Foliage Elements Research Articles

Effects of components of the leaf area distribution on drag relations for Cryptomeria japonica and Chamaecyparis obtusa

The objectives of this study were to clarify the effects of components of the leaf area distribution on the drag coefficient of crowns and streamlining (e.g., leaf area index; LAI, outline of the crown shape, and clumpiness) and to contribute to the accumulation of data on drag relations by quantifying data for Chamaecyparis obtusa and Cryptomeria japonica. We conducted drag experiments while simultaneously capturing dynamic crown images for 28 Ch. obtusa crowns and 13 Cr. japonica crowns to analyze the relationships between the leaf area distribution components and drag coefficient or streamlining. The static drag coefficient increased with the LAI for Ch. obtusa and with decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient decreased with increasing clumpiness for Ch. obtusa and with a combination of increasing LAI and decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient had a clear relationship with the decreasing rate of the dynamic crown projected area of obstacles (foliage elements, branches, and stems) calculated from captured video images under windy conditions for Cr. japonica, while Ch. obtusa did not show clear relationship between them. The drag coefficients assuming non-porous crown; C max estimated by simple model combining LAI and clumpiness were approximately 1.0 in Ch. obtusa and 0.5 in Cr. japonica and were equivalent to the dynamic drag coefficients from video image under windy condition. The combination of LAI and clumpiness provided simple estimation for drag relations and enable to link crown structure to wind damage easier.

Correction of Erroneous LiDAR Measurements in Artificial Forest Canopy Experimental Setups

Terrestrial laser scanning (TLS) data makes possible to directly characterize the three-dimensional (3D) distribution of canopy foliage elements. The scanned edges of these elements may result in incorrectly point measurements (i.e., “ghost points”) impacting the quality of point cloud data. Therefore, estimation of the ghost points’ spatial visibilities, measurement of their characteristics and their removal are essential. In order to quantify the improvements on data quality, a method is developed in this study to efficiently correct for ghost points. Since the occurrence of ghost points is governed by a number of factors, (e.g., scanning resolution and distance, object properties, incident angle); the developed method is based on the analysis of the effects of these factors under controlled conditions where canopy-like objects (i.e., leaves, branches and layers of leaves) were scanned using a continuous-wave TLS system that employs phase-shift technology. Manual extraction of ghost points was done in order to calculate the relative amount of ghost points per scan, or ghost points ratio (gpr). The gpr values were computed in order to: (i) analyze their relationships with variables representing the above factors; and (ii) be used as a reference to evaluate the performance of filters used for extraction of ghost points. The ghost points’ occurrence was modeled by fitting regression models using different predictor variables that represent the variables under study. The obtained results indicated that reduced models with three predictors were suitable for gpr estimation in artificial leaves and in artificial branches, with a relative root mean squared error (RMSE) of 4.7% and 3.7%, respectively; while the full model with four predictors was appropriate for artificial layers of leaves, with relative RMSE of 4.5%. According to the statistical analysis, scanning distance was identified as the most important variable for modeling ghost points occurrence. Results indicated that optimized distance-based filters relative to the scanning distance have improved the outcomes in ghost points detection, in comparison to standard filtering criteria. These results suggest that more accurate characterization of forest canopy 3D structures can be achieved by removing ghost points using the new developed method.

Perancangan PC Game First Person Shooter Menggunakan Unreal Development Kit

The development of hardware increasing rapidly has made game developers take advantage of a variety of new resources that can improve their games. Epic games is a mature game developer who managed to make thousands game and delivered to the hands of gamers . A game engine called Unreal Engine is a big secret behind the success of Epic Games . The game engine is free if you just want to learn or just want to create a personal project and the game is not to be in comercial purposes . It is unfortunate that many students don’t even know of the existence of unreal engine , most of them make use of simpler game engine like game maker , rpg maker , fps creator , and so on. Though unreal engine is superior in any aspect other than the game engine , be it graphics , tools , mechanisms of development , flexible in export-import assets , etc . Based on this information , the author had the idea to make a first person shooter game using the unreal engine as the engine game. Before doing the develpment process, the next step is studying the literature of unreal engine and other supporting software such as 3d studio max to create 3D assets , adobe flash to create the menus , adobe photoshop to create a 2D texture and speedtree assets to create the foliage elements . The next thing is to go into the design phase of scenarios , maps, missions , characters and items that will be placed in the game. The next stage is the development and testing phase to test the game that has finished .The results of the design of this game is the realization of a first person shooter game application using unreal engine with features that can support the player 's interest in playing the game . It’s also introducing unreal engine to students who are interested in designing games.

