LAI-2000 Plant Canopy Analyzer Research Articles

Gap fraction based estimation of LAI in Scots pine stands subjected to experimental removal of branches and stems

We compared estimates of leaf area index obtained by the LAI-2000 plant canopy analyzer (LAIPCA) to direct estimates of LAI ("true" LAI) obtained through allometric relationships. This was done for two Scots pine (Pinus sylvestris L.) stands, where LAI was gradually reduced by removing branches and whole trees. LAI (defined on a hemisurface area basis) decreased from 2.24 to 0.50 in the branch removal experiment and from 1.58 to 0.29 in the tree removal experiment. The aim of the study was to analyse the variation in the ratio of the LAI-2000 estimate to the true LAI (LAIPCA/LAI) with changes in stand structure and total leaf area. In the tree removal plot, which had a smaller proportion of woody (branch) area, LAIPCA/LAI remained fairly stable (0.63‐0.69) and was smaller than that in the branch removal plot, where LAIPCA/LAI increased from 0.76 to 1.16 along with the decrease in leaf area and a subsequent increase in woody (stem) area. The ratio of LAIPCA to the plant area index (PAI) differed less between plots but remained higher in the branch removal plot (increasing from 0.56 to 0.69) than in the tree removal plot, where it varied between 0.55 and 0.60. Results were analysed with the help of a theoretical canopy radiation model, which can be inverted to give LAI based on the gap fraction values measured by the LAI-2000 and stand structural parameters. Model-inverted LAI agreed well with directly measured LAI, suggesting that the model is a useful tool for correcting bias in the LAI-2000 estimates because of grouping of leaf area and the contribution of woody area.

Leaf area index from litter collection: impact of specific leaf area variability within a beech stand

Litter fall collection is a direct method widely used to estimate leaf area index (LAI) in broad-leaved forest stands. Indirect measurements using radiation transmittance and gap fraction theory are often compared and calibrated against litter fall, which is considered as a reference method, but few studies address the question of litter specific leaf area (SLA) measurement and variability. SLA (leaf area per unit of dry weight, m2·g‐1) is used to convert dry leaf litter biomass (g·m‐2) into leaf area per ground unit area (m2·m‐2). We paid special attention to this parameter in two young beech stands (dense and thinned) in northeastern France. The variability of both canopy (closure, LAI) and site conditions (soil properties, vegetation) was investigated as potential contributing factors to beech SLA variability. A systematic description of soil and floristic composition was performed and three types of soil were identified. Ellenberg's indicator values were averaged for each plot to assess nitrogen soil content. SLA of beech litter was measured three times during the fall in 23 plots in the stands (40 ha). Litter was collected bimonthly in square-shaped traps (0.5 m2) and dried. Before drying, 30 leaves per plot and for each date were sampled, and leaf length, width, and area were measured with the help of a LI-COR areameter. SLA was calculated as the ratio of cumulated leaf area to total dry weight of the 30 leaves. Leaves characteristics per plot were averaged for the three dates of litter collection. Plant area index (PAI), estimated using the LAI-2000 plant canopy analyser and considering only the upper three rings, ranged from 2.9 to 8.1. Specific leaf area of beech litter was also highly different from one plot to the other, ranging from 150 to 320 cm2·g‐1. Nevertheless, no relationship was found between SLA and stand canopy closure or PAI. On the contrary, a significant relationship between SLA and soil properties was observed. Both SLA and leaf area had the lowest values in the most hydromorphic soil with the highest nitrogen content. On the other hand, the highest values of SLA and leaf area were observed on the plots with the lowest nitrogen content. This spatial variability of SLA was taken into account to estimate LAI from litter collected at eight plots. For our study site, we conclude that neglecting SLA spatial variability is at the source of 8‐24% error in the calculation of LAI.

Evaluation of four methods for estimating leaf area of isolated trees

The accurate modeling of the physiological and functional processes of urban forests requires information on the leaf area of urban tree species. Several non-destructive, indirect leaf area sampling methods have shown good performance for homogenous canopies. These methods have not been evaluated for use in urban settings where trees are typically isolated and measurement may be complicated by proximity to residential areas, buildings, signs, and other infrastructure elements. We evaluated the accuracy, precision, efficiency and other practical considerations associated with four methods of estimating the leaf area of open-grown deciduous trees in urban forests. The methods included color digital image processing (CD), the LAI-2000 Plant Canopy Analyzer, the CI-100 Digital Plant Canopy Imager, and a logarithmic regression equation. Regression coefficients, adjusted R 2, and confidence intervals were used to determine the best method when using true leaf area of 25 Platanus x acerifolia Willd. and 25 Platanus racemosa Nutt. as an independent variable. Practical considerations included ease of data collection and processing and costs associated with each method. The CD method and LAI-2000 estimates showed good correlation with true leaf area (R 2 ≫ 0.71); however, only the CD method produced estimates within 25 percent of mean true leaf area and met additional requirements for accuracy, precision, and efficient use in urban settings.

