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<br />G~th rate. - Any effect that cloud seeding would have on <br />increasing tree growth would influence the incidence and sever- <br />ity of certain tree diseases. For instance, dwarf mistletoes <br />(Arceuthobiwm) would become less severe in individual trees, <br />and possibly in stands, which had greater height growth, since <br />vigorous conifers on good sites suffer less damage and mortal- <br />ity from these parasites than do trees on poor sites or those <br />suffering moisture stress. Thus, the additional moisture <br />derived from cloud seeding would be beneficial in helping trees <br />with lower growth rates combat such, diseases. <br /> <br />Recent observations on F. annoSU8 in fir suggest that root and <br />butt decay progresses slowly from the heartwood into' sapwood. <br />If the trees are rapidly forming new sapwood, they can survive <br />by '~eeping ahead" of the pathogen. However, a similar process <br />is probably involved with other local host-pathogen associations <br />such as stem and gall rusts or other decays and tipmoth on east- <br />side pine. Here again, the increased moisture from cloud seed- <br />ing would be helpful in lessening damage from pathogens by keep- <br />ing the growth rate high. <br /> <br />Weather modification may not measurably affect trees on good <br />sites or on sites with adequate soil moisture, but it might <br />affect those trees which suffer growth reduction due to periodic <br />drought stress. A 5- to 7-year monitoring program would not be <br /> <br />1-7 <br />