Canopy Geometry Research Articles

Effects of moose Alces alces population density and site productivity on the canopy geometries of birch Betula pubescens and B. pendula and Scots pine Pinus sylvestris

Abstract The instantaneous rate of food intake for mammalian herbivores is controlled by the geometry of plant communities which regulates the encounter rate with bites, bite mass and the processing rate of bites. The geometry of plant canopies is fractal because bite density only occupies a fraction of the entire dimension of the tree canopy and scales allometrically with the search resolution of herbivores. We tested the hypothesis that both the population density of moose Alces alces and site productivity alter the fractal geometry of plant canopies as well as bite mass, and therefore the mechanisms regulating herbivore functional response. Sapling birch Betula pubescens and B. pendula and Scots pine Pinus sylvestris in northern coastal Sweden were sampled in five exclosures that spanned the range of site productivities for the region. Within each exclosure and over four years, the effects of four population densities of moose (0, 10, 30, and 50 moose/1,000 ha) were experimentally simulated within trea...

Study on transient aerodynamic characteristics of parachute opening process

In the research of parachute, canopy inflation process modeling is one of the most complicated tasks. As canopy often experiences the largest deformations and loadings during a very short time, it is of great difficulty for theoretical analysis and experimental measurements. In this paper, aerodynamic equations and structural dynamics equations were developed for describing parachute opening process, and an iterative coupling solving strategy incorporating the above equations was proposed for a small-scale, flexible and flat-circular parachute. Then, analyses were carried out for canopy geometry, time-dependent pressure difference between the inside and outside of the canopy, transient vortex around the canopy and the flow field in the radial plane as a sequence in opening process. The mechanism of the canopy shape development was explained from perspective of transient flow fields during the inflation process. Experiments of the parachute opening process were conducted in a wind tunnel, in which instantaneous shape of the canopy was measured by high velocity camera and the opening loading was measured by dynamometer balance. The theoretical predictions were found in good agreement with the experimental results, validating the proposed approach. This numerical method can improve the situation of strong dependence of parachute research on wind tunnel tests, and is of significance to the understanding of the mechanics of parachute inflation process.

Regional climate modulates the canopy mosaic of favourable and risky microclimates for insects

1. One major gap in our ability to predict the impacts of climate change is a quantitative analysis of temperatures experienced by organisms under natural conditions. We developed a framework to describe and quantify the impacts of local climate on the mosaic of microclimates and physiological states of insects within tree canopies. This approach was applied to a leaf mining moth feeding on apple leaf tissues. 2. Canopy geometry was explicitly considered by mapping the 3D position and orientation of more than 26 000 leaves in an apple tree. Four published models for canopy radiation interception, energy budget of leaves and mines, body temperature and developmental rate of the leaf miner were integrated. Model predictions were compared with actual microclimate temperatures. The biophysical model accurately predicted temperature within mines at different positions within the tree crown. 3. Field temperature measurements indicated that leaf and mine temperature patterns differ according to the regional climatic conditions (cloudy or sunny) and depending on their location within the canopy. Mines in the sun can be warmer than those in the shade by several degrees and the heterogeneity of mine temperature was incremented by 120%, compared with that of leaf temperature. 4. The integrated model was used to explore the impact of both warm and exceptionally hot climatic conditions recorded during a heat wave on the microclimate heterogeneity at canopy scale. During warm conditions, larvae in sunlight-exposed mines experienced nearly optimal growth conditions compared with those within shaded mines. The developmental rate was increased by almost 50% in the sunny microhabitat compared with the shaded location. Larvae, however, experienced optimal temperatures for their development inside shaded mines during extreme climatic conditions, whereas larvae in exposed mines were overheating, leading to major risks of mortality. 5. Tree canopies act as both magnifiers and reducers of the climatic regime experienced in open air outside canopies. Favourable and risky spots within the canopy do change as a function of the climatic conditions at the regional scale. The shifting nature of the mosaic of suitable and risky habitats may explain the observed uniform distribution of leaf miners within tree canopies.

