Changes in tree and liana communities along a successional gradient in a tropical dry forest in south-eastern Brazil

We investigated changes in species composition and structure of tree and liana communities along a successional gradient in a seasonally dry tropical forest. There was a progressive increase in tree richness and all tree structural traits from early to late stages, as well as marked changes in tree species composition and dominance. This pattern is probably related to pasture management practices such as ploughing, which remove tree roots and preclude regeneration by resprouting. On the other hand, liana density decreased from intermediate to late stages, showing a negative correlation with tree density. The higher liana abundance in intermediate stage is probably due to a balanced availability of support and light availability, since these variables may show opposite trends during forest growth. Predicted succession models may represent extremes in a continuum of possible successional pathways strongly influenced by land use history, climate, soil type, and by the outcomes of tree–liana interactions.     

Habitat filtering across tree life stages in tropical forest communities

Tropical tree communities are shaped by local-scale habitat heterogeneity in the form of topographic and edaphic variation, but the life-history stage at which habitat associations develop remains poorly understood. This is due, in part, to the fact that previous studies have not accounted for the widely disparate sample sizes (number of stems) that result when trees are divided into size classes. We demonstrate that the observed habitat structuring of a community is directly related to the number of individuals in the community. We then compare the relative importance of habitat heterogeneity to tree community structure for saplings, juveniles and adult trees within seven large (24–50 ha) tropical forest dynamics plots while controlling for sample size. Changes in habitat structuring through tree life stages were small and inconsistent among life stages and study sites. Where found, these differences were an order of magnitude smaller than the findings of previous studies that did not control for sample size. Moreover, community structure and composition were very similar among tree sub-communities of different life stages. We conclude that the structure of these tropical tree communities is established by the time trees are large enough to be included in the census (1 cm diameter at breast height), which indicates that habitat filtering occurs during earlier life stages.     

How liana loads alter tree allometry in tropical forests

Intense competition with lianas (wood climbers) can limit tree growth, reproduction, and survival. However, the negative effects of liana loads on tree allometry have not yet been addressed. We investigated the hypothesis that liana loading on tree crown alters tree’s allometry, expressed through slenderness (height–diameter ratio). The relationship between trunk slenderness and percentage of tree crown covered by lianas was investigated for 12 tree species from 10 fragments of the Semideciduous Seasonal Forest in Southeastern Brazil. We also tested whether the relationship between slenderness and wood density differ between trees without lianas and trees heavily infested. Liana loads significantly altered tree allometry by decreasing slenderness, even when lianas covered less than 25% of tree crown. Heavy-wood species decreased their trunk slenderness in a greater ratio than light-wood species. Our findings indicate that liana infestation shifts tree allometry, and these effects are stronger on heavy-wood tree species.     

Landscape variation of liana communities in a Neotropical rain forest

We studied local and landscape variation of liana communities across habitats differing in soil and topography in the Lacandon tropical rain forest, southeast Mexico. All liana stems 1 cm diameter breast height (DBH) were sampled within each one of eight 0.5 ha plots. Two plots were sampled in each of the following habitats: alluvial-terrace, flood plain, low-hill, and karst-range. In the whole sampled area, we recorded 2092 liana stems ha^–1 representing a total basal area of 1.95 m² ha^–1 and 90 species within 34 families. Lianas showed a strong clumped spatial pattern and a high taxonomic diversity at the scale of 50 m². On average (± s.e.), we found 10.4±0.6 stems, 4.4±0.2 species and 3.4±0.2 families per 50-m² quadrat. Bignonaceae (19 species), Malpighiaceae (9), and Fabaceae (8) comprised about 40% of total number of recorded species, and almost 50% of the total liana biomass, as expressed by an importance value index that combines species relative abundance, spatial frequency and basal area. Nineteen families (56%) were represented by just one species and Cydista (Bignoniaceae) and Machaerium (Fabaceae) were the most diverse genera with four species each. In the landscape, lianas showed a geometric diversity-dominance relationship with only three species (Combretum argenteum, Hiraea fagifolia and Machaerium floribundum) accounting for more than 50% of total biomass. More than 30% of the species were rare (<15 stems ha^–1) and showed low spatial frequency (recorded in just one of the eight plots). Liana communities differed in structure and composition among sites and habitats. Among sites, lianas exhibited four-fold variation both in stem density and basal area and two-fold variation in species richness. Liana density was significantly and positively correlated with treefall disturbance. Ordination analysis indicated a strong habitat differentiation of lianas at the family and species levels. Most species with non-random distribution among habitats (69% from 25 species) were significantly most abundant in low-hill or flood plain sites, and some (12%) were preferentially found at the karst-range sites. The karst-range habitat was well differentiated from the others in species composition and structure, and shared only 50% of common species with other habitats.Soil water availability, treefall dynamics, as well as tree host identity and abundance may play an important role in the organisation of the liana communities at the Lacandon forest.     

