Relative Height Growth Research Articles

Performance of bioretention systems by umbrella plant (Cyperus alternifolius L.) and common reed (Phragmites australis) for removal of microplastics

Domestic wastewater is one of the main sources of microplastic (MP) contamination in aquatic environment; however, most wastewater treatment plants (WWTPs) have not been designed for the removal of MPs. In this study, the release rate of MPs in the treated water from a WWTP into the river was estimated to be approximately 105 × 103 pcs/capita/day. Thus, bioretention systems are designed as tertiary wastewater treatment systems to reduce the number of MPs in water resources. The objective of this study was to evaluate the performance of bioretention systems using the umbrella plant (Cyperus alternifolius L.) and common reed (Phragmites australis) for MP removal. After 17 weeks, MPs were found in the common reed bioretention system. The common reed root system and substrate influence the MP retention process to a greater extent through physical filtration, substrate ratio, plant roots, and biofilms on the roots. Additionally, the common reed root system played an important role in the removal of low-density MPs. The accumulation of MPs in roots and root hairs inevitably impacts plants. The results showed that the common reed at a 3:2:9 ratio (gravel: sand: soil) had the highest relative height growth rate (RHGR) (1.8 mm cm−1 week−1). These results show that the HSFs–3 at a ratio of 3:2:9 was able to reduce the number of MPs, with an average removal efficiency of 62.89 % and 95.45 % for sizes >1000 µm, 89.21 % for sizes 500–1000 µm, and 44.16 % for sizes <500 µm. The highest average microbeads removal efficiency was 95.24 %. Our results suggest that plant bioretention using Horizontal Subsurface Flow system is an effective treatment for removing MPs from wastewater.

Species selection as a key factor in the afforestation of coastal salt-affected lands: Insights from pot and field experiments

Soil salinization is a significant global issue that leads to land degradation and loss of ecological function. In coastal areas, salinization hampers vegetation growth, and forestation efforts can accelerate the recovery of ecological functions and enhance resilience to extreme climates. However, the salinity tolerance of tree species varies due to complex biological factors, and results between lab/greenhouse and field studies are often inconsistent. Moreover, in salinized areas affected by extreme climatic and human impacts, afforestation with indigenous species may face adaptability challenges. Therefore, it is crucial to select appropriate cross-species salinity tolerance indicators that have been validated in the field to enhance the success of afforestation and reforestation efforts. This study focuses on five native coastal tree species in Taiwan, conducting afforestation experiments on salt-affected soils mixed with construction and demolition waste. It integrates short-term controlled experiments with potted seedlings and long-term field observations to establish growth performance and physiological and biochemical parameters indicative of salinity tolerance. Results showed that Heritiera littoralis Dryand. exhibited the highest salinity tolerance, accumulating significant leaf proline under increased salinity. Conversely, Melia azedarach Linn. had the lowest tolerance, evidenced by complete defoliation and reduced biomass under salt stress. Generally, the field growth performance of these species aligns with the results of short-term pot experiments. Leaf malondialdehyde content from pot experiments proved to be a reliable cross-species salinity tolerance indicator, correlating negatively with field relative height growth and survival rates. Additionally, parameters related to the photosynthetic system or water status, measured using portable devices, also moderately indicated field survival, aiding in identifying potential salt-tolerant tree species. This study underscores the pivotal role of species selection in afforestation success, demonstrating that small-scale, short-term salinity control experiments coupled with appropriate assessment tools can effectively identify species suitable for highly saline and degraded environments. This approach not only increases the success of afforestation but also conserves resources needed for field replanting and maintenance, supporting sustainable development goals.

