicating that iron and phosphorus availability may affect alder growth. In young soil, alder growth was highest with a combination of iron, phosphorus, and sulfur (S), and a positive effect of sulfur in young soil may correspond with a reduced, alkaline soil pH and increased phosphorus and iron availability.

Chitosan exhibits variable effects on pine (Pinus sylvestris L.) and alder (Alnus glutinosa L.) growth and secondary metabolism

Chitosan exhibits variable effects on pine (Pinus sylvestris L.) and alder (Alnus glutinosa L.) growth and secondary metabolism

Influence of Hydrological and Climatic Changes on Tree Growth in Narew National Park, NE Poland, over the Past 50 Years

Over the last 50 years, groundwater levels have been decreasing and air temperatures have been increasing in Poland. Maintaining this trend may make it impossible to maintain hydrogenic habitats in good condition. Reactions to ongoing climate change recorded in tree rings may be a good indicator describing the degree of this threat. The aim of this study was to determine the influence of climatic and hydrological changes on the growth of scotch pine (Pinus sylvestris L.) and black alder (Alnus glutinosa (L.) Gaertn) in the Narew National Park over past 50 years. The research was based on tree increment cores extracted from 42 pine trees and 57 alder trees that were randomly selected and ranged in age from 25 to 88 years, as well as climatic and hydrological data. Standardised data (5-year index) were analysed by species, generation (Y—21–40 years, M—41–60, O—61–90), and decade using correlation analysis. The results of the study show that pine responded more strongly to changes in air temperature and changes in precipitation totals, while alder growth was more strongly related to fluctuations in the water level of the Narew River and changes in precipitation totals. Our research showed that differences in response to environmental factors also occur between tree generations. The decrease in the water level of the Narew River that occurred over the last 50 years did not adversely affect the condition of the trees. Analysis of DBH growth rates showed that the younger generations (Y, M) grow faster than the older generation (O). This is positive news for managers of commercial and protected forests, but accelerated tree growth may be associated with specific consequences, such as increased wind damage as a result of reduced wood density or reduced sensitivity of trees to climate and hydrological changes.

Implications of alder shrub growth for alpine tundra soil properties in Interior Alaska

ABSTRACT The increase in deciduous shrub growth in response to climate change throughout the Arctic tundra has uncertain implications, in part due to a lack of field observations. Here we investigate how increasing alder shrub growth in alpine tundra in Interior Alaska corresponds to active layer thickness and soil physical properties. We documented increased alder growth by combining biomass harvests and dendrochronology with the analysis of remotely sensed Normalized Difference Vegetation Index and fire history. Active layer thickness was measured with a tile probe and carbon and nitrogen pools were assessed via elemental analysis. Shallower organic layers under increasing alder growth indicate that nitrogen-rich, deciduous litter inputs may play a role in accelerating decomposition. Despite the observed reduction in organic carbon stocks, active layer thickness was the same under alder and adjacent graminoid tundra, implying deeper thaw of the underlying mineral soil. This study provides further evidence that the widely observed expansion of deciduous shrubs into graminoid tundra will reduce ecosystem carbon stocks and intensify soil–atmosphere thermal coupling.

Density effects on growth and dominance in pure and mixed stands of red alder and western hemlock in western Oregon