Edge disturbance drives liana abundance increase and alteration of liana–host tree interactions in tropical forest fragments

Closed‐canopy forests are being rapidly fragmented across much of the tropical world. Determining the impacts of fragmentation on ecological processes enables better forest management and improves species‐conservation outcomes. Lianas are an integral part of tropical forests but can have detrimental and potentially complex interactions with their host trees. These effects can include reduced tree growth and fecundity, elevated tree mortality, alterations in tree‐species composition, degradation of forest succession, and a substantial decline in forest carbon storage. We examined the individual impacts of fragmentation and edge effects (0–100‐m transect from edge to forest interior) on the liana community and liana–host tree interactions in rainforests of the Atherton Tableland in north Queensland, Australia. We compared the liana and tree community, the traits of liana‐infested trees, and determinants of the rates of tree infestation within five forest fragments (23–58 ha in area) and five nearby intact‐forest sites. Fragmented forests experienced considerable disturbance‐induced degradation at their edges, resulting in a significant increase in liana abundance. This effect penetrated to significantly greater depths in forest fragments than in intact forests. The composition of the liana community in terms of climbing guilds was significantly different between fragmented and intact forests, likely because forest edges had more small‐sized trees favoring particular liana guilds which preferentially use these for climbing trellises. Sites that had higher liana abundances also exhibited higher infestation rates of trees, as did sites with the largest lianas. However, large lianas were associated with low‐disturbance forest sites. Our study shows that edge disturbance of forest fragments significantly altered the abundance and community composition of lianas and their ecological relationships with trees, with liana impacts on trees being elevated in fragments relative to intact forests. Consequently, effective control of lianas in forest fragments requires management practices which directly focus on minimizing forest edge disturbance.     

Stem and leaf hydraulics of congeneric tree species from adjacent tropical savanna and forest ecosystems

Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Only individuals growing in savanna habitats were studied. Most stem traits, including wood density, the xylem water potential at 50% loss of hydraulic conductivity, sapwood area specific conductivity, and leaf area specific conductivity did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (K _leaf) and leaf capacitance tended to be higher in savanna species. Predawn leaf water potential and leaf mass per area were also higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday K _leaf values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that, compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of K _leaf or to the turgor loss points, suggesting that savanna species were more buffered from changes in leaf water potential. The results of this study suggest that the relative success of savanna over forest species in savanna is related in part to their ability to cope with drought, which is determined more by leaf than by stem hydraulic traits. Variation among genera accounted for a large proportion of the total variance in most traits, which indicates that, despite different selective pressures in savanna and forest habitats, phylogeny has a stronger effect than habitat in determining most hydraulic traits.     

