Tropical Rain Forest Species Research Articles

Phytochemical analysis of mature tree root exudates in situ and their role in shaping soil microbial communities in relation to tree N-acquisition strategy

Eperua falcata (Aublet), a late-successional species in tropical rainforest and one of the most abundant tree in French Guiana, has developed an original strategy concerning N-acquisition by largely preferring nitrate, rather than ammonium (H. Schimann, S. Ponton, S. Hättenschwiler, B. Ferry, R. Lensi, A.M. Domenach, J.C. Roggy, Differing nitrogen use strategies of two tropical rainforest tree species in French Guiana: evidence from (15)N natural abundance and microbial activities, Soil Biol. Biochem. 40 (2008) 487-494). Given the preference of this species for nitrate, we hypothesized that root exudates would promote nitrate availability by (a) enhancing nitrate production by stimulating ammonium oxidation or (b) minimizing nitrate losses by inhibiting denitrification. Root exudates were collected in situ in monospecific planted plots. The phytochemical analysis of these exudates and of several of their corresponding root extracts was achieved using UHPLC/DAD/ESI-QTOF and allowed the identification of diverse secondary metabolites belonging to the flavonoid family. Our results show that (i) the distinct exudation patterns observed are related to distinct root morphologies, and this was associated with a shift in the root flavonoid content, (ii) a root extract representative of the diverse compounds detected in roots showed a significant and selective metabolic inhibition of isolated denitrifiers in vitro, and (iii) in soil plots the abundance of nirK-type denitrifiers was negatively affected in rhizosphere soil compared to bulk. Altogether this led us to formulate hypothesis concerning the ecological role of the identified compounds in relation to N-acquisition strategy of this species.

Foliar chemistry and standing folivory of early and late-successional species in a Bornean rainforest

Background: Few studies have investigated the chemical, morphological and physiological foliar traits and the intensity of standing folivory in a representative set of species of tropical rainforests including species of different successional stages. Aims: (i) To quantify leaf elemental composition, leaf phenolics and tannin concentrations, physical leaf traits and the intensity of standing folivory in a representative set of species of different successional stages in a Bornean tropical rainforest, and (ii) to investigate the relationships among leaf traits and between leaf traits and accumulated standing folivory. Methods: Analyses of leaf elemental concentrations, phenolics (Ph) and tannin (Tan) concentrations, leaf mass area (LMA), C assimilation rate and accumulated standing folivory in 88 common rainforest species of Borneo. Results and Conclusions: Accumulated standing folivory was correlated with the scores of the first axis of the elemental concentrations principal component analysis (mainly loaded by K and C:K and N:K ratios) with lower accumulated standing folivory at high leaf K concentrations (R = –0.33, P = 0.0016). The results show that consistent with growth rate hypothesis, fast-growing pioneer species have lower leaf N:P ratios than late-successional species, that species with higher leaf N concentration have lower LMA according with the ‘leaf economics spectrum’ hypothesis, and that species with lower leaf nutrient concentration allocate more C to leaf phenolics. This study also shows that species with different ecological roles have different biogeochemical ‘niches’ assessed as foliar elemental composition.

Spatial pattern of trees in tropical lowland rain forest in Bawangling of Hainan Island, China

Aims Understanding processes underlying spatial distribution of tree species is fundamental to the study of spe-cies coexistence and diversity.Our objective was to determine the spatial structure and identify the processes that may generate spatial patterns of trees in a tropical lowland rain forest community on Hainan Island of South China.Methods Based on four models of point pattern analysis (homogenous Poisson process,inhomogenous Poisson process,homogenous Thomas process and inhomogenous Thomas process),we evaluated the potential contribu-tion of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species in two 1-hm2 stem-mapped forest dynamic plots.The relative importance of each process was assessed at six different spatial scales ( 2 m,2-5 m,5-10 m,10-15 m,15-20 m and 20-25 m).Important findings All stems combined revealed a strong aggregation at short distance (≤2 m),and the degree of aggregation decreased with increasing distance.Among the four models simulating tree distribution and pat-terning,the homogeneous Thomas process was the best-fit model.This result suggested that spatial patterns of tree species in tropical lowland rain forest might be formed by dispersal limitation.The homogeneous Poisson process that models the effect of spatial complete randomness was the second-best model.The inhomogeneous Thomas process and inhomogeneous Poisson process were equally important to forming spatial patterns of trees;they simulated the joint effects of habitat associations and dispersal limitation and modeled heterogeneity,respec-tively.The proportion of best-fit models differed across different scales.The dispersal limitation was a most im-portant mechanism in spatial patterning of tree species at most scales,while complete randomness process was second in importance.The joint effects of habitat associations and dispersal limitation mainly influenced tree dis-tribution at small scales (0-5 m).However,habitat heterogeneity only affected the distribution at larger scales (15-25 m).

