The pyrolysis chemistry of tree samples from plants commonly found in the forests of the western United States is evaluated and compared with wet chemical analysis of the original material. Wood, leaves, bark, needles, reaction wood, and sticks are individually examined. Molecular beam sampling mass spectrometric detection of pyrolytic compounds at furnace settings of 500 °C with short residence times (on the order of 100 ms) permits mass spectral analysis of the chemical components in the primary decomposition regime. Multivariate analysis of the pyrolysis mass spectra yields three principal factors. One factor identifies leaf, needle, and bark samples and correlates well with the extractive content of the material; there is also a relationship between this factor and the ash content of the material. The other two factors separate hardwood and softwood samples; this distinction is based mainly on differences in the structure of lignin degradation products that are evident in the pyrolysis vapors. These measurements suggest that the extractives content of the fuel may be a natural chemical indicator that is useful for estimating the bulk pyrolysis chemistry in a way that can be practically implemented into wildland fire models.