Foliage randomness and light interception in 3-D digitized trees: an analysis from multiscale discretization of the canopy

Light models for vegetation canopies based on the turbid medium analogy are usually limited by the basic assumption of random foliage dispersion in the canopy space. The objective of this paper was to assess the effect of three possible sources of non-randomness in tree canopies on light interception properties. For this purpose, four three-dimensional (3-D) digitized trees and four theoretical canopies – one random and three built from fractal rules – were used to compute canopy structure parameters and light interception, namely the sky-vault averaged STAR (Silhouette to Total Area Ratio). STAR values were computed from (1) images of the 3-D plants, and (2) from a 3-D turbid medium model using space discretization at different scales. For all trees, departure from randomness was mainly due to the spatial variations in leaf area density within the canopy volume. Indeed STAR estimations, based on turbid medium assumption, using the finest space discretization were very close to STAR values computed from the plant images. At this finest scale, foliage dispersion was slightly clumped, except one theoretical fractal canopy, which showed a marked regular dispersion. Taking into account a non-infinitely small leaf size, whose effect is theoretically to shorten self-shading, had a minor effect on STAR computations. STAR values computed from the 3-D turbid medium were very sensitive to plant lacunarity, a parameter introduced in the context of fractal studies to characterize the distribution of gaps in porous media at different scales. This study shows that 3-D turbid medium models based on space discretization are able to give correct estimation of light interception by 3-D isolated trees, provided that the 3-D grid is properly defined, that is, discretization maximizes plant lacunarity.     

Light interception efficiency explained by two simple variables: a test using a diversity of small- to medium-sized woody plants

? Plant light interception efficiency is a crucial determinant of carbon uptake by individual plants and by vegetation. Our aim was to identify whole-plant variables that summarize complex crown architecture, which can be used to predict light interception efficiency. ? We gathered the largest database of digitized plants to date (1831 plants of 124 species), and estimated a measure of light interception efficiency with a detailed three-dimensional model. Light interception efficiency was defined as the ratio of the hemispherically averaged displayed to total leaf area. A simple model was developed that uses only two variables, crown density (the ratio of leaf area to total crown surface area) and leaf dispersion (a measure of the degree of aggregation of leaves). ? The model explained 85% of variation in the observed light interception efficiency across the digitized plants. Both whole-plant variables varied across species, with differences in leaf dispersion related to leaf size. Within species, light interception efficiency decreased with total leaf number. This was a result of changes in leaf dispersion, while crown density remained constant. ? These results provide the basis for a more general understanding of the role of plant architecture in determining the efficiency of light harvesting.     

Above-ground biomass investments and light interception of tropical forest trees and lianas early in succession

BACKGROUND AND AIMS: Crown structure and above-ground biomass investment was studied in relation to light interception of trees and lianas growing in a 6-month-old regenerating forest. METHODS: The vertical distribution of total above-ground biomass, height, diameter, stem density, leaf angles and crown depth were measured for individual plants of three short-lived pioneers (SLPs), four long-lived pioneers (LLPs) and three lianas. Daily light interception per individual Phi(d) was calculated with a canopy model. The model was then used to estimate light interception per unit of leaf mass (Phi(leaf mass)), total above-ground mass (Phi(mass)) and crown structure efficiency (E(a), the ratio of absorbed vs. available light). KEY RESULTS: The SLPs Trema and Ochroma intercepted higher amounts of light per unit leaf mass (Phi(leaf mass)) because they had shallower crowns, resulting in higher crown use efficiency (E(a)) than the other species. These SLPs (but not Cecropia) were also taller and intercepted more light per unit leaf area (Phi(area)). LLPs and lianas had considerably higher amounts of leaf mass and area per unit above-ground mass (LMR and LAR, respectively) and thus attained Phi(mass) values similar to the SLPs (Phi(mass)=Phi(area)xLAR). Lianas, which were mostly self-supporting, had light interception efficiencies similar to those of the trees. CONCLUSIONS: These results show how, due to the trade-off between crown structure and biomass allocation, SLPs, and LLPs and lianas intercept similar amount of light per unit mass which may contribute to the ability of the latter two groups to persist.     

