Previous studies on the influence of endothelial seeding on graft patency have shown that signifi... more Previous studies on the influence of endothelial seeding on graft patency have shown that significant improvement has only been achieved with Dacron and an experimental, porous PTFE graft. Methods of assessing patency or showing statistical significance could be questioned in some of these studies. To determine if the combination of endothelial cell seeding and antiplatelet agents would improve patency in small-diameter, commercially available expanded polytetrafluorethylene (ePTFE) grafts, we placed ePTFE grafts into the left carotid position in two groups of mongrel dogs. All grafts were 4 mm internal diameter and 60 mm long, and were interposed in an end-to-end fashion. Both groups received aspirin (80 mg daily) and dipyridamole (25 mg daily) for 14 days, beginning immediately prior to surgery. In Group I (n = 12), the grafts were seeded with enzymatically harvested autogenous endothelium just prior to implantation; in Group II (n = 10) the grafts were not seeded. All grafts were...
Across much of the southeastern U.S.A., sandhills have become dominated by hardwoods or invasive ... more Across much of the southeastern U.S.A., sandhills have become dominated by hardwoods or invasive pine species following logging of Pinus palustris (longleaf pine) and fire suppression. At Eglin Air Force Base where this study was conducted, Pinus clausa (sand pine) has densely colonized most southeastern sandhill sites, suppressing groundcover vegetation. The objectives of this study were: to determine if suppressed groundcover vegetation recovers following the removal of P. clausa ; to compare species composition and abundance in removal plots with that in reference, high quality sandhills; to test the assumption that recolonization by P. clausa seedlings decreases with proximity to the centers of removal plots; and to measure the survival of containerized P. palustris seedlings that were planted on P. clausa removal plots. One year post-removal (1995), the number of plant species decreased by 50%, but then increased by 100% from 1995 to 1997, followed by a small reduction in 1998. The number of plant species was greater in reference plots than in removal plots prior to 1997. Eighty-five percent of the original species were recorded 4 years post-harvest in removal plots. Shrubs and large trees remained at low density after harvest. Densities of graminoids, legumes, other forbs, woody vines, and small trees increased after harvest. Plant densities of all life forms, except woody vines, were greater in reference plots than in removal plots. The density of recolonizing P. clausa seedlings 2-4 years post-harvest significantly decreased with increasing proximity to the centers of removal plots. On average, 80% of planted P. palustris seedlings survived their first 2 years. Harvest of P. clausa followed by fire and the planting of P. palustris is a reasonably effective restoration approach in invaded sandhills . However, supplementary plantings of some herbaceous species may be necessary for full restoration.
Restoring ®re-suppressed longleaf pine (Pinus palustris Mill.) sandhill communities often include... more Restoring ®re-suppressed longleaf pine (Pinus palustris Mill.) sandhill communities often includes reducing hardwood structure before re-establishing maintenance ®re regimes. Using a randomized complete block design, we compared the effects of three hardwood reduction techniques (spring burning, application of the ULW 1 form of the herbicide hexazinone, and midstory chainsaw felling/girdling) and a no-treatment control on oak and longleaf pine densities in ®re-suppressed sandhills at Eglin Air Force Base, FL. Treatments were applied in the spring and summer of 1995. Felling/girdling and herbicide plots were also burned for fuel reduction from March to April in 1997. Frequently burned, high-quality sandhill plots were sampled to establish reference conditions. Pre-treatment diameter distributions of oaks followed a negative-exponential curve in all treatments, but were¯at with low tree densities in reference plots. Oak densities were signi®cantly reduced in the herbicide and felling/girdling plots in 1995. Compared to the controls, growing season ®re topkilled up to 20% more hardwoods among smaller trees in 1995, but this value increased to approximately 50% after 1996. In all years, the greatest reduction of oak juvenile density (<1.4 m high) was caused by herbicide application. Control plots contained signi®cantly fewer oak juveniles than the burn and felling/girdling plots. Reference plots contained the lowest and most variable oak juvenile densities. Size distributions of longleaf pine across all plots were bimodal with modes at 0±4.9 and 25±29.9 cm in diameter. The highest mode was at 0±4.9 cm in treatment plots and at 25±29.9 cm in reference plots. Only ®re quantitatively changed the 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 converged to 5±6 stems/200 m 2 in all treatments, including the control. Juvenile densities were slightly higher and more variable in reference plots than in treatments. In 1997, fuel reduction burns in the herbicide and felling/girdling plots decreased densities of recently germinated longleaf pines to <5 seedlings/20 m 2 , a 90% decrease compared to 1996 densities. Seedling densities dropped by approximately 50% in control and burn plots, although these sites received no manipulations after 1995. Seedling densities only decreased by 22% in reference plots (205 seedlings/20 m 2 in 1996), which did experience some ®res. #
