Branch Inclination Research Articles

Idealized branch sections and hydrodynamic analysis characterize rainfall partitioning

AbstractWater flow on plant canopies determines the partitioning of intercepted rainfall between stemflow and throughflow, yet understanding of these flow processes remains minimally developed. Plant canopies may concentrate intercepted water into rivulets that flow beneath branches. If the rivulets remain attached to branches until they encounter the main tree trunk, they form stemflow. If the rivulets detach from branches, however, they form ‘pour points’, regions of concentrated throughfall. Here, rivulet flow below uniform cylinders was studied experimentally. Experimental observations were interpreted using hydrodynamic theory to predict the likelihood of a rivulet detaching based on a critical rivulet height (). Predictions of rivulet detachment were explored for a simplified case where water is introduced at known flow rates at a discrete point above a uniform, cylindrical ‘branch’. Where the branch was straight, the percentage of trials forming a rivulet, or the rivulet formation rate, increased with increasing branch inclination angle to the horizontal axis. Rivulet formation rates did not vary with flow rate. However, the volume of water collected at the end of the branch, analogous to stemflow, decreased with a higher flow rates due to the formation of flow instabilities. Rivulets forming on straight branches did not detach. Instead, the rivulet stream accelerated and reduced in height as it flowed along the cylinder. Rivulets formed on curved branches detached only when the branch axis after the curve approached the horizontal. Future theoretical and experimental studies can extend this work to improve understanding of more complex surfaces and branch architectures to mechanistically understand canopy interception.

Taxation characteristics and life state of Quercus robur l. in various forest conditions in the Tunnel beam (Dnipro city)

Influence of forest conditions on the taxation characteristics and the vital state of Quercus robur L. was analyzed. The plants were planted on artificial plantations laid in a tunnel beam in the city of Dnipro in 1961. The experimental plots was located in thalweg (mesohygrophilic conditions – L3) and on the slope of the northern exposure (mesoxerophilic conditions – L1). The 301 specimen of Q. robur L. trees grow on the slope (SG1), and 357 specimen in the thalweg beam was found. The oak trees of three morphological races were planted in tunnel beam: Q. r. pectinata Schneid, Q. r. longiloba Lash, Q. r. Laciniata Schneid. The Q. r. pectinata Schneid are dominate: in the thalweg – 82.70 % (SG3), on the slope (SG1) – 78.60 %. It was found, that in talweg the plants have a larger average height and average trunk diameter. In mesohygrophilic conditions more plants are assigned to the last two classes of height (16.1–18.0 and 18.1–20.0 m), than in mesoxerophilic. The tallest trees grows in thalweg. There are 22 m heigh, and on the slope – 19.5 m. In accordance with calculations, the average height of trees in thalweg is 16 m; on the slope it is 14 m, diameter 42 cm and 32 cm, respectively. Most of the trees in the the experimental plots are in the category of vitality state: healthy tree. There are more such trees in mesohygrophilic conditions than in mesoxerophilic ones (76.40 and 63.90 %, respectively). Weakened trees on the slope of the beam are 32.70 on the slope of the beam, and in the thalweg 17.40 %. The vital status index of oak plantations on the slope is 88.0 %, and in the talwez – 91.0 %. There is no fresh dead wood and dead wood of previous years on the experimental plots. The indeх of the vitality state of the planting in mesohygrophilic conditions is higher, than in mesoxerophilic conditions. Favorable conditions of water supply conduced to the better growth of branches shoots and leaves on them. Tree pathologies are more common on the slope of the beam in mesoxerophilic growth conditions. The analysis of oak trees damage shown, that the largest part falls on the dry top of slope. There are no fungus cup and tumors on the trunks, only one tree with excrescence was found. Such trunk pathologies as inclination, curvature, multi-stemmeds and dryness of thick skeletal branches was revealed. There were much less of trunk pathologies in mesoxerophilic conditions.

