L. Provencher et al., Longleaf pine and oak responses to hardwood reduction techniques in fire-suppressed sandhills in northwest Florida, FOREST ECOL, 148(1-3), 2001, pp. 63-77
Restoring fire-suppressed longleaf pine (Pinus palustris Mill.) sandhill co
mmunities often includes reducing hardwood structure before re-establishing
maintenance fire regimes. Using a randomized complete block design, we com
pared the effects of three hardwood reduction techniques (spring burning, a
pplication of the ULW (R) form of the herbicide hexazinone. and midstory ch
ainsaw felling/girdling) and a no-treatment control on oak and longleaf pin
e densities in fire-suppressed sandhills at Eglin Air Force Base. FL. Treat
ments were applied in the spring and summer of 1995. Felling/girdling and h
erbicide plots were also burned for fuel reduction from March to April in 1
997. Frequently burned, high-quality sandhill plots were sampled to establi
sh reference conditions. Pre-treatment diameter distributions of oaks follo
wed a negative-exponential curve in all treatments, but were Aat with low t
ree densities in reference plots. Oak densities were significantly reduced
in the herbicide and felling/girdling plots in 1995. Compared to the contro
ls, growing season fire topkilled up to 20% more hardwoods among smaller tr
ees in 1995, but this value increased to approximately 50% after 1996. In a
ll pears, the greatest reduction of oak juvenile density (<1.4 m high) was
caused by herbicide application. Control plots contained significantly fewe
r oak juveniles than the burn and felling/girdling plots. Reference plots c
ontained the lowest and most variable oak juvenile densities. Size distribu
tions of longleaf pine across all plots were bimodal with modes at 0-4.9 an
d 25-29.9 cm in diameter. The highest mode was at 0-4.9 cm in treatment plo
ts and at 25-29.9 cm in reference plots, Only fire quantitatively changed t
he distributions by the attrition of the smallest trees >1.4 m high in all
years. Fire caused approximately 50% decreases in longleaf pine juvenile (<
1.4 m high) density in 1995 and 1997. By 1997, median juvenile densities co
nverged to 5-6 stems/200 m(2) in all treatments, including the control. Juv
enile densities were slightly higher and more variable in reference plots t
han in treatments. In 1997, fuel reduction burns in the herbicide and felli
ng/girdling plots decreased densities of recently germinated longleaf pines
to <5 seedlings/20 m(2), a 90% decrease compared to 1996 densities. Seedli
ng densities dropped by approximately 50% in control and burn plots, althou
gh these sites received no manipulations after 1995. Seedling densities onl
y decreased by 22% in reference plots (205 seldlings/20m(2) in 1996), which
did experience some fires, (C) 2001 Elsevier science B.V. All rights reser
ved.