Maintaining diversity of conifer and hardwood species in riparian and upland areas is of increasing interest to forest managers. For example, having conifer and hardwood inputs into streams increases structural diversity and influences assemblages of aquatic and terrestrial organisms, and the presence of both components in stands may be beneficial in resiliency after disturbances. To examine the impacts of density and weeding on the establishment of red alder (Alnus rubra Bong.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.), combination Nelder and replacement series plots were established on three sites in western Oregon. Species ratios of hemlock:alder were 100:0, 75:25, 50:50, 25:75, and 0:100, with densities ranging from 988 to 85,400 tph. Measurements were available for two sites after 24 years, and one site for 14 years. Weeding increased heights and diameters at lower densities, especially in the early years. As crowns closed, the impacts of weeding decreased through time, but were still evident in some plots after 24 years. Increasing density of red alder resulted in lower survival and growth of both species. Hemlock density did not impact red alder growth through 24 years. Although mixed stands resulted in greater volume in early years, that did not continue in later years. Greater juvenile growth rates of red alder compared to western hemlock resulted in dominance of alder over hemlock in early years, especially at higher densities and ratios of alder. Hemlock growing with lower alder density have maintained co-dominance with alder and will become dominant as alder growth rates decline. Alder density needs to be low enough for hemlock to survive and grow. Density, site, species ratio, animal damage, and presence of other competing vegetation resulted in different scenarios of hemlock and alder dominance, making long-term outcomes difficult to predict with precision.

Age matters: Older Alnus viridis ssp. fruticosa are more sensitive to summer temperatures in the Alaskan Arctic

Abstract The Arctic is rapidly warming, and tundra vegetation community composition is changing from small, prostrate shrubs to taller, erect shrubs in some locations. Across much of the Arctic, the sensitivity of shrub secondary growth, as measured by growth ring width, to climate has changed with increased warming, but it is not fully understood how shrub age contributes to shifts in climate sensitivity. We studied Siberian alder, Alnus viridis ssp. fruticosa, a large nitrogen‐fixing shrub that has responded to climate warming with northward range expansion over the last 50 years. We used serial sectioning of 26 individual shrubs and 94 cross‐sections to generate a 98‐year growth ring chronology, including one 142‐year‐old, Siberian alder in Northern Alaska. We tested how secondary growth sensitivity to climate has changed over the past century (1920–2017) and how shrub age affects climate sensitivity of alder growth through time. We found that over time, alder growth as expressed by the stand chronology became more sensitive to July mean monthly air temperature. Older shrubs displayed higher sensitivity to June and July temperature than younger alders. However, during the first 30 years of growth of any shrub, temperature sensitivity did not differ among individuals. In addition, the June temperature sensitivity of growth series from individual cross‐sections depended on the age of the attached shrub. Our results suggest that age contributes to climate sensitivity, likely through modifying internal shrub carbon budgets by changing size and reducing alder's dependence on N‐fixation over time. Older, more sensitive alder may enhance C and N‐cycling while having greater recruitment potential. Linking alder age to climate sensitivity, recruitment and total N‐inputs will enable us to better predict ecosystem carbon and nitrogen cycling in a warmer Arctic. Read the free Plain Language Summary for this article on the Journal blog.

Assessment of a 20-year-old mixed western redcedar/red alder plantation in southwestern British Columbia

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.

Dendrochronological data from twelve countries proved definite growth response of black alder (Alnus glutinosa [L.] Gaertn.) to climate courses across its distribution range

Abstract Black alder (Alnus glutinosa [L.] Gaertn.) is an important component of riparian and wetland ecosystems in Europe. However, data on the growth of this significant broadleaved tree species is very limited. Presently, black alder currently suffers from the pathogen Phytophthora and is particularly threatened by climate change. The objective of this study was to focus on the impact of climatic variables (precipitation, temperature, extreme climatic events) on the radial growth of alder across its geographic range during the period 1975–2015. The study of alder stands aged 46–108 years was conducted on 24 research plots in a wide altitude range (85–1015 m) in 12 countries of Europe and Asia. The most significant months affecting alder radial growth were February and March, where air temperatures are more significant than precipitation. Heavy frost and extreme weather fluctuations in the first quarter of the year were the main limiting factors for diameter increment. Within the geographical setting, latitude had a higher effect on radial growth compared to longitude. However, the most important variable concerning growth parameters was altitude. The temperature’s effect on the increment was negative in the lowlands and yet turned to positive with increasing altitude. Moreover, growth sensitivity to precipitation significantly decreased with the increasing age of alder stands. In conclusion, the growth variability of alder and the number of negative pointer years increased with time, which was caused by the ongoing climate change and also a possible drop in the groundwater level. Riparian alder stands well supplied with water are better adapted to climatic extremes compared to plateau and marshy sites.

