An automated procedure for estimating the leaf area index (LAI) of woodland ecosystems using digital imagery, MATLAB programming and its application to an examination of the relationship between remotely sensed and field measurements of LAI.

Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional-structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 - 0.0066 LAID; R2 = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID - 0.2371; R2 = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R2 = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers.

[1]  T. Carlson,et al.  On the relation between NDVI, fractional vegetation cover, and leaf area index , 1997 .

[2]  D. J. Watson,et al.  Comparative Physiological Studies on the Growth of Field Crops: II. The Effect of Varying Nutrient Supply on Net Assimilation Rate and Leaf Area , 1947 .

[3]  S. Running,et al.  Relationship of thematic mapper simulator data to leaf area index , 1987 .

[4]  M. Zeppel,et al.  The response of sap flow to pulses of rain in a temperate Australian woodland , 2008, Plant and Soil.

[5]  Julio Calvo-Alvarado,et al.  Calibration of LAI-2000 to estimate leaf area index (LAI) and assessment of its relationship with stand productivity in six native and introduced tree species in Costa Rica. , 2007 .

[6]  A. Cutini,et al.  Estimation of leaf area index with the Li-Cor LAI 2000 in deciduous forests , 1998 .

[7]  D. Watson.  Comparative Physiological Studies on the Growth of Field Crops: I. Variation in Net Assimilation Rate and Leaf Area between Species and Varieties, and within and between Years , 1947 .

[8]  C. Woodcock,et al.  Multiscale analysis and validation of the MODIS LAI product: II. Sampling strategy , 2002 .

[9]  S. Running,et al.  Forest ecosystem processes at the watershed scale: Sensitivity to remotely-sensed leaf area index estimates , 1993 .

[10]  Craig Macfarlane,et al.  Photographic exposure affects indirect estimation of leaf area in plantations of Eucalyptus globulus Labill. , 2000 .

[11]  Craig Macfarlane,et al.  Estimation of leaf area index in eucalypt forest with vertical foliage, using cover and fullframe fisheye photography , 2007 .

[12]  Craig Macfarlane,et al.  Estimating forest leaf area using cover and fullframe fisheye photography: Thinking inside the circle , 2007 .

[13]  M. Huston,et al.  A comparison of direct and indirect methods for estimating forest canopy leaf area , 1991 .

[14]  Yuhong He,et al.  Comparison of different methods for measuring leaf area index in a mixed grassland , 2007 .

[15]  Luciano Mateos,et al.  Non-destructive measurement of leaf area in olive (Olea europaea L.) trees using a gap inversion method , 1995 .

[16]  S. Running,et al.  Synergistic algorithm for estimating vegetation canopy leaf area index and fraction of absorbed photosynthetically active , 1998 .

[17]  S. T. Gower,et al.  Characterizing canopy nonrandomness with a multiband vegetation imager (MVI) , 1997 .

[18]  M. Zeppel,et al.  Seasonal responses of xylem sap velocity to VPD and solar radiation during drought in a stand of native trees in temperate Australia. , 2004, Functional plant biology : FPB.

[19]  Jennifer L. Dungan,et al.  Forest ecosystem processes at the watershed scale: basis for distributed simulation , 1991 .

[20]  M. Zeppel,et al.  A modified Jarvis-Stewart model for predicting stand-scale transpiration of an Australian native forest , 2008, Plant and Soil.

[21]  R. McMurtrie,et al.  Estimation of leaf area index in eucalypt forest using digital photography , 2007 .

[22]  N. Breda.  Ground-based measurements of leaf area index: a review of methods, instruments and current controversies. , 2003, Journal of experimental botany.

[23]  Ranga B. Myneni,et al.  Stochastic transport theory for investigating the three-dimensional canopy structure from space measurements , 2008 .

[24]  Frank Ewert,et al.  Modelling plant responses to elevated CO2: how important is leaf area index? , 2004, Annals of botany.

[25]  L. Johnson.  Temporal stability of an NDVI-LAI relationship in a Napa Valley vineyard , 2003 .

[26]  J. Cihlar,et al.  Plant canopy gap-size analysis theory for improving optical measurements of leaf-area index. , 1995, Applied optics.

[27]  P. de Reffye,et al.  A model simulating above- and below-ground tree architecture with agroforestry applications , 1995, Agroforestry Systems.

[28]  W. J. Shuttleworth,et al.  Incorporating NDVI-Derived LAI into the Climate Version of RAMS and Its Impact on Regional Climate , 2002 .

[29]  R. Hall,et al.  A comparison of digital and film fisheye photography for analysis of forest canopy structure and gap light transmission , 2001 .