Low‐ and moderate‐severity fire offers key insights for landscape restoration in ponderosa pine forests

Abstract

Restoration goals in fire‐prone conifer forests include mitigating fire hazard while restoring forest structural components linked to disturbance resilience and ecological function. Restoration of overstory spatial pattern in forests often falls short of management objectives due to complexities in implementation, regulation, and available data. When historical data is available, it is often collected at plots too small to inform coarse‐scale metrics like gap size and structure of tree patches (e.g., 1 ha). Principles of ecological forestry typically emphasize overstory removal patterns that emulate those of natural disturbances. So, low‐ and moderate‐severity portions of contemporary wildfires may serve as a guide to restoration treatments where mixed‐severity fires occur. Here, we compare forest spatial pattern and configuration in 15 mechanical restoration treatments and low‐ and moderate‐severity portions of three wildfires in ponderosa pine‐dominated forests to determine how they differ in spatial pattern. We obtained satellite imagery of restoration treatments and wildfires and used supervised classification to differentiate canopy and openings. We assessed elements of landscape structure including canopy and gap cover, gap attributes, and landscape heterogeneity for each disturbance type. We found that both mechanical restoration treatments and low‐ and moderate‐severity portions of wildfires reduced forest cover, increased gap cover, and altered pattern and arrangement of gaps relative to undisturbed areas, though the magnitude of changes were greatest in the burned sites. Low‐ and moderate‐severity wildfire consistently increased landscape heterogeneity, but mechanical treatments did not. This suggests that a greater emphasis on increasing gap and patch spatial structure may make mechanical treatments more congruent with natural disturbances. Outcomes of low‐ and moderate‐severity portions of wildfires may provide important information upon which to base management prescriptions where reference data on landscape patterns is unavailable.

Restoration and fuel hazard reduction result in equivalent reductions in crown fire behavior in dry conifer forests

“…This finding suggests that these prescriptions needed to provide more explicit instructions on how marking crews should create the desired numbers and size of tree groups and non-treed openings. Failure to create large groups of trees and non-treed openings has been observed in other studies on spatially complex forest treatments (Cannon et al, 2021;Churchill et al, 2013;Maher et al, 2019).…”

“…By removing adjacent and subordinate trees around these highly valued trees so that they are retained as isolated individuals, crown torching will be less likely due to increased convective cooling (Ritter et al, 2020 ). In other cases, land managers may want to leverage natural disturbance dynamics (i.e., fire caused mortality) to accelerate the restoration of historical forest structure and pattern (Cannon et al, 2021 ; Huffman et al, 2020 ; Larson et al, 2013 ). In this context, the potential for fine‐scale group torching may be an acceptable, or even desirable, treatment outcome as patchy overstory mortality will enhance structural complexity, create snags that provide valuable wildlife habitat, and generate non‐treed openings that will enhance understory plant diversity and provide favorable regeneration sites for shade‐intolerant tree species (Bigelow et al, 2011 ; Jain et al, 2020 ; Matonis & Binkley, 2018 ).…”

Assessing the effects of burn severity on post-fire tree structures using the fused drone and mobile laser scanning point clouds

“…Following a moderate-severity fire, forest structure is altered due to the burning of multiple vegetation strata from ground to canopy (Keeley, 2009;Ager et al, 2013;Kramer et al, 2016). Low-and moderate-severity fires may benefit residual trees with reduced competition and increased seed germination and sprouting (Collins et al, 2018;Jean et al, 2019;Cannon et al, 2021). By contrast, high-severity fires (i.e., crown fires) are characterized by a major loss in the above-ground biomass due to the consumption of surface, ladder, and crown fuels (Chambers et al, 2016;Jones et al, 2016;Garcia et al, 2017).…”