Positive relationships between structural diversity and forest productivity have been documented in controlled experiments and early secondary forests, however, negative relationships have also been ...observed in late successional forests. The mechanisms causing observed relationships between structural diversity and productivity are not well‐established, but complementarity among crowns and asymmetric competition have been suggested.
We used LiDAR and repeated census data to examine the relationship between canopy structural diversity and productivity in nine 1‐ha subtropical forest plots along a disturbance gradient in southeastern China. We quantified the relative importance of community composition, species diversity, canopy structural diversity, leaf area index (LAI) and disturbance regime on productivity using piecewise structural equation modelling. We also tested how vertical leaf area distribution affected productivity.
Contrary to many prior observations, we found a negative relationship between canopy structural diversity and forest productivity. The negative effect may stem from asymmetric competition between overstorey and understorey leaves, leading to a lower leaf area efficiency (i.e. wood production per leaf area). Asymmetric competition was suggested by a negative relationship between understorey leaf area and total productivity. Changes in community composition over the disturbance gradient, but not species diversity, had a significant effect on productivity.
Synthesis. Our study suggests that leaf area and canopy structural diversity have contrasting effects on productivity in this subtropical forest, and this needs to be considered when estimating rates of carbon sequestration in secondary forests. The negative effect of asymmetric competition on productivity is comparable to that of the shift in species composition over succession, highlighting the role of canopy structural diversity in shaping forest productivity.
摘要
很多之前的研究在控制实验和演替早期的次生林中发现了结构多样性对生产力的正效应, 但另一些研究在演替后期的森林中发现结构多样性对生产力具有负效应。目前结构多样性和生产力关系的生态学机制尚不完善, 但是可能的机制是上层和下层树冠之间利用光资源的互补效应或不对称竞争。
我们用9个不同演替阶段的1‐ha森林样地的长期调查数据和激光雷达数据来探究结构多样性与生产力的关系。首先我们用结构方程模型检验了群落物种组成、物种多样性、冠层结构多样性、叶面积指数和演替阶段等多个因素对生产力的影响。同时, 我们进一步检验了叶面积的垂直分布对生产力的影响。
与以往大多数研究结论相反, 我们发现冠层结构多样性对生产力存在负效应, 这种负效应可能源于上层和下层树冠对光资源的不对称竞争, 导致了下层树冠较低的叶面积利用效率。同时, 林下层叶面积与总体生产力之间的负关系为不对称竞争机制提供了进一步的证据。同时, 我们还发现, 演替过程中群落物种组成的变化显著影响生产力, 但物种多样性的变化并不影响生产力。
我们的研究表明, 叶面积总量和冠层结构多样性对生产力的影响相反, 在估计次生林的碳固存速率时应同时考虑叶面积和冠层结构多样性。不对称竞争与演替过程中物种组成变化对生产力的作用强度相当, 凸显了林冠结构多样性在决定森林生产力中的重要性。
Contrary to many prior observations, we found a negative relationship between canopy structural diversity and coarse woody productivity in the subtropical forests along a disturbance gradient in southeastern China. The negative effect may stem from asymmetric light competition between overstorey and understorey crowns in structurally complex forests, leading to a lower leaf area efficiency.
Flagship species have been used widely as umbrella species (i.e., species with large home range whose protection often provides protection for sympatric species) in the management of China's nature ...reserves. This conflation of flagship and umbrella species is best represented by the giant panda (Ailuropoda melanoleuca) and other large, endangered mammals designated as conservation targets in site selection and planning of reserves. Few empirical studies have tested the effectiveness of flagship species as surrogates for a broader range of sympatric species. Using extensive camera‐trap data, we examined the effectiveness of management zones designated to protect flagship (target) species in conserving sympatric species in 4 wildlife reserves (Gutianshan, Changqing, Laohegou, and Wolong). We tested whether the progression from peripheral to core zones was associated with an increasing habitat association for both target and sympatric species. The distribution patterns of the study species across the zones in each reserve indicated a disparity between management zones and the species’ habitat requirements. Management zone was included in the final model for all target species, and most of them had higher occurrence in core zones relative to less‐protected zones, but zone was not a predictor for most of the sympatric species. When management zone was associated with the occurrence of sympatric species, threatened species generally had higher detections in core zones, whereas common species had higher detections outside of the core zone. Our results suggested that reserve planning based on flagship species does not adequately protect sympatric species due to their specialized habitat requirements. We recommend re‐examining the effectiveness of management zoning and urge a multispecies and reserve‐wide monitoring plan to improve protection of China's wildlife.
