Abstract Sierra Nevada mixed-conifer forests have undergone significant changes in structure and composition and are increasingly vulnerable to altered disturbance regimes and climate-related extreme events. Fuel reduction treatments, including thinning and follow-up surface fuel treatments, can reduce this vulnerability by creating forest structural and woody fuel conditions that not only allow forest stands to mitigate wildfire, but also alleviate individual tree stress. However, direct observations that quantify these longer-term effects are lacking. This study compares observed changes in forest structure, tree species composition, and downed woody fuel loads across three distinct time periods: pre-treatment, 1 yr post-treatment, and 10 yr post-treatment. Additionally, using tree ring data, we assessed whether treatments affected individual tree resistance to a severe statewide drought (2012–2015). Thinning treatments were able to effectively reduce tree density and basal area, increase the retention of both larger-sized and shade-intolerant trees, and mitigate tree mortality. Treatments were also associated with significantly lower coarse woody fuel and snag basal area. Snag basal area and time since treatment were related to the accumulation of fine and coarse woody surface fuel loads. Tree ring information indicated that treatments improved drought resistance as well, especially in units with lower residual live basal area. This study complements previous studies on fuel reduction thinning by demonstrating that these treatments have lasting effects on forest structure, which also confers a degree of drought resistance.

中文翻译：

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减少燃料处理对太浩湖盆地森林结构、燃料和抗旱性的长期影响

摘要 内华达山脉混交针叶林的结构和组成发生了显着变化，并且越来越容易受到扰动机制和气候相关极端事件的影响。减少燃料的处理，包括间伐和后续的表面燃料处理，可以通过创造森林结构和木质燃料条件来减少这种脆弱性，不仅可以让林分减轻野火，还可以减轻个体树木的压力。然而，缺乏量化这些长期影响的直接观察结果。本研究比较了在三个不同时间段内观察到的森林结构、树种组成和木质燃料负荷的变化：处理前、处理后 1 年和处理后 10 年。此外，利用年轮数据，我们评估了处理是否影响了个体树木对全州严重干旱（2012-2015）的抵抗力。间伐处理能够有效降低树木密度和基面积，增加大树和不耐荫树木的保留，并降低树木死亡率。处理还与显着降低粗木本燃料和断枝基底面积有关。自处理以来的障碍基底面积和时间与细木本和粗木本表面燃料负荷的积累有关。树木年轮信息表明，处理也提高了抗旱性，尤其是在剩余活基面积较低的单元中。本研究通过证明这些处理对森林结构具有持久影响来补充先前关于减少燃料减少的研究，这也赋予了一定程度的抗旱性。