热带森林的低密度种及其形成及维持机制

低密度种指在热带森林中存在的成年个体密度很低的物种 ,是热带森林中树种的主要存在形式。对低密度种的认识和保护是热带森林生物多样性保育的关键之一。与稀有种相比 ,低密度种的含义更为广阔 ,它还包括那些密度低、分布范围广和绝对个体数量大的物种。低密度种形成的主要原因是母树附近的幼苗和种子的存活率较低 ,密度制约和有限更新也是低密度种形成的重要原因。维持低密度种最重要的外部原因是昆虫较强的飞行能力和传粉能力 ,而其最重要的内部原因是低密度种的生殖特性。     

海南尖峰岭不同热带雨林类型与物种多样性变化关联的环境因子

环境因子是影响物种分布并导致物种多样性形成的重要因素,采伐后恢复的热带森林次生林和原始林的环境因子是否一致是一个很重要的问题.对于该问题的回答对长期监测热带森林次生林的变化具有重要意义.该文基于在海南尖峰岭地区设置的164个625 m2植被公里网格样地数据,记录了每个样地的采伐历史并测定了其他的17个环境变量指标,分析了17个环境因子之间的相关关系;将164个样地划分成3种不同采伐历史的森林,通过典范对应分析(CCA)探讨3种森林类型中影响物种分布的环境因子组成;比较两种多元回归模型的优劣,来揭示3种森林类型中影响物种丰富度形成的环境因子组成的差异.结果表明:驱动海南尖峰岭地区物种分布并导致物种多样性差异的环境因子在森林采伐前后并不是一成不变的,而是与森林采伐历史有关联的.除了人为森林采伐干扰外,海拔梯度是形成海南尖峰岭热带天然林物种多样性的最重要因素.CCA分析显示:原始林中,物种分布与海拔、土壤交换性钙和交换性镁含量3个环境因子有较密切的关系,也与4个土壤物理性质环境因子(土壤密度、土壤最大持水能力、毛细管持水量和毛管孔隙度)关系密切;森林采伐后的恢复森林中,土壤全磷和速效磷含量对物种分布的影响增强,但皆伐后土壤交换性钙和交换性镁含量对物种分布的影响减弱.多元回归分析显示:原始林的物种丰富度与海拔和土壤交换性钙含量显著相关,径级择伐后恢复热带天然林的物种丰富度和海拔、土壤全磷含量和速效钾含量显著相关,皆伐后恢复热带天然林的物种丰富度仅和海拔显著相关.研究结果还显示,如果数据中存在空间自相关,建立多元回归模型时应该考虑数据中的空间自相关属性,虽然它并不总是存在的.     

海南岛热带低地雨林刀耕火种弃耕地恢复过程中落叶树种的变化

落叶是树木适应环境变化的一种方式,水分梯度往往是导致热带森林落叶物种比例产生差异的最主要原因。为研究落叶树种在森林次生演替过程中的变化规律,我们在海南岛霸王岭林区内调查了4个林龄阶段（5年、12年、25年和55年）的刀耕火种弃耕地自然恢复群落样地。在5.25hm2的全部样地内共记录到高H〉0.1m的落叶木本植物24种,隶属于15科21属。其中紫葳科、大戟科、含羞草科是含落叶树种最多的3个科,黄牛木（Cratoxylum cochinchinens）、猪肚木（Canthium horridum）、山柑算盘子（Glochidion fagifolium）是多度最高的3个落叶树种,枫香树（Liquidambar formosana）、黄牛木、山柑算盘子是胸高截面积最大的3个落叶树种。在次生演替过程中,落叶物种比例以5年恢复群落中最高,而后随群落演替进程下降;不同径级大小个体的落叶物种比例也表现出相同的变化趋势,且较大径级个体（DBH≥5cm）比例高于小径级个体（DBH〈5cm）。落叶物种个体密度比例和胸高截面积比例呈现单峰曲线变化：在恢复12年的群落中达到最大,而后随群落演替进程下降。除幼树（H〉1.5m,DBH〈5cm）外,其他各径级个体中的落叶物种密度和胸高截面积比例也表现出相同的变化趋势。我们的研究表明,在海南岛热带低地雨林刀耕火种后的次生演替和自然恢复过程中,落叶物种比例及其密度随恢复过程而发生相应的变化,在一定的恢复时期内呈现一定的季雨林群落特征。     

