Prefire Vegetation Structure of High Severity Wildfires in Nonherbaceous‐Dominated Rangelands in the Western United States

• Published in: Earth's future 2022-10, Vol.10 (10), p.n/a
• Main Authors: Li, Zheng, Angerer, Jay, Ben Wu, X.
• Format: Article
• Language: English
• Subjects: Algorithms; burn severity; Burns; Clusters; Cultural heritage; Ecosystem structure; Ecosystems; Flammability; Flammable materials; Forbs; Forest & brush fires; fractional cover; Fuels; Grasses; prefire vegetation structure; rangeland; Rangelands; Risk reduction; Shrubs; Structure-function relationships; Trends; Vegetation; western US; wildfire; Wildfires
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2021EF002624

High severity rangeland wildfires have enormous negative impacts on human safety and infrastructure and may have long‐term consequences on ecosystem structure, function, and services, across the vast rangelands in the western United States. We explored prefire vegetation structure of all high severity wildfires, as well as associated areas with low and moderate burn severity, in nonherbaceous‐dominated rangelands in western United States from 1985 to 2018, based on fractional cover of annual forbs and grasses, perennial forbs and grasses, shrubs and trees from the Rangeland Analysis Platform. These wildfires were grouped into nine clusters using Expectation Maximization algorithms and patterns of prefire vegetation structure and the major vegetation types were assessed. High woody cover is a common characteristic of the prefire vegetation structure. Four of the clusters, which accounted for more than 70% of the areas of high severity wildfires, were characterized by high (∼50%) woody cover in prefire vegetation structure. The areas with high severity burns also had significantly higher woody cover than the areas with low or moderate severity burns in eight of the nine clusters. Some of these ecosystems can have abundant fine fuel, structural connectivity such as fuel laddering, and/or highly flammable materials, which can facilitate the ignition of the woody crowns, leading to high severity wildfires. Management strategies (such as prescribed burning) that can decrease woody cover and reduce standing dead vegetation and fuel laddering could be effective in reducing the risk and extent of high severity wildfires on rangelands in the western United States. Plain Language Summary Rangeland wildfires are becoming more frequent and larger across the western United States and high severity rangeland wildfires have significant negative impacts on human safety and infrastructure and may affect ecosystem services that rangelands provide. Evaluation of the prefire vegetation structure can help identify vegetation conditions conducive to high severity burns and inform policies and management to reduce the impact of high severity wildfires. This study assessed the prefire vegetation structure of all high severity wildfires in nonherbaceous‐dominated rangelands in western United States from 1985 to 2018, based on satellite derived percent cover data for annual forbs and grasses, perennial forbs and grasses, shrubs and trees. High woody cover is a common characteristic