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1.
Leaf area index (LAI) was estimated at 15 sites in the Swiss Long-Term Forest Ecosystem Research Programme (LWF) in 2004–2005 using two indirect techniques: the LAI-2000 plant canopy analyzer (Licor Inc.) and digital hemispherical photography, applying several exposure settings. Hemispherical photographs of the canopy were analysed using Hemisfer, a software package that offers several new features, which were tested here: (1) automatic thresholding taking the gamma value of the picture into account; (2) implementation of several equations to solve the gap-fraction inversion model from which LAI estimates are derived; (3) correction for ground slope effects, and (4) correction for clumped canopies. In seven broadleaved stands in our sample set, LAI was also estimated semi-directly from litterfall. The various equations used to solve the gap-fraction inversion model generated significantly different estimates for the LAI-2000 measurements. In contrast, the same equations applied in Hemisfer did not produce significantly different estimates. The best relationship between the LAI-2000 and the Hemisfer estimates was obtained when the hemispherical photographs were overexposed by one to two stops compared with the exposure setting derived from the reading of a spotmeter in a canopy gap. There was no clear general relationship between the litterfall and the LAI-2000 or the hemispherical photographs estimates. This was probably due to the heterogeneity of the canopy, or to biased litterfall collection at sites on steep slopes or sites subject to strong winds. This study introduces new arguments into the comparison of the advantages and drawbacks of the LAI-2000 and hemispherical photography in terms of applicability and accuracy.  相似文献   

2.
分别采用半球面影像技术和LAI-2000冠层分析仪对华南地区最常用园林树种小叶榕(Ficus microcarpa)的叶面积指数(Leaf Area Index,LAI)进行测定、比较和分析。研究表明,2种测量仪器所测LAI值存在极显著正相关(P<0.001);用半球面影像技术测量的LAI值与冠幅、胸径和树高之间也存在极显著一元线性关系,构建回归模型分别为:LAI=0.0444Cw+1.6526,LAI=0.0088D+1.8327,LAI=0.0543H+1.6404;通过模型可估测小叶榕单株的叶面积指数,达到95%的置信区间的估测值范围。  相似文献   

3.
叶面积指数(LAI)是森林生态系统的重要结构参数,用来反映植物叶量和群体生长特征[1-4],对生态系统水分和养分循环、地表和大气之间的相互作用等诸多过程都有重要影响[5-6],广泛应用于植物生态、植物生理、生态水文以及一些交叉学科的研究中,也可作为科学培育森林、评价林分质量的定量指  相似文献   

4.
Although decline of Aleppo pine was observed long ago and several climatic and biotic factors have been previously associated with this complex process, site factors involved in this decline remain poorly understood. The objective of the work described here was to identify site factors associated with canopy condition. Canopy condition was estimated both by a visual estimation of defoliation, and by an indirect estimation of leaf area index (LAI) and other stand‐ and light‐related parameters through the analysis of hemispherical photographs. A high percentage of damaged trees (81%) along with high levels of defoliation in plots (up to 53%) and trees (up to 85%) were recorded. Regression models showed that the site factors associated with defoliation were basal area, age, crown depth and elevation, while those associated with LAI were diameter at breast height, tree density and canopy openness. Analysis of hemispherical photographs proved to be a useful method for LAI estimation, but not for estimation of defoliation due to heterogeneous defoliation patterns caused by fungal pathogens detected in the study area. Soils and climatic conditions were common to all plots, so their influence could not be tested, but poor soil conditions and climatic restraints are known in this area, including low soil productivity, frequent summer droughts and high numbers of frost days. The results obtained suggest that several factors were associated with the decline of Pinus halepensis, including age, basal area, canopy openness, diameter, height and tree density. These factors can influence canopy condition, and thus, they might be acting as predisposing factors for the decline. The modulation of these factors is possible if suitable forest management strategies are applied, which could lead to a decrease of the decline incidence.  相似文献   