海南岛霸王岭不同热带森林类型的种-个体关系

 比较分析了海南岛霸王岭自然保护区核心区热带低山雨林、山地雨林、云雾林、山地矮林等4种热带森林类型中不同大小径级树木的物种—个体关系。结果表明：各种植被类型中物种数与个体数对数成线性关系是一种普遍现象,且不受调查树木的径木级影响。在相同个体数的条件下,累积物种数随海拔增高而逐渐减少,也即物种数由热带低山雨林、山地雨林、云雾林到热带山地矮林逐渐减少。对于各种植被类型的种—多度关系,单个体、双个体的物种有相当高的比例,其后一般依个体数的增加,而逐渐降低物种的出现频率,呈典型的倒J型曲线,而且这一比例随树木径级的增加而增加。     

海南岛霸王岭热带低地雨林植被恢复动态

热带次生林具有重要的物种保育和固碳功能, 然而高强度的干扰会导致次生林早期出现类似季雨林的阶段, 因而群落恢复速度和方向是当前热带生态学研究中最为关注的议题之一。该文以海南岛在刀耕火种弃耕地形成的不同演替阶段的次生林为研究对象, 比较森林不同恢复时间(12年、25年、55年)群落中的不同年龄(幼树、小树、成年树)个体与低地雨林老龄林的物种组成、多样性和群落结构差异, 探讨刀耕火种弃耕地恢复过程中的群落组配过程。首先, 在海南岛霸王岭林区内建立7个1 hm²(100 m × 100 m)的样地, 并调查样地内所有胸径≥ 1 cm的木本植物个体(不包括木质藤本)的种类、胸径大小和树高。无度量多维标定法(NMS)排序结果表明, 刀耕火种弃耕地恢复群落与老龄林的物种组成存在明显差异, 并且其物种组成差异随着径级增加而逐渐减小。刀耕火种弃耕地群落物种累积速度缓慢, 25年和55年恢复群落的种面积、种个体和种多度曲线无差异, 存在一个明显的停滞阶段。与物种组成相比, 群落结构恢复相对较迅速, 但仍没有形成老龄林阶段中的复杂结构。萌生个体在早期恢复群落中占有较高比例, 其个体密度和胸高断面积分别占总数的39.9%和55.9%, 但在恢复中后期迅速降低。刀耕火种弃耕地恢复群落中以先锋种和非先锋喜光种为主。虽然耐阴种随演替而逐渐增加, 但恢复中后期群落中的耐阴种重要值仅为老龄林的27.7%。这些结果表明, 虽然刀耕火种弃耕地恢复群落缓慢地逐渐接近最终恢复目标, 但仍然存在 很大的不确定性。刀耕火种弃耕地恢复过程中的异速恢复和停滞阶段需要纳入今后群落演替模型构建和森林固碳效益核甘共苦算中。     

热带森林群落土壤种子库对海拔梯度的响应

在西双版纳海拔800~1400 m的热带森林中,设置海拔梯度垂直样带和样地,研究热带森林群落土壤种子库对海拔梯度的响应。结果发现:(1)土壤种子库的密度和物种丰富度在海拔800 m最大,分别为10540±1578粒·m-2和71个种,最小的土壤种子库密度和物种丰富度则分别出现在海拔1400 m和1200 m。基于Bray-Curtis相似性系数,对4个海拔的土壤种子库物种进行了NMDS排序,发现不同海拔土壤种子库物种组成存在显著的空间分异。(2)土壤种子库中的异质性成分丰富度也因海拔不同存在差异,海拔800 m有9个异质性成分种,海拔1400 m只有5个;而异质性成分种的多度却在海拔1200 m最大。(3)土壤种子库与地上植被的相似性在4个海拔带都低于15%。研究表明,海拔变化对土壤种子库的密度、物种组成格局都能产生显著影响。     

