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首页> 外文期刊>Conservation Biology >Forest structure and fire susceptibility in volcanic landscapes of the eastern high cascades, Oregon
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Forest structure and fire susceptibility in volcanic landscapes of the eastern high cascades, Oregon

机译：俄勒冈东部高小瀑布的火山景观中的森林结构和火灾敏感性

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Multidimensional forest health initiatives-those designed to restore and protect forest integrity in the large sense-require, among other things, a better understanding of the relationship between the structure of forests and (1) their susceptibility to wildfires outside the range of natural variability and (2) the level of treatment (if any) required to lower susceptibility into an acceptable range. Within the ponderosa pine zone (Pinus ponderosa Dougl. ex Laws.) on the eastern slopes of Oregon's Cascade Range, an average of 86% of trees >5 cm in diameter at breast height (dbh) were less than 101 years old, the density of young trees correlating negatively with the density of old trees (> 150 yrs). Species composition differed significantly between age classes: 72% of trees older than 150 years were ponderosa pine, whereas 83% of trees younger than 101 years were either grand fir (Abies grandis [Dougl.]Lindl.) or lodgepole pine (Pinus contorta Dougl. ex). Loud Crown bulk density calculated to reflect the multiple canopy layer structure of these stands (CBDm) averaged 0.049 kg/m(3), compared to 0.093 kg/m(3) using the standard approach (p < 0.001), indicating that the latter significantly overestimates risk of active crown fire in stands with complex canopy structure. Nevertheless, modeling with CBDm predicts that under severe but plausible weather conditions (late summer fuel moisture and 48-kph winds) crown kill would exceed 70% on 5 of 14 plots and 50% on an additional 5 plots. Models also predict that thinning trees of <20 cm dbb, coupled with controlled burning to reduce logging slash, would prevent torching (fire moving from the ground into crowns) on all plots, even under extreme fire conditions (low fuel moisture and 80-kpb winds). The amount of thinning required to prevent spread from crown to crown (active crown fire) varied widely among plots and depended on the degree of risk deemed acceptable. The relationship between stand basal area and the critical wind speed required to maintain active crown fire followed a negative power law (r(2) = 0.92), implying that over certain ranges small changes in basal area result in relatively large changes in susceptibility (assuming that changes in basal area are due to addition or removal of smaller trees). Landsat thematic mapper correlates reasonably well with CBDm (r(2) = 0.80) and may provide a tool for rapid risk assessment.
机译：多维森林健康计划-旨在从广义上恢复和保护森林完整性的森林计划-除其他外，还需要更好地了解森林结构之间的关系，以及（1）它们对自然火灾和自然变化范围之外的野火的敏感性。 （2）将敏感性降低到可接受范围内所需的治疗水平（如果有）。在俄勒冈喀斯喀特山脉东坡的美国黄松区（Pinus tankerosa Dougl。ex Laws）中，平均胸径（dbh）直径大于5厘米的树木中，平均有86％的树龄小于101年幼树的数量与老树的密度（> 150年）呈负相关。物种组成在不同年龄段之间存在显着差异：年龄大于150岁的树木中有72％是黄松，而年龄小于101岁的树木中有83％是大冷杉（Abies grandis [Dougl。] Lindl。）或黑松（Pinus contorta Dougl （例如）。计算得出的反映这些林木多冠层结构（CBDm）的大树冠堆积密度平均为0.049 kg / m（3），而使用标准方法则为0.093 kg / m（3）（p <0.001），表明后者显着高估了具有复杂顶篷结构的林冠发生主动树冠火灾的风险。但是，使用CBDm进行的模型预测在14个地块中的5个地块上，在严峻但合理的天气条件下（夏季燃料湿气和48公里/小时的风速），冠冠死亡将超过70％，另外5个地块将超过50％。模型还预测，＜20 cm dbb的树木变薄，再加上可控的燃烧以减少伐木砍伐，即使在极端火情（低燃油湿度和80 kpb）下，也能防止在所有地块上出现火炬（火从地面移动到树冠）。风）。在地块之间，为防止从树冠到树冠扩散（活动树冠起火）所需的稀疏量差异很大，这取决于认为可接受的风险程度。林分基础面积与维持活动冠火所需的临界风速之间的关系遵循负幂定律（r（2）= 0.92），这意味着在某些范围内，基础面积的微小变化会导致磁化率相对较大的变化（假设基础面积的变化是由于添加或移除了较小的树木造成的）。 Landsat专题制图仪与CBDm的相关性相当好（r（2）= 0.80），并可能提供快速风险评估的工具。

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