Lianas are a crucial component of karst seasonal rainforests, yet research on them has predominantly focused on non-karst regions. Consequently, their abundance and species richness remain relatively understudied within karst ecosystems. We aimed to document the abundance and species richness of lianas and investigate their relationships with abiotic and biotic factors, based on data from a fully mapped 15 ha plot in a karst seasonal rainforest of Nonggang (SW China). Structural equation models (SEMs) were employed to estimate the path coefficients and variation of dependent variables, enabling a comprehensive analysis of the factors affecting the abundance and species richness of liana. Within the 15 ha plot, a total of 23,819 lianas were identified, encompassing 113 species from 34 families. These lianas constituted 24.16% of the total woody plant density and 33.44% of the species present, but only 4.32% of the total woody plant basal area. Lianas are primarily influenced by abiotic factors, especially elevation and phosphorus (P), with less impact from biotic factors. Our findings reveal that lianas, despite constituting a relatively small percentage of the total woody plant basal area, significantly contribute to the density and diversity of the forest. Notably, abiotic factors such as elevation and phosphorus availability predominantly shape the distribution and richness of lianas, highlighting the importance of these environmental variables. The findings offer valuable insights for future liana studies and the preservation of karst forests’ biodiversity.

Caryodaphnopsis, a group of tropical trees (ca. 20 spp.) in the family Lauraceae, has an amphi-Pacific disjunct distribution: ten species are distributed in Southeast Asia, while eight species are restricted to tropical rainforests in South America. Previously, phylogenetic analyses using two nuclear markers resolved the relationships among the five species from Latin America. However, the phylogenetic relationships between the species in Asia remain poorly known. Here, we first determined the complete mitochondrial genome (mitogenome), plastome, and the nuclear ribosomal cistron (nrDNA) sequences of C. henryi with lengths of 1,168,029 bp, 154,938 bp, and 6495 bp, respectively. We found 2233 repeats and 368 potential SSRs in the mitogenome of C. henryi and 50 homologous DNA fragments between its mitogenome and plastome. Gene synteny analysis revealed a mass of rearrangements in the mitogenomes of Magnolia biondii, Hernandia nymphaeifolia, and C. henryi and only six conserved clustered genes among them. In order to reconstruct relationships for the ten Caryodaphnopsis species in Asia, we created three datasets: one for the mitogenome (coding genes and ten intergenic regions), another for the plastome (whole genome), and the other for the nuclear ribosomal cistron. All of the 22 Caryodaphnopsis individuals were divided into four, five, and six different clades in the phylogenies based on mitogenome, plastome, and nrDNA datasets, respectively. The study showed phylogenetic conflicts within and between nuclear and organellar genome data of Caryodaphnopsis species. The sympatric Caryodaphnopsis species in Hekou and Malipo SW China may be related to the incomplete lineage sorting, chloroplast capture, and/or hybridization, which mixed the species as a complex in their evolutionary history.

Spatial patterns can reveal many ecological processes in forest communities; thus, understanding the spatial patterns of trees and their interactions is key to exploring forest dynamics. However, few studies have explored the spatial patterns and interactions between adults and recruits over longer time spans in tropical karst forests. A forest dynamics census was conducted (2011–2021) in a 15-ha karst seasonal rainforest plot at the Nonggang National Nature Reserve, in Guangxi, China. The tree community structure, which included a total of 20 tree species (≥ 50 individuals) at various states of recruitment, survival, and mortality, were selected and investigated via detailed analyses. First, univariate pair correlation functions and bivariate mark correlation functions were utilized to analyze the spatial patterns of dead recruits, surviving recruits, and adults. Aggregation was the dominant intraspecific distribution pattern in the plot that decreased at larger scales, which indicated that dispersal was limited. The segregation of bivariate patterns in most species suggested that there was scramble competition between the surviving and dead recruits, which translated to their not clustering around adults. Second, it was revealed through testing that density dependence was not prevalent. However, negative density dependence was more common in species that exhibited density dependence, as various species respond differently to changes in population density. Third, most recruits had a low probability of survival, which for several dominant species was influenced by neighborhood effects. This study did not support the Janzen-Connell hypothesis, as the survival probability of most recruits was not enhanced with the distance from adults. This meant that the effects of distance from adults on the growth of recruits in Nonggang forests were negligible. These results suggested that dispersal limitations and habitat heterogeneity played more significant roles in the regulation of tree spatial patterns and seedling growth (or mortality) in tropical karst seasonal rain forests. This work will contribute to the restoration and conservation of fragile forest communities in Karst regions, while providing a theoretical basis for biodiversity research, forest management planning, and ecosystem services.