Changes in wood density, wood anatomy and hydraulic properties of the xylem along the root-to-shoot flow path in tropical rainforest trees

It is generally assumed that the largest vessels are occurring in the roots and that vessel diameters and the related hydraulic conductance in the xylem are decreasing acropetally from roots to leaves. With this study in five tree species of a perhumid tropical rainforest in Sulawesi (Indonesia), we searched for patterns in hydraulic architecture and axial conductivity along the flow path from small-diameter roots through strong roots and the trunk to distal sun-canopy twigs. Wood density differed by not more than 10% across the different flow path positions in a species, and branch and stem wood density were closely related in three of the five species. Other than wood density, the wood anatomical and xylem hydraulic traits varied in dependence on the position along the flow path, but were unrelated to wood density within a tree. In contrast to reports from conifers and certain dicotyledonous species, we found a hump-shaped variation in vessel diameter and sapwood area--specific conductivity along the flow path in all five species with a maximum in the trunk and strong roots and minima in both small roots and twigs; the vessel size depended on the diameter of the organ. This pattern might be an adaptation to the perhumid climate with a low risk of hydraulic failure. Despite a similar mean vessel diameter in small roots and twigs, the two distal organs, hydraulically weighted mean vessel diameters were on average 30% larger in small roots, resulting in ∼ 85% higher empirical and theoretical specific conductivities. Relative vessel lumen area in percent of sapwood area decreased linearly by 70% from roots to twigs, reflecting the increase in sclerenchymatic tissue and tracheids in acropetal direction in the xylem. Vessel size was more closely related to the organ diameter than to the distance along the root-to-shoot flow path. We conclude that (i) the five co-occurring tree species show convergent patterns in their hydraulic architecture despite different growth strategies, and (ii) the paradigm assuming continuous acropetal vessel tapering and decrease in specific conductance from fine roots towards distal twigs needs reconsideration.

The Growth of Selected Shorea Spp in Secondary Tropical Rain Forest: The Effect of Silviculture Treatment to Improve Growth Quality of Shorea Spp

Dipterocarpaceae is the main species of tropical rain forest in Indonesia, Malaysia, Brunei and Phillippines and it ranges in eastwards as far as eastern New Guinea. This species is primary product in tropical rain forest of forest concessions. Recently, the quality and quantity of tropical rain forest are decreasing because of the land convertion become forest plantation; illegal logging and shifting cultivation. One of the strategies to reduce the forest degradation is enrichment planting on logged over forest (LOA) using dipterocarps species. The plantation trial was established with two (2) spacing, two (2) fertilizer dosages and five (5) Shorea spp as treatment to support the enrichment planting program in LOA. The research design was split-split plot design with 4 replications. The main plot was 2 spacings i.e. 6x2 m; and 6x4 m. The sub plot was 2 dosages of NPK Fertilizer i.e. 0 and 100 gr species-1. The sub-sub plot was 5 species of Shorea spp., i.e. Shorea leprosula, S.platyclados, S.parvifolia, S.virescens and S.johorensis. Each treatment was established in sguare plot (4x10 trees/treatment). The reserach result showed that spacing, fertilizer dosage and interaction between treatmens were not significant, while species was significant at tα=0.05 fertilizer dosage and interaction between treatmens were not significant, while species was significant at dipterocarps early growth. The highest growth was S.leprosula of DBH and high variables where the value of DBH and high variables were 8.90 cm (2.9 cm.year-1 of mean annual increment/MAI) and 6.31 m (2.1 m. year-1 of MAI) respectively. The lowest growth was S.virescens both on high and DBH variables where the value of DBH and high were 2.27 cm. year-1 and 1.40 m. year-1 respectively.

