Tropical Canopy Tree Research Articles

Water use and mortality risk of four tropical canopy trees with different leaf phenology during the 2016 El Niño drought

The physiological response of plants to water stresses has been a focus in understanding plant-atmosphere feedback. Tropical forests are particularly noteworthy for their remarkable diversity and dynamics. However, a deep understanding of physiological response and associated mortality risk of tropical trees with different leaf phenology under drought is still deficient. In this study, we combined sap flow measurements and a plant hydraulic model to present the water utilization of four canopy trees (two deciduous trees and two evergreen trees) in a Panamanian seasonal tropical forest during the 2016 El Niño drought. The results showed that the transpiration (Td) of deciduous trees rapidly decreased with intensifying soil drought during the dry season, while evergreen trees still maintained high Td and increased with the increase of atmospheric dryness (vapor pressure deficit (VPD)). During the wet season, the Td of both deciduous and evergreen trees was jointly driven by increasing soil moisture (SWC) and reducing VPD. The differential Td pattern during the dry season is closely related to the difference in leaf phenology, with deciduous trees greatly reducing canopy stomatal conductance (Gs) through defoliation, and thereby maintaining leaf water potential (Ψl) and reducing water loss. Additionally, deciduous trees demonstrated a slow increase in the difference between midday (Ψl,md) and predawn (Ψl,pd) leaf water potential (i.e. lower hydraulic sensitivity (σ)) compared to evergreen trees. Evaluation of mortality risk under changing water stresses further indicated that all trees exhibited high hydraulic failure risk (HFR) under decreasing SWC scenarios. Moreover, deciduous trees displayed a much higher stomatal closure risk (SCR) than evergreen trees. These differences in Gs response and σ suggest a key role of the coordination between stomatal regulation and plant hydraulics in mediating physiological response to water stresses. More investigation and mechanism illumination will facilitate the prediction of tropical forest response to drought.

Water uptake patterns of tropical canopy trees in Borneo: species-specific and temporal variation and relationships with aboveground traits

Root water uptake depth and its temporal variation are important determinants of tree mortality, resource partitioning and drought resistance; however, their effects on tropical trees remain poorly understood. In this study, we investigated interspecific differences in water uptake depth and its temporal variation using stable isotope analysis and examined the relationships between water uptake depth and aboveground traits in a humid aseasonal tropical rainforest in Borneo. Species-specific differences in water uptake depth were examined for six dominant dipterocarp species. Temporal variation in water uptake depth for various canopy trees was assessed in three periods with different soil moisture conditions. We then examined the relationships between water uptake depth and aboveground traits including wood density, maximum tree height, flowering frequency and growth rate. Dipterocarpus globosus appeared to be more reliant on deep water resources than the other dipterocarp species. Water uptake from the soil layers varied among the three sampling periods. Trees generally utilized deeper soil water during the second driest sampling period, when temperatures were lowest. During the driest and wettest sampling periods, species with higher flowering frequencies tended to preferentially uptake deep soil water. These results suggest that low temperature and soil moisture promote increased deep soil water uptake in the study region. Dynamic relationships between water uptake patterns and aboveground tree traits may be related to resource partitioning among co-existing species.

Genome assemblies for two Neotropical trees: Jacaranda copaia and Handroanthus guayacan.

The lack of genomic resources for tropical canopy trees is impeding several research avenues in tropical forest biology. We present genome assemblies for two Neotropical hardwood species, Jacaranda copaia and Handroanthus (formerly Tabebuia) guayacan, that are model systems for research on tropical tree demography and flowering phenology. For each species, we combined Illumina short-read data with in vitro proximity-ligation (Chicago) libraries to generate an assembly. For Jacaranda copaia, we obtained 104X physical coverage and produced an assembly with N50/N90 scaffold lengths of 1.020/0.277 Mbp. For H. guayacan, we obtained 129X coverage and produced an assembly with N50/N90 scaffold lengths of 0.795/0.165 Mbp. J. copaia and H. guayacan assemblies contained 95.8% and 87.9% of benchmarking orthologs, although they constituted only 77.1% and 66.7% of the estimated genome sizes of 799 and 512 Mbp, respectively. These differences were potentially due to high repetitive sequence content (>59.31% and 45.59%) and high heterozygosity (0.5% and 0.8%) in each species. Finally, we compared each new assembly to a previously sequenced genome for Handroanthus impetiginosus using whole-genome alignment. This analysis indicated extensive gene duplication in H. impetiginosus since its divergence from H. guayacan.

