Abstract
A 3.6 ha experimental fire was conducted in a black spruce peatland forest that had undergone thinning the year prior. After 50 m of spread in a natural stand at 35–60 m min−1, the crown fire (43,000 kW m−1 intensity using Byram’s method) encountered the 50% stem removal treatment; spread rates in the treatment were 50–60 m min−1. Fuel consumption in the control (2.75 kg m−2) was comparable to the treatment (2.35 kg m−2). Proxy measurements of fire intensity using in-stand heat flux sensors as well as photogrammetric flame heights had detected intensity reductions to 30–40% of the control. Crown fuel load reductions (compensated by higher surface fuel load) appear to be the most significant contributor to the decline in intensity, despite drier surface fuels in the treatment. The burn depth of 5 cm in moss and organic soil did not differ between control and treatment. These observations point to the limited effectiveness (likely reductions in crown fire intensity but not spread rate) of stem removal in boreal black spruce fuel types with high stem density, low crown base height and high surface fuel load. The observed fire behaviour impacts differ from drier conifer forests across North America.
Highlights
Strategies for decreasing home and structure loss in the Wildland-Urban Interface (WUI) have been framed at a variety of scales including building materials [1], vegetation, and environmental characteristics immediately surrounding homes [2], as well as regional scales [3]
An experimental crown fire was ignited in a natural lowland boreal spruce forest in Alberta, Canada, in May 2019
The continuous crown fire burned into a thinned spruce stand with little alteration in spread rate or total fuel consumption
Summary
Strategies for decreasing home and structure loss in the Wildland-Urban Interface (WUI) have been framed at a variety of scales including building materials [1], vegetation, and environmental characteristics immediately surrounding homes [2], as well as regional scales [3] This increasing focus on firebrands (embers) as a primary mode of home ignition allows for a two-tiered approach to wildfire. Fire 2020, 3, 28 risk mitigation: a simultaneous focus on homeowners tackling ignition sources on the home exterior and immediate surroundings [1], while wildfire management agencies and municipalities can reduce factors related to firebrand production and spread Fuel treatments such as thinning and pruning are resource-intensive alternatives to surface prescribed burning in ecosystems with low crown base heights, high surface fuel loads, or dense understory ladder fuels [4]. More rainfall reaches the surface, and root uptake of duff moisture by trees is decreased [8]
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