Application of a forest reflectance model in estimating leaf area index of Scots pine stands using Landsat-7 ETM reflectance data

We tested the Kuusk‐Nilson forest reflectance model in simulating the relationship between leaf area index (LAI) and spectral reflectances of 23 pure Scots pine plots located in southeastern Finland. Landsat-7 enhanced thematic mapper (ETM) reflectance data for channels ETM 3 (red spectral band) and ETM 4 (near-infrared (NIR) band) were used for the analysis. LAI was determined by inversion from canopy gap fraction data measured by the LAI-2000 plant canopy analyzer, using a theoretical forest gap fraction model parameterised for the plots. An independent estimate of LAI was obtained from data on plotwise tree variables using an allometry-based regression developed for Scots pine. The Kuusk‐Nilson model can be run in direct and inverse modes. First, the model was applied in direct mode, in which LAI and stand data were used to simulate reflectances in the red (661 nm) and NIR (838 nm) bands. The model-simulated reflectances in the red band were within approximately the same range as the ETM 3 reflectances. In the NIR band, though, a majority of the simulated values were higher than the ETM 4 values. Empirical and simulated relationships between LAI and reflectance in the red and NIR bands showed similar, weakly negative trends in reflectance with increasing LAI. Second, the model was run in inverse mode, i.e., Landsat ETM reflectance data and stand parameters were used for LAI retrieval. The inversion requires as input an initial estimate of LAI and the uncertainty of it. We used as input the allometric estimates of LAI, with two levels of uncertainty (20 and 50%). As the uncertainty increased, correlation between retrieved and initial LAI decreased.

Leaf area index of ground covers in a subtropical watershed

Leaf Area Index (LAI), an important structural variable descriptive of vegetation, is directly related to evapotranspiration and productivity. The objective of this work was to measure and analyze monthly LAI of different ground covers in a subtropical watershed. A field campaign to collect monthly LAI data was carried out during the year 2001, with a LAI-2000 (plant canopy analyzer) device, in sugarcane, pasture, corn, eucalypt, and riparian forest patches. Riparian forest presented a maximum LAI of 4.90; LAI values decreased as precipitation decreased, as it is a characteristic of this type of semideciduous vegetation. LAI for sugar cane presented the greatest variability throughout the year, related to plant characteristics and crop management in the study area. Results represent an initial step for the understanding of LAI dynamics in the study area and areas under similar conditions.

Comparison of methods for determining leaf area in tree rows

Two methods for determining the leaf area of trees growing in rows using an LAI-2000 Plant Canopy Analyser were tested against destructive measurements for Croton megalocarpus and Melia volkensii, species with differing canopy characteristics. The trees ranged between 4.0 and 8.0 m in height and formed part of an agroforestry experiment in semi-arid Kenya where rapid fluctuations in canopy cover rendered allometric approaches inappropriate for determining leaf area. The first method used unmodified theory for determining leaf area in continuous canopies which has proved suitable for isolated bushes. In the second method, path lengths through the canopy were calculated from simple measurements of canopy dimensions and the importance of subsidiary assumptions concerning leaf angle distribution was tested. Leaf angle distribution, which is required for canopy simulation models, was also determined using both direct and indirect approaches and the effect of using assumed leaf angle distributions when calculating leaf area was assessed. The canopy analyser proved unsuitable for measuring leaf angle distributions in isolated canopies, and it was necessary to make direct canopy measurements for this instrument to be used for smaller canopies. It was also shown that, even when path lengths are measured, calibration may be necessary to avoid bias; uncalibrated leaf area density values were, on average, underestimated by 16% for M. volkensii and overestimated by 8% for C. megalocarpus with respect to destructively determined values.

