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• <br />• <br />Preliminary Pilot Study <br />A pilot study has been conducted to demonstrate the effectiveness of supplemental irrigation on <br />growth and survival of transplanted aspen sapling trees, where the experimental conditions allowed <br />observation on several additional variables. In addition to irrigation (four levels of watering), we were <br />able to observe growth and survival of aspen of different plant type (transplants, natural sprouts, or potted <br />plants), soil type (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 were: <br />Irrigation. Best growth and survival was with low or no irrigation, but salinity of irrigation water in the <br />first two years of the experiment reduced growth of trees receiving high and medium amounts of <br />irrigation. Care must be taken to provide low saline water when irrigating planted aspen trees on <br />reclaimed lands. Low level irrigation and no irrigation growth and survival were similar, suggesting that <br />enough rainfall occurred during the initial years of this experiment so that soil moisture was adequate <br />without irrigation. <br />Plant source. Transplanted trees from local sources grew best once established. Most natural suckers did <br />not survive without removal of competing vegetation. Potted plants had a high rate of survival and <br />seemed to grow well the first year, but growth was lower than for transplants and natural sprouts after <br />three years. Roots of the potted aspen generally stayed in the augured potting hole. <br />Soil !ype. Best growth and survival occurred on roto-cleared/fresh soil compared to dozer cleared/stored <br />soil. More natural sprouts from residual root segments were evident in roto-cleared soil, likely due to the <br />shorter length of soil storage and the soil characteristics rather than the clearing method. The dozer <br />cleared soil appeared to be more compacted and was less well drained than the roto-cleared soil, and it is <br />expected that these physical characteristics and storage effects on the soil were more important to tree <br />growth than the method of clearing. <br />Control of plant competition. The best growth of aspen was with trees that were hand hoed to remove all <br />competing vegetation. This was likely related to lower water stress of the trees, since all adjacent <br />vegetation competed with the trees for the limited water supply. This was particularly apparent on the <br />roto-cleared soils where there was a high biomass of competing vegetation. <br />Root growth. Similar to top growth, root growth on the roto-cleared soil was greater in plots where <br />competing vegetation was removed by hoeing compared to plots where competing vegetation was left <br />intact. Effect of competing vegetation removal on root growth of dozer cleared soils was less evident, <br />likely since amount of competing vegetation was considerably less and growth was less on the dozer <br />cleared soils. Lateral roots in most treatments were of sufficient size support suckering, but sucker <br />initiation was likely inhibited by apical dominance of the growing trees. Lateral root extension was