Carbon stress causes preferential storage over growth in treeline trees

AbstractNon‐structural carbohydrates (NSCs) play an important functional role in determining plant survival as a backup carbon (C) source, while they also represent a large C sink being traded off against other C sinks when facing stress. However, information regarding how such trade‐offs in C allocation under C stress vary among species remains limited. Here, we experimentally induced C stress in juveniles of three tree species by exposing them to in situ artificial shading, and then we quantified the dynamics of whole‐tree C allocation patterns between storage and growth. For light‐demanding deciduous conifer larch and shade‐intolerant deciduous broad‐leaved birch, tree growth (represented by relative tree height growth (RHG) and relative basal area increment (RBAI)) was significantly reduced by shading, whereas for shade‐tolerant evergreen conifer fir, RHG and RBAI remained constant. Variations of whole‐tree NSC reserves were consistent for non‐treeline tree species (i.e., birch and fir), showing that shading remarkably reduced NSC storage. In contrast, shading‐induced NSC accumulation was found only in treeline tree species (i.e., larch). More importantly, C allocation to NSC storage was prioritized over structural growth only in larch under C stress, suggesting a strong trade‐off between survival and growth in treeline trees. Overall, our results discovered different patterns of C allocation in response to C stress across species with different plant functional types, further highlighting the highly conservative survival strategy of treeline tree species. Our study may contribute to an enhanced understanding of how forest biomes mitigate the negative impacts of stressful events in the context of global changes.

Comparative growth and physiological performance of American chestnuts, oaks, hickories, and sugar maple across a silvicultural gradient in overstory retention

The development of a blight-tolerant transgenic American chestnut (Castanea dentata (Marsh.) Borkh.) would provide the potential for reintroducing this species into forests it historically dominated. However, we lack a silvicultural understanding of the environmental conditions most favorable to the growth and survival of American chestnut relative to species with which it historically co-existed. We examined effects of shelterwoods with variable residual densities on the growth and physiology of blight-tolerant chestnut seedlings relative to sugar maple (Acer saccharum Marsh.), and several oak (Quercus spp.) and hickory (Carya spp.) species across a broad range of light availabilities (gap light index; GLI; of 4–50%). To assess the hypothesis that American chestnuts are more physiologically plastic and responsive to light than oaks and hickories, we measured seedling relative diameter and height growth rates and photosynthetic light-response curves across a GLI gradient. The diameter and height growth of chestnut increased with GLI, while oaks and hickories did not. All species varied aspects of their photosynthetic physiology across the GLI gradient in an approximately equivalent manner; the dark respiration rate and light compensation point increased equivalently across species in response to increases in light availability. A multivariate analysis identified three major axes of variation across ten measured traits, largely reflecting differences in species averages and phenotypic plasticity across the GLI gradient. American chestnut seedlings were spread across these multivariate dimensions more than other species, consistent with the hypothesis of higher phenotypic plasticity in this focal species. These results suggest that low residual shelterwood densities may better promote the establishment of underplanted chestnut seedlings relative to associated tree species provided it does not result in detrimental increases in the productivity of competing understory species.

Resource-based growth models reveal opportunities to mitigate climate change effects on beech regeneration by silvicultural measures

Successful European beech (Fagus sylvatica L.) regeneration is both of great ecological and economical importance in European forest ecosystems and severely threatened by climate change impacts. To increase our knowledge of beech regeneration dynamics under climate change and the potential for controlling it through forest management, we studied interactive effects of solar radiation (PHAR), water and nutrient availability on the height growth of artificially (AR) and naturally regenerated (NR) beech seedlings. The study was conducted in the framework of experimental canopy gaps, under the influence of the 2018/19 drought and heatwaves. We measured PHAR by means of hemispherical photography, approximated water availability based on the inverse of modeled fine root density distributions of overstorey beech (BGRB) and oak (BGRO) and approximated nutrient availability based on soil fertility (SF), derived from forest site mapping. Results indicate that seedling resource availability and resulting growth responses increase with canopy gap size and vary among locations within the gap. Multiplicative non-linear mixed models suggest that AR and NR relative height growth (RI) was best explained by interactive effects of PHAR, BGRB, BGRO and SF, which reflect complementary resource use patterns of beech seedlings. At optimal resource availability, AR reached a potential RI of 174%, which is about 20% higher compared to NR. While the low light growth responses of AR and NR both reflect saturation at 5 to 15% PHAR, depending on individual size and the availability of the remaining resources, NR showed a higher RI than AR at intermediate and high PHAR levels in cases of limited BGR and SF. In contrast to AR, NR growth was affected to a lesser extent by SF and BGRB and not significantly affected by BGRO. These results suggest that overstorey oaks have a lower effect on water availability of beech seedlings than overstorey beeches. Additionally, NR showed higher tolerance to water and nutrient limitation than AR, probably due to better root system development. In conclusion, site-specific potential for mitigating the effects of climate change on beech regeneration through forest management lies in the adaptation of silvicultural systems, i.e., the creation of canopy gaps larger than 200 m2, thus significantly exceeding the average gap size of the natural disturbance regime, and the choice of the regeneration method.

