Rainforest Tree Species Research Articles

Distance- and density-dependent leaf dynamics of seedlings of a tropical rainforest tree.

Parental distance and plant density dependence of seedling leaf turnover and survival was examined to investigate predictions of the Janzen-Connell hypothesis. The focal study species, Shorea macroptera is a canopy tree species in a lowland rain forest in peninsular Malaysia. We found that the peak of the distribution of plants shifted from 3-6m to 6-9m during the course of the change from seedling to sapling stage. The leaf demography of the seedlings was influenced by their distance from the adult tree and also by the seedling density. Although significant density- and distance dependence in leaf production was not detected, seedling leaf loss decreased with distance from the parent tree and with seedling density. Similarly, leaf damage was not found to be distance- or density-dependent, but net leaf gain of seedlings increased with distance from the parent tree. Although no significant distance- or density-dependence was evident in terms of leaf damage, significant distance dependence of the net leaf gain was found. Thus, we concluded that positive distance dependence in the leaf turnover of seedlings may gradually contribute to a shift in the distribution pattern of the progeny through reductions in growth and survivorship.

A new approach to spatial entropy measures

Entropy is widely employed in many applied sciences to measure the heterogeneity of observations. Recently, many attempts have been made to build entropy measures for spatial data, in order to capture the influence of space over the variable outcomes. The main limit of these developments is that all indices are computed conditional on a single distance and do not cover the whole spatial configuration of the phenomenon under study. Moreover, most of them do not satisfy the desirable additivity property between local and global spatial measures. This work reviews some recent developments, based on univariate distributions, and compares them to a new approach which considers the properties of entropy measures linked to bivariate distributions. This perspective introduces substantial innovations. Firstly, Shannon’s entropy may be decomposed into two terms: spatial mutual information, accounting for the role of space in determining the variable outcome, and spatial global residual entropy, summarizing the remaining heterogeneity carried by the variable itself. Secondly, these terms both satisfy the additivity property, being sums of partial entropies measuring what happens at different distance classes. The proposed indices are used for measuring the spatial entropy of a marked point pattern on rainforest tree species. The new entropy measures are shown to be more informative and to answer a wider set of questions than the current proposals of the literature.

Long-term fertilization determines different metabolomic profiles and responses in saplings of three rainforest tree species with different adult canopy position.

BackgroundTropical rainforests are frequently limited by soil nutrient availability. However, the response of the metabolic phenotypic plasticity of trees to an increase of soil nutrient availabilities is poorly understood. We expected that increases in the ability of a nutrient that limits some plant processes should be detected by corresponding changes in plant metabolome profile related to such processes.Methodology/Principal findingsWe studied the foliar metabolome of saplings of three abundant tree species in a 15 year field NPK fertilization experiment in a Panamanian rainforest. The largest differences were among species and explained 75% of overall metabolome variation. The saplings of the large canopy species, Tetragastris panamensis, had the lowest concentrations of all identified amino acids and the highest concentrations of most identified secondary compounds. The saplings of the “mid canopy” species, Alseis blackiana, had the highest concentrations of amino acids coming from the biosynthesis pathways of glycerate-3P, oxaloacetate and α-ketoglutarate, and the saplings of the low canopy species, Heisteria concinna, had the highest concentrations of amino acids coming from the pyruvate synthesis pathways.Conclusions/SignificanceThe changes in metabolome provided strong evidence that different nutrients limit different species in different ways. With increasing P availability, the two canopy species shifted their metabolome towards larger investment in protection mechanisms, whereas with increasing N availability, the sub-canopy species increased its primary metabolism. The results highlighted the proportional distinct use of different nutrients by different species and the resulting different metabolome profiles in this high diversity community are consistent with the ecological niche theory.

Pleistocene refugia and genetic diversity patterns in West Africa: Insights from the liana Chasmanthera dependens (Menispermaceae).

