Leaf damage and functional traits along a successional gradient in Brazilian tropical dry forests

Herbivory has significant impacts on individual plants and plant communities, both at ecological and evolutionary time scales. In this context, this study aims to evaluate herbivore damage and its relationship with leaf chemical and structural traits, nutritional status, and forest structural complexity along a successional gradient. We predicted that trees in early successional stages support conservative traits related to drought tolerance (high specific leaf mass and phenolics), whereas trees in light-limited, late successional stages tend to enhance light acquisition strategies (high nitrogen content). We sampled 261 trees from 26 species in 15 plots (50 × 20 m; five per successional stage). From each tree, twenty leaves were collected for leaf trait measures. Phenolic content increased whereas specific leaf mass and nitrogen content decreased from early to late stages. However, leaf damage did not differ among successional stages. Our results partially corroborate the hypothesis that early successional plants in tropical dry forests exhibit leaf traits involved in the conservative use of water. The unexpected decrease in nitrogen content along the chronosequence is likely related to the fact that thinner leaves with low specific leaf mass could have less nitrogen-containing mesophyll per unit area. Mechanisms affecting herbivory intensity varied across scales: at the species level, leaf damage was negatively correlated with tannin concentration and specific leaf mass; at the plot level, leaf damage was positively affected by forest structural complexity. Herbivory patterns in tropical forests are difficult to detect because abiotic factors and multiple top-down and bottom-up forces directly and indirectly affect herbivores.     

Causes and consequences of monodominance in tropical lowland forests

Tropical canopy dominance in lowland, well-drained forests by one plant species is a long-standing conundrum in tropical biology. Research now shows that dominance is not the result of one trait or mechanism. We suggest that the striking dominance of Gilbertiodendron dewevrei in the Ituri Forest of northeastern Congo is the result of a number of traits in adult trees that significantly modify the understory environment, making it difficult for other species to regenerate there. Adults cast deep shade that reduces light levels in the understory of the Gilbertiodendron forest to levels significantly lower than in the mixed-species forest. Moreover, the monodominant forest has deep leaf litter that could inhibit the establishment of small-seeded species, and the leaf litter is slow to decompose, potentially causing the low availability of nitrogen. We expect that juveniles of Gilbertiodendron may have an advantage in this environment over other species. In general, it appears that all tropical monodominant species share a similar suite of traits.     

天坑森林植物群落叶功能性状、物种多样性和功能多样性特征

以天坑内部-边缘-外部森林植物群落为研究对象,通过调查植物的群落结构、叶功能性状,探究天坑内外森林植物群落叶功能性状、物种多样性和功能多样性变化特征及其内在关联,为深入了解负地形森林生态系统的功能和恢复退化喀斯特地区的植被提供一定参考。研究结果如下：（1）比叶面积（SLA: 198.75 cm2/g)）、叶面积（LA: 42.70 cm2）、叶磷含量（LPC: 1.70 g/kg）和叶钾含量（LKC: 10.27 g/kg）在天坑内部最高,叶组织密度（LTD: 0.32 g/cm3）和叶干物质含量（LDMC: 0.41 g/g）在天坑外部最高,天坑内外森林均易受到磷限制,表明随天坑内部-边缘-外部生境变化,植物对环境的适应机制和生存策略发生了部分调整,物种的防御策略增强,生长投入策略减弱。（2）Shannon-Wiener指数（2.82）、Simpson指数（0.92）和Pielou’s均匀度指数（0.87）均以天坑外部最高,功能丰富度（1.05）、功能离散度（1.88）和Rao’s二次熵（4.52）以天坑内部最高,表明随天坑内部-边缘-外部生境的变化,植物功能性状的差异减少,物种分布及其功能性状分布总体上更为均匀、物种数量增多。（3）物种多样性指数之间、功能多样性指数之间存在较强的相关性,表明物种多样性指数之间、功能多样性指数之间存在不同的制约关系。（4）叶功能性状与物种多样性、功能多样性的相关性强,物种多样性和功能多样性之间相关性较弱,表明叶性状对生态学过程的变化较为敏感,叶功能性状与物种多样性之间存在较强的耦合关系。     

Tree functional traits as predictors of microburst-associated treefalls in tropical wet forests

On 19 May 2018, a microburst caused 600 isolated forest gaps in a Costa Rican tropical forest. We surveyed fallen and standing trees within gaps to determine whether certain variables are associated with treefalls. Our results highlight considerations for future research to understand the impacts of microbursts in tropical forests.     

