Selected Tree Species Research Articles

N-fixing tree species promote the chemical stability of soil organic carbon in subtropical plantations through increasing the relative contribution of plant-derived lipids

Biodiversity experiments have shown that soil organic carbon (SOC) is not only a function of plant diversity, but is also closely related to the nitrogen (N) -fixing plants. However, the effect of N-fixing trees on SOC chemical stability is still little known, especially with the compounding effects of tree species diversity. An experimental field manipulation was established in subtropical plantations of southern China to explore the impacts of tree species richness (i.e., one, two, four and six tree species) and with/without N-fixing trees on SOC chemical stability, as indicated by the ratio of easily oxidized organic carbon to SOC (EOC/SOC). Plant-derived C components in terms of hydrolysable plant lipids and lignin phenols were isolated from soils for evaluating their relative contributions to SOC chemical stability. The results showed that N-fixing tree species rather than tree species richness had a significant effect on EOC/SOC. Hydrolysable plant lipids and lignin phenols were negatively correlated with EOC/SOC, while hydrolysable plant lipids contributed more to EOC/SOC than lignin phenols, especially in the occurrence of N-fixing trees. The presence of N-fixing tree species led to an increase in soil N availability and a decrease in fungal abundance, promoting the selective retention of certain key components of hydrolysable plant lipids, thus enhancing SOC chemical stability. These findings underpin the crucial role of N-fixing trees in shaping SOC chemical stability, and therefore, preferential selection of N-fixing tree species in mixed plantations is an appropriate silvicultural strategy to improve SOC chemical stability in subtropical plantations.

Implementation of swampy forest system for acid mine drainage treatment to meet threshold value

Coal mining with the area of the potential acid-forming category can generate acid mine drainage. Acid mine drainage (AMD) that has been formed must be appropriately managed. There are two techniques to treat AMD by the challenge specificity, including the prohibitive cost of the conventional active treatment with an uncertain process and the passive treatment, which faces time constraints and a wider area for preparation. A novel swampy forest system is a development to overcome the weaknesses of conventional processing by naturally responsive mitigation, reducing cost and speed, which results in greater capacity in AMD treatment. The swampy forest system implemented in coal mining relies on three main components: empty fruit bunches as organic matter, grass, and selected tree species planted in the treatment pond. The system effectively changes the non-compliance parameters of wastewater when entered at the system’s inlet to meet the threshold value after processing. It allows for flowing to the public bodies references with the applicable regulation.

Planting of Nectar Plants as Feed of Butterflies Imago in Bantimurung Bulusaraung National Park

Bantimurung Bulusaraung National Park is a forest area designated as a conservation area in Sulawesi. The diversity of flora and the presence of unique wildlife supported by the karst ecosystem are the basis for the protection of thia area. Community presure and habitat destruction is the causes of decreasing butterfly populations. Habitat rehabilitation need to be carried out in order to maintain the butterfly population. The understanding of diversity of butterfly species and the selection of protective tree species and animal nests or food are important aspects for sustainableliyty. Most of the types of forage plants are unknown species, so an understanding of planting methods in the field is needed. The research was conducted in observing the diversity of Rhopalocera (butterfly) species as a preliminary research and planting nectar-producing plants as the main research. Research result showed that Nymphalidae family is highest in species diversity index, Nymphalidae and Papilionidae family are highest in richness index, and all famiies are lowin species dominance index and evenness index. Nimphalidae and Papilionidae family is the largest species has been found. Planting nectar plants i.e mali-mali and dao on degraded land with fertilization treatment showed the best results are 600 grams per planting hole for mali-mali and 900 grams per planting hole for dao.

Crown die-back of peri-urban forests after combined heatwave and drought was species-specific, size-dependent, and also related to tree neighbourhood characteristics

