Tropical Rain Forest Species Research Articles

Leaf warming in the canopy of mature tropical trees reduced photosynthesis due to downregulation of photosynthetic capacity and reduced stomatal conductance.

Tropical forests play a large role in the global carbon cycle by annually absorbing 30% of our annual carbon emissions. However, these forests have evolved under relatively stable temperature conditions and may be sensitive to current climate warming. Few experiments have investigated the effects of warming on large, mature trees to better understand how higher temperatures affect these forests in situ. We targeted four tree species (Endiandra microneura, Castanospermum australe, Cleistanthus myrianthus and Myristica globosa) of the Australian tropical rainforest and warmed leaves in the canopy by 4°C for 8 months. We measured temperature response curves of photosynthesis and respiration, and determined the critical temperatures for chloroplast function based on Chl fluorescence. Both stomatal conductance and photosynthesis were strongly reduced by 48 and 35%, respectively, with warming. While reduced stomatal conductance was likely in response to higher vapour pressure deficit, the biochemistry of photosynthesis responded to higher temperatures via reduced Vcmax25 (-28%) and Jmax25 (-29%). There was no shift of the Topt of photosynthesis. Concurrently, respiration rates at a common temperature did not change in response to warming, suggesting limited respiratory thermal acclimation. This combination of physiological responses to leaf warming in mature tropical trees may suggest a reduced carbon sink with future warming in tropical forests.

Growing-Season Precipitation Is a Key Driver of Plant Leaf Area to Sapwood Area Ratio at the Global Scale.

Leaf area to sapwood area ratio (AL/AS) influences carbon sequestration, community composition, and ecosystem functioning in terrestrial vegetation and is closely related to leaf economics and hydraulics. However, critical predictors of AL/AS are not well understood. We compiled an AL/AS data set with 1612 species-site combinations (1137 species from 285 sites worldwide) from our field experiments and published literature. We found the global mean AL/AS to be 0.63 m2 cm-2, with its variation largely driven by growing-season precipitation (Pgs), which accounted for 18% of the variation in AL/AS. Species in tropical rainforests exhibited the highest AL/AS (0.82 m2 cm-2), whereas desert species showed the lowest AL/AS (0.16 m2 cm-2). Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on AL/AS, whereas soil pH was negatively correlated with AL/AS. Tree density accounted for 7% of the variation in AL/AS. All biotic and abiotic predictors collectively explained up to 45% of the variation in AL/AS. Additionally, AL/AS was positively correlated to the net primary productivity (NPP) of the ecosystem. Our study provides insights into the driving factors of AL/AS at the global scale and highlights the importance of AL/AS in ecosystem productivity. Given that Pgs is the most critical driver of AL/AS, alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches.

No evidence of carbon storage usage for seed production in 18 dipterocarp masting species in a tropical rain forest.

Most canopy species in lowland tropical rain forests in Southeast Asia, represented by Dipterocarpaceae, undergo mast reproduction synchronously at community level during a general flowering event. Such events occur at irregular intervals of 2-10years. Some species do not necessarily participate in every synchronous mast reproduction, however. This may be due to a lack of carbohydrate resources in the trees for masting. We tested the hypothesis that interspecific differences in the time required to store assimilates in trees for seed production are due to the frequency of masting and/or seed size in each species. We examined the relationship between reproductive frequency and the carbon accumulation period necessary for seed production, and between the seed size and the period, using radiocarbon analysis in 18 dipterocarp canopy species. The mean carbon accumulation period was 0.84years before seed maturation in all species studied. The carbon accumulation period did not have any significant correlation with reproductive frequency or seed size, both of which varied widely across the species studied. Our results show that for seed production, dipterocarp masting species do not use carbon assimilates stored for a period between the masting years, but instead use recent photosynthates produced primarily in a masting year, regardless of the masting interval or seed size of each species. These findings suggest that storage of carbohydrate resources is not a limiting factor in the masting of dipterocarps, and that accumulation and allocation of other resources is important as a precondition for participation in general flowering.

