|Forests, Climate, and Hydrology: Regional Impacts (UNU, 1988, 217 pages)|
It has been possible for the workshop to agree to conclusions (chap. 9). They reflect the discussions of each of the review papers and are by nature compromises of the differing views of the participants (listed on page 212). These points of agreement have been discussed, drafted, discussed again by the workshop, redrafted and circulated to the members for comment and correction. Whilst they represent a consensus, the composition of the workshop will have been bound to produce some subjective bias.
Of the ten workshop conclusions, half related essentially to the investigative procedure. This emphasizes the need to improve our methodology before the precision is adequate to allow us to rely on the findings. The workshop presages a change in data collection away from small-scale observations to extensive methods. The scientific community is clearly on the lookout for new, more reliable tracers to use in large-scale hydrology. Throughout the field more rigorous attention to descriptions and scales is demanded; these need to be more relevant to the physical systems operating and the intended use of the information acquired.
The other conclusions incorporate as far as possible quantitative estimates of effects of changing forest cover. This is where greater precision is needed. On the larger to global scales, the workshop's conclusions are mostly qualitative, often indicating little more than whether changes will be positive or negative. However, there is optimism that improved simulation models will yield acceptable estimates of the magnitude of the effects.
It will be apparent that, although there are numerous uncertainties in the models that relate climate to vegetation via general atmospheric circulation, many of these arise from difficulties of parametrization and the quantitative values of inputs. Careful appraisal of the system and more reliable data should resolve these uncertainties. In one area the problems are rather a lack of proper understanding of the processes. These are the hydrological mechanisms occurring in the biosphere. The reason for our ignorance is the bewildering variety of ecophysiological adaptations directed towards the strategy of maintaining plant tissue moisture potentials to permit cellular metabolism and growth to proceed. The regulation of the distribution of plant roots and the resulting pattern of soil moisture extraction are as yet incompletely understood. The disposition, size, and behaviour of stomata controlling the rate of transpiration need further study. More information on the variations of albedo and the aerodynamic roughness of complete vegetation canopies is also required to provide a proper link with micrometeorology. Unless research into these biological phenomena is pursued, relationships between vegetation and climate will remain matters of empirical observation, and choices of land use to fulfil hydrological if not climatological objectives will be less certain.