Growth and Morphological Patterns of Norway Spruce (Picea abies (L.) Karst.) Juveniles in Response to Light Intensities

(1) Background: The growth and morphology of Norway spruce (Picea abies (L.) Karst.) juveniles were observed under different light conditions due to overstory canopy openness. The aim was to investigate the photo-morphological responses of juveniles for the development of a desirable forest structure. The research was located in a higher altitude zone in central Europe. (2) Methods: Light was estimated using hemispherical photographs. Eight different parameters of natural regeneration were measured on individuals within 1 × 1 m around each point on a 3 × 3 m grid. A total of 1214 sapling measurements (from 10 to 431 cm in height) were taken. (3) Results: Light affected the growth and morphological development of juveniles, resulting in variation in the lateral crown growth and crown length. Acclimations manifested as trade-offs between height and lateral crown growth. Similar shifts were found within relative height growth (the terminal length to the total height) and apical dominance ratio (the terminal length to the branch length). The crown length was proven to be highly capable to acclimation. Light influenced the density weakly, however, when a regeneration index (density × median height) was considered, significant relations with light conditions were discovered.

Morpho-Physiological Strategies of Shorea leprosula Miq. and Shorea acuminata Dyer in Response to Light Intensity and Nutrient Amendments

Successfully restoring degraded forest areas depends on seedlings adapting their growth to suit harsh environments. Hence, the requirements for seedlings’ growth need to be addressed before replanting degraded sites. The present study determines the effect of abiotic factors viz. light irradiance (8%, 30%, and 100%), nutrient addition (no fertiliser (NF), NPK, and vermicompost) on the growth performance and photosynthetic capacity of two dipterocarp species seedlings, Shorea leprosula Miq. and Shorea acuminata Dyer. The morphological characteristics assessed for growth performance comprised plant height, stem diameter, leaf count, leaf area, relative chlorophyll concentration, biomass, and root-to-shoot ratio. Li-Cor 6400 and 6800 were used to measure the leaf gas exchange traits, including photosynthetic rate (A), transpiration rate (E), intercellular CO2 concentration (Ci), stomatal conductance (gsw), and water-use efficiency (WUE). Our results demonstrated that different levels of light intensity and nutrient amendment significantly impacted plant-growth performance. Plants grown in 30% irradiance showed better growth performance in terms of relative height growth rate (RHGR), mean number of leaves, and leaf areas 41%, 24%, and 32% higher than the control. The A value was also higher in 30% irradiance, but no significant differences were observed between each level of light irradiance. The addition of vermicompost gave better growth for RHGR, relative diameter growth rate (RDGR), mean number of leaves, biomass, and relative chlorophyll concentrations 47%, 40%, 131%, 19%, and 27% higher than the control, respectively. However, the results obtained for photosynthetic parameters were contrary to growth performance. The photosynthesis rate (A) was higher (14.8%) in NPK compared to the control, and the other photosynthetic parameters did not differ significantly despite different nutrient amendments. In terms of species, S. leprosula has better growth performance and photosynthetic characteristics than S. acuminata in different light irradiance and nutrient amendments, thereby rendering S. leprosula the preferred rehabilitation species. Generally, nutrient addition of either NPK or vermicompost and 30% light irradiance gave better morphological and physiological growth for both species. The outcome of this study could provide a better understanding on the forest rehabilitation strategy to reduce the seedling-mortality rate, particularly for climax tree species.

Polar day syndrome: differences in growth, photosynthetic traits and sink-size patterns between northern and southern Finnish silver birch (Betula pendula Roth) provenances in native and non-native photoperiods.

