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ABSTRACT. Silver iodide is currently the most favored cloud seeding material in weather modification projects. While the literature indicates that its ecological effects are likely to be insignificant, its disposition in the terrestrial ecosystem after snow melt has not been adequately studied. Silver levels in soil, plant and litter material are being monitored twice a year on a mountainous area in southwestern Colorado, to determine whether annual accretion from cloud seeding can be measured with current techniques and whether significant changes in silver concentration take place in grass, aspen, and spruce communities. One AgI generator site is also being monitored. Comparison of silver concentrations in terrestrial components of the target area indicates no measurable increase after the first winter's seeding. On an ash basis, spruce foliage and litter contain about four times as much silver as soil. On a dry weight basis, soil from all three plant communities contains about six times as much silver as foliage. Consistent increases in silver concentration were found in soil and pine foliage within 200 meters of one generator site.

Some recent trends in forest hydrology and forest influences research are discussed, including studies of interception and transpiration, water yields from snow, effects of deforestation and afforestation, mathematical modelling, water us~ by individual trees, factors affecting water quality, and the chemical processes involved in soil erosion. INTRODUCTIONThe growing interest in the non-timber values of fore~try has in recer.t years increased the volume of research work in forest influences and forest hydrology. While those who are actually doing this work are generally aware of the trends, many practising foresters rarely have contact with the suhject. This paper reviews some of the progress which has been made, the direction which current research studies are taking, the sources of some relevant information, and some of the outstanding problems.