Structural and physiological sexual dimorphism estimated from three‐dimensional virtual trees of yerba‐mate (Ilex paraguariensis) is modified by cultivation environment

Yerba‐mate is a subtropical, evergreen, dioecious, South American tree. Sexual dimorphism in photosynthesis, leaf allometry and foliage distribution was hypothesised. Virtual trees (constructed in VPlants software from detailed measurements of plant morphogenesis) of the two genders were compared considering two contrasted cultivation environments and three developmental stages. The total crown volume, leaf area per plant (LA), leaf area index (LAI) and leaf area density (LAD) were calculated. The light interception and photosynthesis were computed from mock‐ups in VegeSTAR. Structural sexual dimorphism concerned general plant form, internode length, leaf allometry, leaf surface, pattern of leaf area distribution and LAD. Cultivation environment and developmental stage acted strongly on sex expression of all observed structural parameters and physiological stages. Sexual differentiation in LA and light interception was related to leaves positioned in the lowest layers (150 cm above ground), whereas sexual specialisation in leaf and plant photosynthesis was related to early vegetative and reproductive stages. Several sexual responses strongly depended on the environment, especially light conditions, with opposite effects observed on female and male plants whether they were cultivated in monoculture or in forest understorey, under high‐light condition or low‐light condition, respectively. Optimised foliage structure and physiology in females may compensate for greater reproductive costs in early developmental stages, but females and males equalise in photosynthetic efficiency after 2‐year regrowth.     

The expression of light-related leaf functional traits depends on the location of individual leaves within the crown of isolated Olea europaea trees

Background The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale.Methods We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day.Key Results All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the sun’s trajectory.Conclusions The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals.     

Light capture efficiency decreases with increasing tree age and size in the southern hemisphere gymnosperm Agathis australis

We investigated leaf and shoot architecture in relation to growth irradiance (Q_int) in young and mature trees of a New Zealand native gymnosperm Agathis australis (D. Don) Lindl. to determine tree size-dependent and age-dependent controls on light interception efficiency. A binomial 3-D turbid medium model was constructed to distinguish between differences in shoot light interception efficiency due to variations in leaf area density, angular distribution and leaf aggregation. Because of the positive effect of light on leaf dry mass per area (M_A), nitrogen content per area (N_A) increased with increasing irradiance in both young and mature trees. At a common irradiance, N_A, M_A and the components of M_A, density and thickness, were larger in mature trees, indicating a greater accumulation of photosynthetic biomass per unit area, but also a larger fraction of support biomass in older trees. In both young and mature trees, shoot inclination angle relative to horizontal, and leaf number per unit stem length decreased, and silhouette to total leaf area ratio (S_S) increased with decreasing irradiance, demonstrating more efficient light harvesting in low light. The shoots of young trees were more horizontal and less densely leafed with a larger S_S than those of mature trees, signifying greater light interception efficiency in young plants. Superior light harvesting in young trees resulted from more planar leaf arrangement and less clumped foliage. These results suggest that the age-dependent and/or size-dependent decreases in stand productivity may partly result from reduced light interception efficiency in larger mature relative to smaller and younger plants.     

Plant growth-form alters the relationship between foliar morphology and species shade-tolerance ranking in temperate woody taxa

Variation in leaf size (area per leaf) and leaf dry weight per area (LWA) in relation to species shade- and drought-tolerance, characterised by Ellenberg's light (ELD) and water demand (EWD) values, respectively, were examined in 60 temperate woody taxa at constant relative irradiance. LWA was independent of plant size, but leaf size increased with total plant height at constant ELD. Canopy position also affected leaf morphology: leaves from the upper crown third had higher LWA and were larger than leaves from the lower third. Leaf size and LWA were negatively correlated, and leaf size decreased and LWA increased with decreasing species shade-tolerance. Mean LWA was similar for trees and shrubs, but trees had larger leaves than shrubs. Furthermore, all relationships were altered by plant growth-form: none of the qualitative tendencies was significant for trees. This implies the considerably lower plasticity of foliar parameters in trees than those in shrubs. Accordingly, shade-tolerance of trees, having relatively constant leaf structure, may be most affected by the variability in biomass partitioning and crown geometry which influence foliage distribution and spacing and finally determine canopy light absorptance. Alteration of leaf form and investment pattern for construction of unit foliar surface area which change the efficiency of light interception per unit biomass investment in leaves, is a competitive strategy inherent to shrubs. EWD as well as wood anatomy did not control LWA and leaf size, though there was a trend of ring-porous tree species to be more shade-tolerant than diffuse-porous trees. Since ring-porous species are more vulnerable to cavitation than diffuse-porous species, they may be constrained to environments where irradiances and consequently evaporative demand is lower.     

