Burning season in mixed conifer forest: understory plant habitat preference predicts response to fire.
Schwilk, Dylan*,1, Knapp, Eric2, Kane, Jeffrey1, Keeley, Jon1, 1 U.S. Geological Survey, Three Rivers, CA, USA2 U.S. Forest Service, Redding, CA, USA
ABSTRACT- In the mixed conifer forests of the western US, prescribed fire is typically conducted in the spring or fall. Historically, however, fires in these areas most commonly burned during the dry mid summer to early fall period. Thus, the timing of prescribed fires may fall outside the range of when historical fires typically burned. Early and late season fires may affect plants differently due to differing fire intensities or through phenological effects of burning season. We conducted replicated early and late season burns to study the effects of fire season on plant response. We categorized plant species according to their pre-treatment habitat occurrence using nonmetric multidimensional scaling. The resulting axes of variation separate species along a habitat gradient from deep forest to open gaps. We tested the hypothesis that plant response to fire and fire intensity could be predicted by pre-treatment habitat preference. For example, species commonly found in areas of the forest with continuous fuels were expected to respond differently to fire compared to species commonly found in areas lacking continuous fuels, where fire may be less likely to burn. Deep forest species showed significant decreases in cover and frequency with both early and late season burns, while species associated with open forest increased in cover after fire. Season of fire had little effect on these groups but did affect shrubs with fire-stimulated germination which showed greatest increases in early season burns. Many shrubs exhibited a humped-shaped response to fire intensity with greatest increase in frequency at intermediate fire intensities.
Key words: Sierra Nevada, fire management, fire and fire surrogates study
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