Continuous light (CL) is available throughout the polar day for plants in the Arctic during the growing season, whereas provenances of the same species experience a very different environment with non-CL (NCL) just a few latitudes to the south. Both provenances need to acclimate to climate warming, yet we lack comprehensive understanding of how their growth, photosynthesis and leaf traits differ. Further, the provenances presumably have morphological and physiological adaptations to their native environments and therefore differ in response to photoperiod. We tested the height growth, leaf longevity, biomass accumulation, biomass allocation and rates of gas exchange of northern (67°N) and southern (61°N) Finnish silver birch (Betula pendula Roth) origins in CL- and NCL-treatments in a 4-month chamber experiment. Irrespective of photoperiod, 67°N had higher area-based photosynthetic rate (Anet), stomatal conductance (gs) and relative height growth rate (RGR), but lower stomatal density and fewer branches and leaves than 61°N. Photoperiod affected height growth cessation, biomass and photosynthetic traits, whereas leaf longevity and many leaf functional traits remained unchanged. In CL, both provenances had lower gs, higher RGR, increased shoot:root ratio and increased sink sizes (more branching, more leaves, increased total plant dry weight) compared with NCL. In NCL, 67°N ceased height growth earlier than in CL, which altered biomass accumulation and distribution patterns. Northern conditions impose challenges for plant growth and physiology. Whether a provenance inhabits and is adapted to an area with or without CL can also affect its response to the changing climate. Northern birches may have adapted to CL and the short growing season with a 'polar day syndrome' of traits, including relatively high gas exchange rates with low leaf biomass and growth traits that are mainly limited by the environment and the earlier growth cessation (to avoid frost damage).

Growth performance and scale insect infestation of Shorea leprosula in a common garden experimental plot

Many tree planting programmes have long been initiated to increase forest cover to mitigate the effects of global climate change. Successful planting requires careful planning at the project level, including using suitable species with favourable traits. However, there is a paucity of improvement data for tropical tree species. An experimental common garden of Shorea leprosula was established to study traits related to growth performance which are key factors in planting success. Seedlings of S. leprosula were collected from nine geographical forest reserves. To study the effects of genetic variation, seedlings were planted in a common environment following a randomized complete block design. From performance data collected 2017‒2019, one population showed the highest coefficient for relative height growth, significantly higher than most of the other populations. Interestingly, this population from Beserah also exhibited the lowest coefficient for scale insect infestation. This study provides preliminary results on growth performance and susceptibility to scale insect infestation in S. leprosula and the first common garden experiment site conducted on dipterocarp species. It lays a foundation for future genome-wide studies.

QTL mapping of drought-related traits in the hybrids of Populus deltoides ‘Danhong’×Populus simonii ‘Tongliao1’

BackgroundPoplar trees provide a large amount of wood material, but many parts of the world are arid or semi-arid areas because of insufficient annual precipitation, which seriously affects the growth of poplar trees. Populus simonii ‘Tongliao1’ shows strong tolerance to stress environments, and Populus deltoides ‘Danhong’ shows a stronger growth rate in a suitable environment. To identify drought tolerance-related QTLs and genes, an F1 population derived from the cross between the ‘Danhong’ and ‘Tongliao 1’ Populus was assessed under drought stress.ResultsWe measured drought-related traits such as the relative height growth, relative diameter growth, leaf senescence number, specific leaf area, and leaf relative water content in the population under control and drought environments. The results showed that drought stress reduced the plant height relative growth, ground diameter relative growth, specific leaf area and leaf relative water content and increased the number of leaf drops. A total of 208 QTLs were identified by QTL mapping analysis, and they consisted of 92, 63 and 53 QTLs under control, drought stress treatment and drought index conditions, respectively. A molecular identification marker for drought tolerance, np2841, which was associated with a QTL (qDLRWC-LG10-1) for relative leaf water content, was initially developed. We mined 187 candidate genes for QTL regions of five traits under a drought environment. The reference genome annotation for Populus trichocarpa and a homologous gene analysis of Arabidopsis thaliana identified two candidate genes, Potri.003G171300 and Potri.012G123900, with significant functions in response to drought stress. We identified five key regulatory genes (Potri.006G273500, Potri.007G111500, Potri.007G111600, Potri.007G111700, and Potri.007G111800) related to drought tolerance through the poplar coexpression network.ConclusionIn this study, our results indicate that the QTLs can effectively enhance the drought tolerance of poplar. It is a step closer towards unravelling the genetic basis of poplar drought tolerance-related traits, and to providing validated candidate genes and molecular markers for future genetic improvement.