Variation of floristic diversity, community composition, endemism, and conservation status of tree species in tropical rainforests of Sri Lanka across a wide altitudinal gradient

Tropical rainforests in Sri Lanka are biodiversity hotspots, which are sensitive to anthropogenic disturbance and long-term climate change. We assessed the diversity, endemism and conservation status of these rainforests across a wide altitudinal range (100–2200 m above sea level) via a complete census of all trees having ≥ 10 cm diameter at breast height in ten one-hectare permanent sampling plots. The numbers of tree families, genera and species and community-scale tree diversity decreased with increasing altitude. Tree diversity, species richness and total basal area per ha across the altitudinal range were positively associated with long-term means of maximum temperature, annual rainfall and solar irradiance. Percentage of endangered species increased with increasing altitude and was positively associated with cumulative maximum soil water deficit, day-night temperature difference and high anthropogenic disturbance. Percentage of endemic species was greater in the lowland rainforests than in high-altitude montane forests. Nearly 85% of the species were recorded in three or less plots, which indicated substantial altitudinal differentiation in their distributions. Less than 10 individuals were recorded in 41% of the endemic species and 45% of the native species, which underlined the need for urgent conservation efforts across the whole altitudinal range.

Occurrence of Volatile Organic Compounds and Extrafloral Nectaries in Tropical Rainforest Species in Danum Valley Conservation Area, Sabah, Malaysia

Plants synthesize numerous classes of secondary metabolites that are crucial in plant defense. Two of the common but non-ubiquitous defenses are the emission of volatile organic compounds (VOCs) and production of extrafloral nectaries (EFN). This study investigates the occurrence of emission of VOC and production of EFN in forest species in Danum Valley Conservation Area, Sabah, Malaysia. From the 165 species screened, 131 species were found to emit VOC while 41 species were EFN-bearing plants. There are 34 species that are both emitting VOC and producing EFN, while 97 species were found to be emitting VOC with no EFN observed. On the other hand, there are 7 species that were EFN bearing but non-VOC emitter, while 27 species were neither emitting VOC nor producing EFN. All 12 dipterocarp species were observed to emit VOC, of these 3 are non-EFN bearing. VOC emissions were further classified into isoprene (C5) and monoterpene (C10) compounds. There are 46 species that were detected to emit both isoprene and monoterpenes, while there are more exclusive monoterpene emitters (62 species) than isoprene-only emitters (23 species). This study showcased the ability of plants to produce a wide array of secondary metabolites as plant defense making them successfully adapt to the complexities of tropical rainforest ecosystem.

ASPECTS OF SEEDLING PRODUCTION OF Clathrotropis brunnea Amshoff, A THREATENED LEGUME TREE FROM COLOMBIAN RAINFORESTS

Seedling production is crucial to assist restoration and conservation practices of tropical rainforest species. In the present study, we evaluated seedling production of Clathrotropis brunnea Amshoff, a legume tree native to tropical forests of Colombia. Seedling emergence parameters were assessed regarding two classes of seed mass (small seeds < 6.0 g and large seeds > 6.1 g) and tree levels of seed moisture content (control, 30% and 25%). Initial growth was evaluated in two sizes of plastic bags (small: 10 cm diameter x 25 cm height, with a volume of 1,700 cm3, and large: 15 cm x 35 cm and volume of 3,900 cm3), besides tree growth periods in the nursery (170, 205 and 235 days after sowing – DAS). Large seeds provided higher seedlings and reached a greater emergence percentage (93%) compared to the small ones (79%). On average, seeds reached 73% of emergence in the three moisture levels, including when desiccated from 47% in the control (fresh seeds) to 25%. To optimize seedling production and costs, large seeds can be sown in small bags, growing for a minimum of 205 DAS. The in-field performance of the produced seedlings remains to be tested according to these recommendations.

Army ant middens - Home and nursery of a diverse beetle fauna.

