Aims To understand the key processes driving the community assembly and diversity patterns in North China.
Methods We investigated species composition of 87 plots from 29 sites. We applied phylogenetic approach, combined with community distribution information, to assess the community structure and diversity along environmental gradients. We then performed a variance partition to explore the relative importance of each environmental factor that influencing the patterns of community assembly and diversity process and a canonical correspondence analysis to analyze reason of community distributions.
Important findings Similar communities showed similar habitat preferences, demonstrating that environments may shape species composition of the communities. The phylogenetic diversity showed a uni-modal pattern with the mean annual temperature (MAT), but increased with the mean annual precipitation (MAP), partly because of the strong disturbance in high-MAT regions. Temperature dominated the phylogenetic structure of the broad- leaved forests in North China. Environmental filtering dominate the community assembly processes in the areas with relatively low MAT. In addition, the effect of environment filtering increased with MAP.

Aims Larch forests are important for timber harvesting and water-soil conservation in North China. To explore the distribution, community structure and species diversity of larch forests is important for the vegetation conservation and sustainable utilization in North China.
Methods We collected species composition and local environment for 215 forest plots dominated by three common larch species, namely, Larix principis-rupprechtii, L. kaempferi and L. chinensis, in North China during 2000-2017. Among these types, L. kaempferi forests are planted, while L. chinensis forests are almost natural, and most of L. principis-rupprechtii forests are natural. Based these data, we used the canonical correspondence analysis (CCA) to explore the relationship between species composition and environment. We also explored the pattern of community structure and species diversity of these three forests in relation to environmental factors.
Important findings Mean annual air temperature (MAT) was the most important factor for the distribution of these larch forests. The proportion of natural forest decreased, while that of planted forest increased, with MAT. Diameter at breast height (DBH) and height distribution of three larch forests were right-skewed, indicating that all of these larch forests are at relatively stable successional stage. Species richness differ remarkably among different larch forests, which was highest in the L. chinensis forests (39.3 ± 17.9), followed by the L. kaempferi forests (37.4 ± 22.4), and lowest in the L. principis-rupprechtii forests (planted forests 27.2 ± 17.7, natural forests 27.5 ± 13.8). Species richness, the maximum DBH and the maximum height decreased with latitudes and longitudes. Species richness, the maximum DBH and the maximum height increased with annual precipitation. However, species richness showed no significant trend, and the maximum height increased, while the maximum DBH decreased, with MAT. The patterns of species richness along geographical and climatic gradients were consistent between the planted, the natural and the overall (including both planted and natural) larch forests. However, the patterns of community structure differed remarkably among planted, natural and overall larch forests. The maximum height of planted forests increased, while that of natural forests decreased, with latitude and longitude. The maximum DBH and height of natural forests decreased, while those of planted forests increased, with MAT and annual precipitation, respectively.

Aims Explore the distribution pattern and the processes controlling the assembly of the Juglans mandshurica dominated forests in North China.
Methods We investigated 84 plots, each with an area of 20 m × 30 m, for the J. mandshurica forests in the North China. We analyzed demography of the J. mandshurica based on its diameters, and applied canonical correspondence analysis (CCA) to explore the relationship between environment and species composition of different formations of the J. mandshurica forests. We then calculated phylogenetic index, i.e., net relatedness index (NRI) and nearest taxonomic index (NTI) and Gaussian Kernel Density Estimation (Gaussian KDE), for each plot to explore the rules controlling community assembly of these forests.
Important findings The population of J. mandshurica is relatively young in the Northern China, with a mean diameters at breast height (DBH) of 5.36 cm. Distribution of J. mandshurica in North China varied significantly with altitude, slope, slope position and human disturbance. Most of the J. mandshurica located at the low part of the massif with lower altitude and less human disturbance. In North China, niche related processes regulated species coexistence of Form. J. mandshurica, with competition controlled the community assembly in Hebei, Shaanxi and Tianjin, while environment filtering dominated in Beijing and Shanxi.

