Does short-interval fire inhibit postfire recovery of chaparral across southern California?

Abstract

Regrowth after fire is critical to the persistence of chaparral shrub communities in southern California, which has been subject to frequent fire events in recent decades. Fires that recur at short intervals of 10 years or less have been considered an inhibitor of recovery and the major cause of 'community type-conversion' in chaparral, primarily based on studies of small extents and limited time periods. However, recent sub-regional investigations based on remote sensing suggest that short-interval fire (SIF) does not have ubiquitous impact on postfire chaparral recovery. A region-wide analysis including a greater spatial extent and time period is needed to better understand SIF impact on chaparral.This study evaluates patterns of postfire recovery across southern California, based on temporal trajectories of Normalized Difference Vegetation Index (NDVI) derived from June-solstice Landsat image series covering the period 1984-2018. High spatial resolution aerial images were used to calibrate Landsat NDVI trajectory-based estimates of change in fractional shrub cover (dFSC) for 294 stands. The objectives of this study were (1) to assess effects of time between fires and number of burns on recovery, using stand-aggregate samples (n = 294) and paired single-and multiple-burn sample plots (n = 528), and (2) to explain recovery variations among predominant single-burn locations based on shrub community type, climate, soils, and terrain. Stand-aggregate samples showed a significant but weak effect of SIF on recovery (p < 0.001; R 2 = 0.003). Results from paired sample plots showed no significant effect of SIF on dFSC among twice-burned sites, although recovery was diminished due to SIF at sites that burned three times within 25 years. Multiple linear regression showed that annual precipitation and temperature, chaparral community *

Short-interval fires and vegetation change in southern California

“…Ninety-eight out of 198 chaparral plots and 91 out of 198 sage scrub plots showed an increase or decrease in woody cover following fire. This heterogeneity in canopy regrowth is consistent with previous findings (Syphard et al, 2018a, Park et al, 2018, Storey et al, 2021).…”

“…The five-year average rainfall following the latter fire was also found to not be a significant driver of vegetation type change, which is in line with other studies (Storey et al, 2020, Meng et al, 2014), although see Storey et al (2021). Storey et al (2020) found climactic water deficit to be a stronger predictor of chaparral recovery compared to total precipitation and water conditions preceding fire were generally more predictive of recovery than conditions following fire.…”

“…While almost all polygons included in this study experienced additional fires before and after the years of analysis, multiple short-interval fires were not included in this analysis nor was the entire fire history (1878-2009) of a location. Storey et al (2021) included additional fire history by comparing locations in southern California that burned once, twice, or three times within 25 years. They found no difference in shrub recovery between stands that burned once or twice but did find a decrease in shrub recovery when locations burned three times within 25 years.…”

“…A single short-interval fire, however, does not always lead to chaparral conversion. Previous work with remotely sensed data suggest that water availability (Park et al, 2018, Syphard et al, 2019a), elevation (Meng et al, 2014), and mean annual temperature (Storey et al, 2021) explain more variation among chaparral stand recovery (although also see Syphard et al (2019b)). These studies utilized imagery with 30-m spatial resolution and/or datasets with a 30-m scale.…”

A New Application of the Disturbance Index for Fire Severity in Coastal Dunes

“…Fires are an ordinary, recurring, and integral part of ecosystems around the globe and across many parts of Australia [1], and provide many benefits to ecosystems [2][3][4]. Shifts in fire regimes (frequency and severity) are associated with climate change, extreme weather events, and drought [5][6][7][8], and may alter vegetation succession [9,10] or landscape stability [11]. Fire severity is a measurement of the effects of fire on landscapes and can be irregular within a burnt area due to variation in fuel loads, fuel type, weather conditions, topography, or maturity of the plant community [12,13].…”