Distribution, productivity and natural regeneration of black alder (Alnus glutinosa (L.) Gaertn.) in Ukrainian Polissya

Abstract The aim of the study was to assess the current state and productivity of black alder (Alnus glutinosa (L.) Gaertn.) stands and determine the optimal conditions for the emergence and further growth of its natural regeneration in Ukrainian Polissya. The area of black alder stands in Ukrainian Polissya (Ukrainian forest zone) is 162,348 ha, reaching 8.4% of the total forest area. Volyn Region has the largest area of alder stands within Ukrainian Polissya (61,271 ha covering 37.7% of the total area). In the forests of this region, a more detailed study of the current condition, productivity, growth and regeneration of alder stands was performed. The natural regeneration under the alder canopy was characterized as poor. The largest numbers of alder seedlings (1,600–1,800 stems per ha) were recorded under the canopy of 76–78-year-old stands with a relative density of stocking of 0.63–0.70 and 80–100% of alder in their composition. Naturally regenerating alder seedlings had mainly group distribution on the area (occurrence is up to 40%). These specificities should be taken into account to promote natural seed regeneration of alder stands.

Growth and Wood Trait Relationships of Alnus glutinosa in Peatland Forest Stands With Contrasting Water Regimes.

Human-driven peatland drainage has occurred in Europe for centuries, causing habitat degradation and leading to the emission of greenhouse gases. As such, in the last decades, there has been an increase in policies aiming at restoring these habitats through rewetting. Alder (Alnus glutinosa L.) is a widespread species in temperate forest peatlands with a seemingly high waterlogging tolerance. Yet, little is known about its specific response in growth and wood traits relevant for tree functioning when dealing with changing water table levels. In this study, we investigated the effects of rewetting and extreme flooding on alder growth and wood traits in a peatland forest in northern Germany. We took increment cores from several trees at a drained and a rewetted stand and analyzed changes in ring width, wood density, and xylem anatomical traits related to the hydraulic functioning, growth, and mechanical support for the period 1994–2018. This period included both the rewetting action and an extreme flooding event. We additionally used climate-growth and climate-density correlations to identify the stand-specific responses to climatic conditions. Our results showed that alder growth declined after an extreme flooding in the rewetted stand, whereas the opposite occurred in the drained stand. These changes were accompanied by changes in wood traits related to growth (i.e., number of vessels), but not in wood density and hydraulic-related traits. We found poor climate-growth and climate-density correlations, indicating that water table fluctuations have a stronger effect than climate on alder growth. Our results show detrimental effects on the growth of sudden water table changes leading to permanent waterlogging, but little implications for its wood density and hydraulic architecture. Rewetting actions should thus account for the loss of carbon allocation into wood and ensure suitable conditions for alder growth in temperate peatland forests.

Eemian to Early Weichselian regional and local vegetation development and sedimentary and geomorphological controls, Amersfoort Basin, The Netherlands