元宝山冷杉(Abies yuanbaoshanensis)是广西特有的珍稀濒危植物,为进一步探究元宝山冷杉的种实特征以及种子萌发特性,本研究分析了其果实和种子特征,采用发芽对照试验测定种子的萌发力.元宝山冷杉种实特征结果显示:球果长(9.44±1.10)cm,球果重(35.88±4.10)g,单果种子数531-711粒,球果重与单果种子数及单粒种子重之间存在显著的正相关关系;种子长度为(17.02±1.16)mm,宽度为(8.86±0.60)mm,厚度为(1.97±0.17)mm,种翅长为(6.99±0.66)mm,种翅宽为(5.30±0.55)mm,千粒重为(19.3±2.5)g;元宝山冷杉种子败育率较高,空粒占53.7％.元宝山冷杉种子萌发特性结果显示:种子最适萌发温度为25℃恒温,低于15℃时基本不萌发,在15-25℃变温下发芽势显著降低(P＜0.01);浸种有利于元宝山冷杉种子的萌发,浸种24 h的种子发芽率极显著高于浸种48 h的种子(P＜0.01);种翅对元宝山冷杉的种子萌发无抑制作用,但去翅后的种子发芽能力更强;纸床更适宜元宝山冷杉种子的萌发;低温贮藏可以保持元宝山冷杉种子的活性,延长种子寿命.因此,元宝山冷杉的种子在去翅条件下浸种24 h后放置在25℃恒温的纸床上更利于其萌发.

Aims:Saplings are an important component of maintaining the species diversity of forest ecosystems.Their diversity is related to forest community structure and growth dynamics.Therefore,it is very important to study the spatial distribution pattern and potential mechanism of sapling regeneration for forest community dynamics.To strengthen the understanding of the dynamic changes of the northern tropical karst seasonal rainforest,we will study the spatial distribution pattern and mechanism of sapling regeneration in 15 ha northern tropical karst seasonal rainforest dynamics plot in Nonggang,southwestern Guangxi. Methods:Based on the survey data from 2011 to 2016,the individual number,spatial pattern characteristics,and influencing factors of new saplings(DBH ≥ 1 cm)in five years were analyzed by spatial point pattern and redundancy analysis. Results:A total of 101 species of new saplings were observed,accounting for 45.3％of the surveyed species in 2011,and the sapling density was 196.5 ind./ha.The newly increased saplings showed aggregated distribution at 0-7 m and 10-16 m scale,and random distribution above 16 m scale.Altitude is the main factor affecting the regeneration of saplings,followed by topographic wetness.Biological factors had a weak impact on sapling regeneration.The number of saplings was negatively correlated with increasing altitude,and positively correlated with topographic wetness.Moderate positive correlation between adult tree individuals and young tree regeneration was observed. Conclusion:In this karst seasonal rainforest,sapling regeneration and spatial distribution pattern are synergistically affected by various influencing factors,which may be related to limited seed dispersal and habitat heterogeneity.