The Rhine River valley of Germany has been facing recurrent and intense spells of drought and heatwaves threatening the health of trees in peri-urban forests. Crown damage intensified by climate change accelerates tree mortality, threatening its ecological, economic, and social benefits; however, the pattern of crown die-back in peri-urban forests remained unclear. We performed a field inventory to estimate the crown die-back of 2578 trees of 51 species from 68 randomly selected peri-urban forest plots in Karlsruhe region on the right bank of the Rhine, after the catastrophic summer heatwave and drought of 2018. We related crown die-back to species-specific drought tolerance, wood anatomical traits, tree size, canopy surface temperature, tree density, Shannon's diversity and Gini coefficient for tree height. Regression results indicate that small-size trees were found to be more susceptible to canopy damage than large trees, with a 1-meter increase in tree height associated with a 0.8 % reduction in crown die-back. This size-dependent process is also species-specific. Among the 12 species with significant (p < 0.05) linear relationship between height and die-back, 9 species demonstrated negative correlations and 3 species showed positive relationships. Species tolerant to drought or cavitation (e.g., trees with diffuse porous xylem, 21 species) had significantly lower crown dieback. For example, with a 1-point-scale increase in drought tolerance crown die-back declined 14.35 %. Trees that experienced high canopy surface temperature and grew with high tree density and species diversity (Shannon's diversity) had more crown die-back. However, high structural diversity (Gini coefficient) was related to lower crown die-back. Our results suggested that future research should focus more on tree species-specific hydraulic and thermal traits and tree density and structure management to improve tree health and species selection in peri-urban forests under future climate change.

Pemilihan jenis pohon untuk pengembangan arboretum Kampus IV Universitas Khairun

Arboretum is an artificial forest that collects various types of plants for educational purposes and plant preservation. The development of an arboretum requires basic information on environmental conditions and tree species suitable for planting. Therefore, this study was carried out with the aim of selecting tree species for the development of the arboretum at Campus IV, Khairun University. The research was carried out at Campus IV of Khairun University which included a study of land conditions, a literature review of local tree species, and tree species selection. A potential location for an arboretum is the triangular park at the campus entrance. This location was planted with the Angsana species (Pterocarpus indicus) in 2019, which has now grown to the pole and tree stage with an average height of 6 m and an average crown diameter of 4.1 m. The soil has a clay texture with a pH of 5.2 and humidity of 55%. Thus, the location can be planted with intolerant tree species on the edges and tolerant species in the middle which has been shaded by angsana vegetation. The tree species selected for species enrichment in the arboretum are local species in the Wallacea region, namely Canarium indicum, Palaquium spp., Syzygium malaccense, Vitex cofassus and Diospyros celebica; timber wood-producing species, namely Swietenia macrophylla and Ochroma pyramidale; producer of gaharu NTFPs, namely Aquilaria malaccensis; and shade-tree for aesthetics, namely Tabebuia rosea.

Tree species identity affects nutrient accumulation and stoichiometric in soil aggregates in mixed plantations of subtropical China

The conversion of monocultural to mixed plantations is an increasing and widespread practice worldwide to improve forest productivity and soil fertility. Although tree species identity can affect soil ecological processes, there is still limited research on how it affects soil aggregate stability and nutrient variability. Here, we investigated the variation of 0–100 cm aggregate stability index (percent of aggregate destruction, PAD; fractal dimension, D; geometric mean diameter, GMD; mean weight diameter, MWD), associated carbon (C), nitrogen (N), phosphorus (P), and stoichiometry in mixed plantations from coniferous trees (Pinus massoniana Lamb.) and a variety of individual broadleaved trees (Camellia oleifera Abel, Manglietia chingii Dandy, Cercidiphyllum japonicum Sieb. et Zucc., Michelia maudiae Dunn, and Bretschneidera sinensis Hemsl.). We discovered that compared to coniferous plantations, most mixed plantations significantly improved the mechanical and water stability of topsoil aggregates. Deep-rooted tree species (e.g., Michelia maudiae Dunn) favored the development of subsoil macro-aggregates to improve aggregate water stability (e.g., PAD = 46.10, MWD = 1.23, GMD = 0.49, D = 2.81). Mixed planting led to the enrichment of soil C, N, and P in microaggregate, which increased by at least 37.14, 20.24, and 61.11 %, respectively. The reduced C:P and N:P in soil aggregates indicate that soil P limitation may be alleviated. Furthermore, tree species and soil depth indirectly affected aggregate stability to regulate the accumulation of C, N, and P. Overall, we emphasize the necessity of selecting tree species combinations with complementary ecological niches in mixed plantations to improve soil stability and support forest productivity.