An Arboriculture Treatment of Biochar, Fertilization, and Tillage Improves Soil Organic Matter and Tree Growth in a Suburban Street Tree Landscape in Bolingbrook, Illinois, USA

Background: Urban tree growth may be reduced due to poor urban soil conditions. Soil management to alleviate poor urban soil conditions often includes organic amendments, fertilization, and/or tillage. A 3-year experiment was conducted in an urban landscape in Bolingbrook, Illinois, USA, to test whether an arboriculture treatment with biochar, fertilization, and tillage could improve soil quality and tree growth. Methods: The urban landscape included 75 street trees (Gleditsia triacanthos, Ulmus parvifolia, and Acer rubrum) growing in compacted, fine-textured soils. Results: The results of this experiment suggest that the arboricultural treatment of biochar, fertilization, and tillage (BFT) may improve soil quality and urban tree growth. Relative height growth was significantly greater (P ≤ 0.05) for Acer rubrum trees with BFT treatment (+ 28.9%) compared to tillage alone (+ 13.3%). Total soil organic matter (SOM), particulate soil organic matter (POM), and a soil quality index (SQI) were significantly (P ≤ 0.05) greater in the BFT treatment (total SOM = 6.00%, POM = 9.73%, and SQI = 70.2) compared to the tillage treatment (total SOM = 5.29%, POM = 7.23%, and SQI = 60.8). The SOM responses to the BFT treatment appear to be relatively short-lived but correlated with measures of tree growth. Conclusion: This arboricultural treatment of biochar, fertilization, and tillage has potential to be used to improve soil quality and promote growth for trees growing in compacted, fine-textured soils in suburban street tree landscapes.

Do Various Conifers Respond Differently to Water Stress? A Comparative Study of White Pine, Concolor and Balsam Fir

Aim of study: Two-year-old containerized balsam and concolor fir and one-year-old Eastern white pine transplants were grown under variable watering regimes with the goal of identifying plant morphological and some physiological traits under water stress. Area of study: This experiment was conducted in a greenhouse at the Tree Research Center on the Michigan State University campus, East Lansing, Michigan. Material and methods: Relative root collar diameter (RRCD), height growth (RHG), and root length (RRL) were measured as growth parameters. Stem water potential (Ψ), stomatal conductance (gs), net photosynthetic rate (Anet), intrinsic water use efficiency (iWUE=Anet/gs), foliar potassium (K+), and calcium (Ca+2) concentration were measured as physiological traits. Main results: Well-watered transplants had significantly higher RRCD, RHG, and RRL in fir species. Balsam fir and white pine transplants had a higher Ψ than concolor fir under severe stress. Fir species had higher Anet, gs, and a lower iWUE than white pine. White pine had a lower foliar K+ concentration, while balsam fir had the highest foliar Ca+2 concentration. Balsam fir had higher growth and Anet, gs, and iWUE under water stress due to their ability to maintain higher water uptake despite a reduced soil water content. Highlights: It is concluded that white pine has better drought tolerance because of the ability to withstand water stress through the mechanism of reduced photosynthetic activities and growth, minimize water loss, and increase water uptake.

Effects of elevated CO2 concentration and nitrogen addition on the chemical compositions, construction cost and payback time of subtropical trees in Cd-contaminated mesocosm soil.

