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Background <p>In the European boreal forest, the structure of the forest floor (e.g. depth, mass) and of the vascular understory plants (e.g. height, mass) are fundamental drivers for fire behavior. Typically, quantitative assessment of this require time-consuming destructive sampling.</p> Methods <p>Using novel techniques and destructively sampled fuel data from a large number of plots, we devised and calibrated a non-destructive method for quantifying surface fuel depth and load in upland forests in the European boreal region. The depth of the potentially flammable moss/litter layer was measured using a simple penetrometer, applying a force of 15 N to the forest floor. Penetrometer depths were compared to density profiles and post-fire consumption of organic soil layers. Based on parallel destructively sampled data from nearly 200 plots, the dry mass of flammable moss/litter and that of understory dwarf-shrubs were determined based on penetrometer depth and the surface coverage and height of dwarf-shrubs, respectively.</p> Results <p>In parallel measurements of pre-fire penetrometer depth and post-flame-passage depth-of-burn during experimental fires in boreal forest, the two were virtually identical, showing that the penetrometer can indeed delineate the fuel potentially available for the flaming front, under sufficiently dry conditions. Using high-resolution density measurements across a gradient of forest floor depths, we found that the penetrometer depth matched the depth at which bulk density reached c. 30 kg m<sup>−3</sup>, which was identical to the transition layer between moss/litter and the much denser humus below. Penetrometer depth was converted to moss/litter dry mass using a power law function (<i>r</i><sup>2</sup> = 0.53). Dry mass of live surface fuels for three dwarf-shrubs, that are near ubiquitous in European boreal forest, was estimated based on the product of visually assessed cover (proportion of the sample area) and height (second order polynomials, <i>r</i><sup>2</sup> &gt; 0.88).</p> Conclusions <p>Our method allows for rapid assessment of surface fuels and should, with site-specific calibration, be applicable to other boreal forest ecosystems. A process time in the field of between one and two minutes per plot greatly facilitates large-scale fuel sampling.</p>

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A rapid and non-destructive method for quantifying boreal forest surface fuels

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月18日

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  • Johan Sjöström,
  • Frida Vermina Plathner,
  • Anders Granström

摘要

Background

In the European boreal forest, the structure of the forest floor (e.g. depth, mass) and of the vascular understory plants (e.g. height, mass) are fundamental drivers for fire behavior. Typically, quantitative assessment of this require time-consuming destructive sampling.

Methods

Using novel techniques and destructively sampled fuel data from a large number of plots, we devised and calibrated a non-destructive method for quantifying surface fuel depth and load in upland forests in the European boreal region. The depth of the potentially flammable moss/litter layer was measured using a simple penetrometer, applying a force of 15 N to the forest floor. Penetrometer depths were compared to density profiles and post-fire consumption of organic soil layers. Based on parallel destructively sampled data from nearly 200 plots, the dry mass of flammable moss/litter and that of understory dwarf-shrubs were determined based on penetrometer depth and the surface coverage and height of dwarf-shrubs, respectively.

Results

In parallel measurements of pre-fire penetrometer depth and post-flame-passage depth-of-burn during experimental fires in boreal forest, the two were virtually identical, showing that the penetrometer can indeed delineate the fuel potentially available for the flaming front, under sufficiently dry conditions. Using high-resolution density measurements across a gradient of forest floor depths, we found that the penetrometer depth matched the depth at which bulk density reached c. 30 kg m−3, which was identical to the transition layer between moss/litter and the much denser humus below. Penetrometer depth was converted to moss/litter dry mass using a power law function (r2 = 0.53). Dry mass of live surface fuels for three dwarf-shrubs, that are near ubiquitous in European boreal forest, was estimated based on the product of visually assessed cover (proportion of the sample area) and height (second order polynomials, r2 > 0.88).

Conclusions

Our method allows for rapid assessment of surface fuels and should, with site-specific calibration, be applicable to other boreal forest ecosystems. A process time in the field of between one and two minutes per plot greatly facilitates large-scale fuel sampling.