5.
In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index(LAI),a Larix principis-rupprechtii plantation was chosen in the small watershed of Xiangshuihe located at the Liupan Mountains of Ningxia Hui Autonomous Region of NW China,the LAI was measured in October 2010,a period from full canopy to the total fall of needles,by using both the LAI- 2000 and litterfall collection method.Then,a comparison was made between the LAI values determined by the litter-fall collection and that calculated based on the figures read from LAI-2000 and the fixed calibration factor(1.49).It showed that the average of LAI measurements of the 2 methods was very close,with a difference of only 5%.However,the calculated LAI from LAI-2000 was obviously higher than the true values determined by litter-fall collection when the canopy was full of needles;and obviously lower than the true value when the canopy was sparse after needle falling.The reason may be that LAI-2000 takes the projection of twigs as needles.So,a dynamic calibration factor is needed,especially in the seasons when the needle amount and the percentage of twigs projection in crown projection change quickly.Therefore,a statistic relation in a quadratic polynomial form between the 2 series of LAI data was well fitted. This relation can be used for a more accurate estimation of LAI based on the data read from the easilyused canopy scanners like LAI-2000.  相似文献   

6.
We evaluated several optical methods for in situ estimation of leaf area index (LAI) in a Belgian Scots pine (Pinus sylvestris L.) stand. The results obtained were compared with LAI determined from allometric relationships established in the same stand. We found high correlations between branch cross-sectional area, diameter at breast height (DBH) and basal area as dependent variables, and leaf mass, needle area and crown projection as independent variables. We then compared LAI estimated by allometry with LAI determined by three optical methods (LAI-2000, TRAC and digital hemispherical photography) both before and after corrections for blue light scattering, clumping and non-leafy material. Estimates of stand LAI of Scots pine ranged from 1.52 for hemispherical photography to 3.57 for the allometric estimate based on DBH. There was no significant difference (alpha = 0.01) between the allometric LAI estimates and the optical LAI values corrected for blue light scattering, clumping and interception by non-leafy material. However, we observed high sensitivity of the optical LAI estimates to the various conversion factors, particularly to the clumping factor, indicating the need for caution when correcting LAI measured by optical methods.  相似文献   

7.
Leaf area index (LAI) is an important parameter to identify the water balance in forested watershed as a biological factor influencing directly on the evapotranspiration in the forest area. The purpose of this study was to estimate the LAI in a small forested watershed in summer and winter by applying the Terra/Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to the LAI estimation method. In this study, the estimation was based on the absorption and scattering processes of the solar radiation in the vegetation canopy and the spectral reflectance characteristics of soil vegetation. First, we estimated LAI based on Price’s model by application of ASTER data on the forested watershed located in the Tenzan Mountains of Saga, Japan. To validate the results of LAI estimation, secondly, we compared them to the measured LAI obtained by a plant canopy analyzer (LAI-2000) on the observation area inside the target region. This study showed that the LAI estimation method was a feasible and accurate method as indicated by the high relationship (r = 0.97) between LAI derived from ASTER data and LAI measured by LAI-2000. This paper is the first report on LAI estimation using Terra/ASTER data based on Price’s model and field investigation. This LAI estimation method is a reliable and applicable method.  相似文献   

8.
Woody materials (woody area index, WAI) is a key error source in estimating leaf area index (LAI) by optical methods, but how to correct the error caused by WAI during different seasons has not reached consensus. In this study, effective plant area index (PAIe) was first estimated using two indirect optical methods (digital hemispherical photography, DHP, and LAI-2000) in a deciduous needleleaf forest, and then four different schemes for correcting the contribution of WAI to PAIe were tested here. We also directly estimated the seasonality of LAI by a litter collection method and an allometric method. Directly subtracting WAI from PAI resulted in a greater degree of uncertainty in correcting seasonal changes of PAIe from both DHP and LAI-2000. Therefore, we introduced a new correction factor, the stem-to-total area ratio, which was reasonable and useful for quantifying seasonal changes in the contribution of WAI to PAIe. We finally recommend a practical scheme for correcting PAIe from both DHP and LAI-2000, with accuracies as high as 88% and 87% during most growing seasons, respectively. Additionally, LAI values estimated from allometry were concordant with those estimated from litter collection, indicating that the allometry method is useful for tracking seasonal changes in LAI.  相似文献   