Army ants provide nourishment to a large variety of animals. This includes birds that feed on animals flushed out by army ant raids, symbiotic arthropods that consume the ants' prey or their brood, and other arthropods that scavenge on army ant refuse deposits. The latter have not received much attention, and the few published studies lack detailed species identifications. Here we provide a first systematic inventory of the beetle fauna associated with refuse deposits of Eciton army ants, with a focus on Eciton burchellii. We collected 8364 adult beetles, 511 larvae, and 24 eggs from 34 deposits at La Selva Biological Station, Costa Rica. We used a combination of DNA barcoding and morphology to identify a subset of 436 specimens to species level. The samples included several new species, and we here formally describe two water scavenger beetles (Hydrophilidae). Refuse deposits harbored a diverse beetle fauna. The identified subset consisted of 91 beetle species from 12 families, with rove beetles being the most abundant and diverse visitors. Of the 85 species found with E. burchellii, 50 species were collected from only one or two refuse deposits. Conversely, seven species were found in 10 or more refuse deposits, indicating a certain level of habitat specialization. We matched adults and immatures for 22 beetle species via DNA barcodes, demonstrating that army ant middens also serve as a beetle nursery. The present survey highlights the significant ecological function of army ants as promoters of biodiversity and their status as keystone species in tropical rainforests.

Seedling growth and photosynthetic response of Pterocarpus indicus L. to shading stress

ABSTRACT In tropical forests, the shade provided by tree canopies and extreme climate causes inhibition of plant seedling growth due to the lack of light. However, the plants can acclimate to such environmental stress by generating specific responses. The present study aimed to investigate the effects of shading conditions on ecophysiological performance of Narra seedlings (Pterocarpus indicus L.) via a mesocosm experiment. A pot experiment was conducted for 20 weeks in a greenhouse with different shading treatments, 75% (control), 25%, and 4% of full sunlight (FS). As a result, the photosynthetic rate (P N), Rubisco enzyme activity, maximum carboxylation rate (V Cmax), and maximum electron transport rate (J max) in 25% FS treatment were higher or similar to those in control after three weeks of the beginning of shade treatment, whereas the highest values after ten weeks were observed in control. In contrast, the photosynthetic pigments were highest in control after three weeks, while the values were highest in 25% FS treatment after ten weeks. The growth parameters, such as biomass and leaf area, were highest in 75% FS treatment. The expression of Rubisco, phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and fructose-1,6-bisphosphatase were up-regulated in 4% FS treatment compared to control after ten weeks, contributing to tolerating the shade stress. Our findings indicated the capacity of P. indicus seedlings to tolerate and acclimate low light conditions causing shade stress by generating specific physiological and morphological responses, especially Rubisco enzyme activity as well as gene expression related to photosynthetic activity. The present study will improve our understanding of the tolerance mechanism of Narra plant under light-deficient conditions, thereby providing a better strategy for efficiently growing seedlings of this species in tropical rainforests.

Nitrogen-Fixing Plants Enhance and Stabilize Rhizospheric Soil Organic Carbon in Tropical Rainforests, Hainan Island, China