As a repository of genetic information of above-ground vegetation, the soil seed bank plays an important role in the natural succession and renewal of vegetation and the construction of ecological restoration. In this paper, three typical plant communities in the rocky desertification area of Gongcheng Yao Autonomous County were selected for the study, and soil seed bank structure and diversity in different communities and their response to soil nutrient characteristics were analyzed. The results were as follows：(1) A total of 3 648 seedlings belonging to 55 species in 51 genera and 33 families were detected, which included 20 species of 1, 2-year-old herbs, 21 species of perennial herbs, 5 species of vines, 3 species of shrubs and 6 species of trees; the average density of soil seed bank of different plant communities in karstic desertification areas of Gongcheng was Prunus salicina economic forest (22 493 grain·m-2) > Cyclobalanopsis glauca secondary forest (1 033 grain·m-2) > Phyllostachys sulphurea shrub (793 grain·m-2). (2) As for the plant life type of the soil seed bank, the soil seed bank life type of Prunus salicina economic forest was mainly annual malignant weeds, the plant life type of the soil seed banks in the Cyclobalanopsis glauca secondary forest and Phyllostachys sulphurea shrub was dominated by perennial herbs, while woody plants account for a relatively small proportion; the species diversity and similarity of the soil seed banks of different vegetation types were generally low, while the species composition of the soil seed banks also had low similarity with the aboveground communities. (3) The soil elements in the study area had higher nitrogen content and lower phosphorus content, and phosphorus was a limiting factor for plant growth in Phyllostachys sulphurea shrub and Quercus glauca secondary forest. In conclusion, the plant community in the stone desertification area of Gongcheng has some native germplasm resources, but overall shows a low species diversity, and it is urgent to introduce native tree species artificially to accelerate the positive vegetation succession on the basis of natural sequestration, and pay attention to nutrient management, especially the regulation of phosphorus elements. The results provide a theoretical reference for karst stone desertification management and vegetation restoration in Gongcheng.

Aims:Mineral elements are important determinants of soil nutrients and are related to forest community composition and nutrient cycling.There is high terrain heterogeneity in karst seasonal rainforest local scale,but there is still lack of research on how terrain and other abiotic and biotic factors affect the spatial distribution of soil mineral elements in karst area. Methods:In this study,we set up 100 litter fall traps along the elevation gradient in the 15 ha northern tropical karst seasonal rainforest dynamics plot in Nonggang,southwestern Guangxi,and conducted soil sampling at the litter fall trap sites.We tested soil samples for the content of mineral elements such as K,Ca,Mg.We performed quantitative analysis of the association between ecological factors and soil K,Ca,Mg in karst seasonal rainforests based on methods such as spatial regression models and variation partitioning. Results:Soil K,Ca and Mg in the study area were all spatially autocorrelated,with Ca significantly positively correlated with elevation and convexity(P＜0.05),mainly clustered in the hilltop;K significantly positively correlated with topographic wetness index,mainly clustered in low-lying land;Mg showed clustering characteristics in the hillside.Variation partitioning shows that ecological factors drove the spatial distribution of soil K,Ca and Mg more than spatial structure.Elevation was the highest predictor variable among the individual ecological factors,and abiotic factors were higher than biotic factors in general,and species richness was the highest among biotic factors,while the aggregation of Mg elements was accompanied by a higher level of species richness. Conclusion:In this study,the soil K,Ca and Mg in the 15 ha northern tropical karst seasonal rainforest dynamics plot in Nonggang have spatial autocorrelation,and the spatial distribution of the three soil elements was significantly different.In the karst seasonal rainforest in southwestern Guangxi,ecological factors such as altitude have a strong driving effect on the spatial distribution of soil K,Ca and Mg.However,in terms of the accuracy of the analysis results,adding more ecological factors and expanding soil sampling points may further enhance the interpretation of ecological factors and spatial variables on the spatial distribution of soil elements.

