Projected Leaf Area Research Articles

Simple equations to estimate light interception by isolated trees from canopy structure features: assessment with three‐dimensional digitized apple trees

* Simple models of light interception are useful to identify the key structural parameters involved in light capture. We developed such models for isolated trees and tested them with virtual experiments. Light interception was decomposed into the projection of the crown envelope and the crown porosity. The latter was related to tree structure parameters. * Virtual experiments were conducted with three-dimensional (3-D) digitized apple trees grown in Lebanon and Switzerland, with different cultivars and training. The digitized trees allowed actual values of canopy structure (total leaf area, crown volume, foliage inclination angle, variance of leaf area density) and light interception properties (projected leaf area, silhouette to total area ratio, porosity, dispersion parameters) to be computed, and relationships between structure and interception variables to be derived. * The projected envelope area was related to crown volume with a power function of exponent 2/3. Crown porosity was a negative exponential function of mean optical density, that is, the ratio between total leaf area and the projected envelope area. The leaf dispersion parameter was a negative linear function of the relative variance of leaf area density in the crown volume. * The resulting models were expressed as two single equations. After calibration, model outputs were very close to values computed from the 3-D digitized databases.

What is the best way to represent surface conductance for a range of vegetated sites?

AbstractSurface conductance Gs is a significant parameter for indicating the evaporative and photosynthetic properties of a vegetated surface. When comparing Gs values between different observation sites, some studies have used Gsmax and others have used Ĝsmax (where Gsmax is the maximum Gs value measured during the measurement period, and Ĝsmax is the maximum Gs value obtained with a vapour pressure deficit (VPD) of ≥ 1·0 kPa during the measurement period).In this study, we demonstrate a clear justification for using Ĝsmax instead of Gsmax when comparing Gs values between different sites. We examined whether both Ĝsmax and Gsmax lead to the same conclusions in classifying vegetated sites. Komatsu (2003b) [Hydrological Processes 17: 2503–2512] reported a clear relationship between canopy height h and Ĝsmax for coniferous forests with a projected leaf area index (LAI) of ≥ 3·0. We examined not only the relationship between h and Ĝsmax but also the relationship between h and Gsmax for coniferous forests with a projected LAI of ≥ 3·0.Both Ĝsmax and Gsmax decreased with increasing h. However, the relationship between h and Gsmax was less well defined than the relationship between h and Ĝsmax because of biased Gsmax data. Consequently, we conclude that Ĝsmax is a more appropriate index than Gsmax to represent Gs for sites with different vegetation. Copyright © 2007 John Wiley & Sons, Ltd.

Patterns of leaf area and growing space efficiency in young even-aged and multiaged coast redwood stands

Projected leaf area estimates were used to predict volume increment and basal area of second-growth coast redwood ( Sequoia sempervirens (D. Don) Endl.) trees on Jackson Demonstration State Forest, Mendocino County, California. Sample plots were established within even-aged and multiaged mixed-species stands. Redwood tree basal area growth was more strongly related to sapwood area than to tree size and differed significantly between canopy strata and overstory stratum crown classes. Projected leaf area was predicted from sapwood area for each tree, and summarized to the stand level, giving a maximum stand leaf area index (LAI) estimate of 14.9 m2/m2. Redwood tree growing space efficiency (GSE; the ratio of stem volume increment to leaf area) was greatest on average among emergent overstory trees, followed by dominant and codominant overstory trees. There was no evidence of declining overstory tree GSE with increasing leaf area over the range of data collected. A nonlinear model predicted increasing understory tree GSE with increasing leaf area. Models that predict basal area and LAI were developed to permit implementation of GSE models from basic inventory data.

