Several researches have reported that under certain conditions forest fires with normal behavior suddenly start to propagate at unusual and very fast rate of spread. A thermochemical approach, based on the ignition of a Volatile Organic Compounds (VOCs) cloud, has been proposed previously to explain these accelerating forest fires. Indeed, some vegetal species when heated emit volatile substances. We have shown using a flash pyrolysis apparatus that a typical Mediterranean plant, Rosmarinus officinalis, emits eighteen components, mainly α-pinene. Laminar burning speeds and Markstein lengths as well as flame thicknesses of α-pinene/air premixed flames are determined using the spherical expanding flames method. Experiments are carried out in a spherical vessel at atmospheric pressure. The effects of equivalence ratio (0.7-1.4) and unburned gas temperature (353-453 K) are studied. Combustion characteristics are obtained using a nonlinear methodology. A correlation is developed to calculate the laminar burning speeds as a function of equivalence ratio and temperature. The experimental results are compared to the computed ones of JP-10 and n-decane as well as to those found in the literature for these compounds.