Physiological epicotyl dormancy and recalcitrant storage behaviour in seeds of two tropical Fabaceae (subfamily Caesalpinioideae) species

Physiological epicotyl dormancy in which the epicotyl elongates inside the seed before the shoot emerges has been reported for only a few tropical rainforest species, all of which are trees that produce recalcitrant seeds. In studies on seeds of Fabaceae in Sri Lanka, we observed a considerable time delay in shoot emergence following root emergence in seeds of the introduced caesalpinioid legumes Brownea coccinea and Cynometra cauliflora. Thus, our aim was to determine if seeds of these two tropical rainforest trees have physiological epicotyl dormancy, and also if they are recalcitrant, i.e. desiccation sensitive. Fresh seeds were (i) dried to various moisture levels, and (ii) stored at -1 and 5 °C to determine loss (or not) of viability and thus type of seed storage behaviour (orthodox, recalcitrant or intermediate). To identify the kind of dormancy, we tested the effect of scarification on imbibition and monitored radicle emergence and epicotyl growth (inside the seed) and emergence. FRESH SEEDS OF BOTH SPECIES HAD HIGH MOISTURE CONTENT (MC): 50 % for C. cauliflora and 30 % for B. coccinea. Further, all seeds of C. cauliflora and the majority of those of B. coccinea lost viability when dried to 15 % MC; most seeds of both species also lost viability during storage at -1 or 5 °C. Intact seeds of both species were water permeable, and radicles emerged in a high percentage of them in <30 days. However, shoot emergence lagged behind root emergence by 77 ± 14 days in B. coccinea and by 38 ± 4 days in C. cauliflora. Further, plumule growth inside seeds of C. cauliflora began almost immediately after radicle emergence but not until ∼30-35 days in B. coccinea seeds. Seeds of both species are recalcitrant and have physiological epicotyl dormancy. The kind of physiological epicotyl dormancy in seeds of C. cauliflora has not been described previously; the formula is C(nd) (root)-[Formula: see text] (epicotyl).

Variation in beetle community structure across five microhabitats in Australian tropical rainforest trees

Abstract Beetles (Coleoptera) are the most species‐rich and ecologically diverse group of organisms in tropical rainforest canopies. This study reports on the distribution of the beetle community on five discrete canopy microhabitats (mature leaves, new leaves, flowers, fruit, and suspended dead wood) on 23 tree species in an Australian tropical rainforest. We tested the hypothesis that the beetle fauna will vary in community structure between microhabitats based on differences in the quantity, quality as a food source and availability of different canopy microhabitats. There was substantial variation in dominant beetle families in terms of abundance between microhabitats. All assemblages contained a high number of rare species, with flowers supporting most of the more abundant species. Consequently, the flower‐visitor assemblage was more heterogeneous than expected by chance, whereas the mature leaf assemblage was more even in the proportional abundances of species than expected. The distribution of singletons was also non‐random and flowers, which are spatially and temporally restricted, supported fewer singletons than expected by chance, whereas mature leaves and dead wood supported more. These differences were insensitive to beetle feeding guild, and are most likely related to variation in microhabitat distribution and availability, which influenced relative sampling efforts and the probability of random microhabitat/beetle associations. High dissimilarity in species overlap between microhabitats suggests that each microhabitat attracts a unique beetle assemblage, which has an additive effect on canopy‐wide species richness patterns. Consequently, biodiversity studies that focus on single microhabitats may inadvertently omit a large proportion of canopy species.

Interspecific variation in leaf water use associated with drought tolerance in four emergent dipterocarp species of a tropical rain forest in Borneo

By use of tree-tower and canopy-crane systems we studied variations in the water use, including transpiration, stomatal conductance, and leaf water potential, of the uppermost sun-exposed canopy leaves of four emergent dipterocarp species in an aseasonal tropical rain forest in Sarawak, Malaysia. Midday depression in stomatal conductance and leaf water potential was observed in all the species studied. Interspecific differences were clearly observed in the maxima of transpiration rates and stomatal conductance and the minima of leaf water potential among the four dipterocarp species. These interspecific variations were closely related to wood density and to factors affecting ecological patterns of distribution. Specifically, Shorea parvifolia and S. smithiana, both of which have a relatively low wood density for Dipterocarpaceae and are found on clay-rich soil, had a high transpiration rate in the daytime but had a large midday depression and a low leaf water potential. In contrast, Dryobalanops aromatica, which has a high wood density and is found in sandy soil areas, consumed less water even during the daytime. Dipterocarpus pachyphyllus, which has a high wood density and is found on clay-rich soil, stood intermediate between Shorea and D. aromatica in leaf water use. The two Shorea species had higher mortality than the others during the severe drought associated with El Niño in 1998, so daily pattern of leaf water use in each dipterocarp species might be correlated with its susceptibility to unusual drought events.