Liana and tree below-ground water competition-evidence for water resource partitioning during the dry season.

To date, reasons for the increase in liana abundance and biomass in the Neotropics are still unclear. One proposed hypothesis suggests that lianas, in comparison with trees, are more adaptable to drought conditions. Moreover, previous studies have assumed that lianas have a deeper root system, which provides access to deeper soil layers, thereby making them less susceptible to drought stress. The dual stable water isotope approach (δ18O and δ2H) enables below-ground vegetation competition for water to be studied. Based on the occurrence of a natural gradient in soil water isotopic signatures, with enriched signatures in shallow soil relative to deep soil, the origin of vegetation water sources can be derived. Our study was performed on canopy trees and lianas reaching canopy level in tropical forests of French Guiana. Our results show liana xylem water isotopic signatures to be enriched in heavy isotopes in comparison with those from trees, indicating differences in water source depths and a more superficial root activity for lianas during the dry season. This enables them to efficiently capture dry season precipitation. Our study does not support the liana deep root water extraction hypothesis. Additionally, we provide new insights into water competition between tropical canopy lianas and trees. Results suggest that this competition is mitigated during the dry season due to water resource partitioning.

Decoupled dimensions of leaf economic and anti-herbivore defense strategies in a tropical canopy tree community.

Trade-offs among plant functional traits indicate diversity in plant strategies of growth and survival. The leaf economics spectrum (LES) reflects a trade-off between short-term carbon gain and long-term leaf persistence. A related trade-off, between foliar growth and anti-herbivore defense, occurs among plants growing in contrasting resource regimes, but it is unclear whether this trade-off is maintained within plant communities, where resource gradients are minimized. The LES and the growth-defense trade-off involve related traits, but the extent to which these trade-off dimensions are correlated is poorly understood. We assessed the relationship between leaf economic and anti-herbivore defense traits among sunlit foliage of 345 canopy trees in 83 species on Barro Colorado Island, Panama. We quantified ten traits related to resource allocation and defense, and identified patterns of trait co-variation using multivariate ordination. We tested whether traits and ordination axes were correlated with patterns of phylogenetic relatedness, juvenile demographic trade-offs, or topo-edaphic variation. Two independent axes described~60% of the variation among canopy trees. Axis 1 revealed a trade-off between leaf nutritional and structural investment, consistent with the LES. Physical defense traits were largely oriented along this axis. Axis 2 revealed a trade-off between investments in phenolic defenses versus other foliar defenses, which we term the leaf defense spectrum. Phylogenetic relationships and topo-edaphic variation largely did not explain trait co-variation. Our results suggest that some trade-offs among the growth and defense traits of outer-canopy trees may be captured by the LES, while others may occur along additional resource allocation dimensions.

