Effects of sclerophyllous shrub sprout competition on the morphological development of 1 + 0 containerized Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were monitored above- and below-ground for 5 years after planting. Seedlings were planted among dead shrub sprouts 0.25 m in height (treatment C1), stumps of mature shrubs slashed just before planting (treatment C2), and shrub sprouts 0.5 m in height (treatment C3). In treatments C2 and C3, stumps sprouted quickly and sprouts grew vigorously, whereas C1 seedlings grew initially without competition. Above- and below-ground growth were reduced substantially and similarly by increasing competition. Root and shoot biomass of C1 seedlings were approximately 9–10 times and 22–25 times larger than that of C2 and C3 seedlings, respectively. During the first growing season, root biomass of seedlings in all three treatments increased relatively more than did shoot biomass. This growth pattern was reversed during subsequent seasons, and over the 5-year period resulted in greater growth in shoot biomass than in root biomass. Both shoot/root and height/diameter ratios increased over time in C2 and C3 seedlings. In contrast, the shoot/root ratio increased and the height/diameter ratio decreased in C1 seedlings. Allometric regression analyses showed no significant difference in biomass allocation to shoot and root among treatments over time.
Stem analysis of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and white fir (Abiesconcolor (Gord. & Glend.) Lindl.) advance regeneration 20 years after overstory removal showed that both species can respond in height growth to become dominant components of future stands on medium- to low-quality sites with a Mediterranean climate. Average annual height growth of both species nearly doubled on site classes III and IV during the first 5 years after release and continued to increase over the 20-year period of observation. Trees on the poorer site class V responded more slowly, but achieved similar 5-year periodic annual height growth after 20 years. Regression analyses indicated that prerelease height growth and site class were generally the most important variables in describing height growth after overstory removal, but regression equations left much variability in growth unexplained. Discriminant analysis was used to develop functions that identified trees meeting or exceeding specified levels of average annual height growth 5, 10, or 20 years after release; the classifications were generally successful at least 70% of the time.
Damaged and undamaged Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings and saplings, ranging in height from 15 to 450 cm, were monitored for 6 years after overstory removal to evaluate recovery from an assortment of logging wounds. Mortality (26%) was concentrated in seedlings less than 75 cm tall and was not related to damage. Surviving trees recovered from most wounds within the 6-year period. In most cases, lateral branches turned up to replace broken terminal leaders or stems; bole wounds healed over; and trees that had been pushed over returned to an upright position. A combination of a bole wound and being pushed to the ground resulted in the poorest recovery, especially for larger trees. With discriminant analysis, initial crown ratio alone enabled correct reclassification of sample trees as crop trees from 64 to 71% of the time; small trees were the most difficult to classify correctly. The addition of preharvest height growth and percentage of bole girdled variables improved the reclassification slightly. Across all three size classes analyzed, damaged trees with initial crown ratios of at least 0.66 were classified as crop trees a minimum of 75% of the time after 6 years. Significant height growth reductions were found only for damaged trees taller than 150 cm.
Model projections of newly planted Douglas-fir (Pseudotsuga menziesii) seedlings grown under three competition regimes were compared across three site classes with growth of three height classes of Douglas-fir and white fir (Abies concolor) advance regeneration for 20 years following overstory removal. Plantations growing without competition were projected to grow about as fast as advance regeneration on the best sites and slower on the poorer sites. However, over the 20-year period, the projected height of planted trees exceeded only that of released small white fir. Competing vegetation reduced projected plantation growth, thus increasing the height advantage of advance regeneration over planted trees after 20 years. Comparisons such as these are influenced by the time required to establish new plantations, competition faced by released and planted trees, and the species composition, vigor, and initial height of the advance regeneration. These results suggest that managing advance regeneration may be a viable reforestation alternative in southwestern Oregon, particularly on poorer sites. West. J. Appl. For. 7(2):44-47
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