Biomass production and allometric above- and below-ground relations for young birch stands planted at four spacings on abandoned farmland

Summary The objective of the study was to quantify above- and below-stump biomass of silver ( Betula pendula Roth) and downy ( Betula pubescens Ehrh.) birches planted at four spacing intervals and growing on two soil types on an area of farmland. The 12-year-old birches had been grown at four spacings (1.3, 1.5, 1.8 and 2.6 m) on two sites: one on medium clay soil and the other on fi ne sand soil. The dry weight of the stem, branches, leaves, stumps and roots was estimated by drying and weighing subsamples. The projected leaf area (PLA) m − 2 of trees, leaf area index of stands and basic density (kg m − 3 ) of stems were also estimated. A signifi cant greater dry weight of stem, branches, stump and roots and species and spacing for pendula birch were found. The root length of silver birch was signifi cantly greater than that for downy birch and for both species the root length was greatest at the widest spacing (2.6 m). There was also a signifi cant difference between leaf weights of birch of the same species growing on the two soil types. Signifi cant differences were also found between PLA and species, and for both species, between PLA spacing. Basic density of stems was signifi cantly different between soil types. Equations for estimating the above-ground biomass and root biomass from diameter at breast height were developed for birches growing on fi ne sand and on medium clay soils. The total biomass production per hectare on fi ne sand was higher for silver birch (19.9 – 65.9 tonnes ha − 1 ), than for downy birch (13.0 – 48.3 tonnes ha − 1 ). On medium clay soil, total biomass production for silver and downy birches was 30.8 – 52.8 and 16.8 – 42.8 tonnes ha − 1 , respectively.

Réponse de l’index foliaire (LAI) et de la dynamique de chute de litière du Douglas à la rouille suisse dans la zone côtière du Nord Oregon

Sources of variation in leaf area index (LAI; m 2 of projected leaf area per m 2 of ground area) and its seasonal dynamics are not well known in managed Douglas-fir stands, despite the importance of leaf area in forecasting forest growth, particularly in stands impacted by insects or disease. The influence of Swiss needle cast (SNC) on coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb) Franco) LAI and litterfall dynamics was quantified by destructively sampling 122 stems from 36 different permanent plots throughout north coastal Oregon, USA, and by monitoring litterfall for 3 years in 15 of these plots. LAI, total annual litterfall, and the seasonal distribution of foliage and fine woody litterfall were all influenced by stand structural attributes, physiographic features, and SNC severity. Mean LAI in this study was 5.44 ± 2.16. The relatively low LAIs were attributed primarily to the effects of SNC on foliage retention, and secondarily to its direct measurement by hierarchical foliage sampling in contrast to indirect measurement by light interception or tree allometry. For a given stand structure and SNC severity, LAI was 36% greater in the fall after current year foliage was fully developed and older aged classes had not yet senesced. Annual litterfall expressed as a proportion of LAI at the start of the growing season varied from 0.13 to 0.53 and declined with increasing initial LAI. SNC also shifted more of the annual foliage litterfall to earlier in the spring. Fine woody litterfall experienced a different seasonal shift as the peak occurred later in the year on sites with high SNC, but this only occurred on northerly aspects. Defoliation from the endemic SNC pathogen can drastically reduce LAI and change both total and seasonal foliage litterfall patterns.

Specific leaf area and nitrogen distribution in New Zealand forests: Species independently respond to intercepted light

The foliage of five forested sites across a climatic gradient on the South Island of New Zealand were studied to assess whether the distribution of specific leaf area (SLA) and leaf nitrogen (N) were due to the light environment or intrinsic species characteristics. Within both mixed and single species stands, SLA and N were correlated with relative light interception ( τ) but varied greatly. For N, this variation was reduced by expressing N values as relative site N (N/maximum site N) that increased correspondence between N and ln( τ) across sites ( r 2 = 0.79). However, comparison of mixed species composition to a monoculture stands showed difference in the N- τ especially in stands with high species richness. The nitrogen extinction coefficient ( k N) was estimated for canopies based on profiles of measured projected leaf area indices (PLAI) and leaf N, with an average value of 0.17 ± 0.06 indicating a conservative relationship between N and τ in these forests. Site maximum leaf N is correlated positively with annual incident irradiance further corroborating the N and light relationship as well as providing a potential mechanism for estimating canopy N over larger areas.