Variation in crown light utilization characteristics among tropical canopy trees

BACKGROUND AND AIMS: Light extinction through crowns of canopy trees determines light availability at lower levels within forests. The goal of this paper is the exploration of foliage distribution and light extinction in crowns of five canopy tree species in relation to their shoot architecture, leaf traits (mean leaf angle, life span, photosynthetic characteristics) and successional status (from pioneers to persistent). METHODS: Light extinction was examined at three hierarchical levels of foliage organization, the whole crown, the outermost canopy and the individual shoots, in a tropical moist forest with direct canopy access with a tower crane. Photon flux density and cumulative leaf area index (LAI) were measured at intervals of 0.25-1 m along multiple vertical transects through three to five mature tree crowns of each species to estimate light extinction coefficients (K). RESULTS: Cecropia longipes, a pioneer species with the shortest leaf life span, had crown LAI <0.5. Among the remaining four species, crown LAI ranged from 2 to 8, and species with orthotropic terminal shoots exhibited lower light extinction coefficients (0.35) than those with plagiotropic shoots (0.53-0.80). Within each type, later successional species exhibited greater maximum LAI and total light extinction. A dense layer of leaves at the outermost crown of a late successional species resulted in an average light extinction of 61% within 0.5 m from the surface. In late successional species, leaf position within individual shoots does not predict the light availability at the individual leaf surface, which may explain their slow decline of photosynthetic capacity with leaf age and weak differentiation of sun and shade leaves. CONCLUSION: Later-successional tree crowns, especially those with orthotropic branches, exhibit lower light extinction coefficients, but greater total LAI and total light extinction, which contribute to their efficient use of light and competitive dominance.     

Growth and crown efficiency of height repressed lodgepole pine; are suppressed trees more efficient?

Leaf area, crown projection area and growth over the last 5 years were measured to assess growth efficiency (GE) and crown efficiency (CE) of dominant (D), codominant (CD) and suppressed (SP) trees growing in height-repressed (P sites) and normally developing (M sites) lodgepole pine stands. Leaf area index (LAI), hydraulic characteristics, and needle nutrient concentrations were also measured. Volume growth of P site trees between 1994 and 1999 was 46% that of M site trees. Volume growth was closely associated with both hydraulic supply capacity (Q*) and leaf area. Height repression was not associated with lower GE, but P site trees had CE that was 24.5% lower than M site trees. Average GE of D and CD trees was 28% lower than that of SP trees, while mean CE for the D trees was 46% greater than that of CD, and 80% greater than for SP trees. Between M and P sites, canopy LAI and Q* per unit leaf area did not differ. Needle nitrogen (N) concentrations of M site trees were 7.6% greater than for P site trees. SP tree needles had the highest concentration of N and phosphorus. The nutrient advantage enjoyed by SP trees presumably allowed them to maintain higher GE for a given Q*/A_l. The fastest growing trees were the large D and CD trees from M sites. As LAI did not differ between sites, height repression on P sites may be a result of total leaf area being distributed among too many small trees.     

The effect of two growth forms of Norway spruce on stand development and radiation interception: a model analysis

Summary Development of tree and canopy structure, and interception of photosynthetically active radiation (PAR) were studied in two model stands of Norway spruce consisting of trees with rapid versus slow site capture. The tree models were derived using Burger's (1953) sample tree material, from which two subpopulations of dominant trees were selected using the rate of horizontal site capture of the tree crowns as the criterion of division. The development of stand structure and interception of PAR were simulated in the two model canopies. The simulation period covered the period from tree age 15–80 years. The average development of the trees in the two subpopulations proved to be very different. The rapidly expanding trees were characterized by low mean within-crown needle area density and a long crown. The slowly expanding trees were smaller but had a higher mean within-crown needle area density. Up to approximately 40 years of age the stand of rapidly expanding trees contained more leaf area and intercepted more radiation than the stand of slowly expanding trees, when canopy cover was held constant. After 40 years of age this relationship was reversed due to the subsequent decline of leaf area in the stand of rapidly expanding trees and the increase in leaf area in the stand of slowly expanding trees. The biological relevancy and silvicultural implications of the simulated patterns of tree and stand development are discussed.     

