Study On Health Diagnosis Of Ancient Sophora Japonica Trees In Chongxin County,Gansu Province

Ancient trees are precious natural resources and cultural heritage,and have important biological,ecological,cultural and social values.There are abundant ancient tree resources of Sophora japonica in Chongxin County,Gansu Province,but their health status is still unclear,which makes the protection of ancient trees with great blindness.Health diagnosis is helpful to scientifically carry out the protection and rejuvenation of ancient trees,and health evaluation is the premise and basis of health diagnosis.Health evaluation for single tree species is beneficial to improve the accuracy and effectiveness of ancient tree protection,but there are few reports on the construction of health evaluation model of ancient Sophora japonica.In this study,29 grade I,36 grade II and 15 grade III ancient S.japonica trees in Chongxin County of Gansu Province were selected as the research objects,and 14 indexes such as branches,leaves and trunks that can reflect the health status of trees were selected.The health evaluation model of ancient S.japonica trees was constructed by structural equation method.On this basis,combined with the results of root distribution and habitat quality evaluation,the causes of the decline of the millennium ancient tree ’ King of Sophora japonica ’ were analyzed and an effective protection and rejuvenation scheme was formulated.In addition,taking 40-year-old S.japonica and 95-year-old Platycladus orientalis in the campus of Northwest A & F University as the objects,the thermal diffusion probe technology was used to monitor the sap flow variation characteristics of S.japonica with different crown asymmetry degrees and P.orientalis with different health conditions,and the relationship between tree growth status and sap flow variation was discussed,which provided a basis for the possibility of applying the thermal diffusion probe technology in the health monitoring and management of ancient trees.The main research results are as follows:(1)The health evaluation model of ancient S.japonica trees constructed by structural equation model can well meet the needs of health evaluation of ancient S.japonica trees.In this study,14 indicators in 4 categories were selected to construct the health evaluation model of ancient S.japonica.The fitness indexes NC(1.178),RMSEA(0.047),NFI(0.923),TLI(0.983)and CFI(0.987)were within a reasonable range,and the fitting effect of the model and the observation data was ideal.(2)The standardized results of model path coefficient showed that among the four aspects reflecting tree health,the weight of branch status was the largest,which was 0.3113;the overall condition and leaf condition were 0.2542 and 0.2231,respectively.The minimum weight of trunk status is 0.2114.Among the 14 indexes,the weight of tree vigor(0.0812)and top tip dead(0.0803)was higher,and the weight of inclination(0.0428)and disease and insect invasion(0.0526)was lower.(3)The cluster analysis results of health index showed that the health status of ancient S.japonica can be divided into five grades according to the comprehensive score,namely,health(0～0.81),sub-health(0.81～1.40),decline(1.40～2.19),extreme decline(2.19～3.22)and imminent dying(3.22～4.0)according to the comprehensive score,and most of them were in healthy(35.0 %)and sub-health(30.0 %).However,in the first and second grade of S.japonica,the proportion of unhealthy plants was relatively high,accounting for 86.21 % and 63.89 %respectively in decline and below grades.(4)The growth of the millennium ancient tree ’King of Sophora japonica’ has declined,and there are hidden dangers in tree stability,mainly related to their own biological factors and habitat quality.The results of health evaluation showed that the millennium tree was in a decline state(the comprehensive score was 1.416).The specific performance was as follows: serious northward crown asymmetry,high degree of dead branches,slightly sparse leaves,large dead area of bark and more holes.The results of empty rot detection showed that the empty rot rate of trunk base was 52.2%,and the degree was serious.Three backbone branches also appeared mild or moderate empty rot,and the tree stability was poor.The detection results of root distribution in 1 m deep soil showed that roots above 1 cm in diameter were mainly distributed in the depth of 60-100 cm,and densely distributed in the northwest and northeast sides of the crown projection,accounting for more than 30%.Soil bulkiness,poor nutrient conditions,lack of nitrogen and phosphorus,and low habitat quality around the trunk may be important reasons for uneven distribution of underground roots and decline of aboveground growth.(5)Crown asymmetry and health status have significant effects on diurnal variation of sap flow and its response to environmental factors.The observation results show that the thermal diffusion probe technology can be used to monitor the growth dynamics of trees or the health status of ancient trees.The diurnal variation trends of sap flow of S.japonica and P.orientalis were similar,showing a “single peak”.The sap flow vecolity of S.japonica and P.orientalis were significantly positively correlated with water vapor pressure deficit,temperature and wind speed,and negatively correlated with relative humidity.The effect of tree crown deviation caused by crown asymmetry on sap flow rate was obvious,which showed that the greater the degree of crown deviation,the lower the daily average sap flow rate,and the stronger the response to environmental factors.There are also differences in sap flow of P.orientalis in different health conditions.With the deterioration of health condition,sap flow rate decreases and is more sensitive to environmental factors.