Aims Understanding the spatial patterns and maintenance mechanisms of biodiversity is one of the central issues in ecology and biogeography. Specifically, altitudinal patterns of biodiversity have been widely explored to represent to mimic the latitudinal patterns. However, previous studies on altitudinal patterns of plant diversity have focused mainly on the taxonomic diversity, with less attention paid to the comprehensive information of taxonomic, phylogenetic evolution and functional traits. In this study, we explored maintenance mechanisms of diversity of forest communities in Mount Guandi, by comparing the altitudinal patterns of taxonomic, phylogenetic and functional diversity, based on the systematic investigation of forest communities.
Methods 52 forest plots, each with an area of 30 m × 20 m and divided into six subplots (10 m × 10 m), were investigated along the altitudinal gradient (1 409-2 150 m) in Mount Guandi, Shanxi. Name, diameter at breast height (DBH) and height were identified and measured for each tree stem with DBH ≥3 cm at each plot; name, average height, coverage and basal diameter for each shrub species were identified and measured in two of the six subplots; name, abundance, coverage and average height for each herbaceous species were identified and measured for one quadrat of 1 m × 1 m in each subplot. The indices of taxonomic, phylogenetic and functional α and β diversity were then calculated.
Important findings Species richness (S), phylogenetic diversity (PD) and functional richness (FRic) increased along the altitudinal gradient, especially in altitudes above 1 800 m. Total β diversity (β_total) and replacement β diversity (β_repl) increased, while the richness difference (β_rich) decreased, along the altitudinal gradient. The patterns of taxonomic, phylogenetic and functional diversity were significantly different between woody and herbaceous plants. S and Shannon-Wiener diversity (H′) of herbaceous plants increased more obvious along the altitude than those of woody plants. Topographic factors regulated the pattern of the herbaceous plant richness, while historical process regulated the woody plant richness. Along the altitude, β_total increased more obvious for the woody plants than for the herbaceous plants. β_repl and β_rich of woody plant showed a unimodal pattern and U-shaped pattern, while those of herbaceous plants increased or decreased, respectively. Taxonomic, phylogenetic and functional β diversity of both woody and herbaceous plants among communities increased with the environmental and geographical distances. Environmental distance had a relatively stronger effects than geographical distance on β diversity of woody plants, while environmental distance and geographical distance jointly influenced β diversity of the herbaceous plants.

Aims To develop a statistically appropriate species distribution model for the abundance of five species from Quercus in the northern China, and to predict the change of abundance under climate change.
Methods We surveyed abundance data of five Quercus species from 1 045 plots in the northern China, and then fit the abundance with climatic variables using random forest model (RF). We then predict the abundance of these five Quercus species in 2050 and 2070 under Representation Concentration Pathways (RCP) 2.6 and 8.5.
Important findings The change magnitudes of abundance for all 5 species under RCP 8.5 were larger than under RCP 2.6. Except for Quercus variabilis, abundances of other four species declined under climate change to 2050 and 2070 in more than half of the current distribution areas. Moreover, the northeastern part of Nei Mongol and the northern part of Heilongjiang will be the hotspots of decrease of abundance. Therefore, it is necessary to strengthen the monitoring and species protection in the areas mentioned above with the increasing threaten of climate change.

Aims Temperate forest is one of the most important components of the global forests and main carbon pools. Nitrogen (N) is considered as the limiting nutrient for the forest growth. However, the heterogeneities in plant species and stem sizes were largely ignored in previous researches on the effects of N addition on plant growth. Quercus wutaishanica is one of the most common and dominant tree species in the temperate forests in North China. In this study, we investigated the responses of growth of trees and forests to N addition in the Quercus wutaishanica forests in Mt. Dongling in Beijing.
Methods We conducted a 7-year N fertilization experiment in Quercus wutaishanica forests in Mt. Dongling, Beijing, since 2011. The N addition was conducted at three treatment levels, i.e., 0 kg hm ^-2·a ^-1, 50 kg hm ^-2·a ^-1 and 100 kg hm ^-2·a ^-1. Nitrogen was added at the beginning of each month from May to October each year. We used electronic vernier caliper to measure tree growth rate for each year. All trees were divided into three groups based on their diameter at breast height (DBH), namely small trees (DBH = 3-10 cm), median trees (DBH =10-20 cm) and large trees (DBH > 20 cm). Particularly, we considered growth at species level for all Quercus wutaishanica and the growth at community level for all tree species in the stands.
Important findings (1) At species level, N addition enhanced the growth rate of Q. wutaishanica. (2) At community level, the growth rate showed no difference among different N addition treatments. (3) Small trees were restrained, while median and large Q. wutaishanica trees were not significantly influenced, by the N addition.

