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1. Modeling the short-term fire effects on vegetation dynamics and surface energy in southern Africa using the improved SSiB4/TRIFFID-Fire model

   https://doi.org/10.5194/gmd-14-7639-2021  

   Huang, Huilin; Xue, Yongkang; Liu, Ye; Li, Fang; Okin, Gregory S. (January 2021, Geoscientific Model Development)

   Abstract. Fire causes abrupt changes in vegetation properties and modifies fluxexchanges between land and atmosphere at subseasonal to seasonal scales. Yetthese short-term fire effects on vegetation dynamics and surface energybalance have not been comprehensively investigated in the fire-coupledvegetation model. This study applies the SSiB4/TRIFFID-Fire (the SimplifiedSimple Biosphere Model coupled with the Top-down Representation of InteractiveFoliage and Flora Including Dynamics with fire) model to studythe short-term fire impact in southern Africa. Specifically, we aim toquantify how large impacts fire exerts on surface energy throughdisturbances on vegetation dynamics, how fire effects evolve during the fireseason and the subsequent rainy season, and how surface-darkening effectsplay a role besides the vegetation change effects. We find fire causes an annual average reduction in grass cover by 4 %–8 %for widespread areas between 5–20∘ S and a tree cover reductionby 1 % at the southern periphery of tropical rainforests. The regionalfire effects accumulate during June–October and peak in November, thebeginning of the rainy season. After the fire season ends, the grass coverquickly returns to unburned conditions, while the tree fraction hardlyrecovers in one rainy season. The vegetation removal by fire has reduced theleaf area index (LAI) and gross primary productivity (GPP) by 3 %–5 % and5 %–7 % annually. The exposure of bare soil enhances surface albedo andtherefore decreases the absorption of shortwave radiation. Annual meansensible heat has dropped by 1.4 W m−2, while the latent heat reductionis small (0.1 W m−2) due to the compensating effects between canopytranspiration and soil evaporation. Surface temperature is increased by asmuch as 0.33 K due to the decrease of sensible heat fluxes, and the warmingwould be enhanced when the surface-darkening effect is incorporated. Ourresults suggest that fire effects in grass-dominant areas diminish within1 year due to the high resilience of grasses after fire. Yet fire effectsin the periphery of tropical forests are irreversible within one growingseason and can cause large-scale deforestation if accumulated for hundredsof years. 

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2. Modeling long-term fire impact on ecosystem characteristics and surface energy using a process-based vegetation–fire model SSiB4/TRIFFID-Fire v1.0

   https://doi.org/10.5194/gmd-13-6029-2020  

   Huang, Huilin; Xue, Yongkang; Li, Fang; Liu, Ye (January 2020, Geoscientific Model Development)

   null (Ed.)

   Abstract. Fire is one of the primary disturbances to the distribution and ecologicalproperties of the world's major biomes and can influence the surface fluxesand climate through vegetation–climate interactions. This study incorporatesa fire model of intermediate complexity to a biophysical model with dynamicvegetation, SSiB4/TRIFFID (The Simplified Simple Biosphere Model coupledwith the Top-down Representation of Interactive Foliage and Flora IncludingDynamics Model). This new model, SSiB4/TRIFFID-Fire, updating fire impact onthe terrestrial carbon cycle every 10 d, is then used to simulate theburned area during 1948–2014. The simulated global burned area in 2000–2014is 471.9 Mha yr−1, close to the estimate of 478.1 Mha yr−1 inGlobal Fire Emission Database v4s (GFED4s), with a spatial correlation of0.8. The SSiB4/TRIFFID-Fire reproduces temporal variations of the burnedarea at monthly to interannual scales. Specifically, it captures theobserved decline trend in northern African savanna fire and accuratelysimulates the fire seasonality in most major fire regions. The simulatedfire carbon emission is 2.19 Pg yr−1, slightly higher than the GFED4s(2.07 Pg yr−1). The SSiB4/TRIFFID-Fire is applied to assess the long-term fire impact onecosystem characteristics and surface energy budget by comparing model runswith and without fire (FIRE-ON minus FIRE-OFF). The FIRE-ON simulationreduces tree cover over 4.5 % of the global land surface, accompanied bya decrease in leaf area index and vegetation height by 0.10 m2 m−2and 1.24 m, respectively. The surface albedo and sensible heat are reducedthroughout the year, while latent heat flux decreases in the fire season butincreases in the rainy season. Fire results in an increase in surfacetemperature over most fire regions. 