Processes shaping the African Guineo-Congolian rain forest, especially in the West African part, are not well understood. Recent molecular studies, based mainly on forest tree species, confirmed the previously proposed division of the western African Guineo-Congolian rain forest into Upper Guinea (UG) and Lower Guinea (LG) separated by the Dahomey Gap (DG). Here we studied nine populations in the area of the DG and the borders of LG and UG of the widespread liana species, Chasmanthera dependens (Menispermaceae) by amplified fragment length polymorphism (AFLP), a chloroplast DNA sequence marker, and modelled the distribution based on current as well as paleoclimatic data (Holocene Climate Optimum, ca. 6 kyr BP and Last Glacial Maximum, ca. 22 kyr BP). Current population genetic structure and geographical pattern of cpDNA was related to present as well as historical modelled distributions. Results from this study show that past historical factors played an important role in shaping the distribution of C. dependens across West Africa. The Cameroon Volcanic Line seems to represent a barrier for gene flow in the present as well as in the past. Distribution modelling proposed refugia in the Dahomey Gap, supported also by higher genetic diversity. This is in contrast with the phylogeographic patterns observed in several rainforest tree species and could be explained by either diverging or more relaxed ecological requirements of this liana species.

Breeding system, gene dispersal and small-scale spatial genetic structure of a threatened food tree species, Pentadesma butyracea (Clusiaceae) in Benin

Pentadesma butyracea Sabine, a rain forest food tree species, plays a vital role in the socio-economic livelihood of some West African rural communities due to its various products. However, its scattered populations are threatened in Benin. Defining appropriate conservation strategies requires a good knowledge of mating patterns and their consequences for population genetics. The outcrossing rate, levels of correlated paternity and fine-scale spatial genetic structure of adults and maternal sibships were estimated for one small population and three large populations in Benin using microsatellite markers. Similar outcrossing rates (88–95%) were found in all populations, showing that P. butyracea is mainly an outbreeding species. We found no evidence of inbreeding depression from a decay of inbreeding with age. The spatial genetic structure within the large populations (Sp statistic = 0.003–0.038) was consistent with isolation-by-distance expectations, showing that gene dispersal is spatially limited. Limited pollen dispersal is highlighted by the decay of the degree of correlated paternity between sibships with spatial distance. The mean pollen dispersal distance was estimated between 50 m and 450 m, but up to 21% pollen may migrate from external sources. The smallest population displayed slightly higher correlated paternity than the large populations (r p = 0.37 vs. r p = 0.17–0.30). In conclusion, our results suggest that small populations may show a reduction in sire numbers in seed, while the fragmented populations, large and small, are connected through gene flow. There is little inbreeding and no evidence of inbreeding depression.

C, N and P stoichiometric characteristics of soil and litter fall for six common tree species in a northern tropical karst seasonal rainforest in Nonggang, Guangxi, southern China

C, N and P stoichiometric characteristics of soil and litter fall for six common tree species in a northern tropical karst seasonal rainforest in Nonggang, Guangxi, southern China

Variation in leaf and soil nitrogen isotope ratio in diverse tree species in a lowland dipterocarp rainforest, Malaysia

Variation in leaf and soil nitrogen isotope ratio in diverse tree species in a lowland dipterocarp rainforest, Malaysia

Calibration of a multi-species model for chlorophyll estimation in seedlings of Neotropical tree species using hand-held leaf absorbance meters and spectral reflectance

Abstract: The aim of the present study was to calibrate a multi-species model for assessing leaf chlorophyll content in seedlings of six Neotropical rainforest tree species. Two hand-held chlorophyll absorbance meters (SPAD-502 and ClorofiLog) and the chlorophyll normalized difference leaf reflectance index (ND705) were tested. Measurements of leaf absorbance and reflectance, contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chl t), leaf area (LA), and leaf mass per area (LMA) were performed on fully expanded leaves. A total of 200 leaves were used for the calibration of the multiple-species model. The relative root mean square calibration errors (RMSec, %) were calculated based on estimated chlorophyll values for multiple-species models and on measured values for each of the six species. The average values of LA varied between 14.2 and 29.5 cm-2, LMA between 34.8 and 98.9 g m-2, and Chl t between 3 and 815 mg m-2. For all indices, the highest values of the coefficients of determination (R2) were observed for Chl a (R2 ≥ 0.91), followed by Chl t (R2 ≥ 0.89) and Chl b (R2 ≥ 0.82). The highest values of R2 were obtained for ND705 (R2 ≥ 0.86) followed by SPAD-502 (R2 ≥ 0.83) and ClorofiLog (R2 ≥ 0.82). The present study showed that ClorofiLog and SPAD-502 indices could be safely interconverted by a simple linear regression model (R2 = 0.98). RMSec values were lower than 20%, which confirmed the feasibility of the multi-species model for estimating the chlorophyll content using hand-held chlorophyll absorbance meters and leaf reflectance.