Lianas reduce community‐level canopy tree reproduction in a Panamanian forest

AbstractLianas are a key component of tropical forests, where they compete intensely with trees, reducing tree recruitment, growth and survival. One of the most important potential outcomes of liana competition is the reduction of tree reproduction; however, no previous study has experimentally determined the effects of lianas on tree reproduction beyond a single tree species.We used a large‐scale liana removal experiment to quantify the effect of lianas on community‐level canopy and understorey tree and palm reproduction. In 2011, we removed lianas from eight 6,400‐m2plots (eight plots served as controls) and surveyed understorey tree reproduction in 2012, canopy tree and palm reproduction in 2013, and a second census of all plants in 2016.We found that lianas significantly reduced canopy tree community flowering and fruiting after liana removal. Two years after liana removal, the number of canopy trees with fruits was 173% higher, fruiting individuals had 50% more of their canopy covered by fruits and the number of tree species with fruits was 169% higher than in control plots where lianas were present. Five years after liana removal, the number of canopy trees with fruits was 150% higher, fruiting individuals had 31% more of their canopy covered by fruits and the number of tree species with fruits was 109% higher than in unmanipulated control plots.Liana removal had only a slight positive effect on palms and on understorey tree flower and fruit production, even though understorey light levels had increased 20% following liana cutting.Synthesis. Our findings provide the first experimental demonstration that competition from lianas significantly reduces community‐level canopy tree reproduction. Reduced reproduction increases canopy tree seed and dispersal limitations, and may interfere with deterministic mechanisms thought to maintain tropical canopy tree species diversity, as well as reduce food availability to many animal species. Because lianas are increasing in abundance in many neotropical forests, the effects of lianas on tree reproduction will likely increase, and if the effects of lianas on tree reproduction vary with tree species identity, lianas ultimately could have a destabilizing effect on both tree and animal population dynamics.

Persistence of long-distance, insect-mediated pollen movement for a tropical canopy tree species in remnant forest patches in an urban landscape.

As deforestation and urbanization continue at rapid rates in tropical regions, urban forest patches are essential repositories of biodiversity. However, almost nothing is known about gene flow of forest-dependent tree species in urban landscapes. In this study, we investigated gene flow in the insect-pollinated, wind-dispersed tropical tree Koompassia malaccensis in and among three remnant forest patches in the urbanized landscape of Singapore. We genotyped the vast majority of adults (N=179) and a large number of recruits (N=2103) with 8 highly polymorphic microsatellite markers. Spatial genetic structure of the recruit and adult cohorts was significant, showing routine gene dispersal distances of ~100-400 m. Parentage analysis showed that 97% of recruits were within 100 m of their mother tree, and a high frequency of relatively short-distance pollen dispersal (median ~143-187 m). Despite routine seed and pollen dispersal distances of within a few hundred meters, interpatch gene flow occurred between all patches and was dominated by pollen movement: parentage analysis showed 76 pollen versus 2 seed interpatch dispersal events, and the seedling neighborhood model estimated ~1-6% seed immigration and ~21-46% pollen immigration rates, depending on patch. In addition, the smallest patch (containing five adult K. malaccensis trees) was entirely surrounded by >2.5 km of 'impervious' substrate, yet had the highest proportional pollen and seed immigration estimates of any patch. Hence, contrary to our hypothesis, insect-mediated gene flow persisted across an urban landscape, and several of our results also parallel key findings from insect-pollinated canopy trees sampled in mixed agricultural-forest landscapes.

Habitat fragmentation changes the adaptive value of seed mass for the establishment of a tropical canopy tree

AbstractTo cope with the limiting light conditions in the rain forest understory, many tropical tree species have evolved large seeds that provide the emerging seedlings with nutritional reserves. Habitat fragmentation might change the adaptive value of seed size by modifying the biotic and physical conditions of the forest understory. We experimentally assessed the potential of fragmentation to alter how seed mass affects seedling survival, vigor, and attack by natural enemies of the tropical tree Nectandra ambigens. Seeds from different mother trees (families) were individually weighed and sown in experimental sites established in continuous forest and in forest fragments. Seedling survival, vigor, and damage by herbivores and pathogens were recorded periodically. While seedlings derived from larger seeds had higher survival rates in both habitats, seedling survival and vigor were significantly greater in forest fragments, and the seedlings also suffered fewer attacks by natural enemies. We found genetic variance for seed mass among families with a heritability value (h2) of 0.66, and we found evidence for selection on seed size. Average seed size differed between dead and living seedlings in three sites. In one fragment, seed size was selectively neutral in relation to survival. Overall, selection for seed size promoted survival and thus appears to affect the distribution of this trait. The maintenance of genetic variance could be related to the stochastic nature of the formation of light gaps. Our results highlight the importance of evaluating the adaptive value of traits susceptible to environmental changes for conservation purposes.