A Multi-layer Radiation Model for Urban Neighbourhoods with Trees

A neighbourhood-scale multi-layer urban canopy model of shortwave and longwave radiation exchange that explicitly includes the radiative effects of tall vegetation (trees) is presented. Tree foliage is permitted both between and above buildings, and mutual shading, emission and reflection between buildings and trees are included. The basic geometry is a two-dimensional canyon with leaf area density profiles and probabilistic variation of building height. Furthermore, the model accounts for three-dimensional path lengths through the foliage. Ray tracing determines the receipt of direct shortwave irradiance by building and foliage elements. View factors for longwave and shortwave diffuse radiation exchange are computed once at the start of the simulation using a Monte Carlo ray tracing approach; for subsequent model timesteps, matrix inversion rapidly solves infinite reflections and interception of emitted longwave between all elements. The model is designed to simulate any combination of shortwave and longwave radiation frequency bands, and to be portable to any neighbourhood-scale urban canopy geometry based on the urban canyon. Additionally, the model is sufficiently flexible to represent forest and forest-clearing scenarios. Model sensitivity tests demonstrate the model is robust and computationally feasible, and highlight the importance of vertical resolution to the performance of urban canopy radiation models. Full model evaluation is limited by the paucity of within-canyon radiation measurements in urban neighbourhoods with trees. Where appropriate model components are tested against analytic relations and results from an independent urban radiation transfer model. Furthermore, system response tests demonstrate the ability of the model to realistically distribute shortwave radiation among urban elements as a function of built form, solar angle and tree foliage height, density and clumping. Separate modelling of photosynthetically-active and near-infrared shortwave bands is shown to be important in some cases. Increased canyon height-to-width ratio and/or tree cover diminishes the net longwave radiation loss of individual canyon elements (e.g., floor, walls), but, notably, has little effect on the net longwave loss of the whole urban canopy. When combined with parametrizations for the impacts of trees on airflow and hydrological processes in the urban surface layer, the new radiation model extends the applicability of urban canopy models and permits more robust assessment of trees as tools to manage urban climate, air quality, human comfort and building energy loads.

An assessment of vegetation and canopy structure of moderately exploited natural forest area in Yagirala forest reserve

Study assessed the vegetation composition and structure and the forest canopy structure in terms ofLeaf Area Index (LAI), Mean Leaf Angle (MLA) and canopy openness in different elevationalclasses of moderately exploited natural forest area which covers about 82% of total natural forestcover in Yagirala forest reserve, a tropical lowland rain forest selectively logged by State TimberCooperation in late 70's.Canopy architecture termed as angle distribution of foliage elements (Chen et al. 1992), can bequantified by the leaf area index (LAI) and mean leaf angle (MLA). In this study Hemisphericalphotographic method was used to characterize canopy architecture at three elevational classes (i.e.valley, mid-slope and ridge top). At each elevational class, hemispherical photos ofthe forest canopywere taken at each sampling point at a height of l m above the ground along transects up to 200m at50m intervals. Hemispherical photographs were analyzed using Hemiview 2.1 canopy analysis softwareA vegetation survey was carried out to determine floristic composition of dam inant species and fam i!ies,which contribute more to the forest canopy. The enumeration was carried out using 0.05 ha circularplots at three elevational classes, totally covering 0.6ha of the area. Individuals taller 1m were enumeratedand species, diameter at breast height (dbh) and total height measurements were recorded and relativebasal area, relative frequency, relative density and Importance Value Index (IVI), diameter classdistribution were estimated.Leaf area index (LAI) and mean leaf angle (MLA) did not show significant variation between threeelevational classes. LAlmean value of low elevation areas show high value of2.256 and mean valueof high elevation areas show low value of 2.087. Average MLA value for the moderately exploitedarea is 29.14. Canopy openness given in terms of visual sky fraction is also not significantly diferentbetween three elevational classes. The results give an estimation of homogeneity of canopy opennesswithin the moderately exproited natural forest.

