The Effects Of Tending Thinning On Community Characteristics Of Pinus Tabulaeformis Plantation

Tending thinning is an important way for near-natural management of plantations.Studying the impacts of thinning on artificial forest communities can practically provide decision-making basis for the development of planted forests with different management objectives;theoretically,exploring the effects and mechanisms of thinning on plantation communities is conducive to comprehend the biological and non-biological processes,which has a profound implication for evaluating the ecological service functions of the plantations under the thinning.However,the influence and driving factors of thinning on plant and microbial communities are still unclear,restricting people's knowledge of ecological processes and mechanisms and the execusion of forest management measures.In this study,by taking the 54 stand age Pinus tabulaeformis plantations with the following four reserved densities800(heavy),1500(medium),2200(light)and 2900(unthinning)stems/hm~2 after tending thinning in the Ziwuling area of Loess Plateau as the research objects,we analyzed effects of thinning on plant community,soil characteristics and microbial community and their influencing factors.Our main research results showed that:(1)Thinning intensity affected plant community characteristics.Under heavy thinning,Pinus tabulaeformis had the largest tree size,the spatial structure of the forest was the optimal,the plant diversity was the highest,the medium thinning was the second,and the light thinning was the worst.Canopy closure and litter thickness was the main reason affecting the understory species composition.In addition,the regeneration status of the seedlings and saplings of Quercus liaotungensis under heavy thinning is best,contributing to the transition from artificial forests to near-natural forests(coniferous and broad-leaved mixed forests),which is of great significance in guiding the near-natural management of plantations.Although there was a better renewal of Pinus tabulaeformis under medium thinning,a long-term observations are required,for large-diameter pine young trees have not yet emerged in the forest.(2)Both of medium and heavy thinning significantly improved soil properties.Although the soil surface SOC content(14.18 and 13.41 g/kg)was significantly lower than that of the control(17.14 g/kg)under medium and heavy thinning,it could increase soil surface water content,EOC and Total phosphorus content,reduced soil bulk density and carbon-nitrogen ratio,consequently improving soil quality.In addition,medium and heavy thinning significantly reduced the activity of the four hydrolase enzymes associated with the carbon,nitrogen,and phosphorus cycle,as the liable components increased at the thinning intensity,decreasing microbial investment in resource acquisition.(3)Light and medium thinning can significantly increase the carbon storage of plantations,of which,the light thinning is the highest(217.57 t/hm~2)in ecosystem ecosystem of Pinus tabulaeformis plantation,followed by medium thinning(205.37t/hm~2).The arboreal layer was the largest carbon pool in the plantation ecosystem,which accounted for 73.21%and 74.62%of the total carbon storage of the plantation under light and medium thinning,which is the main reason for the increase of carbon storage in the plantation system,but reduction in soil layer is the main reason for the decrease in carbon stocks under heavy thinning.Although the existing amount of leaf litter under medium and heavy thinning decreased by 34.34%and 51.85%compared with the control,the biomass of understory shrubs increased significantly,which had a certain compensatory effect on forest carbon sinks.(4)Different thinning intensities have different effects on microbial communities.Thinning had slight effect on the total microbial content,but changed the microbial community composition,such as fungi(1.07 and 1.31 nmol/g)under medium and heavy thinning was significantly lower than the control and light thinning(2.46 and1.85 nmol/g).The fungal bacteria ratio also showed the same pattern.The diversity of microbial community showed a trend of decreasing first and then increasing with the increase of the thinning intensity,and the heavy thinning(2.92)recovered to the level of unthinning(2.98),which is of great significance for maintaining the stability and activity of the soil ecosystem in the Loess Plateau.The increase of plant diversity and the change of SOC were driving forces to the change of microbial community characteristics.This study found that heavy thinning can not only optimize the community structure of plantation,increase plant diversity and promote native species regeneration,but also improve soil physical and chemical properties and increase soil microbial diversity;light thinning is the best way to develop carbon sink plantations,followed by medium thinning.The research results have reference value for the management of Pinus tabulaeformis plantation in Loess Plateau.