Trait Acclimation Mitigates Mortality Risks of Tropical Canopy Trees under Global Warming.

There is a heated debate about the effect of global change on tropical forests. Many scientists predict large-scale tree mortality while others point to mitigating roles of CO2 fertilization and – the notoriously unknown – physiological trait acclimation of trees. In this opinion article we provided a first quantification of the potential of trait acclimation to mitigate the negative effects of warming on tropical canopy tree growth and survival. We applied a physiological tree growth model that incorporates trait acclimation through an optimization approach. Our model estimated the maximum effect of acclimation when trees optimize traits that are strongly plastic on a week to annual time scale (leaf photosynthetic capacity, total leaf area, stem sapwood area) to maximize carbon gain. We simulated tree carbon gain for temperatures (25–35°C) and ambient CO2 concentrations (390–800 ppm) predicted for the 21st century. Full trait acclimation increased simulated carbon gain by up to 10–20% and the maximum tolerated temperature by up to 2°C, thus reducing risks of tree death under predicted warming. Functional trait acclimation may thus increase the resilience of tropical trees to warming, but cannot prevent tree death during extremely hot and dry years at current CO2 levels. We call for incorporating trait acclimation in field and experimental studies of plant functional traits, and in models that predict responses of tropical forests to climate change.

Tree Height Reduction After Selective Logging in a Tropical Forest

AbstractBy harvesting scattered large trees, selective logging increases light availability and thereby stimulates growth and crown expansion at early‐life stage among remnant trees. We assessed the effects of logging on total and merchantable bole (i.e., lowest branch at crown base) heights on 952 tropical canopy trees in French Guiana. We observed reductions in both total (mean, −2.3 m) and bole (mean, −2.0 m) heights more than a decade after selective logging. Depending on local logging intensity, height reductions resulted in 2–13 percent decreases in aboveground tree biomass and 3–17 percent decreases in bole volume. These results highlight the adverse effects of logging at both tree and stand levels. This decrease in height is a further threat to future provision of key environmental services, such as timber production and carbon sequestration.

Phylogenetic Structure of Foliar Spectral Traits in Tropical Forest Canopies

The Spectranomics approach to tropical forest remote sensing has established a link between foliar reflectance spectra and the phylogenetic composition of tropical canopy tree communities vis-à-vis the taxonomic organization of biochemical trait variation. However, a direct relationship between phylogenetic affiliation and foliar reflectance spectra of species has not been established. We sought to develop this relationship by quantifying the extent to which underlying patterns of phylogenetic structure drive interspecific variation among foliar reflectance spectra within three Neotropical canopy tree communities with varying levels of soil fertility. We interpreted the resulting spectral patterns of phylogenetic signal in the context of foliar biochemical traits that may contribute to the spectral-phylogenetic link. We utilized a multi-model ensemble to elucidate trait-spectral relationships, and quantified phylogenetic signal for spectral wavelengths and traits using Pagel’s lambda statistic. Foliar reflectance spectra showed evidence of phylogenetic influence primarily within the visible and shortwave infrared spectral regions. These regions were also selected by the multi-model ensemble as those most important to the quantitative prediction of several foliar biochemical traits. Patterns of phylogenetic organization of spectra and traits varied across sites and with soil fertility, indicative of the complex interactions between the environmental and phylogenetic controls underlying patterns of biodiversity.

Age-related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light-demanding tree species to persist in the community. Recent studies have demonstrated age-related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age-related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large-statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age-related crown thinning. We conclude that age-related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.

