Negative density dependence may cause reduced clustering among individuals of the same species, and evidence is accumulating that conspecific density-dependent self-thinning is an important mechanism regulating the spatial structure of plant populations. This study evaluates that specific density dependence in three very large observational studies representing three successional stages in a temperate forest in northeastern China. The methods include standard spatial point pattern analysis and a heterogeneous Poisson process as the null model to eliminate the effects of habitat heterogeneity. The results show that most of the species exhibit conspecific density-dependent self-thinning. In the early successional stage 11 of the 16 species, in the intermediate successional stage 18 of the 21 species and in the old growth stage all 21 species exhibited density dependence after removing the effects of habitat heterogeneity. The prevalence of density dependence thus varies among the three successional stages and exhibits an increase with increasing successional stage. The proportion of species showing density dependence varied depending on whether habitat heterogeneity was removed or not. Furthermore, the strength of density dependence is closely related with species abundance. Abundant species with high conspecific aggregation tend to exhibit greater density dependence than rare species.

Growth rates of male and female trees are often different in a dioecious species. In this study, we analyzed sex ratios and the effect of gender, neighborhood competition and habitat factors on the stem growth of dioecious Fraxinus mandshurica trees in a secondary conifer and broad‐leaved mixed forest in the Changbai Mountains of northeastern China. The sex ratio in the 5.2‐ha study area does not deviate significantly from the expected 1:1 ratio, except for trees in the large diameter classes. For dbh >40 cm, the sex ratio is male‐biased. This result suggests that males have a faster rate of stem growth than females, which is usually explained by the higher cost of reproduction in the fruit‐bearing females. An analysis of the dbh distributions of two successive measurements showed that the rate of stem growth of the (27) females drops off with increasing dbh and remains below that of the (35) males. A causal model was used to analyze factors affecting the rate of stem growth, showing that these rates are affected significantly and positively by soil moisture and tree size in both genders and that within‐gender competition is mainly for nitrogen. Our study suggests that neighborhood competition does not affect stem growth significantly, which is a rather surprising result.

As human living environments face increasing challenges with resilience, the concept of nature-based solutions (NBS) was proposed in recent years as a way to promote sustainable living in urban environments. Urban forests and trees play important roles in urban ecosystems, while their potential as an NBS is promising. A bibliometric analysis was first conducted to explore the research pattern of NBS in urban environments. Studies of urban forest and tree-based green infrastructure in NBS research were further investigated using a systematic literature review method. The initial studies on NBS have increased since 2015 with 493 documents published from 142 sources in over 70 countries and regions. Keyword analysis showed green infrastructure had a rather high frequency of utility and received considerable attention. As for urban forests as nature-based solutions (UF-NBS) research, the most prominent study approaches used at different scales and the main benefits and typologies of urban forest studied in the articles were identified. UF-NBS research is still relatively scarce at present. Despite the role of urban forest and trees in addressing environmental challenges being well recognized, UF-NBS studies still need to be conducted in a more comprehensive context, taking social and economic aspects into account.

To quantitatively reflect the relationship between dust and plant spectral reflectance. Dust from different sources in the city were selected to simulate the spectral characteristics of leaf dust. Taking Euonymus japonicus as the research object. Prediction model of leaf dust deposition was established based on spectral parameters. Results showed that among the three different dust pollutants, the reflection spectrum has 6 main reflection peaks and 7 main absorption valleys in 350–2500 nm. A steep reflection platform appears in the 692–763 nm band. In 760–1400 nm, the spectral reflectance gradually decreases with the increase of leaf dust coverage, and the variation range was coal dust > cement dust > pure soil dust. The spectral reflectance in 680–740 nm gradually decreases with the increase of leaf dust coverage. In the near infrared band, the fluctuation amplitude and slope of its first derivative spectrum gradually decrease with the increase of leaf dust. The biggest amplitude of variation was cement dust. With the increase of dust retention, the red edge position generally moves towards short wave direction, and the red edge slope generally decreases. The blue edge position moved to the short wave direction first and then to the long side direction, while the blue edge slope generally shows a decreasing trend. The yellow edge position moved to the long wave direction first and then to the short wave direction (coal dust, cement dust), and generally moved to the long side direction (pure soil dust). The yellow edge slope increases first and then decreases. The R2 values of the determination coefficients of the dust deposition prediction model have reached significant levels, which indicated that there was a relatively stable correlation between the spectral reflectance and dust deposition. The best prediction model of leaf dust deposition was leaf water content index model (y = 1.5019x − 1.4791, R2 = 0.7091, RMSE = 0.9725).

