2009-01-30_GENERAL DOCUMENTS - C1980005

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I. Irrigation treatment - For this experiment rainfall was plentiful and not typical for the first two years during the study and soil moisture was relatively high even in un-irrigated plots, as indicated by soil moisture matrix potential values and low leaf water potential data for all treatments. This prevented a good examination of the irrigation treatment effects. Aspen growth and survival did not appear to be dependent on, or in some cases consistent with, irrigation treatment, suggesting that soil moisture from the frequent rain events was sufficient even in the non-irrigated plots. The supposition of adequate moisture available to all trees is further evident in that there appeared to be no relationship between irrigation treatment and average leaf area, total leader growth, terminal leader growth, stem diameter growth or caliper, or survival (data previously shown in earlier reports). Growth of second, third, and fourth lateral branches appeared to be similar for all treatments, but are reflected in total growth. Pre-dawn leaf water potential levels also indicate moisture stress was generally less than 8 bars (0.8 mPa) pressure, and did not appear to be related to irrigation treatments during the years when these measurements were taken. II. Transplant type -The aspen saplings used in the irrigation study that were transplanted from the Yoast site exhibited considerably more injury and had considerably more disease infections than natural sprouts arising from buried root segments or potted plant. Transplant shock was evident only the first year. Leaf area growth, leader growth, stem diameter growth, and survival were considerably less with these plants than with natural sprouts or potted plants during the first year of the study, but the transplanted trees grew well the second and third year of the study (depending on treatment). Potted plants survival was 100% and growth on these trees appeared better than transplanted cuttings the first year. Growth of the transplants was better than potted plants in subsequent years. III. Soil type -Roto-cleared soil provided sufficient natural sprouting to provide an adequate stand of aspen trees, and these trees appeared to grow better and survival appeared higher than adjacent transplanted trees growing in the same soil in the first two years of the study. Dozer- cleared soil which had been temporarily stored, had considerably lower numbers of natural sprouts than roto-cleared soil, and stocking was sparse (data not shown). Natural sprouts appeared to have greater total leaf area and greater stem diameter growth on roto-cleared soil than dozer-cleared soil, but terminal leader growth appeared similar on both soil types (data presented in earlier reports). Natural root sprouts had no lateral branches. Leaves also appeared to be larger on these trees (data not shown). Nevertheless, these trees apparently experienced somewhat greater pre-dawn water stress in July and September than trees in the irrigated treatments, including the irrigated controls with no water added. The data suggest that pre-dawn water stress levels as high as 14 bars, and afternoon water stress levels as high as 20-25 bars, were not of sufficiently high levels to cause enough stress to reduce survival or growth of these trees. Soil moisture stress appeared to be less with transplanted sprouts in the irrigation experiment, including the un-irrigated controls, than with natural root sprouts or potted plants. It is interesting to note that leaves appeared smaller and terminal growth appeared less on these apparent less-stressed transplanted trees, suggesting that growth of root sprouts, potted plants, and natural sprouts was not limited by the apparent higher moisture stress levels they experienced. Maximum leaf water potentials at mid-afternoon found stress levels of about 25 bars or less, levels that appeared unrelated to treatment, or to growth and survival.