Rural agricultural activity generates cropland, secondary vegetation and straggling primary forest and can modify the soil seed bank (SSB), potentially impacting the restoration of preferred species. The interaction between vegetation and seed banks during the recovery process is dependent on management practices and recovery pathways. This study was carried out in Guilin of southwest China to assess the variation in plant diversity and species composition of both aboveground and soil seed banks across three typical vegetation types with different human interventions: orchard, bamboo shrub and primary forest. The results show that there were significant differences in the species composition and diversity of aboveground vegetation and SSB, as well as in soil properties among three typical vegetation types. The primary forest had the highest aboveground species diversity, while the orchard had the highest species diversity and seed density of SSB. In addition, principal component analysis (PCA) and canonical correspondence analyses (CCAs) showed that the species composition and plant life forms of the three typical vegetation types were significantly influenced by soil properties. Based on these findings, the characteristics of aboveground vegetation and the soil seed bank and their correlations with soil properties are expected to drastically change with human intervention. These results imply that unsustainable land use has greatly impacted soil properties, and consequently, the aboveground vegetation and SSB. Nevertheless, vegetation will recover quickly after farming is abandoned. The successful restoration of fragmented ecosystems requires the addition of seeds and seedlings of target species, especially perennial woody plants from the relevant natural ecosystems, to accelerate succession from bamboo shrub to forest.

以广西弄岗北热带喀斯特季节性雨林15 hm2森林动态监测样地为对象,结合2011年和2016年两次调查数据,分析5年间样地树木死亡个体的数量、径级结构和空间格局特征等.结果显示:2011年至2016年,样地有86.5％的树种出现了个体死亡的现象,死亡个体占个体总数的14.4％;死亡个体的聚集程度随空间尺度的增大而逐渐减弱;小径级个体死亡与周边邻体和环境的关联性较大;竞争是影响弄岗北热带喀斯特季节性云林树木死亡的主要因素.综合来看,北热带喀斯特季节性雨林内树木死亡并非是一个完全随机的过程,而是树木本身特征和生物与非生物环境共同作用的结果.

森林凋落物是森林生态系统极其重要的组成部分,了解凋落物分解过程有助于理解森林生态系统的物质循环和养分平衡的机理.本研究以桂西南喀斯特季节性雨林凋落叶为研究对象,将2018年全年收集的凋落叶混合均匀后采用分解袋法进行原位分解实验,探讨桂西南喀斯特季节性雨林凋落物的分解特征.结果发现:凋落叶在分解过程中整体失重模式呈现先快后慢的变化趋势,且不同生境类型下凋落叶失重率为:洼地>坡地>峰顶;分解过程中C含量呈波动状态,但总体表现为下降趋势,而N含量呈无规则波动;失重率与海拔呈显著负相关,并在分解初期和中后期与坡度呈显著负相关,C含量变化同海拔呈显著正相关,而与其他环境因子的相关性则随分解时间的变化而变化.桂西南喀斯特季节性雨林凋落叶分解速率低于亚热带常绿落叶阔叶混交林,但与同类型的喀斯特森林退化区相当;喀斯特季节性雨林不同生境类型代表的微环境因子对凋落叶的分解具有重要影响,其中海拔引起的温度和湿度的差异是影响喀斯特季节性雨林凋落叶分解速率和C、N含量变化的主要因素.

木质藤本是生物多样性的重要组成,木质藤本通过影响支持木进而影响群落的结构和功能,但在生物多样性丰富的北热带喀斯特森林中,木质藤本与支持木的关系鲜为人知.以喀斯特季节性雨林的五桠果叶木姜子(Litsea dilleniifolia)群落为研究对象,对木质藤本的密度、分布格局及其与主要树种的关系进行调查研究,分析木质藤本对树木的影响.结果 显示:(1)五桠果叶木姜子群落内木质藤本平均密度为0.0913株/m2,木质藤本在0-20m空间尺度整体表现为聚集分布,且随着尺度增大,聚集强度逐渐减弱;不同径级木质藤本在不同尺度上的分布格局不同.(2)木质藤本对不同径级、不同种类、不同聚集强度的支持木选择表现以下体征:随着支持木径级增加,木质藤本攀附的比例和每木藤本数有增加趋势,且木质藤本胸径与支持木胸径呈极显著正相关;附藤率较高的支持木有紫葳科(Bignoniaceae)种类和东京桐(Deutzianthus tonkinensis),单木附藤数量多的是南方紫金牛(Ardisia thyrsiflora);物种的聚集强度与附藤率、附藤数量呈负相关.(3)木质藤本的密度与支持木死亡率关系不显著,而物种的附藤率与死亡率呈极显著负相关.以上结果表明,木质藤本密度在原生性喀斯特季节性雨林中并不高,且木质藤本对支持木具有选择性,但其对五桠果叶木姜子群落的死亡率并未产生显著影响.该研究可为喀斯特原生性季节性雨林的物种共存、极小植物种群保育提供理论依据,也可为石漠化区域的植被修复提供科学参考.