Factors controlling bark decomposition and its role in wood decomposition in five tropical tree species.

Organic matter decomposition represents a vital ecosystem process by which nutrients are made available for plant uptake and is a major flux in the global carbon cycle. Previous studies have investigated decomposition of different plant parts, but few considered bark decomposition or its role in decomposition of wood. However, bark can comprise a large fraction of tree biomass. We used a common litter-bed approach to investigate factors affecting bark decomposition and its role in wood decomposition for five tree species in a secondary seasonal tropical rain forest in SW China. For bark, we implemented a litter bag experiment over 12 mo, using different mesh sizes to investigate effects of litter meso- and macro-fauna. For wood, we compared the decomposition of branches with and without bark over 24 mo. Bark in coarse mesh bags decomposed 1.11–1.76 times faster than bark in fine mesh bags. For wood decomposition, responses to bark removal were species dependent. Three species with slow wood decomposition rates showed significant negative effects of bark-removal, but there was no significant effect in the other two species. Future research should also separately examine bark and wood decomposition, and consider bark-removal experiments to better understand roles of bark in wood decomposition.

Topographic species–habitat associations of tree species in a heterogeneous tropical karst seasonal rain forest, China

Topographic species–habitat associations of tree species in a heterogeneous tropical karst seasonal rain forest, China

Regression models for estimating leaf area of seedlings and adult individuals of Neotropical rainforest tree species.

Individual leaf area (LA) is a key variable in studies of tree ecophysiology because it directly influences light interception, photosynthesis and evapotranspiration of adult trees and seedlings. We analyzed the leaf dimensions (length - L and width - W) of seedlings and adults of seven Neotropical rainforest tree species (Brosimum rubescens, Manilkara maxima, Pouteria caimito, Pouteria torta, Psidium cattleyanum, Symphonia globulifera and Tabebuia stenocalyx) with the objective to test the feasibility of single regression models to estimate LA of both adults and seedlings. In southern Bahia, Brazil, a first set of data was collected between March and October 2012. From the seven species analyzed, only two (P. cattleyanum and T. stenocalyx) had very similar relationships between LW and LA in both ontogenetic stages. For these two species, a second set of data was collected in August 2014, in order to validate the single models encompassing adult and seedlings. Our results show the possibility of development of models for predicting individual leaf area encompassing different ontogenetic stages for tropical tree species. The development of these models was more dependent on the species than the differences in leaf size between seedlings and adults.

Gambeya korupensis (Sapotaceae: Chrysophylloideae), a new rain forest tree species from the Southwest Region in Cameroon

Gambeya korupensis Ewango & Kenfack (Sapotaceae: Chrysophylloideae), a new rain forest tree species from the Southwest Region in Cameroon, is described and illustrated. A distribution map is provided. G. korupensis has the leaf blade below pubescent on the midribs and secondary nerves, flowers with a pedicel 0.5 – 1 mm long, and a fruit which is ovoid, attenuate at the apex, 5-ridged, verrucose between the ridges, and bright red at maturity. The conservation status of G. korupensis is assessed as Vulnerable according to IUCN criteria.

