| Forest hydrology is one of the important functions of forest ecosystems,forest structure is a important factor that influence hydrological processes,and previous studies on the relationship between stand structure and forest hydrological process mainly focused on single stand structure index or one-dimensional structure index,but they ignored the vertical and horizontal spatial arrangement of the plants.Using the spatial structure index such as mixed degree,angular scale,forest competition index and non-spatial structural indicators such as crown width,tree height and leaf area index,the relationship between forest structure and hydrological effect was studied,provide reference for forest ecological water balance research and structured forest management.In this paper,Pinus massoniana plantation in Jiulingtou Forest Farm of Zigui County,three Gorges Reservoir area,was taken as the research object,and the hydrologic factors and stand structure factors in Pinus massoniana forest were measured and investigated.We used Pearson correlation to analyze relationships between canopy structure parameters and spatial variability of throughfall and stemflow,the Monte Carlo simulations was used to determine the amount of rainfall collectors to accurately estimate throughfall within a certain error range.Pearson correlation analysis,principal component analysis,redundant analysis and other analytical methods were used to analyze the hydrological effects of canopy,litter layer and soil layer through the growth factors such as DBH,crown width and canopy thickness,as well as spatial heterogeneity and competition factors such as forest index.And the main influencing factors of hydrological effects were obtained.The main findings are as follows:(1)During the study period(June-October 2017),the total rainfall was 1008.4 mm,and the amounts of canopy interception,throughfall and stemflow were 164.2mm,829.8 mm and 14.4mm,accounted for 16.3%,82.3%and 1.4%of the total rainfall,respectively.The canopy interception rate had a very significant logarithmic function relationship with the rainfall.With the increase of rainfall,the throughfall ratio increases firstly,and when the rainfall reaches 20mm,it tends to be stable,and the degree of variation gradually decreasing.The relationship between the throughfall ratio and rainfall was better fitted with the"S"function,and throughfall ratio increased with the rainfall.The stemflow ratio increased rapidly with the increase of rainfall.When the rainfall was more than 40 mm,the variation range of stemflow ratio was 1.3%～2.4%.The log function was better to fit the stemflow ratio with the rainfall.(2)The spatial variation coefficient of throughfall and stemflow decreased with the increase of rainfall.The spatial variation of stemflow in Pinus massoniana forest was related to crown area and DBH.The stemflow increased with crown area and DBH.The effects of various canopy structures(LAI,CT,D,CC)on the spatial distribution of throughfall vary with the size of rainfall,within the rain scale of 0～10 mm,the leaf area index had the greatest influence on the throughfall,and there was a significant negative correlation between them(P<0.05).In the rain range of 10-20 mm and 20-40 mm,the maximum influence of canopy coverage.When the rainfall was more than 40 mm,the distance from the trunk was the largest,and there was a significant positive correlation with the penetrating rainfall(P<0.05),while the leaf area index,canopy thickness and the penetrating rainfall were significantly negatively correlated(P<0.05).P<0.05)(3)Different rainfall levels reached the same error level in the same confidence interval,and the number of throughfall collectors used was different.With the increase of rainfall level,the same level of error could be achieved with less throughfall collectors.When the rainfall level was 0～10 mm,the number of throughfall collectors used was the largest,under the 95%confidence interval and within the 5%error range,the minimum number of throughfall collectors required was 13.When the rainfall level was greater than 40 mm,the number of throughfall collectors used to achieve the same error level was the least,under the 95%confidence interval and when the measured throughfall was maintained within the 5%error range,the minimum number of throughfall collectors was six.(4)The canopy interception ratio was mainly affected by the leaf area index,basal area,the crown area,and the volume.The throughfall ratio was mainly affected by the leaf area index and the basal area.Stemflow ratio was significantly negatively correlated with tree height and canopy thickness,and a significant positive correlation with leaf area index and stand density(P<0.05).The redistribution characteristics of hydrological effects can be explained by the combination variable of the stand structure factor 59.61%(P<0.05).The Monte Carlo displacement test results show that the canopy interception ratio and the throughfall ratio were mainly affected by the forest volume.The larger the accumulation,the higher the canopy interception rate and the lower the penetration rate.And the stemflow ratio was mainly affected by forest competition status factor and horizontal structure(R~2=0.46,P<0.05)and the forest volume(R~2=0.51,P<0.05).(5)The forest competition index,leaf area index and stand density were significantly positively correlated with the maximum water holding capacity of the soil and the total effective water storage capacity of the litter layer(P<0.05).The Margltf richness index was significantly positively correlated with the maximum water holding capacity of the soil.The redundant analysis method was used to analyze the relationship between the variable combination of the stand structure and the hydrological effect of the litter layer of Pinus massoniana forest.The hydrological effects of litter layer can be explained by 54.06%of the three structural parameters:forest competition and volume,growth factor,interspecific isolation degree and vertical structure complexity(P<0.05).The results of Monte Carlo test show that the effective water storage capacity of the undecomposed layer and the total effective water storage capacity of the litter are mainly affected by the forestry competition index and growth factor.The hydrological function of soil layer was explained by 61.80%of the comprehensive parameters of stand structure(P<0.05),the maximum water holding capacity of soil layer was the strongest correlation with forest competition factors and growth factors.Therefore,at least 13 or 11 collectors should be installed with a cross-sectional area of 3000 cm~2 in a 50×50 m plot if the value of throughfall was controlled within the range of the 5%error.The leaf area index and stand density have an important influence on the hydrological effects of each functional layer(canopy,soil layer,litter layer).The larger the leaf area index,the stronger the hydrological effect of each functional layer.In the variable combination parameters of the stand structure,the forest volume and the forestry competition factor had a good explanation for each common functional layer.The better the growth of forest trees,the stronger the forest competition and the more the forest reserves,the better the water conservation effect of Pinus massoniana forest. |
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