| The water conservation function of forests has always been a hot spot in the study of forest ecological functions.The evaluation of the water conservation function of forests at the watershed scale mostly adopts hydrological models or extrapolation based on the measured results of forest land.However,hydrological simulation involves complex ecological hydrological processes,large data requirements,time-consuming simulation parameter adjustment,and accompanied by model uncertainties.At present,the extrapolation based on the actual measurement results of forest land is mostly based on simple extrapolation calculations based on the area of different vegetation types in the watershed.Due to the high temporal and spatial heterogeneity of hydrological elements and ecological environment elements,simply pushing up the quantitative results of forest water conservation function to the watershed scale will cause serious deviations and fail to reflect the true forest water conservation function of the watershed.Aiming at the problem of forest water conservation function scaling from woodland to watershed scale,this study took Zagunao Watershed in the upper reaches of Minjiang River as an example to construct a forestland-watershed water conservation function scaling model based on environmental factors,so as to realize the rapid evaluation and prediction of watershed water conservation function.Firstly,by establishing 30 standard sample plots,collecting ground cover and soil samples,using the soaking method and the ring knife method to experimentally measure the ground cover and soil water conservation parameters,and quantify the water conservation function of the forest ground cover and soil layer at the forest scale;Use correlation analysis,regression analysis and factor analysis to screen environmental factors related to ground cover and soil layer water conservation;finally establish a forest ground cover and soil layer water conservation function scale conversion model based on environmental factors to predict watershed scale The spatial distribution of forest water and ground cover and soil water conservation.This study will provide decision-making basis and reference for water resources management and forest restoration management in the upper reaches of the Minjiang River.The main conclusions of this study are as follows:(1)Field survey results show that due to the different restoration succession stages of different vegetation types and the influence of human activities,the composition of the vegetation within the forest and the characteristics of the vegetation under the forest are significantly different.The dominant tree species in natural coniferous forests is Minjiang Abies,with an average age of over 90 years,and its tree height,diameter at breast height and crown are significantly higher than other types of forests;the dominant tree species in artificial natural coniferous and broad-leaved mixed forests are spruce,birch,etc.,which are mainly distributed In the area of 2700m-3200m above sea level,the canopy density of forest land is reduced,the quality and function are reduced,and the vegetation composition is relatively degraded.(2)At the watershed scale,mixed forests are the most widely distributed,accounting for 25.43%of the watershed area.They are mainly distributed in the 2500m-4500m altitude range,mainly on sunny slopes;followed by alpine meadows and evergreen coniferous forests.They account for 16%and 13.42%of the vegetation area of the basin respectively.Among them,more than 95%of alpine meadows are distributed in areas with an altitude of 3500m-4500m,and evergreen coniferous forests are mainly distributed in areas with an altitude of 2500m-3500m,with shady slopes and semi-shady slopes.(3)There are significant differences in the accumulation of ground cover of different vegetation types,and their maximum water holding capacity is also significant.Among them,natural coniferous forest ground cover has the largest accumulation and its maximum water holding capacity is also the highest.Compared with plantation forests,the average effective retention volume of natural forest covers is higher than that of planted forests,about 1.24 times that of planted forests,and the overall natural forest covers have stronger water conservation capacity.Among the five natural forests,natural coniferous forest ground cover has the strongest water holding capacity,followed by natural coniferous and broad-leaved mixed forest,while natural evergreen broad-leaved forest has the lowest maximum water holding capacity and effective retention capacity,which is mainly compared with it.Low accumulation is related.Among the four plantations,there are significant differences in the effective retention capacity and maximum water holding capacity of ground cover.The stand structure of high canopy closure plantations is more complete than other types of plantations,and the maximum water retention capacity and effective retention capacity are significantly higher.In other plantations.The effective interception rate is related to the maximum water holding capacity and natural moisture content,and is not affected by the storage capacity,and there is no significant difference among all vegetation types.(4)The maximum soil water holding capacity and absorption water storage in natural forest were significantly higher than those in artificial forest,while the residual water storage had no significant difference.Natural coniferous forest had the highest water holding capacity and artificial forest had the highest water holding capacity.Since the main body of water conservation in woodland is soil layer,the mixed planting of coniferous and broad-leaved tree species in artificial afforestation will be beneficial to improve the stand structure,increase the abundance and richness of plants under artificial forest,and improve the ability of artificial forest to hold precipitation.(5)In the scale-up model of forest water conservation based on the environmental factors of the watershed,the maximum ground cover accumulation model R~2 reached0.91(p<0.05),and the average relative error range of the verification points was 6.5%-7.4%;The highest natural water content model R~2 reached 0.909(p<0.05),and the average relative error range of verification points was 5.69%-8.35%;the maximum water retention model R~2 of ground cover reached 0.877(p<0.05),and the average relative error of verification points The range is 4.67%-7.22%;the maximum effective storage capacity of ground cover model R~2 reaches 0.852(p<0.05),and the average relative error range of verification points is 5.62%-6.56%;the maximum water holding capacity model R~2 of 0-30cm soil reaches 0.888(P<0.05),the average relative error range of the verification points is 5.14%-5.72%;the maximum R~2 of the 0-30cm soil retention water storage model is 0.846(p<0.05),and the average relative error range of the verification points is 5.13%-6.22%;0-30cm soil retention water storage model R~2 is up to 0.915(p<0.05),and the average relative error range of verification points is 3.51%-10.19%.The establishment of this type of model provides an effective evaluation tool for realizing the scale conversion of forest land-watershed forest water conservation function and the prediction of regional forest water conservation function without measured data of water conservation function. |
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