Rising atmospheric CO2 concentration ([CO2]) and nitrogen (N) deposition are changing plant growth, physiological characteristics and chemical compositions; however, few studies have explored such impacts in a heavy metal-contaminated environment. In this study, we conducted an open-top chamber experiment to explore the impacts of 2 years of elevated atmospheric [CO2] and N addition on the growth, physiological characteristics and chemical compositions of five subtropical tree species in a cadmium (Cd)-contaminated environment. Results showed that N addition significantly increased concentration of leaf N and protein in five tree species and also decreased payback time (PBT) and leaf carbon:nitrogen ratios and increased tree relative height growth rate (RGR-H) and basal diameter growth rate (RGR-B) in Liquidambar formosana Hance and Syzygium hainanense Chang et Miau. Elevated [CO2] increased leaf maximum photosynthetic rate (Amax) and concentration of total non-structural carbohydrates and shortened PBT to offset the negative effect of Cd contamination on RGR-B in Acacia auriculiformis A. Cunn. ex Benth. The combined effects of elevated [CO2] and N addition did not exceed their separate effects on RGR-H and RGR-B in Castanopsis hystrix Hook. f. & Thomson ex A. DC. and Cinnamomum camphora (L.) presl. The addition of N significantly increased the concentration of leaf Cd by 162.1% and 338.0%, and plant Cd bio-concentration factor by 464% and 861% in C. hystrix and C. camphora, respectively, compared with only Cd addition. Among the five tree species, the decrease in PBT and the increase in Amax, RGR-B and concentrations of leaf protein in response to N and Cd addition under elevated [CO2] were on average 86.7% higher in A. auriculiformis than other species, suggesting that the mitigation of the negative effects of Cd pollution by elevated [CO2] and N addition among five species was species-specific. Overall, we concluded that N addition and elevated [CO2] reduced Cd toxicity and increased the growth rate in A. auriculiformis, S. hainanense and L. formosana, while it maintained the growth rate in C. hystrix and C. camphora by differently increasing photosynthetic rate, altering the leaf chemical compositions and shortening PBT.

EXAMINATION OF GAS EXCHANGE PARAMETERS OF Abies balsamea (L) MILL. AND Abies concolor SAPLINGS, GROWN UNDER VARIOUS WATER REGIME, EXPOSED TO EXTREME DROUGHT STRESS AT THE END OF THE GROWING SEASON

Two-year-old (plug+1) containerized Abies balsamea (L) Mill. and Abies concolor saplings were grown under various irrigation in the greenhouse to examine gas exchange parameters end of the growing period when they were exposed to extreme drought stress. Relative height growth (RHG) and relative root collar diameter (RRCD) were measured next to gas exchange parameters, such as net photosynthetic rate (Anet), stomatal conductance (gs), transpiration rate (E), intrinsic water use efficiency (iWUE=Anet/gs), and water use efficiency (WUE=Anet/E). As a result, Abies balsamea saplings had a higher RHG and RRCD than Abies concolor. Species had a significant effect on leaf gas exchange parameters that Abies balsamea had a higher Anet, gs, and a lower iWUE than Abies concolor. Increasing irrigation increased Anet and E. The interaction of species and time was statistically significant for gs and iWUE measurement. İncreasing prolonged drought decreased gs and did not change iWUE values for Abies balsamea, while increased gs and reduced iWUE for Abies concolor saplings. Even though Anet, E, and WUE were not statistically significant under the interaction of species and time, there is a decreasing trend for Abies balsamea on these parameters. In contrast, Abies concolor had a decreasing trend on Anet, and WUE and an increasing trend for gs when the saplings were exposed to extreme drought or extended the dehydration period were observed. Abies balsamea had a better performance and drought tolerance than Abies concolor when exposed to a prolonged drought.

The growth rate of hydroponic lettuce at various nutrient compositions from liquid synthetic, solid synthetic, and liquid organic fertilizers

The hydroponic system of lettuce cultivation has become popular in the new normal era after the Covid 19 pandemic. So that the efficiency of input and the ease of supplying nutrients in hydroponic farming deserves to be a concern. Hydroponics commonly uses synthetic fertilizers that are completely available and sold commercially. Efforts are needed to make media choices by utilizing easier and cheaper resources, among others by making various alternative nutrient source compositions from widely available, cheap, and commonly used synthetic fertilizers such as NPK and Gandasil. Another option that also needs to be tested for the efficiency of its utilization is the use of liquid organic fertilizers from chicken feather waste. Calculation of the growth rate of lettuce grown on various nutrient compositions of liquid organic and synthetic fertilizers was carried out. The types of fertilizer composition tested were P1= AB-mix (control) 50 ml in 10 liters of water, P2= NPK 10 g + Gandasil 5 g in 10 liters of water, P3= AB-mix 25 ml + 5 g NPK + 2.5 g Gandasil in 10 liters of water, P4= AB-mix 25 ml + 400 ml chicken feather LOF in 10 liters of water, and P5= 5 g NPK + 2.5 g Gandasil + 400 ml chicken feather LOF in 10 liters of water. The results showed that the highest growth rate of lettuce was obtained in the P4 composition, with the best results for Net assimilation rate (NAR), total wet biomass production per plant, ratio of wet weight of shoot: wet weight roots, relative plant height growth rate, relative leaf number growth rate, and relative plant growth rate.