热带森林碳汇或碳源之争

热带森林生产和储存有世界40%的生物量碳,这一碳汇的存在对于全球碳循环和人类的生态安全是极其重要的。由于气候变化热带森林碳储存量已经发生了一系列的变化。一种观点认为自20世纪80年代后期起热带森林的基面积(生物量)、茎个体密度、茎个体周转率均呈现显著增长,并归结为热带森林结构和动态协调一致的变化,同时将生物量的增加归功于高浓度CO2施肥。进而推断热带森林现今和今后数十年,它仍然是一个中等的碳汇。另一种观点认为热带森林生物量并无增加,其森林碳汇已沦落为碳源。在实验室中设置高浓度CO2条件栽培热带植物进行观测的多数结果是,无结构碳水化合物增加,而生物量并无增加。同时,随着CO2浓度升高,高温和干旱对热带森林将产生一系列更严重的负面影响,如森林生长量下降、死亡率以及森林火险增加;厄尔尼诺事件将会更加剧旱情和火灾,致使树木出现枯梢和死亡高峰。未来人类开发森林及林地利用改变将日益加剧,在自然和人为的综合影响下,不论是对热带森林生物量增加持肯定立场的生态学家,或对此持反对立场的生态学家,双方都一致认为未来退化的热带森林系统碳汇必然转变为碳源,甚至是一大规模的碳源。     

Species abundance is jointly determined by functional traits and negative density dependence in a subtropical forest in southern China

植物物种多度受功能性状和负密度依赖共同影响——以中国南亚热带黑石顶森林样地为例 影响植物群落中植物物种多度的因素较多,确定关键影响因素及阐明其具体机制一直是群落生态学的研究重点之一。目前确定性的影响因素主要有两大类：植物功能性状和负密度依赖。功能性状通过影响植物的竞争能力、资源的获取效率、对环境的适应能力等方面进而影响植物的多度;负密度依赖表现在同种或异种植物个体在空间上聚集,特异性的寄主(病原菌、昆虫等)传播容易导致植物个体(主要为幼苗和小树)死亡,种群发生自疏,进而影响植物的多度。到目前为止,单一探究植物功能性状或负密度依赖对植物多度影响机制的研究已有大量报道,而将两者结合来探讨对植物多度的影响的工作相对较少。为了更深入地探索影响植物多度的机制,本研究中我们综合分析了功能性状与负密度依赖对植物多度的影响。研究地点为广东省黑石顶亚热带森林50 ha大样地;功能性状方面选取了叶面积(LA)、比叶面 积(SLA)、叶片干物质含量(LDMC)、叶片氮含量(LNC)和最大电子传输速率(ETR_max);植物物种所受负密度依赖强度通过构建小树在样地两次普查期间的存活状况受邻体密度影响的层次贝叶斯模型计算;通过结构方程模型构建功能性状-负密度依赖-物种多度的内在联系框架。结构方程模型结果显示,物种多度受功能性状和负密度依赖共同作用,其中功能性状对物种多度的影响包括直接作用和通过负密度依赖的间接作用。具体来说,SLA对多度的影响包括直接和间接两种;LDMC和LNC仅间接影响物种多度;LA和ETR_max对多度只有直接影响;负密度依赖与物种多度之间存在直接的负相关关系,说明多度较高的物种受到的负密度依赖效应更强。结构方程模型对物种多度差异的解释度达到20%。以上结果表明,黑石顶植物多度分布是功能性状与负密度依赖共同作用的结果;比叶面积在所研究的因素中贡献最大。该项工作有助于提高我们对亚热带森林植物常见种和稀有种分布格局的理解。     

