Abstract
Leaf area index (LAI) is an important variable in the study of forest ecosystem processes, but very few studies are designed to monitor LAI and the seasonal variability in a mixed forest using non-destructive sampling. In this study, first, true LAI from May 1st and November 15th was estimated by making several calibrations to LAI as measured from the WinSCANOPY 2006 Plant Canopy Analyzer. These calibrations include a foliage element (shoot, that is considered to be a collection of needles) clumping index measured directly from the optical instrument, TRAC (Tracing Radiation and Architecture of Canopies); a needle-to-shoot area ratio obtained from shoot samples; and a woody-to-total area ratio. Second, by periodically combining true LAI (May 1st) with the seasonality of LAI for deciduous and coniferous species throughout the leaf-expansion season (from May to August), we estimated LAI of each investigation period in the leaf-expansion season. Third, by combining true LAI (November 15th) with litter trap data (both deciduous and coniferous species), we estimated LAI of each investigation period during the leaf-fall season (from September to mid-November). Finally, LAI for the entire canopy then was derived from the initial leaf expansion to the leaf fall. The results showed that LAI reached its peak with a value of 6.53 m2 m−2 (a corresponding value of 3.83 m2 m−2 from optical instrument) in early August, and the mean LAI was 4.97 m2 m−2 from May to November using the proposed method. The optical instrument method underestimated LAI by an average of 41.64% (SD = 6.54) throughout the whole study period compared to that estimated by the proposed method. The result of the present work implied that our method would be suitable for measuring LAI, for detecting the seasonality of LAI in a mixed forest, and for measuring LAI seasonality for each species.
Highlights
Leaf area index (LAI) is one of the most important characteristics of plant canopy structure and has attracted many scholars’ attention [1]
LAI is required as an input variable in most ecosystem models simulating carbon and water cycles [6], and it often serves as a convenient surrogate measure of gross primary productivity (GPP) [7]
3.1 Clumping index The clumping index of each sample point on May 1st and November 15th was directly obtained from DHP and TRACWin 3.9.1 software, and the difference in the results was not significant (Table 1)
Summary
Leaf area index (LAI) is one of the most important characteristics of plant canopy structure and has attracted many scholars’ attention [1]. An accurate measurement of LAI is essential for converting leaf-level processes to the canopy level [8]. Direct methods include destructive sampling, allometry, and litter traps [13]. Litter traps method is non-destructive, and collecting leaf litter to determine LAI is very accurate [17,18]. Litter traps method is more successful in deciduous forests that have a single leaf-fall season than in evergreen or mixed forests that have more continuous leaf loss and replacement, and it provides little information about LAI during the leaf-expansion season. Litter traps method should not be used to monitor LAI seasonality in a mixed forest stand [15,19]
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