Camellia longzhouensis (Theaceae) is an endemic evergreen shrub or small tree with a distribution restricted to South China. It is listed as Grade-II in the National Key Protected Wild Plants List. In this study, we surveyed its distribution, examined its population structure, identified factors affecting its survival, and reassessed its extinction risk. We found that C. longzhouensis was only distributed in the Nonggang National Nature Reserve and the surrounding area. Its individuals only grew under the secondary forest canopy in the karst mountain. A total of 58 individuals of C. longzhouensis in three sub-populations were found. Soil fertility and understory light availability were the main habitat factors influencing the survival of C. longzhouensis. Anthropogenic disturbances and reproductive obstacles have caused a low seed-setting rate, poor seedling survival, and a lack of adult plants of C. longzhouensis in the natural habitat. The population structure of C. longzhouensis is spindle-shaped, indicating poor natural regeneration and inhibited seedling recruitment. Cleistanthus petelotii had a significant positive interspecific interaction with C. longzhouensis in the community. Based on the information obtained here and IUCN criterion C2ai, we recommend that C. longzhouensis be categorized in the International Union for Conservation of Nature (IUCN) Red List as Critically Endangered. We also developed a comprehensive protection strategy, consisting of in situ conservation, ex situ conservation, reintroduction, and commercial utilization. This strategy can be readily applied to protect other endangered plants with economic value in karst poor regions.

Tree mortality plays a vital role in forest dynamics and contributes to species coexistence and community assembly. However, the mechanisms that control tree mortality are poorly understood, particularly in species-rich tropical forests. Size-dependent abiotic constraints and biotic interactions act simultaneously to cause tree mortality in natural forests. However, these drivers are often studied independently, which can limit our understanding of how they interact to affect tree mortality in natural forests. We employed a hierarchical Bayesian logistic regression modeling approach to quantify the simultaneous effects of tree size, topography, neighborhoods, and their interactions on tree mortality in a 15-ha fully mapped tropical karst seasonal rainforest in Southern China. Of the variables tested, tree size exhibited the most consistent and strongest negative effect on tree mortality, while topography and neighborhood competition were of secondary importance. Neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering mortality, while only several species showed conspecific negative density dependent on mortality. The topographical wetness index had a significant positive effect on tree mortality. Size-dependent and neighborhood competition-induced tree mortality was stronger for shade-intolerant than for shade-tolerant species, and the size-dependent mortality was the strongest for shrub species among the three growth forms. Our results indicated that the size-dependent effect was the dominant cause of tree mortality; however, neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering tree mortality. Furthermore, the relative importance of these mechanisms for tree mortality differed within life-history strategies guilds. Our study highlighted the value of simultaneously considering the individual and interactive effects of multiple mechanisms toward understanding the dynamics and coexistence of highly diverse metacommunities in harsh environments.

森林凋落物是森林生态系统极其重要的组成部分,关系着森林生态系统的物质循环和养分平衡.然而,有关异质性自然森林生态系统中生物与非生物因子对凋落物凋落量的影响机制还存在较大争议.本文以广西弄岗15ha森林动态监测样地中设置的90个凋落物收集器所收集的凋落叶为研究对象,选取2013-2018年连续6年的凋落叶数据探讨了森林叶凋落量的时空动态,旨在深入了解该地区森林生态系统的物质循环过程及凋落量的影响因子.结果 显示:2013-2018年的年均叶凋落量为4,099.44 kg/ha,标准误为232.34,变异系数为0.15,这表明不同年际间叶凋落量存在明显差异;不同年际间叶凋落量的节律性变化为双峰型、三峰型或多峰型,说明不同年份的叶凋落量存在明显的节律性差异,但总体而言高峰期主要出现在每年的春季(3-4月)和秋季(8-10月);生态因子对叶凋落量年际动态存在显著影响,其累计解释率为69.3％,其中海拔对叶凋落量的影响最强,解释率为46.5％;而生物因子如胸径变异系数、单位面积胸高断面积之和和物种丰富度则对叶凋落量的影响较弱.多年的连续监测表明,喀斯特季节性雨林不同年际间叶片的凋落量和节律性存在显著差异,而非生物因子,如海拔是形成叶凋落量空间变异的主要因素.

