The presented doctoral thesis aims to provide a comprehensive overview of recommendations and proven procedures for working with sap flow measurements and their efficient use in the estimation of canopy transpiration and stomatal conductance as a function of environmental factors. The work is based on the author's long-term involvement in ecophysiological research, the innovation of measuring methods, and the development of measuring equipment. The main objective of the thesis is to describe the whole methodological, theoretical, and fundamental evolution of ecophysiological instrumentation, followed by applied research that helps scientists to describe and understand plant-environment interactions. The doctoral thesis includes significant technical-methodological notes on the instrumentation of ecophysiological research and specific research results published as scientific articles. These works, among other things, describe various applications of theoretical and methodological approaches and procedures in ecological and forestry research. In conclusion, the author also devotes himself to the education and popularization of his scientific work, documented by presentations at conferences, seminars, and workshops.