Eucalypt forests as indicators of the gradients within the central Queensland serpentine landscape of Australia

The eucalypt forests of the central Queensland serpentine landscape on the eastern coast of Australia are dominated by two overstorey species. These are Eucalyptus fibrosa F.Muell. subsp. fibrosa, the most dominant tree occurring throughout the landscape, and Corymbia xanthope A.R.Bean & Brooker, a serpentine endemic species which has a more restricted distribution. We hypothesised that the structure and foliage elements of the eucalypt forests could be used as biological indicators of the severity of the serpentine soils. This was tested by surveying 30 plots (50 × 20 m) within the upland landform patterns of the central Queensland serpentine landscape. The structure of the forests and abundance of the species were recorded and foliage samples from the dominant tree E. fibrosa subp. fibrosa were collected and analysed for metal and nutrient content. Soil samples from each site were collected and analysed for major cations, bio-available metals and fertility. Analysis of the data showed that there are significant correlations between the structure of the eucalypt forests and the landform patterns and soil chemistry. The relative basal area of C. xanthope is a useful measure of the severity of the serpentine soils and correlates to the soil Mg : Ca quotients. The tree E. fibrosa subsp. fibrosa was found to regulate its uptake of soil elements and cannot be used as an indicator of soil elements.

Computational-Geometry-Based Retrieval of Effective Leaf Area Index Using Terrestrial Laser Scanning

Quantifying the 3-D forest canopy structure and leaf area index of an individual tree or a forest stand is challenging. The canopy structural information implicitly contained within point cloud data (PCD) generated from terrestrial laser scanning (TLS) makes it possible to characterize directly the spatial distribution of foliage elements. In this paper, a new voxel-based method titled “point cloud slicing” is presented to retrieve the biophysical characteristics of the forest canopy including extinction coefficient, gap fraction, overlapping effect, and effective leaf area (ELA) from PCD. These extractions were performed not only from the whole canopy but also from layers of the canopy to depict the distribution patterns of foliage elements within the canopy. The results showed that the TLS-based ELA estimation method could explain 88.7% (rmse = 0.007, p <; 0.001, and n = 30) variation of the destructive-sample-based leaf area measurement results. It was found that the sampling resolution was a key parameter in defining the dimension of a single voxel. Furthermore, the TLS-based method can also serve as a calibration tool for airborne laser scanning application with ground sampling.

Leaf Orientation Retrieval From Terrestrial Laser Scanning (TLS) Data

Tree leaf orientation, including the distribution of the inclinational and azimuthal angles in the canopy, is an important attribute of forest canopy architecture and is critical in determining the within and below canopy solar radiation regimes. Characterizing leaf orientation is a key step to the retrieval of leaf area index (LAI) based on remotely sensed data, particularly discrete point data such as that provided by light detection and ranging. In this paper, we present a new method that indirectly and nondestructively retrieves foliage elements' orientation and distribution from point cloud data (PCD) obtained using a terrestrial laser scanning (TLS) approach. An artificial tree was used to develop the method using total least square fitting techniques to reconstruct the normal vectors from the PCD. The method was further validated on live tree crowns. An equation with a single parameter for characterizing the leaf angular distribution of crowns was developed. The TLS-based algorithm captures 97.4% (RMSE = 1.094 degrees, p <; 0.001) variation of the leaf inclination angle compared to manual measurements for an artificial tree. When applied to a live tree seedling and a mature tree crown, the TLS-based algorithm predicts 78.51% (RMSE = 1.225 degrees, p <; 0.001) and 57.28% (RMSE = 4.412 degrees, p <; 0.001) of the angular variability, respectively. Our results indicate that occlusion and noisy points affect the accuracy of normal vector estimation. Most importantly, this work provides a theoretical foundation for retrieving LAI from PCD obtained with a TLS.