Phylogenetic composition and structure of tree communities shed light on historical processes influencing tropical rainforest diversity

The Neotropics, Afrotropics and Madagascar have different histories which have influenced their respective patterns of diversity. Based on current knowledge of these histories, we developed the following predictions about the phylogenetic structure and composition of rainforest tree communities: (Hypothesis 1) isolation of Gondwanan biotas generated differences in phylogenetic composition among biogeographical regions; (H2) major Cenozoic extinction events led to lack of phylogenetic structure in Afrotropical and Malagasy communities; (H3) greater angiosperm diversification in the Neotropics led to greater phylogenetic clustering there than elsewhere; (H4) phylogenetic overdispersion is expected near the Andes due to the co‐occurrence of magnoliids tracking conserved habitat preferences and recently diversified eudicot lineages. Using abundance data of tropical rainforest tree species from 94 communities in the Neotropics, Afrotropics and Madagascar, we computed net relatedness index (NRI) to assess local phylogenetic structure, i.e. phylogenetic clustering vs. overdispersion relative to regional species pools, and principal coordinates of phylogenetic structure (PCPS) to assess variation in phylogenetic composition across communities. We observed significant differences in phylogenetic composition among biogeographical regions (agreement with H1). Overall phylogenetic structure did not differ among biogeographical regions, but results indicated variation from Andes to Amazon. We found widespread phylogenetic randomness in most Afrotropical and all Malagasy communities (agreement with H2). Most of central Amazonian communities were phylogenetically random, although some communities presented phylogenetic clustering (partial agreement with H3). We observed phylogenetic overdispersion near the Andes (agreement with H4). We were able to identify how differences in lineage composition are related to local phylogenetic co‐occurrences across biogeographical regions that have been undergoing different climatic and orographic histories during the past 100 Myr. We observed imprints of the history following Gondwana breakup on phylobetadiversity and local phylogenetic structure of rainforest tree communities in the Neotropics, Afrotropics and Madagascar.

Interactions between terrestrial mammals and the fruits of two neotropical rainforest tree species

Mammalian frugivory is a distinctive biotic interaction of tropical forests; however, most efforts in the Neotropics have focused on cases of animals foraging in the forest canopy, in particular primates and bats. In contrast much less is known about this interaction when it involves fruits deposited on the forest floor and terrestrial mammals. We conducted a camera-trapping survey to analyze the characteristics of the mammalian ensembles visiting fruits of Licania platypus and Pouteria sapota deposited on the forest floor in a well preserved tropical rainforest of Mexico. Both tree species produce large fruits but contrast in their population densities and fruit chemical composition. In particular, we expected that more species of terrestrial mammals would consume P. sapota fruits due to its higher pulp:seed ratio, lower availability and greater carbohydrate content. We monitored fruits at the base of 13 trees (P. sapota, n = 4 and L. platypus, n = 9) using camera-traps. We recorded 13 mammal species from which we had evidence of 8 consuming or removing fruits. These eight species accounted for 70% of the species of mammalian frugivores active in the forest floor of our study area. The ensemble of frugivores associated with L. platypus (6 spp.) was a subset of that associated with P. sapota (8 spp). Large body-sized species such as Tapirus bairdii, Pecari tajacu and Cuniculus paca were the mammals more frequently interacting with fruits of the focal species. Our results further our understanding of the characteristics of the interaction between terrestrial mammalian frugivores and large-sized fruits, helping to gain a more balanced view of its importance across different tropical forests and providing a baseline to compare against defaunated forests.

Ecological distribution of leaf stomata and trichomes among tree species in a Malaysian lowland tropical rain forest.

The vertical structure of a tropical rain forest is complex and multilayered, with strong variation of micro-environment with height up to the canopy. We investigated the relation between morphological traits of leaf surfaces and tree ecological characteristics in a Malaysian tropical rain forest. The shapes and densities of stomata and trichomes on the abaxial leaf surfaces and their relation with leaf characteristics such as leaf area and leaf mass per area (LMA) were studied in 136 tree species in 35 families with different growth forms in the tropical moist forest. Leaf physiological properties were also measured in 50 canopy and emergent species. Most tree species had flat type (40.4%) or mound type (39.7%) stomata. In addition, 84 species (61.76%) in 22 families had trichomes, including those with glandular (17.65%) and non-glandular trichomes (44.11%). Most leaf characteristics significantly varied among the growth form types: species in canopy and emergent layers and canopy gap conditions had higher stomatal density, stomatal pore index (SPI), trichome density and LMA than species in understory and subcanopy layers, though the relation of phylogenetically independent contrasts to each characteristic was not statistically significant, except for leaf stomatal density, SPI and LMA. Intrinsic water use efficiency in canopy and emergent tree species with higher trichome densities was greater than in species with lower trichome densities. These results suggest that tree species in tropical rain forests adapt to a spatial difference in their growth forms, which are considerably affected by phylogenetic context, by having different stomatal and trichome shapes and/or densities.

