Broad-scale forest restoration projects are implemented across the western United States to restore seasonally dry, frequent-fire-adapted ecosystems to improve ecological function and enhance resilience by increasing resistance to crown fire and climatic stressors. Despite the widespread use of restoration treatments that center on tree thinning and application of prescribed fire, the longevity of beneficial effects and the robustness of outcomes under future climate change predictions remains unclear. In this study, we remeasured a set of experimental areas established a minimum of 20 years ago that comprise a network of ponderosa pine (Pinus ponderosa) forest restoration study sites in northern Arizona. We analyzed ecological resiliency by evaluating forest conditions in terms of resistance to climatic stressors and potential crown fire in units that were thinned following evidence-based restoration guidelines (ERG), then burned with prescribed fire at multiple intervals, compared against paired untreated controls. Resilience indicators included forest structure, tree mortality, tree growth, regeneration, canopy fuels, and crowning index. We also simulated future forest conditions under a warming climate scenario (RCP 4.5) with a range of prescribed fire return intervals. Results indicated that experimental areas where restoration treatments were implemented remained more resilient to climate stressors compared to controls after 20 years. Treated areas had significantly lower tree mortality and greater average diameter growth compared to controls. Furthermore, forest structure generally remained similar to historical reference conditions in treated units with the exception of increases in ingrowth of sprouting species at the drier sites. Canopy fuel load and crown fire hazard in treated units remained significantly lower than controls, indicating that treatments remained effective in reducing crown fire potential over the 20-year study period without the need for additional tree thinning. Modeling basal area, crowning index, and the proportion of basal area in large trees under a future warming scenario suggested that the treated units underwent less changed than untreated areas. Under climate change, management of fire regimes even at longer-than-historical intervals (historical ≈ 5 yr, tested 5, 10, and 20 yr) would maintain basal area within our historical range of variability and maintain fire resistant forest over the next several decades. However, decline by the end of the century is concerning. Our results suggest that forest restoration treatments, guided by historical reference conditions, promote ecological resilience in the long-term and continued maintenance burning into the future is likely warranted even with continued drought and warming.

在美国西部实施了大规模的森林恢复项目，以恢复季节性干燥，适应大火的生态系统，从而通过增加对树冠火灾和气候压力的抵抗力来改善生态功能并增强抵御力。尽管广泛使用了以树木稀疏和开明的火为中心的恢复治疗方法，但是在未来的气候变化预测下，有益效果的持续时间和结果的稳健性仍不清楚。在这项研究中，我们重新测量了至少20年前建立的一组实验区域，其中包括美国黄松（Pinus）在亚利桑那州北部的森林恢复研究地点。我们通过评估森林条件对气候压力的抵抗力和潜在冠火的程度来分​​析生态恢复力，这些单位按照循证的恢复准则（ERG）进行了稀释，然后与指定的未经处理的对照相比，以规定的间隔多次燃烧。复原力指标包括森林结构，树木死亡率，树木生长，再生，冠层燃料和树冠指数。我们还模拟了在气候变暖的情况下（RCP 4.5）在规定的回火间隔范围内的未来森林状况。结果表明，与对照组相比，实施了恢复处理的实验区域在20年后对气候胁迫的抵抗力仍然更高。与对照组相比，治疗区的树木死亡率显着降低，平均直径增长幅度更大。此外，除干燥地区发芽物种向内生长的增加外，经处理单位的森林结构通常保持与历史参考条件相似。经过处理的单位的冠层燃料负荷和树冠火灾危险性仍显着低于对照，这表明在20年的研究期内，治疗仍可有效降低树冠火灾的可能性，而无需额外砍伐树木。在未来变暖的情况下，对大树的基础面积，树冠指数和基础面积比例进行建模，表明与未处理区域相比，处理后的单元变化较小。在气候变化下 甚至比历史间隔更长的时间（历史≈5年，经测试的5、10和20年）进行火情管理也将使基础面积保持在我们的历史变率范围内，并在接下来的几十年中维持耐火森林。然而，到本世纪末的衰退是令人担忧的。我们的结果表明，在历史参考条件的指导下，森林恢复处理可长期提高生态适应力，即使持续干旱和变暖，也有可能继续维持燃烧直至未来。