Aims Shrublands are widely distributed in the North China. Understanding species composition and community assembly of the shrublands has important implications for promoting vegetation restoration in this area. Community phylogenetic structure can reflect community assembly process. In the present study, we explored the distribution patterns, species composition and phylogenetic structure of major shrubland types from North China, and then analyzed the effects of temperature and precipitation on these patterns with the help of the WorldClim dataset.
Methods A total 2 331 plots were setup to survey species composition and phylogenetic structure of major shrubland types in North China. A multiple stepwise regression was used to determine the effects of climatic factors on community phylogenetic structure, and a generalize linear model was used to test the interaction of environmental factors and formation types or vegetation types.
Important findings A total of 570 woody species belonging to 207 genera from 75 families, together with 1 221 herb species belonging to 491 genera from 99 families were recorded during the investigation. Five vegetation types and 195 formation types were identified, and the major formation types were Ostryopsis davidiana formation, Vitex negundo var. heterophylla, Vitex negundo var. heterophylla + Hippophae rhamnoides and Hippophae rhamnoides formation. The species richness of herb layer was higher than that of shrub layer. The phylogenetic structure was over-dispersed for herb layer and was convergent for shrub layer. The phylogenetic structure differed remarkable among different vegetation types. The phylogenetic structures of both shrub and herb layers were significantly correlated with climatic factors, and the interaction of climate factors and vegetation types or formation types as well. Our results indicates that large scale variation of climatic factors regulate community phylogenetic structure of different layers in shrub community, and the effects depend on vegetation types and formation types.

Aims Helianthemum songaricum is an ancient Mediterranean remnant plant species endemic to central Asia, and it is a dominant species of a unique desert community in west Erdos, Nei Mongol, China. We studied the distributions, classification and characteristics of the H. songaricum communities.
Methods We collected species composition for 18 plots from literatures and field investigation during the growing seasons of 2016 and 2017. We then applied TWINSPAN to classify community types.
Important findings (1) The H. songaricum communities were primarily distributed in the north and south of the Arbas Mountains and Qianli Ravine in west Erdos, with some in the southern and northern Helan Mountain. (2) In total, 58 seed plant species belonging to 39 genera from 17 families were recorded, including 18 shrub and subshrub, 27 perennial and 13 annual herbaceous species. Super-xerophytes and xerophytes were the two major ecological types, accounting for 26% and 50%, respectively. The Central Asia-Eastern Asia was the major floristic elements, followed by the Palaeo-Mediterranean and the Gobi elements. (3) Based on the life forms and species composition, the H. songaricum communities was divided into three major association groups, i.e., H. songaricum-herbs desert group, H. songaricum-shrubs-herbs desert group and H. songaricum-subshrub desert group, which were further divided into 10 associations.

Aims Tamarix chinensis is a pioneering shrub species in temperate coastal saline wetlands, which plays an important role in plant community succession and preventing seawater intrusion in coastal wetlands. This study, which is focused on Tamarix chinensis population distribution characteristics and the correlations between Tamarix chinensis population distribution with individual diameters, can reveal the characteristics of population development and provide reference for species conservation and management of protected areas. This study may also provide basic information for scientific research on the succession and ecological management of coastal wetland vegetation ecosystems.
Methods In the core area of Changyi National Marine Ecological Special Protection Zone, two sample tapes with a spacing of about 800 m are arranged along the parallel coastline. Each sample tape has three plots of 50 m × 50 m. A total of six sample plots are set up for each wood survey. The spatial distribution map of Tamarix chinensis population is drawn by Origin. The obtained data is divided into three different diameter grades according to their base diameter: diameter grade I (base diameter ≤ 4 cm) and diameter grade II (4 < base diameter ≤ 8 cm), diameter grade III (base diameter > 8 cm). The distribution pattern of Tamarix chinensis population and the relationship between different diameter grades are analyzed by the point pattern analysis method and Programita software.
Important findings (1) A total of 374 individuals of Tamarix chinensis are investigated in six plots, including 14 in plot 1, 20 in plot 2, 36 in plot 3, 45 in plot 4, 221 in plot 5, and 38 in plot 6. (2) There is a large difference in population density of Tamarix chinensis between different plots, which indicates that Tamarix chinensis is not evenly distributed on the regional scale. (3) Tamarix chinensis populations show a clustered distribution on small scale (less than 5 m) while they appear as random distribution on large scale (greater than 15 m). The population of Tamarix chinensis exhibits a trend of transition from clustered distribution to random distribution with the increase of spatial scale. (4) The spatial association of Tamarix chinensis between any two diameter grades is positive on small scale and there is no significant spatial association between them on large scale. However, negative spatial association on diameter grade II and diameter grade III is detected at the scale of 15 m probably due to space competition.