Origin and history of the Dahomey Gap separating West and Central African rain forests: insights from the phylogeography of the legume tree Distemonanthus benthamianus

AbstractAimThe aim of this study was to understand the origin of the forest flora currently found in the Dahomey Gap (DG), a 200‐km‐wide forest‐savanna mosaic separating the West African and Central African rain forest blocks. More specifically, using a widespread rain forest tree species, Distemonanthus benthamianus (Fabaceae), we will test the hypothesis that the DG populations are remnants of a population dating back from the African Humid Period of the Holocene, when West African and Central African rain forests were supposedly connected.LocationTropical forests of Upper Guinea (West Africa) and Lower Guinea (Atlantic Central Africa) and the forest‐savanna mosaic of the DG extending from eastern Ghana to Benin.MethodsFour hundred and twenty‐nine D. benthamianus samples from West to Central Africa were genotyped with 11 nuclear microsatellite markers. After detecting geographically coherent gene pools, their genetic diversity and differentiation were estimated and their demographic histories were inferred using coalescent simulations and approximate Bayesian computation (ABC) tests.ResultsFive parapatric gene pools were identified: three in Lower Guinea, one in Upper Guinea and one in the DG. ABC tests indicate that the DG gene pool probably originates from the admixture of adjacent Upper and Lower Guinean gene pools, with a higher contribution from Upper Guinea, at a timeframe consistent with the early Holocene (around 13–7 ka). The lower genetic diversity documented in the DG could result from a founder effect and/or from a demographic decline consistent with the Holocene climatic pejoration documented around 3 ka.Main conclusionsThis phylogeographical study inferring the history of the DG populations of D. benthamianus is consistent with palaeovegetation data that suggest that the forest flora of the DG might be essentially relicts of the early Holocene period when the Guineo‐Congolian forest reached its maximum geographical distribution.

Tree traits and canopy closure data from an experiment with 34 planted species native to Sabah, Borneo.

The data presented in this paper is supporting the research article “Life history traits predict the response to increased light among 33 tropical rainforest tree species” [3]. We show basic growth and survival data collected over the 6 years duration of the experiment, as well as data from traits inventories covering 12 tree traits collected prior to and after a canopy reduction treatment in 2013. Further, we also include canopy closure and forest light environment data from measurements with hemispherical photographs before and after the treatment.

Life history traits predict the response to increased light among 33 tropical rainforest tree species

Rainforest restoration is an important application in today’s multipurpose management of secondary forest. However, our knowledge of tree species’ traits and responses to treatment is insufficient for foresters to make good decisions for sustainable management. The aim of our study was to see whether it is possible to predict tree species’ responses to increased light based on species’ traits, and to relate these responses to a possible pioneer–climax continuum of life history traits, also among species with presumed climax properties. We examined 33 taxa (including 19 from the dipterocarp family) replicated 20 times and randomly planted in lines over a 3ha area in the interior of Sabah, Borneo. Four years after establishment we performed a canopy reduction treatment to increase the light conditions up to levels present in tree gaps in the forest. We created a PLS (Partial Least Square Regressions) model with the two predicted variables HGR (height growth response) and Q3 HGR (the 75 percentile of a species’ HGR, interpreted as the potential HGR). The model captured 47% of the variation for the predicted variables. We found significant tree species’ responses in height growth to the increased light. High specific leaf area, strong early height growth, high foliar N content, high leaved stem length and large crown were linked to fast growth, while high wood density and high foliar K content were associated with slow growth. We also found a trade-off between growth response and survival among the species. We conclude that climax tree species have specific life history adaptations along a pioneer–climax continuum, which can be predicted from species’ traits. The importance of easily observed or extracted traits such as initial growth rate, specific leaf area and wood density for predicting growth suggests the possibility of fast screening of species with unknown characteristics, which could be of great value in practical forest management.

