Plant species which have survived fires for tens of thousands of years may not only have selected survival mechanisms, but also inherent flammable properties that contribute to the perpetuation of fire—dependent plant communities. This concept goes by beyond the commonly accepted fire climate—fuel moisture basis of wildland fire occurrence. Plant communities may be ignited accidentally or randomly, but the character of burning is not random. The following hypothesis treats this interaction between fire and the ecosystem: Fire—dependent plant communities burn more readily than non—fire—dependent communities because natural selection has favored development of characteristics that make them more flammable. The hypothesis was experimentally derived following laboratory combustion tests with litter of eucalyptus (Eucalyptus obliqua L'Herit), ponderosa pine (Pinus ponderosa Laws.), and tropical hardwood leaves.