Efectividad del Manejo de Zonación Diseñada para Especies Bandera en la Protección de Especies Simpátricas
Resumen
Las especies bandera se han utilizado ampliamente como especies paraguas (es decir, especies con una extensa distribución cuya protección frecuentemente proporciona protección para especies simpátricas) en el manejo de las reservas naturales de China. Esta combinación de especie bandera y especie paraguas tiene su mejor representación en el panda gigante (Ailuropoda melanoleuca) y otros grandes mamíferos en peligro de extinción designados como objetivos de conservación en la selección de sitio y la planeación de reservas. Pocos estudios empíricos han probado la efectividad de las especies bandera como sustitutas de una especie simpátrica con una distribución más amplia. Con datos numerosos de cámaras trampa, examinamos la efectividad de las zonas de manejo designadas para proteger a las especies bandera (objetivo) en la conservación de especies simpátricas dentro de cuatro reservas de fauna (Gutianshan, Changqing, Laohegou y Wolong). Probamos si la progresión de las zonas periféricas hacia las zonas núcleo estaba relacionada con asociaciones crecientes de hábitat tanto para las especies objetivo como para las simpátricas. Los patrones de distribución del estudio de especies a lo largo de las zonas en cada reserva indicaron una disparidad entre las zonas de manejo y los requerimientos de hábitat de las especies. La zona de manejo se incluyó dentro del modelo final para todas las especies objetivo y la mayoría de ellas tuvo una presencia más alta en las zonas núcleo en relación con las zonas de menor protección. Cuando la zona de manejo se asoció a la presencia de especies simpátricas, las especies amenazadas generalmente tuvieron un mayor número de detecciones en la zona núcleo, mientras que las especies comunes tuvieron un número más elevado de detecciones fuera de la zona núcleo. Nuestros resultados sugieren que la planeación de reservas basada en las especies bandera no protege adecuadamente a las especies simpátricas debido a sus requerimientos especializados de hábitat. Recomendamos una reexaminación de la efectividad del manejo de zonación y urgimos que se genere un plan de monitoreo multiespecífico en toda la reserva para mejorar la protección de la fauna en China.
摘要
旗舰物种被广泛地作为伞护物种 (指活动范围广、对其投入的保护措施能够同时有益于其它同域分布物种的物种) 用于中国自然保护区的管理。旗舰种和伞护种概念的混淆最为突出地体现在, 选择以大熊猫为代表的大型濒危兽类作为主要保护对象来确定保护区的选址和规划。很少有实证性的研究来检验伞护种是否能有效代表同域分布物种的保护需求。我们基于大数据量的红外相机调查, 评估了中国4个野生动物保护区 (古田山、长青、老河沟和卧龙) 针对旗舰物种 (即主要保护对象) 划定的管理分区对同域分布物种保护的有效性。我们分析了从保护区实验区向缓冲区、核心区过渡的过程中, 主要保护对象和其它同域分布物种是否均表现出更强的选择性。多个物种在保护区各个分区内的分布格局显示, 管理分区和物种的栖息地需求并不一致。分区是影响主要保护对象分布的因素之一。相比实验区和缓冲区, 多数保护对象更多地出现在核心区。然而, 分区对绝大多数同域分布物种而言, 并不是一个影响其分布的显著因素。对于部分分布受分区影响的同域分布物种而言, 受威胁物种通常偏好核心区内的生境, 而常见种则偏好实验区内的生境。我们的研究结果表明, 旗舰物种通常有特化的栖息地需求, 将它们作为同域分布物种的代表以指导保护区规划, 并不能有效保护其它同域分布物种。我们建议保护区应重新评估管理分区的有效性, 并采用基于多物种的、覆盖保护区全境的监测方案, 以促进对中国野生动物的有效保护。
Article impact statement: Zoning designations in China's wildlife reserves aimed at conserving flagship species may not meet the habitat needs of most sympatric species.
