Effects Of Thinning And Pruning On Growth And Soil Physical And Chemical Characteristics Of Typical Stands In The Yellow River Delta

Forest thinning and pruning are important measures for forest structure adjustment.Scientific forest structure adjustment can improve forest growth,increase understory plant species,improve soil physical and chemical properties and regulate soil enzyme activity.At present,due to the stand growth decline and forest soil degradation in some areas of the typical Yellow River Delta,this may be closely related to stand density or coverage.In this study,the 8-year-old plantations of Fraxinus mandshurica,Salix matsudana and Ulmus pumila in Wangzhuangsha District,Lijin County,Dongying City,Shandong Province,and the8-year-old natural secondary shrub of Tamarix ramosissima in Binzhou Port,Binzhou New District,Binzhou City,Shandong Province were selected as the research objects.The plantation density was adjusted from 3 m × 3 m(control)to 3 m × 6 m by thinning,and the canopy density of natural secondary forests was adjusted from original 0.8(control)to 0.5 and0.3 by pruning.The changes of stand growth,number characteristics of understory plant communities,soil physical and chemical properties and soil enzyme activity of artificial forest and natural secondary forest after thinning for 3 years and pruning for 3 years were studied.The effects of stand structure adjustment(artificial forest thinning and natural secondary forest pruning)on the growth characteristics and soil physical and chemical characteristics of each stand were explored.The results can provide reference for the rational management of artificial forests and the maintenance of ecological functions of natural secondary forests in the Yellow River Delta.The main conclusions are :(1)Thinning can promote the stand growth and undergrowth plant diversity of artificial forest,and the growth effect of Ulmus pumila plantation is the best.Pruning increased the diversity index of understory plants,and different canopy density resulted in different height-diameter ratio and biomass of understory plants.(2)Thinning mainly affected soil water physical properties of Ulmus pumila plantation,reduced soil bulk density,increased soil non-capillary porosity,capillary porosity and total porosity,and mainly affected soil water physical properties of 0-20 cm soil layer under the forest.Pruning has a certain influence on the physical properties of soil moisture under forest,and it is related to the canopy density.The canopy density of 0.5 has a great influence on it,mainly affecting the 40-60 cm soil layer under forest,reducing soil bulk density,increasing non-capillary porosity,total porosity,capillary water holding capacity and saturated water holding capacity.(3)Thinning significantly affected soil total nitrogen,total phosphorus and total potassium content in plantations and was related to stand types.Thinning significantly affected understory soil total nitrogen,total phosphorus and total potassium content of Salix matsudana plantation,which was related to soil layer distribution,and the maximum value was mainly distributed in 0-20 cm soil layer.Pruning significantly affected the soil total potassium content of Tamarix austromongolica natural secondary forest,which was independent of canopy density.Pruning significantly increased in 0-60 cm soil layer under the forest,and the maximum value was distributed in 0-20 cm soil layer.(4)Thinning significantly affected soil enzyme activity of plantations,and it was related to stand types.Thinning significantly increased soil enzyme activity in 20-40 cm soil layer.The maximum soil enzyme activity was mainly distributed in 0-20 cm soil layer,and the change of soil enzyme activity under different plantations was related to soil layer distribution.Pruning significantly increased soil invertase and soil catalase activities of Tamarix austromongolica natural secondary forest,which were related to canopy density and soil layer distribution.Soil enzyme activities were mainly distributed in 0-20 cm soil layer.(5)Thinning and pruning affect the correlation between stand growth,undergrowth plant growth,soil physical and chemical properties and soil enzyme activity,and change the main influencing factors and weights of various types.