Department of Ecology and Conservation Biology, Texas A&M University, College Station, TX, USA.
USDA Agricultural Research Service, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT, USA.
Sci Total Environ. 2022 Nov 1;845:157214. doi: 10.1016/j.scitotenv.2022.157214. Epub 2022 Jul 8.
Large wildfires have increased in western US rangelands over the last three decades. There is limited information on the impacts of wildfires with different severities on the vegetation in these rangelands. This study assessed the impacts of large wildfires on rangeland fractional cover including annual forbs and grasses (AFG), perennial forbs and grasses (PFG), shrubs (SHR) and trees (TREE) across the western US, and explored relationships between changes in fractional cover and prefire soil moisture conditions. The Expectation Maximization (EM) algorithm was used to group wildfires into nine clusters based on the prefire rangeland fractional cover extracted from the Rangeland Analysis Platform. The Standardized Precipitation Evapotranspiration Index (SPEI) with various lag scales from the Gridded Surface Meteorological (GRIDMET) dataset was used to represent antecedent soil moisture conditions. The results showed generally that fractional cover decreased most for AFG and PFG during the fire year, one year postfire for SHR, and two years postfire for TREE. High severity wildfires led to the greatest decrease in cover for all plant functional types, while low severity wildfires caused the least decrease in the functional type cover in most cases, though some variations existed. Furthermore, the impacts of wildfires on vegetation cover were greater in woody (SHR and TREE) types than in herbaceous (AFG and PFG) types. Significant negative correlation existed between percent changes in AFG and PFG cover and SPEI indicating higher prefire soil moisture conditions likely increased fine fuel loads and led to a larger decrease in AFG and PFG cover following wildfires. Significant positive correlation existed between percent changes in SHR and TREE cover and SPEI indicating drier prefire conditions resulted in larger decreases in SHR and TREE cover following wildfires. These findings help better understand the impacts of wildfires on rangelands and provide insights for rangeland management.
在过去的三十年中，美国西部的大规模野火有所增加。关于不同严重程度的野火对这些牧场植被的影响，信息有限。本研究评估了大型野火对牧场分盖度的影响，包括美国西部的一年生草本植物和草类（AFG）、多年生草本植物和草类（PFG）、灌木（SHR）和树木（TREE），并探讨了分盖度变化与火灾前土壤水分条件之间的关系。期望最大化（EM）算法基于从牧场分析平台提取的火灾前牧场分盖度，将野火分为九个群集。使用来自网格化表面气象（GRIDMET）数据集的不同滞后尺度的标准化降水蒸散指数（SPEI）来表示前期土壤水分条件。结果表明，在火灾当年，AFG 和 PFG 的分盖度通常下降最大，SHR 在火灾后一年下降，TREE 在火灾后两年下降。高严重程度的野火导致所有植物功能类型的盖度下降最大，而低严重程度的野火在大多数情况下导致功能类型盖度下降最小，尽管存在一些变化。此外，野火对植被覆盖的影响在木本（SHR 和 TREE）类型中大于草本（AFG 和 PFG）类型。AFG 和 PFG 盖度的变化百分比与 SPEI 之间存在显著的负相关关系，这表明较高的火灾前土壤水分条件可能增加了细可燃物负荷，并导致野火后 AFG 和 PFG 盖度的较大下降。SHR 和 TREE 盖度的变化百分比与 SPEI 之间存在显著的正相关关系，这表明火灾前较干燥的条件导致野火后 SHR 和 TREE 盖度的较大下降。这些发现有助于更好地了解野火对牧场的影响，并为牧场管理提供见解。