Abstract Nitrogen (N)-fixing plants play an important role in stimulating soil nitrogen supply, but the effect of N-fixing plants on soil organic carbon (SOC) sequestration has not been well documented. In this study, we measured rhizospheric carbon components and N content of first to second (1–2)-order and third to fifth (3–5)-order roots of N-fixing and non-N-fixing plants in a montane tropical rainforest in Hainan Island, China, to examine the effects of N-fixing plants on SOC and soil heavy fraction carbon (HFC), and to ascertain the main regulating factors. The results showed that rhizospheric SOC between (1–2) and (3–5)-order roots was 14.2% and 10.5% greater, respectively, for N-fixing plants compared with non-N-fixing plants. Similarly, the HFC was 0.9% (1–2) and 3.6% (3–5) greater for N-fixing plants than non-N-fixing plants. Redundancy analysis showed that spatial variance in rhizospheric SOC and HFC associated with 1–2-order roots was explained by specific root length (SRL) of second-order roots (55.8%) and specific leaf area (SLA) (14.6%), whereas spatial variance was better explained for 3–5 roots by total soil N (44.6%), diameter of fifth-order roots (16.4%), and leaf C (17.9%), respectively. Within the rhizospheric soil of 1–2 roots, N-fixing plants with smaller SRL of second-order roots presented greater SOC and HFC, whereas smaller SLA was associated with greater HFC. By contrast, rhizospheric soil of 3–5 roots under N-fixing plants had greater SOC and HFC levels in environments with higher total soil N and smaller diameters of fifth-order roots. Our study revealed that N-fixing plants enhanced rhizospheric SOC and HFC compared with non-N-fixing plants. The rhizospheric SOC and HFC were correlated strongly by root morphology traits, leaf morphology, and soil properties. Study Implications: In this article, we compared rhizospheric soil of N-fixing and non-N-fixing species in a montane tropical rainforest in Hainan Island, China, to examine the effects of N-fixing plants on SOC and HFC. Our results suggest the N-fixing plants enhance and stabilize rhizospheric SOC and HFC; rhizospheric SOC and HFC for first- to second-order roots of N-fixing plants were mostly negatively regulated by SRL of second-order roots; and N-fixing plants had positive effects on rhizospheric SOC and HFC for third- to fifth-order roots through increased soil N. Understanding these mechanisms could improve and accumulation of soil C sink in tropical areas.

Comparison of Fecal Antimicrobial Resistance Genes in Captive and Wild Asian Elephants.

The Asian elephant (Elephas maximus) is a flagship species of tropical rainforests, and it has generated much concern. In this case, the gut bacterial communities of captive and wild Asian elephants are particularly noteworthy. We aim to compare the differences in bacterial diversity and antibiotic resistance gene (ARG) subtypes in fecal samples of Asian elephants from different habitats, which may affect host health. Analyses reveal that differences in the dominant species of gut bacteria between captive and wild Asian elephants may result in significant differences in ARGs. Network analysis of bacterial communities in captive Asian elephants has identified potentially pathogenic species. Many negative correlations in network analysis suggest that different food sources may lead to differences in bacterial communities and ARGs. Results also indicate that the ARG levels in local captive breeding of Asian elephants are close to those of the wild type. However, we found that local captive elephants carry fewer ARG types than their wild counterparts. This study reveals the profile and relationship between bacterial communities and ARGs in different sources of Asian elephant feces, providing primary data for captive breeding and rescuing wild Asian elephants.

Trait based niche differentiation in tetrakas (Bernieridae) endemic to Madagascar: A multi-isotope approach

Introduction Tropical rainforest species interact with each other and their environment over a wide range of spatiotemporal scales. However, our understanding of resource partitioning and the mechanisms of avian species coexistence is largely restricted to subjective visual observations or acoustic monitoring. Therefore, the relative magnitudes of interspecific and intraspecific differences in resource use have remained difficult to quantify, particularly regarding different diets and habitat use. The eastern rainforest belt of Madagascar is inhabited by several species of insectivorous tetrakas belonging to an endemic bird family of Madagascar (Bernieridae). These species occupy similar habitats in the forest understory and are morphologically similar but because of likely differences (e.g., in foraging behaviors) we expect their foraging niches to be segregated allowing coexistence. Methods We examined the niche differentiation of four of these species: the Grey-crowned Tetraka ( Xanthomixis cinereiceps ), Long-billed Tetraka ( Bernieria madagascariensis ), Spectacled Tetraka ( Xanthomixis zosterops ), and White-throated Oxylabes ( Oxylabes madagascariensis ) in the Maromizaha rainforest in eastern Madagascar combining morphometry with stable carbon, nitrogen, and sulfur isotope ratios (δ 13 C, δ 15 N, and δ 34 S) from feathers. Results We show considerable variation in isotopic niche positions, niche breadth and interspecific niche overlap. In two species, the Long-billed Tetraka and Spectacled Tetraka, we found an indication of sex-specific niche space, with males exhibiting a larger isotopic niche-area relative to females. Morphological traits of five species (including the Wedge-tailed Tetraka, Hartertula flavoviridis ) coupled with stable isotope data provided explanations of patterns of niche overlap and isotopic position. Discussion The observed isotopic niche differences may be explained by differences in resource acquisition strategies that might be associated with specific morphological traits and spatial distribution. This may play an important role in niche differentiation among coexisting and phylogenetically closely related species.

