Multiple wildfires with minimal consequences: Low-severity wildfire effects on West Texas pinon-juniper woodlands

摘要

Pinon-juniper (PJ) woodlands comprise an important and extensive dry-site forest cover-type that has historically experienced high spatiotemporal variation in fire frequency and extent. We re-measured a network of permanent monitoring plots in a fire-suppressed PJ site the Davis Mountains of West Texas after prescribed fire (Rx) treatments and three subsequent wildfires to 1) quantify wildfire effects on PJ woodland stand structure and fuel loadings, and 2) evaluate the effects of Rx fires followed by wildfire. Although fire weather was extreme during the wildfire years, all three wildfires burned as low-severity fire events. Simultaneous autoregressive modeling revealed that total tree density and basal area declined significantly (P < 0.05) over the time-series, while surface fuel loadings increased significantly (P < 0.05), likely in response to fuel inputs from fire-induced tree mortality. However, tree mortality largely occurred in smaller tree size-classes (i.e. < 25 cm diameter at breast height). Neither fire severity, nor changes in stand structure varied significantly over the time-series among recent fire history types (i.e. no fire, Rx fire only, Rx fire + wildfire, or wildfire only) indicating that Rx fires had little effect on subsequent wildfire effects on forest structure or species composition. The low-severity nature of these recent wildfires under severe fire weather and in the wake of almost a century of fire suppression suggests that just because fires have been absent from a site for decades contemporary wildfires will not always result in fire regime characteristics that differ from historical fires in PJ-dominated areas.