Are tree ontogenetic structure and allometric relationship independent of vegetation formation type? A case study with Cordia oncocalyx in the Brazilian caatinga

In temperate and tropical rainforests, ontogenetic structure and allometry during tree ontogeny are often associated with light gradients. Light is not considered a limiting resource in deciduous thorny woodland (DTW), but establishment and growth occur during a short rainy period, when the canopy is fully leaved and light in the understory may be modified. Our aim was to investigate whether the light gradient in DTW and the biomechanical limitations of tree growth would be enough to produce an ontogenetic structure and allometric growth similar to rainforest canopy trees. We investigated the ontogenetic stages and diameter–height relationship of Cordia oncocalyx (Boraginaceae), a dominant canopy tree of the DTW of semiarid northeastern Brazil. We tagged, measured and classified the ontogenetic stages of 2.895 individuals in a 1 ha area (5°6′58.1″S and 40°52′19.4″W). In the rainy season only 4.7% of the light falling on the canopy reached the ground. Initial ontogenetic stages, mainly infant (50.9%) and seedling (42.1%), were predominant in the population, with the remaining 7% distributed among juvenile, immature, virginile and reproductive. The ontogenetic structure was similar to that of rainforest tree species, but the population formed both permanent seed and infant banks in response to long dry periods and erratic rainy spells. Like many other Boraginaceae tree species in tropical rainforests, C. oncocalyx has a Prévost architectural model, but allometric growth was quite different from rainforest trees. C. oncocalyx invested slightly more in diameter at first, then in height and finally invested greatly in diameter and attained an asymptotic height. The continued high investment in diameter growth at late stages and the asymptotic height point to low tree density and more frequent xylem embolism as the main drivers of tree allometric shape in DTW. This indicates that tree ontogenetic structure and allometric relationships depend on vegetation formation type.

Change in biomass of symbiotic ants throughout the ontogeny of a myrmecophyte, Macaranga beccariana (Euphorbiaceae)

Macaranga myrmecophytes (ant-plants) provide their partner symbiotic ants (plant-ants) with food bodies as their main food, and they are protected by the plant-ants from herbivores. The amount of resource allocated to food bodies determines the plant-ant colony size and consequently determines the intensity of ant defense (anti-herbivore defense by plant-ants). As constraints in resource allocation change as plants grow, the plant-ant colony size is hypothesized to change with the ontogenesis of Macaranga myrmecophyte. To determine the ontogenetic change in the relative size of the plant-ant colony, we measured the dry weights of the whole plant-ant colony and all of the aboveground parts of trees at various ontogenetic stages for a myrmecophytic species (Macaranga beccariana) in a Bornean lowland tropical rain forest. Ant biomass increased as plant biomass increased. However, the rate of increase gradually declined, and the ant biomass appeared to reach a ceiling once trees began to branch. The ant/plant biomass ratio consistently decreased as plant biomass increased, with the rate of decrease gradually accelerating. We infer that the ontogenetic reduction in ant/plant biomass ratio is caused by an ontogenetic change in resource allocation to food rewards for ants related to the physiological changes accompanying the beginning of branching.

Disturbance and tropical pioneer species: Patterns of association across life history stages