Geometric Properties of Parachutes Using 3-D Laser Scanning

The technology of gliding parafoils is currently being pursued by the U.S. Army for precision airdrop of cargos and personnel. The performance of parafoils (lift and drag) and round parachutes (drag) is closely related to their 3-D geometry. There have been some studies on the geometry of round parachutes, but hardly any on parafoils. The technology of 3-D whole body scanning provides a viable tool to investigate the 3-D geometry of parachutes. In this paper, we present an investigation on the 3-D geometry, surface area and volume of small-scale models of parafoil, round parachute, ring-slot parachute, and cross parachute using a 3-D laser scanning apparatus. Scan data from these model parachutes were obtained in a climatic chamber with a steady air velocity. Surface areas and volumes of these parachutes were calculated from the scan data using specially developed mathematical methods. In addition, cross sections of the parachute canopies were obtained from the scan images. These cross sections provide valuable information on the relationship between model parachutes and full-scale parachutes, fabric properties on canopy geometry, and parachute canopy design and manufacturing.

Leaf functional traits of tropical forest plants in relation to growth form

Summary 1We tested the generality of global leaf trait relationships among 44 tropical plant species from a broad array of growth forms (trees, lianas and understorey plants) in lowland Panama to determine how leaf trait relationships vary with whole-plant morphology within one site. 2We observed significant variation among growth forms for seven out of 10 leaf traits. Variation in leaf traits among growth forms was more pronounced per area than per mass. Thirteen bivariate leaf trait relationships that describe how plants allocate resources to photosynthesis were significant across all species. Growth forms showed distinct slopes, intercepts or shifts in the common slope for 12 of the 13 relationships. 3Trait relationships within trees and lianas showed good agreement with a global leaf trait data set. However, for understorey plants, trait relationships that included specific leaf area (SLA) deviated from the global data set, suggesting that understorey leaf-allocation patterns optimize SLA, and hence growth. 4Lianas showed lower values and rates of gas exchange than trees, and longer leaf life span for a given SLA, illustrating variation in leaf traits associated with growth form and canopy geometry. 5Functional variation in allocation to photosynthetic capacity among tropical forest species is related to microhabitat variations in light availability and whole-plant morphology among growth forms.

3D ORCHARD CANOPY ARCHITECTURAL MODELLING FOR USE IN AIRFLOW AND DRIFT PREDICTIONS

The current trend in studying the interaction of vegetation canopies with their environment and numerical prediction of drift is mainly based on porous media approaches. The methods involve several approximations and estimations that give the global effect of the canopies to airflow and drift without investigating the detailed local effects of the vegetation elements. These approaches also require precise estimation of certain parameters such as drag coefficient and leaf area density. To make some advances in the field and to address some of the above problems a new approach needed to be developed, where real canopy architecture was modelled and linked to a computational Fluid Dynamics (CFD) software to model airflow through the canopies. This helped to investigate the real effects of the vegetation elements on atmospheric airflow which directly affects drift and drift prediction. In this work, 3D orchard canopy architecture was modelled using a combined discrete-continuous plant growth simulation model, which considered the phenomenological plant growing behaviour and the effect of temperature. Two canopy geometries were introduced into a fluid domain and the domain was meshed. Airflow around and through the canopy was simulated using the Reynolds-averaged Navier-Stokes (RANS) equations and k-H turbulence model. The airflow simulation results agreed both qualitatively with wind tunnel validation experiment and quantitatively with previous works done in the area, ensuring the prospect of the architectural modelling for further application. It was also possible to show the detailed effects of canopy elements on airflow.

Experimental Investigation of Three Rotating Parachutes

INCE they were first invented, parachutes have been widely used to lower men and goods to the ground safely, and to decelerate aircraft, race cars, etc. Although new types of parachutes were designed, this mission remained the same for years. During the last decades, new tasks began to be given to parachutes. These tasks are related to controlling the trajectories of their payloads and following complex flight patterns to carry out defined flight requirements. Today, rotating parachutes are a means of introducing dynamic maneuvers to their payloads to follow a predefined flight path and/or traces on the ground. In the design of a rotating parachute-payload system, the appropriate parachute system can be found by studying the aerodynamic properties of rotating parachutes in wind tunnels. While different types of parachutes are designed and studied in a windtunnel[1],thesameparachutecanalsobetestedbychangingits geometrical parameters such as suspension line length and staggering distance [2–6]. Inthisexperimentalstudy,threerotatingparachutesweretestedin a wind tunnel. Each canopy had the same surface area but had a different shape. The affects of the canopy geometry and the physical parameters (suspension line length and staggering distance) on the tangential force coefficient and the spin rate were studied [7]. Because the same size cross canopies and the same canopy fabric materialwereused,thespinrateandtheforcecoefficientresultswere compared with the corresponding results of the experimental studies found in the literature. During the tests, the oscillations of the configurations constructed from their symmetry axes were also observed, and different dynamic behaviors were classified.