Machine Vision Systems for Plant Growth Measurement and Modeling

Recent developments of microcomputer-based machine vision systems has offered convenient and non-destructive ways for measurements of plant characteristics that allow plant growth assessment. This paper presents brief reviews and comparisons of machine vision approaches for non-destructive plant growth measurement. The simple approach of using projected silhouette image of a plant was most commonly used in acquiring growth data in various experiments. Plant fresh or dry weight can be indirectly estimated from projected leaf area by calibration with data from standard measurement methods. However, the estimation error usually increases as the extent of overlapped leaves increases. Images acquired from different views or utilizing dual cameras allow the estimation of leaf area without predetermined calibration relationship but the image processing algorithms usually become more sophisticated. By incorporating multiple images of a plant, three-dimensional and structural information may be extracted for more detailed growth analyses and modeling.

A note on the G-function for needle leaf canopies

Formulas to calculate the radiation extinction coefficient or ‘ G-function’ for plant canopies originally were derived under the assumption of flat leaves. The G-function in that case is obtained as the ratio of the expected value (with respect to the leaf normal distribution function) of the projected leaf area to the one-sided leaf area. Although the corresponding formulas have later been presented also for conifer needles of different shapes they have rarely been used to determine conifer specific G values for parameterization of radiation models for coniferous stands. Instead, these models have typically been based on the erroneous assumption that the G-functions for flat leaves and needles are equivalent if only the one-sided leaf area (used as denominator in G) is replaced by the vertically projected, planimetric needle area. The importance of consistent definition of leaf area index and G for conifers is discussed in this study which presents an overview of previous studies on the G-function of needles and an easily applicable approach to calculate it for needles of different shapes.

Forest categorization according to dry‐canopy evaporation rates in the growing season: comparison of the Priestley–Taylor coefficient values from various observation sites

AbstractSummarizing observed dry‐canopy evaporation (hereafter, evaporation) data from earlier papers, we developed a scheme for forest categorization according to evaporation rates in the growing season. Evaporation rates were represented by the Priestley–Taylor coefficient α calculated for daytime. We examined relationships between forest properties (e.g. climatic regions, leaf types) and α values. We obtained α data for 67 forest sites from earlier papers. Based on these data, we found (i) a clear difference in α values between broad‐leaved and coniferous forests, (ii) a greater variation in α values between individual coniferous forests than between individual broad‐leaved forests, and (iii) a clear relationship between canopy height and α values for coniferous forests. These three results were supported by surface conductance data summarized from earlier papers. We concluded that forests should be primarily classified into broad‐leaved and coniferous forests, and that coniferous forests should be further classified according to canopy height. This classification scheme is applicable only to forests with projected leaf area index (LAI) ≥3·0. Regardless of this LAI limitation, this classification will be useful because many forests satisfy this LAI limitation.This paper shows valuable results in the following two respects. First, this paper explicitly shows the difference in evaporation rates between broad‐leaved and coniferous forests. Although this difference would have been implicitly recognized, this difference has not been shown based on adequate amounts of observed data. Second, it is shown that classifying coniferous forests according to canopy height is as important as classifying forests according to leaf type (broad‐leaved or coniferous). Although studies have recognized the effect of canopy height on evaporation rates, the significant effect of canopy height on evaporation rates, compared with the effects of other factors on evaporation rates, has not previously been shown. Copyright © 2005 John Wiley & Sons, Ltd.

Physiological and morphological variations of Picea asperata populations originating from different altitudes in the mountains of southwestern China

Population differences in dry matter accumulation and allocation, conifer leaf nitrogen status, stomata parameters and water use efficiency were studied in a 7-year-old Picea asperata Mast. plantation that contains seven populations grown from seed collected from different altitudes in the mountains of southwestern China. In our study, we measured dry matter accumulation (DMA), total projected leaf area (LA), specific projected leaf area (SLA), root/shoot ratio (RS), root mass/projected leaf area ratio (R/LA), projected leaf area/stem cross-sectional area ratio (LA/SA), leaf stomatal density (SD), stomatal length (SL) and total stomatal length (TSL), nitrogen content per unit leaf mass (N mass) and nitrogen content per unit projected leaf area (N area), and carbon isotope composition ( δ 13C). Significant differences in these properties among the populations were detected, but these morphological and physiological responses to altitudinal gradients of origins varied non-linearly with increasing altitude. We found that seed source near 2950 m altitude was likely an optimum zone for P. asperata; growth was most vigorous at this altitude, and with increasing altitudinal distance from this optimum the growth decrease. In addition, seedling early growth, including DMA and LA, negatively correlated with RS, R/LA, N mass, N area and δ 13C, and positively correlated with SLA, LA/SA, SD, SL and TSL. Our results provided strong evidence that variations in these physiological and morphological properties of P. asperata populations reflected genetic adaptations to native habitats. These differences may be used as criteria for genotype selection in the mountains of southwestern China.

