Remote Sensing for the Determination of the Woody-to-total Area Ratios in Mixedwood Forest Stands

Abstract

Leaf area index (LAI) is a biophysical variable that is important for estimating processes such as productivity and yield rates in forest stands. Indirect methods for estimating LAI (e.g., digital hemispherical photography (DHP)), provide efficient and reliable measurements. However, DHP utilizes gap-fraction-based methods that are unable to both discriminate between leafy and other plant material and compensate for the non-random positioning of canopy elements. Therefore, LAI estimates obtained with these techniques can be termed effective leaf area index (LAIe). Woody-to-total area ratios are applied to these measurements to compensate for the inclusion of non-photosynthetic canopy components, but these parameters vary amongst tree species and are not well studied. This project attempts to determine LAI for mixedwood stands (i.e., deciduous and coniferous) by examining the woody-to-total area ratio for species in the Haliburton Forest located in southeastern Ontario. Two sets of DHPs were taken for 23 stem-mapped forest plots during field campaigns carried out in leaf-on and leaf-off periods to establish the impact of non-photosynthetic materials on estimating LAI. For solely deciduous stands, the woody-to-total area ratio is assumed to be directly equal to the difference in LAIe values between these two periods. For purely coniferous stands, the woody-total area ratio will be derived in the same manner for leaf-on and leaf-off conditions (i.e., with correction factors applied based on published ratios and corresponding to the basal area ratio of conifers). For mixed stands, the proportions of conifers (in terms of BA) to deciduous species will be used to determine appropriate models for estimating LAIe.