Pioneer tree species of tropical rain forests in the seedling and sapling size classes are generally associated with disturbances to the forest canopy. Pioneers have usually been lumped together within the same broad guild. Many studies have demonstrated differentiation of late successional shade-tolerant species within a forest but only a few studies have shown pioneers to be complex in differentiation. Most assume pioneers to be generalist and similar in growth and establishment. It is therefore not well understood, how sympatric pioneer species differ across life history stages in relation to disturbance characteristics such as canopy openness, type, intensity and historical condition of disturbance. Here we studied seedlings, saplings and larger trees of eight pioneer species common in and around the Sinharaja World Heritage Reserve in Sri Lanka to characterize species differences in relation to canopy openness, type and intensity of disturbance. We analyzed canopy hemispherical photographs and conditions of disturbance and assessed the probability of species’ occurrence and the relative importance of disturbance characteristics by fitting progressively more complex multinomial logistical regression models. Canopy openness demonstrated the greatest association with seedling and sapling distribution. Trema orientalis, was found in the highest light conditions, while all other species showed a decrease in the probability of occurrence with increasing canopy openness. For larger trees, the historical condition of disturbance was shown to be a more important factor than the light characteristics. Irrespective of size classes, T. orientalis and Macaranga peltata were restricted to high light environments and large disturbances whereas Macaranga indica, Dillenia triquetra, Schumacheria castaneifolia, and Wendlandia bicuspidata were found in relatively lower light environments and smaller disturbances. Alstonia macrophylla and Melastoma malabathricum were able to exist across wide ranging light conditions. In seedlings and saplings, disturbance type was more influential than both the historical condition of disturbance and the intensity of the disturbance, with some evidence that species do occur differentially in certain disturbance types. In summary this study provides evidence that pioneers of all life history stages differentiate in relation to amount of light and disturbance characteristics and that such differentiations are important mechanisms for the coexistence and diversity of early seral tropical tree species. Findings from our study suggests that pioneers used for reforestation and site amelioration need to be selected carefully to match degree of exposure, history and type of disturbance of the site that is to be reforested.

The effect of the G‐layer on the viscoelastic properties of tropical hardwoods

This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood. Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a G‐layer, whilst the tension wood from the latter three had no G‐layer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage. Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer. It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.

Butterfly behavioural responses to natural Bornean tropical rain-forest canopy gaps

Abstract:Natural tree canopy gaps allow sunlight to penetrate to the forest floor, a major environmental component and resource for many tropical rain-forest species. We compare here how butterflies use sunny areas created by the natural gaps in canopies in comparison with adjacent closed-canopy areas. We chose butterflies as our focal organisms as they are taxonomically tractable and mobile, yet habitat sensitive. Previous studies have shown that butterfly diversity in tropical forests responds to varying degrees of canopy openness. Here we assess butterfly behavioural responses to gaps and equivalent sized closed-canopy patches. Butterfly occupancy time and behaviour were simultaneously observed 61 times in gaps and 61 times in equivalent sized closed-canopy patches across four sites in a tropical rain forest in northern Borneo. Out of the 20 most frequently recorded species, 12 were more frequently recorded or spent more time in gaps, four occurred more frequently in closed-canopy areas, and four showed no significant differences. Overall agonistic, basking, patrolling and resting were more common in gaps compared with the closed canopy. Many butterfly species have complex behavioural requirements for both gaps and closed canopies, with some species using these different areas for different behaviours. Each butterfly species had particular habitat requirements, and needed both canopy gaps and closed canopy areas for ecological and behavioural reasons, emphasizing the need for natural light heterogeneity within these systems.

Ecology of hemiepiphytism in fig species is based on evolutionary correlation of hydraulics and carbon economy

Woody hemiepiphytic species (Hs) are important components of tropical rain forests, and they have been hypothesized to differ from non-hemiepiphytic tree species (NHs) in adaptations relating to water relations and carbon economy; but few studies have been conducted comparing ecophysiological traits between the two growth forms especially in an evolutionary context. Using common-garden plants of the genus Ficus, functional traits related to plant hydraulics and carbon economy were compared for seven NHs and seven Hs in their adult terrestrial "tree-like" growth phase. We used phylogenetically independent contrasts to test the hypothesis that differences in water availability selected for contrasting suites of traits in Hs and NHs, driving evolutionary correlations among functional traits including hydraulic conductivity and photosynthetic traits. Species of the two growth forms differed in functional traits; Hs had substantially lower xylem hydraulic conductivity and stomatal conductance, and higher instantaneous photosynthetic water use efficiency. Leaf morphological and structural traits also differed strikingly between the two growth forms. The Hs had significantly smaller leaves, higher leaf mass per area (LMA), and smaller xylem vessel lumen diameters. Across all the species, hydraulic conductivity was positively correlated with leaf gas exchange indicating high degrees of hydraulic-photosynthetic coordination. More importantly, these correlations were supported by correlations implemented on phylogenetic independent contrasts, suggesting that most trait correlations arose through repeated convergent evolution rather than as a result of chance events in the deep nodes of the lineage. Vatiation in xylem hydraulic conductivity was also centrally associated with a suite of other functional traits related to carbon economy and growth, such as LMA, water use efficiency, leaf nutrient concentration, and photosynthetic nutrient use efficiency, indicating important physiological constraints or trade-offs among functional traits. Shifts in this trait cluster apparently related to the adaptation to drought-prone canopy growth during the early life cycle of Hs and clearly affected ecophysiology of the later terrestrial stage of these species. Evolutionary flexibility in hydraulics and associated traits might be one basis for the hyper-diversification of Ficus species in tropical rain forests.

