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Spatial and temporal dynamics of disturbance interactions along an ecological gradient

机译:沿生态梯度扰动相互作用的时空动态

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摘要

Interactions among site conditions, disturbance events, and climate determine the patterns of forest species recruitment and mortality across landscapes. Forests of the American Southwest have undergone significant changes over a century of altered disturbance regimes, human land uses, and changing environmental conditions. This study reconstructs the interactions between fire, spruce beetle outbreaks, climate, and anthropogenic factors and their influence on the species composition, spatial extent, and structure of four upper elevation forest types. We found that fire-climate associations changed following fire exclusion and recent high-severity fires occurred during less severe conditions than in several larger, lower severity fires in the historical record. Contemporary fires are burning with higher severity than similarly-sized historical fires, suggesting a shift toward higher-severity fire as a result of changes to forest structure and fuels over much of the upper elevation forest. In high elevation forests, the area occupied by Engelmann spruce and corkbark fir doubled in size over the four decades following fire exclusion. The increase in spruce beetle outbreak size and severity in the 20th century appears to be linked to significant expansion of host extent, accelerated growth of spruce in mixed-conifer forest, and incidence of anomalously warm summer temperatures followed by up to a decade of low precipitation. Trends toward warming, drying conditions are expected to increase the risk of future high-severity outbreaks, especially in locations of recent spruce population expansion. Forest conversion from disturbance-adapted to competition-adapted species following fire exclusion was a function of site productivity. Species assemblages in the lowest and highest productivity sites were the most stable over the century following fire exclusion. Frequent low severity fires maintained the stocking of forests in moderate productivity sites below their biological potential, conferring a degree of resistance to drought, insect outbreaks, and high-severity fire prior to fire exclusion. Current forests located on moderate productivity sites are now the most vulnerable to drought and future disturbance. Aggressive action to restore historical species composition, stocking and fire component of these forests may return resilience to this system in the face of projected changes to fire and climate dynamics.
机译:场地条件,干扰事件和气候之间的相互作用决定了整个景观中森林物种招募和死亡的模式。一个多世纪以来,美国西南地区的森林发生了显着变化,其干扰机制,人类土地利用和环境条件都发生了变化。本研究重建了火灾,云杉甲虫暴发,气候和人为因素之间的相互作用,以及它们对四种高海拔森林类型的物种组成,空间范围和结构的影响。我们发现,火灾-气候关联在火灾被排除之后发生了变化,并且与历史记录中几场较大的,严重程度较低的火灾相比,最近的高强度火灾发生在较不严重的条件下。与类似规模的历史大火相比,当代大火的燃烧程度更高,这表明由于森林结构的变化和大部分高海拔森林的燃料的使用,向着高度大火的方向转移。在高海拔森林中,在火灾排除后的四十年中,Engelmann云杉和科克柏冷杉所占面积增加了一倍。 20世纪云杉甲虫暴发规模和严重程度的增加似乎与寄主范围的显着扩大,混合针叶林中云杉的加速生长以及夏季异常温暖的发生率以及随后长达十年的低降水量有关。变暖,干燥条件的趋势预计会增加未来发生高强度疫情的风险,特别是在最近云杉人口激增的地区。火灾排除后,森林从适应干扰的物种转变为适应竞争的物种是场地生产力的函数。火灾发生后的一个世纪中,生产率最低和生产率最高的物种集合最为稳定。频繁的低度火灾将中等生产力的森林中的林木保持在低于其生物潜能的水平,从而在排除火灾之前赋予了一定程度的抗旱性,昆虫暴发和高强度火灾的抵抗力。目前,生产力中等的森林目前最容易遭受干旱和未来的干扰。面对预计的火势和气候变化,采取积极的行动来恢复这些森林的历史物种组成,种群和火情,可能会使该系统恢复活力。

著录项

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    OConnor Christopher Daniel;

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  • 年度 2013
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