Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE, 68503-0984, USA.
Center for Resilience in Agricultural Working Lands, University of Nebraska, Lincoln, NE, 68503-0984, USA.
J Environ Manage. 2021 Aug 1;291:112550. doi: 10.1016/j.jenvman.2021.112550. Epub 2021 May 6.
A key pursuit in contemporary ecology is to differentiate regime shifts that are truly irreversible from those that are hysteretic. Many ecological regime shifts have been labeled as irreversible without exploring the full range of variability in stabilizing feedbacks that have the potential to drive an ecological regime shift back towards a desirable ecological regime. Removing fire from grasslands can drive a regime shift to juniper woodlands that cannot be reversed using typical fire frequency and intensity thresholds, and has thus been considered irreversible. This study uses a unique, long-term experimental fire landscape co-dominated by grassland and closed-canopy juniper woodland to determine whether extreme fire can shift a juniper woodland regime back to grassland dominance using aboveground herbaceous biomass as an indicator of regime identity. We use a space-for-time substitute to quantify herbaceous biomass following extreme fire in juniper woodland up to 15 years post-fire and compare these with (i) 15 years of adjacent grassland recovery post-fire, (ii) unburned closed-canopy juniper woodland reference sites and (iii) unburned grassland reference sites. Our results show grassland dominance rapidly emerges following fires that operate above typical fire intensity thresholds, indicating that grassland-juniper woodlands regimes are hysteretic rather than irreversible. One year following fire, total herbaceous biomass in burned juniper stands was comparable to grasslands sites, having increased from 5 ± 3 g m to 142 ± 42 g m (+2785 ± 812 percent). Herbaceous dominance in juniper stands continued to persist 15-years after initial treatment, reaching a maximum of 337 ± 42 g m eight years post-fire. In juniper encroached grasslands, fires that operate above typical fire intensity thresholds can provide an effective method to reverse juniper woodland regime shifts. This has major implications for regions where juniper encroachment threatens rancher-based economies and grassland biodiversity and provides an example of how to operationalize resilience theory to disentangle irreversible thresholds from hysteretic system behavior.
当代生态学的一个主要目标是区分真正不可逆转的生态系统状态转变与滞后性的生态系统状态转变。许多生态系统状态转变被标记为不可逆转，而没有探索具有将生态系统状态转变回理想生态系统状态潜力的稳定反馈的全部变化范围。从草原去除火灾可以驱动生态系统状态转变为杜松林地，而使用典型的火灾频率和强度阈值无法将其逆转，因此被认为是不可逆转的。本研究使用一个独特的、长期的实验性火景观，该景观由草原和封闭树冠杜松林地共同主导，以确定极端火灾是否可以使用地上草本生物量作为生态系统状态特征的指标，将杜松林地状态转变回草原主导地位。我们使用时空替代法来量化极端火灾后 15 年内杜松林地中的草本生物量，并将其与以下各项进行比较：(i) 火灾后 15 年的相邻草原恢复，(ii) 未燃烧的封闭树冠杜松林地参考点和 (iii) 未燃烧的草原参考点。我们的研究结果表明，在典型火灾强度阈值以上的火灾后，草原主导地位迅速出现，这表明草原-杜松林地生态系统是滞后性的，而不是不可逆转的。火灾后一年，火烧杜松林中的总草本生物量与草地相似，从 5±3 g m 增加到 142±42 g m (+2785±812%)。在初始处理后 15 年内，杜松林中的草本植物优势继续持续存在，在火灾后 8 年达到最大值 337±42 g m。在杜松入侵的草原中，高于典型火灾强度阈值的火灾可以提供一种有效的方法来逆转杜松林地状态转变。这对杜松入侵威胁以牧场为基础的经济和草原生物多样性的地区具有重大意义，并提供了一个如何实施弹性理论以区分不可逆阈值和滞后系统行为的例子。
