Numerical simulation and experiments of burning douglas fir trees

Fires spreading in elevated vegetation, such as chaparral or pine forest canopies, are often more intense than fires spreading through surface vegetation such as grasslands. As a result, they are more difficult to suppress, produce higher heat fluxes, more firebrands and smoke, and can interact with, or create, local weather conditions that lead to dangerous fire behavior. Such wildland fires can pose a serious threat to wildland–urban interface communities. A basic building block of such fires is a single tree. In the work presented here, a number of individual trees, of various characteristics, were burned without an imposed wind in the Large Fire Laboratory of the National Institute of Standards of Technology. A numerical model capable of representing the spatial distribution of vegetation in a tree crown is presented and evaluated against tree burning experiments. For simplicity, the vegetation was assumed to be uniformly distributed in a tree crown represented by a well defined geometric shape (cone or cylinder). Predictions of the time histories of the radiant heat flux and mass loss rates for different fuel moisture contents and tree heights compared favorably to measured values and trends. This work is a first step toward the development and application of a physics-based computer model to spatially complex, elevated, vegetation present in forest stands and in the wildland–urban interface.