Aims To explore the factors controlling the spatial distribution, as well as the species diversity, of the Vitex negundo var. heterophylla shrublands in North China.
Methods We investigated the species composition and environments for 370 shrubland plots of Vitex negundo var. heterophylla shrublands in North China. We calculated biodiversity indices (Shannon-Wiener index, Simpson index and Pielou’s evenness index) and then applied multivariate regression trees (MRT), analysis of variance (ANOVA), Pearson correlation analysis to disentangle distribution of the Vitex negundo var. heterophylla community and patterns of species diversity along both horizontal and elevational gradients.
Important findings The results showed that Vitex negundo var. heterophylla shrublands distributed in a large area stretching for more than 10° of both latitude and longitude, together with an elevational range of more than 1 000 m (117 m to 1 248 m). The Shannon-Wiener index, Simpson index and Pielou’s evenness index were higher in the herbaceous layer than those in the shrub layers. The species diversity of shrub layer increased with latitude but decreased with elevation. In contrast, that of the herbaceous layer decreased with latitude but increased with elevation. The Shannon-Wiener indexes of both layers were significantly correlated with environmental factors. The results of Pearson correlation analysis indicated that the Shannon-Wiener indexes of shrub layer had a significantly negative relationship with its temperature and slope position, and a significantly positive relationship with its precipitation. However, that of herb layer showed opposite trends.

Aims Many competing theories seek to identify the mechanisms behind the community assembly. Niche theory and neutral theory are among the two most competing mechanisms. Exploring factors controlling the patterns of β-diversity is an approach to reveal the underlying mechanisms of community assembly. In this paper, we aim to reveal the β-diversity pattern of understory in planted forests of the central Loess Plateau and to evaluate the relative influences of deterministic (environmental filtering) and stochastic (dispersal limitation) processes on the community assembly.
Methods We sampled in total 107 sites of planted forests spatially spreading over the central Loess Plateau. In each site, three plots (10 m × 10 m) were randomly designed each at a distance of about 50 m. The floristic composition, community structure, and environmental conditions were investigated in each plot. We calculated the dissimilarity (β_sim) of species composition, geographic distance and environmental divergence for each of the 5 671 site pairs. We used random forest (RF) to quantify the influence of the selected factors on species composition, and distance-based multivariate regression method (MRM) to fit the relationship between dissimilarity, geographic distance and environmental divergence. To quantify how and in what extent the environmental filtering and the dispersal limitation influence the species composition among sites, we performed the principle coordinates of neighbor matrices (PCNM) and distance-based RDA (db-RDA) to select the pronounced independent variables. We then partitioned the variance into three parts, namely, 1) independent contributions of geographic distance; 2) independent contributions of environmental divergence; and 3) the joint contribution of both.
Important findings The community similarity declined with increasing geographical distance and environmental divergence. Geographical distance and environmental divergence together explained 47.8% of variance in the dissimilarity in species composition. The spatial variables accounted for 14.1%, while the environmental variables accounted for another 9.8% of the variance in dissimilarity of species composition. Annual precipitation and basal area of trees are the two most important environmental factors influencing the pattern of dissimilarity of species composition. These results implied that both environmental filtering and the dispersal limitation play important roles in shaping the community assembly of the herbaceous layers of planted forests in the central Loess Plateau.