气候变化领域集成服务门户

Most studies of fire-regime changes in western North American forests rely on a reference period that predates Euro-American settlement. Less is known about fire-regime changes relative to the early onset of major change agents, i. e. fire suppression and timber harvesting. We digitised ledgers that contained over 18 000 individual fire records from 1911 through 1924 (early suppression period). We performed analyses comparing a subset of these fire records, largely in mixed-conifer forests, to similar records from 2002 through 2015 (contemporary period). Mapped ignition frequencies indicated similar geographic patterns for lightning-caused fires between periods, but notable shifts in certain areas for human-caused fires. There was no statistical difference in annual number of human-caused fires between the early suppression and contemporary time periods. However, there was a major shift in the distribution of burned area across fire size classes. Fires. 12 145 ha accounted for 0-6% of total burned area in the early suppression period, and 5373% in the contemporary period. Also, both the total number and percentage of fires.2024 ha occurred significantly earlier in the year in the contemporary period. These shifts are likely driven by large-scale changes in fuel loads and continuity, and possibly exacerbated by climatic warming.