西双版纳不同森林类型的树洞密度及其特征

树洞是森林生态系统的重要组成部分,它能为许多动物提供栖息、筑巢、繁殖和躲避天敌的场所。因而,树洞的密度和特征通常被认为是限制树洞巢居动物多样性和丰富度的主要因子,然而目前国内外对热带森林的树洞密度和洞口特征研究较少。选取西双版纳20 hm~2热带森林动态监测样地(包括热带季节雨林和热带山地常绿阔叶林)为研究对象,采用地面观测法调查了所有胸径≥5 cm的活体乔木上的树洞,分析其树洞密度和特征(高度、洞口大小、类型和洞口方位,并探讨树洞在不同森林类型间的差异)。结果表明:(1)热带季节雨林和热带山地常绿阔叶林的树洞密度不存在显著差异;(2)两种森林类型的树洞均以高度较低、洞口较小、干中部洞口为主,受盛行风的影响洞口朝向主要集中在东北方向;(3)树洞高度、类型和洞口方位在两种森林间的分布差异显著(P0.01),而洞口大小不存在明显差异。结果表明森林类型会影响树洞的特征,因而加强森林生境异质性的保护对维持树洞巢居动物的需要具有重要意义。     

海南霸王岭热带山地雨林森林循环与树种多样性动态

通过对海南岛霸王岭热带山地雨林的调查 ,研究了热带山地雨林树种多样性特征随森林循环的动态变化规律。结果表明 :( 1 )热带山地雨林森林循环不同阶段斑块在森林景观中所占的面积比例分别是 :林隙阶段 ( G)占 38.5 0 % ,建立阶段 ( B)占 2 8.5 0 % ,成熟阶段 ( M)占 2 7.0 0 % ,衰退阶段 ( D)占 6 .0 0 %。 ( 2 )热带山地雨林中乔木树种的密度随森林循环的变化趋势是由 G→B→M呈现出逐渐增加的趋势 ,以成熟阶段达到最大 ,而到衰退阶段又趋于下降。灌木树种则表现出 G阶段斑块的密度最大 ,B阶段的最小 ,从 B到 M有所增加 ,到 D又稍有下降。 ( 3)热带山地雨林中不同高度级和不同径级的树木的密度在森林循环的不同阶段表现出不同的增减趋势 ,其随森林循环过程呈现出的动态变化可能与不同阶段斑块内的空间、环境及物种生物学特性有关。 ( 4 )热带山地雨林中树木的平均胸径、平均高、平均胸高断面积、平均单株材积随森林循环过程呈现出不断增加的趋势 ,其中平均胸径和平均高随森林循环的变化较为平缓 ,而平均胸高断面积和平均单株材积之变化较为陡急。 ( 5 )热带山地雨林森林循环不同阶段的物种多样性指数不同 ,其中 G和 B阶段的物种丰富度和多样性指数值较接近 ,M阶段的物种丰富度达到最大 ,D阶段则最小。     

The Contribution of Tropical Secondary Forest Fragments to the Conservation of Fruit-feeding Butterflies: Effects of Isolation and Age

Concomitant with the rapid loss of tropical mature forests, the relative abundance of secondary forests is increasing steadily and the latter are therefore of growing interest for conservation. We analysed species richness of fruit-feeding nymphalid butterflies in secondary forest fragments of different age and isolation and in mature forest at the eastern margin of the Lore Lindu National Park in Central Sulawesi, Indonesia. From April to August 2001 we collected 2322 individuals of fruit-feeding butterflies, belonging to 33 species. Butterfly species richness increased with succession, but was significantly higher in mature forests than in all types of secondary forest. Isolation of the forest fragments did not have a significant effect on butterfly species richness in the range of distances (up to 1700 m) studied. Rather it appeared to affect only a few species. Species richness of endemic species was higher than of non-endemic species. Although endemic species were most diverse in mature forests, many species captured were restricted to secondary forests. Our results show that mature forest is essential for the conservation of nymphalid butterflies and for the endemic species in this area. However, considering the relatively large number of species found in these rather small habitat islands, secondary forest fragments, especially older successional stages, can be taken into account in conservation efforts and thus contribute to the preservation of tropical biodiversity on a landscape scale.     