Large leaf hydraulic safety margins limit the risk of drought‐induced leaf hydraulic dysfunction in Neotropical rainforest canopy tree species

Abstract The sequence of key water potential thresholds from the onset of water stress to mortality, and the timing of stomatal closure with regard to leaf xylem embolism formation are essential to characterizing plant adaptive strategies to drought. This constitutes a critical knowledge gap for tropical rainforest species, which may be less vulnerable to drought than previously thought. We recorded key leaf and stem water potential thresholds, leaf hydraulic safety margins (HSMleaf), leaf stomatal safety margins (SSMleaf) and estimated native embolism levels during a normal‐intensity dry season across 18 neotropical rainforest tree species. We also solved a sequence of key water potential thresholds. Additionally, we provide a cross‐biome analysis of SSMleaf encompassing 97 species from four major biomes based on a literature survey. In the studied rainforest species, leaf turgor loss point, used as a surrogate for stomatal closure, typically occurred before the onset of leaf xylem embolism. Most species exhibited positive HSMleaf and SSMleaf, with contrasting values across species and nearly absent embolism levels during the dry season irrespective of the experienced midday leaf water potentials. Our results point out that leaf xylem embolism is not routine for Neotropical rainforest tree species. Based on our proposal of the water potential sequence for tropical rainforest trees, we argue that leaf xylem embolism is a rare event for these species. This was supported by the literature survey, indicating that across biomes, most woody species have rather large SSMleaf and that leaves of tropical rainforest trees are not necessarily more vulnerable than in other biomes. However, we found evidence that some tropical rainforest species may be more vulnerable than others to ongoing climate change. Our data provide an opportunity to parametrize tree‐based or land‐surface models for tropical rainforests. Read the free Plain Language Summary for this article on the Journal blog.

Seasonal Patterns and Species Variability in the Leaf Traits of Dominant Plants in the Tropical Rainforests of Hainan Island, China

The leaf traits measured in multiple species are known to vary between seasons, but there is a knowledge gap relating to the seasonal variability and environmental adaptation of plants in tropical rainforests. To investigate the dynamics of the functional traits of dominant species in tropical rainforests and the differences in their adaptation strategies to seasonal drought, the results of this study can provide a scientific basis for tropical rainforest conservation resource protection. Six dominant species, including three trees (Hopea reticulata, Vatica mangachapoi, and Diospyros chunii) and three vine plants (Ancistrocladus tectorius, Phanera khasiana, and Uvaria sanyaensis), in tropical lowland rainforest in the Ganzaling Nature Reserve of Hainan province were selected as study objectives. The key leaf traits were studied using the paraffin section method, leaf epidermis segregation method, and Li-6400 portable photosynthesis system in June, September, December, 2019, and March, 2020. Results showed that significant differences in photosynthetic physiology and morphological and structural parameters among species, as well as seasonal variability, were observed in leaf photosynthetic physiology, but not in leaf morphological or structural parameters. A phenotypic plasticity index (PPI) analysis revealed more variability in leaf photosynthetic physiology (Average PPI = 0.37) than in leaf anatomical structure and morphology (Average PPI = 0.26), suggesting that they adapt to seasonal changes primarily by regulating photosynthetic physiological parameters rather than leaf morphology or anatomical structure. The dominant trees were found to have higher water use efficiency, leaf dry-matter content, and smaller leaf areas compared to vine plants. This indicates that the dominant tree species depend on high water use efficiency and leaf morphological characteristics to adapt to seasonal changes. The majority of leaf anatomical structure parameters associated with drought tolerance were higher in the three dominant vine species, indicating that the dominant vine species adapted to drought stress primarily by altering the leaf anatomical structure This study provides information on how tropical rainforest plants adapt to seasonal drought as well as supporting the protection of tropical rainforest ecosystems.