The Structure of the Shear Layer in Flows over Rigid and Flexible Canopies

Flume experiments were conducted with rigid and flexible model vegetation to study the structure of coherent vortices (a manifestation of the Kelvin–Helmholtz instability) and vertical transport in shallow vegetated shear flows. The vortex street in a vegetated shear layer creates a pronounced oscillation in the velocity profile, with the velocity near the top of a model canopy varying by a factor of three during vortex passage. In turn, this velocity oscillation drives the coherent waving of flexible canopies. Relative to flows over rigid vegetation, the oscillation in canopy geometry has the effect of decreasing the amount of turbulent vertical momentum transport in the shear layer. Using a waving plant to determine phase in the vortex cycle, each vortex is shown to consist of a strong sweep at its front (during which the canopy is most deflected), followed by a weak ejection at its rear (when the canopy height is at a maximum). Whereas in unobstructed mixing layers the vortices span the entire layer, they encompass only 70% of the flexibly obstructed shear layer studied here.

Genetic and Environmental Effects on Water Use Efficiency in Peach

Two unpruned narrow-leaf and two unpruned standard-leaf peach [Prunus persica (L.) Batsch.] selections were evaluated for physiological components related to water use efficiency {WUE [carbon assimilation (A) per unit of transpiration (T)]}. The purpose of the study was to assess the value of narrow-leaf phenotypes to improve WUE in peach and separate the environmental component of canopy geometry from the genetic components. The narrow-leaf characteristic itself did not confer improved WUE. The interception of light was a key determinant of WUE in these genotypes. Internal shading of the tree by excessive leaf area reduced daily WUE measured in gas exchange studies. Canopies that intercepted more than 75% of the photosynthetically active radiation (PAR) had reduced daily WUE. Dormant season pruning of the four genotypes lowered isotopic carbon discrimination and therefore increased seasonal WUE compared to unpruned trees. None of the genotypes had a significant correlation of seasonal WUE with leaf and fruit weight. Analysis of covariance indicated that `Bounty' and both narrow-leaf genotypes had greater leaf and fruit weight than `Redhaven' for a given level of PAR interception. `Bounty' had the least internal canopy shading of the four genotypes. Genetic differences in peach growth types can be selected for factors increasing WUE as well as increased productivity. Future work in peach breeding to improve WUE and productivity must take into consideration light interception, productivity, and WUE in an integrated manner to make real progress in the efficient use of water and light in the orchard environment.

Oscillatory flow through submerged canopies: 1. Velocity structure

Many benthic organisms form very rough surfaces on the seafloor that can be described as submerged canopies. Recent evidence has shown that, compared with a unidirectional current, an oscillatory flow driven by surface waves can significantly enhance biological processes such as nutrient uptake. However, to date, the physical mechanisms responsible for this enhancement have not been established. This paper presents a theoretical model to estimate flow inside a submerged canopy driven by oscillatory flow. To reduce the complexity of natural canopies, an idealized canopy consisting of an array of vertical cylinders is used. The attenuation of the in‐canopy oscillatory flow is shown to be governed by three dimensionless parameters defined on the basis of canopy geometry and flow parameters. The model predicts that an oscillatory flow will always generate a higher in‐canopy flow when compared to a unidirectional current of the same magnitude, and specifically that the attenuation will monotonically increase as the wave orbital excursion length is increased. A series of laboratory experiments are conducted for a range of different unidirectional and oscillatory flow conditions, and the results confirm that oscillatory flow increases water motion inside a canopy. It is hypothesized that this higher in‐canopy flow will enhance rates of mass transfer from the canopy elements, a problem formally investigated in a companion paper (Lowe et al., 2005b).

Measurement of canopy geometry characteristics using LiDAR laser altimetry: a feasibility study

Airborne scanning laser altimetry offers the potential for extracting high-resolution vegetation structure characteristics for monitoring and modeling the land surface. A unique dataset is used to study the sensitivity of laser interception profiles and laser-derived leaf area index (LAI) to assumptions about the surface structure and the measurement process. To simulate laser interception, one- and three-dimensional (3-D) vegetation structure models have been developed for maize and sunflower crops. Over sunflowers, a simple regression technique has been developed to extract laser-derived LAI, which accounts for measurement and model biases. Over maize, a 3-D structure/interception model that accounts for the effects of the laser inclination angle and detection threshold has enabled the fraction of radiation reaching the ground surface to be modelled to within 0.5% of the observed fraction. Good agreement was found between modelled and measured profiles of laser interception with a vertical resolution of 10 cm.

