An efficient and comprehensive field protocol for assessing fuel characteristics for fire behaviour modelling in Australian open forests

Abstract

Knowledge of fuel characteristics and their spatial and temporal distribution is increasingly important as fire managers rely on this information to quantify fire risk, plan prescribed burning activities, forecast fire danger and predict wildland fire behaviour and effects. Current fuel inventory approaches used in Australia largely rely on visual assessment methods that are subjective and lack the consistency and accuracy required for fire management applications. We describe a protocol to quantify characteristics for various fuel strata considered in Australian fire modelling applications, namely: litter and suspended dead fuels; downed wood debris; live understorey; bark; and overstorey canopy. The method provides information about:•Cover and height (or depth) of each strata;•Mass of fine fuels of litter, dead suspended and live understorey layers (dead fuel diameter (d) ≤ 0.6 cm, live fuel d ≤ 0.4 cm); and•Mass and size class distribution of downed woody fuels (d>0.6 cm). The protocol integrates a variety of sampling methods including destructive sampling for fine fuel particles, line intersect method for downed woody fuel, and indirect approaches relying on double sampling techniques to estimate live understorey, bark and overstorey canopy fuels. The protocol can be adapted to enable application to situations with distinct accuracy requirements. Data collected using the protocol will have direct use in developing models of forest fuel dynamics and evaluating outputs from remote sensing approaches to describe these fuels.

Keywords: Bark; Coarse woody debris; Fuel cover; Fuel height; Fuel load; Fuel strata; Fuel structure; Litter; Woody fuel.

Fig. 1

Definitions of the different fuel strata considered for fire behaviour modelling in dry eucalypt forests.

Fig. 2

Flow chart of protocol for field assessment of fuel structure in open eucalypt forests. Numbers in parenthesis denote protocol step. FA represents Field Assessor, with white boxes denoting tasks carried out by Field Assessor 1 (FA1), and grey boxes tasks associated with Field Assessor 2 (FA2).

Fig. 3

Example of general plot layout targeting an area previously burned with moderate severity. Transect location aimed to suit a 30 × 30 m pixel size (such as that used by Landsat) and to avoid edge effects caused by road or areas burned with different severities.

Fig. 4

(a) General view of plot layout at sampling area with location of the various sampling plots; (b) Detailed view of transect with location of point intersect method sampling locations.

Fig. 5

Example forest fuel field form for collection of fuel data in open forests (printable version and completed example are included in Supp. Materials).

Fig. 6

Position transect photos looking directly down the tape measure and with the Height Pole cantered vertically and horizontally in the photograph. The Height Pole is located on the photopoint.

Fig. 7

(a) Oblique and (b) top view of placement of the dead (⌀ = 0.252 m) and live (⌀ = 0.505 m) fuel sample rings. The dead fuel sample ring is positioned inside the live fuel ring.

Fig. 8

General view of two open forest stands, FD07_Mon2024 (top) and Ken7PHS743H (bottom), as seen along a transect at a photopoint. Both stands were burned 7 years prior to sampling. Height pole is 2 m tall. See Table 2 for fuel complex information.