Relationship between the Floristic Composition and Soil Characteristics of a Tropical Rainforest (TRF)

Hutan Rimba Alam (HRA), Putrajaya is an urban forest which is the habitat for various tropical rainforest species. A field survey was undertaken to state the floristic composition, investigate the soil characteristics and identify the relationship between the recorded plant communities and soil characteristics. Six plots sized 10 × 10 m square were established in a lowland area of which 93 individual trees were identified. Moreover, the floristic composition revealed vascular tree communities consisting of 10 botanical families, 15 genera, and 27 species with Dipterocarpaceae as being predominant. Based on the important value index (IVI), Mangifera odorata (Anacardiaceae) was the highest (IVI = 68.80%). Furthermore, large trees such as Koompassia excelsa (Becc.) Taub. (Fabaceae) and Sandoricum koetjape (Burm.f.) Merr. (Meliaceae), with heights ranging from 17 m to 24 m, indicated that HRA is on the way to becoming a mature forest. The soil pH in all plots showed acidic properties, with a mean pH of 4.69 that is considered normal for tropical rainforests. The pH of the soils in HRA, Putrajaya had a positive correlation with the CEC and with nitrogen, but the value was low; however, the correlation was negative with C and P. The CEC had a relatively low correlation with C, N and P. Carbon had a very high correlation with N but low with P. Meanwhile, nitrogen had a very negatively low correlation with P. Extractable phosphorus exhibited a mean of 2.22 mg/kg which is normally used in plants for fruits, roots, and flower development. The present study revealed that plant communities in the urban forest in Putrajaya, meaning the diversity of the plant species belonging to a wide range of families, were established on acid soil, matching with the overall characteristics of tropical forest soils. With regard to the climate change context, which is leading to many altered ecosystems, the authors expect that the outputs of this research will be valued by decision makers for a better management of the forest.

Effects of ENSO events on the intensity, seasonality, and diversity of reproductive phenology of Miconia (Melastomataceae) species in tropical rainforest.

We evaluated the phenology and reproductive phenological diversity of three sympatric species of Miconia in a gallery forest in the Chapada Diamantina mountains, Bahia, Brazil. The reproductive phenophases (bud, flower, immature fruit, and mature fruit) of M. alborufescens (N=38), M. holosericea (N=46), and M. prasina (N=44) were evaluated monthly, between June/2008 and June/2015. The Fournier index was used to assess the intensities of the reproductive phenophases; synchrony and seasonality were analyzed using circular statistics and the Rayleigh (Z) test. The Frideman and Wilcoxon tests were used to verify interannual variations in phenological patterns. Reproductive phenological diversity was measured by calculating the Shannon-Wiener index; ANOVA tested possible differences in the means of diversity among the different years. The reproductive phenophases of the studied Miconia species occurred sequentially (M. alborufescens, then M. holoserica, followed by M. prasina), in the transition between the dry and rainy seasons, with little overlap between them. In general, the species showed seasonal and synchronic phenological patterns, with some variations that coincided with El Niño and/or La Niña events, e.g., demonstrating changes in the periodicity, synchrony, and intensity of their phenophases. The intensity of fruiting, for example, showed increases during La Niña years. Reproductive phenological diversity appears to respond to climate changes resulting from El Niño events and periods of prolonged drought, with high Shannon-Wiener index values. The results also suggest that the effects of global climatic phenomena (El Niño and La Niña) that alter regional climatic seasonality can also cause variations in the reproductive phenological rhythms of the Miconia species studied.