Variação do índice de área foliar em clones de eucalipto ao longo de seu ciclo de crescimento

O índice de área foliar (IAF) é uma das principais variáveis biofísicas de um dossel florestal, estando diretamente relacionado com a sua evapotranspiração e sua produtividade. Este trabalho apresenta um levantamento da variabilidade temporal do IAF em cinco diferentes clones (designados para efeito deste trabalho como MG1, MG2, MG3, MG4 e MG5) de plantações de eucalipto (híbridos de Eucalyptus grandis), na regional de produção de Aracruz-ES, Brasil. Utilizou-se o equipamento LAI-2000 para medir o IAF em 98 talhões, com didade variando de 12 a 84 meses. o IAF variou de 1,7 a 4,3. Houve correlação negativa significativa entre IAF e idade para os clones MG1, MG2, e MG3. Para os clones MG4 e MG5 foi constatado que não houve relação significativa entre IAF e idade, o que evidencia que sejam adotados valores médios de IAF destes clones como descritores estruturais do dossel para fins de modelagem ou outros (2,57 e 3,04, respectivamente).

Relationships between stand parameters and understorey light in boreal aspen stands

Data from six aspen stands in northeastern British Columbia ranging in age from 12 to 40 years were used to examine relationships between understorey light levels and stand attributes (basal area, stand density, and age). Sample points were selected in each stand to characterize the observed range in tree density and size. Fractional transmittance of light (DIFN) was measured at each sample point using a LAI-2000 Plant Canopy Analyzer and a circular plot 3.99 m or 5.64 m in radius was established for density and basal area determination.Results indicated that data from the six stands could be pooled into a single model describing the relationship between understorey light and basal area. Light levels below 40% are found when basal area of aspen in these stands exceeds 14 m2/ha and light levels below 60% are found when basal area of aspen exceeds 8 m2/ha. The potential implications of these light levels to growth of understorey spruce are discussed.A diagrammatic representation of light-density–diameter relationships is presented that could provide a useful tool for management decisions in young mixedwood stands in northeastern British Columbia.

Quantitative relationships between field-measured leaf area index and vegetation index derived from VEGETATION images for paddy rice fields

In an effort to develop the quantitative relationships between fieldmeasured leaf area index (LAI ) and VEGETATION-derived vegetation indices for paddy rice fields, we have measured LAI of paddy rice fields at 10-day intervals at five sampling sites in Jiangning County, Jiangsu Province of China during the rice growing season (July to October) of 1999, using a LI-COR LAI-2000 plant canopy analyser. Twenty-seven 10-day VEGETATION (VGT) synthesis products (VGT-S10) from 1-10 March to 21-30 November 1999 were acquired. Normalized difference vegetation index (NDVI) values were calculated for the VGT-S10 products, using ground surface reflectance values of VGT spectral bands (B3-near-infrared; B2-red). After rice transplanting in mid to late June, LAI increased rapidly and reached its plateau by early to mid August. There were similar temporal dynamics of NDVI and LAI among the five sampling sites over the growing season of paddy rice in 1999. Simple linear regression analyses indicate that there are statistically significant linear relationships between NDVI and LAI data over the growing season of paddy rice in 1999.

Rapid methods to estimate sky‐view factors applied to urban areas

AbstractA common parameter used to characterize the geometry of urban canyons is the sky‐view factor (ψs). Here, two simple alternatives are presented that can be used both objectively and rapidly to estimate ψs. The first method uses a Nikon CoolPix 950 digital camera fitted with a Nikon FC‐E8 fisheye lens. The second method involves a LI‐COR LAI‐2000 Plant Canopy Analyzer to measure automatically diffuse non‐interceptance (DIFN) light using a fisheye optical sensor. Through a series of intercomparisons for urban canyons of known geometry, the digital camera is shown to provide accurate estimates of ψs. The LAI‐2000 also performs well, although it tends to over‐estimate ψs (for the conditions considered here, the mean absolute error is 0.04), and has a more restricted set of sky conditions under which it performs well (ideally, uniform overcast skies). For both methods, data collection and post‐processing is rapid, and storage of data is straightforward. Thus, mobile data collection is possible which allows detailed information on the spatial variability of ψs in urban areas to be determined. An example of such an application for a small US city, Bloomington, IN, is presented. Copyright © 2001 Royal Meteorological Society

Comparison of methods to estimate weed populations and their performance in yield loss description models