Abstract Two new records from the Amersfoort glacial basin are investigated by means of pollen analysis. The cores are situated in the deeper part, close to the original Eemian stratotype Amersfoort 1 (Zagwijn, 1961) and at the margin of the basin. The aim is to reconstruct the Eemian and Early Weichselian vegetation development and to explore the impact of accommodation space, influx of allochthonous pollen and geomorphology on the vegetation composition. The results of the Amersfoort Basin are compared to the current Eemian stratotype in the Amsterdam Basin and other Eemian sites in the Netherlands. An almost complete Eemian to Early Weichselian sequence (E2-EWII) was retrieved from the deeper part of the Amersfoort basin. The late Saalian (LS) to early Eemian transition is not recorded in the Amersfoort basin, in contrast to the deeper Amsterdam Basin. The basin marginal core Den Treek reveals a condensed late Eemian (E5-6) and Early Weichselian (EW I-II) succession showing the importance of accommodation space. The first impact of the Eemian transgression is registered at the E3 to E4a boundary in the Amersfoort and Amsterdam basins, and highest sea level is proposed at the end of pollen zone E5. Upstream in the Eemian delta, in the palaeo-Vecht valley and IJssel Basin, the transgression is recorded later. The influx of reworked (allochthonous) pollen in clastic sediment units hampers vegetation and climatic reconstructions during the LS and Eemian. The early appearance of Picea in zone E4 and Abies in zone E5 in clastic sediment intervals can be related to long-distance transport by the river Rhine and redistribution in the Eemian delta. Local vegetation development can complicate regional biostratigraphic correlations. Alnus, considered characteristic for the late Eemian (E5-6), shows large differences over short distances in the Amersfoort Basin, related to local alder growth since Eemian E3. Carpinus, diagnostic for pollen zone E5, shows high values in the basins adjacent to higher, well-drained ice-pushed ridges, but low values in low-relief environments. Salt- to brackish-water marshes were present during high sea level in zone E5 in the Amsterdam and Amersfoort basins, while further upstream in the Rhine delta brackish to fresh-water tidal conditions dominated. In line with Zagwijn (1961), the E6 to EWI boundary is defined at the first opening of the vegetation cover with Calluna, Poaceae and Artemisia increase, often coinciding with a lithological change from organic to clastic deposition, reflecting increased landscape instability. The cores from the Amersfoort basin reveal a complete Eemian to Early Weichselian record. It is suggested to define the boundary stratotype for the base of the Weichselian Stage in the Amersfoort Basin. The current stratotype Amsterdam-Terminal reveals a fully developed LS to Eemian transition and contains the boundary stratotype for the base of the Eemian Stage.

Fresh litter acts as a substantial phosphorus source of plant species appearing in primary succession on volcanic ash soil

Plants have difficulty absorbing phosphorus from volcanic ash soils owing to the adsorption of phosphorus by aluminum and iron in the soils. Thus, on volcanic ash soils, the phosphorus source for natural vegetation is expected to be organic matter, however, there is a lack of experimental evidence regarding this occurrence. Here, we studied the effect of organic matter on plant growth of some species that occur in primary successions of volcanic ash soil ecosystems, based on growth experiments and chemical analyses. We found that a large amount of inorganic phosphorus (but only a limited amount of inorganic nitrogen) is leached from fresh leaf litter of the pioneer spices Fallopia japonica at the initial stage of litter decomposition. Phosphorus from the fresh litter specifically activated the growth of subsequently invading nitrogen-fixing alder when immature volcanic soil was used for cultivation. In contrast, old organic matter in mature soil was merely a minor source of phosphorus. These results suggest that fresh litter of F. japonica is essential for growth of nitrogen-fixing alder because the litter supplies phosphorus. We consider that rapid phosphorus cycles in fresh litter-plant systems underlie the productivity of natural vegetation even in mature ecosystems established on volcanic ash soils.