Tree growth as an effect indicator of silvopastoral systems in the low hilly area of western Henan province, China

The low hilly area is a major landform in the west of Henan province, China, and it is suffering soil and water loss because of human activities. The silvopastoral system that combines trees and grasses has been widely used to restore this fragile area. We conducted in situ field experiments in 2011 in the low hilly area of Henan province involving pure forests of Populus simonii (PS; Salicaceae), Platycladus orientalis (PO; Cupressaceae), Quercusvariabilis (QV; Fagaceae), and Robinia pseudoacacia (RP; Fabaceae), and also with each forest tree species being combined with Medicago sativa (MS; Fabaceae) as silvopastoral systems, i.e., PS-MS, PO-MS, QV-MS, and RP-MS, respectively. We recorded tree diameter at breast height (DBH) and tree height (TH) in the years 2014–2016, 2018, 2020, and 2022 for all the different vegetation types. Tree biomass load (TBL, i.e., tree biomass per unit area) was estimated based on DBH and TH using allometric equations for each tree species. Generally, the results showed that the DBH, TH, and TBL were promoted in the silvopastoral systems PS-MS, PO-MS, and QV-MS. Specially, the DBH and TBL of PS-MS and PO-MS tended to be higher and were significantly higher than the pure forests of PS and MS, respectively, in 2014–2016; the silvopastoral systems were not significantly different from the pure forests for DBH in 2018 and 2022, and for TBL in 2018 and 2020. TH was lower in PS-MS and PO-MS than that in PS and PO in 2014–2016, while there was no difference of TH between PS-MS and PS in 2018 and 2022, and TH was higher in PO-MS than that in PO in 2018, 2020 and 2022. The DBH, TH, and TBL were all higher in QV-MS than QV. The TBL in RP-MS was non-significant or lower compared to that in RP. Moreover, TBL tended to be lower in upslope positions than downslope in the pure forests, while there was no difference in most silvopastoral systems. In summary, PS and PO may be suggested as the tree species selection in vegetation restoration processes for about five years, QV may be a better alternative for a long term, while RP is not recommended.

Water-use characteristics of Syzygium antisepticum and Adinandra integerrima in a secondary forest of Khao Yai National Park in Thailand with implications for environmental management.

Southeast Asia has experienced widespread deforestation and change in land use. Consequently, many reforestation projects have been initiated in this region. However, it is imperative to carefully choose the tree species for planting, especially in light of the increasing climate variability and the potential alteration of plantation on the watershed water balance. Thus, the information regarding water-use characteristics of various tree species and sizes is critical in the tree species selection for reforestation. We estimated tree water use (T) of dominant species including Syzygium antisepticum and Adinandra integerrima, hereafter Sa and Ai, respectively, in a secondary tropical forest in Khao Yai National Park, Thailand, using sap flow data, and compared T between species and size classes. Additionally, we evaluated the responses of T of both species in each size class to environmental factors including soil moisture and vapor pressure deficit (VPD). Results showed consistently higher T in Sa compared to Ai across ranges of VPD and soil moisture. Under low soil moisture, T of Sa responded to VPD, following a saturating exponential pattern while Ai maintained T across different VPD levels, irrespective of tree size. No responses of T to VPD were observed in either species when soil water was moderate. When soil moisture was high, T of both species significantly increased and saturated at high VPD, albeit the responses were less sensitive in large trees. Our results imply that Ai may be suitable for reforestation in water-limited areas where droughts frequently occur to minimize reforestation impact on water availability to downstream ecosystems. In contrast, Sa should be planted in regions with abundant and reliable water resources. However, a mixed species plantation should be generally considered to increase forest resilience to increasing climate variation.

Using stomatal conductance capacity during water stress as a tool for tree species selection for urban stormwater control systems

