Effects of forestry management and environmental factors on water and light use efficiencies in a cool-temperate mixed forest in northern Japan

Over a period of 9 years covering both disturbed and undisturbed periods, we evaluated long-term variations in water and light use efficiency (WUE, LUE) in a cool-temperate mixed forest in northern Hokkaido, Japan: our study clarified the relationship of WUE and LUE to environmental and vegetation variables. WUE and LUE markedly decreased after deforestation: they were negatively correlated with the seasonal variations in photosynthetically active radiation (PAR) and water vapor deficit, and LUE increased with the increase in the leaf area index (LAI) coincident with the vegetation recovery. Other environmental and vegetation variables did not explain the changes in the WUE and LUE. The effect of clear-cutting on LUE was well explained by the change in the LAI; on the other hand, vegetation composition (developed forest or young tree seedling with dense undergrowth) had little effect on the magnitude and variation of LUE. In contrast, the change in LAI had little effect on WUE, because WUE is more sensitive to the atmospheric water deficit than it is to vegetation structure.