Seedling Growth and Biomass Production under Different Light Availability Levels and Competition Types

Light availability is a crucial resource determining seedling survival, establishment, and growth. Competition for light is asymmetric, giving the taller individuals a competitive advantage for obtaining light resources. Species-specific traits, e.g., shade tolerance, rooting depth, and leaf morphology, determine their strategical growth response under limited resource availability and different competitive interactions. We established a controlled pot experiment using European beech, Norway spruce, and Douglas fir seedlings and applying three different light availability levels—10%, 20%, and 50%. The experiment’s main aim was to better understand the effects of light availability and competition type on the growth, growth allocation, and biomass production of recently planted seedlings. We planted four seedlings per pot in either monocultures or mixtures of two species. Relative height and diameter growth and aboveground woody biomass of seedlings increased with increasing light availability. All seedlings allocated more growth to height than diameter with decreasing light availability. Seedlings that reached on average greater height in the previous year allocated less growth to height in the following year. Additionally, there were general differences in growth allocation to the height between gymnosperms and angiosperms, but we did not find an effect of the competitor’s identity. Our mixture effect analysis trends suggested that mixtures of functionally dissimilar species are more likely to produce higher biomass than mixtures of more similar species such as the two studied conifers. This finding points towards increased productivity through complementarity.

Growth Characteristics of &lt;i&gt;Quercus serrata&lt;/i&gt; and &lt;i&gt;Quercus glauca&lt;/i&gt; Seedlings in a Restored Urban Forest After Approximately 20 Years Since Construction

To clarify the regeneration processes of two Quercus (Fagaceae) species, Quercus serrata, deciduous broad-leaved tree and Quercus glauca, evergreen broad-leaved tree in an urban forest, 163 research quadrats (163 m2) on the forest floor in a restored deciduous broad-leaved forest, "Inochi- No-Mori" in Kyoto city after approximately 20 years since construction were set up. Growth characteristics, recruitment, mortality and relative height growth rates of seedlings of these two species were investigated. As a result, the recruitment rate of Q. serrata seedlings tends to be higher than that of Q. glauca seedlings, when diffuse site factor was larger than 15.0%, particularly. The relative height growth rate of Q. serrata seedlings in the 15–50-cm height class was relatively high when diffuse site factor was larger than 15.0%. On the other hand, the mortality rate of Q. glauca seedlings in the 15–50-cm height class was very lower than that of Q. serrata seedlings. These results indicate that in order to promote the regeneration of Q. serrata in this site, it is necessary to maintain a light environment with a diffuse site factor amount of larger than 15.0% around the mature Q. serrata trees, by thinning the upper trees and to selectively remove Q. glauca seedlings.

Eighth-year survival and growth of planted replacement tree species in black ash (Fraxinus nigra) wetlands threatened by emerald ash borer in Minnesota, USA

