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A semi-empirical model was developed which forms shrub geometries from distinct fuel elements (e.g. leaves) and describes flame spread from element to element. Ignition, flame growth and flame decay patterns were based on combustion data of single leaves. Extension of the model to various heating conditions was achieved by scaling the flame growth parameters using physics-based heat transfer models. The resulting model offers a novel approach to examine fire spread and to explicitly describe both distinct fuel elements and fire behavior. This approach balances computational speed and modeling detail while providing a unique perspective into fire spread phenomena. Comparisons of the tuned model to fire spread behavior measured in an open-roofed wind tunnel benchmarked the model’s ability to simulate fire spread in manzanita shrubs.

Burning behaviors of individual live and dead leaves were measured in a well-instrumented, well-controlled flat-flame burner. Manzanita (Arctostaphylos glandulosa) branches were harvested from the Chaparral near Riverside, California. Leaves were conditioned to several moisture contents. Two “live” (i.e., not fully dried) groups remained above the fiber saturation point at 34% moisture content (MC; dry basis) and 63% MC. Two “dead” groups were dried to about 4% MC, and one was rehydrated back up to 26% MC. Distinct plateaus in surface temperatures at 175°C were observed while burning live leaves, but dead leaves showed weaker plateaus, if any. Evidence of high internal leaf pressures during burning of live leaves was seen in flame patterns. Moisture was retained in live and dead leaves with local surface temperatures in the 160°C to 220°C range. This article describes the measured results, while a second article describes mass release modeling for the same data set.

Improved models of fire spread and fire characteristics are desired for live shrub fuels, since the majority of existing research efforts focus on either dead fuel beds or crown fires in trees. Efforts have been made to improve live fuel modeling, including detailed studies of individual leaf combustion, with results incorporated into a shrub combustion model for broadleaf species. However, this approach was not well-suited to non-broadleaf shrubs since their fuel consists of long needle-covered branches rather than easily discretized leaves. Methods were therefore developed to simulate the branching structure of chamise ( Adenostoma fasciculatum ) and Utah juniper ( Juniperus osteosperma ). The plant structure was based on a form of fractal theory called Lindenmayer systems (i.e., L-systems). Correlations to predict branch number from crown diameter were made based on data from the literature, to ensure that the modeled shrubs would have the same bulk density as live shrubs. The structure model was designed to match the specific characteristics of each species, such as branching angles, the number of stems exiting at ground level, and the fuel element length. This method can be used to generate shrub geometries for detailed shrub combustion models or for realistic artistic renditions.