Effect of 3D nitrogen, dry mass per area and local irradiance on canopy photosynthesis within leaves of contrasted heterogeneous maize crops.

Nitrogen partitioning within stands has been described fairly comprehensively, especially for C(3) plants in dense stands where the horizontal heterogeneity of foliage distribution is relatively small. Nitrogen has been shown to be distributed vertically and in parallel to light, maximizing carbon assimilation and stand productivity. Conversely, row crops such as maize (C(4) plants) are characterized by strong horizontal heterogeneity of foliage distribution, and a three-dimensional (3D) approach is required to investigate the combined effect of spatial distribution of nitrogen and light on canopy photosynthesis. The 3D geometry of maize canopies was modelled with varying densities and at different developmental stages using plant digitizing under field conditions. For lamina parts, photosynthesis was measured and nitrogen content per unit area (N(a)) was described from analysis of nitrogen content per unit mass (N(m)) and dry mass per unit area (M(a)). Hyperbolic relationships between photosynthesis at irradiance saturation (P(max)) and N(a) were established as well as a linear relationship between dark respiration (R(d)) and N(a), whereas quantum efficiency (alpha) was found to be independent of N(a). N(m), M(a) and N(a) were shown to change over time vertically (i.e. between laminae), which has been largely reported previously, and horizontally (i.e. within laminae), which has scarcely been described previously. Even if M(a) played a major role in N(a), a strong relationship between N(a) and M(a) could not be demonstrated, whereas several previous studies have found that N(a) was essentially related to M(a) rather than N(m). From simulations of radiative exchange using a 3D volume-based approach and lamina photosynthesis using a hyperbola, it was shown that real patterns of N(a) partitioning could increase daily crop photosynthesis by up to 8 % compared with uniform patterns of N(a), especially for the earliest stages of stand development.

Measurements of net radiation absorbed by isolated acid lime trees (Citrus latifolia Tanaka)

SummaryBy using net radiometers mounted on a circular frame rotating around the canopy, measurements of total all-wave radiation absorbed by two ‘Tahiti’ acid lime trees were carried out in an orchard in Piracicaba, São Paulo State, Brazil. The rotating system around the canopy of a tree was formerly idealized and used in New Zealand, allowing integration of all-wave radiation and photosynthetically active radiation absorbed. In an experiment in December 1997, a first device using six net radiometers mounted on a light frame was used. A bigger device, more like the one used in New Zealand, in terms of the number of radiometers and the frame, with a different torque system, was used in another tree on some days from July to September 2000. The performance of both devices is discussed, including the possible error sources when using the first model (1997) and the problems of torque transmission on the second. Despite the lack of a test to check the performance of the device and the problems presented in the year 2000, the results confirm the possibility of providing reliable measurements of the net radiation absorbed by isolated trees. Relations of the net radiation per unit area of projected canopy on the ground were determined with integrated values over different time scales (from 15 min to 24 h). Unique relations between net radiation and incoming solar radiation were obtained for both trees over several time scales. These relations are applicable only to high leaf density conditions and canopy geometry similar to the used in this study.

Imaging spectroscopy for early detection of nitrogen deficiency in grass swards

The potential of an experimental imaging spectroscopy system with high spatial (0.16–0.28 mm 2) and spectral resolution (5–13 nm) was explored for early detection of nitrogen (N) stress. From June through October 2000, a greenhouse experiment was conducted with 15 Lolium perenne L. mini-swards and 5 N treatments. Images were recorded twice a week. With the experimental system, spectra of grass leaves in the canopy can be obtained. Treatment effects on ground cover (GC) and changes in leaf spectral characteristics were studied separately. Leaf pixels with similar reflection intensity were grouped in intensity classes (IC). An index of reflection intensity (IRI) indicates the percentages of strongly reflecting grass pixels. Blue edge, green edge and red edge positions were calculated for each IC. Both GC and IRI increased until harvest, with largest increases for liberal N treatments. The width of the chlorophyll-dominated absorption band around 680 nm (CAW) increased up to a maximum of 133 nm for both liberal and limited N in the first two weeks after harvesting. CAW decreased for limited N in the second half of the growth period in contrast to liberal N. At harvest CAW explained 95% of the variation in relative dry matter (DM) yield between treatments. Principal component analyses showed an intertwined response of the principal components to both DM yield and N content. Edge positions changed strongly with IC. Possible effects of sensor characteristics, canopy geometry, leaf angle and changes in leaf characteristics with canopy position on the observed relation between IC and edge position are discussed.

