Center for Fire Research and Outreach, University of California, Berkeley, California, 94720-3114, USA.
Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, 94720, USA.
Ecol Appl. 2017 Dec;27(8):2475-2486. doi: 10.1002/eap.1622. Epub 2017 Nov 17.
Many western North American forest types have experienced considerable changes in ecosystem structure, composition, and function as a result of both fire exclusion and timber harvesting. These two influences co-occurred over a large portion of dry forests, making it difficult to know the strength of either one on its own or the potential for an interaction between the two. In this study, we used contemporary remeasurements of a systematic historical forest inventory to investigate forest change in the Sierra Nevada. The historical data opportunistically spanned a significant land management agency boundary, which protected part of the inventory area from timber harvesting. This allowed for a robust comparison of forest change between logged and unlogged areas. In addition, we assessed the effects of recent management activities aimed at forest restoration relative to the same areas historically, and to other areas without recent management. Based on analyses of 22,007 trees (historical, 9,573; contemporary, 12,434), live basal area and tree density significantly increased from 1911 to the early 2000s in both logged and unlogged areas. Both shrub cover and the proportion of live basal area occupied by pine species declined from 1911 to the early 2000s in both areas, but statistical significance was inconsistent. The most notable difference between logged and unlogged areas was in the density of large trees, which declined significantly in logged areas, but was unchanged in unlogged areas. Recent management activities had a varied impact on the forest structure and composition variables analyzed. In general, areas with no recent management activities experienced the greatest change from 1911 to the early 2000s. If approximating historical forest conditions is a land management goal the documented changes in forest structure and composition from 1911 to the early 2000s indicate that active restoration, including fire use and mechanical thinning, is needed in many areas.
许多北美西部森林类型由于火灾排除和木材采伐这两个因素，其生态系统结构、组成和功能发生了很大变化。这两个因素在很大一部分干旱森林中同时发生，使得很难单独了解其中任何一个因素的强度，或者这两个因素之间可能存在的相互作用。在这项研究中，我们使用了系统历史森林清查的当代复测数据来调查内华达山脉的森林变化。这些历史数据偶然跨越了一个重要的土地管理机构的边界，该边界保护了清查区域的一部分免受木材采伐。这使得我们能够对采伐区和未采伐区的森林变化进行有力的比较。此外，我们评估了相对于历史上相同区域和没有最近管理活动的其他区域，最近旨在进行森林恢复的管理活动的效果。基于对 22007 棵树（历史数据：9573 棵；当代数据：12434 棵）的分析，在采伐区和未采伐区，活基面积和树木密度从 1911 年到 21 世纪初显著增加。在这两个地区，灌木覆盖和松树物种占据的活基面积比例都从 1911 年到 21 世纪初下降，但统计显著性不一致。采伐区和未采伐区之间最显著的差异是大树的密度，它在采伐区显著下降，但在未采伐区没有变化。最近的管理活动对分析的森林结构和组成变量产生了不同的影响。一般来说，没有最近管理活动的地区从 1911 年到 21 世纪初变化最大。如果近似于历史森林条件是土地管理的目标，那么从 1911 年到 21 世纪初森林结构和组成的变化表明，在许多地区需要进行积极的恢复，包括使用火和机械疏伐。
