Contemporary fires are less frequent but more severe in dry conifer forests of the southwestern United States

Wildfires in the southwestern United States are increasingly frequent and severe, but whether these trends exceed historical norms remains contested. Here we combine dendroecological records, satellite-derived burn severity, and field measured tree mortality to compare historical (1700-1880) and contemporary (1985-2020) fire regimes at tree-ring fire-scar sites in Arizona and New Mexico. We found that contemporary fire frequency, including recent, record fire years, is still <20% of historical levels. Since 1985, the fire return interval averages 58.8 years, compared to 11.4 years before 1880. Fire severity, however, has increased. At sites where trees historically survived many fires over centuries, 42% of recent fires resulted in high tree mortality. Suppressed wildfires tended to burn more severely than prescribed burns and fire use wildfires. These findings suggest that expanded use of low-severity prescribed and managed fire would help restore forest resilience and historical fi..., To quantify tree mortality from contemporary fires, we sampled fire effects at 74 of the 406 fire history sites used in the study. We located the field sites across a gradient of contemporary burn severity and fire management strategies. For example, proportion of fires in the full suppression category ranged from 100% in the Pinaleño and Santa Catalina Mountains to 14% on the Kaibab Plateau. Similarly, the proportion of sites which burned with high probability of tree mortality (CBI > 1.61) ranged from 73% in the Santa Catalina Mountains to 0% on the Kaibab. Data collection focused on six key geographic areas where networks of fire history sites had been established prior to wildfires occurring over the past ten years (2011-2020): the Jemez, Rincon, Santa Catalina, Pinaleño, and Chiricahua Mountains, and the Kaibab Plateau. In the Jemez Mountains, sites are in Bandelier National Monument (including the Bandelier Wilderness), the Valles Caldera National Preserve, and the Santa Fe Nat..., , # Data from: Contemporary fires are less frequent but more severe in dry conifer forests of the southwestern United States

[https://doi.org/10.5061/dryad.98sf7m0sn](https://doi.org/10.5061/dryad.98sf7m0sn)

## Description of the data and file structure

Field data were collected in Survey123, then adapted into .csv files for import and analysis in R. Sampling was performed in June - August 2021, and involved visits to 74 previously sampled tree-ring fire-scar sites. At each site center or found sampled tree, a 10-meter radius plot was installed, in which we recorded tree diameter at breast height (dbh), species, and status (live or dead). We measured diameter and assigned species for downed logs and recorded an overall count of trees both live and dead, standing and down. We also completed a modified (simplified) CBI protocol to assess severity, and counted seedlings by species across the plot. Sampling was focused on 6 geographic areas where networks of fire history sites had been est...

美国西南部野火愈发频发且烈度攀升，但此类趋势是否超越历史常态仍存争议。本研究结合树轮生态学记录（dendroecological records）、卫星反演火烧烈度（satellite-derived burn severity）数据与野外实测树木死亡率（field measured tree mortality）数据，对比美国亚利桑那州与新墨西哥州树轮火烧疤痕样地（tree-ring fire-scar sites）的历史（1700–1880年）与当代（1985–2020年）火制度（fire regime）。研究发现，当代野火发生频率（包括近年创纪录的火烧年份）仍不足历史水平的20%。1985年以来，火烧间隔期（fire return interval）平均为58.8年，而1880年之前仅为11.4年。但火烧烈度已显著提升。在历史上数百年间树木可多次经受火烧的样地中，近期有42%的火烧导致了高树木死亡率。受人工压制的野火往往比计划火烧（prescribed burn）与火利用型野火（fire use wildfires）的火烧烈度更高。上述研究结果表明，扩大低烈度计划火烧与管理用火的应用范围，将有助于恢复森林韧性与历史火制度。
为量化当代火烧导致的树木死亡率，本研究在研究涉及的406个火历史样地中选取74个开展火烧效应采样。野外样地覆盖了当代火烧烈度与火管理策略的梯度范围。例如，全压制火烧类型的占比在皮纳莱诺山（Pinaleño）与圣卡塔利娜山（Santa Catalina Mountains）为100%，在凯巴布高原（Kaibab Plateau）则为14%。同理，树木死亡率高概率发生（复合火烧烈度指数（Composite Burn Index, CBI）>1.61）的样地占比在圣卡塔利娜山为73%，在凯巴布高原则为0%。数据采集聚焦于6个关键地理区域，这些区域的火历史样地网络在2011–2020年过去十年间的野火发生前已建成：赫梅斯山（Jemez Mountains）、林孔山（Rincon Mountains）、圣卡塔利娜山、皮纳莱诺山、奇里卡瓦山（Chiricahua Mountains）以及凯巴布高原。在赫梅斯山区域，样地分布于班德利尔国家纪念地（含班德利尔荒野）、巴莱斯卡尔德拉国家保护区以及圣达菲国家...（原文截断）
# 数据来源：美国西南部干旱针叶林野火发生频率更低但烈度更高
"[https://doi.org/10.5061/dryad.98sf7m0sn](https://doi.org/10.5061/dryad.98sf7m0sn)"
数据与文件结构说明
野外数据通过Survey123采集，随后整理为.csv格式文件，用于R语言环境下的导入与分析。采样工作于2021年6–8月开展，共走访了74个此前已采样的树轮火烧疤痕样地。在每个样地中心或已采样的树木位置，设置半径10米的样方，记录树木的胸径（diameter at breast height, dbh）、物种以及存活状态（活立木或枯立木）。对倒木测量直径并判定物种，同时统计样方内所有活立木、枯立木以及倒木的总数量。同时采用改良（简化）版复合火烧烈度指数（Composite Burn Index, CBI）方案评估火烧烈度，并按物种统计样方内的幼苗数量。采样工作聚焦于6个已建成火历史样地网络的地理区域，（原文截断）