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

Abstract

Leaf area index (LAI) is one of the most frequently used parameters for the analysis of canopy structure and it has also been shown to be an important structural characteristic of the forest ecosystem and forest productivity. The objectives of this study were: (1) to calibrate optical estimates of PAI (plant area index) from the LAI-2000 using leaf area index derived from allometric models for six different tropical tree species and (2) to explore the corresponding relationship of calibrated LAI-2000 with stand productivity indices and environmental factors along a strong environmental gradient in the southern region of Costa Rica. From sixteen 6-year-old pure stand plantations (trees spaced 3 m × 3 m) of four fast growing native species ( Terminalia amazonia, Vochysia ferruginea, Vochysia guatemalensis and Hieronyma alchorneoides) and two introduced species ( Pinus caribaea var hondurensis and Gmelina arborea), the plant area index (PAI) was estimated indirectly using the LAI-2000 plant canopy analyzer (LI-COR, Lincoln, NE), under cloudy sky conditions at a fixed height of 1.3 m above the ground with a 45° view cap. In addition, leaf area index (LAI) was estimated allometrically by felling four selected trees and measuring the area and biomass of leaves. The specific leaf area (SLA) showed typical values for each tree species that ranged between 81 cm 2 g −1 ( V. ferruginea) and 106 cm 2 g −1 ( G. arborea). Based on the characteristic SLA, for all tree species, the leaf area per tree could be estimated by allometric equations using the dbh (diameter at 1.3 m) as the independent variable. The calibration of the LAI-2000 PAI data versus the allometric estimate of leaf area showed strong and unbiased relationship for the species: T. amazonia, V. guatemalensis, H. alchorneoides and P. caribaea. In the case of G. arborea and V. ferruginea the LAI-2000 PAI values underestimated and overestimated the allometric measurements of LAI. For all tree species, calibrated LAI-2000 values were used as an independent variable in highly significant regression equations to estimate dominant tree height in each stand (in m) and stand yield in m 3 ha −1 year −1, implying that calibrated LAI-2000 can be used to evaluate site quality and stand productivity. The generalized relationships for all species, between average calibrated LAI-2000 with stands yield or dominant tree height among four Eco-regions, indicated that as soil nutrient and water supply become optimal for tree growth, maximum LAI, dominant stand height and yield values are obtained.