Estimate of Leaf Area Index in an Old-Growth Mixed Broadleaved-Korean Pine Forest in Northeastern China

Leaf area index (LAI) is an important variable in the study of forest ecosystem processes, but very few studies are designed to monitor LAI and the seasonal variability in a mixed forest using non-destructive sampling. In this study, first, true LAI from May 1st and November 15th was estimated by making several calibrations to LAI as measured from the WinSCANOPY 2006 Plant Canopy Analyzer. These calibrations include a foliage element (shoot, that is considered to be a collection of needles) clumping index measured directly from the optical instrument, TRAC (Tracing Radiation and Architecture of Canopies); a needle-to-shoot area ratio obtained from shoot samples; and a woody-to-total area ratio. Second, by periodically combining true LAI (May 1st) with the seasonality of LAI for deciduous and coniferous species throughout the leaf-expansion season (from May to August), we estimated LAI of each investigation period in the leaf-expansion season. Third, by combining true LAI (November 15th) with litter trap data (both deciduous and coniferous species), we estimated LAI of each investigation period during the leaf-fall season (from September to mid-November). Finally, LAI for the entire canopy then was derived from the initial leaf expansion to the leaf fall. The results showed that LAI reached its peak with a value of 6.53 m2 m−2 (a corresponding value of 3.83 m2 m−2 from optical instrument) in early August, and the mean LAI was 4.97 m2 m−2 from May to November using the proposed method. The optical instrument method underestimated LAI by an average of 41.64% (SD = 6.54) throughout the whole study period compared to that estimated by the proposed method. The result of the present work implied that our method would be suitable for measuring LAI, for detecting the seasonality of LAI in a mixed forest, and for measuring LAI seasonality for each species.

The characteristics of rare earth elements in bulk precipitation, throughfall, foliage and lichens in the Lesní potok catchment and its vicinity, Czech Republic

ABSTRACT A comparison of rare earth elements' (REE) atmospheric signatures in various ecosystem compartments was carried out in the vicinity of the Lesní potok catchment (LP), Czech Republic. REE signatures were investigated from 2004 to 2006 in rainwater, throughfall, tree foliage ( Picea abies , Fagus sylvatica ) and lichens ( Hypogymnia physodes ) for selected elements (Al, Ca, Fe, K, Mg, Mn, Na, P, S, Si). REE concentrations increased in the following sequences: bulk precipitation &lt; beech throughfall &lt; spruce throughfall and spruce needles &lt; beech leaves ≪ lichens. The crustal origin of REEs in bulk precipitation was confirmed by its high correlation with lithogenic elements, by the seasonal variation in REE concentrations and by comparison of REE distribution patterns of the upper continental crust, local granites and soil. Enrichment factors calculated in relation to bulk precipitation and normalized to Na enabled elimination of the influence of dry deposition and wash-out. Higher REE concentrations in throughfall were then identified to be the result of the wash-out of dry deposition, while REEs were found to bioaccumulate in vegetation, although at a much smaller rate than the essential elements K, Mn, P, Mg and Ca. Supplementary material: various REE and major ions concentrations are available at http://www.geolsoc.org.uk/SUP18437.

Sampling gap fraction and size for estimating leaf area and clumping indices from hemispherical photographs

Hemispherical photography is becoming a popular technique for gap fraction measurements to characterize biophysical parameters and solar radiation in plant canopies. One of the crucial steps in the measurement of canopy gap fraction using hemispherical photography is determining the resolution of the sampling grid. In this work, the effects of varying resolutions of sampling grids by modifying the angle widths of zenithal annuli and azimuthal sectors were evaluated for leaf area and clumping indices computations. Sensitivity analysis was performed to test these effects using artificial photographs simulating ideal canopies with varying leaf area index and aggregation levels of foliage elements. Contrasting forest types, including natural tropical cloud forest and exotic plantations, were tested as real canopies. Results indicate that leaf area and clumping indices estimates are significantly affected by the variation of sampling grids. A new approach to solve the problem of null-gap segments, obscured completely by foliage, is proposed. However, the determination of optimal combinations of zenithal annuli and azimuthal sector angular widths that suit all canopy types remains a difficult practical problem that is often overlooked. Finally, theoretically sound gap fraction and size sampling regions were demonstrated for reliable estimates of canopy biophysical parameters.