Black ash (Fraxinus nigra) is native to lowland forests of the western Great Lakes region, USA, where it often comprises a majority of trees. Like all native ash in North America, black ash is threatened by emerald ash borer (EAB; Agrilus planipennis), but the impacts from EAB mortality may be particularly severe in these forests given the foundational role of black ash at regulating ecosystem function. Compounding the problem is that associated tree species occur in low abundance and their abundance may be further reduced as habitat declines with climate change. These converging threats point to the need for silvicultural intervention to establish replacement tree species in anticipation of EAB invasion. Here we report on a large-scale management experiment from Minnesota, USA that includes different silvicultural approaches for establishing replacement tree species in black ash forests. Specifically, we examined eighth-year survival and growth of planted seedling in treatments that included clearcutting, group selection, uncut forest, and emulation of EAB mortality by girdling black ash. Species included nine that are native to the ecosystem, two from the next southern climate zone, and one exotic species, Manchurian ash (Fraxinus mandshurica). Among species and treatment combinations, survival was highest for American elm (Ulmus americana), averaging around 81% in uncut, group selection, and girdle treatments. Swamp white oak (Quercus bicolor), a species from the next southern climate zone, also had high survival in these treatments (ranging from 61% to 79%). Both species had survival under 60% in the clearcut treatment. Most native southern boreal species, as well as Manchurian ash, had low survival (0% to less than 40%) in most treatments. In the clearcut, girdle, and group selection treatments relative diameter and relative height growth was highest for balsam poplar (Populus balsamifera), averaging, respectively, around 0.25 mm mm−1 yr−1 and 0.20 cm cm−1 yr−1, followed by swamp white oak and red maple (Acer rubrum). Non-native Manchurian ash had consistently low growth in all treatments compared to other species. All species had low growth rates in the uncut treatment. An integration of survival and diameter growth pointed to group selection as the treatment that provides the best balance between survival and growth. Our results indicate promising survival and growth of at least some replacement species, including several predicted to be future climate-adapted, as well as a silvicultural approach in group selection that is an effective method to regenerate these species.

Climate influences the value of a plant structural defence against browsing

Abstract The circumstances that select for plant anti‐herbivore defences are not well understood. In New Zealand, the ‘divaricate’ cage‐like architecture of many woody plants may have arisen as a defence against avian browsing; it also has some ability to deter browsing by introduced deer. Its prominence on alluvial soils in frosty and droughty areas led us to hypothesize that structural defences are of most value where fertile soils coincide with climatic constraints that prevent plants from quickly growing out of the browse zone. We tested this hypothesis by growing seedlings of three divaricate species and their broadleaved congeners on fenced and unfenced plots beneath tree‐fall gaps at three humid frost‐free sites in the North Island of New Zealand, and at three colder and drier sites in the South Island. Soil total phosphorus levels were moderate to high at all sites (344–961 ppm), and pellet counts indicated similar average deer densities at North and South Island sites, enabling us to attribute variation in seedling growth and survival primarily to climatic differences between our sites. On fenced plots, average relative height growth rates in the North Island exceeded those on the southern sites by 64%, and growth of broadleaved species averaged 132% and 99% greater than that of divaricate congeners at North and South Island sites, respectively. On the northern sites, broadleaved species also held a large (137%) net height growth advantage over divaricates even on unfenced plots. In contrast, exposure to browsing on the coldest sites resulted in complete loss of the broadleaved net height growth advantage. Synthesis. Even in the presence of deer, divaricate plants were overgrown on humid frost‐free sites, but not on colder and drier sites, where browsing neutralized the superior growth potential of broadleaved species. The cost of structural defences therefore paid off only on sites where climatic adversity reduces the ability of plants lacking such defences to grow quickly out of the browse zone, in agreement with our hypothesis.

The millennium shift: Investigating the relationship between environment and growth trends of Norway spruce and Scots pine in northern Europe

For boreal forests in colder climates, changes in environmental conditions are hypothesised to substantially affect ecosystem processes. In this study, trends of top height growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were analysed using permanent sample plot data from more than 300 long-term experimental sites distributed from temperate zones to the boreal forest conditions in Sweden. By regression analyses, the effects of temperature-sum and precipitation-sum on top height growth were assessed in the period 1986–2018. A significant upward temporal trend in height growth was observed for both species, with the trend more pronounced after the millennium shift. The magnitude of the annual relative height growth after the millennium was about 16.92% and 9.54% higher than expected, respectively for Scots pine and Norway spruce. A potential climate response on height growth was found for both species with temperature-sum positively correlated with top height growth. No significant effect of precipitation-sum on height growth was observed for either species. Our results suggest improved growing conditions and forest sites became more productive in response to increasing temperature in the northern temperate and boreal regions. The increasing growth trends may offer shorter rotation periods and increased forest value for Norway spruce and Scots pine, coupled with contributions of boreal forests to the emerging bio-economy and the regulation of global atmospheric carbon.