FoliageߝSapwood Area Relationships for Balsam Fir in North-Central Minnesota

Abstract Leaf area is an important determinant of plant productivity. Because foliage is difficult to measure directly, allometric relationships often are used to predict branch-level and tree-level attributes such as total mass, needle mass, crown biomass, and projected leaf area. Two modeling approaches (i.e., the “crown weighing” and the “branch summation” approach) and two model forms (i.e., a nonlinear model form and a linear logarithmic model form) have generally been used to develop allometric relationships. It is unclear, however, whether these approaches result in similar predictions, which of these model forms provides us with the better predictions, and whether allometric equations developed for the same tree species in one region can be safely applied in another region. To investigate these questions, allometric equations to predict branch-level attributes (mass and leaf area) were constructed for balsam fir (Abies balsamea (L.) Mill.) in Minnesota. The “branch summation” approach was used to construct equations to predict crown biomass and projected leaf area from sapwood area, dbh, and crown length. These predictions were compared to those from the crown weighing approach. No statistically significant differences were detected. Results also indicated that the logarithmic form of the allometric model was the model of choice over the nonlinear form. Furthermore, branch-level and tree-level equations developed for balsam fir from north-central Minnesota differed from those of other regions within the range of data for the trees sampled. This reinforces the need for developing localized allometric equations.North. J. Appl. For. 22(3):203–210.

Why do Polytrichaceae have lamellae?

Light-response curves of chlorophyll-fluorescence parameters from 12 species of Polytrichaceae show photosynthetic electron flow giving a good fit to negative-exponential saturation curves up to high irradiances; 95%-saturation irradiances for the species of unshaded habitats approached or exceeded noon summer sunlight. The species showed little or no indication of the non-saturating electron flow at high irradiances, or the very high values of non-photochemical quenching, seen in many other mosses of dry, sun-exposed habitats. Calculation of CO2 diffusion rates from first principles on a cell-area basis indicates that photosynthesis of mosses with unistratose leaves is likely to be limited by CO2 diffusion resistance at high irradiances. In Polytrichaceae the area for CO2 uptake is often >6 times the projected leaf area. By lowering the whole-leaf resistance to CO2 uptake, the lamellae remove the CO2-diffusion constraint that limits mosses with unistratose leaves and allow Polytrichaceae to utilize efficiently the high irradiance of direct sunlight.

The influence of thinning and tree size on the sapwood area / leaf area ratio in coigue

The effect of thinning and crown class on the projected leaf area, specific leaf area, and projected leaf area / sapwood area ratio was evaluated in a 48-year-old even-aged stand of coigue (Nothofagus dombeyi (Mirb.) Oerst.). The data were collected through destructive sampling of 27 trees and analyzed with analysis of variance and regression models. The projected leaf area was greater in trees from more intensely thinned stands. The specific leaf area and the projected leaf area / sapwood area ratio did not vary between treatments. The sapwood cross-sectional area at breast height (1.3 m) and at the base of the live crown provided the best fit for the relationship between projected leaf area and sapwood area. The current sapwood area provided the worst fit, suggesting that at an early age, coigue sapwood does not present permeability problems associated with tyloses.