Expanding global mapping of the foliage clumping index with multi-angular POLDER three measurements: Evaluation and topographic compensation

The clumping index measures the spatial aggregation (clumped, random and regular) of foliage elements. The global mapping of the clumping index with a limited eight-month multi-angular POLDER 1 dataset is expanded by integrating new, complete year-round observations from POLDER 3. We show that terrain-induced shadows can enhance bi-directional reflectance distribution function variation and negatively bias the clumping index (i.e. indicating more vegetation clumping) in rugged terrain. Using a global high-resolution digital elevation model, a topographic compensation function is devised to correct for this terrain effect. The clumping index reductions can reach up to 30% from the topographically non-compensated values, depending on terrain complexity and land cover type. The new global clumping index map is compared with an assembled set of field measurements from 32 different sites, covering four continents and diverse biomes.

The computation of foliage clumping index using hemispherical photography

Hemispherical photography (HP) is extensively used for both canopy architecture such as leaf area index (LAI), and solar radiation regime determinations under forest canopies. This is done mainly by assuming that foliage elements occur in a spatially random manner. However, the majority of world forests occur in heterogeneous ecosystems and topography with rather complex canopy architecture. To improve the estimates of canopy structures and solar radiation regimes, a non-random spatial distribution parameter called clumping index (CI) has been used. We compared varying methodologies of CI determination on real HP acquired in contrasting forest types growing on sloping ground, and on simulated HP representing different aggregation levels of foliage elements. The major aim was the comparative analysis of the effects of forest types, forest density, slope and gap fraction acquisition accuracy on estimation of CI using the five different approaches. The result indicated that CI estimates based on gap size distribution approaches performed the best and were less affected by topography and forest density compared to approaches based on solely logarithmic gap averaging techniques.

Improved nutritional status of Cupressus lusitanica when grown adjacent to Pinus radiata

We examined how a mixture of Pinus radiata D. Don and Cupressus lusitanica Mill. influences foliage element concentrations at 20 sites, covering a fertility gradient. Foliage element concentrations of plants at plot boundaries, where the two species grew adjacent to each other, were compared with those of plants at plot centres, where they were surrounded by plants of the same species. For C. lusitanica, plot position significantly affected nitrogen (N), phosphorus (P), and sulphur (S) with concentrations of these elements at the plot boundary exceeding concentrations at the plot centre by 10%–14%. For P. radiata, plants at the plot boundary had a significantly greater P concentration and lower N/P ratio than plants at the centre, but differences between positions were less than that for C. lusitanica (&lt;7%). For C. lusitanica, the difference between foliage concentrations of N and P at the plot boundary and centre significantly declined as the mean plot concentrations of these elements increased. It is likely that C. lusitanica at the boundary benefited from the greater availability of N, P, and S in the root rhizosphere, where they were mobilized from soil organic matter by the ectomycorrhizae of P. radiata. We also suggest that P. radiata at the plot boundary may have benefited from mobilization of P by the endomycorrhizae of C. lusitanica.

Assessing the effects of the clumping phenomenon on BRDF of a maize crop based on 3D numerical scenes using DART model

Inverting radiative transfer (R-T) models against remote sensing observations to retrieve key biogeophysical parameters such as leaf area index (LAI) is a common approach. Even if new inversion techniques allow the use of three-dimensional (3D) models for that purpose, one-dimensional (1D) models are still widely used because of their ease of implementation and computational efficiency. Nevertheless, they assume a random distribution of foliage elements whereas most canopies show a clumped organization. Due to that crude simplification in the representation of the canopy structure, sizeable discrepancies can occur between 1D simulations and real canopy reflectance, which may further lead to false LAI values. The present investigation aims to appraise to which extent the incorporation of a clumping index (noted λ) into 1D R-T model could improve the simulations of Bidirectional Reflectance Distribution Function (BRDF). Canopy BRDF is simulated here for three growth stages of a maize crop with the Discrete Anisotropic Radiative Transfer (DART) model in the visible and near infrared spectral bands, for two contrasted soil types (dark and bright) and different levels of heterogeneity to represent the canopy structure. 3D numerical scenes are based on in-situ structural measurements and associated BRDF simulations are thus considered as references. 1D scenarios assume either that leaves are randomly distributed ( λ = 1) or clumped ( λ < 1). If BRDF simulations seem globally reliable under the assumption of a random distribution in near infrared, it can also lead to relative errors on the total BRDF up to 30% in the red spectral band. It comes out that the use of a clumping index in a 1D reflectance model generally improves BRDF simulations in the red considering a bright soil, which seems relatively independent of LAI. In the near infrared, best results are usually obtained with homogeneous canopies, except with the dark soil. Clearly, influent factors are mainly the LAI and the spectral contrast between soil and leaves.

