Consumption of precipitation by evapotranspiration indicates potential drought for broadleaved and coniferous plantations in hilly lands of South China

Abstract

Quantifying the water use effects of tree plantations on regional hydrological processes is vitally important for evaluating the reforestation strategies related to a sustainable use of water resources. We conducted a comprehensive study to investigate the precipitation partitioning and hydrological effect of three different plantations (Schima wallichii, Acacia mangium, and Cunninghamia lanceolata) by monitoring sap flow and using a water balance equation during a two-year period (from January 2017 to December 2018) in hilly lands of South China. Owing to the abundant precipitation and radiation, both monthly stand-scale transpiration and evapotranspiration of the tree plantations were higher in the wet season than in the dry season. Strong stand-scale transpiration (Tstand) and evapotranspiration (ET) were observed in the broadleaved S. wallichii and A. mangium with a large proportion (more than 90%) of ET in precipitation (P). Whereas the coniferous C. lanceolata plantation possessed lower Tstand and ET but higher surface runoff, indicating a water surplus for the water yield. Following the uneven distribution pattern of precipitation, clear seasonal variation was observed for the ratio of ET/P that exceeded 1 during majority of the dry season. The observed vigorous transpiration and the higher ET/P values of the broadleaved S. wallichii and A. mangium plantations than those of the coniferous C. lanceolata suggests that broadleaved plantations are more likely to pose a potential threat to the catchment water yield and water balance in this region. However, the C. lanceolata, which limited the water exchange between the atmosphere and plants, is also considered to prevent its growth. Our findings quantified the hydrological effects of different plantations and will help to address the increasing water resource concerns related to the rapid expansion of plantations in hilly lands of South China.