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3. Simulating the Potential for Invasive Grass Expansion to Alter Wildfire Behavior in Southern California With WRF‐Fire

   https://doi.org/10.1029/2024JG008574  

   Wang, Bowen; Madakumbura, Gavin_D; Juliano, Timothy_W; Williams, A_Park (August 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Invasion by non‐native annual grasses poses a serious threat to native vegetation in California, facilitated through interaction with wildfires. Our work is the first attempt to use the coupled fire‐atmosphere model, WRF‐Fire, to investigate how shifts from native, shrub‐dominated vegetation to invasive grasses could have affected a known wildfire event in southern California. We simulate the Mountain Fire, which burned >11,000 ha in July 2013, under idealized fuel conditions representing varying extents of grass invasion. Expanding grass to double its observed coverage causes fire to spread faster due to the lower fuel load in grasses and increased wind speed. Beyond this, further grass expansion reduces the simulated spread rate because lower heat release partially offsets the positive effects. Our simulations suggest that grass expansion may generally promote larger faster‐spreading wildfires in southern California, motivating continued efforts to contain and reduce the spread of invasive annual grasses in this region. 

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4. Fire frequency, state change and hysteresis in tallgrass prairie

   https://doi.org/10.1111/ele.13676  

   Collins, Scott_L; Nippert, Jesse_B; Blair, John_M; Briggs, John_M; Blackmore, Pamela; Ratajczak, Zak; Comita, ed., Liza (January 2021, Ecology Letters)

   Abstract Hysteresis is a fundamental characteristic of alternative stable state theory, yet evidence of hysteresis is rare. In mesic grasslands, fire frequency regulates transition from grass‐ to shrub‐dominated system states. It is uncertain, however, if increasing fire frequency can reverse shrub expansion, or if grass‐shrub dynamics exhibit hysteresis. We implemented annual burning in two infrequently burned grasslands and ceased burning in two grasslands burned annually. With annual fires, grassland composition converged on that of long‐term annually burned vegetation due to rapid recovery of grass cover, although shrubs persisted. When annual burning ceased, shrub cover increased, but community composition did not converge with a long‐term infrequently burned reference site because of stochastic and lagged dispersal by shrubs, reflecting hysteresis. Our results demonstrated that annual burning can slow, but not reverse, shrub encroachment. In addition, reversing fire frequencies resulted in hysteresis because vegetation trajectories from grassland to shrubland differed from those of shrubland to grassland. 

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5. Siberian taiga and tundra fire regimes from 2001–2020

   https://doi.org/10.1088/1748-9326/ac3f07  

   Talucci, Anna C.; Loranty, Michael M.; Alexander, Heather D. (January 2022, Environmental Research Letters)

   Abstract Circum-boreal and -tundra systems are crucial carbon pools that are experiencing amplified warming and are at risk of increasing wildfire activity. Changes in wildfire activity have broad implications for vegetation dynamics, underlying permafrost soils, and ultimately, carbon cycling. However, understanding wildfire effects on biophysical processes across eastern Siberian taiga and tundra remains challenging because of the lack of an easily accessible annual fire perimeter database and underestimation of area burned by MODIS satellite imagery. To better understand wildfire dynamics over the last 20 years in this region, we mapped area burned, generated a fire perimeter database, and characterized fire regimes across eight ecozones spanning 7.8 million km²of eastern Siberian taiga and tundra from ∼61–72.5° N and 100° E–176° W using long-term satellite data from Landsat, processed via Google Earth Engine. We generated composite images for the annual growing season (May–September), which allowed mitigation of missing data from snow-cover, cloud-cover, and the Landsat 7 scan line error. We used annual composites to calculate the difference Normalized Burn Ratio (dNBR) for each year. The annual dNBR images were converted to binary burned or unburned imagery that was used to vectorize fire perimeters. We mapped 22 091 fires burning 152 million hectares (Mha) over 20 years. Although 2003 was the largest fire year on record, 2020 was an exceptional fire year for four of the northeastern ecozones resulting in substantial increases in fire activity above the Arctic Circle. Increases in fire extent, severity, and frequency with continued climate warming will impact vegetation and permafrost dynamics with increased likelihood of irreversible permafrost thaw that leads to increased carbon release and/or conversion of forest to shrublands. 

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