Growth form and functional traits influence the shoot flammability of tropical rainforest species

Canopy fires are increasing globally with anthropogenic climate and land-use changes, even in fire-sensitive rainforest ecosystems. Identifying the ecological drivers that may be aiding canopy fires, such as species or growth form flammability, is crucial to recognising and mitigating fire risks. To address this, we quantified the shoot-flammability of 124 rainforest plant species using an experimental approach. We compared three flammability measures (burnt biomass, total burn time and maximum temperature reached) with plant functional traits across seven different growth forms (i.e., canopy, pioneer, and understory trees; pioneer, understory and invasive shrubs, and vines) and nine common plant families and other higher-level clades, such as conifers, hereafter abbreviated to families. From burning > 600 sun-exposed shoots, we found trees were higher in flammability than shrubs and vines, and the plant families: Sapindaceae, Proteaceae, Fabaceae, and Lauraceae, had especially high flammability, whereas Moraceae was very low. Of the functional traits examined, leaf dry matter content was consistently and significantly positively associated with species flammability. Invasive shrubs as a group were not particularly flammable, although there were exceptions, e.g., wild tobacco (Solanum mauritianum) was highly flammable. This study has two important implications for the management of fire in rainforests. First, we have demonstrated that many tropical rainforest trees may readily burn under severe fire conditions if fire were to reach the rainforest canopy. Second, a large proportion of the > 1 million rainforest trees planted in the Wet Tropics under restoration planting schemes are from our most flammable rainforest plant families, as these families are often recommended for their carbon sequestration potential. Hence, these plantings may be highly vulnerable to fire and if planted along the borders of primary forest they may carry fire into their canopies. Therefore, where fire risk is high, we recommend planting species with low flammability along borders of plantings and forests to act as ‘green firebreaks’ to reduce the risk of fire incursions.

Floristic composition, growth temperament and conservation status of woody plant species in the Cameroonian tropical rainforests

IntroductionCameroon’s tropical rainforests are nowadays strewn with rural forests maintained by local populations; however, these forests are not officially recognized in the non-permanent forest domain. Rural forests are non-delimited riparian areas within the dense moist forest, reserved for rural housing, agricultural activities and agroforestry practices, freely exploited by the local communities for their livelihood without them having any rights to artisanal and commercial logging. This study aimed at contributing to the flora knowledge and the conservation state of woody plant species in rainforests. The study was carried out in two rural forests located in the Eastern and Southern agroforestry zones of Cameroon.MethodsThe method adopted for floristic inventories combined a fixed area sampling unit and a variable area sampling unit. Woody individuals with diameter at breast height (dbh) < 3.2 cm were counted and shrubs of 3.2 ≤ dbh < 10 cm were measured to analyse the understorey, while trees with dbh ≥ 10 cm were measured and identified to characterize the canopy.ResultsIn the Essiengbot-Mbankoho rural forest in Eastern Cameroon, 468 species belonging to 61 families were recorded in the understory while 227 species belonging to 53 families were identified at the canopy level. A total of 40 (7.68%) threatened species, 18 (3.45%) Near Threatened species and 408 (78.31%) Least Concern species were recorded. In the Nbgwassa-Opkweng rural forest in Southern Cameroon, 534 species belonging to 64 families were identified in the understory while 225 species belonging to 43 families were recorded in the canopy. A total of 54 (9.69%) threatened species, 25 (4.49%) Near Threatened species and 421 (75.58%) Least Concern species were identified in this forest. Shannon’s diversity indices were above five in the understories and canopies of both forests. Shade-bearer species were the most represented in the understories while the non-pioneer light-demanding and shade-bearer species were the most abundant in the canopies.ConclusionsDespite the influence of slash-and-burn agriculture and subsistence farming practices, rural forests managed by local populations provide opportunities for preserving plant biodiversity. However, the presence of threatened species, pioneer species and non-pioneer light-demanding species in these forests is an indicator of moderate and man-induced disturbances that, in the absence of a forest management plan or sustainable management, may threaten this biodiversity. Legal management of rural forests could help in limiting the anthropogenic activities and pressures on community forests.

