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Long-term Effects of Fire Hazard Reduction Treatments in the Southern Cascades and Northern Sierra Nevada, California.

机译：加利福尼亚南部小瀑布和内华达山脉北部的减少火灾隐患的长期效果。

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摘要

Treating wildland fuels to reduce wildfire hazards has become a primary focus of contemporary forest management, particularly in the wildland-urban interface. The specific objectives of treatment are diverse, but in general, treatments address accumulated surface fuels, the fuel ladders that carry fire into the forest canopy, and surface and canopy fuel continuity. This dissertation uses a chronosequence of treated stands to examine the temporal influence of treatment on forest structure, the understory plant community, and wildfire hazard.;The first chapter examines the effects of fuels reduction treatment on stand structure, overstory species composition, and ground and surface fuels. The stand structures and reduced surface fuel loads created by fuels modification are temporary, yet few studies have assessed the lifespan of treatment effects. The structural legacies of treatment were still present in the oldest treatment sites. Treatments reduced site occupancy (stand density and basal area) and increased quadratic mean diameter by approximately 50%. The contribution of shade-tolerant true firs to stand density was also reduced by treatment. Other stand characteristics, particularly timelag fuel loads, seedling density, and shrub cover, exhibited substantial variability, and differences between treatment age classes and between treatment and control groups were not statistically significant.;The second chapter evaluates fuel treatment longevity based on potential wildfire behavior and effects on vegetation. Forest managers must divide scarce resources between fuel treatment maintenance, which is necessary to retain low hazard conditions in treated stands, and the construction of new treatments. Yet the most basic questions concerning the lifespan of treatment effectiveness have rarely been engaged in the literature. In this study, field-gathered fuels and vegetation data were used to aid fuel model selection and to parameterize a fire behavior and effects model, Fuels Management Analyst Plus. In addition, a semi-qualitative, semi-quantitative protocol was applied to assess ladder fuel hazard in field sampling plots. Untreated sites exhibited fire behavior that would challenge wildfire suppression efforts, and projected overstory mortality was considerable. In contrast, estimated fire behavior and severity were low to moderate in even the oldest fuel treatments, those sampled 8-26 years after treatment implementation. Findings indicate that in the forest types characteristic of the northern Sierra Nevada and southern Cascades, treatments for wildfire hazard reduction retain their effectiveness for more than 10-15 years and possibly beyond a quarter century.;Fuel treatment activities disturb the forest floor, increase resource availability, and may introduce non-native plant propagules to forest stands. Non-native plant invasions can have profound consequences for ecosystem structure and function. For these reasons, there is concern that treatment for fire hazard reduction may promote invasion by exotic species. Several short-term studies have shown small increases in non-native abundance as a result of treatment, but the long-term effects have rarely been addressed in the literature. The final chapter examines treatment effects on the understory plant community and on cover of the forest floor, as mineral soil exposure has been linked to invasion. Regression tree analysis provided insights into the influence of treatment and site characteristics on these variables. Treatments increased forb and graminoid cover, but temporal trends in abundance were opposite. An initial increase in forb cover in the most recently treated sites was followed by a gradual decline, while mean graminoid cover was highest in the oldest treatments. Shrubs dominated live plant abundance. Shrub cover showed few temporal trends, but was negatively associated with canopy cover. Mineral soil exposure was increased by treatment and declined slowly over time, remaining elevated in the oldest treatments. Non-native plant species were very rare in the treatment sites sampled in this study. Despite the availability of bare mineral soil and the proximity of transportation corridors, a source of non-native propagules, non-natives were recorded in only 2% of sampling plots. This study suggests that forest disturbance associated with treatment for hazardous fuels reduction may not produce significant invasions in these forest types. (Abstract shortened by UMI.).
机译：处理野外燃料以减少野火危害已成为当代森林管理的主要重点，特别是在野地与城市的交界处。处理的具体目标各不相同，但总的来说，处理针对的是累积的地表燃料，将火带入林冠层的燃料梯子以及地表和冠层燃料的连续性。本文采用经处理林分的先后顺序，研究了林分处理对森林结构，林下植物群落和野火危害的时间影响。第一章研究了节油对林分结构，林下物种组成，地面和地面的影响。表面燃料。林分结构和因燃料改良而产生的减少的表面燃料负荷是暂时的，但很少有研究评估治疗效果的寿命。在最古老的治疗地点仍然存在治疗的结构遗留问题。处理减少了位点占用（林分密度和基底面积），并使二次平均直径增加了约50％。耐荫真杉木对林分密度的贡献也因处理而降低。其他林分特征，特别是时滞燃料负荷，幼苗密度和灌木覆盖率表现出较大的变异性，并且处理年龄等级之间以及处理组和对照组之间的差异无统计学意义。第二章根据潜在的野火行为评估了燃料处理寿命。及其对植被的影响森林管理者必须将稀缺资源分配给燃料处理维护和保持新的处理之间，燃料维护是维持低危害条件的必要条件，燃料保持在已处理林分中。然而，有关治疗有效性寿命的最基本问题很少在文献中涉及。在这项研究中，使用现场收集的燃料和植被数据来帮助选择燃料模型并参数化火灾行为和效果模型“燃料管理分析家Plus”。此外，半定性，半定量方案被应用于评估田间采样区的梯子燃料危害。未经处理的场所表现出的火灾行为可能会挑战野火扑灭的努力，并且预计楼上的死亡率很高。相比之下，即使是最古老的燃料处理，估计的射击行为和严重程度也从中到低，这些都是在实施处理后的8-26年取样的。研究结果表明，在内华达山脉北部和喀斯喀特山脉南部的典型森林类型中，减少野火危害的治疗方法可以保持其有效性超过10-15年，甚至可能超过25年。可用性，并且可能会将非本地植物繁殖体引入林分。非本地植物的入侵会对生态系统的结构和功能产生深远的影响。由于这些原因，人们担心减少火灾隐患的治疗可能会促进外来物种的入侵。几项短期研究显示，由于治疗，非本地性丰度有少量增加，但长期影响在文献中很少涉及。最后一章探讨了处理对地下植物群落和森林地面覆盖的影响，因为矿物土壤的暴露与入侵有关。回归树分析提供了有关处理和部位特征对这些变量的影响的见解。治疗增加了前肢和类动物体的覆盖，但是丰度的时间趋势却相反。在最近接受治疗的部位，最初的前肢覆盖率最初增加，随后逐渐下降，而在最老的治疗中，平均类固醇覆盖率最高。灌木占据了活植物的丰度。灌木覆盖几乎没有时间趋势，但与冠层覆盖负相关。矿物质土壤暴露通过处理增加，并随时间缓慢下降，在最旧的处理中保持较高水平。在本研究采样的处理部位中，非本地植物物种非常罕见。尽管有裸露的矿质土壤和靠近运输走廊（非本地繁殖体的来源），但只有2％的采样区记录了非本地繁殖体。这项研究表明，与减少有害燃料的处理相关的森林扰乱可能不会对这些森林类型造成重大入侵。 （摘要由UMI缩短。）。

著录项

  • 作者

    Chiono, Lindsay Aney.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Biology Ecology.;Environmental Management.;Natural Resource Management.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 81 p.
  • 总页数 81
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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