New Tools for Mechanical Thinning of Apricot Fruitlets

In this study, the thinner machine with yellow rod equipment was tested in relation to tree branch length and orientation in April 2019, in a narrow-canopied apricot orchard of Emilia Romagna Region, Italy. The trees were mechanically thinned with manual finishing, and comparative tests were carried out simultaneously with the ordinary hand thinning (control). Three groups of two plants were identified as replication for a total of six plants per row. Three rows were checked, considering field uniformity average. The branches were grouped into four classes according to their length: <30 cm, 30–60 cm, 60–90 cm and >90 cm. Branch inclination on the plant, radial or longitudinal with respect to the row, was evaluated. Fruit number before the thinning, after the first and the second machine intervention, after three days of the mechanical thinning and after the hand finishing was recorded. This experience showed satisfactory results in terms of thinning efficiency and reduced damage to both fruits and branches, as a function of the class length and insertion point in the main branch of the plant. Thinning efficiency was always kept above 37% of the left load after hand finishing, and on average between the treatments close to 44%. Fruit damages always remained below the economic thresholds to marketable production or to the plant.

Fracturing and Damage of 3D-Printed Materials with Two Intermittent Fissures under Compression.

The crack propagation and failure of 3D-printed samples with prefabricated K–S fissures (a kinked fissure and a straight fissure) were observed under uniaxial compression, and the strain and displacement of the sample surface were quantified by the digital image correlation (DIC) method. The experimental results show that the branch inclination angle of the kinked fissure is an important factor affecting the crack initial position, and the evolution of the strain field during the failure process of the sample can better reflect the cracking law of the internal fissures. Furthermore, two coalescence modes are classified: Mode I is a tension–shear composite failure formed by the penetration of the tension–shear composite crack; Mode II is a tensile failure that penetrates the whole samples during the failure process without rock bridge damage. In addition, the numerical simulation results were well consistent with the cracking and failure modes.

Elastic and Irreversible Bending of Tree and Shrub Branches Under Cantilever Loads.

Tree and shrub branches subjected to cantilever loads such as intercepted snowfall undergo, in addition to the familiar instantaneous elastic bending, a conspicuous retarded-elastic bending, which is commonly 30–50% of their instantaneous bending and occasionally even more. The resultant bending creep that occurs after loading also often includes a slow, time-dependent irreversible bending. These phenomena occur quite generally among woody plants of different major biomes, taxonomic groups, and structural types. We give some of branch bending viscoelasticity’s basic physical properties such as load dependence and stress relaxation. These properties belong to the secondary walls of branches’ xylem (wood) cells; some properties differ notably from those reported for primary cell walls, a difference for which we propose explanations. A method for separating the overlapping time courses of retarded-elastic and time-dependent irreversible bending shows that multiple retarded-elastic (“Kelvin”) elements of branches span a wide range of retardation times (a retardation spectrum, approximate examples of which we calculate), and that irreversible bending can occur in different cases either only in the first few h after loading, or more extensively through 24 h, or (rarely) for several days. A separate time-independent irreversible bending, permanent set, involving a substantial yield stress, also occurs. In three species of shrubs rapid irreversible bending began only several (up to 24) h after loading, implying an unusual kind of viscoelasticity. Deductions from the dynamics of bending suggest that retarded elasticity can help protect branches against breakage by wind gusts during storms. Irreversible bending probably contributes both to the form that tree and shrub crowns develop over the long term, involving progressive increase in the downward curvature and/or inclination of branches, and also to certain other, more specialized, developmental changes.