Impacts of Selective Logging and Agricultural Clearing on Forest Structure, Floristic Composition and Diversity, and Timber Tree Regeneration in the Ituri Forest, Democratic Republic of Congo

Mature tropical forests at agricultural frontiers are of global conservation concern as the leading edge of global deforestation. In the Ituri Forest of DRC, as in other tropical forest areas, road creation associated with selective logging results in spontaneous human colonization, leading to the clearing of mature forest for agricultural purposes. Following 1-3 years of cultivation, farmlands are left fallow for periods that may exceed 20 years, resulting in extensive secondary forest areas impacted by both selective logging and swidden agriculture. In this study, we assessed forest structure, tree species composition and diversity and the regeneration of timber trees in secondary forest stands (5-10 and ~40 years old), selectively logged forest stands, and undisturbed forests at two sites in the Ituri region. Stem density was lower in old secondary forests (~40 years old) than in either young secondary or mature forests. Overall tree diversity did not significantly differ between forest types, but the diversity of trees ≥10 cm dbh was substantially lower in young secondary forest stands than in old secondary or mature forests. The species composition of secondary forests differed from that of mature forests, with the dominant Caesalpinoid legume species of mature forests poorly represented in secondary forests. However, in spite of prior logging, the regeneration of high value timber trees such as African mahoganies (Khaya anthotheca and Entandrophragma spp.) was at least 10 times greater in young secondary forests than in mature forests. We argue that, if properly managed and protected, secondary forests, even those impacted by both selective logging and small-scale shifting agriculture, may have high potential conservation and economic value.     

Prediction of neotropical tree and liana species richness from soil and climatic data

We present an analysis of local species richness in neotropical forests, based on a number of 0.1 ha samples of woody plants collected by the late Alwyn Gentry. For each of 69 forests, soils were analysed and climatic data were collated. Using transformed independent variables and interaction terms, multiple regression equations were developed that explained the greatest possible amount of variation in species richness, and the best equations were selected on the basis of regression diagnostics. The best models are presented for (a) all neotropical forests, (b) forests west of the Andes (transandean) and (c) east of the Andes (cisandean), and for various subsets based on elevation and annual rainfall. For the whole dataset, and for most subsets, annual rainfall and rainfall seasonality were the most important variables for explaining species richness. Soil variables were correlated with precipitation — drier forests have more nutrient-rich soils. After the inclusion of rainfall variables, available soil nutrient concentrations contributed little to explaining or accounting for additional variation in species numbers, indicating that tropical forest species richness is surprisingly independent of soil quality. The results are consistent with the hypothesis that plants in mature tropical forests may obtain nutrients through the process of direct cycling, in which mineral nutrients are extracted from litterfall before they enter the soil. The strong relationship between community species richness and rainfall patterns has implications for biodiversity conservation. Wet forests with an ample year-round moisture supply harbour the greatest number of woody plant species and should be a focus of conservation efforts.Died 3 August 1993.     

