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Areas of low natural regeneration potential post-fire in shrublands of southern California (selected years between 2008 and 2020)

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Jan 27, 2023 version files 30.94 MB

Abstract

Identifying locations where shrubland vegetation will not recover naturally post-fire is a challenge given the vast areas that are regularly burned in southern California. When shrublands are within the historic fire return interval, e.g., 55 years for low-elevation shrubland (Keeley and Safford 2016, Van de Water and Safford 2011), biomass accumulates and shrub cover recovers after 10–14 years (Black et al. 1987, Bohlman et al. 2018). However, in many parts of southern California, the fire return interval has decreased, often in conjunction with an increase in non-native plant species, drought, and nitrogen deposition (Pratt et al. 2014, Allen et al. 2018, Syphard et al. 2019, Safford et al. 2022). Under these conditions, post-fire biomass recovery can be impeded and, in some cases, may result in type conversion from native shrubland to non-native grassland (Syphard et al. 2019). We developed a repeatable method to identify areas of low regeneration potential in southern California using fire history data (FRAP 2021), using two rules guided by the published literature (Zedler et al. 1983, Haidinger and Keeley 1993, Keeley and Brennan 2012, Syphard et al. 2019, Underwood et al. 2021, Underwood and Safford 2021). First, we set the threshold of the ‘number of fires in the last 40 years’ to three or more fires, and second, we set the ‘time since last fire’ to a threshold of <10 years.  We identified pixels that met these criteria as having low natural regeneration potential post-fire and, as a consequence, these areas could represent candidate areas for post-fire restoration in shrublands.  

The rasters of low natural regeneration potential are a key input into the online web mapping tool SoCal EcoServe, developed for US Department of Agriculture Forest Service resource managers to calculate the long-term impacts of wildfire on carbon lost. The tool is available at https://manzanita.forestry.oregonstate.edu/ecoservices/ and described in Underwood et al. (2022). The resulting rasters of low natural regeneration potential provide a basis for integrating additional factors that might affect the post-fire recovery of shrubands, including climatic water deficit or nitrogen deposition.