Climate stressors on the forests of the American Southwest are shifting species distributions across spatial scales, lengthening potential fire seasons, and increasing the incidence of drought and insect-related die-off. A legacy of fire exclusion in forests once adapted to frequent surface fires is exacerbating these changes. Reducing stand densities and surface fuel loads has been proposed as a means of moderating fire behavior while reducing competition for water, but it is not established whether thinning treatments and restoration of surface fire regimes will be enough to offset the multiple manifestations of a changing climate. We examined the potential for prescribed fuel treatments and restoration of historical fire frequencies to mitigate the effects of climate on forest species distributions, composition, total biomass, and fire severity. We used an ecosystem process model to simulate the effects of projected climate, fire, and active management interactions along an ecological gradient of shrublands, woodlands, and forests on a mountain range in Arizona in the United States. We used historical climate conditions as a baseline to compare results from projected climate for the period 2005–2055 with and without fire and with no fuel treatments, a single-entry fuel treatment, and a second fuel treatment after 20 years. Simulated desert grassland and shrub communities remained compositionally stable and maintained or expanded their extents while woodland and forest communities lost basal area and total biomass and receded to the coolest and wettest aspects and drainages even without fire. Initial fuel treatments reduced the extent and relative mortality of high-severity patches for the first two decades, and secondary treatments at simulation year 20 extended these effects for the remaining 30 years of simulation. Immediate and future fuel treatments showed potential to mitigate the severity of fire effects under projected conditions and slow the transition from forest to shrubland in some vegetation types, however, a reduction in basal area and spatial extent of some forest species occurred regardless of management actions. Results are being used to inform local land managers and partners of potential landscape changes resulting from climate alone and from climate–fire interactions and to coordinate active management of fuels across ownerships.

中文翻译：

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预计的气候-火灾相互作用推动亚利桑那天空岛上的森林向灌木丛过渡

美国西南部森林的气候压力因素正在改变空间尺度上的物种分布，延长潜在的火灾季节，并增加干旱和昆虫相关死亡的发生率。曾经适应频繁地表火灾的森林防火遗产正在加剧这些变化。降低林分密度和地表燃料负荷已被提议作为缓和火灾行为同时减少对水的竞争的一种手段，但尚未确定减薄处理和地表火灾状况的恢复是否足以抵消气候变化的多种表现。我们研究了规定燃料处理和恢复历史火灾频率的潜力，以减轻气候对森林物种分布、组成、总生物量和火灾严重程度的影响。我们使用生态系统过程模型来模拟预测的气候、火灾和积极管理相互作用的影响，沿着美国亚利桑那州山脉的灌木丛、林地和森林的生态梯度。我们使用历史气候条件作为基线来比较 2005 年至 2055 年期间预测气候的结果，其中有火和没有火，没有燃料处理、一次性燃料处理和 20 年后的第二次燃料处理。模拟的荒漠草地和灌木群落在组成上保持稳定并保持或扩大了它们的范围，而林地和森林群落失去了基础面积和总生物量，即使没有火灾，也退化到最凉爽和最潮湿的地方和排水系统。最初的燃料处理降低了前 20 年高严重性斑块的范围和相对死亡率，模拟第 20 年的二次处理将这些影响扩展到模拟的剩余 30 年。即时和未来的燃料处理显示在预测条件下有可能减轻火灾影响的严重程度，并减缓某些植被类型从森林到灌木地的过渡，但是，无论管理措施如何，某些森林物种的基础面积和空间范围都发生了减少。结果被用来告知当地土地管理者和合作伙伴单独因气候和气候-火灾相互作用而导致的潜在景观变化，并协调跨所有权的燃料积极管理。模拟第 20 年的二级处理将这些影响扩展到模拟的剩余 30 年。即时和未来的燃料处理显示在预测条件下有可能减轻火灾影响的严重程度，并减缓某些植被类型从森林到灌木地的过渡，但是，无论管理措施如何，某些森林物种的基础面积和空间范围都发生了减少。结果被用来告知当地土地管理者和合作伙伴单独因气候和气候-火灾相互作用而导致的潜在景观变化，并协调跨所有权的燃料积极管理。模拟第 20 年的二级处理将这些影响扩展到模拟的剩余 30 年。即时和未来的燃料处理显示在预测条件下有可能减轻火灾影响的严重程度，并减缓某些植被类型从森林到灌木地的过渡，但是，无论管理措施如何，某些森林物种的基础面积和空间范围都发生了减少。结果被用来告知当地土地管理者和合作伙伴单独因气候和气候-火灾相互作用而导致的潜在景观变化，并协调跨所有权的燃料积极管理。即时和未来的燃料处理显示在预测条件下有可能减轻火灾影响的严重程度，并减缓某些植被类型从森林到灌木地的过渡，但是，无论管理措施如何，某些森林物种的基础面积和空间范围都发生了减少。结果被用来告知当地土地管理者和合作伙伴单独因气候和气候-火灾相互作用而导致的潜在景观变化，并协调跨所有权的燃料积极管理。即时和未来的燃料处理显示在预测条件下有可能减轻火灾影响的严重程度，并减缓某些植被类型从森林到灌木地的过渡，但是，无论管理措施如何，某些森林物种的基础面积和空间范围都发生了减少。结果被用来告知当地土地管理者和合作伙伴单独因气候和气候-火灾相互作用而导致的潜在景观变化，并协调跨所有权的燃料积极管理。