Seasonal dynamics in leaf area index in three typical temperate montane forests of China: a comparison of multi-observation methods

Abstract

Aims Leaf area index(LAI)is one of the most frequently used parameters for analysis of canopy structure and forest productivity.It can be determined by direct or indirect methods.Sources of errors in indirect LAI measure-ments with optical instruments include non-photosynthetic components,element clumping,and a topography ef-fect.Our objective was to find an appropriate method for evaluating LAI and its seasonal dynamics in typical temperate montane forest.Methods We examined the applicability of three indirect methods(LAI-2000 plant canopy analyzer,CI-110 plant canopy analyzer and digital hemispherical photograph(DHP))and one direct method(litterfall)to determine the seasonal dynamics of LAI in three typical temperate forests in Dongling Mountain of Beijing.The forests in-cluded a secondary deciduous broad-leaved forest dominated by Quercus mongolica and two plantations(Larix gmelinii var.principis-rupprechtii and Pinus tabuliformis).These represent deciduous broad-leaved forest,de-ciduous needle-leaved forest and evergreen needle-leaved forest,respectively.The optically-based effective leaf area index(LAIe)values were corrected to eliminate wood elements and clumping effects and then compared with the direct measurement of LAI based on litter collection.Important findings For all the three forests,the LAI seasonal dynamic shows a uni-modal pattern with a peak in July.Optically-based LAIe underestimated the amplitude of the seasonal dynamics.Wood element elimination can strengthen the seasonal sensitivity of LAI,especially in the seasonally distinct deciduous forest.The order of LAIe measured by the three optically-based methods in three stands is LAI-2000 plant canopy analyzerDHP CI-110 plant canopy analyzer.There was good correspondence with the direct measurement LAI for the corrected LAI of LAI-2000 plant canopy analyzer and DHP.The correction method based on gap-size distribution was ap-propriate for the LAI-2000 plant canopy analyzer and the method based on both gap fraction and gap-size distri-bution for DHP.Considering economics and practical convenience,we recommend DHP for LAI evaluation in these temperate montane forests.