Background and aims
Home-field advantage (HFA) hypothesis predicts that plant litter decomposes faster beneath the plant species from which it was derived than beneath other plant species. However, ...it remains unclear, which groups of soil organisms drive HFA effects across a wide range of litter quality and forest types.
Methods
We set up a reciprocal transplant decomposition experiment to quantify the HFA effects of broadleaf, coniferous and bamboo litters. Litterbags of different mesh sizes and high-throughput pyrosequencing of microbial rRNA gene were used to test the contribution of different decomposer groups to HFA effect.
Results
The recalcitrant broadleaf litter and the labile bamboo litter exhibited HFA. Presence of meso-and macrofauna did not substantially change the HFA effects. Bacterial and fungal community composition on litters were significantly influenced by litter type. Bacterial community composition remained unchanged when the same litter was decomposed in different forest types, whereas fungal community composition on broadleaf and bamboo litters were significantly influenced by incubation site.
Conclusions
Our data demonstrate specific association between fungal community composition and faster litter decomposition in the home site, suggesting that fungi probably participate in driving the HFA effect of broadleaf and bamboo litters.
Observed biodiversity–ecosystem function (BEF) relationships are highly variable, particularly in natural forests. However, our understanding of the factors that generate these often contradictory ...patterns, especially the role of different mycorrhizal associations, is still limited.
By relating tree species richness and above‐ground biomass (AGB) in a fully mapped 24‐ha subtropical forest dynamics plot, we evaluated the impacts of soil fertility and tree mycorrhizal type in mediating BEF relationships at multiple spatial scales.
Our results demonstrate a highly positive total richness effect on AGB for arbuscular mycorrhizal (AM) trees but a negative effect on AGB for ectomycorrhizal (EcM) trees, and their relationships were highly spatial scale dependent. However, the observed BEF relationships turned into positive at small spatial scales (i.e. 10 and 20 m) after controlling for other confounding factors (i.e. topography, soil fertility and AM proportion). In addition, we found significant interactions between soil fertility and species richness on AGB. Specifically, the positive effect of total species richness on AGB for major mycorrhizal types gradually weakened with increasing soil fertility, while the positive effect of EcM species richness on AM AGB gradually enhanced at small spatial scales, suggesting the observed diversity effects can be largely attributed to resource niche complementarity and the role of EcM fungi.
Synthesis. We conclude that the variable BEF relationships among forest communities could be explained by spatial variation in abiotic environments and community mycorrhizal composition because different types of symbionts perform different nutrient uptake strategies and ability in protection from antagonists. Our findings provide novel insights into the understanding of the variation in the shape of BEF relationships in natural forests, which is critical for forest management, conservation and restoration in a changing world.
