Forest Influences on Streamflow: Case Studies from the Tatsunokuchi-Yama Experimental Watershed, Japan, and the Leading Ridge Experimental Watershed, USA

Abstract

Forested watersheds provide multiple ecosystem benefits to society, playing a key role in the supply of fresh water and the regulation of climate. In this chapter we review two classic paired watershed studies carried out in temperate forests in contrasting world regions; Tatsunokuchi-Yama Experimental Watershed in Japan and at the Leading Ridge Experimental Watershed in the United States. Long-term measurements of the water balance have been made at both experimental watersheds, with observations at the Tatsunokuchi-Yama Experimental Watershed beginning in 1937 and at the Leading Ridge Experimental Watershed in 1957. The catchments were observed over a range of changing climatic conditions. The forests changed over time due to a number of factors, such as changing tree species, gypsy moth defoliation, pine wilt disease, forest fire, clear-cutting, herbicide application, selective logging, and forest management. We summarize results from monitoring of these watersheds from 1937 to 2002 in Japan and from 1957 to 2007 in the United States. In the Tatsunokuchi-Yama watersheds annual precipitation ranged from about 600 to 1730 mm averaging 1220 mm year⁻¹, with about 33% of the average annual incident precipitation delivered as streamflow in the watersheds. In the Leading Ridge watersheds annual precipitation ranged from about 470 to 1470 mm averaging 1060 mm year⁻¹, with about 45% of the average annual precipitation delivered to streamflow. Results from these studies show that increases in water yield occur on small watersheds in response to removal of vegetation and that increases in streamflow diminish as vegetation is replanted or naturally recovers. Long-term watershed monitoring data are becoming increasingly useful to link the impacts of changing climate, vegetation, soil, and water as the data are synthesized and shared publicly, allowing application to new research questions and hypotheses.