Leaf water use in heterobaric and homobaric leafed canopy tree species in a Malaysian tropical rain forest

Tropical canopy tree species can be classified into two types by their heterobaric and homobaric leaves. We studied the relation between both leaf types and their water use, together with the morphological characteristics of leaves and xylem, in 23 canopy species in a tropical rain forest. The maximum rates of photosynthesis and transpiration were significantly higher in heterobaric leaf species, which also underwent larger diurnal variations of leaf water potential compared to homobaric leaf species. The vessel diameter was significantly larger and the stomatal pore index (SPI) was significantly higher in heterobaric than that in homobaric leaf species. There was a significant positive correlation between the vessel diameter, SPI, and maximum transpiration rates in all the studied species of both leaf types. However, there was no significant difference in other properties, such as leaf water-use efficiency, leaf mass per area, leaf nitrogen content, and leaf δ13C between heterobaric and homobaric leaf species. Our results indicate that leaf and xylem morphological differences between heterobaric and homobaric leaf species are closely related to leaf water-use characteristics, even in the same habitat: heterobaric leaf species achieved a high carbon gain with large water use under strong light conditions, whereas homobaric leaf species can maintain a high leaf water potential even at midday as a result of low water use in the canopy environment.

Explaining biomass growth of tropical canopy trees: the importance of sapwood

Tropical forests are important in worldwide carbon (C) storage and sequestration. C sequestration of these forests may especially be determined by the growth of canopy trees. However, the factors driving variation in growth among such large individuals remain largely unclear. We evaluate how crown traits [total leaf area, specific leaf area and leaf nitrogen (N) concentration] and stem traits [sapwood area (SA) and sapwood N concentration] measured for individual trees affect absolute biomass growth for 43 tropical canopy trees belonging to four species, in a moist forest in Bolivia. Biomass growth varied strongly among trees, between 17.3 and 367.3 kg year−1, with an average of 105.4 kg year−1. We found that variation in biomass growth was chiefly explained by a positive effect of SA, and not by tree size or other traits examined. SA itself was positively associated with sapwood growth, sapwood lifespan and basal area. We speculate that SA positively affects the growth of individual trees mainly by increasing water storage, thus securing water supply to the crown. These positive roles of sapwood on growth apparently offset the increased respiration costs incurred by more sapwood. This is one of the first individual-based studies to show that variation in sapwood traits—and not crown traits—explains variation in growth among tropical canopy trees. Accurate predictions of C dynamics in tropical forests require similar studies on biomass growth of individual trees as well as studies evaluating the dual effect of sapwood (water provision vs. respiratory costs) on tropical tree growth.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-015-3220-y) contains supplementary material, which is available to authorized users.

Sapwood allocation in tropical trees: a test of hypotheses.

Carbon allocation to sapwood in tropical canopy trees is a key process determining forest carbon sequestration, and is at the heart of tree growth and dynamic global vegetation models (DGVM). Several allocation hypotheses exist including those applying assumptions on fixed allocation, pipe model, and hierarchical allocation between plant organs. We use a tree growth model (IBTREE) to evaluate these hypotheses by comparing simulated sapwood growth with 30 year tree ring records of the tropical long-lived tree Toona ciliata M. Roem. in Thailand. Simulated annual variation in wood production varied among hypotheses. Observed and simulated growth patterns matched most closely (r2=0.70) when hierarchical allocation was implemented, with low priority for sapwood. This allocation method showed realistic results with respect to reserve dynamics, partitioning and productivity and was the only one able to capture the large annual variation in tree ring width. Consequently, this method might also explain the large temporal variation in diameter growth and the occurrence of missing rings often encountered in other tropical tree species. Overall, our results show that sapwood growth is highly sensitive to allocation principles, and that allocation assumptions may greatly influence estimated carbon sequestration of tropical forests under climatic change.

Functional and biological diversity of foliar spectra in tree canopies throughout the Andes to Amazon region.