Simulation of drought for a Scots pine forest (Pinus sylvestris L.) in the southern upper Rhine plain

For the period 1978 to 2001, the physically based model BROOK90 has been applied to simulate the water balance of the Scots pine forest (Pinus sylvestris L.) at the forest meteorological experimental site Hartheim with emphasis on drought. The forest is located in the southern upper Rhine plain, which shows climate conditions similar to those predicted by regional climate models for Central Europe. The transpiration index (ratio of actual transpiration and potential transpiration) has been chosen as an ecophysiologically based drought index on a daily basis. Simulations exhibit that the transpiration index depends not only on the weather conditions but also on forest characteristics like maximum leaf conductance and projected leaf area index. Taking into account different time scales for the transpiration index (daily, monthly and annual basis), a tendency of the occurrence of drought significant to the forest could not be determined for the investigation period. August turned out to be the month with the highest drought risk. Drought for the forest was most pronounced in the year 1991 (annual transpiration index: 0.53), whereas the year 2000 was the only one with an optimal water supply of the Scots pine forest (annual transpiration index: 1.0).

Sapwood area – leaf area relationships for coast redwood

Coast redwood (Sequoia sempervirens (D. Don) Endl.) trees in different canopy strata and crown positions were sampled to develop relationships between sapwood cross-sectional area and projected leaf area. Sampling occurred during the summers of 2000 and 2001 and covered tree heights ranging from 7.7 to 45.2 m and diameters at breast height ranging from 9.4 to 92.7 cm. Foliage morphology varied greatly and was stratified into five types based on needle type (sun or shade) and twig color. A strong linear relationship existed between projected leaf area and sapwood area at breast height or sapwood at the base of the live crown despite the variability in foliage morphology. Ratios of leaf area to sapwood were 0.40 m2/cm2 at breast height and 0.57 m2/cm2 at crown base. Measurements of sapwood at the base of the live crown improved leaf area predictions because of sapwood taper below the crown base. A sapwood taper model was also developed.

Comparing PAR transmission models for forest understorey vegetation

AbstractQuestion: Do Beer's Law models, multi‐layer scattering models, and a semi‐empirical model for predicting PAR transmission through understorey vegetation give comparable results? Do different driving variables (LAI, PLAI and percentage cover) give different results? How do the models vary when fit with species‐specific, species‐average and the ‘default’ parameters recommended in the literature?Location: Upland boreal forests of western North America.Methods: In calibration and validation plots, PAR transmission was measured, total cover visually estimated, and leaf dispersion, PLAI and cover estimated for each species using a point‐frame. Leaf inclination was measured by clinometer. PAR transmission was modelled using empirically‐fit Beer's Law models, a semi‐empirical model based on hemispherical gap fraction and first‐order scattering, and a multi‐layer model allowing multiple scattering. All models were modified to use leaf area index (LAI), vertically projected leaf area index (PLAI), or percentage cover data.Results: The empirical Beer's Law models had the least bias and best precision in predicting PAR transmission. The semi‐empirical model also had little bias and good precision, since the scattering coefficient compensated for problems in the estimation of gap fraction. The multi‐layer model consistently underestimated transmission. There was little benefit in accounting for species separately. LAI and PLAI‐based models were the most precise, but percentage cover models also provided reasonable predictions of PAR transmission.Conclusions: PAR transmission through forest understories can be simply modelled with Beer's Law using one empirical coefficient representing the average understorey species. More complex scattering models are less effective, likely because they fail to account for the complexity of the dispersion of this vegetation layer and its effect on radiation scattering.

NON-DESTRUCTIVE GROWTH MEASUREMENT OF SELECTED VEGETABLE SEEDLINGS USING ORTHOGONAL IMAGES

A non-destructive measurement method of plant features using image processing technique provides a means toanalyze the continuous growth process of a plant. In a previous study, we developed a non-destructive measurement methodby using elliptical Hough transform to search for seedling leaves from a top-view image. To improve the accuracy of the leafnumber estimation and leaf area measurement, this study further incorporates two side-view images with a top-view imageto extract and reconstruct the three-dimensional structure of selected vegetable seedlings, and thus to measure the featuresrelated to plant growth. By registering correspondences between the three orthogonal images, the position, orientation, anddimensions of leaves in a seedling can be more exactly derived than from a single top-view image alone. The leaf skeletonstraced in the side-view images can be used to correct the projected leaf area in the top-view image for better estimation ofleaf area. Experiments were performed to test the performance of the measurement system by comparing the non-destructivelyestimated leaf area and the actual leaf area of selected vegetable seedlings. The average relative errors of total leaf estimationfor cabbage and broccoli seedlings were 14.5% and 13.1%, respectively, using a single top-view image. By incorporatingorthogonal images, the relative errors were significantly reduced to 1.6% and 4.9%, respectively. Using this non-destructivemeasurement system, the continuous growth of vegetable seedlings can be effectively measured.

