Another good reference on methods . Campbell and Norman. My 'bible' for Environmental Physics. Physicochemical and environmental plant physiology. A good, if somewhat dense, book that mixes environmental physics and ecophysiology .
Plant stems, physiology and functional morphology.
A good synthesis of how woody stems play a role in woody-plant ecophysiology. Kozlowski and Pallardy, 1997. Physiology of Woody Plants, 2nd Edition. Smith and Hinckley. Smith and Hinckley.