| The lithoid hilly area of North-China is an important ecological barrier in North China Plain, and the key areas of the forest ecological programme such as returning farmland to forest. Quercus variabilis and Eucommia ulmoides are the typical plantation in the lithoid hilly areas of North-China. The spatial variation characteristics of sap flow of the two species were analysed, including the sap flow radial distribution and the sap flow in different directions. The results are:1,Radial sap flow of Quercus variabilis showed the trend of "low-high-low" in the whole growing season. The value of Fd30 was higher than Fd50 and Fd10.Throughout the whole growing season, Fd10, Fd10 and Fd50 were different from the average sap flow through the sapwood. If any one of the values of Fd10, Fd30 and Fd50 was selected as the average sap flow through the sapwood, the final sap flow outcome will lead to large errors. Throughout the whole growing season, Quercus variabilis radial sap flow at different depths maintain a significant positive correlation with air temperature and solar radiation, and a significant negative correlation with air relative humidity. Wind speed significantly affected Fd10, but affected Fd 30 and Fd50 smaller. The radial sap flow had not significant correlation with precipitation but showed significant positive correlation with 20cm deep soil moisture content throughout the whole growing season.The relationship is Fd30>Fd10>Fd50 in the successive droughts and soil moisture stress conditions, and the relationship is Fd30>Fd50>Fd10 in non-stress conditions.The sap flows in four azimuths had the similar trend. Moreover. The sap flow showed a significant correlation in four directions, and the correlation coefficient is higher than 0.90, moreover, the relationship of sap flow in four directions was N10 significant. If any one of the values of Fd10 and Fd 30 was selected as the average sap flow through the sapwood, the final sap flow outcome will lead to large errors.The radial sap flow of Fd10 and Fd30 all had the significant correlation with solar radiation, air temperature, relative humidity and wind speed throughout the whole growing season. It had not significant correlation with precipitation, but had significant correlation with soil moisture content. The radial sap flow of Eucommia ulmoides showed Fd30>Fd10 in the typical whether condition.The sap flows in the four azimuths had the similar trend. The sap flow showed a significant correlation in four directions, and the correlation coefficient is higher than 0.90. The sap flow in four directions showed W |
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