Bushfires NT, P.O. Box 37346, Winnellie, Northern Territory 0830, Australia.
Ecol Appl. 2010 Sep;20(6):1615-32. doi: 10.1890/09-1553.1.
Much of our understanding of the response of savanna systems to fire disturbance relies on observations derived from manipulative fire plot studies. Equivocal findings from both recent Australian and African savanna fire plot assessments have significant implications for informing conservation management and reliable estimation of biomass stocks and dynamics. Influential northern Australian replicated fire plot studies include the 24-year plot-scale Munmarlary and the five-year catchment-scale Kapalga, mesic savanna (> 1000 mm/yr of rainfall) experiments in present-day Kakadu National Park. At Munmarlary, under low-to-moderate-intensity fire treatments, woody vegetation dominated by mature eucalypts was found to be structurally stable. At Kapalga, substantial declines in woody biomass were observed under more intense fire treatments, and modeling assessments implicate early-season fires as having adverse effects on longer-term tree recruitment. Given these contrasting perspectives, here we take advantage of a landscape-scale fire response monitoring program established on three major northern Australian conservation reserves (Kakadu, Litchfield, and Nitmiluk National Parks). Using statistical modeling we assess the decadal effects of ambient fire regime parameters (fire frequency, severity, seasonality, time since fire) on 32 vegetation structure components and abundance of 21 tree and 16 grass species from 122 monitoring plots. Over the study period the mean annual frequency of burning of plots was 0.53, comprising mostly early-dry-season, low-severity fires. Structural and species responses were variable but often substantial, notably resulting in stem recruitment and declines in juveniles, but only weakly explained by fire regime and habitat variables. Modeling of these observations under three realistic scenarios (increased fire severity under projected worsening climate change; modest and significant reductions in fire frequency to meet conservation criteria) indicates that all scenarios have positive and negative structural implications. Effecting significant regional fire regime change (e.g., reduction in frequency and size of severe fires) is demonstrably feasible, but it incurs risks and potentially some undesirable structural consequences. Given recent Australian and African experience, the generality and application of landscape-scale implications derived from manipulative fire assessments (including variable grazing and browsing regimes) in savanna require more critical assessment.
我们对热带稀树草原系统对火灾干扰的反应的理解在很大程度上依赖于从操纵性火灾斑块研究中得出的观测结果。最近澳大利亚和非洲热带稀树草原火灾斑块评估的模棱两可的结果对通知保护管理和可靠估计生物量存量和动态具有重要意义。有影响力的澳大利亚北部复制火灾斑块研究包括 24 年规模的芒马拉拉里（Munmarlary）和 5 年集水区规模的卡帕尔加（Kapalga）实验，位于当今卡卡杜国家公园（Kakadu National Park），中湿润稀树草原（> 1000 毫米/年降雨量）。在芒马拉拉里（Munmarlary），在低至中等强度的火灾处理下，以成熟桉树为主的木本植被被发现结构稳定。在卡帕尔加（Kapalga），在更强烈的火灾处理下，木本生物量大量减少，模型评估表明，早期火灾对长期树木繁殖有不利影响。鉴于这些相互矛盾的观点，在这里，我们利用在三个主要的澳大利亚北部保护储备区（卡卡杜（Kakadu），利奇菲尔德（Litchfield）和尼特米卢克（Nitmiluk）国家公园）建立的景观尺度火灾响应监测计划。使用统计模型，我们评估了环境火灾发生参数（火灾频率，严重程度，季节性，火灾后时间）对 32 个植被结构成分和 21 种树木和 16 种草种的 122 个监测斑块的丰度的十年影响。在研究期间，斑块的平均年燃烧频率为 0.53，主要由早干季，低严重度的火灾组成。结构和物种的反应是多变的，但往往是实质性的，特别是导致茎的繁殖和幼树的减少，但仅由火灾发生和栖息地变量弱解释。在三个现实情景（预测气候变化恶化下火灾严重程度增加；为满足保护标准适度且显著减少火灾频率）下对这些观察结果进行建模表明，所有情景都有积极和消极的结构影响。显著改变区域火灾发生模式（例如，减少严重火灾的频率和规模）是可行的，但会带来风险，并且可能会产生一些不理想的结构后果。鉴于最近澳大利亚和非洲的经验，需要对从操纵性火灾评估中得出的景观尺度影响（包括可变放牧和觅食制度）的普遍性和应用进行更严格的评估。
