The papers presented at this meeting have given us a comprehensive account of the state of the art in what one is tempted to call 'forest meteorology' though 'meteorological forestry' is probably nearer the mark. Older members of the audience like myself who can recall the descriptive and anecdotal nature of the subject in the early 1950s have enjoyed hearing how it has come of age through the painstaking collection of measurements in the field and through the emergence of principles that have

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... uided the development of mathematical models. Forest meteorologists have been fortunate that much of the foundation of their subject has been laid by the pioneers of agricultural meteorology who have had an easier task experimentally and are therefore a little ahead, but not much! A psychologist might have felt quite at home at this meeting because there have been so many references to the way systems ' behave '.It seemed that systems were ' well behaved ' when processes being observed were consistent with theoretical predictions where they existed, or with intuition where they did not. Bad behaviour (by a forested catchment in Rob Roy's territory for example) meant a discrepancy between performance and expectation. We should remember, however, that the recognition of so-called bad behaviour is the first step towards new developments in most branches of science; and that progress in forest meteorology will depend on the skill and patience of people who feel challenged to tackle the anomalies, the uncertainties and the loose ends that we have heard about yesterday and today. Closely associated with this somewhat anthropomorphic view of forest meteorology has been the contrast between success in using simple models (e.g. the ' big leaf' canopy) in some analyses and frank admissions of failure in others where essential features are still missing. As one speaker put it ' models are the best way of using physics to sort out the complexities of biological measurements '. He might have added ' and the complexities of interactions between forests and the atmospheric boundary layer', a subject that several speakers have dealt with. I believe that success in modelling depends on identifying what corners can safely be cut without violating the laws of physics or the principles of biology, so that the final product is no more complicated than it needs to be to fit independent observations or to guide decisions for management. None of the models discussed here has been unnecessarily complex, but most speakers have drawn our attention to weaknesses in current models that reveal our limited understanding of how trees and forests respond to the atmosphere and vice versa. One of the most striking aspects of the papers that have been presented has been the very wide range of scales they have encompassed both in space and in time. In space, we have moved from the functioning of stomata with dimensions around 10-5 m to atmospheric processes on a global scale, say 107 m, a range of 12 orders of magnitude. In time, we have been concerned with transfer processes induced by eddies sweeping past sensors in 10_1 s or less; but we have also considered the response of trees to climate over annual cycles (1 year « 3 x 107 s). Dealing with such a broad space-time spectrum makes heavy demands on instrumentation, and the [ 259 ]