Spectral properties of foliage express fundamental chemical interactions of canopies with solar radiation. However, the degree to which leaf spectra track chemical traits across environmental gradients in tropical forests is unknown. We analyzed leaf reflectance and transmittance spectra in 2567 tropical canopy trees comprising 1449 species in 17 forests along a 3400-m elevation and soil fertility gradient from the Amazonian lowlands to the Andean treeline. We developed quantitative links between 21 leaf traits and 400-2500-nm spectra, and developed classifications of tree taxa based on spectral traits. Our results reveal enormous inter-specific variation in spectral and chemical traits among canopy trees of the western Amazon. Chemical traits mediating primary production were tightly linked to elevational changes in foliar spectral signatures. By contrast, defense compounds and rock-derived nutrients tracked foliar spectral variation with changing soil fertility in the lowlands. Despite the effects of abiotic filtering on mean foliar spectral properties of tree communities, the spectra were dominated by phylogeny within any given community, and spectroscopy accurately classified 85-93% of Amazonian tree species. Our findings quantify how tropical tree canopies interact with sunlight, and indicate how to measure the functional and biological diversity of forests with spectroscopy.

Understanding recruitment failure in tropical tree species: Insights from a tree-ring study

Many tropical tree species have population structures that exhibit strong recruitment failure. While the presence of adult trees indicates that appropriate regeneration conditions occurred in the past, it is often unclear why small individuals are absent. Knowing how, when and where these tree species regenerate provides insights into their life history characteristics. Based on tree age distributions inferences can be made on past forest dynamics and information is obtained that is important for forest management. We used tree-ring analyses to obtain tree ages and reconstruct >200years of estimated establishment rates in a sparsely regenerating population of Afzelia xylocarpa (Fabaceae), a light-demanding and long-lived canopy tree species. We sampled all 85 Afzelia trees >5cm diameter at breast height (dbh) in a 297-ha plot in a seasonal tropical forest in the Huai Kha Khaeng (HKK) Wildlife Sanctuary, western Thailand. The age distribution of the sampled Afzelia trees revealed two distinct recruitment peaks centred around 1850 and 1950. The presence of distinct age cohorts provides a strong indication of disturbance-mediated recruitment. Additionally we found three lines of evidence supporting this interpretation. (1) Similarly aged trees were spatially aggregated up to ∼500m, a scale larger than single tree-fall gaps. (2) High juvenile growth rates (5–10mmdbhyear−1) of extant small and large trees indicate that recruitment took place under open conditions. (3) A significant positive correlation between tree age and local canopy height indicates that trees recruited in low-canopy forest patches. Likely causes of these severe canopy disturbances include windstorms and ground fires, which are common in the region. In addition, successful establishment seems to be favoured by wetter climate conditions, as the estimated establishment rate was correlated to the Palmer Drought Severity Index (PDSI). Thus, the co-occurrence of canopy disturbance and favourable climatic conditions may provide a window of opportunity for Afzelia establishment. Our results indicate that forest patches with occurrence of large Afzelia trees have undergone high-severity canopy disturbance prior to establishment, suggesting that these disturbances have shaped forests at HKK. Tree-ring analyses provide a powerful tool to understanding tropical tree establishment patterns. Rare, high-severity canopy disturbances may play a key role in the regeneration of long-lived tropical canopy tree species with recruitment failure, potentially in interaction with climate variability to determine variation in establishment success over decades or centuries.

Lianas have a greater competitive effect than trees of similar biomass on tropical canopy trees

Lianas (woody vines) reduce growth and survival of host trees in both temperate and tropical forests; however, the relative strength of liana‐tree competition in comparison to tree‐tree competition remains unexplored. When controlling for biomass, lianas may have greater competitive effects than trees because the unique morphology of lianas allows them to reach the forest canopy at relatively small stem diameters and deploy a substantial crown above their host. We tested the hypothesis that lianas have a greater negative effect on canopy trees than do trees of similar biomass with a liana‐ and tree sapling‐cutting experiment in a seasonal tropical moist forest in Panama. The response of canopy trees to the cutting treatments was characterized as the change in their daily water use by measuring their sap velocity before and after cutting. We compared the responses of canopy trees around which a similar biomass of either lianas or tree saplings had been cut to control trees with no cutting. Liana cutting increased canopy‐tree sap velocity by ∼8% from before to after cutting relative to control trees during the dry season. In contrast, canopy‐tree sap velocity did not respond to tree cutting, probably because trees with biomass similar to lianas were confined to the forest understory. We observed a similar pattern of sap velocity changes during the wet season, but treatment differences were not significant. Our results demonstrate that release from liana competition, but not tree competition, resulted in increased water transport in canopy trees, and suggests that relative to their biomass, lianas have greater competitive effects on canopy tree performance than do competing trees.