Forest dynamics in unexploited birch ( Betula pendula) stands in the Vosges (France): structure, architecture and light patterns

Two adjacent forest stands composed of birch ( Betula pendula) and beech ( Fagus sylvatica) in the Vosges (France), aged 15 and 50 years, respectively, and representing a possible chronosequence of 35 years of forest evolution, have been studied. The objectives of the research were to compare structural and architectural changes at the level of tree population and forest ecosystem. In each forest stand, a profile of 2500 m 2 was carried out in which trees and juveniles were measured and mapped, as well as dead woody debris. Forest architecture was represented by crown projection and vertical drawings. In addition, we have drawn some typical birch and beech morphologies observed in the two plots and interpreted them on the basis of their social status: tree of the present, potential tree, suppressed tree, tree of the past. These concepts have been developed by the architectural model of [Oldeman, R.A.A., 1990. Forests: Elements of Silvology. Springer, Berlin]. Changes in canopy geometry (canopy openness, LAI), and light pattern (PPFD; R:IR) were examined with the help of hemispherical photographs and analysed by two computer programs (Gap Light Analyser, GLA and Winphot). The study of this temperate succession shows that there is a functional link between structure, tree architecture, forest architecture, light pattern and succession. Analysis of birch architecture during succession reveals a remarkable variety of architectural developments that are related to the strong infraspecific competition during site colonisation. The architecture of beech depends on the forest environment created by the birch. Beech is a very flexible species, which may grow in light as well as in alternating conditions of light and shade. In birch forest, the good light availability explains its architectural traits where growth is close to the open. Because such good light conditions are constant during the whole development phase of the birch eco-unit, beech growth does not pass through alternating periods of suppression and released growth as observed under beech canopy. Forest architecture and structure change significantly during succession, with a decrease in birch density and a global increase in tree dimensions for the birch and the understorey beech. Juveniles are more numerous among the dense herb coverage. Like young beeches, other tree species (mainly Sorbus aria and Quercus petraea) appreciate the light pattern created by birch canopy, with both good light availability and protection against wind and drought. After 50 years of dominance, the birch begins to die, creating big gaps in the canopy which favour beech growth and a rich herbaceous coverage. We predict that after 80 years, the canopy will be dominated by beeches with very broad crowns under which juveniles will grow with periods of suppression.

Pesticide Spraying in Indian River Grapefruit: II. Overview of Factors Influencing Spray Efficacy and Off-target Deposition

Foliar application of spray materials is an integral component of commercial citrus production. An intensive assessment of spray application practices has been stimulated by low fruit value and increased concern about potential surface water contamination in the Indian River citrus region of Florida. Many publications report research results regarding distribution of spray materials within orchards and off-target deposition, but interpretation is challenging because so many factors influence spray results, and integrating this information into practical recommendations is difficult. Canopy geometry and density are prominent factors contributing to variable deposition and spray drift. Environmental factors such as temperature, relative humidity, wind speed, and wind direction also greatly influence spray deposition and drift, and substantial changes can occur within seconds. In addition the physical and/or mechanical set up of the sprayer interact significantly with the other factors. A better understanding of these interactions should help growers optimize spray effectiveness and efficiency while reducing potential off-target effects.

Evaluation of a digital echo sounder system for detection of submersed aquatic vegetation

A technique is presented for rapid detection of submersed aquatic vegetation (SAV) using a high-frequency, high-resolution digital echo sounder linked with global positioning system equipment. The acoustic reflectivity of SAV allows for detection and explicit meaqsurement of canopy geometry using a digital signal processing algorithm described here. Comparing output data from this system with physical measurements shows good detection and measurement performance over a wide range of conditions for freshwater tape grass (Vallisneria americana) and seagrasses (Thalassia testudinum, Halodule wrightii, andSyringodium filiforme) in a sandy-bottom, south Florida estuary. The range of environmental conditions for which the system can be used is defined. Based on these measured performance data and a review of existing literature, this system appears to fill a gap in the inventory of established methods for measuring the distribution and abundance of submersed macrophytes.