9.
We compared leaf area index (LAI) estimates of a broad-leaf tropical hardwood, Metrosideros polymorpha Gaud (‘Ōhi’a), using a optical method (LI-COR LAI-2000) and direct determination (harvest and allometry). There was a strong correlation between LAI estimates by the two methods, but direct estimates were higher than the optical estimates by a factor of 2.44. The ratio of harvest leaf area to projected leaf area within twigs was similar (2.42) to that of whole plots, suggesting that aggregation of leaves at this scale of branching may account for most of the underestimate by the optical method. The within-branch ratio of actual to projected leaf area did not differ among three sites on three islands of varying land surface age but similar climate, suggesting that a correction factor determined by harvest could be used to adjust optical estimates of LAI in other M. polymorpha forests.  相似文献   

10.
We assessed the accuracy with which the LAI-2000 plant canopy analyzer measured changes in leaf area index (LAI) and plant area index (PAI) in a 25-year-old Scots pine (Pinus sylvestris L.) stand. Stand density was 2100 stems ha(-1) and mean tree height was 8.7 m. Needle and branch areas of the stand were reduced progressively to zero by the stepwise removal of branches on all trees growing in a circular plot with a radius of 25 m. An LAI-2000 estimate was taken after each step reduction. The needle and branch surface areas removed at each step were estimated from direct measurements and were compared with the changes in the LAI-2000 estimates. Initially (before removal of branches), directly measured PAI was 5.2 (needles = 86%, branches = 8% and stems = 6%). The LAI-2000 estimate of total surface area was 66% of direct PAI and 77% of direct LAI. There was a nonlinear relationship between the LAI-2000 estimate and directly measured PAI, such that their ratio (equivalent to the clumping factor) increased from 0.66 to 1.05 with decreasing PAI. At the last measurement, when only stems were left, the LAI-2000 estimate agreed well with the direct measurement of PAI. The LAI-2000 underestimated the direct measurement of LAI at the first three steps when LAI was > 2 and the proportion of woody area was small (< 20%). However, because the LAI-2000 estimate included stem and branch areas, it overestimated the direct measurement of LAI at the last three measurements when the proportion of woody area was large (> 20%).  相似文献   

11.
A simple measure of the amount of foliage present in a forest is leaf area index (LAI; the amount of foliage per unit ground surface area), which can be determined by optical estimation (gap fraction method) with an instrument such as the Li-Cor LAI-2000 Plant Canopy Analyzer. However, optical instruments such as the LAI-2000 cannot directly differentiate between foliage and woody components of the canopy. Studies investigating LAI and its calibration (extracting foliar LAI from optical estimates) in tropical forests are rare. We calibrated optical estimates of LAI from the LAI-2000 with leaf litter data for a tropical dry forest. We also developed a robust method for determining LAI from leaf litter data in a tropical dry forest environment. We found that, depending on the successional stage of the canopy and the season, the LAI-2000 may underestimate LAI by 17% to over 40%. In the dry season, the instrument overestimated LAI by the contribution of the woody area index. Examination of the seasonal variation in LAI for three successional stages in a tropical dry forest indicated differences in timing of leaf fall according to successional stage and functional group (i.e., lianas and trees). We conclude that when calculating LAI from optical estimates, it is necessary to account for the differences between values obtained from optical and semi-direct techniques. In addition, to calculate LAI from litter collected in traps, specific leaf area must be calculated for each species rather than from a mean value for multiple species.  相似文献   

