Beginning in 1991, periodic surface fires (frontal fire intensities <200 kW
m–1) were introduced into a mixed red pine
(Pinus resinosa Ait.) and white pine
(P. strobus L.) plantation (dbh 16–60 cm).
Replicated plots of 0.4–0.5 ha were either burned three times at
biennial intervals (early May of 1991, 1993, and 1995), burned once (early May
1991), or not burned. Measurements were conducted during the 1994 and 1995
growing seasons. The pine overstory was largely unaffected by the fires. The
understory on unburned plots contained 16 111 large seedlings (>1 m, ≤
1.9 cm dbh) and 3944 saplings (2.0–5.9 cm dbh) per ha, consisting of 23
woody angiosperm taxa. Plots burned once contained 60% of the large
seedlings, 7% of the saplings, and 6 fewer taxa than unburned plots. No
large seedlings and few saplings were found in plots burned biennially. Cover
of low (<1 m) woody and herbaceous vegetation in plots burned once or three
times was twice that of unburned plots, even in the growing season immediately
following the May 1995 re-burn. Recovery of low vegetative cover in the
re-burned plots was rapid, exceeding that in once-burned or unburned plots by
late summer following the burn. Species richness of low vegetation was
20–25% higher in burned than unburned plots, except in the year
immediately following reburning. Taxa dominating this site following burning
were Sassafras albidum (Nutt.) Nees,
Rubus spp., Phytolacca americana
L., and Dryopteris spinulosa (O.F. MÜll.) Watt.
Restoration of low-intensity surface fires to ecosystems dominated by mature
red pine or white pine is feasible, but major changes in understory structure
and composition will occur.