Variation In Stand Environment Quality And Its Influence On LAI Of A Typical Deciduous Broad-leaved Mixed Forest In Songshan,Beijing

Understanding the characteristics of environmental changes of natural forests and their impact on vegetation canopy structure is of great significance for maintaining the ecological environment and scientific management of forest stands.The construction site of the Winter Olympics Yanqing Division is located in Songshan National Nature Reserve,Yanqing District,Beijing.The impact of infrastructure construction on the ecological environment of the reserve has aroused widespread concern.In this study,the air pollution indicators?SO₂,PM2.5,PM10?and forest meteorological factors?air temperature,air humidity,vapor pressure deficit,wind speed?were continuously measured in situ from January to December in Songshan deciduous broad-leaved mixed forest outside the Yanqing Winter Olympics area,along with continuous manual measurement of leave area index?LAI?in growing season.We analyzed the temporal variations in atmospheric pollution indicators and their correlation with meteorological factors,and effect of environment factors and pollution indicators on LAI.The main results were as below:?1?The annual mean values of air temperature?Ta?,relative humidity?RH?,wind speed?Ws?and vapor pressure deficit?VPD?in 2019 were 6.32?,45%,2.4m/s and 0.69 kpa,respectively.?2?The average SO₂ concentration in 2019 was 4.88ug/m³.During one-year-long period,the concentration of SO₂ reached the national standard of"ambient air quality standard".The average PM2.5concentration in 2019 was 28.29ug/m³.There were 262 days?72%days of a year?with the concentration of PM2.5 of meeting the first-level standard in terms of the 24-hour mean.The seasonal variation trend of PM10 concentration in the monitoring site was the same as that of PM2.5,with an annual mean of 38.23ug/m³ in 2019.and the percentage of days reached the standard was 72%.?3?There was clear phenological variation in the concentration of pollutants.The concentration of pollutants is the lowest when the plant is fully leafing,and the concentration of pollutants in the growing season is lower than that in the non-growing season.?4?The leaf area index?LAI?had obvious seasonal changes.The average LAI of the typical deciduous broad-leaved mixed forest in Songshan in 2019 was 2.99 m²/m².LAI had a significant correlation with the meteorological factors and pollutants.In conclusion,the air quality outside the Yanqing Winter Olympic Games generally reached the national air quality standard during the study period,and the air pollution indicators had obvious seasonal variation pattern and phenological characteristics.This study provides the basic data and scientific support for forest ecological environmental management in Songshan nature reserve.