Tripartite symbioses regulate plant–soil feedback in alder

Abstract Plant–soil feedbacks regulate plant productivity and diversity, but potential mechanisms underpinning such feedbacks, such as the allocation of recent plant assimilate, remain largely untested especially for plants forming tripartite symbioses. We tested how soils from under alder Alnus glutinosa and beneath other species of the same and different families affected alder growth and nutrition, and colonization of roots by nitrogen‐fixing Frankia bacteria and ectomycorrhizal fungi. We also measured how the soil environment affected carbon capture and allocation by pulse labelling seedlings with 13CO2. We then tested for linkages between foliar nutrient stoichiometry and carbon capture and allocation and soil origin using statistical modelling approaches. Performance of alder and nitrogen nutrition were best on home and birch Betula pendula soils (both Betulaceae), whereas performance on Douglas fir Pseudotsuga menziesii (Pinaceae) soil was poor. Plants growing in P. menziesii soil were virtually devoid of Frankia and ectomycorrhizas, and the natural abundance 15N signatures of leaves were more enriched indicating distinct nitrogen acquisition pathways. Seedlings in these soils also had smaller 13C fixation and root allocation rates, leading to smaller 13C respiration rates by microbes. Statistical models showed that the best predictors of foliar N concentration were 13C allocation rates to fine roots and net CO2 exchange from the mesocosms. The best predictors for foliar phosphorus concentration were net CO2 exchange from the mesocosms and soil origin; seedlings in home soils tended to have greater foliar phosphorus compared to birch soils while seedlings from Douglas fir soils were no different from the other treatments. Foliar phosphorus concentration was not correlated with plant available or total soil phosphorus for any of the soils. Home soils also resulted in distinct ectomycorrhizal communities on seedlings roots, which could be responsible for greater foliar phosphorus concentration. Our findings show how the association of alder with nitrogen‐fixing Frankia relieved nitrogen limitation in the seedling triggering a performance feedback loop. We propose that relief of nitrogen limitation likely increases plant phosphorus demand, which may promote the formation of ectomycorrhizas in nutrient‐deficient soils. The formation of tripartite symbioses therefore generates positive plant–soil feedbacks, which enables plants to acquire mineral nutrients otherwise inaccessible in trade for carbon. A free Plain Language Summary can be found within the Supporting Information of this article.

Growth and structure of italian alder (Alnus cordata /Loisel./ Duby) linear plantation at age 11 and 16 years at Fruška gora (Serbia)

Growth and structure of Italian alder (Alnus cordata /Loisel/ Duby) trees were analyzed in a linear plantation established by planting two-year-old seedlings at Fruška Gora (Serbia). The aim of this paper is to point out the growth characteristics and the structure of the Italian alder linear plantation at age 11 and 16 years and contribute to the knowledge of adaptive and productive potential of the species in the available plantation in Serbia. The spacing between the trees was 7 m (200 trees per hectare). The plantation is located on anthropogenically changed pedunculate oak and hornbeam site at 125 m above sea level. On the basis of 35 measured trees at age 11 and 16 years, the top height was 15 and 21 m, and the Lorey’s mean height 13.4 and 19.5 m. The dominant diameter was 32.4 cm at age 11 and 59.4 cm at age 16 years. The mean quadratic diameter was 25.1 and 47 cm.The productivity of the plantation is high. At age 11 years, the basal area was 9.9 m2∙ha−1, and the standing volume 107.2 m3∙ha−1 while at age 16 years, it was 34.7 m2∙ha−1 and 305.1 m3∙ha−1, respectively. In the period from 11 to 16 years of age, the periodic annual increment in diameter was 4.4 cm∙year−1, height 1.22 m∙year−1, and in basal area and volume 4.9 m2∙ha−1·year−1and 39.6 m3·ha−1·year−1, respectively, pointing to fast growth of Italian alder. Despite the limits due to a small sample and the fact that the linear plantation was analyzed, we generalise the ­following conclusion: the measured growth characteristics at age 11 and 16 years of Italian alder trees show that the species can grow fast and could be usable in similar areas.