Accurate weed population estimation and yield loss prediction are important components of integrated weed management. Field experiments using Italian ryegrass as a weed in broccoli were conducted from 1994 to 1997 to compare weed density to other methods of weed population estimation, to evaluate the performance of weed population estimates in yield description models, and to study the affect of environmental variability on the predictive ability of models. A strong linear relationship was obtained between Italian ryegrass density and direct leaf area (r2 = 0.60 to 0.99). For Italian ryegrass, density and estimates of canopy from the optical device (crosswire device) had a hyperbolic relationship with high coefficients of determination (r2 > 0.72). Both direct leaf area and canopy estimates described broccoli yield as well as or better than Italian ryegrass density. The Li-Cor LAI-2000 Plant Canopy Analyzer (PCA) provided poor estimates of Italian ryegrass population (r2 from 0.00 to 0.63) that failed to describe broccoli yield. No relationship was observed between estimates of light interception through the plant canopy obtained with the Li-Cor LI-191-S Line Quantum Sensor (LQS) and either Italian ryegrass density or broccoli yield. The low performance of the PCA and lack of performance of the LQS were likely due to the smaller size of the plants and larger gaps in the plant canopy caused by wide bed spacing. At similar densities, Italian ryegrass competition with broccoli was stable from year to year. Under high Italian ryegrass density, water supply affected competition. This may limit construction of robust yield prediction models, especially in areas where water is mainly from rainfall.

A comparison of optical and direct methods for monitoring the seasonal dynamics of leaf area index in deciduous forests

During the 1996 growing season the seasonal dynamics of the Leaf Area Index (LAI) were determined by 3 different methods in two forest types: a mixed oak (Quercus robur L.) – beech (Fagus sylvatica L.) stand and an ash dominated (Fraxinus excelsior L.) stand. The results obtained from the two indirect methods, i.e. hemispherical photography and LAI-2000 Plant Canopy Analyser (Li-COR), were compared with the results of the direct measurement of litter fall collected in litter trap systems. In this study the direct method is considered to be the reference, giving the most accurate LAI-values. Both the hemispherical photography and the LAI-2000 PCA introduced an underestimation of LAI when the actual canopy leaf distribution in the crown layer deviates from a random distribution of leaf area in space as is found in the mixed oak/beech stand. However, when the condition of random leaf distribution is nearly fulfilled (ash stand), the LAI-2000 PCA gave LAI-values which were close to the results obtained from the direct method. Regression curves with R2 > 0.93 could be calculated for both indirect methods.

Test of Accuracy of LAI Estimation by LAI-2000 under Artificially Changed Leaf to Wood Area Proportions

The accuracy of LAI-2000 Plant Canopy Analyzer for leaf (LAI) and plant (PAI) area indexes measurements was tested in 20-year-old Norway spruce stand using the reduction of canopy biomass. Needle and branch areas were reduced progressively upward every one meter. Values of effective leaf area index (LAIe), as an uncorrected product of LAI-2000, were compared with directly estimated LAI and PAI values after each reduction step. LAI-2000 underestimates PAI and LAI values according to LAI-2000 rings readings, and varied proportions between leaf and wood areas. The values of LAIc have been increased with decreasing of the view angle of the relevant LAI-2000 rings. Therefore, the underestimation of LAI becomes smaller when the readings near the horizon are masked. More accurate results, for projected LAI (LAIp) calculation, are produced by LAI-2000 when some dense grids of measurement points and the most vertical ring readings (0 -13 °) are used. Correction factor 1.6 is possible to use for unreduced canopy hemi-surface LAI estimation, when the last rings (i.e. 5th and 4th rings, 47 -74 °) are excluded. Correction factor of 1.25 can be used to compute LAIp if the angle readings under 43 °are also masked.

Measuring Fractional Cover and Leaf Area Index in Arid Ecosystems: Digital Camera, Radiation Transmittance, and Laser Altimetry Methods

Field measurement of shrubland ecological properties is important for both site monitoring and validation of remote sensing information. During the May 1997 NASA Earth Observing System Jornada Prototype Validation Exercise, we calculated plot-level plant area index, leaf area index, total fractional cover, and green fractional cover with data from four instruments: (1) a Dycam Agricultural Digital Camera (ADC), (2) a LI-COR LAI-2000 plant canopy analyzer, (3) a Decagon sunfleck Ceptometer, and (4) a laser altimeter. Estimates from the LAI-2000 and Ceptometer were very similar (plant area index 0.3, leaf area index 0.22, total fractional cover 0.19, green fractional cover 0.14), while the ADC produced values 5% to 10% higher. Laser altimeter values, depending on the height cutoff used to establish total fractional cover, were either higher or lower than the other instruments' values: a 10-cm cutoff produced values