Patterns of liana community diversity and structure in a tropical rainforest reserve,Ghana: effects of human disturbance

Most studies have concluded that liana diversity and structure increase with disturbance. However, a contradictory pattern has emerged recently calling for more research in the area. Liana diversity and structure were investigated in three forest types that differ in disturbance intensity (nondisturbed, moderately disturbed and heavily disturbed forest: NDF, MDF and HDF, respectively) in the Atewa Range Forest Reserve, Ghana. In each forest type, 10 square plots of 0.25 ha were demarcated. Lianas with diameter ≥1 cm located on trees with diameter ≥10 cm were enumerated. A total of 429 individuals representing 40 species, 29 genera and seventeen families were identified in the study. Shannon diversity and species richness of lianas were significantly lower in the HDF (P < 0.05). Liana density and basal area differed significantly across all forest types (P < 0.0001). The importance value index (IVI) of most liana species varied greatly across the forest types. The current study has provided evidence to support the pattern of decreasing liana diversity and structure with disturbance in some tropical forests. Further studies are recommended to gain more understanding of the factors that are responsible for the divergent liana responses to disturbance in tropical forests.     

Soil phosphorus and disturbance influence liana communities in a subtropical montane forest

Questions: What are the effects of soil, topography, treefall gaps, tree species composition, and tree density on liana species composition and total liana abundance? Location: A 6‐ha permanent plot in a subtropical montane forest in northwest Argentina. Methods: Multiple regressions were used to quantify associations of liana species composition and total liana abundance with edaphic, disturbance and tree community variables. Gradients in liana and tree species composition were quantified using principal components analysis (PCA). Results: Liana species composition was correlated most strongly with soil phosphorus concentration (R²=0.55). Total liana aanased with phosphorus and the density of recent treefall gaps (R²=0.60). Conclusions: In our study area, liana composition and abundance are most strongly correlated with features of the physical environment, rather than host tree characteristics. Our results support the hypothesis that recent increases in liana abundance in mature tropical forests may be related to increased rates of gap formation.     

Vegetation and microclimatic edge effects in two mixed-mesophytic forest fragments

Forest edges are known to consist of microenvironments that may provide habitat for a different suite of species than forest interiors. Several abiotic attributes of the microenvironment may contribute to this change across the edge to center gradient (e.g., light, air temperature, soil moisture, humidity). Biotic components, such as seed dispersal, may also give rise to changes in species composition from forest edge to interior. We predicted that abiotic and biotic measures would correlate with distance from forest edge and would differ among aspects. To test these predictions, we measured abiotic and biotic variables on twelve 175 m transects in each of two 24 ha forest fragments in east-central Illinois that have remained in continuous isolation for upwards of 100 years. Both univariate and multivariate techniques were used to best describe the complex relationships among abiotic factors and between abiotic and biotic factors. Results indicate that microclimatic variables differ in the degree to and distance over which they show an edge effect. Relative humidity shows the widest edge, while light and soil moisture have the steepest gradients. Aspect influences are evidenced by the existence of more pronounced edge effects on south and west edges, except when these edges are protected by adjacent habitat. Edges bordered by agricultural fields have more extreme changes in microclimate than those bordered by trees. According to PCA results, species richness correlates well with microclimatic variation, especially light and soil moisture; however, in many cases species richness had a different depth of edge influence than either of these variables. The herbaceous plant community is heavily dominated by three species. Distributions of individual species as well as changes in plant community composition, estimated with a similarity index, indicate that competition may be influencing the response of the vegetation to the edge to interior gradient. This study indicates that edge effects must be considered when the size and potential buffering habitat of forest preserves are planned.     

Structure and function in two tropical gallery forest communities: implications for forest conservation in fragmented systems

1. Composition, growth and turnover of trees in two species-rich tropical gallery forests were examined to evaluate what community reorganization may be needed to transform recently created tropical forest fragments into stable refugia for regional forest biotas.
2. Rates of tree growth and turnover over a 5-year interval were comparable to those recorded in continuous forests and in both communities there had been some tree species turnover in the measured stem size classes during the 5-year interval.
3. The more abundant tree species in both communities formed three functional groups along gradients between streams and forest edges: edge-concentrators, core-concentrators and generalists.
4. Soil fertility showed no consistent increase close to streams and neither tree growth nor recruitment rates were increased in this zone. In contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests are light-limited rather than soil-limited, and that forest edge zones are generally favourable habitats for tree populations.
5. Both communities showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth-limited core habitats is attributed to their fire sensitivity.
6. Rapid development of an edge zone of fire-insensitive tree species is considered to be essential to the survival of forest community fragments in the fire-prone landscapes of the tropics, and the edges of gallery forests are recommended as potential sources of species with which to fashion these protective ecotones.
7. Preservation of a diverse forest biota in the fire-protected interiors of fragments will require natural or artificially enhanced immigration rates that are sufficient to offset local extinctions.     