12.
Canopy gap fraction and leaf area index (LAI) were measured using hemispherical photography in 91 mature forests across Switzerland, including coniferous, broadleaved and mixed stands. The gap fraction and LAI derived from five photographs per site could be reproduced with a high coefficient of determination (R2 > 0.7) by regression against simple stand parameters obtained from vegetation surveys: coverages of the tree, shrub and herb layers, and tree height. The method appeared to be robust across the different types of forests. Applied to 981 sites across Switzerland, the regression model produced LAI values ranging from 1.4 to 6.7. These predictions were compared with site variables not included in the regression. LAI appeared limited by the altitude, with maximal values decreasing by one third from 400 to 2000 m above see level. Water availability was also clearly a limitation at sites with a negative water balance, i.e. where the yearly potential evapotranspiration exceeded the precipitation. High or low values of a humidity index based on the ground vegetation also corresponded to a limitation of the LAI, with shorter trees at dry sites and more open canopies at wet sites. Compared to optical measurements (including hemispherical photography), our regression method is fast and inexpensive. Such an approach appears very promising for obtaining reliable estimates of LAI for many sites with low costs. These estimates can then be fed into process models at the stand level.  相似文献   

13.
The leaf area index (LAI) of 16 sample plots was estimated based on terrestrial three-dimensional laser scanning. The point-cloud data of stand canopy were first scaled and projected onto a hemisphere according to Lambert azimuthal equal-area projection or stereographic projection, and the resulting hemispherical point-cloud images were used to extract the canopy porosity coefficients. Then, single-angle inversion and Miller formula inversion methods were used, respectively, to calculate the effective leaf area indices with canopy porosity coefficients. Results showed that the effective LAIs estimated by single-angle inversion method with Lambert projection and stereographic projection were within the range of 2.14~5.36 and 1.83~4.67, respectively. The effective LAIs obtained by Miller formula inversion method with Lambert projection and stereographic projection were within the range of 1.84~4.67 and 1.68~4.34, respectively. As a comparison, the LAI measured with a fish-eye camera ranged from 1.55 to 3.87. The LAI values estimated with four different calculation methods were linearly correlated with those measured by a fish-eye camera. The highest coefficient of determination (R2) 90.28% was obtained by the Miller formula inversion method combined with stereographic projection, and Duncan’s new multiple range test also further showed that this method had a relatively higher precision compared to other three methods.  相似文献   

14.
Abstract

Interpretation and tree height measurements in aerial photographs using photogrammetric workstations are frequently performed in standwise forest inventory. Images acquired by digital aerial cameras are now replacing the traditional film-based aerial photographs. In this study, digital images from the airborne Z/I DMC system for standwise estimation of stem volume, tree height and tree species composition were investigated at a 1200 ha forest area located in southern Sweden (58°30′N, 13°40′E). The 56 selected stands were dominated by Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) with stem volume in the range of 30–630 m3 ha?1 (average 300 m3 ha?1) and tree height in the range of 6–28 m (average 20 m). The large-format pansharpened colour infrared images were captured at a flight altitude of 4800 m above ground level corresponding to a pixel size of 0.48 m. The photo-interpretation was conducted by four professional interpreters, independently. In particular, two different base-to-height ratios (i.e. the ratio between the ground distance between image centres at the time of exposure and the flight altitude above ground level) of 0.26 and 0.39 were evaluated, but no significant difference in the estimation accuracy for stem volume and tree height was found. The accuracy for stem volume estimation in terms of relative root mean square error, corrected for systematic errors, was on average 24% (in the range of 17–39%). The corresponding accuracy for tree height estimation was on average 1.4 m (in the range of 0.9–1.6 m). The tree species composition accuracy assessment using a fuzzy set evaluation procedure showed that 95% of the stands were correctly classified. The estimation accuracies are in agreement with previous results using conventional film-based aerial panchromatic photographs.  相似文献   

