The impacts of thinning, fertilization and crown position on seasonal growth of current-year shoots and foliage were studied in a 13-year-old loblolly pine (Pinus taeda L.) plantation in the sixth post-treatment year (1994). Length of new flushes, and their needle length, leaf area, and oven-dry weight were measured in the upper and lower crown from March through November. Total shoot length was the cumulative length of all flushes on a given shoot and total leaf area per shoot was the sum of leaf areas of the flushes.
By the end of June, first-flush foliage reached 70% of the November needle length (14.3 cm) and 65% of the final leaf area (15.0 cm2). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3 cm), whereas total leaf area per shoot was 55% of the final value (75.3 dm2). Fertilization consistently stimulated fascicle needle length, dry weight, and leaf area in the upper crown. Mean leaf area of upper-crown shoots was increased by 64% six years after fertilization. A significant thinning effect was found to decrease mean leaf area per shoot in the crown. For most of the growing season, the thinned-fertilized trees produced substantially more leaf area per shoot throughout the crown than the thinned-nonfertilized trees. These thinned-fertilized trees also had greater needle length and dry weight, longer first flush shoots, and more leaf area per flush than trees in the thinned-nonfertilized plots. Needle length and leaf area of first flush shoots between April and July were linearly related to previous-month canopy air temperature (Ta). Total shoot length strongly depended on vertical light gradient (PPFD) within the canopy, whereas shoot leaf area was a function of both PPFD and Ta. Thus, trees produced larger and heavier fascicles, more and longer flush shoots, and more leaf area per shoot in the upper crown than the lower crown. We conclude that thinning, fertilization, and crown position regulate annual leaf area production of current-year shoots largely by affecting the expansion of first flush shoots and their foliage during the first half of the growing season. 相似文献
Beech trees occur in significantly lower latitudes in continental East Asia than in Europe and North America. They are common deciduous trees in the deciduous forests of the temperate zone in Europe, the eastern part of North America and Japan. In continental East Asia, however, they are absent in the deciduous forests of the temperate zone, but occur in the forests of mountains in the moist subtropical zone, south of 34° Northern Latitude. The lower limits of their distribution in these mountains show a significantly different pattern from the usual distribution pattern of plants and vegetation: it declines as the latitude decreases. The altitudinal belts of beech species lie higher in the northern than in the southern parts of their distribution areas in China. Based on an analysis of the climate and the phenology of these deciduous trees, we show that the prevailing monsoon conditions are the main factor affecting the distribution of the Chinese beech species. 相似文献