Successional trajectory of bacterial communities in soil are shaped by plant-driven changes during secondary succession

This study investigated the potential role of a nitrogen-fixing early-coloniser Alnus Nepalensis D. Don (alder) in driving the changes in soil bacterial communities during secondary succession. We found that bacterial diversity was positively associated with alder growth during course of ecosystem development. Alder development elicited multiple changes in bacterial community composition and ecological networks. For example, the initial dominance of actinobacteria within bacterial community transitioned to the dominance of proteobacteria with stand development. Ecological networks approximating species associations tend to stabilize with alder growth. Janthinobacterium lividum, Candidatus Xiphinematobacter and Rhodoplanes were indicator species of different growth stages of alder. While the growth stages of alder has a major independent contribution to the bacterial diversity, its influence on the community composition was explained conjointly by the changes in soil properties with alder. Alder growth increased trace mineral element concentrations in the soil and explained 63% of variance in the Shannon-diversity. We also found positive association of alder with late-successional Quercus leucotrichophora (Oak). Together, the changes in soil bacterial community shaped by early-coloniser alder and its positive association with late-successional oak suggests a crucial role played by alder in ecosystem recovery of degraded habitats.

Effect of Fertilization and Bacterial Inoculation on the Growth of Alder (Alnus sibirica) in Coal Mine Soil

This study was conducted to evaluate the effect of fertilization and nitrogen fixing (N-fixing) bacterial inoculation on the vegetative growth of alder (Alnus sibirica) plant species while grown in coal mine soil. The study was conducted in a greenhouse of the Forest Science Department, Chungbuk National University, South Korea, during the period of May 2019 to July 2019. A completely randomized design (CRD) comprising of four treatments, including T0—non-fertilized non-inoculation (control), T1—fertilization, T2—bacterial inoculation and T3—fertilization along with bacterial inoculation with three replications were used in the study. The results of the study showed that maximum growth of all studied parameters of alder were observed in fertilization along with bacterial inoculation treatment (T3) and this treatment had significant effect on the growth of these parameters as compared to control, except root dry weight and shoot/root ratio. Fertilization treatment (T1) showed significant increase of stem height, shoot fresh and dry weight, plant dry weight, canopy spread, number of leaves, branches and nodes per plant, leaf area and leaf area index of alder in coal mine soil, as compared to control. Bacterial inoculation treatment (T2) also had positive effect on the vegetative parameters of plants comparing to control, excluding root length, root dry weight, shoot/root ratio, and canopy spread. Therefore, it can be summarized that fertilizer application and bacterial inoculation to the soil have a significant role in improving the vegetative growth of alder in coal mine soil.

Alnus glutinosa L. Gaertn. as potential tree for brackish and saline habitats

Over 800 million hectares of land worldwide are affected by salinity. Predicted scenarios of global climate change include a rise in sea level, which may severely affect coastal forest areas. Black alder (Alnus glutinosa) is a tree species known to tolerate heavily waterlogged soils, but its salt resistance is still unclear. The aim of our study was to assess A. glutinosa growth under soil salinity as a possible tree for wet, salt-affected sites in a changing coastal environment due to climate change. We hypothesised that: a) growth parameters are directly related to soil conditions; and b) salinity and waterlogging can limit black alder growth. For our research, we evaluated 9-11-year-old black alder plantations in Poland, one in a saline area and two reference sites on non-saline soils (one with higher moisture content). The growth of trees at each site was characterised by calculating the growth success, mean diameter at breast height, the mean height and the standard deviations from the means. We also calculated the distribution of diameters in each population, regression models for growth as the relationship between diameter and height, and coefficients of variance. The means between sites were compared by one-way ANOVA with Scheffe’s post-hoc comparisons. To characterise soil conditions we took soil samples for each site and compared their properties by the same statistical tests.Under saline conditions, black alder growth was limited in terms of height, diameter at breast height and growth success. Salinity also affected the trees’ variability, growth form and growth pattern. However, these effects were comparable to those observed in the non-saline waterlogged site. The models of growth described by regression demonstrated similar reduction of growth dynamics in these two sites. Moreover, the coefficients of variation in diameter and height of trees in these sites were similar and higher than in non-stressed site. In addition, at the saline and waterlogged sites black alder trees had relatively large number of root suckers, whereas in non-stressed site this was not the case. On the plantations in stressed environments there had been losses in the A. glutinosa stand, which had been spontaneously settled by other species of trees and shrubs, which increased species richness. Therefore, regarding climate change, in our opinion black alder can be considered as an option for planting in brackish coastal areas, where nature conservation and watershed management are at least as important as wood production.

