A Study On Health Assessment Of Roadside Trees Fraxinus Ssp.in Core Area Of Beijing

This study aims at the problems of rapid,productive,and accurate urban tree health assessment,and takes Fraxinus ssp.in the core area of Beijing as the object.The main research objectives are to build a roadside Fraxinus ssp.health assessment system with refined and comprehensive morphological indicators,and to find the relationship between morphological indicators and physiological indicators,and to explore the changes in the physiological status in defoliation period and their differences under different health conditions.The study focused on 870 roadside trees in 11 roads in Dongcheng District and Xicheng District.41 indicators of the above sample trees were investigated,involving basic growth,damage,habitat and other aspects,and the ratio distribution was counted to summarize the structure of the roadside Fraxinus ssp.in the area.On this basis,11 morphological indicators related to crown morphology,branch and leaf conditions,trunk damage,base damage,etc.were extracted and evaluated by factor analysis to construct a health assessment model suitable for roadside Fraxinus ssp.,and the model was used to divide the sample trees into 3 categories: "excellent","medium",and "poor".On this basis,12 excellent trees,11 medium trees,and 4 poor trees were randomly selected,and their absolute leaf water content,leaf nutrients,relative chlorophyll content and specific leaf area were measured after sampling in 5 times from October to November 2019.The measurement was conducted to explore the relationship between the health level based on morphological indicators and physiological indicators,and to determine the dynamic changes of various indicators of roadside trees during the autumn defoliation period,and the differences between such changes in health levels.The main research conclusions are as follows:1.Most of the height of roadside Fraxinus ssp.in the core urban area of Beijing are distributed in 10-15m(average at 11.78m).The largest number of trees have a DBH between 20 cm and 30cm(average at 31.89cm).The growth of the trees is generally good,with not many damaged or risk of dumping trees.But there are very few trees have slight expansions of the base or larger damage or greater risk of dumping.48.5% of the trees have a maximum brunch angle between 75 ° and 90 °,which may be subject to snow pressure.The phenomenon of pruning and stubble remains,reflecting the irregular pruning.The mat formation of tree pools are more heterogeneous,and some roads are not covered.The habitat needs to be improved.89.1% of the trees have buildings with a height of 0-30 m within 20 m,which may block the light.62% of the trees are less than 5m from the building,and there is not much space for tree expansion.62% of the trees have no green space on the sidewalk,which is not conducive to the growth of tree roots.72.1% of roadside Fraxinus ssp.have an impact on driving,and 45.9% of them are severely affected,which is not conducive to driving safety.2.In Dongcheng and Xicheng District of Beijing,the excellent trees of roadside Fraxinus ssp.account for 46.44% of the total,the medium trees account for 50.92%,and the poor trees account for 2.64%.Most roadside Fraxinus ssp.are in good health,and very few of them have certain health problems.The average score is “medium” in this assessment system.According to the direction of the road,the roadside trees on the south side grow better.3.There is a correlation between the health score of roadside Fraxinus ssp.and the leaf N mass fraction,specific leaf area and relative chlorophyll content,of which there is a positive correlation with the relative chlorophyll content(correlation coefficient is 0.393)and a negative correlation with the other two(correlation coefficient are-0.293and-0.248).The health score of roadside Fraxinus ssp.has a significant effect on its leaf P mass fraction,leaf K mass fraction,and relative chlorophyll content.The relative chlorophyll content of the excellent trees was significantly higher(47.63 SPAD),while that of the poor trees are significantly lower(43.93 SPAD).The leaf P mass fraction and leaf K mass fraction of the medium trees was significantly lower(0.30% and 0.56%).The suggestions are as follows: the existing measures be continued to protect Fraxinus ssp.in the core area of Beijing to ensure the health of trees;the mode of management be standardized and personnel training be strengthened;strengthen fine management and transfer the focus of management and protection.