Strong Legacy Effects of Prior Burn Severity on Forest Resilience to a High-Severity Fire
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Strong Legacy Effects of Prior Burn Severity on Forest Resilience to a High-Severity Fire Lucas B. Harris,1* Stacy A. Drury,2 and Alan H. Taylor3 1 Department of Geography, The Pennsylvania State University, 302 Walker Building, University Park, Pennsylvania 16802, USA; USDA Forest Service, Pacific Southwest Research Station, Davis, California, USA; 3Department of Geography, Earth and Environmental Systems Institute, The Pennsylvania State University, 302 Walker Building, University Park, Pennsylvania 16802, USA
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ABSTRACT Legacy effects from one disturbance may influence successional pathways by amplifying or buffering forest regeneration after the next disturbance. We assessed vegetation and tree regeneration in nonserotinous Sierra lodgepole pine (Pinus contorta var. murrayana) stands after a 1984 wildfire which burned with variable severity and again after a high-severity subsequent fire in 2012. The legacy effects of the 1984 fire were amplified; seedlings and saplings were abundant in areas initially burned at low severity (1267 stems ha-1) despite high reburn severity, but regeneration was low in areas twice burned at high severity (31 stems ha1 ). Our results suggest that the severity of the 1984 fire may have influenced post-2012 tree regeneration by creating variable fuel loading, which may
have affected soils, litter cover and shade after the 2012 fire and therefore affected seedling establishment and survival. A canopy seed bank of unburnt cones from trees killed by the 2012 fire potentially contributed to a strong effect of prior burn severity on regeneration after the 2012 fire despite a lack of serotinous or resprouting tree species, although the influence of this canopy seedbank was likely limited to the year following the fire. Our results suggest that a low- to moderate-severity fire increases forest resilience relative to a high-severity fire even when the next fire burns at high severity.
HIGHLIGHTS
Forests twice burned at high severity had sparse tree regeneration Low-severity fire increased forest resilience to a subsequent high-severity fire
Severity of a prior fire determined tree regeneration after a high-severity reburn
Key words: Repeated fires; Tree regeneration; Legacy effects; Forest resilience; High-severity wildfire; Pinus contorta.
INTRODUCTION Received 6 March 2020; accepted 15 August 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00548-x) contains supplementary material, which is available to authorized users. Author Contributions LBH and AHT collected data, LBH performed analysis and wrote the first draft of the manuscript, and all authors designed the study and contributed substantially to revisions. *Corresponding author; e-mail: [email protected]
Successive disturbances, especially when occurring at relatively short intervals, may lead to persistent and sometimes surprising changes in vegetation (Zedler and others 1983; Paine and others 1998; Buma 2015). Such changes arise in part due to legacy effects
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