Study On The Spatiotemporal Variation Patterns Of Soil Water Repellency In Different Forests After Fire

Soil water repellency(SWR)is the phenomenon that the soil surface can not be wetted by water or rainfall,and it shows poor soil permeability.It is an important indicator of soil quality evaluation and a potential driver of complexity that links soil,hydrology,and vegetation dynamics.Recently,extreme high temperature events frequently occur due to global warming,and frequent forests fires arise in China.How to reduce the risks of forestry management and production assessment,and increase the forest resource management is a common concern of all circles globally.At present,there are many reports on soil water repellency in areas with severe drought and soil erosion,but there are few reports on the recovery of soil water repellency in subtropical forests under fire.It is of great significance to study the soil water repellency recovery of four typical forests in subtropical of China under different fire intensities,aiming to supplement the basic data of soil water repellency in subtropical forests,improve the soil water repellency recovery process,and improve the soil water repellency recovery model under fire disturbance.The precision and stability of the subtropical forests have a guiding role in improving the soil quality of forests and increasing the quality of forests.It is of practical significance for the future scientific research of natural forests and plantations in subtropical areas.This study selected four typical forests in subtropical zone of China(three kinds of plantations:Cunninghamia lanceolate-Schima superba,Pinus massoniana-Schima superba,Sassafras tzumu-Cunninghamia lanceolate,and one natural forest:Liquidambar formosana).Selecting the mid-subtropical humid monsoon climate zone(Zhuzhou Huangfeng Bridge,Huangtuling and Xiangtan Zhaoshan Demonstration Zone)as the research site,the soil water repellency recovery test after two years of fire disturbance with different fire intensity,through the drip penetration time method.The soil water repellency of different soil layers under different fire intensities was measured after 3 days,30 days,180 days,365 days and 730 days.The distribution patterns of soil water repellency in different forest stands,different soil depths,different fire intensities and different recovery times were analyzed,and the soil water repellency recovery models of different soil layers under different fire intensities were established.The main conclusions are as follows:(1)When not burning,the soil of natural forest(Liquidambar formosana secondary forest)has better water holding capacity than the artificial forest,and the topsoil of the three subtropical plantations all show different degrees of slight water repellency,and four forest stands.The soil water repellency decreases as the soil depth increases.Under the disturbance of fire,the soil water repellency of natural forest is still lower than that of planted forest.Under the influence of fire,the soil water holding effect of natural forest is still better than that of artificial forest.The fire intensity gradient has significant influence on soil water repellency.There was a significant difference in soil water repellency(P<0.05),and soil water repellency increased with the increase of fire intensity level.(2)Fire disturbance is the main factor affecting the increase of soil water repellency in subtropical forests,and the increase of fire:intensity will worsen soil water repellency,but soil depth can alleviate the effect of soil water repellency.Soil water repellency was highest in 0-5 cm soil.Soil water repellency decreased in 6-10 cm soil,and soil water repellency was the least affected in deep soil(below 10 cm).The soil water repellency of Pinus massoniana-superba mixed forest decreased with the increase of soil depth weaker than other stands.Due to the disturbance of fire,the soil water repellency was significantly increased in the topsoil(0-5 cm and 6-10 cm),and the 0-5 cm soil layer was most seriously affected by soil water repellency,which was significantly larger than the other soil layers.Among them,the Pinus massoniana-superba mixed forest was most affected by soil water repellency due to fire interference,which not only affected the topsoil,but also affected the 11-15 cm soil layer.(3)The soil water repellency caused by fire disturbance in the four forest stands decreased with the increase of recovery time,and the recovery under different fire intensity was different.The soil water repellency of the three artificial mixed forests was highest at 3 days and 30 days after the fire,and recovered significantly after 180 days,and then gradually decreased.The effect of high fire intensity on the three artificial mixed forests was significantly greater than that caused by low and medium fires.It took 365 days for the soil water repellency to return to the unburned fire,and at this time did not reach the non-water repellent level,730 days after the fire.Reach the water-free state.In the short-term,the soil water repellency of Liquidambar formosana secondary forest was severely affected.The recovery in 30 days was not obvious in the long term.The recovery rate was significant in 180 days.The soil water repellency was significantly improved 180 days after the fire,close to WDPT when not burning.(4)The effect of fire on soil water repellency is mainly in the topsoil(0-10 cm).With the increase of soil depth,the soil water repellency tends to moderate,and the fire intensity will significantly affect the recovery of soil water repellency.The effects of velocity,medium and high fire intensity are significantly higher than low fire strength.