NOAA/WDS Paleoclimatology - Farris fire data from Mica Mountain - IMPD US03_19C

Fire scars are used widely to reconstruct historical fire regime parameters in forests around the world. Because fire scars provide incomplete records of past fire occurrence at discrete points in space, inferences must be made to reconstruct fire frequency and extent across landscapes using spatial networks of fire-scar samples. Assessing the relative accuracy of fire-scar fire history reconstructions has been hampered due to a lack of empirical comparisons with independent fire history data sources. We carried out such a comparison in a 2780-ha ponderosa pine forest on Mica Mountain in southern Arizona (USA) for the time period 1937–2000. Using documentary records of fire perimeter maps and ignition locations, we compared reconstructions of key spatial and temporal fire regime parameters developed from documentary fire maps and independently collected fire-scar data (n = 60 plots). We found that fire-scar data provided spatially representative and complete inventories of all major fire years (>100 ha) in the study area but failed to detect most small fires. There was a strong linear relationship between the percentage of samples recording fire scars in a given year (i.e., fire-scar synchrony) and total area burned for that year (y = 0.0003x + 0.0087, r2 = 0.96). There was also strong spatial coherence between cumulative fire frequency maps interpolated from fire-scar data and ground-mapped fire perimeters. Widely reported fire frequency summary statistics varied little between fire history data sets: fire-scar natural fire rotations (NFR) differed by <3 yr from documentary records (29.6 yr); mean fire return intervals (MFI) for large-fire years (i.e., ≥25% of study area burned) were identical between data sets (25.5 yr); fire-scar MFIs for all fire years differed by 1.2 yr from documentary records. The known seasonal timing of past fires based on documentary records was furthermore reconstructed accurately by observing intra-annual ring position of fire scars and using knowledge of tree-ring growth phenology in the Southwest. Our results demonstrate clearly that representative landscape-scale fire histories can be reconstructed accurately from spatially distributed fire-scar samples.

火疤（fire scars）被广泛应用于重建全球森林的历史火灾制度（fire regime）参数。由于火疤仅能在空间离散点上提供过往火灾发生的不完全记录，因此需借助火疤样本的空间网络，推断并重建整个景观范围内的火灾发生频率与过火范围。由于缺乏与独立火灾历史数据源的实证对比，评估火疤重建火灾历史的相对准确性一直存在阻碍。我们于美国亚利桑那州南部云母山（Mica Mountain）一片2780公顷的黄松林中，针对1937—2000年时段开展了此类对比研究。我们借助火灾边界图（fire perimeter maps）与起火点位置的文献记录，对比了基于文献火灾地图与独立采集的火疤数据（n=60个样地）所重建的关键时空火灾制度参数。研究发现，火疤数据可在空间上完整且具代表性地记录研究区内所有大型火灾年份（过火面积>100公顷）的情况，但无法探测多数小型火灾。特定年份中记录火疤的样本占比（即火疤同步性）与该年总过火面积之间存在极强的线性相关关系（y = 0.0003x + 0.0087，r²=0.96）。由火疤数据插值得到的累积火灾频率图，与野外测绘的火灾边界图之间也存在高度的空间一致性。不同火灾历史数据集间广泛报道的火灾频率汇总统计值差异极小：火疤法得到的自然火灾轮回期（natural fire rotations, NFR）与文献记录（29.6年）相差不足3年；大型火灾年份（即过火面积≥研究区25%）的平均火灾返回间隔期（mean fire return intervals, MFI）在两个数据集间完全一致（25.5年）；所有火灾年份的火疤法平均火灾返回间隔期与文献记录仅相差1.2年。此外，通过观测火疤的年轮年内位置，并结合美国西南部的树木年轮生长物候学知识，可准确重建基于文献记录已知的过往火灾季节发生时间。我们的研究结果明确证实，借助空间分布的火疤样本，可准确重建具有代表性的景观尺度火灾历史。