Determination Of Leaf Area Index Of Three Typical Forest Types In Guizhou Province

LAI is one of the most important parameters in quantifying the canopy structure of forest ecosystems.It is closely related to many forest physiological and ecological processes.The accurate determination of LAI seasonal changes is useful for predicting forest growth,assessing forest ecosystem productivity and formulating reasonable forest management and management strategies are essential.Under non-destructive conditions,use litter method,allometric growth equation method,digital hemispherical photography(DHP)and LAI-2200plant canopy analyzer(LAI-2200)to accurately estimate the LAI seasonal dynamics of karst forests There is less research on sex.In this study,DHP and LAI-2200 were first used to determine the seasonal dynamics of the effective leaf area index(effective LAI,Le),and then the error sources(woody-to-total area ratio(α),agglomeration)of Le were determined by DHP.The clumping index(Ω_E),needle-to-shoot area ratio(γ_E)and automatic exposure)are reasonably quantified,and the first three parameters are corrected for Le measured by LAI-2200;Secondly,in order to obtain relatively accurate LAI,the seasonal dynamics of LAI of three forest types were determined based on the leaf-spreading survey combined with the litter method,and the measurement results can represent the real LAI.Using the real LAI as a reference,the Le measured by DHP and LAI-2200 and the LAI obtained after correction of the error source are evaluated.The results show:(1)The leaf spread survey found that there are obvious differences in the increase rate of leaf area of various tree species in different forest types during the growing season.The peak of leaf development of most tree species occurs in April,a few occur in March,and the total leaf area reaches its maximum in early July.(2)The specific leaf area(SLA)of different forest types varies greatly.The clumping effects(Ω_E)at the canopy level of each forest type showed small seasonal fluctuations(0.86-0.93)with seasonal changes.The contribution rate of woody materials to LAI varies significantly with the seasons.The value ofαgradually decreases with the spread of the leaves,and it gradually increases with the fall of the leaves.(3)Throughout the survey season,the LAI measured by different methods for each forest type showed a unimodal change pattern,reaching its peak in July.DHP determined that the Le of evergreen and deciduous broad-leaved mixed forests was 48%underestimated on average than the real LAI(litter method);the LAI of evergreen coniferous forests was underestimated by 57%on average;and the LAI of coniferous and broad-leaved mixed forests was underestimated by 54%on average.Relatively speaking,the Le measured by LAI-2200 was 39%,32%,and 37%underestimated on average than the real LAI in the three forest types,respectively.(4)After the automatic exposure,α,Ω_E,andγ_Ecorrection of the Le measured by DHP,the accuracy is significantly improved,but the LAI of evergreen and deciduous broad-leaved mixed forest,evergreen coniferous forest and coniferous and broad-leaved mixed forest,it is still 4%underestimated than the real LAI-12%,4%-16%and 5%-17%,The difference between the various forest-type Le measured by LAI-2200 afterα,Ω_E,andγ_Ecorrection and the real LAI are all less than 4%,and the accuracy is significantly improved.(5)In evergreen coniferous forests,there is no significant difference in LAI measured by the allometric growth equation method and the litter method in each season(P<0.05),indicating that the allometric growth equation method has a wide range of applicability as long as it is used reasonably.