Effects of controlled weed densities and soil types on soil nitrate accumulation, spruce growth, and weed growth

Soil nitrate (NO 3 −) accumulation rates were assessed among seven weed species grown in small plots during the summer of 1997, at a northern Ontario location. Objectives were (1) to quantify soil nitrate accumulation rates at varying weed densities established on three soil types (clay, loam, and sand) and (2) to assess the effects of soil nitrate levels on weed and black spruce ( Picea mariana (Mill.) B.S.P.) seedling growth and weed growth. Controlled densities (0, 0.5, 2, 8 stems per m 2) of red raspberry ( Rubus idaeus L. var. strigosus (Michx.) Maxim.), fireweed ( Epilobium angustifolium L.), and a grass species ( Calamagrostis canadensis (Michx.) Nutt.) were planted along with spruce seedlings (1 m spacing) early in the summer of 1994. Concurrently, four more deciduous weed species, trembling aspen ( Populus tremuloides Michx.), white birch ( Betula papyrifera Marsh.), green alder ( Alnus crispa (Ait.) Pursh), and willow ( Salix humilis Marsh.) were also established at four densities (0, 0.5, 2, 4 stems per m 2). In mid-summer (July) 1997, soil samples collected from the respective weed densities were placed in polyethylene bags and the bags were incubated in the respective plots for 34 days at a depth of 12 cm. Nitrate accumulation rates (μg per 100 gm of dry soil per day), weed heights, and the effective leaf area index (LAIe, in m 2 m −2, measured with a Licor LAI-2000 Plant Canopy Analyzer) of competing vegetation were consistently higher (1.4–3.0 times) for clay soil. Nitrate levels were significantly ( p < 0.05) higher in clay soils obtained from plots planted with raspberry, grass, aspen, and willow. Carbon : nitrogen (C : N) ratios were higher for loam soils than those for clay or sand soils, and these higher ratios may have resulted in more immobilization than mineralization of soil nitrogen. Nitrate levels for clays and loams correlated significantly with the LAIe of competing vegetation ( r = 0.62–0.78) and with weed growth ( r = 0.75–0.96), but non-significantly, and often negatively, with spruce stem volume. To date, soil nitrate accumulation appears to have primarily benefited cultivated weeds and not to have improved spruce growth. These findings affirm that weeds must be controlled for seedlings to benefit nutritionally.

Comparison of direct and indirect estimation of leaf area index in mature Norway spruce stands of eastern Germany

IIn three mature Norway spruce (Picea abies (L.) Karst.) stands of the Erzgebirge (Ore Mountains) in eastern Germany, the performance of the LAI-2000 plant canopy analyzer (LI-COR instruments) was tested for indirect estimation of leaf area index (LAI). The LAI-2000 calculates effective leaf area index (LAIe, m2/m2) resulting from radiation measurements and subsequent model calculations. LAIe underestimated directly estimated half the total leaf area index (LAI0.5t, m2/m2) by 37-82% as determined from allometric relationships derived from subsample harvesting. The degree of underestimation was dependent upon stand density in two of three spruce stands examined; it was the highest in sparsely stocked plots. The relationship of LAIe to allometrically determined LAI0.5t for one of the three stands differed significantly from the other two spruce stands and the underestimation of LAI0.5t was less distinct. This was explained by stand structure, i.e., higher amounts of nonassimilating surfaces relative to LAI0.5t. These results indicate that the LAI-2000 is not generally applicable for estimation of LAI in mature spruce stands of the Erzgebirge because of effects of stand structure on LAIe-LAI0.5t relationships, which are stand specific.

Sampling methodology for LAI measurements with LAI-2000 in small forest stands

Leaf Area Index (LAI) plays a prominent role as an indicator of forest ecosystem condition in research on change detection. For this, rapid and reliable estimation of the effective LAI (LAIe) — this is the ratio of the total one-sided area of vegetation elements over the unit ground area) — at various scales is of utmost importance. We used the Licor LAI-2000 Plant Canopy Analyzer (PCA) for the acquisition of point LAI values within small (about 1 ha) stands. Canopy influences, external to the stand for which LAI was being assessed, and direct sunlight were excluded from respectively the LAIe computations and the fields of view of the PCA sensors by the use of a 270° viewcap. The effect of sampling scheme and data aggregation method on LAIe was quantified by means of a Monte Carlo simulation. The methodology presented is generalized and can be applied to forest stands with different canopy architectures. Our results show that for our study area the LAIe populations are normally distributed. A power function relationship was shown to exist between the relative accuracy of the acquired LAIe value and the sampling intensity. Based on this information, an appropriate sampling scheme can be selected for a predetermined relative accuracy. The method allowed us to quantitatively assess LAIe in small stands often occurring in very heterogeneous environments, which is typically the case for large parts of Western Europe.

