Olevi Kull's lifetime contribution to ecology

In this article dedicated to Olevi Kull (June 22, 1955-January 31, 2007), we draw on his writings (in English and translated) to outline his thoughts on the relationship between scientists and science. We provide a brief synthesis of his most important work, give a short account of his career and, to bring the man into focus, share some personal stories of interactions with him. Kull considered that for a personal understanding to become scientific knowledge it must be explained convincingly based on theory and empirical support, and then taught to others in both spoken and written words. He saw the last step as the main distinction between learning and science. Olevi Kull's approach to science relied on two principles: first, linking theory and experiments in challenging settings, e.g., to test the generality of his ideas he often challenged them in multi-layered, mixed-species canopies. Second, he insisted on setting experiments to test assumptions used in quantitative analyses or in explaining an observed outcome; this, at times, led to falsification of commonly held ideas, thus enhancing ecophysiological understanding. After describing Kull's application of these principles, we give a brief synthesis of his most important work, in which he demonstrated through experimentation and modeling how the vertical distribution of leaves in canopies is consistent with the acclimation of the photosynthetic apparatus. We also review some of his findings on the interactive effects of carbon dioxide and ozone on canopy photosynthesis.