Background Understanding the ecological strategies of urban trees to the urban environment is crucial to the selection and management of urban trees. However, it is still unclear whether urban tree pit cover will affect plant functional traits. Here, we study the response of urban trees to different tree pit covers, analyzed the effects of different cover types on soil properties and their trade-off strategies based on leaf functional traits. Results We found that there were obvious differences in the physical properties of the soil in different tree pit covers. Under the different tree pit cover types, soil bulk density and soil porosity reached the maximum under cement cover and turf cover, respectively. We found that tree pit cover significantly affected the leaf properties of urban trees. Leaf thickness, chlorophyll content index and stomatal density were mainly affected by soil bulk density and non-capillary porosity in a positive direction, and were affected by soil total porosity and capillary porosity in a negative direction. Leaf dry matter content and stomata area were mainly negatively affected by soil bulk density and non-capillary porosity, and positively affected by soil total porosity and capillary porosity. Covering materials of tree pits promoted the functional adjustment of plants and form the best combination of functions. Conclusion Under the influence of tree pit cover, plant have low specific leaf area, stomata density, high leaf thickness, chlorophyll content index, leaf dry matter content, leaf tissue density and stomata area, which belong to “quick investment-return” type in the leaf economics spectrum.

& Key messageWe present comparisons about biomass allocation between males and hermaphrodites of androdioecious Acer tegmentosum Maxim.. Different biomass allocation patterns were found, and males were shown to have a larger investment into coarse roots and foliage. & Context Sexual dimorphism in differences of reproductive costs between genders has been widely reported for trees, but we still know little about allometric relationships between tree components in both genders. & Aims We present biomass allocation patterns and relationships between components of the androdioecious A. tegmentosum in a broad-leaved mixed forest in northeastern China. The objectives of this study were to examine how gender affects the biomass structure of androdioecious species and how the gender-related reproductive efforts affect the allometric relationships. & Methods We harvested 31 hermaphrodite and 29 male A. tegmentosum trees and opted for diameter at breast height, tree height, and crown length as the independent variables and various biomass components as the dependent variables. Five types of function were used to model allometry equations. & Results Biomass allocation between genders was different, and the best biomass model for each biomass component varies between genders. Males have a higher investment in foliage and coarse root biomass than hermaphrodites, and hermaphrodites invested more in reproduction than males.& Conclusion Biomass equations are strongly gender-related. Males tended to invest a larger fraction of the vegetative biomass into leaves and coarse roots.

This study evaluates stoichiometry patterns in the androdioecious Acer tegmentosum, a species characterized by a rare reproductive system where males and hermaphrodites coexist. Altogether 31 hermaphrodites and 29 male plants were harvested and samples of leaves, current-year shoots, branches and coarse roots were analyzed to explore gender differences in biomass, C, N and P concentrations of these four components. The nitrogen to phosphorus relationship of each component was examined using SMA estimates. Males had significantly greater amounts of leaf and coarse root dry matter content than hermaphrodites. C, N and P stoichiometry differed significantly between genders, especially in the newly emerging vegetative components (leaves and shoots). Males had higher C/N and C/P ratios in current-year shoots and lower C/P ratios in leaves and branches. Hermaphrodites had higher N/P ratios in the leaves and branches. Males had higher rates of increase in leaf P content than hermaphrodites. This study suggests that stoichiometry patterns may be significantly affected by gender.

Studies on the influence of parasitism on plants based on hyperspectral analysis have not been reported so far. To fully understand the variation characteristics and laws of leaf reflectance spectrum and functional traits after the urban plant parasitized by Cuscuta japonica Choisy. Osmanthus fragrans (Thunb.) Lour. was taken as the research object to analyze the spectral reflectance and functional traits characteristics at different parasitical stages. Results showed that the spectral reflectance was higher than those being parasitized in the visible and near-infrared range. The spectral reflectance in 750~1400 nm was the sensitive range of spectral response of host plant to parasitic infection, which is universal at different parasitic stages. We established a chlorophyll inversion model (y = −65913.323x + 9.783, R2 = 0.6888) based on the reflectance of red valley, which can be used for chlorophyll content of the parasitic Osmanthus fragrans. There was a significant correlation between spectral parameters and chlorophyll content index. Through the change of spectral parameters, we can predict the chlorophyll content of Osmanthus fragrans under different parasitic degrees. After being parasitized, the leaf functional traits of host plant were generally characterized by large leaf thickness, small leaf area, small specific leaf area, low relative chlorophyll content, high leaf dry matter content and high leaf tissue density. These findings indicate that the host plant have adopted a certain trade-off strategy to maintain their growth in the invasion environment of parasitic plants. Therefore, we suspect that the leaf economics spectrum may also exist in the parasitic environment, and there was a general trend toward the “slow investment-return” type in the global leaf economics spectrum.