Improving our understanding of how different tree species function in urban stormwater management systems is important, as tree pits may provide a temporary reservoir for stormwater and as trees have the potential to actively reduce stormwater runoff by transpiration. While urban tree planting pits are increasingly used for short-term water storage during stormwater runoff events, this storage can have negative effects on both tree vitality and water removal capacity, since stress from waterlogging result in stomatal closure. However, sensitivity to water stress varies by species. It is therefore important to determine which tree species can maintain long-term vitality and continued transpiration even under water stress, and thus are suitable for such locations. Here, we studied how nine different tree species, varying in expected tolerance to water stress, were affected by short-term and seasonal waterlogging, in a greenhouse experiment. The seedlings (Magnolia x loebneri, Tilia tomentosa, and Sorbus torminalis – low water logging tolerance; Cercidiphyllum japonicum, Rhamnus cathartica, and Fraxinus ornus – medium water logging tolerance; Quercus palustris, Acer saccharinum, and Fraxinus pennsylvanica – high water logging tolerance) were exposed to two days, five days and seasonal waterlogging. The treatments reflected best practice (optimal), suboptimal and total lack of tree pit drainage, using Swedish standards. Stomatal conductance and leaf water potential were determined regularly over a period of 71 days, and morphological adjustments were registered. Four of the species were affected already after two days of waterlogging, with reduced stomatal conductance either during the waterlogging or immediately after, and only the most waterlogging tolerant species were unaffected by the five-day treatment. However, all plants survived waterlogging for almost 30 days before the estimated permanent wilting was reached in some plants. We suggest that tree species selection for stormwater management systems should consider the species’ capacity to maintain high stomatal conductance during waterlogging, as there were clear differences between species. The effectiveness of the selected species could have an important impact on the stormwater management capacity of cities, as well as on other aspects of ecosystem service delivery from urban trees.

Shoot Flammability Patterns in Native and Exotic Street Tree Species at the Wildland–Urban Interface of Eastern Australia

Street trees provide ecosystem services such as heat mitigation, improved community well-being, and biodiversity conservation. At the wildland–urban interface (WUI), high-flammability street trees also provide a conflicting ecosystem disservice, heightening risks of wildfire spread into urban areas. We addressed this service–disservice conflict by assessing shoot flammability patterns in 10 street tree species, to identify low-flammability species that can potentially mitigate wildfire risks at the WUI. We found significant differences among species in flammability attributes including time-to-flame (TTF), flame duration (FD), number of flaming events (nF), and flame temperature (FT), and identified low-flammability species for each attribute. Overall, species’ rankings from least to most flammable differed considerably across the four attributes. For example, native water gum (Tristaniopsis laurina) had the slowest TTF, but had the longest FD. Among nine shoot traits, we found that high leafing intensity was the most frequent trait correlated with flammability. In particular, high leafing intensity was significantly related to fast TTF and high FT. Lack of coordination among flammability attributes suggests that, in general, selection of low-flammability street tree species should consider how each flammability attribute differentially contributes to wildfire spread risk. Nonetheless, native Tuckeroo (Cupaniopsis anacardioides) emerged as a potential candidate for further exploration as a low-flammability street tree as it had comparatively long TTF, short FD, and low nF. We found no consistent evidence that exotic species were less flammable than native species, and suggest that native trees be the focus of further research to identify low-flammability street trees.

Shading and species diversity act as safety nets for seedling survival and vitality of native trees in dryland forests: Implications for restoration

Restoring degraded dryland requires a diverse mix of trees and shrubs with suitable characteristics. Unfortunately, many restoration projects have failed in tropical drylands due to monoculture plantations or a lack of understanding regarding specific species requirements like shading. Therefore, the central question is whether species diversity and shading can improve seedling survival and vitality in dryland conditions. We conducted a tree diversity experiment in northern Ethiopia as part of the International Diversity Experiment Network with Trees (IDENT). We used 17,280 seedlings from 9 native dry Afromontane tree and shrub species, distributed across 270 plots in three replication blocks. Each block contains a shading treatment (shaded versus non-shaded) with three levels of species richness: one-, two- and four-species mixtures with varying levels of functional diversity (FD) categorized as low, medium, and high. Survival and vitality data of the seedlings were analyzed using generalized linear mixed models (GLMMs) and linear mixed-effects models (LMMs). After two growing seasons, the overall seedling survival rate was 84%. We found significantly higher seedling survival, vitality, and chlorophyll content (SPAD value) in shaded conditions, irrespective of the tree diversity level. However, increasing species richness did improve seedling vitality in non-shaded conditions, but its impact diminished in shaded situations. The findings from this study suggest that careful selection of tree species, appropriate shading, and optimal levels of species diversity can greatly enhance the survival and performance of seedlings. This is particularly important for the successful restoration of dryland forests.

Tree species differ in plant economic spectrum traits in the tropical dry forest of Mexico.