不同密度红桦幼苗苗冠结构与竞争对CO2浓度升高的响应

研究了两个种植密度下,红桦（Betula albosinensis）苗冠结构特征对CO2浓度的响应,在此基础上探讨了CO2浓度升高对植物竞争压力的影响。结果表明,冠幅、冠高、苗冠表面积和苗冠体积均受CO2浓度升高的影响而增加,但是受密度增加的影响而降低。CO2浓度升高对苗冠的促进效应在低密度条件下大于高密度处理,高密度条件下苗冠基本特征部分地受到CO2浓度升高的促进作用;升高种植密度的效应则在高CO2浓度条件下大于现行CO2浓度处理。高CO2浓度和高密度条件下,LDcpa（单位苗冠投影面积叶片数）、LDcv（单位苗冠体积叶片数）和苗冠底部枝条的枝角均低于相应的现行CO2浓度处理和低密度处理,这主要是由于冠幅和冠高的快速生长所造成的。升高CO2浓度对枝条长度的影响与枝条在主茎上所处位置有关。总之,升高CO2浓度有利于降低增加种植密度对苗冠所带来的负效应,而增加种植密度降低了升高CO2浓度的正效应。LDcpa和LDcv的降低表明,红桦在升高CO2浓度和种植密度的条件下,会作出积极的响应,从而缓解由于生长的增加所带来的竞争压力的增加。     

Drought alters the canopy architecture and micro-climate of Hevea brasiliensis trees

 In this study a comparison of the canopy architecture and the growth and distribution of roots was made in 10-year-old trees of Hevea brasiliensis grown in a severely drought-prone area on the west coast of India under rainfed and irrigated conditions. LAI and light interception increased significantly in the irrigated compared to the rainfed trees. Girth and height of the tree were 29 and 19% more while width and height of the canopy were 19 and 20% more in the irrigated than rainfed trees. There were 22% more primary branches which had 26% more diameter in the irrigated trees than rainfed trees. The branches were inserted on the main trunk at an angle of 58.36° in the irrigated and 44.22° in rainfed trees. The above changes led to more light penetration which altered the light distribution inside the rainfed trees during summer and inhibited leaf photosynthesis particularly in the top canopy leaves. In the rainfed trees most of the growth occurred during the short favorable season immediately after the monsoon between June and October and no growth or even shrinking of the trunk was seen during summer. In the irrigated trees a higher growth was seen throughout the year and summer had no adverse effect. Although there was some difference in the root distribution pattern, the total root density per unit soil volume did not vary between the irrigated and rainfed trees. Key words  Hevea brasiliensis· Drought · Crown architecture · Micro-climate · Root growth Received: 8 May 1998 / Accepted 8 October 1998     

Modelling foliage characteristics in 3D tree crowns: influence on light interception and leaf irradiance

Because of the difficulty and time involved in making exhaustive measurements of the geometric parameters of large tree crowns, simplifying hypotheses are often used in 3D virtual plant modelling, but the effects on the radiation balance of each approximation are rarely assessed. Three hybrid walnut trees aged 7–9 years were digitized to analyse the effect of the crown geometric variables on light capture. The six studied variables were: (1) leaf area, (2) number of leaves per annual shoot, (3) position of leaves, (4) orientation of leaves, (5) leaflet inclination, and (6) lamina shape. For each variable, a sensitivity analysis compared a reference, based on observed values, with scenarios consisting of simplifying hypotheses. The total incident light intercepted during a bright day and the distributions of leaf irradiance were calculated using the Archimed radiative transfer model. Since some of the crown parameters were generated stochastically, the radiation simulations were repeated until results stabilised. Simplified models can be used to calculate with satisfactory results individual leaf area and number of leaves per shoot. Conversely, differentiating statistical distributions of individual leaf area between short and long shoots is more difficult and may generate errors up to 30%. Leaf clumping is a determining factor and requires correct grouping of leaves around the annual shoots bearing them. The effect of position of leaves along the shoot is less than 2%. Simple statistical distributions are adequate for representing leaf angle. Finally, the effect of specific leaf geometry is very important, but it can be approached using a limited number of representative leaf shapes.     