摘要
在自然森林群落中，物种多样性与生态系统功能之间的关系通常具有较高的空间变异。但是我们对这些变异产生的原因，特别是植物菌根类型所发挥的作用，仍知之甚少。
本研究以古田山24公顷亚热带常绿阔叶林动态监测样地为研究平台，通过植物多样性与地上生物量关联分析，评估了壤肥力和植物菌根类型对不同空间尺度物种多样性与生态系统功能关系的影响。
研究结果表明，总物种多样性与丛枝菌根植物地上生物量存在较强的正相关关系，而与外生菌根植物生物量呈现显著负相关关系，并且其相互关系具有显著的尺度依赖效应。但是，当我们排除其它干扰因子(如地形、土壤肥力以及丛枝菌根植物比率)影响后，发现总物种多样性与植物地上生物量的相关关系在较小尺度转变为正相关。此外，物种多样性对地上生物量的影响显著依赖于土壤肥力。具体而言，随着土壤肥力的增加，总物种多样性与地上生物量的正相关关系逐渐减弱，而外生菌根植物多样性与丛枝菌根植物地上生物量的正相关关系在较小空间尺度逐渐增强，表明资源生态位互补效应和外生菌根真菌的保护效应可能是影响物种多样性和生物量关系的关键机制。
结论:我们发现由于不同类型菌根植物具有不同的养分利用策略和对天敌的防御能力，物种多样性和生产力的关系可能会同时受到资源空间异质性和群落菌根植物组成的影响。该研究为理解天然林中物种多样性与生态系统功能关系提供了新见解，这对全球变化情景下的森林管理、保护和恢复至关重要。
We conclude that the variable BEF relationships among forest communities could be explained by spatial variation in abiotic environments and community mycorrhizal composition because different types of symbionts perform different nutrient uptake strategies and ability in protection from antagonists. Our findings provide novel insights into the understanding of the variation in the shape of BEF relationships in natural forests, which is critical for forest management, conservation and restoration in a changing world.
Determining the patterns and drivers of the small‐scale species–area relationship (SAR) is crucial for improving our understanding of community assembly and biodiversity patterns. Niche‐based and ...stochastic processes are two principal categories of mechanisms potentially driving SARs. However, their relative importance has rarely been quantified rigorously owing to scale dependence and the simplified niche volumes often used.
In a fully mapped, 24‐hm2 plot of a typical subtropical forest, we built the SARs and well‐defined niche hyper‐volumes of a broad range of environmental variables at scales of 10–70 m (cell sizes). We then simulated passive sampling and partitioned the variances of the SAR slopes to disentangle these two contrasting mechanisms.
We found that the small‐scale SAR best followed a power‐law relationship, consistent with large‐scale SARs. The SAR slope declined with increasing scale; it was lower than expected under passive sampling at scales below 30 m and higher at larger scales. Environmental niches explained more (39%–64%) of the slope at larger scales, exceeding 50% at scales >30 m, and these niches always captured the majority of the structured slopes. Environmental position (environmental mean values) effects were steady in absolute strength across scales and explained most (98%–68%) of the niche effect, but this proportion decreased with increasing scale. The effect of environmental heterogeneity increased with spatial scales, starting to rise at the 30 m scale after controlling for environmental position. Excluding soil properties from analyses strongly reduced these niche effects, highlighting the importance of soils for structuring the small‐scale SAR. There was also substantial stochasticity in the SAR slopes, which was only partially explained by passive sampling.
Synthesis. Our results show that the small‐scale SAR in the studied subtropical forest follows a power law, exhibits a scale shift in SAR slope at 30 m, and is strongly shaped by niche effects that are dominated by environmental position relative to heterogeneity. However, soil heterogeneity controls the increase in niche effect and the shift in the SAR slope with increasing spatial scales. Hence, edaphic factors can be responsible for scale dependence in small‐scale SARs, thereby linking small‐scale and large‐scale SARs.
