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Post-fire delayed tree mortality in mesic coniferous forests reduces fire refugia and seed sources

Published Article

Oregon

Publication date: May 15, 2025

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Fire refugia are critical for conifer forest resilience, yet their persistence is uncertain as fire‑injured trees die in the years following wildfire. Using 3‑m satellite imagery from Oregon’s western Cascades, this study mapped annual changes in live tree cover for three years after high‑severity fires. Delayed mortality reduced live forest cover by 8.5%, disproportionately affecting mature and fire‑sensitive conifers. Refugia patches declined by ~20%, with most remaining patches small and edge‑dominated. High‑severity burned area expanded by 9%, and zones lacking adequate seed sources increased by 375%. These shifts reveal how delayed mortality alters the size, isolation and configuration of fire refugia, emphasizing the need to incorporate species‑specific fire adaptations into post‑fire management and long‑term forest resilience planning.

Subject Tags

  • Forest
  • Fire management

Abstract

Context

Ecological functions provided by fire refugia are critical for supporting conifer forest resiliency under increased fire activity across the western United States. The spatial distribution and persistence of fire refugia over time are uncertain as fire-injured trees continue to die over subsequent years post-fire.

Objectives

We examined how post-fire delayed tree mortality affects the spatial distribution and attributes of fire refugia at patch and landscape scales following high-severity wildfires.

Methods

To explore changes in fire refugia patch size, isolation and fragmentation over time, we used high-resolution satellite imagery (3 m pixel size) following high-severity fires in Oregon’s western Cascades to map annual changes in the extent of live tree cover up to three years post-fire.

Results

Delayed mortality decreased live forest cover across all fire perimeters by 8.5% between one month and three years post-fire. Though prevalent across all forest types, adult to mature and fire-sensitive conifer species were the most vulnerable to delayed mortality. The number of refugia patches decreased by ca. 20%, and most (ca. 77%) were small, non-core patches (< 60 m from the patch edge). In response to delayed mortality, which increased the extent of high-severity burned areas by 9% (ca. 12,000 ha), the area with little to no seed sources based on refugia distance2-weighted density increased by 375% (7632 ha).

Conclusions

Delayed mortality altered the size and spatial configuration of fire refugia across landscapes. Considering species-specific fire adaptations may help improve post-fire management strategies and a framework of conifer forest resiliency under novel fire regimes.

Citation

Dyer, A. S., Busby, S., Evers, C., Reilly, M., Zuspan, A., & Holz, A. (2025). Post-fire delayed tree mortality in mesic coniferous forests reduces fire refugia and seed sources. Landscape Ecology, 40(5), 101. https://doi.org/10.1007/s10980-025-02111-2

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