15.
Hemispherical photographs combined with litter collection were applied to determine seasonal dynamics of leaf area index (LAI) between the period of maximum leaf area and the leafless period from an old-growth temperate forest in the Xiaoxing’an Mountains, northeastern China. Our objective is to explore the change in the relationship between “true” LAI and effective LAI (calculated only from hemispherical photography) and to find the best LAI estimation models. Effective LAI in November is corrected for contribution of woody material and clumping at shoot and beyond shoot levels, to give minimum “true” LAI. The “true” LAI in each period is estimated as a sum of the minimum “true” LAI and litter collection LAI in each period. Power function regression calibration models were then carried out between “true” LAI and effective LAI in each period and the entire litter-fall period. Then, significance tests were applied to detect the differences among different models. The results showed that the average “true” LAI ranged from 2.74 ± 0.54 on November 1 to 6.64 ± 1.34 on July 1. For the entire season, average effective LAI was 53.16 % lower than the average “true” LAI. After significance tests, calibration models were classified into two types: (1) maximum LAI period and the period of maximum leaf fall; (2) the period during which leaves began falling and all deciduous leaves had fallen. Based on our experience, we believe that the classified models can produce reliable and accurate LA1 values for the needle and broad-leaved mixed forest stands under the non-destructive condition.  相似文献   

16.
Uncertainties about the implications of land-cover heterogeneity on the Amazonian carbon (C) and water cycles are, in part, related to the lack of information about spatial patterns of key variables that control these fluxes at the regional scale. Leaf area index (LAI) is one of these key variables, regulating a number of ecosystem processes (e.g. evaporation, transpiration and photosynthesis). In order to generate a sampling strategy for LAI across a section of Amazonia, we generated a landscape unit (LU) map for the Tapajós region, Eastern Amazonia, as a basis for stratification. We identified seven primary forest classes, stratified according to vegetation and/or terrain characteristics, and one secondary forest class, covering 80% of the region. Primary forest units were the most representative, covering 62% of the total area. The LAI measurements were carried out in 13 selected LUs. In each LU, we marked out three 50 m × 50 m plots giving a total number of 39 plots (9.75 ha). A pair of LAI-2000 plant canopy analysers was used to estimate LAI. We recorded a total of 25 LAI measurements within each plot. We used the field data to verify the statistical distribution of LAI samples, analyse the LAI variability within and among sites, and show the influence of sample size on LAI variation and precision. The LAI showed a high coefficient of variation at the plot level (0.25 ha), from 5.2% to 23%, but this was reduced at the landscape unit level (three co-located plots, 1.8–12%). The level of precision was <10% and 15% at the plot and landscape unit level, respectively. The LAI decreased from a dense lowland forest site (5.10) to a secondary forest (3.46) and to a pasture site (1.56). We found evidence for differences in the scale of spatial heterogeneity of closed canopy forest versus open canopy forest and palm forests. Landscape variables could, in part, explain differences in LAI among forest sites, and land use is an important modifier of LAI patterns. The stratified LAI sampling proposed in the present study could cope with three important aspects of C and water fluxes modelling: (1) optimise the information obtained from field measurements, which is an advance for models parameterisation, compared to the usual random sampling; (2) generate information for a subsequent scaling up of point field measurements to surfaces covering the whole region; and (3) build a useful basis for validation of estimations, based on remote sensing data, of LAI in the Tapajós region. The variability of LAI in the Tapajós region showed that this variable is a source of uncertainty for large-scale process modelling.  相似文献   

17.
Sources of variation in leaf area index (LAI; m2 of projected leaf area per m2 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.  相似文献   