In tropical dry forests, studies on wood anatomical traits have concentrated mainly on variations in vessel diameter and frequency. Recent research suggests that parenchyma and fibers also play an important role in water conduction and in xylem hydraulic safety. However, these relationships are not fully understood, and wood trait variation among different functional profiles as well as their variation under different water availability scenarios have been little studied. In this work, we aim to (1) characterize a set of wood anatomical traits among six selected tree species that represent the economic spectrum of tropical dry forests, (2) assess the variation in these traits under three different rainfall regimes, and (3) determine the relationships between wood anatomical traits and possible functional trade-offs. Differences among species and sites in wood traits were explored. Linear mixed models were fitted, and model comparison was performed. Most variation occurred among species along the economic spectrum. Obligate deciduous, low wood density species were characterized by wood with wide vessels and low frequency, suggesting high water transport capacity but sensitivity to drought. Moreover, high cell fractions of carbon and water storage were also found in these tree species related to the occurrence of abundant parenchyma or septate fibers. Contrary to what most studies show, Cochlospermum vitifolium, a succulent tree species, presented the greatest variation in wood traits. Facultative deciduous, high wood density species were characterized by a sturdy vascular system that may favor resistance to cavitation and low reserve storage. Contrary to our expectations, variation among the rainfall regimes was generally low in all species and was mostly related to vessel traits, while fiber and parenchyma traits presented little variation among species. Strong functional associations between wood anatomical traits and functional trade-offs were found for the six tree species studied along the economic spectrum of tropical dry forests.

Remote-Sensed Tree Crown Diameter as a Predictor of Stem Diameter and Above-Ground Biomass in Betula pendula Roth and Populus tremuloides Michx. × Populus tremula L. Plantations

Striving for climate neutrality and wider implementation of climate change mitigation measures including tree introduction in agricultural land, request for approaches and general allometric models for estimating carbon (C) stock in tree above-ground biomass (AGB) based on relatively easily obtainable remote sensing data is increasing. Here, we present estimates of individual trees’ crown diameters (CDs) for Betula pendula Roth (B. pendula) and Populus tremuloides Michx. × Populus tremula L. (P. tremuloides × P. tremula) in 11-year-old tree plantations (tree height ranged up to 12.8 and 18.1 m, respectively) in the hemiboreal region of Europe (in Latvia). Individual trees’ CDs were measured using a drone orthophoto map. Afterwards, linear equations were developed to predict individual trees’ stem diameters at breast height (DBHs) and, consequently, tree AGB (which was then converted to C stock) from remote-sensed tree CD data. RMSEs of the prediction models of tree stem DBH were in the ranges of 1.87–2.12 cm for B. pendula and 2.50–3.12 cm for P. tremuloides × P. tremula. This demonstrated approach is applicable to carry out, for instance, a self-assessment and approximate C stock in the AGB of selected tree species by land owners, managers, and other implementers of climate change mitigation measures.

Linkages of soil CO2 emission with plant functional traits in young subtropical plantations.

Soil respiration is a key process in forest biogeochemical cycling. Exploring the relationship between plant functional traits and soil respiration can help understand the effects of tree species conversion on soil carbon cycling. In this study, we selected 15 common subtropical tree species planted in the logging site of second-generation Chinese fir forest to measure soil CO2 emission fluxes, soil physicochemical properties, leaf and root functional traits of each species, and explored the effects of plant functional traits on soil respiration. The results showed that the annual flux of soil CO2 emissions varied from 7.93 to 22.52 Mg CO2·hm-2, with the highest value under Castanopsis carlesii (22.52 Mg CO2·hm-2) and the lowest value under Taxus wallichiana (7.93 Mg CO2·hm-2). Results of stepwise regression analysis showed that the annual flux of soil CO2 emission decreased with the increases of leaf nitrogen content and fine root diameter, and increased with increasing leaf non-structural carbohydrate. In the structural equation model, leaf non-structural carbohydrate had a direct and significant positive effect on soil CO2 emission fluxes, while leaf nitrogen content and fine root diameter had a direct negative effect by decreasing soil pH and soluble organic nitrogen content. Plantations of different tree species would affect soil CO2 emission directly by changing functional traits related to water and nutrient acquisition or indirectly through soil properties. When creating plantations, we should select tree species based on the relationship between plant functional traits and ecosystem functions, with a view to improving forest productivity and soil carbon sequestration potential.