Evolutionary correlations of polycyclic shoot growth in Acer (Sapindaceae)

Two strategies have evolved in understory trees in relation to light availability: maximization of light capture and shade tolerance. In the genus Acer, light capture is favored by a suite of traits maximizing twig thickness and leaf size and minimizing the density of branching in the crown. In contrast, shade tolerance is enhanced by minimizing crown area, crown volume, and total leaf area per unit height. Maples with polycyclic shoot growth (i.e., successive flushes of shoot growth separated by a resting phase within the same vegetative period) may benefit from the prolonged growth by growing more and increasing total leaf area; thus we hypothesize that polycyclism is evolutionarily correlated with the suite of traits related to light capture. We tested this hypothesis using different phylogenetic trees to explore correlations between polycyclism and both suites of traits. Polycyclism was correlated with the suite of traits maximizing light capture, suggesting that polycyclic maples are "optimists" (i.e., they make vigorous vertical extensions in rich light) and monocyclic maples are "pessimists" (i.e., they wait in the dark understory until a gap is opened). Both strategies have been described for different floras, and interestingly, polycyclic species recruit over a wider range of environments than the monocyclic species.     

A tropical epiphytic orchid uses a low‐light interception strategy in a spatially heterogeneous light environment

Light is considered a non‐limiting factor for vascular epiphytes. Nevertheless, an epiphyte's access to light may be limited by phorophyte shading and the spatio‐temporal environmental patchiness characteristic of epiphytic habitats. We assessed the extent to which potential light interception in Rodriguezia granadensis, an epiphytic orchid, is determined by individual factors (plant size traits and leaf traits), or environmental heterogeneity (light patchiness) within the crown of the phorophyte, or both. We studied 104 adult plants growing on Psidium guajava trees in two habitats with contrasting canopy cover: a dry tropical forest edge, and isolated trees in a pasture. We recorded the number of leaves and the leaf area, the leaf position angles, and the potential exposure of the leaf surface to direct irradiance (silhouette area of the leaf blade), and the potential irradiance incident on each plant. We found the epiphytes experience a highly heterogeneous light environment in the crowns of P. guajava. Nonetheless, R. granadensis plants displayed a common light interception strategy typical of low‐light environments, resembling terrestrial, forest understory plants. Potential exposure of the total leaf surface to direct irradiance correlated positively with plant size and within‐plant variation in leaf orientation. In many‐leaved individuals, within‐plant variation in leaf angles produced complementary leaf positions that enhanced potential light interception. This light interception strategy suggests that, in contrast to current wisdom, enhancing light capture is important for vascular epiphytes in canopies with high spatio‐temporal heterogeneity in light environments.     

The relationship between anatomy and photosynthetic performance of heterobaric leaves

Heterobaric leaves show heterogeneous pigmentation due to the occurrence of a network of transparent areas that are created from the bundle sheaths extensions (BSEs). Image analysis showed that the percentage of photosynthetically active leaf area (Ap) of the heterobaric leaves of 31 plant species was species dependent, ranging from 91% in Malva sylvestris to only 48% in Gynerium sp. Although a significant portion of the leaf surface does not correspond to photosynthetic tissue, the photosynthetic capacity of these leaves, expressed per unit of projected area (Pmax), was not considerably affected by the size of their transparent leaf area (At). This means that the photosynthetic capacity expressed per Ap (P*max) should increase with At. Moreover, the expression of P*max could be allowing the interpretation of the photosynthetic performance in relation to some critical anatomical traits. The P*max, irrespective of plant species, correlated with the specific leaf transparent volume (lambda(t)), as well as with the transparent leaf area complexity factor ((CF)A(t)), parameters indicating the volume per unit leaf area and length/density of the transparent tissues, respectively. Moreover, both parameters increased exponentially with leaf thickness, suggesting an essential functional role of BSEs mainly in thick leaves. The results of the present study suggest that although the Ap of an heterobaric leaf is reduced, the photosynthetic performance of each areole is increased, possibly due to the light transferring capacity of BSEs. This mechanism may allow a significant increase in leaf thickness and a consequent increase of the photosynthetic capacity per unit (projected) area, offering adaptive advantages in xerothermic environments.     