摘要
揭示小尺度种‐面积关系变化及其驱动机制对我们深入理解群落构建和生物多样性格局至关重要。生态位和随机过程是种‐面积关系变化的两大主要驱动机制，但由于尺度依赖和当前常用的生态位维度过于简化，很少有研究对这两大主要机制在驱动种‐面积关系变化中的相对重要性进行严格的量化分析。
本研究以典型的亚热带常绿阔叶林24‐ha样地为研究对象，样地内木本植物个体和环境因子变量空间信息明确；在10 ‐ 70 m 尺度（样地网格单元边长大小），对每个网格单元，我们建立了种‐面积关系曲线和由大量环境变量组成的生态位超维空间，同时模拟了被动取样过程，利用方差分解的方法量化区分两大主要驱动机制对种‐面积关系的相对重要性。
我们发现，如同大尺度种‐面积关系，幂函数模型（power‐law model）也是小尺度种‐面积关系的最优拟合。种‐面积关系斜率随尺度增加而减小，当尺度小于30 m时，该斜率小于被动取样过程产生的期望斜率；当尺度大于30 m时，该斜率大于被动取样过程产生的期望斜率。环境生态位在较大尺度解释了更多的种‐面积斜率的空间变异（39% ‐ 64%），当尺度大于30 m，该解释率大于50%；环境生态位主导了种‐面积关系斜率在空间的结构性变化。在环境生态位中，环境位置（environmental position），即环境变量的平均值，对种‐面积关系斜率的绝对效应随尺度变化是稳定的，其解释了大部分的环境生态位效应（98% ‐ 68%），但解释比例随尺度增加而下降；相对而言，生境异质性对种‐面积关系斜率的效应随尺度增加而增加，控制生境位置效应后，生境异质性效应自30 m尺度开始增加。将土壤变量从分析中移除导致环境生态位效应被严重低估，这一结果突显了土壤变量在决定小尺度种‐面积关系中的重要性。同时，种‐面积关系斜率也表现出很强的随机性，这种随机性仅部分被动取样过程解释。
4. 综上所述，该研究表明典型亚热带森林小尺度种‐面积关系遵循幂函数变化规律，其斜率在30 m尺度呈现尺度转换。环境生态位过程强烈地影响着小尺度种‐面积关系的变化；相对于环境异质性，环境位置主导了小尺度上环境生态位效应。但是，土壤异质性是导致环境生态效应随尺度增加而增加的原因，并控制了种‐面积关系斜率的尺度转换。因此，土壤因素决定了小尺度种‐面积关系的尺度依赖性，从而将小尺度和大尺度种‐面积曲线关联起来。
Our results show that the small‐scale species‐area relationship (SAR) in a typical subtropical forest follows a power law, exhibits a scale shift in SAR slope at 30 m scale, and is strongly shaped by niche effects that are dominated by environmental position relative to heterogeneity. However, soil heterogeneity controls the increase in niche effect and shift in the SAR slope with increasing spatial scales. Hence, edaphic factors can be responsible for scale dependence in small‐scale SARs, thereby linking small‐scale and large‐scale SARs.
The classical environmental control model assumes that species distribution is determined by the spatial variation of underlying habitat conditions. This niche-based model has recently been ...challenged by the neutral theory of biodiversity which assumes that ecological drift is a key process regulating species coexistence. Understanding the mechanisms that maintain biodiversity in communities critically depends on our ability to decompose the variation of diversity into the contributions of different processes affecting it. Here we investigated the effects of pure habitat, pure spatial, and spatially structured habitat processes on the distributions of species richness and species composition in a recently established 24-ha stem-mapping plot in the subtropical evergreen broad-leaved forest of Gutianshan National Nature Reserve in East China. We used the new spatial analysis method of principal coordinates of neighbor matrices (PCNM) to disentangle the contributions of these processes. The results showed that (1) habitat and space jointly explained ~53% of the variation in richness and ~65% of the variation in species composition, depending on the scale (sampling unit size); (2) tree diversity (richness and composition) in the Gutianshan forest was dominantly controlled by spatially structured habitat (24%) and habitat-independent spatial component (29%); the spatially independent habitat contributed a negligible effect (6%); (3) distributions of richness and species composition were strongly affected by altitude and terrain convexity, while the effects of slope and aspect were weak; (4) the spatial distribution of diversity in the forest was dominated by broad-scaled spatial variation; (5) environmental control on the one hand and unexplained spatial variation on the other (unmeasured environmental variables and neutral processes) corresponded to spatial structures with different scales in the Gutianshan forest plot; and (6) five habitat types were recognized; a few species were statistically significant indicators of three of these habitats, whereas two habitats had no significant indicator species. The results suggest that the diversity of the forest is equally governed by environmental control (30%) and neutral processes (29%). In the fine-scale analysis (10 × 10 m cells), neutral processes dominated (43%) over environmental control (20%).