Examines the role of prescribed fire in the restoration of longleaf pine forests. Longleaf pines ... more Examines the role of prescribed fire in the restoration of longleaf pine forests. Longleaf pines at Eglin Air Force Base in Florida; How fire influences the effects of a hurricane on stand structure of longleaf pines; Impact of prescribed fires on the plant, arthropod, herpetofauna and bird communities of burned plots
We tested whether the intensity of hardwood midstory reduction causes commensurate improvements o... more We tested whether the intensity of hardwood midstory reduction causes commensurate improvements of herbaceous groundcover in fire-suppressed Pinus palustris (longleaf pine) sandhills. Using a complete randomized block design, we compared the effects of three hardwood reduction techniques (spring burning, application of the ULW ® form of the herbicide hexazinone, chainsaw felling/girdling) and a no-treatment control on plant species richness, and on life form and common species densities at Eglin Air Force Base, Florida, U.S.A., from 1995 to 1998. ULW ® and felling/girdling plots were burned for fuel reduction two years after initial treatment application. We also sampled the same variables in frequently-burned reference sandhills to establish targets for restoration. Spring burns achieved partial topkill of oaks (17.6-41.1% from 1995 to 1998) compared to reductions of 69.1-94% accomplished by ULW ® and of 93.2-67.8% by felling/girdling treatments. We predicted that plant species richness and densities of herbaceous groundcover life forms would increase according to the percent hardwood reductions. Predictions were not supported by treatment effects for species richness because positive responses to fire best explained increases in plant richness, whereas ULW ® effects accounted for the largest initial decreases. Legumes, non-legume forbs, and graminoids did not respond to treatments as predicted by the hypothesis. Again, positive responses to fire dominated the results, which was supported by greater herbaceous densities observed in reference plots. Overall, we found that the least effective and least expensive hardwood midstory reduction method, fire, resulted in the greatest groundcover improvements as measured by species richness and herbaceous groundcover plant densities.
Previous studies on the influence of endothelial seeding on graft patency have shown that signifi... more Previous studies on the influence of endothelial seeding on graft patency have shown that significant improvement has only been achieved with Dacron and an experimental, porous PTFE graft. Methods of assessing patency or showing statistical significance could be questioned in some of these studies. To determine if the combination of endothelial cell seeding and antiplatelet agents would improve patency in small-diameter, commercially available expanded polytetrafluorethylene (ePTFE) grafts, we placed ePTFE grafts into the left carotid position in two groups of mongrel dogs. All grafts were 4 mm internal diameter and 60 mm long, and were interposed in an end-to-end fashion. Both groups received aspirin (80 mg daily) and dipyridamole (25 mg daily) for 14 days, beginning immediately prior to surgery. In Group I (n = 12), the grafts were seeded with enzymatically harvested autogenous endothelium just prior to implantation; in Group II (n = 10) the grafts were not seeded. All grafts were...
Across much of the southeastern U.S.A., sandhills have become dominated by hardwoods or invasive ... more Across much of the southeastern U.S.A., sandhills have become dominated by hardwoods or invasive pine species following logging of Pinus palustris (longleaf pine) and fire suppression. At Eglin Air Force Base where this study was conducted, Pinus clausa (sand pine) has densely colonized most southeastern sandhill sites, suppressing groundcover vegetation. The objectives of this study were: to determine if suppressed groundcover vegetation recovers following the removal of P. clausa ; to compare species composition and abundance in removal plots with that in reference, high quality sandhills; to test the assumption that recolonization by P. clausa seedlings decreases with proximity to the centers of removal plots; and to measure the survival of containerized P. palustris seedlings that were planted on P. clausa removal plots. One year post-removal (1995), the number of plant species decreased by 50%, but then increased by 100% from 1995 to 1997, followed by a small reduction in 1998. The number of plant species was greater in reference plots than in removal plots prior to 1997. Eighty-five percent of the original species were recorded 4 years post-harvest in removal plots. Shrubs and large trees remained at low density after harvest. Densities of graminoids, legumes, other forbs, woody vines, and small trees increased after harvest. Plant densities of all life forms, except woody vines, were greater in reference plots than in removal plots. The density of recolonizing P. clausa seedlings 2-4 years post-harvest significantly decreased with increasing proximity to the centers of removal plots. On average, 80% of planted P. palustris seedlings survived their first 2 years. Harvest of P. clausa followed by fire and the planting of P. palustris is a reasonably effective restoration approach in invaded sandhills . However, supplementary plantings of some herbaceous species may be necessary for full restoration.