18.
立地水分条件决定的植被承载力是干旱缺水地区森林合理经营的重要依据。考虑到干旱缺水地区的森林蒸散耗水在水分输出中占据绝对主导地位,其大小直接与叶面积指数(LAI)相关,将林冠LAI在生长季一段时间内的最大值(LAImax)作为植被承载力(LAIc)的量化指标,利用冠层分析仪(LAI-2000),在六盘山香水河小流域和叠叠沟小流域的44个华北落叶松人工林样地,实测了冠层LAI的季节动态变化,研究了生长季内LAImax与林分断面积、郁闭度、平均树高、密度等常用林分结构指标的关系。结果表明:LAImax与林分不同结构指标均呈幂函数关系,其决定系数(R2)依次为0.84、0.82、0.56、0.47,说明能同时反映林分密度和树体大小的林分断面积与林冠LAI相关最紧密。将LAImax与林分断面积的幂函数关系嵌入了林分平均胸径与林分密度和林龄关系的模型,用以描述LAImax与林龄和密度的关系,并利用样地实测数据拟合了模型参数。拟合建立的模型对所有样地的LAImax的计算值与实测值的相对误差平均为8.6%(0%20.4%),能较好地描述LAI与林龄和密度的关系。利用此模型,进一步导出了能依据给定的LAIc,简捷计算出不同林龄时的可承载林分密度的模型,从而为基于立地水分植被承载力的林分密度管理和森林多功能经营等提供技术支持。  相似文献   

19.
A two-year study was conducted evaluating Puffer® aerosol dispensers (Suterra LLC, Bend, OR, USA) for mating disruption of codling moth, Cydia pomonella (L.), and the oriental fruit moth, Grapholita molesta (Busck). The Puffer® dispenser consists of a pressurized metal canister loaded with pheromone active ingredients dissolved in solvent and housed within a circuit-controlled, plastic dispensing cabinet programmed to release an aerosol spray of pheromone at regular intervals. Puffers® were deployed at the label-recommended rate of 2.5 ha?1 and released ca. 5–10 mg of pheromone (depending on treatment) per 15 min during a 12-h cycle beginning each day at 15:00 h for the duration of the season. In 2005, commercially-managed apple plots (3.2–4.9 ha) were treated with Puffers® releasing both species’ pheromone simultaneously (dual-species) or with twice the number of adjacently-deployed Puffers® (4–6 m apart) releasing each individual species’ pheromones (single-species), while maintaining comparable overall release rates of pheromone between these two treatments. Plots 100 m away and not treated with pheromone served as the control. Disruption of male C. pomonella and G. molesta orientation to pheromone-baited traps was 46–75 and 91–98%, respectively, in Puffer®-treated plots compared with untreated controls. There was no statistical difference in moth disruption between plots treated with dual-species and single-species Puffers®. Fruit injury was not statistically different between Puffer®-treated plots and control plots not receiving pheromone. In 2006, disruption of male moth orientation to traps was 24–26 and 84–97% in Puffer®-treated plots (2.9–5.7 ha) for C. pomonella and G. molesta, respectively, compared with untreated controls. During this season, fruit injury was lower in pheromone-treated plots compared with untreated controls at mid-season, but not at pre-harvest. Combining the pheromone of both species into single Puffer® units did not decrease efficacy of disruption compared with deploying twice as many Puffers® releasing a similar amount of each individual species’ pheromone suggesting that multi-species disruption using Puffers® is a viable option. However, we conclude that the efficacy of disruption attained with low-densities (2.5 ha?1) of Puffers® at the moth densities recorded in this study is insufficient for effective control of C. pomonella without input of companion insecticides.  相似文献   

20.
In order to quantify the light conditions of a deciduous broad-leaved forest, we proposed a method to determine the threshold level of the brightness of a hemispherical photograph when converting it into a one-bit screen image. The coefficient of determination was examined for the regression between the measured ISF (indirect site factor) using the quantum sensors and the estimated ISF from the photographs, by changing the threshold level for the photographs. In the range of threshold levels between 60 and 180, the coefficients of determination (r 2) were all significant, andr 2 had a single maximum value at the threshold level of 115. This method was found to be effective for determining a single threshold level without subjectivity at any season.  相似文献   

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