Effect of inclination angle on the forced convective flow of a power-law fluid in a 2-D planar branching channel

Branching T-channel is a very common element of a piping system for the transportation of liquids and gases. The brachesbranches of the T-channel can be inclined at different angles which affects the flow dynamics and heat transfer characteristics significantly. Thus, the present work focuses on the flow and thermal characteristics of the laminar forced convection of power-law fluids in a rectangular branching channel which have been numerically investigated over a wide range of parameters such as Reynolds number, 50 ≤ Re ≤ 300, Prandtl number, 10 ≤ Pr ≤ 50, inclination angle, 30° ≤ α ≤ 90° and power-law index, 0.2 ≤ n ≤ 1.4 (includes shear-thinning, n < 1, shear-thickening, n > 1 and Newtonian, n = 1 fluids). This is perhaps the first systematic study which examines the role of power-law fluid behaviour and of branch inclination on momentum and heat transfer characteristics. New extensive results for the flow and temperature fields are presented in terms of streamline contours and separated-flow zones, pressure coefficient, recirculation length, critical Reynolds number, isotherm contours, temperature profiles and local Nusselt number. The pressure coefficient is found to be higher for shear-thickening fluids than that for the Newtonian and shear-thinning fluids while the inclination angle has only a weak effect. The recirculation length bears a positive dependence on the Reynolds number and inclination angle while an inverse relationship is observed with power-law index in both branches. The critical Reynolds number, at which the onset of flow recirculation is observed, is found to be lower for higher inclination angles and a strong influence of the power-law index is also seen on the critical Reynolds number in both branches. Also, the local Nusselt number is seen to be higher at lower Prandtl numbers, low power-law index values and high inclination angles for both branches. Overall, the inclination angle plays a significant role in determining the heat transfer characteristics.

Terrestrial Laser Scanning to Predict Canopy Area Metrics, Water Storage Capacity, and Throughfall Redistribution in Small Trees

Urban trees deliver many ecological services to the urban environment, including reduced runoff generation in storms. Trees intercept rainfall and store part of the water on leaves and branches, reducing the volume and velocity of water that reaches the soil. Moreover, trees modify the spatial distribution of rainwater under the canopy. However, measuring interception parameters is a complex task because it depends on many factors, including environmental conditions (rainfall intensity, wind speed, etc.) and tree characteristics (plant surface area, leaf and branch inclination angle, etc.). In the few last decades, remotely sensed data have been tested for retrieving tree metrics, but the use of this derived data for predicting interception parameters are still being developed. In this study, we measured the minimum water storage capacity (Cmin) and throughfall under the canopies of 12 trees belonging to three different species. All trees had their plant surface metrics calculated: plant surface area (PSA), plant area index (PAI), and plant area density (PAD). Trees were scanned with a mobile terrestrial laser scan (TLS) to obtain their individual canopy point clouds. Point clouds were used to calculate canopy metrics (canopy projected area and volume) and TLS-derived surface metrics. Measured surface metrics were then correlated to derived TLS metrics, and the relationship between TLS data and interception parameters was tested. Additionally, TLS data was used in analyses of throughfall distribution on a sub-canopy scale. The significant correlation between the directly measured surface area and TLS-derived metrics validates the use of the remotely sensed data for predicting plant area metrics. Moreover, TLS-derived metrics showed a significant correlation with a water storage capacity parameter (Cmin). The present study supports the use of TLS data as a tool for measuring tree metrics and ecosystem services such as Cmin; however, more studies to understand how to apply remotely sensed data into ecological analyses in the urban environment must be encouraged.

Agronomic performance of soybean genotypes submitted to different population densities in the city of Uberlândia - MG

Sowing density is widely studied in the soybean crop in order to define the best plant population for each cultivar available on the market. The objective of this work was to evaluate the agronomic traits of three soybean geno­types (UFUS LVR, UFUS 7910, and UFUS 8301) in four population densities (12; 14; 16; 18 pl m -1 ), in Uberlândia-MG. The design was a randomized complete block with four replicates, with sowing performed on February 12, 2016. The following were evaluated: plant height at flowering (PHF) and maturity (PHM); number of branched nodes (NBN); lateral branch inclination (LBI); first pod insertion height (FPIH); number of pods per plant (NPP); number of seeds per pod (NSP); hundred-grain weight (HGW); and grain yield (kg ha -1 ). There were sig­nificant interactions between genotypes and densities for all characters, except for LBI and NSP. When increasing the sowing density from 14 to 18 pl m -1 , cultivar UFUS 7910 showed a reduction in plant height at maturity, and strain UFUS LRV had the first pod insertion height increased. The hundred-grain weight was not altered for culti­vars UFUS LRV and UFUS 7910 when increasing the density from 12 to 18 pl m -1 . For the three genotypes, there was a reduction in grain yield when sown in a higher sowing density (density of 18 pl m -1 ). The densities of 16 pl m -1 and 12 pl m -1 provided better grain yields for genotypes UFUS LVR and UFU 7910, respectively. The densi­ties of 12 pl m -1 and 14 pl m -1 allowed a greater number of pods and higher yield for cultivar UFUS 8301.

