LAI estimation of natural pine forest using a non-standard sampling technique

Abstract

Indirect methods to estimate the leaf area index (LAI) in forests have been less successful than the more costly direct (allometric) methods. Our aim was to find an indirect method to estimate LAI efficiently, using the LAI-2000, Plant Canopy Analyzer, in forest stands of Pinus halepensis. The direct LAI estimate of individual trees was carried out through destructive sampling. In forest stands, direct estimates were derived from the allometric relationship between leaf area per tree and diameter at breast height (DBH). Indirect estimates were conducted with a standard strategy (i.e., multiple readings per plot placing the sensor at sites selected systematically on a transect) and with our non-standard strategy consisting of reading at a single point per plot, standardising the distance and orientation from a subject tree to reduce variability. The non-standard sampling strategy was a procedure as effective and accurate as the indirect standard strategy (transects), but more labour-efficient. The indirect estimate of the LAI-STAND using the LAI-2000, with either strategy was unbiased. These results advocate the use of a non-standard strategy scattering the sampling points throughout the stand rather than concentrating all the effort on a few plots following a standard strategy and leaving the rest of the stand unchecked. Also, both the standard and the non-standard strategy yielded significant regression models to estimate forest stand parameters, which are labour expensive to measure using direct methods. Thus, the LAI-2000 could be used as a tool to estimate such parameters indirectly.