Abstract: In ecology, theory should be considered not only as a conceptual framework for research, but an ultimate product of ecological studies as well. Model may serve as the basic unit for many theoretical and applied studies. Theory and model can be used to generate new hypotheses, to clarify and test existing hypotheses, to identify key components in complex systems, to suggest critical experiments, to synthesize knowledge across disciplines and scales, and to make assessment or optimization for decision-making processes. Models become indispensable when we deal with both spatial and temporal dynamics of systems simultaneously, and when the scales of the phenomenon become large. Ecologists should keep themselves up-to-date of the state of the art in their field,and try to equip themselves with advanced methods and approaches. Empirical and theoret- ical ecology are interdependent and interactive. Minimizing the gap between theoreticians and empiricists will certainly help promote the development of the science of ecology.

Key words: Quercus variabilis, trunk diameter, sap flow, water regime, meteorological factor.