Fillet weld effective lengths in CHS X-connections. II: Finite element modelling, parametric study and design

Finite element (FE) modelling was performed to extend the results of a recently completed experimental test program to evaluate the static strength of fillet welds in X-connections between circular hollow sections (CHS). Non-linear FE models with weld fracture were validated by comparison of spot strains, load-deformation response, and fracture load with 12 experimental tests. Two hundred and fifty-six FE weld-critical CHS-to-CHS X-connections, with varied branch-to-chord diameter ratio, chord wall slenderness, branch inclination angle, and branch-to-chord thickness ratio, were analysed under quasi-static branch tension. The effect of these parameters on fillet weld strength is illustrated, and the structural reliability (or safety index) of North American specification provisions for weld effective lengths is confirmed. An alternative method for estimating fillet weld strength, with specific weld effective lengths, is proposed. Recommendations for a new design approach that meets the minimum target safety index in North America are made.

Fillet weld effective lengths in CHS X-connections. I: Experimentation

For the first time, an experimental test program was conducted to assess the strength of fillet welds in circular hollow section (CHS) connections. Six large-scale, fillet-welded CHS-to-CHS X-connections were designed with varied key parameters that affect the weld strength: branch-to-chord diameter ratio, chord wall slenderness, and branch inclination angle. By means of quasi-static tension applied to the branches, fracture of 12 test welds (two per connection) was obtained. Strain distributions measured adjacent to the welds indicated a weld effective length less than the total weld length, under pure axial load. Branch loads at rupture were also measured and used to determine the structural reliability of existing AWS provisions for weld effective lengths in CHS-to-CHS X-connections. For the range of parameters studied, the provisions are found to be very conservative. Hence, methods are assessed to accurately quantify the weld effective length. A parametric modelling study is presented in a companion paper to develop more liberal recommendations.

Testing a New Approach to Quantify Growth Responses to Pruning Among Three Temperate Tree Species

In settled areas, electrical line safety is maintained by pruning encroaching trees. Identifying key predictors of branch elongation growth rate following pruning would assist in developing predictive models and optimizing pruning cycles. However, measuring branches in trees near electrical lines is complex and challenging. This paper describes an innovative approach using a handheld laser rangefinder to safely and accurately estimate growth from the ground. In-tree and ground-based laser measurements were highly correlated. This was followed by testing for correlations between branch growth response over a number of years after pruning and many biotic and abiotic factors for Fraxinus pennsylvanica, Acer platanoides, and Acer saccharinum, in the city of Montreal, Canada. In a sample of 59 trees, A. saccharinum had the greatest branch growth, followed by F. pennsylvanica, and finally A. platanoides. Branch growth increased following pruning and subsequently strongly declined, with A. platanoides declining the fastest. Branch inclination angle was positively correlated with growth rate for two species, but not for A. saccharinum. Among the types of pruning used, directional pruning techniques resulted in the least branch regrowth rate. Tree diameter was weakly related to branch growth rates. These results suggest that while growth conditions for street trees may be perceived as homogenous, there is substantial variation in branch growth response. This variation may be related to pruning history, or unmeasured abiotic or biotic variables. Estimating pruning cycle duration is a complex task and further work is needed to develop a predictive model for more accurate estimation of return times.