Tree height effects on vascular anatomy of upper-canopy twigs across a wide range of tropical rainforest species

AbstractVessel diameter variation along the hydraulic pathway determines how much water can be moved against the force of gravity from roots to leaves. While it is well-documented that tree size scales with vessel diameter variation at the stem base due to the effect of basipetal vessel widening, much less is known whether this likewise applies to terminal sun-exposed twigs. To analyze the effect of tree height on twig xylem anatomy, we compiled data for 279 tropical rainforest tree species belonging to 56 families in the lowlands of Jambi Province, Indonesia. Terminal upper-canopy twigs of fully grown individuals were collected and used for wood anatomical analysis.We show that hydraulically weighted vessel diameter (Dh) and potential hydraulic conductivity (Kp) of upper canopy twigs increase with tree height across species although the relationship was weak. When averaged across given tree height classes irrespectively of species identity, however, a strong dependency of tree height on Dh and Kp was observed, but not on the lumen-to-sapwood area ratio (Al:Ax) or vessel density (VD).According to the comparison between actual tree height and the maximum tree height reported for a given species in the stand, we show that the vascular xylem anatomy of their terminal twigs reflects their canopy position and thus ecological niche (understory versus overstory) at maturity. We conclude that the capacity to move large quantities of water during the diurnal peak in evaporative demand is a prerequisite for growing tall in a humid tropical environment.

Numerical Modelling and Optimization of Bioethanol Concentration Produced from Local Sawdust following Response Surface Methodology

This work studies the modelling and optimization of bioethanol production from locally sourced saw dust waste. The saw dust samples are obtained from common wood species in the Nigerian tropical rain forest. Nigeria is one of the producers of wooden products in the world. Many species of wood can be found in Nigeria’s tropical rain forest. Some of the most common wood species include; Astonia boonei (duku), Bombax bounopozense (West African bombax), Brachystegia eurycoma (Okwen), Terminalia superba (White afara). Sawdust samples were obtained from a local saw mill in Edo State, Nigeria. The samples were pre-treated, hydrolyzed, fermented and the bioethanol distilled out. Optimization of bioethanol was performed by using Central Composite design of response surface methodology. Four variables such as acid concentration, hydrolyzing time, hydrolysis temperature and fermentation time were considered as influencing factors on the yield of bioethanol. The optimization of ethanol was investigated in this study under the following conditions: acid concentration (0.5-2.5 %w/w), hydrolysis temperature (100-130 °C), hydrolysis time (10-50 minutes) and fermentation time (2-6 days). It was observed from the statistical analysis that the maximum ethanol yield of 24.85 % (g/L) was obtained at optimum acid hydrolysis of acid concentration 2.0 %w/w, Hydrolysis time 40 minutes, Hydrolysis temperature 122.50 °C, and Fermentation time 5 days.

Tropical rainforest species have larger increases in temperature optima with warming than warm-temperate rainforest trees.

Summary While trees can acclimate to warming, there is concern that tropical rainforest species may be less able to acclimate because they have adapted to a relatively stable thermal environment. Here we tested whether the physiological adjustments to warming differed among Australian tropical, subtropical and warm‐temperate rainforest trees.Photosynthesis and respiration temperature responses were quantified in six Australian rainforest seedlings of tropical, subtropical and warm‐temperate climates grown across four growth temperatures in a glasshouse. Temperature‐response models were fitted to identify mechanisms underpinning the response to warming.Tropical and subtropical species had higher temperature optima for photosynthesis (T optA) than temperate species. There was acclimation of T optA to warmer growth temperatures. The rate of acclimation (0.35–0.78°C °C–1) was higher in tropical and subtropical than in warm‐temperate trees and attributed to differences in underlying biochemical parameters, particularly increased temperature optima of V cmax25 and J max25. The temperature sensitivity of respiration (Q 10) was 24% lower in tropical and subtropical compared with warm‐temperate species.Overall, tropical and subtropical species had a similar capacity to acclimate to changes in growth temperature as warm‐temperate species, despite being grown at higher temperatures. Quantifying the physiological acclimation in rainforests can improve accuracy of future climate predictions and assess their potential vulnerability to warming.