We investigated the effects of low-intensity, prescribed spring surface fires at varying intervals in a widely spaced, mature red pine plantation growing on a high quality sandy loam soil in northern Lower Michigan. Measurements of overstory characteristics, as well as the composition and development of the herbaceous and woody understory, were taken in unburned plots and during the seventh growing season following a single burn, the second growing season following the last of two burns at 5 yr intervals, and the growing season immediately following the last of four burns 2 yr intervals. Except for loss of a few trees due to crown scorch early in the study when fuel loadings were high, the red pine overstory was minimally affected by fires at any return interval. Compared to unburned plots, fire had no effect on total species richness or percent cover of ground flora < 1.4 m tall, but species composition shifted; cover of mosses and lichens declined and black cherry seedlings increased at the two shortest fire intervals. Although percent cover of grasses, bracken fern, and Rubus spp. appeared to increase following fire, the clumped distribution of vegetation and interplot variability in overstory density obscured the statistical significance of these trends. Species richness and density of stems in the woody understory (> 1.4 m tall but < 10 cm dbh) declined abruptly as burning interval decreased and number of burns increased. Fewer than two woody understory species, on the average, persisted on plots burned every 2 yr, whereas nearly 12 grew on unburned plots. Postburn conditions were conducive to the re-establishment of black cherry and paper birch in the understory; density of all other major species dropped sharply after more than one fire. As time after the last fire increased, however, red maple, choke cherry, and white ash densities began to recover slowly, largely by sprouting. The significance of these findings to red pine managers in the Lake States is discussed. North. J. Appl. For. 13(3):140-146.