Urban Forest Management Policy Analysis (Case of Serang City)

Urban forests are an instrument of urban ecosystems, their existence is very important in the midst of declining environmental quality in urban areas, besides that urban forests also have various environmental service functions such as being able to absorb CO2 content, as an oxygen supply, then urban forests also have economic value. The policy on urban forest management is important so that its sustainability is maintained. Therefore, this study aims to analyze urban forest policies in forest management. This research was conducted in Serang City. This research approach uses the ANP (Analysis Network Process) approach, involving respondents from the Government (Regional Government Development Agency and Environmental services), forestry academics, forest researchers, KLHK employees in the forestry sector, practitioners engaged in forestry and environmental non-governmental organizations. The results of this study that from the three levels analyzed are factors, actors, and alternatives. The results from the level factor (policy support, quality improvement, evaluation and monitoring) show that policy support is the most priority thing. Meanwhile, from the level of actors (Government, Community, Private, government and private, NGOs) shows that the most influential actor in urban forest management is a combination of government and private sector. Then at the alternative level (evaluation of regulations, selection of tree species, expansion of urban forests, incentives, and sanctions) shows that the expansion of urban forests is the most important thing to implement.

Species-Specific Level Variation in Polyamines in Coniferous and Deciduous Woody Plant Species in Urban Areas

Urban heat islands (UHIs) and global warming will unavoidably have a negative impact on human health in urban areas, making urban forests much more susceptible to the risk of heat waves than forests. It is pivotal for urban forest management to understand tree species’ adaptation mechanisms by focusing on the species-dependent variability of polyamines (PAs), significant players in the amelioration of biotic and abiotic stress in plants, to mitigate the negative effects of UHIs and global warming on human health. Based on this background, the content of major polyamines (PAs) (putrescine, spermidine, and spermine) and total phenolics and the corresponding antioxidant capacities were determined and analyzed in the 24 most prevalent deciduous and coniferous tree species found in urban areas, namely Futoški Park in Novi Sad (Serbia). High-performance liquid chromatography (HPLC) coupled with fluorometric detection (HPLC-FD) was used to separate and quantify major PAs from tree species. Results showed a species-specific level variation in polyamines, total phenolic, and antioxidant capacity in coniferous and deciduous woody plant species in inspected urban areas. In terms of total PA content, the most notable deciduous tree species were Betula pendula, Junglans regia, and Quercus rubra, while the coniferous tree species Thuja occidentalis, Taxodium distichum, Pinus nigra, and Abies concolor stand out. The most dominant foliar PA in most of the inspected species was putrescine (ranging from 527.67 to 10,049.3 nmol g−1 DW), followed by spermidine (from 250.56 to 2015.92 nmol g−1 DW) and spermine (from 168.8 to 718.41 nmol g−1 DW). Furthermore, significant intra-genus variability in terms of PA content was recorded within the genera Pinus, Thuja, and Picea. This study demonstrated that the PA and phenolic compounds, in combination with antioxidant assays, can serve as reliable and trustworthy criteria and descriptors for the selection of adaptable tree species in the context of urban climate–smart forestry.

Chimpanzees select comfortable nesting tree species

Every evening, chimpanzees build sleeping “nests” in trees. In some studied communities, individuals appear to be selective about the tree species used, which has led researchers to hypothesize whether chimpanzees prefer trees that repel troublesome insects or/and that provide comfortable and stable structures. We investigate these hypotheses, or a trade-off between both, though study of tree species preference based on their biomechanical and/or biochemical properties in the Sebitoli chimpanzee community in Kibale National Park, Uganda. The ten tree species most frequently used for nesting were compared with ten abundant in their environment but not preferred for nesting. For these 20 tree species, we determined their biomechanical and morphological characteristics such as foliar density, foliar units form (shape and size) and branch rigidity. Their spatial repellent activity, previously tested against Anopheles gambiae was incorporated into the analysis. Chimpanzees chose tree species with medium-sized and elongated foliar units, high foliar density and branch with stiffer wood. In addition, most tree species with such mechanical and morphological properties also have mosquito repellent activity. These tree properties may provide a comfortable sleeping environment enhancing sleep quality. Finally, a comparison across chimpanzee communities would be relevant to understand whether these choices are not only ecological but also cultural.

