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Initial analyses indicate that soil type and weed competition affected rate of photosynthesis and <br />respiration. Highest rates of photosynthesis seemed to be in the weeded plots on roto-cleared <br />soils, suggesting that these conditions are best for aspen growth and survival. Plant top and root <br />growth on these plants would seem to verify that finding. Plant water status measurements <br />indicated that when these tests were conducted during the 2007 growing season (June 28 and <br />August 1) the plants were not water stressed, with pre-dawn leaf water potential pressures not <br />exceeding 10 bars and most often less than 5 bars (Figures 10-11). <br />Root growth: <br />Root growth of transplants was best in weeded plots on roto-cleared soil and lateral roots <br />extended far from the base of the original tree (Figures 12). They were of sufficient size (4 mm <br />or more) where suckering could begin, but many were too deep (15 cm or deeper), a result of the <br />deep planting of the transplanted trees. Trees in other treatments are surviving and roots are <br />extending out, but it will take additional years for most to obtain sufficient size at depths <br />necessary for suckering. In any case, suckers are more likely to appear after injury or death of <br />parent trees when apical dominance is inhibited. Roots growing from the potted trees were <br />mostly confined to the potting hole. This was also true for some of the transplants on dozer- <br />cleared soil, perhaps a result of the high density and compaction of this dozer cleared and stored <br />soil. <br />Depth of the roots systems for the transplanted aspen ranged from about 15 to 40 cm, with <br />transplants in the roto-cleared soil planted somewhat deeper than those on the dozer cleared soil. <br />These depths are too deep to allow effective suckering. Even though roto-cleared trees were <br />planted somewhat deeper than dozer-cleared trees, growth was better on the roto-cleared trees. It <br />is expected that trees planted deep will take longer to produce roots at a depth conducive to <br />suckering, but those deep planted trees that survived are now producing shallower roots. Lateral <br />root systems were already developing on most of the transplanted trees, and roots were observed <br />near the surface several meters from the base of some trees suggesting that these trees were <br />becoming well established. Apical dominance of the rapidly growing transplanted trees likely <br />prevented suckering of these lateral roots. It is expected that enough root system has developed <br />that further irrigation of these trees is not necessary. <br />Competing vegetation: <br />Weeds were an important competitor for soil moisture in the planted aspen plots. Soil moisture <br />was higher in the weeded plots, suggesting more soil moisture available for tree growth in these <br />plots (Figure 4). Weeding was particularly important for survival of natural sprouts occurring <br />from residual aspen roots in the replaced topsoil. Trees growing on weeded plots grew <br />considerably better and had higher rates of survival. Of 34 natural sprouted trees initially marked <br />for study on the roto-tilled fresh soil in year 1, half were weeded and half un-weeded in years 2 <br />and 3. All of the weeded trees survived into year 3 while only 4 of the un-weeded trees survived <br />the first three years of the experiment. Of the 21 natural sprouts on the dozer-cleared stored soil, <br />8 of the 11 weeded trees but only 2 of the 10 non-weeded trees survived after 3 years. Most of