Performance of Seedlings of a Shade-Tolerant Tropical Tree Species after Moderate Addition of N and P

Nitrogen deposition to tropical forests is predicted to increase in future in many regions due to agricultural intensification. We conducted a seedling transplantation experiment in a tropical premontane forest in Ecuador with a locally abundant late-successional tree species (Pouteria torta, Sapotaceae) aimed at detecting species-specific responses to moderate N and P addition and to understand how increasing nutrient availability will affect regeneration. From locally collected seeds, 320 seedlings were produced and transplanted to the plots of the Ecuadorian Nutrient Manipulation Experiment (NUMEX) with three treatments (moderate N addition: 50 kg N ha-1 yr-1, moderate P addition: 10 kg P ha-1 yr-1 and combined N and P addition) and a control (80 plants per treatment). After 12 months, mortality, relative growth rate, leaf nutrient content and leaf herbivory rate were measured. N and NP addition significantly increased the mortality rate (70 % vs. 54 % in the control). However, N and P addition also increased the diameter growth rate of the surviving seedlings. N and P addition did not alter foliar nutrient concentrations and leaf N:P ratio, but N addition decreased the leaf C:N ratio and increased SLA. P addition (but not N addition) resulted in higher leaf area loss to herbivore consumption and also shifted carbon allocation to root growth. This fertilization experiment with a common rainforest tree species conducted in old-growth forest shows that already moderate doses of added N and P are affecting seedling performance which most likely will have consequences for the competitive strength in the understory and the recruitment success of P. torta. Simultaneous increases in growth, herbivory and mortality rates make it difficult to assess the species’ overall performance and predict how a future increase in nutrient deposition will alter the abundance of this species in the Andean tropical montane forests.

Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia

The invasive rust Puccinia psidii (myrtle rust) was detected in Australia in 2010 and is now established along the east coast from southern New South Wales to far north Queensland. Prior to reaching Australia, severe damage from P. psidii was mainly restricted to exotic eucalypt plantations in South America, guava plantations in Brazil, allspice plantations in Jamaica, and exotic Myrtaceous tree species in the USA; the only previous record of widespread damage in native environments is of endangered Eugenia koolauensis in Hawai’i. Using two rainforest tree species as indicators of the impact of P. psidii, we report for the first time severe damage to endemic Myrtaceae in native forests in Australia, after only 4 years’ exposure to P. psidii. A 3-year disease exclusion trial in a natural stand of Rhodamnia rubescens unequivocally showed that repeated, severe infection leads to gradual crown loss and ultimately tree mortality; trees were killed in less than 4 years. Significant (p < 0.001) correlations were found between both incidence (r = 0.36) and severity (r = 0.38) of P. psidii and subsequent crown loss (crown transparency). This provided supporting evidence to conclude a causal association between P. psidii and crown loss and tree mortality in our field assessments of R. rubescens and Rhodomyrtus psidioides across their native range. Assessments revealed high levels of damage by P. psidii to immature leaves, shoots and tree crowns—averaging 76 % (R. rubescens) and 95 % (R. psidioides) crown transparency—as well as tree mortality. For R. psidioides, we saw exceptionally high levels of tree mortality, with over half the trees surveyed dead and 40 % of stands with greater than 50 % tree mortality, including two stands where all trees were dead. Tree mortality was less prevalent for R. rubescens, with only 12 % of trees surveyed dead and two sites with greater than 50 % mortality. Any alternative causal agents for this tree mortality have been discounted. The ecological implications of this are unclear, but our work clearly illustrates the potential for P. psidii to negatively affect Australia’s biodiversity.