NOAA/WDS Paleoclimatology - Johnston fire data from Thompson Creek - IMPD USTHO001

Describing the climate influences on historical wildland fire will aid managers in planning for future change. This study uses existing historical climate reconstructions and a new fire history from the southern Blue Mountains in eastern Oregon, USA, to: 1) characterize historical fire-climate relationships, and 2) determine if climatic influences on fire differed among dry sites dominated by ponderosa pine (Pinus ponderosa Dougl. ex Laws) and more productive sites with significant older fire intolerant grand fir (Abies grandis [Dougl.] Lindl.) structure. Similar to results from other fire history studies across the American West, this research documents an increased incidence of burning in the southern Blue Mountains prior to 1900 associated with more arid conditions as measured with Palmer Drought Severity Index (PDSI). Positive values of the El Niño-Southern Oscillation (ENSO) were associated with fire years when multiple sites burned within the 688 000 ha study area. Although ponderosa pine and grand fir study sites were significantly different with respect to site productivity as well as historical and contemporary species composition, there were only marginal differences in historical mean fire return intervals between these forest types. There was also no significant difference in reconstructed mean temperature, precipitation, drought index, or ENSO during fire years between forest types prior to 1900 CE. However, the years prior to fire in ponderosa pine sites were moister than average, suggesting that antecedent climate was more important in the production of herbaceous fuel in ponderosa pine sites.

解析气候对历史野火（wildland fire）的影响机制，可辅助管理者制定未来气候变化应对规划。本研究依托已有的历史气候重建数据，以及取自美国俄勒冈州东部布鲁山脉南部的全新野火历史数据集，旨在达成两个研究目标：1）刻画历史野火与气候的关联特征；2）厘清气候对野火的影响在两类生境中是否存在差异：一类是以黄松（Pinus ponderosa Dougl. ex Laws）为优势种的干旱生境，另一类是生产力更高、以老龄且耐火性差的大冷杉（Abies grandis [Dougl.] Lindl.）为群落结构的生境。
与美国西部其他野火历史研究的结果一致，本研究证实，1900年之前的布鲁山脉南部地区，野火发生频次随帕尔默干旱指数（Palmer Drought Severity Index, PDSI）所表征的干旱程度加剧而升高。在本研究覆盖的68.8万公顷区域内，厄尔尼诺-南方涛动（El Niño-Southern Oscillation, ENSO）处于正相位的年份，对应多生境同时发生野火的年份。
尽管黄松与大冷杉研究生境在生境生产力、历史与当代物种组成方面均存在显著差异，但两类林型的历史平均火轮回期仅存在细微差别。
在公元1900年之前的野火年份中，两类林型的重建平均气温、降水量、干旱指数以及ENSO状态均无显著差异。
但黄松生境的野火发生前期气候条件较常年更为湿润，这表明前期气候对黄松生境中草本燃料的生成更为关键。