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Forests 2017, 8(3), 74;

The Relationship between Sap Flow Density and  Environmental Factors in the Yangtze River Delta  Region of China

Co‐Innovation Center for Sustainable Forestry in Southern China, Jiangsu Province Key Laboratory of Soil and Water Conservation and Ecological Restoration, Nanjing Forestry University, 159 Longpan Road, Nanjing 210037, China
Department of Biology, University of Miami, Coral Gables, FL 33124, USA
Author to whom correspondence should be addressed.
Academic Editor: Kevin L. OʹHara
Received: 17 January 2017 / Accepted: 8 March 2017 / Published: 10 March 2017
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Canopy transpiration is an important component of evapotranspiration, integrating physical and biological processes within the water and energy cycles of forests. Quercus acutissima and Cunninghamia lanceolata are two important, fast‐growing and commercial tree species that have been extensively used for vegetation restoration, water conservation and building artificial forests in the Yangtze River Delta region of China. The primary objective of this study was to characterize sap flow densities of the two species by comparing daytime and nocturnal sap flow patterns and their relationships with environmental factors. Sap flow densities (Sd) were measured between September 2012 and August 2013 using the commercially‐available thermal dissipation probes. Hourly meteorological data were measured in an open field, located 200 m away from the study site, including photosynthetically‐active radiation (Par), air temperature (Ta), relative air humidity (Rh), vapor pressure deficit (Vpd) and precipitation (P). Soil water content (Swc) data were logged hourly in different layers at Q. acutissima and C. lanceolata forests. Results indicated that the mean Sd in summer was higher than that in spring and autumn. Both the Sd of Q. acutissima and C. lanceolata showed distinct diurnal patterns. Nocturnal sap flow densities (Sdn) were noticeable, and both species followed similar declining patterns during our study period. The daytime sap flow density (Sdd) was more sensitive to environmental factors than Sdn. Sap flow density was significant linearly correlated with Par, Vpd and Ta, and Par and Vpd explained the greatest amount of variation in daytime sap flow of Q. acutissima and C. lanceolata, respectively. Our study will enrich knowledge of plantation forest physical and biological processes and provide valuable information for plantation forest management in the Yangtze River Delta region of China. View Full-Text
Keywords: canopy transpiration; daytime and nocturnal sap flow; vapor pressure deficit; soil  water content canopy transpiration; daytime and nocturnal sap flow; vapor pressure deficit; soil  water content

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Liu, X.; Zhang, B.; Zhuang, J.; Han, C.; Zhai, L.; Zhao, W.; Zhang, J. The Relationship between Sap Flow Density and  Environmental Factors in the Yangtze River Delta  Region of China. Forests 2017, 8, 74.

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