Characterizing leaf geometry for grass and crop canopies from hotspot observations: A simulation study

The potential of canopy reflectance distributions in the hotspot region for characterizing leaf geometry (leaf size and shape) of grass and crop canopies is explored with computer simulations. In this article, a computer graphics method—Lindenmayer-systems (L-systems)—is used to render a series of leaf (grass) and architecturally realistic row-planted crop (corn-like) canopies that have a variety of geometrical structures. A radiosity–graphics combined model is then employed to calculate the radiation regime in a canopy, including canopy directional reflectance. An effectiveness ratio ( E ratio) is proposed, which is able to evaluate the performance of a given measure or index in estimation of the parameter of interest under the influence of a number of “noise” factors (other geometric and optical parameters of the canopy) at various noise levels. This E ratio is then applied to evaluate reflectance and normalized reflectance in the hotspot region for leaf geometry characterization. The result from simulated hotspot reflectance demonstrates that for both canopies, leaf geometry is estimable by using normalized reflectance within ±4–8° (or ±2–4°) around the hotspot direction in the principal cone (or principal plane). However, the center position and angular width of the optimal sampling region are affected by the number of noise factors [such as leaf area index, leaf angle distribution for leaf canopies, plus row structure for row-plant crop canopies] and their variation ranges. In most cases, normalized spectral reflectance in the near-infrared at a high solar zenith angle in the PC produces the most reliable results. The reason for better estimation of leaf geometry for grass and crop canopies than forests from hotspot observations is also discussed in this article.

Thermal infrared hot spot and dependence on canopy geometry

We perform theoretical calculations of the canopy thermal infrared (TIR) hot spot using a first principles 3-D model described earlier. Various theoretical canopies of varying leaf size and for differing canopy height are used to illustrate the magnitude of the TIR effect. Our results are similar to predicted behavior in the reflective hot spot as a function of canopy geometry and comparable to TIR measurements from the literature and our own simple ground experiments. We apply the MODTRAN atmospheric code to estimate the at-sensor variation in brightness temperature with view direction in the solar principal plane. For simple homogeneous canopies, we predict canopy thermal infrared hot spot variations of 2 degrees C at the surface with respect to nadir viewing. Dependence on leaf size is weak as long as the ratio of leaf size to canopy height is maintained. However, the angular width of the hot spot increases as the ratio of leaf diameter to canopy height increases. Atmospheric effects minimize but do not eliminate the TIR hot spot at satellite altitudes.

Leaf area distribution and radiative transfer in open-canopy forests: implications for mass and energy exchange.

Leaf area and its spatial distribution are key canopy parameters needed to model the radiation regime within a forest and to compute the mass and energy exchange between a forest and the atmosphere. A much larger proportion of available net radiation is received at the forest floor in open-canopy forests than in closed-canopy forests. The proportion of ecosystem water vapor exchange (lambda E) and sensible heat exchange from the forest floor is therefore expected to be larger in open-canopy forests than in closed-canopy forests. We used a combination of optical and canopy geometry measurements, and robust one- and three-dimensional models to evaluate the influence of canopy architecture and radiative transfer on estimates of carbon, water and energy exchange of a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest. Three-dimensional model simulations showed that the average probability of diffuse and direct radiation transmittance to the forest floor was greater than if a random distribution of foliage had been assumed. Direct and diffuse radiation transmittance to the forest floor was 28 and 39%, respectively, in the three-dimensional model simulations versus 23 and 31%, respectively, in the one-dimensional model simulations. The assumption of randomly distributed foliage versus inclusion of clumping factors in a one-dimensional, multi-layer biosphere-atmosphere gas exchange model (CANVEG) had the greatest effect on simulated annual net ecosystem exchange (NEE) and soil evaporation. Assuming random distribution, NEE was 41% lower, net photosynthesis 3% lower, total lambda E 10% lower, and soil evaporation 40% lower. The same comparisons at LAI 5 showed a similar effect on annual NEE estimates (37%) and lambda E (12%), but a much larger effect on net photosynthesis (20%), suggesting that, at low LAI, canopies are mostly sunlit, so that redistribution of light has little effect on net photosynthesis, whereas the effect on net photosynthesis is much greater at high LAIs.