Comparison of different ground techniques to map leaf area index of Norway spruce forest canopy

Abstract

The leaf area index (LAI) of three monocultures of Norway spruce (Picea abies (L.) Karst), different in age and structure, was measured by means of two indirect optical techniques of LAI field mapping: 1/ plant canopy analyser LAI-2000, and 2/ digital hemispherical photographs (DHP). The supportive measurements with the TRAC instrument were conducted to produce mainly the element clumping index. The aim of the study was to compare the performances of LAI-2000 and DHP and to evaluate effect of three different sampling strategies on field estimation of leaf area index. One of the suggested sampling designs introduced spatial oversampling around one-point measurement. The oversampling was expected to reveal the importance of sampling point position with respect to surrounding trees. In general, the LAI-2000 instrument produced higher estimates of effective leaf area index than DHP in all experimental stands. On the other hand, the higher true estimates of LAI were obtained from DHP. All three sampling strategies produced consistent estimates of effective and true LAI in all forest sites. The spatial oversampling of LAI measurement point did not significantly improve the LAI estimate of the canopy subplots.