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Landscape evaluations and prescriptions for post-fire landscapes - Final Report to the Joint Fire Science Program

Author(s): Andrew J. Larson, C. Alina Cansler, Van R. Kane, Derek J. Churchill, Paul F. Hessburg, James A. Lutz, Nicholas A. Povak
Year Published: 2020
Description:

Wildfires are modifying the structure and composition of forests at rates that far exceed mechanical thinning and prescribed fire treatments. We responded to this by analyzing recent wildfires to understand drivers of fire-severity and post-fire vegetation development, with an emphasis on how pre-and post-fire management and prior disturbance history modulate these responses, and by evaluating the degree to which fire reduced landscape departure and restored fire-prone forest landscapes. We used field and remote sensing methods to investigate these topics, with forests of northeastern Washington, USA as a model system for our work.

There was abundant post-fire tree regeneration one to three decades after fire, with little evidence of recruitment failure. We found an influence of both average climate and post-fire weather, with higher seedling densities associated with cooler and moister conditions. This weather and climate signal portends potential recruitment limitation following future fires that occur in warmer and drier conditions. Post-fire harvest had a simplifying effect on residual forest structure relative to paired controls, but the effect of fire severity was stronger than that of post-fire treatments. Post-wildfire prescribed fire applied in areas that burned at lower severity further decoupled surface and canopy fuels, promoting fire-resistant open canopy structure. Daily weather and annual climate anomalies had the strongest influence on burn severity, but recent prior vegetation management, and especially prior prescribed fire and wildfire, moderated burn severity. Large, unplanned wildfires caused variable and contrasting outcomes—they rapidly reorganized the vegetation mosaic in ways that planned vegetation treatments do not. In some areas, fires made progress towards restoration and climate adaption goals, improving alignment of the forest structural mosaic with HRV-FRV envelopes and reestablishing stabilizing fire-vegetation feedbacks. However, wildfires sometimes increased departures from HRV-FRV benchmarks, for example by creating vast open patches, reducing or eliminating large-tree dominated patches, or causing transitions to uncharacteristically large non-forest patches.

Post-fire landscape management principles synthesized from our work include:

•Protect fire refugia and legacy large diameter trees.

•Use places where fire reinitiated or strengthened stabilizing feedbacks as core areas from which to grow forest landscape resilience.

•Differentiate irreversible conversions to non-forest due to climate-limited tree establishment from reversible transitions due to dispersal limitation.

•Align species composition and structure with future fire regimes and climate.

We illustrate application of these principles using the landscape prescription concept in a geospatial framework. An important theme is a shift away from a post-fire management paradigm focused on economic salvage harvest in individual easily accessed stands that burned with high severity, with little regard for overall landscape pattern or context. Our post-fire management principles help align overall landscape pattern with HRV-FRV benchmarks that promote resilience and adaptation to future climate and fire regimes, using a variety of post-fire treatments, such as planting climate-adapted species in dispersal limited areas, and green tree thinning, “salvage from below,” and post-wildfire prescribed fire in places that burned at lower severity.

Citation: Larson, Andrew J.; Cansler, C. Alina; Kane, Van R.; Churchill, Derek J.; Hessburg, Paul F.; Lutz, James A.; Povak, Nicholas A. 2020. Landscape evaluations and prescriptions for post-fire landscapes - Final Report to the Joint Fire Science Program. JFSP Project No. 16-1-05-24. Missoula, MT: University of Montana. 51 p.
Topic(s): Fire Ecology, Fire Effects, Fuels, Fuel Treatments & Effects, Prescribed Fire-use treatments, Post-fire Management, Recovery after fire, Restoration
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 22540
FRAMES RCS number: 62669
Record updated: Feb 25, 2021