Vessel diameter and xylem hydraulic conductivity increase with tree height in tropical rainforest trees in Sulawesi, Indonesia

In humid environments, where trees rarely experience severe soil water limitation, the hydraulic system of trees requires a functional architecture for effectively transporting of water to the crown despite a comparably low atmospheric evaporative demand for most of the year. Strategies of tropical trees to adapt their hydraulic properties to a perhumid climate are not well studied, as is the impact of tree height on the hydraulic conductivity and vessel anatomy of tropical canopy trees. We analyzed the dependence of hydraulic architecture on tree height in several phylogenetically different canopy tree species growing under the non-seasonal wet climate of a lower montane rainforest in Sulawesi, Indonesia. We determined leaf-specific conductivity (LSC), sapwood-area specific hydraulic conductivity ( k S), and wood anatomy (vessel diameter and density) of sun-exposed twigs and of the trunk of 51 trees of eight abundant species ranging in tree height between 6.5 and 44 m. LSC and k S significantly increased with tree height ( r a d j 2 = 0.50 and 0.46, respectively) as did mean vessel diameter. We found this trend consistent for both, trunk ( r a d j 2 = 0.61 ) and twig ( r a d j 2 = 0.47 ) xylem vessel diameters. In contrast, vessel density and tree height were significantly negative correlated in twigs but not in the trunks. We assume that in a tropical perhumid climate with prevailing high atmospheric humidity, it seems more advantageous for tall trees to promote a high hydraulic conductivity in the conducting tissue of both the trunk and the upper crown, rather than to minimize the risk of drought-induced xylem embolism. However, the tree size-effect as observed in our study has to be validated in a larger sample of tropical tree species before universal rules could be deduced.

Impacts of temperate lianas on tree growth in young deciduous forests

Lianas are often overlooked in temperate ecological studies even though they are important components of forest communities. While lianas have been shown to damage tropical canopy trees and reduce the growth of juvenile trees, the impact of lianas on canopy tree growth in temperate systems is largely unknown. Growth of trees ≥8 cm dbh was examined over a 9-year period within 50-year old post-agricultural secondary forests in the Piedmont region of New Jersey, USA. Five lianas, Celastrus orbiculatus, Lonicera japonica, Parthenocissus quinquefolia, Toxicodendron radicans, and Vitis species, occurred throughout the forest. Total liana basal area, number of stems, and percent cover within host trees were evaluated to assess liana burdens on 606 previously censused trees. These data were related to tree growth to assess liana impacts. Forest trees were separated based on their dominance in the canopy to determine whether lianas had the potential to influence forest composition. In general, lianas in the forests were fairly abundant, with 68% of the trees having at least one liana present. On average, each tree supported 9.7 cm 2 of liana basal area and 23% of the canopy was covered by lianas. Most of the variation in tree growth was related to the dominance of trees within the canopy, with canopy dominant and co-dominant trees growing 2.5× more than suppressed trees. Liana basal area and number of lianas stems were not related to tree growth, but liana canopy cover decreased tree growth. However, not all trees were equally affected as canopy cover of lianas only reduced growth in dominant and co-dominant trees. Lianas were most influential on host tree growth in unsuppressed trees when occupying a majority of the canopy, only a minority of forest trees. This suppression was not related to differential liana colonization of canopy trees as all canopy classes supported equivalent liana burdens. Though lianas impacted only a minority of the trees in this system, some liana species, C. orbiculatus and Vitis spp., are still increasing and may pose future risks to forest growth and development.