The majority of species in many communities are rare, and it is an enduring challenge to understand the mechanism of species rarity and commonness in local communities. The niche partitioning ...hypotheses posit that common species occupy wide and core positions, while rare species occupy narrow and outlying niche positions. We test these hypotheses here, simultaneously considering both an environmental and a functional perspective on niches.
We examined how niches correlate with species abundance in environmental and functional space by quantifying relationships between species abundance and niche width and niche position. Environmental niches were defined as the section of an environmental gradient where each species occurred, and functional niches using species traits were thought to be related to resource acquisition. Hypotheses were tested using a dataset including functional traits collected from 4,302 individual trees of 423 species and environmental data in one subtropical and one tropical forest in China.
Consistent with the niche partitioning hypotheses, rare species in our two study systems tended to occupy the edges of the functional and environmental niche space. This likely allows rare species to avoid competition from dominant species. However, rare species tended to have a similar or larger niche width than common species in functional space, which contrasts with their narrower niche width in environmental space.
Synthesis. Our results support the prediction that rare species occupy outlying niches to avoid competition with common species. We found inconsistent evidence, though, about the niche width of rare species. Rare species may be less constrained in functional space, and persist by dint of their functional lability and ability to use a variety of resources. Our work supports previously hypothesized mechanisms underlying local species abundance patterns, but highlights new idiosyncrasies when considering environmental niche or functional space alone.
A free Plain Language Summary can be found within the Supporting Information of this article.
摘要
群落中大部分物种都是只有少数个体的稀有种，理解局部群落中物种稀有性的机制是一个持续的挑战。生态位分化假说认为：优势物种占据较宽的核心生态位位置，但稀有种则占据狭窄的边缘生态位位置。我们同时从环境生态位和功能生态位的角度检验这个假说。
我们通过量化物种多度和生态位位置和宽度的关系来检验生态位在环境和功能生态位空间是如何影响物种多度的。环境生态位是指每个物种发生环境条件的范围，而功能生态位与资源获取的物种功能性状相关。我们采用取自分属423个物种的4302个树木个体的功能性状以及中国的一个热带森林和一个亚热带森林的环境数据来检验生态位分化假说。
与生态位分化假说一致，两个森林的稀有种趋向于占据功能和环境生态位的边缘位置。这允许稀有物种通过利用稀有资源来避免与优势物种竞争。另一方面，与稀有种在环境生态位空间狭窄的生态位宽度相反，稀有种在功能生态位空间通常有与优势种相似或更大的生态位宽度。
总之，我们的研究结果支持稀有种占据边缘生态位位置的预测，从而避免与优势种的竞争。另一方面我们发现生态位宽度在功能和环境生态位空间是不同的。稀有种在功能空间受制约较少，有较宽的生态位从而能利用较多类型的资源。我们的研究结果支持生态位分化假说可用于解释物种多度格局，同时，但也突显稀有物种在环境和功能生态位上的差异。
A free Plain Language Summary can be found within the Supporting Information of this article.
Forging strong links between traits and performance is essential for understanding and predicting community assembly and dynamics. Functional trait analyses of trees that have correlated single-trait ...values with measures of performance such as growth and mortality have generally found weak relationships. A reason for these weak relationships is the failure to use individual-level trait data while simultaneously putting that data into the context of the abiotic setting, neighborhood composition, and the remaining axes constituting the overall phenotype. Here, utilizing detailed growth and trait data for 59 species of trees in a subtropical forest, we demonstrate that the individual-level functional trait values are strongly related to individual growth rates, and that the strength of these relationships critically depends on the context of that individual. We argue that our understanding of trait-performance relationships can be greatly improved with individuallevel data so long as that data is put into the proper context.
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