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Dryad

Recent fire history enhances semi-arid conifer forest drought resistance

Norlen, Carl1; Hemes, Kyle2; Wang, Jonathan3; Randerson, James1; Battles, John4; Tubbesing, Carmen4; Goulden, Michael1

Published Oct 28, 2024 on Dryad. https://doi.org/10.5061/dryad.s4mw6m9f2

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Abstract

Interaction effects from past climate change-amplified disturbances in fire-prone forests can produce ecological feedbacks that amplify or dampen subsequent disturbances. Climate change is increasing wildfire burned area, wildfire severity, and incidents of drought-induced forest dieback (widespread tree mortality). These climate change amplified disturbances threaten forest’s ability to regulate climate, provide water, and store carbon. Greater burned area makes interaction effects due to past fires more likely, which highlights the importance of understanding whether interaction effects produce negative or positive feedback on subsequent disturbances such as forest dieback. We constructed a forest chrono-sequence by combining a geospatial database of historical fire with a time series of Landsat satellite observations for forests in the Sierra Nevada of California to assess the impact of fire history on vegetation recovery, water use (evapotranspiration), and as feedback on subsequent forest dieback. We used these data sets to assess: 1.) How does a history of prescribed fire versus wildfire change forest cover and water use? 2.) How sensitive are forest structure and water use to fires of varying severity? 3.) How do these fire-induced changes to forest structure and water use impact forest dieback intensity? Forests with recent fire history had reduced tree cover, increased shrub cover, and decreased water use, with the greatest changes due to high-severity wildfires. Through 20 years post-fire water use neared pre-fire conditions across all fire types and severities, while decreased tree cover and increased shrub cover persisted following high severity wildfires and gradually returned to pre-fire conditions for moderate and low severity fire. Fire history decreased forest dieback intensity compared to unburned controls, which suggests a dampening (negative) feedback. The reductions in forest dieback intensity were equal to or greater than reductions in tree cover and greater than reductions in water use, which suggests that post-fire reductions in tree cover combined with reductions in water use enhanced forest drought resistance more than either reduction individually.  In fire-prone conifer forests, interaction effects from past fires will dampen subsequent drought-induced forest dieback, introducing novel ecological feedback with implications for forest management and climate mitigation.