关键词: 优先流, 喀斯特地区, 染色示踪试验, 纯林, 混交林

Abstract:

Objective: To clarify the soil preferential flow characteristics in typical forests of pure forest and mixed forest in this special habitat in southwest karst area, so as to provide a theoretical basis for local forest vegetation restoration. Method: Two typical stand types (pure Platycladus orientalis forest and mixed Platycladus orientalis, Pinus massoniana, and Eucalyptus maideni forest) were selected and two simulated rainfall amounts were set. Through field staining tracing experiments, the soil was stained with bright blue dye solution to excavate the stained vertical and horizontal profiles of the soil. With the help of image processing technology, five characteristic parameters of preferential flow, such as dyeing area ratio, maximum infiltration depth, matrix flow depth, preferential flow ratio and length index, were extracted, and the distribution, quantity, and proportion of preferential path of the soil at different depths were also obtained. Result: Under the same simulated rainfall, the ratio of soil staining area and maximum infiltration depth of mixed forest were higher than that of pure forest. When the simulated rainfall increased from 25 mm to 60 mm, the ratio of dyed area of mixed forest changed from 12.36% to 16.44%, and the average maximum infiltration depth changed from 22.21 cm to 30.64 cm. The increase of dyeing area ratio and average maximum infiltration depth was similar. The dyeing area ratio of pure forest changed from 7.42% to 15.89%, and the average maximum infiltration depth changed from 12.50 cm to 17.59 cm. The increase of dyeing area ratio was significantly higher than the average maximum infiltration.The soil under the mixed forest is finger-shaped or branched with independent patches, while the pure forest is funnel-shaped, without independent patches.When the simulated rainfall was 25 mm, the matrix flow depth, preferential flow ratio and length index under the mixed forest were 1.65 cm, 76.70%, and 352.61% respectively, which were higher than those of pure P. orientalis forest by 1.31 cm, 74.33%, and 184.20%. When the simulated rainfall increased to 60 mm, the matrix flow depth, preferential flow ratio and length index under the mixed forest were 2.21 cm, 77.18%, and 497.02%, while those of the pure Platycladus orientalis forest were 4.29 cm, 53.83%, and 331.27%. The preferential paths of mixed forest and pure forest in karst area were mainly distributed above 15 cm soil layer, and most of them were less than 5 mm in radius. The preferential paths under mixed forest changed more with the depth of soil layer, and the proportion of priority paths with large impact radius (> 5 mm) (19.0%) was higher than that of pure forest (9.0%). Conclusion: There are certain preferential flows under pure Platycladus orientalis forest and mixed Platycladus orientalis, Pinus massoniana, and Eucalyptus maideni forest in karst area. Due to the influence of its special earth-rock structure, there are more preferential paths in forest soil. The development degree and spatial variability of preferential flow under mixed forest is higher than that of pure forest, which is directly related to the high proportion of preferential paths with large influence radius and strong variability of preferential paths.

Key words: preferential flow, karst areas, dye tracer experiment, pure forest, mixed forest