Plant functional traits with particular reference to tropical deciduous forests: a review

Functional traits (FTs) integrate the ecological and evolutionary history of a species, and can potentially be used to predict its response as well as its influence on ecosystem functioning. Study of inter-specific variation in the FTs of plants aids in classifying species into plant functional types (PFTs) and provides insights into fundamental patterns and trade-offs in plant form and functioning and the effect of changing species composition on ecosystem functions. Specifically, this paper focuses on those FTs that make a species successful in the dry tropical environment. Following a brief overview, we discuss plant FTs that may be particularly relevant to tropical deciduous forests (TDFs). We consider the traits under the following categories: leaf traits, stem and root traits, reproductive traits, and traits particularly relevant to water availability. We compile quantitative information on functional traits of dry tropical forest species. We also discuss trait-based grouping of plants into PFTs. We recognize that there is incomplete knowledge about many FTs and their effects on TDFs and point out the need for further research on PFTs of TDF species, which can enable prediction of the dynamics of these forests in the face of disturbance and global climate change. Correlations between structural and ecophysiological traits and ecosystem functioning should also be established which could make it possible to generate predictions of changes in ecosystem services from changes in functional composition.     

Interannual variation in rainfall,drought stress and seedling mortality may mediate monodominance in tropical flooded forests

Flood tolerance is commonly regarded as the main factor explaining low diversity and monodominance in tropical swamps. In this study we examined seedling mortality in relation to seasonality, i.e., flooding versus drought, of the dominant tree species (Prioria copaifera), and three associated species (Pterocarpus officinalis, Carapa guianensis and Pentaclethra macroloba), in seasonally flooded forests (SFF) in Darien, Panama. Seedling mortality differed among species, years and seasons. Prioria seedlings experienced the lowest overall mortality, and after 3 years many more Prioria seedlings remained alive than those of any of the associated species. In general, within species, larger seedlings had greater survival. Seed size, which can vary by close to 2 orders of magnitude in Prioria, had a confounding effect with that of topography. Large-seeded Prioria seedlings experienced 1.5 times greater mortality than small-seeded seedlings, as large-seeded Prioria seedlings were more likely to be located in depressions. This finding suggests that seed size, plant size and topography are important in understanding SFF regeneration. For all species, seedling mortality was consistently greater during the dry season than during flooding. For Prioria, dry season seedling mortality was correlated with drought stress, that is, high mortality during the long El Niño dry season of 1998 and the normal dry season of 2000, but very low dry season mortality during the mild dry season of 1999. Prioria’s ability to dominate in seasonally flooded forest of Central America is partly explained by its low drought-related mortality in comparison to associated species.     

Do we need to devalue Amazonia and other large tropical forests?

Attempts to determine global priorities for conservation and studies aimed at highlighting the conservation value of one continental region over another often devalue specific regions. Amazonia has been a particular recipient of this treatment in a number of recent studies. We suggest that this type of approach is not necessary at this scale, and we argue that the consequences could be devastating for the largest forests of the world. Among our concerns about the treatment of these forests (Amazonia, the Congo Basin and New Guinea) is that there seems to be a lack of appreciation for, or sufficient study of, important biogeographic subdivisions within these regions. In Amazonia, the south‐eastern portion of the basin (the Belém/Pará region) has not been considered a global conservation priority, despite the fact that it is experiencing by far the highest deforestation rates. Parsimony Analyses of Endemicity and genetic data suggest that many Amazonian forest taxa are comprised of numerous regionally distinct units, and this may also be true in other large tropical forests. Such patterns need to be documented for adequate conservation of tropical biodiversity, but this might not happen if these regions are not recognized as priorities for conservation at a global scale.     