Comparing PAR transmission models for forest understorey vegetation

Abstract Question: Do Beer's Law models, multi-layer scattering models, and a semi-empirical model for predicting PAR transmission through understorey vegetation give comparable results? Do different driving variables (LAI, PLAI and percentage cover) give different results? How do the models vary when fit with species-specific, species-average and the ‘default’ parameters recommended in the literature? Location: Upland boreal forests of western North America. Methods: In calibration and validation plots, PAR transmission was measured, total cover visually estimated, and leaf dispersion, PLAI and cover estimated for each species using a point-frame. Leaf inclination was measured by clinometer. PAR transmission was modelled using empirically-fit Beer's Law models, a semi-empirical model based on hemispherical gap fraction and first-order scattering, and a multi-layer model allowing multiple scattering. All models were modified to use leaf area index (LAI), vertically projected leaf area index (PLAI), or per...

Long-term trends in loblolly pine productivity and stand characteristics in response to thinning and fertilization in the West Gulf region

Two levels each of thinning and fertilization were applied to a 7-year-old loblolly pine ( Pinus taeda L.) plantation on a nitrogen- and phosphorus-deficient West Gulf Coastal Plain site in Louisiana. Levels of thinning were no thinning, or thinning applied 7 and 14 years after stand initiation. Levels of fertilization were no fertilization or broadcast fertilization with diammonium phosphate at age 7 years plus refertilization with urea, monocalcium phosphate, and potash at age 14 years. Long-term measurements of climate, stand development and productivity, projected leaf area index, and foliar nutrition were initiated at age 11 years. We found that by age 17 years, thinning increased mean live-crown length from 4.2 to 7.8 m, and mean tree diameter from 15.0 to 21.8 cm compared to the unthinned treatment. After rethinning at age 14 years, stand basal area increased 1.2 and 19.2% between ages 15 and 17 years on the unthinned and thinned plots, respectively. Refertilization at age 14 years reestablished foliar N, P and K sufficiency, which increased leaf area index from 4.2 to 6.0 m 2 m −2 on the unthinned plots and from 3.2 to 3.8 m 2 m −2 on the thinned plots, and subsequently, increased gross stand biomass from 114 to 141 Mg ha −1 on the unthinned plots and from 78 to 95 Mg ha −1 on the thinned plots by age 17 years. Leaf area was an important factor controlling loblolly pine productivity. At our study site, however, competition for light and water and nutrition-limited foliage growth influenced the variability and scope of this relationship. Our results suggest that a positive and linear relationship between leaf area and loblolly pine productivity does not universally occur on loblolly pine sites.

画像処理によるレタス生長計測―線形判別手法による定植後経過日数判別―

This research was conducted to develop an algorithm to recognize the number of days after planting of lettuce in a plant factory. Speaking Plant Approach (SPA) has been recognized in a growth control system. Growth information should be utilized actively for environmental control. An instrumentation that can acquire the growth information is necessary to incorporate the SPA into the growth control system. This research is a fundamental analysis for a growth monitoring method. Two varieties of lettuces, the Telme lettuce and the Tango lettuce, were examined. Digital images of the lettuces were photographed by a digital still camera. Several image features, such as the top projected leaf area, the color attributes and the texture features, were calculated using an image processing algorithm. Linear discriminant analysis was adopted for the image features. This research focused on three dates in a growth term. As for the Telme lettuce, the 10th, 20th and 30th days after planting were set as the target dates to note. For the Tango lettuce, the 7th, 14th and 21st days were fixed as objectives. The developed algorithm showed a 2.5% error rate for the Telme lettuce and 20% for the Tango lettuce. Therefore, this recognition method could be utilized for a growth diagnosis of the Telme lettuce. On the other hand, for the Tango lettuce, it is necessary for the algorithm to be further improved.