Selection of shade trees in forest restoration plantings should not be based on crown tree architecture alone

The planting of tree seedlings is a common restoration technique in the tropics, and using large‐crowned, fast‐growing shade species is recommended to suppress invasive grasses and accelerate forest succession. We analyzed the effectiveness of shade species in shading the forest floor during the rainy and dry seasons at young forest restoration sites, whether shade changes according to site for a given species, and whether crown architecture can predict the shade level. We measured the photosynthetically active radiation (PAR) intercepted by the tree crowns of 14 species in two 3‐year‐old restoration plantings. The ability to predict shade based on crown architecture traits was evaluated using multiple linear regressions. The interception of PAR varied according to species, site, and season for seven species and was generally higher during the rainy season. Low values of tree and first branch height and high values of trunk diameter and mean area of a leaf predicted greater light interception. For the dry season, the ability to predict PAR interception was weaker than that for the rainy season and affected by a shorter tree height and a greater crown area. The crown architecture of shade species did not completely predict their shading ability, and the preselection of shade species for forest restoration purposes based only on crown architecture traits is not effective. Therefore, it is important to consider other factors, such as how long trees retain their leaves throughout the year and the soil and management conditions of the sites undergoing restoration, during the selection of species.     

Using terrestrial laser scanner for estimating leaf areas of individual trees in a conifer forest

A method that applies the terrestrial laser scanning to estimate leaf areas of individual trees in a mature conifer forest is presented. It is based on the theory of conventional optical LAI determinations, but refined for the inclusion of 3D depth information from the laser scanner. For each objective tree, we first used a single scan to measure local gap fractions beyond determined crown depths and combined this scan with other scans to delineate the geometrical dimensions of the crown. Then, through integrating the information from both aspects, the local leaf area density and the corresponding volume were derived. Finally, the total leaf area was obtained as the scalar product of these two variables. As most procedures were implemented on segmented 2D range images, the method possesses high efficiency. Additionally, through using gap fraction beyond determined crown depths, it solved the zero gap fraction problem encountered in segmented hemispherical photograph analysis. The method was tested on 11 trees in a 39 years old Norway spruce (Picea abies [L.] Karst.) stand located in southern Bavaria, Germany. Through correlation of the results with the estimates obtained with allometric equations, the accuracy was validated. The influence of the crown depth, for measuring gap fraction, and the segment size on estimation were also analyzed.     

LEAF DISPLAY,CANOPY STRUCTURE,AND LIGHT INTERCEPTION OF TWO UNDERSTORY PALM SPECIES

The implications of leaf size, leaf display, and crown size for whole-plant light interception were investigated in Geonoma cuneata and Asterogyne martiana, two understory palm species native to Central American rain forests. Adults of A. martiana had longer leaves, more leaves per plant, and greater total leaf area than G. cuneata adults. Geometric measurements within whole crowns were used to calculate light interception efficiency, a leaf-based measure of the proportion of total incident light that is intercepted by a crown. Light interception efficiency was higher in adult G. cuneata than in adult A. martiana; seedlings of the two species did not differ significantly in light interception efficiency. Decreased efficiency of adult A. martiana crowns was largely due to an increased proportion of pendent leaves. Compared to G. cuneata, adults of A. martiana had greater light interception capacity (the product of light interception efficiency and total leaf area), but they also had higher biomass costs of light interception. Lower biomass costs of light interception in adult G. cuneata enable this species to exploit successfully the most deeply shaded microsites in the rain forest understory.     

Does shade improve light interception efficiency? A comparison among seedlings from shade-tolerant and -intolerant temperate deciduous tree species

Here, we tested two hypotheses: shading increases light interception efficiency (LIE) of broadleaved tree seedlings, and shade-tolerant species exhibit larger LIEs than do shade-intolerant ones. The impact of seedling size was taken into account to detect potential size-independent effects on LIE. LIE was defined as the ratio of mean light intercepted by leaves to light intercepted by a horizontal surface of equal area. Seedlings from five species differing in shade tolerance (Acer saccharum, Betula alleghaniensis, A. pseudoplatanus, B. pendula, Fagus sylvatica) were grown under neutral shading nets providing 36, 16 and 4% of external irradiance. Seedlings (1- and 2-year-old) were three-dimensionally digitized, allowing calculation of LIE. Shading induced dramatic reduction in total leaf area, which was lowest in shade-tolerant species in all irradiance regimes. Irradiance reduced LIE through increasing leaf overlap with increasing leaf area. There was very little evidence of significant size-independent plasticity of LIE. No relationship was found between the known shade tolerance of species and LIE at equivalent size and irradiance.