Predictability of stemflow in a species‐rich tropical forest

AbstractNumerous studies investigated the influence of abiotic (meteorological conditions) and biotic factors (tree characteristics) on stemflow generation. Although these studies identified the variables that influence stemflow volumes in simply structured forests, the combination of tree characteristics that allows a robust prediction of stemflow volumes in species‐rich forests is not well known. Many hydrological applications, however, require at least a rough estimate of stemflow volumes based on the characteristics of a forest stand. The need for robust predictions of stemflow motivated us to investigate the relationships between tree characteristics and stemflow volumes in a species‐rich tropical forest located in central Panama. Based on a sampling setup consisting of ten rainfall collectors, 300 throughfall samplers and 60 stemflow collectors and cumulated data comprising 26 rain events, we derive three main findings. Firstly, stemflow represents a minor hydrological component in the studied 1‐ha forest patch (1.0% of cumulated rainfall). Secondly, in the studied species‐rich forest, single tree characteristics are only weakly related to stemflow volumes. The influence of multiple tree parameters (e.g. crown diameter, presence of large epiphytes and inclination of branches) and the dependencies among these parameters require a multivariate approach to understand the generation of stemflow. Thirdly, predicting stemflow in species‐rich forests based on tree parameters is a difficult task. Although our best model can capture the variation in stemflow to some degree, a critical validation reveals that the model cannot provide robust predictions of stemflow. A reanalysis of data from previous studies in species‐rich forests corroborates this finding. Based on these results and considering that for most hydrological applications, stemflow is only one parameter among others to estimate, we advocate using the base model, i.e. the mean of the stemflow data, to quantify stemflow volumes for a given study area. Studies in species‐rich forests that wish to obtain predictions of stemflow based on tree parameters probably need to conduct a much more extensive sampling than currently implemented by most studies. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Modeling qualitative and quantitative elements of branch growth in saplings of four evergreen broad-leaved tree species growing in a temperate Japanese forest

Factors influencing branch growth differed between a qualitative element (whether a branch grows) and a quantitative element (the amount of biomass accretion). We measured branch growth in saplings of four evergreen broad-leaved tree species growing in a temperate Japanese forest. A hierarchical Bayesian approach was used to model two elements of branch growth: a qualitative component [whether branches produce new annual shoots (ASn)] and a quantitative component (total ASn mass). The two components were influenced by somewhat different factors. The probability that a branch would produce ASn was affected by the total mass of previous-year annual shoots (total ASn–1 mass), branch age, relative branch height, canopy openness measured at the branch tip, maximum canopy openness within a single sapling, and the interaction between canopy openness and maximum canopy openness. The total ASn mass was influenced by the total ASn–1 mass, relative branch height, branch inclination, and maximum canopy openness. These two components of branch growth should be considered separately when tree architecture is modeled. In addition, we detected interactive responses among branches within individual saplings. The relative importance of interactive modular response and branch autonomy may differ depending on the status of plants, such as individual age, environmental conditions, and the timing of the measurements. We found considerable similarities in the responses of branch growth to the internal and environmental factors among the species studied. We also found some among-species differences in branch growth responses to the explanatory variables measured.

Forest Canopy Interception Loss Across Temporal Scales: Implications for Urban Greening Initiatives

Increasing urban forest canopy coverage due to greening initiatives requires watershed managers to balance societal water practices with forest hydrological processes. One such process, canopy rainfall interception, can remove substantial portions of precipitation from catchments by simply intercepting, storing, and evaporating meteoric water. We performed a field study examining interception losses across temporal scales comparing two landscaping species of contrasting crown structures (Fagus grandifolia Ehrh., American beech, and Liriodendron tulipifera L., yellow poplar), native to the highly urbanized northeastern United States, to highlight the effect of landscape design on urban water and storm water management. Results show that landscape designs using the rougher bark texture, lower branch inclination, and thinner canopy of L. tulipifera can increase water losses during rainfall and, therefore, can be used to improve storm water management. On the other hand, the smoother bark, higher branch inclination, and deeper canopy of F. grandifolia decreased water losses, allowing greater water transfer to the surface or subsurface. Thus, interception-related water resource losses during urban forestry projects can be manipulated to benefit urban sustainability efforts if designers consider the multifaceted ramifications of planting different tree species with differing canopy structures.