神农架海拔梯度上4种典型森林的乔木叶片功能性状特征

研究植物群落叶片功能性状沿环境梯度的变化可以更好地认识群落对环境的适应机制,海拔梯度在较小的空间范围内浓缩了不同的群落类型和环境梯度,是研究和理解群落与环境关系的理想场所。以神农架海拔梯度上4种典型森林为研究对象,分析了4种典型森林优势乔木树种的LMA、LDMC、N_area、N_mass、叶片厚度及叶片叶绿素含量等主要叶片功能性状随海拔的变化规律及各功能性状之间的相关性,以期从叶片功能性状角度揭示群落适应环境的机制。研究结果表明:在780-1970 m范围内,神农架海拔梯度上典型森林乔木优势种叶片的、N_area和叶片厚度随海拔升高而下降,而海拔2570 m的亚高山针叶林的LMA、N_area和叶片厚度最高,分别为187.37 g/cm²、1.92 g/m²和385.31 um,且针叶林的LMA是常绿阔叶林的2倍、落叶阔叶林的3.7倍;除常绿落叶阔叶混交林的N_mass小于落叶阔叶林外,N_mass随海拔升高(780-2570 m)而下降;海拔最高(2570 m)的针叶林和海拔最低(780 m)的常绿阔叶林的LDMC和叶绿素含量最高,分别为454.93 g/kg、407.64 g/kg和48.84、44.12;而海拔介于二者之间的常绿落叶阔叶混交林和落叶阔叶林的LDMC和叶绿素含量则最低,分别为338.93 g/kg、337.3 g/kg和38.73、38.19。叶片各功能性状之间存在着显著的相关性:叶片厚度与LMA/LDMC及LMA显著正相关。叶片叶绿素含量与N_area显著正相关。LMA与LDMC、N_area、叶片厚度、叶绿素含量显著正相关,LDMC与N_area、叶绿素含量、叶片厚度显著正相关,N_area与叶片厚度、叶绿素含量显著正相关,叶片厚度、叶绿素含量显著正相关。本研究进一步表明,随着海拔梯度上升环境条件的变化,森林群落不同物种功能性状间的相互作用共同决定着森林群落对环境的适应性。     

海南岛霸王岭热带云雾林木本植物功能性状的分异规律

研究植物功能性状的分异,有助于理解植物适应环境的方式和策略,也能为预测物种分布和环境变化提供依据。以海南霸王岭热带云雾林为对象,建立21个20 m×20 m固定样方,划分为336个5 m×5 m小样方;测定胸径在5cm以上所有乔灌木植物个体的功能性状(叶面积LA;叶干重LDW;比叶重LMA;叶绿素含量Chl;叶厚度LTh;木材密度WD)和土壤养分含量,通过方差分解分析植物功能性状在个体、种内、种间、群落水平的分异大小,探究土壤养分对功能性状分异的影响。结果表明,LA、LDW、LMA、CHl、LTh、WD在个体、种内、种间、群落水平的解释方差范围分别为0.06—0.47、0.09—0.35、0.35—0.72、0—0.07,在个体、种内、种间、群落层次上,种间水平的功能性状分异最大,而群落水平的分异最小。逐步回归分析表明,不同尺度的功能性状变化与土壤有机质、氮和磷含量都有密切关系。     