Leaf area index estimation in mountain even-aged Pinus silvestris L. stands from hemispherical photographs

In this study a stand level approach is proposed for estimating leaf area index (LAI) in even-aged Scots pine stands using gap fraction data derived from hemispherical photographs. The approach includes both the effect of the spatial distribution of the foliage elements as well as the slope of the terrain. Two chronosequences consisting of 11 plots were established in two Scots pine ( Pinus sylvestris L.) forests in the Central Mountain Range of Spain. 12 hemispherical photographs were taken in each plot and variables related to the stage of development, density, relative spacing and site index were calculated. The gap frequency Poisson model was used to estimate the leaf area index. A new function is proposed to assess the effect of the foliage inclination on light transmittance for Scots pine, based on the assumption that the foliage elements show circular horizontal cross-sections. A new model was also developed to restrict the clumping effect on the vertical component in the Poisson model. The effect of the slope on LAI estimates was determined and included in the model. The results indicate that both the clumping effect correction and the slope correction improve the fitting of the Poisson model to the gap frequency experimental curves, and that the function proposed for the inclination angle correction may provide an acceptable approach for some coniferous species. The relationship between the parameters of the gap fraction model (the foliage inclination angle and the clumping coefficient) and stand level variables, that is, the stage of development, density, spacing of the stand and the site index, is analysed.

Correcting non-linearity and slope effects in the estimation of the leaf area index of forests from hemispherical photographs

The leaf area index (LAI) of forest canopies can be estimated indirectly by measuring their light transmission, either with a specific sensor or by hemispherical photographs. The angle at which the transmission is measured enters the calculations at two different points: (1) as angle of incidence determining the travel distance of a light ray through the whole canopy and (2) relatively to the zenith for the statistical distribution of the angle at which the single foliage elements are seen. On a flat ground, any direction is sufficiently described by its zenith angle. On a slope, however, the angle of incidence is not identical to the zenith angle. Each direction in the canopy has thus to be classified according to both angles. We propose here an iterative method to introduce this slope effect into the calculation of LAI (and mean leaf angle) from hemispherical pictures. This method was tested both on artificial pictures simulating ideal canopies and on photographs taken in forests of different LAI, growing on slopes up to 37°. This method was found to give accurate results, while neglecting the effect of the slope would lead to underestimations of LAI, especially in dense canopies. On a flat ground, the proposed method also improves the accuracy of the calculations because it better accounts for the non-linear relationship between light transmission and LAI.

Size‐Dependent Variation in Shoot Light‐Harvesting Efficiency in Shade‐Intolerant Conifers