Differential stemflow yield from European beech saplings: the role of individual canopy structure metrics

Stemflow production is affected by a suite of biotic and abiotic factors. It has proven difficult to determine the importance of individual canopy structure metrics on stemflow production. The disentanglement of the role and importance of individual canopy structure metrics would advance our understanding of the dynamics of stemflow production. This work employed ten isolated (i.e. no overlapping crowns) experimental European beech (Fagus sylvatica L.) saplings to examine the effects of various canopy structural metrics on stemflow production in east-central Germany. The following canopy structural metrics were utilized in a hierarchical cluster analysis using Ward's method to separate the saplings into groups: primary branch count per unit projected crown area, secondary branch count per unit projected crown area, total branch count per unit projected crown area, mean branch inclination angle, minimum branch inclination angle, maximum branch inclination angle, total dry woody biomass per unit projected crown area, total foliar dry biomass per unit projected crown area and total dry biomass per unit projected crown area. Cluster group means revealed that saplings, which generate the largest stemflow yields, once controlled for sapling size, have straighter boles (but some trunk lean), more steeply inclined branches, a larger number of branches, more woody surface area and fewer numbers of leaves. Our results may prove valuable as a guide to researchers wishing to couple LiDAR and fine-scale architectural models with the canopy metrics that govern stemflow to provide a better understanding of the canopy on the hydrology and biogeochemistry of forests. Copyright © 2013 John Wiley & Sons, Ltd.

Long-term physiological and morphological acclimation by the evergreen shrub Buxus sempervirens L. to understory and canopy gap light intensities

Physiological and morphological plasticity are essential for growth and reproduction in contrasting light environments. In dry forest ecosystems, light generalists must also cope with the trade-offs involved in synchronous acclimation to light availability and drought. To understand how the broadleaf evergreen tree-shrub Buxus sempervirens L. (common box) inhabits both understory and successional terrain of Mediterranean forest, we measured photosynthesis–fluorescence light response, morphological traits and architectural characteristics across a light gradient. Our results show that B. sempervirens exhibits stress resistance syndrome, with little change in net photosynthesis rate across a light availability gradient, due to compensatory physiological and morphological acclimation. Light energy processing and dissipation potential were highest in leaves of well-illuminated plants, with higher electron transport rate, fraction of open photosystem II reaction centres, non-photochemical quenching, photorespiration and dark respiration. In contrast, traits reducing light capture efficiency were observed in high light shrubs, including higher leaf mass per unit area, leaf clumping, leaf inclination and branch inclination. We suggest that both physiological and morphological plasticity are required for B. sempervirens to survive across a light gradient in a dry forest ecosystem, while exhibiting homoeostasis in photosynthetic gas exchange. We further speculate that the low growth rate of B. sempervirens is effective in full sun only due to a lack of competition in low resource microsites.

Separation of a Two-Phase Slug Flow in Branched 90 deg Elbows

Novel experimental data for phase separation of air-water mixtures in horizontal 90 deg branched elbows are presented in this work. The branched elbows were formed by attaching a pipe to a 90 deg elbow on the side of maximum radius of curvature, and halfway between the inlet and outlet sections of the elbow. All three arms coming from the junction were in the horizontal plane. Both the branch orientation and branch diameter were varied. Three different branch/elbow diameter ratios were tested, as well as three different branch inclination angles. In addition, the static pressure was monitored at different points along the ramified elbow using a set of pressure transducers in order to analyze and associate the pressure drop with the phase separation. At the inlet section of the elbow, the two-phase flow pattern was mainly slug flow. Based on the experimental data, a correlation for the liquid phase separation is proposed. Finally, the volume-weighted phase separation in the branched elbow was compared with the phase separations on the T-junction, and it was found that in some cases the branched elbows have a similar performance to that of the T-junctions.