Canopy openness and leaf area in chronosequences of coastal temperate rainforests

We examined spatial and temporal differences in canopy openness and effective leaf area (Le) in a series of eight forest chronosequences located on southern Vancouver Island, British Columbia. Structural attributes were measured on the west and east side of the island in immature, mature, and old-growth stands using hemispherical photography and the LAI-2000 plant canopy analyzer (PCA). Old-growth forest canopies were distinct from those of younger stands: they were more open, more heterogeneous in their openness, and maintained a lower stand Le. Although the overall developmental trajectories of forests were similar across the study sites, site-to-site differences in the rate and magnitude of these temporal changes indicated that site-specific factors also play a significant role in determining the character of forest canopies and their development. The most significant changes in canopy structure did not emerge until the later stages of stand development (150-200 years). Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) dominated east-side forests were, on average, more open, more heterogeneous, and had a lower stand Le than the stands dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn.) forming the west-side chronosequences. Shoot clumping, along with other evidence, suggested that species-related differences in leaf display and the geometry of branching structure might have contributed significantly to these regional patterns.

Photographic exposure affects indirect estimation of leaf area in plantations of Eucalyptus globulus Labill

Calibrations of indirect methods for estimating leaf area are usually based on small data sets and are often species-specific and may even be stand-specific. We used the Licor LAI-2000 plant canopy analyser (PCA) as a reference to calibrate leaf area measurements based on hemispherical photography. Ten stands of 6–8 year-old, plantation grown Tasmanian bluegum ( Eucalyptus globulus Labill.) in Western Australia were used to investigate the effects of variations in sampling position, photographic exposure and image processing on leaf area (or leaf area index, L) estimated using hemispherical photography. We also compared our photographic estimates of L with those obtained via destructive sampling (allometry) in both evenly spaced and highly clumped stands of E. globulus. Varying exposure by one stop affected estimated L by approximately 13% but we confirmed that correct exposure can be approximately predicted by metering exposure outside the canopy. In situations where metering exposure outside the canopy is impractical, we recommend the use of empirically derived relationships between L estimated from photographic images made at a constant exposure and actual L derived from other means. Mean tilt angle obtained for E. globulus from the photographic method (68.7° ± 2.5 s.e.) agreed well with estimates for Eucalyptus species from other studies. Owing to the non-random arrangement of crowns within plantations, sampling position significantly affected mean tilt angle. In highly clumped stands with closely spaced double rows and wide inter-double row gaps, underestimation of L by 16–30% with the photographic method was probably the result of greater foliage clumping at the crown level. We concluded that, in stands of E. globulus and probably other broadleaf species with evenly distributed crowns, foliage clumping at the shoot or branch level is unlikely to be a significant source of error in indirect estimates of L. Scattering of blue light may result in large underestimates of L when using the PCA. In stands with ‘extreme’ architecture, indirect, light interception-based methods are likely to greatly underestimate L, although, positioning the sensor so as remove large gaps from view may allow accurate estimates of L even in these stands.

Comparison of direct and indirect estimation of leaf area index in mature Norway spruce stands of eastern Germany

IIn three mature Norway spruce (Picea abies (L.) Karst.) stands of the Erzgebirge (Ore Mountains) in eastern Germany, the performance of the LAI-2000 plant canopy analyzer (LI-COR instruments) was tested for indirect estimation of leaf area index (LAI). The LAI-2000 calculates effective leaf area index (LAIe, m2/m2) resulting from radiation measurements and subsequent model calculations. LAIe underestimated directly estimated half the total leaf area index (LAI0.5t, m2/m2) by 37-82% as determined from allometric relationships derived from subsample harvesting. The degree of underestimation was dependent upon stand density in two of three spruce stands examined; it was the highest in sparsely stocked plots. The relationship of LAIe to allometrically determined LAI0.5t for one of the three stands differed significantly from the other two spruce stands and the underestimation of LAI0.5t was less distinct. This was explained by stand structure, i.e., higher amounts of nonassimilating surfaces relative to LAI0...