Forest gap is the dominant form of disturbance in many forest ecosystems.Gaps play an important role in forest helping to maintain forest regeneration and dynamics.Little is known about the gap pattern and characteristics of karst seasonal rain forests.In this study, high-spatial-resolution Worldview-3 satellite imagery was coupled with field data to assess gap disturbance regime and its pattern in a 15 tropical karst seasonal rain forest dynamic plot in Nonggang National Nature Reserve, Guangxi.Total 305 gaps were identified, ranging in size from 10 to 371with mean size 52.3 m2.The canopy gap fraction was 10.6％, and gap density was about 20 per hectare.The spatial pattern of gaps was clustered at scale 0-50 m.Significant association was found between gaps and big trees (DBH≥10 cm), and null associations between gaps and small trees (DBH＜10 cm) and between gaps and standing dead trees.The prevailing ecological factors had different influence on gap distribution and gap characteristics.Convexity, altitude above channel (AAH) and tree species richness had significant effect on the gaps distribution.Gap size was significantly influenced by slope, mean elevation and tree species richness.Gap perimeter was mainly affected by mean elevation, rock-bareness rate (RBR), topographic wetness index (TWI), AAH and tree species abundance.These results indicated that gap disturbance was very frequent in karst seasonal rain forests, and there were topographic differentiation in spatial distribution and characteristics of gaps resulted by the combination effects of unique special karst geological conditions, habitats and the biological characteristics of karst forest.

To enrich niche partition and species coexistence theory in karst seasonal rain forest, and provide reference for species selection and configuration for rocky desertification control, we exami-ned foliar stable carbon isotope composition (δ13C) and water use efficiency (WUE) of the representative species in different habitats and the same tree species in different habitats. The results showed that foliar δ13C value in karst seasonal rain forest ranged from -34.13‰ to -29.69‰, with a mean value of (-31.40±1.19)‰. WUE ranged from 9.08-58.76 μmol·mol-1, with a mean value of 41.79 μmol·mol-1. Both of them were lower than subtropical and warm temperate forests at higher latitude, but higher than tropical rain forests at lower latitude and non-karst seasonal rain forests at the same latitude. The foliar δ13C value and WUE of representative species gradually increased with the increases of drought index from the depression to the top of the mountain. The foliar δ13C value and WUE of the same tree species increased with altitude. These results indicated that water use efficiency of tree species was not only related to climate factors, but also related to the geological background and water availability of the habitat. The water use efficiency of plants in karst area was higher than that in non-karst area, and was higher in dry habitat than in wet habitat under the same climatic condition. It showed that having different water use efficiencies was one of the strategies for plants in karst area to adapt to different habitats and maintain species coexistence.