Convergent elevation trends in canopy chemical traits of tropical forests

The functional biogeography of tropical forests is expressed in foliar chemicals that are key physiologically based predictors of plant adaptation to changing environmental conditions including climate. However, understanding the degree to which environmental filters sort the canopy chemical characteristics of forest canopies remains a challenge. Here, we report on the elevation and soil‐type dependence of forest canopy chemistry among 75 compositionally and environmentally distinct forests in nine regions, with a total of 7819 individual trees representing 3246 species collected, identified and assayed for foliar traits. We assessed whether there are consistent relationships between canopy chemical traits and both elevation and soil type, and evaluated the general role of phylogeny in mediating patterns of canopy traits within and across communities. Chemical trait variation and partitioning suggested a general model based on four interconnected findings. First, geographic variation at the soil‐Order level, expressing broad changes in fertility, underpins major shifts in foliar phosphorus (P) and calcium (Ca). Second, elevation‐dependent shifts in average community leaf dry mass per area (LMA), chlorophyll, and carbon allocation (including nonstructural carbohydrates) are most strongly correlated with changes in foliar Ca. Third, chemical diversity within communities is driven by differences between species rather than by plasticity within species. Finally, elevation‐ and soil‐dependent changes in N, LMA and leaf carbon allocation are mediated by canopy compositional turnover, whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. Our findings have broad implications for understanding the global ecology of humid tropical forests, and their functional responses to changing climate.     

Leaf chemistry and the biomass of folivorous primates in tropical forests

Summary Recent results have suggested that the biomass of folivorous arboreal primates per unit area in Africa and Asia is positively correlated with the average quality of leaves, expressed as the ratio of protein to fiber concentrations in a given forest. This hypothesis has been tested in different forests of Madagascar. Leaf selection of all folivorous femus species was studied in relation to leaf chemistry. Except for two populations ofLepilemur subspecies all other folivorous lemur species (including two other subspecies ofLepilemur) select leaves with high concentrations of easily extractable protein or low concentrations of fiber, or both. This confirms the prominent role of these two components in leaf selection by folivorous lemurs. The average quality of mature leaves in a given forest, expressed as the ratio of protein to fiber concentrations, is positively correlated with the biomass of folivorous lemurs. This confirms the hypothesis tested and suggests rather uniform selection processes for arboreal folivorous primates across the world.     

Soil does not explain monodominance in a Central African tropical forest

Background

Soil characteristics have been hypothesised as one of the possible mechanisms leading to monodominance of Gilbertiodendron dewerei in some areas of Central Africa where higher-diversity forest would be expected. However, the differences in soil characteristics between the G. dewevrei-dominated forest and its adjacent mixed forest are still poorly understood. Here we present the soil characteristics of the G. dewevrei forest and quantify whether soil physical and chemical properties in this monodominant forest are significantly different from the adjacent mixed forest.

Methodology/Principal Findings

We sampled top soil (0–5, 5–10, 10–20, 20–30 cm) and subsoil (150–200 cm) using an augur in 6 × 1 ha areas of intact central Africa forest in SE Cameroon, three independent patches of G. dewevrei-dominated forest and three adjacent areas (450–800 m apart), all chosen to be topographically homogeneous. Analysis – subjected to Bonferroni correction procedure – revealed no significant differences between the monodominant and mixed forests in terms of soil texture, median particle size, bulk density, pH, carbon (C) content, nitrogen (N) content, C:N ratio, C:total NaOH-extractable P ratio and concentrations of labile phosphorous (P), inorganic NaOH-extractable P, total NaOH-extractable P, aluminium, barium, calcium, copper, iron, magnesium, manganese, molybdenum, nickel, potassium, selenium, silicon, sodium and zinc. Prior to Bonferroni correction procedure, there was a significant lower level of silicon concentration found in the monodominant than mixed forest deep soil; and a significant lower level of nickel concentration in the monodominant than mixed forest top soil. Nevertheless, these were likely to be the results of multiple tests of significance.

Conclusions/Significance

Our results do not provide clear evidence of soil mediation for the location of monodominant forests in relation to adjacent mixed forests. It is also likely that G. dewevrei does not influence soil chemistry in the monodominant forests.     