Shoots and foliage elements of shade‐intolerant conifers strongly vary in size, but the effects of size on shoot light‐harvesting efficiency have not been quantified. We investigated shoot adaptation to seasonal average integrated quantum flux density in gymnosperms Pinus palustris Mill., P. patula Schlect. & Cham., and P. radiata D. Don. and angiosperm Casuarina glauca Sieb. ex Spreng. In addition, P. sylvestris L., sampled from infertile and fertile sites, and P. taeda L. were included to test for general correlations among shoot architecture and size. All studied species possess needle‐like photosynthetic elements. A shoot model was fitted to the data to separate the determinants of shoot light‐harvesting efficiency. The model estimated shoot light harvesting on the basis of angular distribution of foliage surface areas, degree of spatial clumping, foliage area density in shoot volume, and beam path length in shoot volume. Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume, and to a minor degree, to changes in foliage area angular distribution. Greater foliage aggregation resulted in lower efficiency of light harvesting but greater investment of foliar biomass in high light where the photosynthetic returns are greater. The species behave similarly except that the light‐harvesting characteristics of P. patula, which has long, strongly bending needles, were independent of light. In all species, the shoots were larger in higher irradiance, and the fraction of biomass in shoot axis increased with increasing irradiance, indicating greater costs for light harvesting in high light. There were further significant species differences in light‐harvesting efficiency that were linked to differences in foliage and shoot size. Foliage element length varied between 1.1 and 31.4 cm and shoot axis length between 1.2 and 36.5 cm among the species, leading to 4 orders of magnitude variation in shoot cylinder volume and three orders of magnitude variation in foliage area density (ρ); ρ decreased with increasing foliage element length and shoot volume. The degree of foliage clumping scaled positively with ρ and negatively with foliage element length. Foliage clumping was positively associated with foliage dry mass to shoot silhouette area ratio, signifying a trade‐off between efficient light harvesting and large photosynthetic biomass accumulation. These data demonstrate a general increase of light‐harvesting efficiency with increasing length of foliage elements, but they also demonstrate that this increase is limited by enhanced bending of longer foliage elements and by augmented support costs.

Modelling the size-dependent collection efficiency of hedgerows for ambient aerosols

A model for estimating the size-segregated particle collection efficiencies of three hedgerow species of different aerodynamic porosities has been developed and tested in the particle size range 0.5– 20 μ m . Collection efficiency (CE) has been described in terms of the coupled effects of the deviation of the approach flow ( CE flow ) and the filtration through the foliage elements ( CE filtration ) . Variations in barrier porosities with wind speed, which govern both the flow and the particle collection mechanism, have been modelled using an empirical parameter called the “rigidity factor” ( r) for representative leaf-sizes of the three hedge types. Computational fluid dynamics (CFD) allows simulation of velocity fields and turbulence around the barriers, leading to identification of prominent flow separation zones in the wake of denser hedges. Application of different turbulence closure schemes in the CFD model influences the predicted CE only for particles above ( 5 μ m ) . Field validations obtained for a porous (hawthorn) and a denser (yew) hedge indicate that CE filtration ranges between 10 and 35% for “coarse” particles (10– 20 μ m ) and 1–5% for “fine” particles (0.5– 3.5 μ m ), the porous hedge showing higher values in the former case and vice versa in the latter. Model predictions of CE over the particle size range studied for the porous hedge lie within 1–30% and for the denser hedge within 0.4–3%.

Use of Digital Photography for Analysis of Canopy Closure

The relationships between trees and understory crops are very important in agroforestry systems. Also, above ground interactions can be related to canopy structure. However, measurements of canopy structural parameters, either destructive or indirect, are time-consuming or prohibitively expensive. The present work explored the use of digital photography as a simple method to characterise the extent of canopy closure (CC), defined as the area of tree canopies projected onto the horizontal ground surface beneath, and expressed as a percentage of the ground covered. Measurements were made in two Eucalyptus (Eucalyptus nitens, Deane and Maiden) plantations and a subtropical mixed legume woodland dominated by Albizia (Albizia sp), Kidneywood (Eysenhardtia sp.) and Desert Fern (Lysiloma sp.). Images were captured at dawn to minimise light scattering and the number of sunlit foliage elements. Mean CC estimates provided by analysis of images obtained using digital cameras with contrasting performance, a Kodak DC-120 and a Canon EOS D1, were similar in precision and accuracy both between the two cameras and to those provided by a Li-Cor LAI-2000 canopy analyser. Bias between the estimates provided by the Kodak and Canon cameras was –0.02, between the Kodak and LAI-2000 was –0.07 and between the Canon and LAI-2000 was –0.05. Data from a pruning experiment using alder also demonstrated the repeatability of estimates obtained with a photographic method using the Kodak camera. The number of ring sensors within the LAI-2000 used to estimate CC affected agreement between the photographic method and the LAI-2000.