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• <br />Preliminary Background Studies: <br />A pilot study was conducted to demonstrate the effectiveness of supplemental <br />irrigation on growth and survival of transplanted aspen sapling trees, but the <br />experimental conditions allowed observation on several additional variables. In addition <br />to irrigation (four levels of watering), we were able to observe growth and survival of <br />aspen of different plant type (transplants, natural sprouts, or potted plants), soil type <br />(roto- cleared /fresh or dozer - cleared /stored soil), and different levels of plant <br />competition (hand removal of competing vegetation or no removal). Results of the <br />preliminary study are reported here as background and rationale for the current study: <br />Irrigation: <br />Best growth and survival was with low or no irrigation, but salinity of irrigation <br />water in the first two years of the experiment reduced growth of trees receiving high <br />and medium amounts of irrigation. Care must therefore be taken to provide low saline <br />water when irrigating planted aspen trees on reclaimed lands. Low level irrigation and <br />no irrigation growth and survival were similar, suggesting that enough rainfall occurred <br />during the initial years of this experiment so that soil moisture was adequate without <br />irrigation. <br />Plant source <br />Transplanted trees from local sources grew best once established. Most natural <br />suckers did not survive without removal of competing vegetation. Potted plants had a <br />high rate of survival and seemed to grow well the first year, but growth was lower than <br />for transplants and natural sprouts after three years. Roots of the potted aspen <br />generally stayed in the augured potting hole. <br />Soil type: <br />Best growth and survival occurred on roto - cleared (fresh) soil compared to dozer <br />cleared (stored) soil. More natural sprouts from residual root segments were evident in <br />roto- cleared soil. It is expected that the higher number of natural sprouts was due to <br />the shorter length of soil storage and the soil characteristics rather than the clearing <br />6 <br />