Effects Of Forest Regeneration Approaches On Hydrological Process In Mid-Subtropical China

Hydrological cycle is closely related to ecosystem productivity,nutrient cycling and the global climate change.The effects of forest management practices on hydrological processes have been a salient topic in forest hydrology.In southern China,Chinese fir plantations(Cunninghamia lanceolata)are replacing many of the broadleaved forests.A major concern of such land use change is how it might affect hydrological processes.The soil disturbance and the changes of rainfall partitioning form forest regeneration would easily lead the generation of surface runoff and soil erosion.A number of studies have examined rainfall partitioning in forest plantations but few have taken understory vegetation and litterlayer into consideration.We conducted a comprehensive study of rainfall partitioning that included both overstory and understory components and the water and soil losses that included both sapling stage and mature forest stage between a Chinese fir plantation and a nearby naturally regenerated Castanopsis carlesii forest of the same age and with a similar land use history in southeastern China.From 201 3 to 2014,we mesured one hundred rainfall events and analysis the data of throughfall,stemflow and surface runoff in each forest regeneration approache,including assisted natural regenration and forest plantation.The results indicate that although Chinese fir had a greater partitioning in throughfall(78%)than Castanopsis carlesii forest(70%)likely due to smaller canopy leaf area index(3.1 and 4.0),it had a smaller partitioning in stemflow(2%)than the Castanopsis carlesii forest(5%)possibly due to more rough bark of the Chinese fir trees in the mature forest stage.While the Castanopsis carlesii forest had a greater overstory interception(25%)than the Chinese fir plantation(20%),it had a smaller understory interception(11%by vegetation and litterlayer)than Chinese fir plantation(14%)mostly due to a lusher understory vegetation in the Chinese fir plantation.Surface runoff was only about 1%in both forests indicating that the greater rainfall under the overstory of Chinese fir plantation did not lead to a greater runoff generation due to understory interception.The water and soil losses between the Chinese fir plantation and the Castanopsis carlesii forest were closed and trivial in the mature forest stage of forest regeneration,but in the sapling stage the surface runoff in the Chinese fir plantation was two and half times of in the Castanopsis carlesii forest,especially,the soil losses in the Chinese fir plantation was twenty three times than that in the Castanopsis carlesii forest.Rainfall erosivity was significant influenced by land cover.There was little soil erosion in slope with hight land cover ratio.We suggest that the understory layer play a key role in soil and water conservation in the mature forest stage of forest regeneration,the amount of soil and water losses in the sapling stage of forest regeneration was determined by the land cover.We also indicated that the sapling stage of forest regeneration should be an important cause of productivity decline in Chinese fir plantation.Our results strongly suggest that a comprehensive evaluation of effects of forest land use change on hydrological processes must take understory components in mature forest and take the sapling stage of forest regeneration into consideration.Our results also highlight the importance of maintaining a healthy understory cover in forest plantations for maintaining/promoting ecosystem services on soil and water conservation.