[目的]研究北热带喀斯特季节性雨林优势木本植物种群生态位特征,了解群落内各种群对资源的利用状况及生态适应性,为生物多样性保护及退化生态系统的植被恢复提供参考.[方法]在对弄岗 1 5 hm2北热带喀斯特季节性雨林进行样方划分及植被调查的基础上,以375 个20 m×20 m的样方作为不同的资源位,以各样方物种重要值作为生态位计测的状态指标,运用 Levins和 Pianka公式计算、分析样地内 30 个优势种群的生态位宽度和生态位重叠度.[结果]生态位宽度较大的种群为苹婆、广西牡荆、茎花山柚、假玉桂和日本五月茶等,生态位宽度分别为 207.04,195.01,176.88,142.05 和 126.23;生态位宽度较小的是三角车、肥牛树、对叶榕、米扬噎和中国无忧花等,分别为 37.95,35.79,33.83,25.87 和 15.76;重要值排序靠前的闭花木、蚬木、海南椴和劲直刺桐的生态位宽度居于中间位置,生态位宽度为 107.54,77.54,113.48,95.12.生态位重叠值等于 1 的种对有0 对;生态位重叠值大于或等于 0.5、小于 1 的种对有 20对,占总种对数的 4.6%,生态位重叠值大于 0 小于 0.5 的种对有401 对,占 92.2%;生态位重叠度等于 0 的种对有 14 对,占种对数 3.2%.[结论]喀斯特季节性雨林中适应性强、分布范围广的种群,生态位宽度较大,且绝大部分种对的生态位重叠度较小.苹婆、金丝李和茎花山柚等生态位宽度比较大,资源利用和环境适应能力较强、而且兼具生态和经济价值,在岩溶石漠化地区进行植被恢复时应作为优先考虑物种.要建立完整的石漠化地区植被恢复参照系统,应在不同岩溶气候带建立不同演替阶段的天然植被监测样地,分析其环境条件、群落结构及 种间关系等.在针对某个地区某个恢复阶段进行植被恢复设计时,应参照该地区这个恢复阶段的天然群落,选择生态位宽度大的物种作为先锋种,选择生态位重叠度较小的物种作为伴生种.

Climate is widely recognised as an important determinant of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate, which substantially hinders our understanding of how climate constrains biodiversity globally. Using data from 35 large forest plots, we test hypothesised relationships amongst climate, topography, forest structural attributes (stem abundance, tree size variation and stand basal area) and tree species richness to better understand drivers of latitudinal tree diversity patterns. Climate influences tree richness both directly, with more species in warm, moist, aseasonal climates and indirectly, with more species at higher stem abundance. These results imply direct limitation of species diversity by climatic stress and more rapid (co-)evolution and narrower niche partitioning in warm climates. They also support the idea that increased numbers of individuals associated with high primary productivity are partitioned to support a greater number of species.

Abstract In an era of global environmental change, understanding how disturbance affects the dynamics of ecological communities is crucial. However, few studies have theoretically explored the potential influence of disturbance including both intensity and frequency on compositional change over time in communities with stage structure. A spatially explicit, individual‐based model was constructed incorporating the various demographic responses to disturbance of plants at two different growth stages: seedlings and adults. In the model, we assumed that individuals within each stage were demographically equivalent (neutral) but differed between stages. We simulated a common phenomenon that seedlings suffered more from disturbance such as grazing and fire than adults. We showed how stage‐structured communities of seedlings and adults responded to disturbance with various levels of disturbance frequency and intensity. In “undisturbed” simulations, the relationship between average species abundance (defined here as the total number of individuals divided by species richness) and community composition turnover (measured by the Bray–Curtis similarity index) was asymptotic. However, in strongly “disturbed” simulations with the between‐disturbance intervals greater than one, this relationship became unimodal. Stage‐dependent response to disturbance underlay the above discrepancy between undisturbed and disturbed communities.

Both deterministic and stochastic processes have been linked to forest community assembly; however, their contribution to beta diversity has not been properly explored, and no studies to date have investigated their impacts on sparse depleted soils in forests that contain widespread exposed limestone karst. We found that the pairwise differences in species composition between quadrates was determined by a balanced variation in abundance, whereby the individuals of some species at one site were substituted by an equivalent number of individuals of different species at another site. Both the total beta diversity and its balanced variation in abundance declined with increasing sampling grain size. Our research indicated that environmental differences exert a strong influence on beta diversity, particularly total beta diversity and its balanced abundance variation in larger grain sizes. It was evident that deterministic and stochastic processes worked together, and that deterministic processes were more important than stochastic processes in the regulation of beta diversity in this heterogeneous tropical karst seasonal rainforest of Southern China. However, in future research a functional trait based approach will be required to tease out the relative degree of deterministic and stochastic processes toward an assessment of the temporal changes in species composition.