Seasonal variation of tropical forest LAI based on field measurements in Central African Republic

The research presented in this paper focuses on the measurement over a large area of seasonal variation in foliage of a tropical forest. This effort is part of a larger experiment linking ground and space observations over time. A dedicated 8-month field campaign was carried out in Ngotto, a semi-deciduous forest in the Central African Republic to study the spatial and temporal variability of Leaf Area Index (LAI). First, the sensitivity of the LAI-2000 Plant Canopy Analyser instrument was tested. Five sensitivity variables were tested in all: measurement procedure, positioning error, Solar Zenith Angle (SZA) effects, foliage changes, and cloud cover variations. Secondly, the LAI spatial variability was assessed based on geostatistical analysis of measured transects with lags ranging from 30 cm to 10 m. The variogram analysis, showed an overall variance estimate of 0.47 (sill) and a loss of spatial correlation at a distance of 30 m (range). These values were used to calculate the sample size and the minimum distance between adjacent positions, respectively, in order to design a relevant sampling scheme for assessing forest foliage seasonality. Throughout the 8-month field campaign, the LAI was measured at least monthly at 64 positions within 4 km(2) forest sites. A seasonal change of LAI of 0.34 was measured for this tropical forest and found to be in sync with the dry season which lasts three months. (C) 2003 Elsevier B.V. All rights reserved.

[1]  F. White,et al.  La végétation de l'Afrique : mémoire accompagnant la carte de végétation de l'Afrique UNESCO/AETFAT/UNSO , 1986 .

[2]  S. T. Gower,et al.  Rapid Estimation of Leaf Area Index in Conifer and Broad-Leaf Plantations , 1991 .

[3]  J. Fownes,et al.  Effects of leaf aggregation in a broad-leaf canopy on estimates of leaf area index by the gap-fraction method , 1997 .

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

[5]  T. Whitmore,et al.  An Introduction to Tropical Rain Forests , 1990 .

[6]  Giles M. Foody,et al.  Assessing the ground data requirements for regional scale remote sensing of tropical forest biophysical properties , 2000 .

[7]  J. Walter,et al.  Comparaison de méthodes optiques pour estimer l’ouverture de la canopée et l’indice foliaire en forêt feuillue , 2001 .

[8]  S. T. Gower,et al.  Measurements of branch area and adjusting leaf area index indirect measurements , 1998 .

[9]  Paul J. Curran,et al.  Simple size for ground and remotely sensed data , 1986 .

[10]  J. Welles.  Some indirect methods of estimating canopy structure , 1990 .

[11]  P. Stenberg,et al.  Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scots pine stands. , 1994, Tree physiology.

[12]  Pol Coppin,et al.  Sampling methodology for LAI measurements with LAI-2000 in small forest stands. , 2000 .

[13]  C. Wessman,et al.  Photosynthetically active radiation heterogeneity within a monodominant Congolese rain forest canopy , 2000 .

[14]  M. Marek,et al.  Test of Accuracy of LAI Estimation by LAI-2000 under Artificially Changed Leaf to Wood Area Proportions , 2000, Biologia Plantarum.

[15]  Ian B. Strachan,et al.  Spatial and vertical leaf area index of a deciduous forest resolved using the LAI-2000 plant canopy analyzer , 1996 .

[16]  Sylvain G. Leblanc,et al.  A practical scheme for correcting multiple scattering effects on optical LAI measurements , 2001 .

[17]  Carina Gardiner.  Atlas Climatique du Bassin Congolais , 1971 .

[18]  P. Meir,et al.  Photographic method to measure the vertical distribution of leaf area density in forests , 2000 .

[19]  Reflectance, leaf area index and structural studies of a rain forest canopy using the “Opération Canopée” association's tree top raft ‐ hot air airship combination , 1994 .

[20]  P. Richards,et al.  The Tropical Rain Forest: An Ecological Study , 1953 .

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

[22]  J. Norman,et al.  Instrument for Indirect Measurement of Canopy Architecture , 1991 .

[23]  P. Stenberg,et al.  Response of LAI-2000 estimates to changes in plant surface area index in a Scots pine stand. , 1996, Tree physiology.

[24]  Peter M. Atkinson,et al.  Optimal ground-based sampling for remote sensing investigations: estimating the regional mean , 1991 .

[25]  Timothy C. Coburn,et al.  Geostatistics for Natural Resources Evaluation , 2000, Technometrics.

[26]  C. Evrard,et al.  Recherches écologiques sur le peuplement forestier des sols hydromorphes de la Cuvette central congolaise , 1968 .

[27]  Philip J. Radtke,et al.  Laser point-quadrat sampling for estimating foliage-height profiles in broad-leaved forests , 2001 .