Wood density explains architectural differentiation across 145 co‐occurring tropical tree species

Summary1.Because of its mechanical properties, wood density may affect the way that trees expand their stem and crown to exploit favourable light conditions in a mechanically stable way. From engineering theory and wood density properties, it is predicted that in terms of biomass investment, low‐density wood is more efficient for vertical stem expansion, while high‐density wood is more efficient for horizontal branch expansion. So far, these predictions have rarely been tested by empirical studies.2.We tested these predictions for 145 co‐occurring tree species in a Malaysian tropical rainforest. For each species, we selected trees across a broad size range and measured architectural dimensions (stem diameter, height of the lowest foliage and crown width). We used a hierarchical Bayesian model to estimate species‐specific allometric relationships between architectural dimensions including estimated stem biomass. Then, we examined correlations between species wood density and estimated architectural variables at standardized heights.3.When species were compared at standardized tree heights, wood density correlated negatively with stem diameter and positively with stem biomass at most reference heights. This indicates that species with low wood density produce thicker stems but at lower biomass costs. Wood density correlated positively with crown width and negatively with height of the lowest foliage, which indicates that high wood density species have wider and deeper crowns than low wood density species. These relationships were maintained at most reference heights. However, the relationship with crown width was nonsignificant above 18 m height. This may reflect large plastic response of lateral crown expansion to a local condition.4. Wood density explains the trade‐off between effective vertical stem expansion and horizontal crown expansion across co‐occurring tropical tree species. Such mechanical constraints characterize the difference in tree architecture between low wood density species that show an efficient height expansion to attain better light conditions in the exposed canopy and high wood density species that show an efficient horizontal crown expansion to enhance current light interception and persistence in the shaded forest understorey. Our study thus suggests that the mechanical constraints set by wood density contribute to the co‐existence of species differing in architecture and light capture strategy.

Trade-offs between growth and survival of non-pioneer light-demanding tree seedlings in tropical forest of Hainan Island, China

Abstract:We performed a pot experiment in which 540 seedlings of nine non-pioneer light-demanding tree species were grown for 12 months in shade houses at three light levels, 46% daylight, 13% daylight and 2% daylight, to examine the mechanisms contributing to the coexistence of seedlings of non-pioneer light-demanding tree species in secondary successional tropical rain forest in Hainan, China. Growth and survival of tree seedlings were compared at different light levels, and the morphological and physiological correlates of high-light seedling growth and low-light survival across species were determined. For all species, mortality was very low in the 46% daylight and 13% daylight treatment but increased significantly in the 2% daylight treatment. Seedling survival in 2% daylight treatment was positively related to seed mass. Trade-off between high-light growth and low-light survival was more evident in the relationship with 2% daylight treatment as compared with 13% daylight treatment. Relative growth rate in the 2% daylight treatment was not significantly related to relative growth rate in the 13% daylight or 46% daylight treatment; although a slight negative correlation was apparent. Interspecific variation in RGRm was only closely correlated with net assimilation rate (NAR). The results provide some support for the niche-partitioning hypothesis.

A Point-Process Model for Variance-Occupancy-Abundance Relationships

The relationship between species abundance, the variance of the number of individuals, and species occupancy is a fundamental ecological characteristic of a community. Moreover, this relationship varies across scales, and any model for the variance-occupancy-abundance (VOA) relationship has to address its scale dependency in a consistent way. In this study, point-process theory was used to define a multiscale model that jointly predicts the VOA relationship across scales in a consistent way. This provides a tool to jointly analyze data sets collected at different scales and to give insights into the biological processes underlying the VOA relationship. This model can also account for different types of individual spatial pattern (clustered, random, or regular). Three stand-mapping data sets of tree species in tropical rain forests were used to assess the relevance of this model. When compared with four existing models, the model based on point-process theory provided the best fit to the data and was the most often ranked as the model with the best predictive performance.

