Study On Thinning Improvement Of Cupressus Funebris Plantation In The Hilly Area Of Central Sichuan

Cupressus funebris plantation as the main forest types in hilly area of central Sichuan.Because of the unreasonable structure of the forest,the ability of soil and water conservation of the forest land is low,which affects the ecological and economic benefits of the forest in this area.In order to understand the ecological effects of thinning improvement,this paper takes the Cupressus funebris plantation in Yanting County of Sichuan Province as the research object,four standard plots with different thinning intensity were set up:control experiment?no thinning?,mild?10%-15%?,moderate?20%-25%?and severe?35%-40%?,three 20m×20m plots were set for each strength,totaling 12 plots.Through the determination and analysis of forest,shrub,herb,litter and other related indicators in each sample plot,comprehensive evaluation by principal component analysis,the effects of thinning intensity on cypress plantation were compared.The results can provide theoretical basis and technical reference for sustainable management of Cupressus funebris plantations in this area.The main results were as follows:1.Thinning intensity significantly affects the growth of Cupressus funebris plantations.Severe thinning significantly promoted the annual growth of tree height and DBH,which were 0.19m·a^-1 and 0.48 m·a^-1,respectively,and significantly greater than control and mild thinning.There is no significant difference in stand volume and annual average growth rate under different thinning intensities.2.The effect of severe thinning on understory shrubs and herbs is more significant.The herbaceous species increased by 7 species,3 species and 1 species under the intensity,moderate and mild conditions,respectively,compared with the control experiment,and the shrub species increased by 8 species,6 species and 3 species under intensity,moderate and mild conditions,respectively,compared with the control experiment.The Simpson index,Shannon-Wieiner index,Pielou index and richness index of shrubs and herbs after thinning were consistent,from large to small,they are severe,moderate,mild and control respectively.With the increase of thinning intensity,the biomass accumulation of shrubs and herbs under the forest also increased.3.Thinning affected the characteristics of litter,and the effect of intensive thinning was significant.The maximum total litter accumulation was 4.07 t/hm² of severe thinning,which increased by 1.12 t/hm²,2.03 t/hm² and 2.66 t/hm²,respectively,compared with moderate thinning,mild thinning and control.The maximum and effective interception of litter were13.1t/hm² and 11.3t/hm² under severe thinning,respectively.and were significantly larger than those under control and mild thinning.The relationship between water holding capacity and time is consistent,and the water holding rate under severe thinning is the largest.4.Analysis of soil physical and chemical properties,the contents of chemical elements and physical properties of soil increased with thinning intensity.Soil total carbon,organic matter,total nitrogen,porosity and soil water storage capacity were significantly higher in the upper layer?0-10cm?than in the lower layer?20-30cm?under the same thinning intensity?P<0.05?,while soil bulk density showed the opposite regular pattern.5.The correlation analysis showed that the correlation between soil physical and chemical properties and shrub-grass biomass was strong,and it was an important indicator of shrub-grass biomass.In addition,litter accumulation and water holding capacity have a strong correlation with soil physical and chemical properties and diversity of shrub and grass layers.Comprehensive evaluation of thinning effect of Cupressus funebris plantation based on principal component analysis,The comprehensive score was in the order of severe thinning?2.04?>moderate thinning?0.32?>control?-0.97?>mild thinning?-1.38?.Based on the above analysis,compared with other thinning intensities and control experiments,heavy thinning?35%-40%?and moderate thinning?20%-25%?is beneficial to the improvement of tree growth,biodiversity,soil properties and litter properties of Cupressus funebris plantation in this area,that is,the stand density after thinning is 2257-1515 trees per hectare.It can significantly improve the quality and ecological benefits of the forest.The conclusions of this paper can provide theoretical basis and technical reference for the third phase of the Yangtze River shelter forest project and the precise upgrading of forest quality in hilly areas of central Sichuan.