Disentangling spatial,environmental and historical effects on tropical forest tree species turnover

空间、环境和历史因素对热带森林树种周转的影响本文通过回答以下问题来分析空间距离、当前和过去的环境差异及这几个因素对树木群落分类和系统发育转换的影响：(i)树木群落分类和系统发育转换是否与空间距离通过环境差异产生的间接影响相关？(ii)树木群落分类和系统发育转换是否随古气候(末次盛冰期和中全新世)的变化而变化？本文对巴西的14个大西洋雨林样点(采样面积20.4 ha) 83个科615个种进行了研究,获得了当前、中全新世和末次盛冰 期的地块地理坐标、土壤变量和样点生物气候变量。我们使用基于距离的结构方程模型(SEM)来(i)检测空间距离和环境差异的直接影响,以及(ii)检测空间距离通过环境差异对分类(Bray-Curtis距离)和系统发育转换(Comdist和Comdistnt距离)的间接影响。研究结果表明,空间距离通过环境差异对分类和系统发育转换的间接影响较弱。基于生态位中性的历史过程带来的直接影响驱动了树木群落的转换。因此,我们推断古气候(历史过程)促进了产生当前植物区系分支的选择,而空间距离(中性的过程)限制了物种从区域种库向外扩散的范围,环境条件(基于生态位的过程)则在本地选择能够持续生存的分类群。     

Hydraulic and photosynthetic characteristics differ between co-generic tree and liana species: a case study of Millettia and Gnetum in tropical forest

木质藤本是热带森林的重要组成部分, 显著影响森林的结构和功能。已有研究发现木质藤本与乔木的水力结构存在显著差异: 木质藤本的缠绕或攀缘茎细小, 但其木质部具有粗大的长导管, 输水效率高, 抗栓塞能力低。为降低基因型差异对比较结果的影响, 该研究选取热带崖豆藤属(Millettia)和买麻藤属(Gnetum)的乔木和木质藤本, 比较同属内不同生长型植物的水力和光合性状的差异, 分析水分传导效率与抗栓塞能力之间以及水力与光合性状之间的相关关系。结果发现: (1)崖豆藤属植物水力性状的种间差异大, 与生活型和需光性有关。耐阴的木质藤本反而具有较低的水分传导效率和较高的抗栓塞能力。(2)买麻藤属植物是裸子植物较为进化的类群(具有导管和阔叶), 其乔木的水分传导效率很低, 但是其木质藤本的水分传导效率高于其他阳生性的被子植物。(3)不论乔木还是木质藤本, 水分传导的有效性与安全性在枝条和叶片水平上均没有显著的权衡关系。(4)与同属乔木相比, 木质藤本的叶片较枝条的抗栓塞能力更强, 在旱季具有更高的最大净光合速率和气孔导度, 支持了木质藤本的“旱季生长优势假说”。该研究揭示了热带木质藤本水力性状的多样性和重要性, 为阐明环境变化对这一重要植物类群的影响, 需要对它们的水力特征进行更广泛的研究。     

