Temporal And Spatial Variation Of Leaf Area Index And Its Influencing Factors In Karst Forest Of Maolan

Leaf Area Index(LAI)is an important index to describe forest canopy structure and a key parameter of forest ecological process.At present,there are few studies on the temporal and spatial dynamics of LAI in Karst forest,and there is also a lack of in-depth research.In this study,the LAI of Karst forest in Maolan was measured by LAI-2200 instrument at the center of 12810m×10m 2021 in April,July,October and January 2020,at the same time,the soil factors,topographic factors and forest factors were investigated.The spatial Heterogeneity of LAI in different seasons was analyzed by Kriging interpolation method in GS+software,and the relationship between LAI and environmental factors was established by generalized additive model(GAMs).The main results were as follows:(1)The xylem ratios(α)of Karst forest in January,April,July and October showed a single-peak seasonal pattern,which correlated with seasonal defoliation,with the maximum appearing in January(0.104±0.079);The minimum value appeared in October(0.073±0.029),and the aggregation indexΩ_Eranged from(0.785±0.128)to(0.912±0.104),and both xylem proportion and aggregation index varied with the seasons.(2)There was a significant seasonal difference in LAI,showing a single-peak seasonal variation,with the maximum value appearing in July(5.64±1.30)and the minimum value appearing in January(1.55±1.19),the seasonal variation of LAI was consistent with the phenology of forest plants in Karst,Maolan.(3)The spatial autocorrelation of LAI was strong in April,July and October except that in January it was moderate The semi-variance function analysis shows that the theoretical models for January,April,July and October are exponential model(R~2>0.5),Gauss Model(R~2>0.5),Gauss Model(R~2>0.5)and Spherical Model(R~2>0.5)with a range of 15m-21m.(4)The spatial distribution pattern of LAI varied with the seasons because the factors affecting LAI variation were different in each season.January,July and October show a banded distribution,and April shows a plate distribution.The factors affecting LAI variability in January were tree height,medium tree density,soil Ph,soil organic matter and soil available nitrogen,while the factors affecting LAI variability in April were the proportion of evergreen tree species,elevation and slope aspect The factors affecting LAI variation in July were altitude and slope aspect,and the factors affecting LAI variation in October were slope gradient.