Six experimental fires were carried out within pure trembling aspen and mixed deciduous stands in the US Lake States region during both spring and late fall (ie, leafless stage). Available surface fuel loads averaged 2.5 t/ha. High to extreme burning conditions prevailed as determined by the Canadian Forest Fire Weather Index (FWI) System. Head fire spread rates varied from 1.5 to 8.8 m/min and were highly correlated with the Initial Spread Index component of the FWI System (r=0.91). Frontal fire intensities ranged from 115 to 672 kW/m. Extensive mortality was observed in trees less than 7.6 cm in diameter at breast height (DBH) while overstory stems greater than 15 cm dbh were seldom affected. Most shrub species were readily top-killed by fire but quickly resprouted. The total number of woody understory stems (deciduous shrubs and small trees) often increased following the fires.