Primate communities: Their structure and role in tropical ecosystems

The structure of primate communities living in a number of undisturbed areas is described and compared. Species richness is highest in tropical rain forests of Africa and South America, where up to 14 different species can share the same habitat. The number of sympatric primates in woodlands and savannas is always much lower. Some striking differences in community structure may be observed between communities living in apparently similar habitats. Three major factors may be held responsible for such discrepancies: history and paleoecology, present spatial heterogeneity of the vegetation, and competition with other taxonomic groups. The role of primates in the functioning of forest ecosystems is discussed. Though their trophic impact may be important, the role they play in seed dispersal appears to be more significant; they contribute greatly to homeostasis, as well as to regeneration, of the rain forests. A number of ecological traits are particularly developed among primates and may have contributed to the rapid evolutionary success of the order. Their predominantly vegetarian diet allows them to build up higher population densities than sympatric carnivorous mammals;their arborealism permits them to make use of all edible plant material available in a tridimensional environment; the opportunistic tendencies of some cebids, cercopithecids, and pongids enable them to take advantage of a variety of habitats and situations; and finally, an extended socialization period and a long life-span, allowing them to develop social traditions, give to many of them a further possibility to adapt quickly to novel situations. This paper is a revised version of the third Osman Hill Memorial Lecture delivered at the joint meeting of the Primate Society of Great Britain and the Association for the Study of Animal Behaviour, held in London on 2/3 December 1982.     

Responses of communities of tropical tree species to elevated CO2 in a forest clearing

Communities of ten species of tropical forest tree seedlings from three successional classes were grown at ambient and elevated CO₂ in large open-top chambers on the edge of a forest in Panamá. Communities grew from 20?cm to approximately 2?m in height in 6 months. No enhancements in plant biomass accumulation occurred under elevated CO₂ either in the whole communities or in growth of individual species. Reductions in leaf area index under elevated CO₂ were observed, as were decreases in leaf nitrogen concentrations and increases in the C:N ratio of leaf tissue. Species tended to respond individualistically to elevated CO₂, but some generalizations of how successional groupings responded could be made. Early and mid-successional species generally showed greater responses to elevated CO₂ than late-successional species, particularly with respect to increases in photosynthetic rates and leaf starch concentrations, and reductions in leaf area ratio. Late-successional species showed greater increases in C:N ratios in response to elevated CO₂ than did other species. Our results indicate that there may not be an increase in the growth of regenerating tropical forest under elevated CO₂, but that there could be changes in soil nutrient availability because of reductions in leaf tissue quality, particularly in late-successional species.     

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr^-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen.Tree mortality averaged 2.3% yr^-1 and exceeded recruitment (1.5% yr^-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11% yr^-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago.Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1–3.5% yr^-1), mortality and recruitment rates, and small-litter fall (5.52 t ha^-1 yr^-1).Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.Abbreviations dbh diameter at breast height (1.3 m) - gbh girth at breast height died May 1984     

氮磷添加对树木生长和森林生产力影响的研究进展

人为活动所导致的氮、磷输入和大气氮、磷沉降使生态系统中的氮、磷可利用性大幅提高, 对陆地生态系统的碳循环过程产生了显著影响。树木生长和森林生产力在全球碳循环中发挥着重要作用, 它决定着陆地碳固存的大小和方向。目前, 在全球范围内开展了很多氮、磷添加调控树木生长和森林生产力的野外控制实验, 但是研究结果并不一致, 受到多种生物、环境和实验处理条件等因素的影响。该文从野外氮添加和磷添加实验的文献数量、实验数量及其全球空间分布三个方面概述了氮、磷添加对树木生长和森林生产力影响的研究现状, 并总结了氮、磷添加实验中树木生长和森林生产力的评估方法, 包括相对生长速率和绝对增长量。基于相关的研究结果, 阐述了氮、磷添加影响树木生长和森林生产力的调控因素及其潜在影响机制, 包括气候、树木径级与林龄、植物功能性状(共生菌根类型、树木固氮属性和保守性与获得性性状)、植物和微生物相互作用关系、区域养分沉降速率和实验处理条件等。最后, 基于当前的研究进行了系统总结, 并指出今后需要加强的几个方面的研究, 以期为后续研究提供参考: 树木生长响应氮、磷添加的生理学机制, 树木各部分生长对氮、磷添加响应的权衡与分配, 植物功能性状在调节与预测树木生长响应氮、磷添加中的作用, 树木之间的竞争关系如何调控氮、磷添加对树木生长的影响, 以及开展长期的和联网的氮、磷添加对树木生长和森林生产力影响的野外控制实验。     

A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems

Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth and forest productivity, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and forest productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and forest productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.