Resilience of tropical dry forests – a meta‐analysis of changes in species diversity and composition during secondary succession

Assessing the recovery of species diversity and composition after major disturbance is key to understanding the resilience of tropical forests through successional processes, and its importance for biodiversity conservation. Despite the specific abiotic environment and ecological processes of tropical dry forests, secondary succession has received less attention in this biome than others and changes in species diversity and composition have never been synthesised in a systematic and quantitative review. This study aims to assess in tropical dry forests 1) the directionality of change in species richness and evenness during secondary succession, 2) the convergence of species composition towards that of old‐growth forest and 3) the importance of the previous land use, precipitation regime and water availability in influencing the direction and rate of change. We conducted meta‐analyses of the rate of change in species richness, evenness and composition indices with succession in 13 tropical dry forest chronosequences. Species richness increased with succession, showing a gradual accumulation of species, as did Shannon evenness index. The similarity in species composition of successional forests with old‐growth forests increased with succession, yet at a low rate. Tropical dry forests therefore do show resilience of species composition but it may never reach that of old‐growth forests. We found no significant differences in rates of change between different previous land uses, precipitation regimes or water availability. Our results show high resilience of tropical dry forests in term of species richness but a slow recovery of species composition. They highlight the need for further research on secondary succession in this biome and better understanding of impacts of previous land‐use and landscape‐scale patterns. Synthesis Secondary forests account for an increasing proportion of remaining tropical forest. Assessing their resilience is key to conservation of their biodiversity. Our study is the first meta‐analysis of species changes during succession focussing on tropical dry forests, a highly threatened yet understudied biome. We show a gradual species accumulation and convergence of composition towards that of old‐growth forests. While secondary tropical dry forests offer good potential for biodiversity conservation, their capacity for recovery at a sufficient rate to match threats is uncertain. Further research on this biome is needed to understand the effect of land use history and landscape processes.     

Successional Change and Resilience of a Very Dry Tropical Deciduous Forest Following Shifting Agriculture

We analyzed successional patterns in a very dry tropical deciduous forest by using 15 plots differing in age after abandonment and contrasted them to secondary successions elsewhere in the tropics. We used multivariate ordination and nonlinear models to examine changes in composition and structure and to estimate forest recovery rates and resilience. A shrub phase characterized early succession (0–3 yr); afterwards, the tree Mimosa acantholoba became dominant. Below its canopy, sprouts and seed-regenerated individuals of mature forest species slowly accumulated. Canopy height, plant density, and crown cover stabilized in less than 15 yr, whereas species richness, diversity, and basal area continued to increase. The pioneer species group has very low diversity and the long-lived pioneer phase typical of humid forests is absent; species composition may therefore recover soon as suggested by convergence toward mature forest species composition. The time trend of plant density also differed from humid forests for it lacked its characteristic density decline, presumably because of differences in regeneration mechanisms between very dry and other less water-stressed forest types. As opposed to the prevailing hypothesis, resilience was not higher than in moister forests, and thus factors other than structure relative simplicity must be accounted for when assessing resilience.     

Richness and Density of Birds in Timber <Emphasis Type="Italic">Nothofagus pumilio</Emphasis> Forests and their Unproductive Associated Environments

Research on forest management impact focuses mainly on timber stands, and leaves out the unproductive forest environments. These stands are spatially mixed with timber forests. The objective was to evaluate richness and density of birds in timber Nothofagus pumilio forests and their unproductive associated environments, and discuss forest management implications. These stands showed significant differences in their forest structure, which generate a great variety of ecological environments. A total of 1881 individuals belonging to 30 bird species were observed during the sampling, in spring and summer seasons. These species were mainly migratory and insectivores, Passeriforms being the most important group. From 12 to 17 birds/ha were found, which varied with the forest environments and seasons. Timber stands of Nothofagus pumilio support a low number of bird species. Most of them are opportunistic and a few prefer these woods over other forested or afforested areas. Low bird density and richness characterize these austral forests, which share their diversity with a high variety of ecosystems along Patagonia. Timber N. pumilio forests has a marginal value for bird species conservation, considering its richness, density and the percentage of this forest in the total forested landscape of Tierra del Fuego (Argentina).     

