Multivariate Coupling Relationship Of Site-Age-Structure-Function Of Main Tree Species In Shelterbelts Of Northern North China

The Bashang Plateau and the northern mountain areas of North China are important ecological functional areas in China and important ecological barriers in Beijing-Tianjin-Hebei region.In the 1960s,this area began to construct protective forest in a large scale mainly for farmland shelterbelts.Aiming at the problems of serious soil erosion,unreasonable structure and low function of protective forest in this area,this paper conducted research about relationships between structure and function of protective forest of typical tree species.In this paper,the typical tree species of Poplar,Pinus sylvestris and Larch plantations were studied.The main ecological functions were windbreak and sand fixation,water conservation,biodiversity protection and wind-induced dust control.This paper can provide scientific basis for multi-function management of protective forest.(1)The main tree shelterbelts in the study area were mostly distributed in the gentle slope area,and the soil was sandy loam.The contents of total potassium and available potassium in the distribution areas of Populus simonii were higher than those of Pinus sylvestris and Larix Sylvestris.The soil was slightly alkaline.Soil N and P contents in Pinus sylvestris and Larix var.sylvestris distribution areas were higher than those in Populus simonii distribution areas.The soil was slightly acidic.(2)In this paper,the structural characteristics of shelterbelt of typical tree species were studied.The results showed that:poplar,pinus sylvestris and larch plantations were mostly of the same age,single layer and pure forest;the diameter distribution and tree height distribution were normal distribution,skewed distribution and multi-peak distribution;with the increase of stand age in poplar plantations,stand mean DBH and basal area increased significantly,while stand density and LAI showed a decreasing trend;diameter distribution of mixed forest could be divided into inverse"J"type,unimodal type and multi-imodal type;compared with pure forest,diameter distribution range of mixed forest was larger and more continuous;the tree height distribution of mixed forest was mainly multi-peak distribution,which was a typical multi-layered forest;shrubs were Seabuckthorn,Caragana,Medlar,etc.,with the majority of shrubs pure forest and coverage of 25%-75%.(3)The functions of wind speed and soil erosion reduction,water conservation,biodiversity protection and wind-induced dust control of typical tree shelterbelts were studied.The results showed that:taking farmland as the control,protective forest effectively reduced wind speed at 2 m height,while shrub effectively reduced wind speed at 0.2 m height;average wind speed reduction of protective forest was29.8%,followed by shrubland(17.3%)and grassland(4.25%);daily sediment transport rate of farmland was 83.4 kg ha^-1d^-1,followed by protective forest(67.5 kg ha^-1d^-1),shrubland(51.7 kg ha^-1d^-1)and grassland(25.9 kg ha^-1d^-1);with the increase of stand age,the water conservation function of poplar,pinus sylvestris and larch plantations increased firstly and then decreased,with the highest value for middle aged forest;Herbaceous biodiversity showed an increasing trend with the increase of stand age;poplar shelterbelt reduced PM₁₀concentrations and diffusion rate of PM₁₀on the leeward side of the shelterbelt,with less effect on PM₁ and PM_2.5.(4)Pearson/Spearman correlation and partial correlation analysis were used to analyze the influencing factors of forest attributes,single functional factors and comprehensive functional index.Dominant tree height was positively correlated with slope and stand density;mean DBH of stand was positively correlated with altitude,stand age,total nitrogen and total phosphorus,but negatively correlated with stand density and total potassium;stand basal area was positively correlated with stand density and available potassium;altitude,stand age,diameter at breast height and height under branches affect the function of windbreak and sand fixation of shelterbelts;The function of water conservation in shallow soil of 0-40 cm decreased with increasing soil chemical properties,while increasing with invreasing sand content of soil;herbaceous biodiversity index was negatively correlated with canopy density and leaf area index.(5)A series of site-age-structure models,site-age-structure-single function models and site-structure-age-comprehensive function index models were established by using stepwise regression method,with 60-80%variations of the dependent variables explained by these models.The variance in function factors explained by structural factors and site factors were calculated by using the variance partitioning analysis.For Populus simonii plantations,site and structure factors accounted for 45.2%and29.2%of the variation,respectively,and together accounted for 9.8%of the variation.(6)In this paper,the relationship between the functional factors and stand density was indirectly established by studying functional factors and stand volume.We than established density management diagrams for the function of wind speed and soil erosion reduction,water conservation and biodiversity protection.On the basis of literature review,multifunctional structure regulation technologies and modes of protective forest were summarized:mixed forest construction technology and vertical hierarchy promotion technology;mixed structure regulation mode with trees,shrub and grass for wind and sand break forest;and water conservation forests near natural forest stand structure regulation mode.These technologies and models provide theoretical and technical support for multi-functional management of shelterbelt which is oriented by ecological functions and have certain practical significance.