Dynamic path selection along branched faults: Experiments involving sub‐Rayleigh and supershear ruptures

Building upon previous laboratory earthquake experiments of dynamic shear rupture growth taking place along faults with simple kinks, new and complex fault geometries involving cohesively held fault branches are studied. Asymmetric impact at the specimen boundaries controls the incoming shear ruptures, which are manipulated to propagate at either sub‐Rayleigh or supershear velocities. High‐speed photography and dynamic photoelasticity are used with a model material, Homalite‐100, to monitor incoming and outgoing rupture propagation, acceleration, deceleration, or arrest at the vicinity of the branch location. Differences and similarities of rupture velocity history between cases involving faults with either simple kinks or branches, on the one hand, and sub‐Rayleigh and supershear incoming ruptures, on the other, are highlighted and explained. Results of the experiments show a clear general bias toward large branch inclination, smaller branch angles appearing to be overshadowed and suppressed by the stress field associated with the main fault. Of great interest, also, is the sustenance of rupture propagation along a branch by the Mach cone, when the initial rupture is supershear driven. Generally, higher rupture speeds favors larger arrays of branching angles to be triggered. A companion analysis by Templeton et al. (2009) featuring detailed numerical simulations of these experiments provides further insight into the observed phenomena.

Déterminants botaniques de l’agrégation du feuillage et de l’interception de la lumière pour des taillis de peupliers âgés de deux ans : caractérisation à partir de maquettes 3-D

Botanical parameters (e.g., shoot and branch inclination, petiole length, leaf phyllotaxy, size and shape) that influence light interception and foliage clumping in dense two-year-old monoclonal poplar (Populus spp.) coppice crops were analysed with a three-dimensional simulation model. Crop LAI varied from 1 to 2 for clone Ghoy and from 2.5 to 7.4 for clone Trichobel from May to September. Canopies were strongly clumped, with a clumping index (μ) about 0.5. Canopy light transmittance (τ) varied from 0.59 in May to 0.41 in September for clone Ghoy and from 0.42 to 0.08 for clone Trichobel, and was strongly associated with LAI. The overall effect of a simulated shift in botanical parameters was relatively small and resulted in limited changes in μ and τ by ± 0.05 and ±0.1, respectively. Petiole length had the most notable effect on μ and τ, while the other parameters were less effective. However, biomass cost analyses showed that actual petiole length optimised the efficiency of biomass investment into light capture.

Mechanical and ecophysiological significance of the form of a young Acer rufinerve tree: vertical gradient in branch mechanical properties

Most tree biomechanics models assume uniformity of mechanical properties within a tree, and only a few studies have focused on differences in mechanical status among branches. We examined mechanical properties of 49 branches of two 10-year-old trees of Acer rufinerve Sieb. et Zucc. For each branch, bending moment due to its own fresh mass, elastic modulus, section modulus and flexural stiffness were obtained. Elastic modulus of the branch was correlated with the density and thickness of the fiber cell wall and decreased with crown depth, indicating that branches at lower positions were more elastic than branches at upper positions. Compared to lower branches, upper branches were less inclined, possessed thicker growth rings, more long shoots and were subject to smaller stresses. The leaf arrangement in the upper branches might be effective in transmitting more light to the lower branches. In contrast, the lower branches were more inclined toward the horizontal and subject to greater stresses than the upper branches. Lower branch inclinations were attributed to smaller dry matter investment in diameter growth. Upper and lower branch inclinations were slightly greater and smaller, respectively, than those predicted by beam theory. The alleviation in inclination of the lower branches is probably caused by negative gravitropic responses such as tension wood formation or upward shoot elongation, or both. The horizontal display of leaves in the lower branches would be effective in light interception. The reduction in cost of the lower branches can be adaptive because they have a shorter life expectancy than the upper branches. The results showed that an adaptive tree form is realized by a vertical gradient in branch mechanical properties.