Effect of urban pavement on nutrient strategies of common greening tree species in northern China

There are many factors that affect how urban tree species absorb and use nutrients, but little is known about the impact of pavement in urban areas. In this study, we selected four common urban tree species—Platanus x acerifolia, Metasequoia glyptostroboides, Robinia pseudoacacia, and Pinus thunbergii—and three pavement coverage categories—unpaved, semi-paved, and fully paved—in Qingdao, a typical city in northern China, to investigate changes in the leaf nutrient utilization strategies of tree species in paved environments. The nitrogen (N) resorption efficiency (NRE) and phosphorus (P) resorption efficiency (PRE) of R. pseudoacacia and the NRE of M. glyptostroboides increased in semi- and fully paved environments. Additionally, the N resorption proficiency of M. glyptostroboides increased significantly with pavement coverage, indicating that the biochemical limitation on N resorption was weakened. Similarly, the contents of N, P, and potassium (K) in R. pseudoacacia and N and K in M. glyptostroboides significantly increased with pavement coverage. This indicates that R. pseudoacacia, a nitrogen-fixing Fabaceae tree species, and M. glyptostroboides, a deciduous Cupressaceae tree species, can better adapt to pavement in urban settings, and even high pavement coverage levels can induce higher nutrient contents and resorption capacities. In addition, M. glyptostroboides showed potentially poor adaptability for N, P, and K uptake in the more stressful pavement environments, and P. x acerifolia showed relatively poor adaptability in P-limited environments. Robinia pseudoacacia associates with nodule-forming nitrogen-fixing bacteria, thus retaining more N in its leaves and showing a low NRE. These findings not only provide additional insight into tree growth at varying pavement coverages but also preliminary guidance for tree species selection to promote resilience in urban areas.

Comparing water uptake patterns of two tree species using stable isotopes on the Loess Plateau, China

AbstractThe water consumption mechanism of plantations is important to understand for the selection of afforestation tree species and sustainable watershed management in semi‐arid regions. In this study, Robinia pseudoacacia and Pinus tabuliformis, which are commonly planted on the Loess Plateau of China, were selected to investigate the possible difference in water uptake modes. In 2019–2020, the stable isotopic compositions (δ2H, δ18O) of precipitation and the xylem and soil water of these two trees were sampled and compared using the direct inference approach and MixSIAR model. The difference in soil moisture was also measured. The results showed that the δ18O content of surface soil water (0–40 cm) was closely related to precipitation, while that of deep soil layers (100–200 cm) remained stable. The MixSIAR model performed appropriately in quantifying water apportionment, especially in the drought year of 2019. In July–August 2019, R. pseudoacacia showed strong drought resilience by absorbing water from the deep soil. The 0–40 cm and 100–200 cm soil layers contributed 0.325 and 0.376 to water absorption of R. pseudoacacia, and 0.675 and 0.151 to that of P. tabuliformis, respectively. However, there was a minor difference in the soil water uptake modes between the two species in the humid year of 2020. Compared with P. tabuliformis, R. pseudoacacia increased its consumption of water by 9.9% and 25.1% in the drought and humid year, respectively, which indicated that R. pseudoacacia plantations may contributed to drier deep soil layers. This study helps to improve our understanding of the water uptake mechanisms of common afforestation tree species on the Loess Plateau.

The right tree for the right street canyons: An approach of tree species selection for mitigating air pollution

Trees planted in street canyons affect the dispersion and deposition of air pollutants primarily through their aerodynamic and deposition effects to change the air quality. However, the potential of trees to improve air quality is uncertain as it depends on a combination of tree forms (species), street canyon geometry and local meteorological conditions. We developed a method to select tree forms with appropriate morphology in specific street canyons based on Computational Fluid Dynamics (CFD) simulation, aiming to promote the dispersion and concentration reduction of pollutants at pedestrian height. In this method, we combined the leaf area density (LAD), crown diameter (CD), tree height (H), and trunk height (TH) as representative metrics for various tree forms. The effects of street canyon aspect ratio, wind direction, and wind speed on the potential of trees to regulate pollutant concentrations were comprehensively considered. In a case study in Wuhan, China, 15 tree forms and corresponding 36 tree species adapted to different street canyons were identified using the validated ENVI-met model. Our research offers practical recommendations and effective tools for professionals and policymakers to select tree species that can enhance the air quality in street canyons.