Plant Water Stress and Soil Depletion in Variable-Density, Red Alder/Western Hemlock Coastal Oregon Plantations

Abstract 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.

Effects of litter and straw mulch amendments on compacted soil properties and Caucasian alder (Alnus subcordata) growth

Application of mulch on compacted soil is a common engineering measure to suppress runoff and soil loss during ground-based mechanized forest operations. Despite the expanded use, efficacy of these rehabilitation treatments on soil quality as well as seedling survival and growth rate are crucial issues that require further attention. This study aimed to assess the efficacy of two soil amendment techniques including straw (1.27 kg m−2) and litter (1.67 kg m−2) mulch on soil properties and growth properties of Caucasian alder. Three treatments: straw mulch (SM), litter mulch (LM) and untreated trail (U) were applied on newly established machine operating trails subjected to low, medium, and high machine traffic intensity classes and compared to the undisturbed area (i.e., control; UND). Approximately 22 months after ground-based machine traffic and mulching application, seeds of Caucasian alder were sown in each treatment and in the undisturbed area and further extracted after the first growing season to assess their growth rates. Three years after applying mulch on the compacted soil, recovery values of soil physical and chemical properties (with the exception of soil C/N ratio) in all traffic intensities were significantly higher in LM than SM, compared to U treatment. Nevertheless, recovery values of soil physical and chemical properties were still higher than values in UND area over a 3-year period. All the measured growth and biomass responses of Caucasian alder seedlings changed significantly with increasing traffic intensities (all P ≤ 0.05). Significantly higher seed germination percentage was recorded in LM with low traffic intensity (54%). Significantly higher seedling stem height (17.3 cm), main root length (23.6 cm), seedling total (7.68 g), shoot (2.87 g), and root dry (4.81 g) biomass were observed in the UND area followed by LM with low traffic ≈ LM with medium traffic treatments, whereas the lowest values of seedling size and biomass were detected on U with low, medium, and high traffic intensities. Seedling root mass ratio (RMR; 61%) and root to shoot ratio (R/S; 1.89) were greatest in the UND area, while the RMR (40%) and R/S (0.86) were least in the U plots with high traffic intensity. We can conclude that the highest seedling growth, biomass, and allocation ratios and favorable soil physical, chemical, and bio-chemical properties can be attributed to UND, LM with low and medium traffic, and SM with low traffic treatments.

Growth Response of Aspen and Alder to Fresh and Stockpiled Reclamation Soils

Soil stockpiling is a common reclamation practice used in oil sands mining in the boreal forest region of Canada to conserve soil resources; but stockpiling may have detrimental effects on soil quality and plant growth. We examined growth response of trembling aspen (Populus tremuloides Michx.), a fast-growing early successional tree, and green alder (Alnus viridis (Chaix) DC. ssp crispa (Ait.) Turrill), a nitrogen-fixing shrub, to stockpiling and fertilization treatments on two reclamation soils (forest floor mineral mix (FFMM) and peat mineral mix (PMM)). Aspen and alder seeds were planted and their growth monitored for four months in the greenhouse. We found that unfertilized stockpiled FFMM supported significantly higher aspen and alder aboveground biomass than the other fresh and stockpiled soils. Phosphorus and potassium supply rates were highest in stockpiled FFMM and were positively correlated with aboveground plant biomass. There was no significant difference in aspen and alder aboveground biomasses between unfertilized fresh FFMM and PMM soils. Aspen grown in combination with nitrogen-fixing alder did not experience competition or facilitation except on fresh PMM, where aspen height declined. Fertilization increased both aspen and alder growth and eliminated differences in growth between soil types and stockpiling treatments. Our study showed that individual soil properties are more important for revegetation purposes than type of soil or stockpiling treatment.