NOAA/WDS Paleoclimatology - Heyerdahl fire data from Iron Mountain South, Palouse northwestern United States - IMPD USIMS001

Prairie-forest ecotones are ecologically important for biodiversity and ecological processes. While these ecotones cover small areas, their sharp gradients in land cover promote rich ecological interaction and high conservation value. Our objective was to understand how historical and current fire occurrences and human development influenced the Palouse Prairie-forest ecotone. We used General Land Office survey field notes about the occurrence of bearing trees to locate historical (1870s to 1880s) prairie, pine savanna, and forest at the eastern edge of the bioregion. We combined LANDFIRE Existing Vegetation classes to contrast historical land cover with current land cover. We reconstructed historical fire occurrence (1650 to 1900) from fire-scarred trees. We used fire and lightning records from 1992 to 2015 to interpret the role of people and lightning. Historically, the ecotone was a matrix of prairie with some pine savanna and forest (72%, 16%, and 12% of GLO points, respectively). The prairie and pine savanna have been largely converted to agriculture, perennial vegetation under the Conservation Reserve Program, or residential development while the forest has not been converted. Fires were historically frequent, occurring on average every 5 to 8 years at most sites. Lightning was not frequent but could likely have been sufficient to ignite fires that could spread readily given the rolling terrain and long fire season. Fire was far more frequent historically than currently. Lightning and people may ignite fires that spread readily in the future as conservation, restoration, and other land-use changes result in more continuous vegetation and hence fuel for fires. Understanding the past and potential future of fire in the Palouse Prairie bioregion may help us live with fire while conserving ecological values here and in similar prairie-forest ecotones.

草原-森林交错带（prairie-forest ecotones）在生物多样性维持与生态过程调控方面具有关键生态意义。尽管此类交错带的覆盖面积相对狭小，但其土地覆被的显著梯度能够催生丰富的生态相互作用，并具备极高的保护价值。本研究旨在探明历史与当前的火灾发生情况以及人类开发活动如何影响帕卢斯草原-森林交错带。我们借助美国土地管理总局（General Land Office）的野外调查记录中关于立木分布的记载，定位该生物区域东部边缘历史时期（19世纪70至80年代）的草原、松树稀树草原与森林分布范围。我们结合火灾与现有植被数据集（LANDFIRE）的现有植被分类体系，对比历史与当前的土地覆被状况。我们通过火疤木样本重建了1650年至1900年的历史火灾发生序列。我们利用1992年至2015年的火灾与雷击记录，解析人类活动与雷击在火灾发生中的作用。历史上，该交错带以草原为景观基质，辅以少量松树稀树草原与森林（分别占美国土地管理总局调查样点的72%、16%与12%）。当前，草原与松树稀树草原已大规模转为农业用地、保护储备计划（Conservation Reserve Program）管护下的多年生植被覆盖区，或是住宅开发用地，而森林则未发生此类土地利用转换。历史上该区域火灾频发，多数站点的火灾平均复发间隔为5至8年。雷击事件虽不频繁，但考虑到区域起伏的地形与漫长的火险季，雷击足以引燃火源并支持火灾快速扩散。历史火灾发生频率远高于当前。随着保护、修复与其他土地利用变化带来植被连通性提升，进而增加火灾可燃物载荷，未来雷击与人类活动仍可能引燃可快速扩散的火灾。探明帕卢斯草原生物区域火灾的历史与未来潜在趋势，有助于我们在保护该区域及类似草原-森林交错带生态价值的同时，实现与火的和谐共存。