Table_1_A Framework for Quantifying Resilience to Forest Disturbance.docx

The concept of ecological resilience is an invaluable tool to assess the risk of state transitions and predict the impact of management on an ecosystem's response to future disturbances. However, resilience is difficult to quantify and the factors contributing to resilience are often unknown in systems subject to multiple disturbances. Here, we develop and demonstrate a framework to assess the potential of ponderosa pine and dry mixed conifer forests to be resilient to future disturbance (recover as the same forest type within a managerially significant timeframe) by combining indicators of short-term resilience (ability to withstand disturbance) to fire, insect, and drought disturbances using data from the Rio Tusas-Lower San Antonio landscape in northern New Mexico. The dry mixed conifer forests displayed an average resilience score of 4.54, while ponderosa pine forests had an average score of 3.45 (total possible of nine points) Stand density index was the most important driver of the overall score in the dry mixed conifer type. In the ponderosa pine type, overall basal area was the strongest driver of the overall score. These indicators have the greatest impact on the resilience score and provide the most effective targets for management to increase the possibility of resilience in these forest types. We applied the model in both forest types by comparing individual stands to an “ideal” score for a stand that is within the historic range of variation (HRV) of forest structure for each forest type and confirmed that stands outside of HRV had a low possibility of resilience and stands that had received restoration-based treatments were more likely to be resilient. Our results provide evidence that the changes to forest structure and species composition that have occurred since the onset of fire exclusion have degraded the potential of these forest types to be resilient to future fire, insect, and drought-related disturbances. By modifying disturbances and resilience indicator thresholds this model can be applied to assess resilience to other disturbances within these forest types and across various regions and ecosystem types.

生态韧性（ecological resilience）概念是评估生态系统状态转换风险、预测管理措施对生态系统应对未来扰动响应影响的宝贵工具。然而，韧性的量化难度较大，且在受多重扰动影响的生态系统中，其驱动因子往往尚不明确。本研究构建并验证了一套评估框架，以评估黄松（ponderosa pine）林与干旱混交针叶林（dry mixed conifer forests）对未来扰动的韧性潜力——即在具有管理重要性的时间尺度内恢复为原有林分类型的能力。该框架结合了林分针对火灾、虫害与干旱扰动的短期韧性指标（即抵御扰动的能力），所用数据取自新墨西哥州北部的里奥图萨斯-下圣安东尼奥景观（Rio Tusas-Lower San Antonio landscape）区域。
研究结果显示，干旱混交针叶林的平均韧性得分为4.54，黄松林的平均得分为3.45（满分9分）。林分密度指数（Stand density index）是影响干旱混交针叶林整体韧性得分的最关键驱动因子；而在黄松林中，胸高断面积（basal area）对整体得分的影响最为显著。上述指标对韧性得分的影响程度最高，可为提升这两类森林的韧性水平提供最具针对性的营林目标。
我们将该模型应用于两类森林：将单个林分的得分与对应林分类型的森林结构历史变异范围（historic range of variation）内的‘理想’得分进行对比，结果证实，处于历史变异范围外的林分韧性概率较低，而接受过修复性营林措施的林分韧性概率更高。研究结果表明，自森林禁火政策实施以来，森林结构与物种组成发生的变化已削弱了这两类森林应对未来火灾、虫害及干旱相关扰动的韧性潜力。通过调整扰动类型与韧性指标阈值，该模型可用于评估这两类森林内、乃至不同区域与其他生态系统类型中，森林对各类扰动的韧性水平。