Context Montane grasslands and forest-grassland ecotones are unique and dynamic components of many landscapes, but the processes that regulate their dynamics are difficult to observe over ecologically relevant time spans. Objectives We aimed to demonstrate the efficacy of using grassland-forest ecotone trees to reconstruct spatial and temporal properties of the historical fire regime in a complex landscape of montane forests and adjacent grasslands. Methods We sampled and crossdated fire-scarred trees along ecotones and compared variations in historical fire occurrence within and among nine adjoining valle basins in a 10,158 ha landscape. We analyzed fire year extensiveness, climate regulation, and the occurrence of consecutive fire years. Results The resulting tree-ring record covers 1240–2005 AD, with 296 trees recording 125 replicated fire years during the analysis period 1601–1902 AD . Mean fire intervals for all events recorded on two or more trees ranged from 4.7 to 13.6 years in individual valles , and a mean of 2.4 ± 1.7 (SD) years at the landscape scale. Between 1660 and 1902, extensive fires occurring in six or more valles occurred 15 times, on average at ~ 17-year intervals; 29 moderately widespread fires (3–5 valles ) occurred during this period, at 8.7 year intervals on average. Widespread events occurred in years with a significantly lower Palmer Drought Severity Index (PDSI) preceded by years of significantly positive PDSI, indicating conditions favorable for fine fuel production. Spatial reconstruction of fire extent revealed multiple occurrences of consecutive-year fires burning non-overlapping areas, associated with persistent low PDSI anomalies preceded by positive conditions in antecedent years. Conclusions A landscape spatiotemporal approach to reconstructing fire regimes of montane forest-grassland complexes provides a valuable baseline for guiding prescribed and natural fire management at large spatial scales.

中文翻译：

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火谷：美国新墨西哥州 Valles Caldera 国家保护区山地景观中森林-草地交错带的历史火灾状况

背景山地草原和林草交错带是许多景观中独特的动态组成部分，但在生态相关的时间跨度内很难观察到调节其动态的过程。目标我们旨在证明使用草原森林交错带树木重建山地森林和邻近草原复杂景观中历史火灾状况的时空特性的有效性。方法 我们沿交错带对火灾伤痕累累的树木进行采样和交叉测年，并比较了 10,158 公顷景观中九个相邻山谷盆地内部和之间历史火灾发生的变化。我们分析了火灾年的广泛性、气候调节和连续火灾年的发生。结果 由此产生的年轮记录涵盖了公元 1240-2005 年，在公元 1601 年至 1902 年的分析期间，296 棵树记录了 125 个重复的火灾年份。在单个山谷中记录在两棵树或更多树上的所有事件的平均火灾间隔范围为 4.7 到 13.6 年，在景观尺度上平均为 2.4 ± 1.7 (SD) 年。从 1660 年到 1902 年，六个或更多山谷发生的大面积火灾发生了 15 次，平均间隔约 17 年；在此期间发生了 29 次中等范围的火灾（3-5 山谷），平均间隔为 8.7 年。大范围事件发生在帕尔默干旱严重程度指数 (PDSI) 显着较低的年份，然后是 PDSI 显着正值的年份，表明条件有利于精细燃料生产。火灾范围的空间重建显示连续一年发生多次火灾，燃烧非重叠区域，与前几年的积极条件之前持续的低 PDSI 异常相关。结论 重建山地森林-草地复合体火灾状况的景观时空方法为指导大空间尺度的规定和自然火灾管理提供了有价值的基线。