Ilangakoon, N. T. | Search bioRxiv

bioRxiv2024

Good fire: quantifying the beneficial ecosystem work of western U.S. wildfires (2010-2020)

Wildfires are integral for western US forests that have evolved with fire. Here we define "good wildfire" as areas that burn in an ecologically beneficial way, with a severity and return interval analogous to their historical fire regimes prior to European settlement. When severities match what an ecosystem historically experienced they can regulate forest structure while promoting regeneration, even in a warming climate1. We quantified the amount of forested area (i.e., deciduous, conifer, or mixed forest types) burned with a severity and frequency matching its regime, and compared that to the area of prescribed burns in forests (2010-2020). Of forests that burned in the western US, 49% of the area burned as low-moderate severity good wildfire. High severity good wildfire (in systems that historically experienced this type of fire) represented an additional 9% of forest area burned, bringing the total area of good wildfire to 58% of forested area burned. The low-moderate severity good wildfires burned 3.1 million forest ha (N = 18,061 events), more than double the 1.4 million ha of prescribed burning (N = 24,817 events on federal land) over the same period. Knowing that fires are likely going to increase in frequency and area with warming2, our key challenge will be promoting good wildfire while still protecting lives and property.

ecology↗

bioRxiv2023

Postfire recovery of western US conifer forests (1984-2017) using space-borne lidar data

Coniferous forests account for 78% of the western US forests and store a substantial amount of carbon. Wildfires significantly alter vegetation structure, and hence the forest carbon stock. This study evaluates post-fire vegetation recovery trajectories and rates across the western US using recently launched Global Ecosystem Dynamic Investigations (GEDI) mission lidar data. Three ecoregions studied here, the Pacific Northwest, Southern Rockies, and Northern Rockies, show fire severity and ecoregion specific recovery trajectories for canopy height (CH), plant area index (PAI), and the foliage height diversity (FHD). The recovery trajectories are characterized by an initial decline in vegetation structure (CH, PAI, and FHD) during the first 9-25 years postfire followed by a gain of the structure. Regions of low burn severity can fully recover to the unburned background state within the first three decades while the high burn severity regions may recover in the first century, but only in the absence of fires within this period. The PNW exhibits the slowest recovery rate. According to our results, all three ecoregions feature a loss of growing stock volume (GSV) (-1% - - 48%). Time since fire, fire severity, and altitude were identified as the most significant drivers of postfire vegetation recovery, likely because they integrate the distance to seed source, vegetation composition, and the local climate. Our study suggests that, if fire return intervals become shorter than 50 years, these three ecoregions will have significantly reduced their woody vegetation, hence the carbon stocks. In addition, all the ecoregions studied here exhibit extensive impacts from other disturbances such as beetle invasion. It is therefore important to consider the effects of compound disturbances on vegetation recovery trajectories to infer the future carbon potential in these ecosystems.

ecology↗