Soil seed banks in dry Afromontane forests of Ethiopia

Abstract. The soil seed bank was investigated in four dry Afromontane forests of Ethiopia. At least 167 plant species were identified in the 0–9 cm soil layer with total densities ranging between 12 300 and 24 000 seeds/m². Herbs were represented with the largest numbers of species and seeds in the seed bank, while the contribution of tree species was generally low. The overall vertical distribution of seeds was similar at all sites with the highest densities occurring in the upper three cm of soil and gradually decreasing densities with increasing depth. Relatively high densities also occurred in the litter layer. There were large differences in depth distribution between species, suggesting differences in seed longevity. A large number of species in dry Afromontane forests evidently store quantities of seeds in the soil and this is in contrast to the situation in most tropical rain forests, dry lowland forests and savannas, where both the number of seeds and the number of species are relatively small. It is possible that the strongly seasonal and unpredictable climate of this region may have selected for high levels of dormancy, and that herb regeneration is associated with small scale disturbance. The fact that most of the dominant tree species do not accumulate seeds in the soil suggests that their regeneration from seed would be unlikely if mature individuals disappeared. Most tree species have relatively large seeds and poor long-distance dispersal; this implies that restoration of Afromontane forests after destruction would be difficult. Since there is a diverse seed bank of the ground flora, this component of the vegetation would have a better chance of reestablishing. However, because most cleared forest land is used for agricultural crop production, it is probable that the seed bank will be depleted in only a few years. Therefore, the future of the Afromontane forest flora seems to depend on the successful conservation of the few fragments of remaining natural forest.     

The Emerging Era of Novel Tropical Forests

In 1966 Eugene P. Odum delivered a speech before the Ecological Society of America that transformed the way ecologists looked at succession. His comparison of mature and successional systems lead ecologists to place secondary forests in an inferior position relative to mature ones to the point that today, prominent tropical biologists argue for and against the conservation value of secondary forests. Nevertheless, we live in the era of secondary forests that is rapidly giving way to a new era of novel tropical forests. Research in Puerto Rico documents the emergence of novel forests, which are different in terms of species composition, dominance, and relative importance of species from forests that were present before the island was deforested. These novel forests emerged without assistance. They are a natural response to the new environmental conditions created by human activity. Natural processes have remixed or reassembled native and introduced plant and animal species into novel communities adapted to anthropogenic environmental conditions. Novel forests are expected to protect soils, cycle nutrients, support wildlife, store carbon, maintain watershed functions, and mitigate species extinctions. The dawn of the age of tropical novel forests is upon us and must not be ignored.     

Density dependence in forests is stronger in tropical and subtropical climates among closely related species

Density dependence has long been considered an important mechanism for species coexistence in forests. Density‐dependent processes can be important mechanisms driving differences in species diversity across latitudes. Here we examined the decline in strength of density dependence with increasing latitude, and particularly how density dependence affected both conspecifics and heterospecifics. Conspecific individuals within a species were predominantly aggregated at the three different latitudes of the three study sites in China. The percentage of aggregated species declined with increasing spatial scale and growth stages, which confirmed the overall importance of density dependence. Compared with a latitudinal gradient, the intensity of aggregation in the most northerly temperate (Changbaishan) plot was significantly higher than that in the tropical (Bawangling) or subtropical (Heishiding) plots. This showed that the strength of density dependence among conspecific individuals at low latitudes was stronger than that for high latitudes. We found that the more closely related species were more spatially adjacent in the temperate plot, while the opposite was true in the tropical and subtropical plots at most scales. After calculating the recruitment probability of all species of mature trees, we found that 19 of the 32 species in the tropical plot and 7 of the 12 species in the subtropical plot were less likely to recruit near closely related species. In the northern temperate plot, only one species demonstrated this phenomenon. These results therefore suggest that latitudinal variation in the intensity of negative density‐dependent recruitment resulting from specialist natural enemies (the Janzen–Connell hypothesis) may contribute to the latitudinal gradient of diversity in trees. The strength of density dependence at low latitudes was stronger than at high latitudes, regardless of whether this dependence was measured between only conspecific individuals or between individuals of closely related species.