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• (roto-cleared/fresh or dozer-cleared/stored soil), and different levels of plant competition <br />(hand removal of competing vegetation or no removal). Results of the preliminary study <br />were: <br />Irrigation. Best growth and survival was with low or no irrigation, but salinity of <br />irrigation water in the first two years of the experiment reduced growth of trees receiving <br />high and medium amounts of irrigation. Care must be taken to provide low saline water <br />when irrigating planted aspen trees on reclaimed lands. Low level irrigation and no <br />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. Transplanted trees from local sources grew best once established. Most <br />natural suckers did not survive without removal of competing vegetation. Potted plants <br />had a high rate of survival and seemed to grow well the first year, but growth was lower <br />than for transplants and natural sprouts after three years. Roots of the potted aspen <br />generally stayed in the augured potting hole. <br />• Soil type. Best growth and survival occurred on roto-cleared/fresh soil compared to <br />dozer cleared/stored soil. More natural sprouts from residual root segments were evident <br />in roto-cleared soil, likely due to the shorter length of soil storage and the soil <br />characteristics rather than the clearing method. The dozer cleared soil appeared to be <br />more compacted and was less well drained than the roto-cleared soil, and it is expected <br />that these physical characteristics and storage effects on the soil were more important to <br />tree growth than the method of clearing. <br />Control of plant competition. The best growth of aspen was with trees that were hand <br />hoed to remove all competing vegetation. This was likely related to lower water stress of <br />the trees, since all adjacent vegetation competed with the trees for the limited water <br />supply. This was particularly apparent on the roto-cleared soils where there was a high <br />biomass of competing vegetation. <br />Root growth. Similar to top growth, root growth on the roto-cleared soil was greater in <br />plots where competing vegetation was removed by hoeing compared to plots where <br />competing vegetation was left intact. Effect of competing vegetation removal on root <br />• growth of dozer cleared soils was less evident, likely since amount of competing