Litter decomposition and nutrient dynamics of ten selected tree species in tropical rainforest of Ebom, southwest Cameroon

Litter decomposition processes in tropical rainforests are still poorly understood. Leaf litter decomposition and nutrient dynamics of ten contrasting tree species, Entandraphragma utile, Guibourtia tessmannii, Klainedoxa gabonensis, Musanga cecropioides, Panda oleosa, Plagiostyles africana, Pterocarpus soyauxii, Strombosia scheffleri, Vitex grandifolia and Xylopia aethiopica were studied in the tropical rainforest of Ebom, Southwest Cameroon. After 23 weeks of field incubation in litterbags, mass loss of litter samples varied from 24.08% in E. utile to 92.35% in V. grandifolia. Decomposition rate constants (k) ranged from 0.014 in M. cecropioides to 0.165 week-1 in V. grandifolia. The nutrient content in original litter samples also varied widely among species and showed low levels of Na, P and Mg, and high levels of N, Ca and K. Averagenutrient releases was 89.04%, 60.80%, 46.19%, 40.99% and 24.17% of mean initial content for K, Ca, Mg, N and P, respectively. For nutrient-related litter chemistry, correlations with the mass losses at the end of litter incubation were significant (P

Mechanisms of rainforest persistence and recruitment in frequently burnt wet tropical eucalypt forests

AbstractThe role of fire in governing rainforest–eucalypt forest ecotone dynamics is of theoretical interest and has conservation management implications. Several eucalypt forests in the Wet Tropics of Australia have an endangered status due to extensive conversion to rainforest. Rainforest plants are known to survive occasional low intensity fires in the eucalypt forest ecotone. However, the ability of rainforest plants to survive frequent fires remains untested. The timing of rainforest expansion is also a subject of interest, and is generally considered to be delayed until fire has been absent for several years. We used 14 years of data collected across 13 plots in the Wet Tropics of north‐eastern Australia to test predictions regarding rainforest seedling recruitment and post‐fire regenerative capacity. The 13 plots received different numbers of fires, between zero and five, over the 14‐year study. The recruitment of new rainforest plants in the ecotone was most abundant in the initial year after fire. If this post‐fire pulse of recruitment is left undisturbed, it can facilitate the subsequent germination of additional rainforest species. The removal of grass cover, whether temporarily in the immediate post‐fire environment or once a developing rainforest mid strata shades out grasses, appears crucial to abundant rainforest recruitment. A variety of tropical rainforest species can persist under a frequent fire regime through resprouting. The difference in the mode of resprouting, between ground‐level coppicing rainforest plants and canopy resprouting eucalypt forest trees, is the critical mechanism that causes regular fire to maintain an open structure in eucalypt forests. The inability of rainforest species to maintain their height when fires fully scorch their crowns, temporarily resets the forest's open structure and delays the rainforest's ability to dominate through shading out grasses to transform the ecosystem into a closed forest.

Environment and tree size controlling stem sap flux in a perhumid tropical forest of Central Sulawesi, Indonesia

We studied stem sap flux density in seven common tree species in a perhumid tropical rainforest at pre-montane elevation in Sulawesi with the aims (1) to analyse the among-species variation in flow patterns, (2) to search for an assumed convergence in the response to controlling environmental factors, and (3) to investigate the effect of tree size on xylem flux. Sap flux density was measured for 20 months in 39 tree individuals of seven species (from six of the most dominant families in the area). Synchronous sap flux density in the outermost xylem differed more than threefold among the species and was highest in the tall Fagaceae Castanopsis acuminatissima. Across the seven species, a tight exponential correlation was found between tree diameter (or tree height) and tree daily water use. Daily sap flux density correlated better with atmospheric vapour pressure deficit than with shortwave radiation, in spite of the permanently high atmospheric humidity. Soil moisture did not vary significantly and therefore showed no effect on mean daily sap flux density. The hysteresis in the diurnal plot of xylem flux density against vapour pressure deficit or radiation was larger for radiation supporting the close coupling of flux variation to vapour pressure deficit, which exists even in this perhumid climate. We conclude that the species of this perhumid forest show convergent patterns in the environmental control of sap flux. Largely different water consumption rates of coexisting trees were mainly caused by differences in tree size and the position of the tree within the canopy. Our extrapolated daily stand transpiration rates are low in comparison to other tropical forests which may be a consequence of the permanently high air humidity.