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首页> 外文学位 >Pathogens and plant community structure in an old-growth mixed-conifer forest of the Sierra Nevada, California.
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Pathogens and plant community structure in an old-growth mixed-conifer forest of the Sierra Nevada, California.

机译：加利福尼亚内华达山脉的一个老混混针叶林中的病原体和植物群落结构。

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The Teakettle Ecosystem Experiment consists of an old-growth mixed-conifer forest with over 30,000 mapped trees in the Sierra Nevada Mountains, California. Multiple research projects emphasize the impacts of various old-growth restoration techniques. As is typical in western coniferous forests with fire suppression for the past 100+ years, Teakettle forest stands have become denser with a shift from shade-intolerant fire-resistant species (Pinus lambertiana and P. jeffreyi) to younger shade-tolerant fire-susceptible species (Abies concolor, A. magnifica, and Calocedrus decurrens). We utilized the forest to investigate the impacts of these stand changes on patterns of tree mortality, canopy gaps and pathogens in the absence of wildfire.; Overall mortality as measured by standing dead trees was found to be 8.7% of all stems 5cm dbh or greater. Mortality levels were proportional to the population size for the five conifer species with no significant difference between shade tolerant and intolerant species. Mortality was significantly higher than expected for large diameter trees (>100cm dbh) except for Jeffrey pine. Mortality was higher than expected in dense stand areas and lower than expected in open areas. All dead trees and small diameter dead trees (5--20cm dbh) were highly clustered within plots and within areas of high stand density.; Canopy gaps were analyzed using repeat aerial photography. Within the forest, the area in canopy gaps increased from 9.7% in 1940 to 43.1% in 2001. Gap locations were significantly related to shallow depth to bedrock. Annosum root rot (caused by Heterobasidion annosum) and bark beetles were significantly associated with canopy gaps.; Of all white firs, 25% were infected with the white fir dwarf mistletoe (Arceuthobium abietinum f. sp. concoloris). Average dwarf mistletoe rating (DMR) was 0.701. Average dwarf mistletoe index (DMI) was 2.834. Incidence, DMR and DMI all increased with increasing stem diameter and tended to increase with decreasing stand density. Bark beetles were significantly attracted to non-infected trees over mistletoe-infected trees for all but the smallest diameter white firs (5--20cm dbh).
机译：茶壶生态系统实验由一个古老的混合针叶林组成，在加利福尼亚内华达山脉中有30,000棵以上的树木。多个研究项目强调了各种旧式修复技术的影响。在过去的100多年里，西部针叶林通常具有抑制火的作用，茶壶森林的林分变得越来越茂密，从耐荫性耐火树种（Pinus lambertiana和P. jeffreyi）转向了较年轻的耐荫性火易感性。物种（Abies concolor，A。magnifica和Calocedrus decurrens）。在没有野火的情况下，我们利用森林调查了这些林分变化对树木死亡率，树冠间隙和病原体模式的影响。用立死树测得的总死亡率为5cm dbh或更高的所有茎的8.7％。死亡率与五个针叶树种的种群大小成正比，耐荫性和不耐荫性物种之间无显着差异。除Jeffrey松树外，死亡率大大高于大直径树木（> 100cm dbh）的预期。在茂密林分地区，死亡率高于预期，而在空旷地区，死亡率则低于预期。所有枯树和小径枯树（5--20cm dbh）都高度聚集在地块内和高林分密度区域内。冠层间隙使用重复的航空摄影进行分析。在森林中，树冠间隙的面积从1940年的9.7％增加到2001年的43.1％。间隙的位置与基岩的浅层深度显着相关。番荔枝根腐烂（由番荔枝异色引起）和树皮甲虫与冠层间隙显着相关。在所有白色冷杉中，有25％感染了白色冷杉矮槲寄生（Arceuthobium abietinum f。sp。concoloris）。矮小槲寄生的平均评分（DMR）为0.701。平均矮小槲寄生指数（DMI）为2.834。发生率，DMR和DMI均随茎直径的增加而增加，并随着林分密度的降低而增加。除最小直径的白杉外（5--20cm dbh），树皮甲虫被槲寄生感染的树吸引到未感染的树上。

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