叶脉网络功能性状及其生态学意义

叶脉网络结构是叶脉系统在叶片里的分布和排列样式。早期叶脉网络结构研究主要集中在其分类学意义上; 近年来叶脉网络功能性状及其在植物水分利用上的意义已成为植物生态学研究的热点。该文介绍了叶脉网络功能性状的指标体系(包括叶脉密度、叶脉直径、叶脉之间的距离、叶脉闭合度等), 综述了叶脉网络功能性状与叶脉系统功能(包括水分、养分和光合产物等物质运输、机械支撑和虫害防御等)的关系, 叶脉网络功能性状与叶片其他功能性状(包括比叶重、叶寿命、光合速率、叶片大小、气孔密度等)的协同变异和权衡关系, 以及叶脉网络功能性状随环境因子(包括水分、温度、光照等)的变化规律等方面的最新研究进展。此外, 叶脉网络功能性状的研究成果也被应用于古环境重建、城市交通规划、流域规划及全球变化研究中。由于叶脉网络功能性状是环境因子与系统发育共同作用的结果, 未来开展分子—叶片—植物—生态系统等多尺度的叶脉网络功能性状研究, 理清叶脉网络功能性状与气孔失水—茎干导水—根系吸水等植物水分利用的关系, 将为预测植物及生态系统对全球变化的响应提供新的启示。     

Leaf litter decomposition rates in degraded and fragmented tropical rain forests of Borneo

Previously extensive tracts of primary rain forest have been degraded by human activities, and we examined how the effects of forest disturbance arising from habitat fragmentation and commercial selective logging affected ecosystem functioning in these habitats by studying leaf litter decomposition rates in litter bags placed on the forest floor. The rain forests of Borneo are dominated by trees from the family Dipterocarpaceae, and we compared leaf litter decomposition rates of three dipterocarp species at eight forest fragment sites (area 3–3529 ha) that had different histories of disturbance pre‐fragmentation: four fragments had been selectively logged prior to fragmentation and four had been formed from previously undisturbed forest. We compared these logged and unlogged forest fragments with sites in continuous forest that had been selectively logged (two sites) and fully protected and undisturbed (two sites). After 120 d, undisturbed continuous forest sites had the fastest rates of decomposition (52% mass loss). Forest fragments formed from unlogged forest (32% mass loss) had faster decomposition rates than logged forest fragments (28% mass loss), but slower rates than continuous logged forest (39% mass loss). Leaves of a light‐demanding species (Parashorea malaanonan) decomposed faster than those of a shade‐tolerant species (Hopea nervosa), but decomposition of all three dipterocarp species that we studied responded similarly to logging and fragmentation effects. Reduced decomposition rates in logged and fragmented forest sites may affect nutrient cycling and thus have detrimental consequences for forest regeneration. Conservation management to improve forest quality should be a priority, particularly in logged forest fragments.     

Beta diversity and oligarchic dominance in the tropical forests of Southern Costa Rica

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional‐landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1‐ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands. Abstract in Spanish is available with online material.     

热带森林植物功能群及其动态研究进展

热带森林极高的物种多样性和结构复杂性给生态学研究带来了很多挑战。植物功能群是对特定环境响应相似或对主要的生态过程具有相似作用的物种组合。应用植物功能群的方法是有效减少热带森林群落复杂性,并揭示其格局和过程的良好途径。在介绍植物功能群概念和划分途径的基础上,分析了热带森林植物功能群的时空动态规律。一般来讲,划分植物功能群通常有3种途径,并可通过5个步骤来完成。热带森林植物功能群的空间分布常受景观格局的制约,而环境异质性往往是影响不同植物功能群组配比例变化的直接原因。不同类型的植物功能群随演替过程发生显著的替代,而干扰体系和全球气候变化对功能群的动态过程具有重要的驱动作用。以功能群为基础的动态模型在模拟热带林群落动态和预测植被潜在分布等方面具有广阔的发展前景。探索有效的植物功能分类方法、构建完善的植物功能性状数据库、开发更为精确的功能群动态模型以及加强基于景观水平的植物功能群动态机制的认识等是未来热带森林植物功能群及其动态研究的重要方向。