Restoring ®re-suppressed longleaf pine (Pinus palustris Mill.) sandhill communities often include... more Restoring ®re-suppressed longleaf pine (Pinus palustris Mill.) sandhill communities often includes reducing hardwood structure before re-establishing maintenance ®re regimes. Using a randomized complete block design, we compared the effects of three hardwood reduction techniques (spring burning, application of the ULW 1 form of the herbicide hexazinone, and midstory chainsaw felling/girdling) and a no-treatment control on oak and longleaf pine densities in ®re-suppressed sandhills at Eglin Air Force Base, FL. Treatments were applied in the spring and summer of 1995. Felling/girdling and herbicide plots were also burned for fuel reduction from March to April in 1997. Frequently burned, high-quality sandhill plots were sampled to establish reference conditions. Pre-treatment diameter distributions of oaks followed a negative-exponential curve in all treatments, but were¯at with low tree densities in reference plots. Oak densities were signi®cantly reduced in the herbicide and felling/girdling plots in 1995. Compared to the controls, growing season ®re topkilled up to 20% more hardwoods among smaller trees in 1995, but this value increased to approximately 50% after 1996. In all years, the greatest reduction of oak juvenile density (<1.4 m high) was caused by herbicide application. Control plots contained signi®cantly fewer oak juveniles than the burn and felling/girdling plots. Reference plots contained the lowest and most variable oak juvenile densities. Size distributions of longleaf pine across all plots were bimodal with modes at 0±4.9 and 25±29.9 cm in diameter. The highest mode was at 0±4.9 cm in treatment plots and at 25±29.9 cm in reference plots. Only ®re quantitatively changed the 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 converged to 5±6 stems/200 m 2 in all treatments, including the control. Juvenile densities were slightly higher and more variable in reference plots than in treatments. In 1997, fuel reduction burns in the herbicide and felling/girdling plots decreased densities of recently germinated longleaf pines to <5 seedlings/20 m 2 , a 90% decrease compared to 1996 densities. Seedling densities dropped by approximately 50% in control and burn plots, although these sites received no manipulations after 1995. Seedling densities only decreased by 22% in reference plots (205 seedlings/20 m 2 in 1996), which did experience some ®res. #
Examines the role of prescribed fire in the restoration of longleaf pine forests. Longleaf pines ... more Examines the role of prescribed fire in the restoration of longleaf pine forests. Longleaf pines at Eglin Air Force Base in Florida; How fire influences the effects of a hurricane on stand structure of longleaf pines; Impact of prescribed fires on the plant, arthropod, herpetofauna and bird communities of burned plots
We tested whether the intensity of hardwood midstory reduction causes commensurate improvements o... more We tested whether the intensity of hardwood midstory reduction causes commensurate improvements of herbaceous groundcover in fire-suppressed Pinus palustris (longleaf pine) sandhills. Using a complete randomized block design, we compared the effects of three hardwood reduction techniques (spring burning, application of the ULW ® form of the herbicide hexazinone, chainsaw felling/girdling) and a no-treatment control on plant species richness, and on life form and common species densities at Eglin Air Force Base, Florida, U.S.A., from 1995 to 1998. ULW ® and felling/girdling plots were burned for fuel reduction two years after initial treatment application. We also sampled the same variables in frequently-burned reference sandhills to establish targets for restoration. Spring burns achieved partial topkill of oaks (17.6-41.1% from 1995 to 1998) compared to reductions of 69.1-94% accomplished by ULW ® and of 93.2-67.8% by felling/girdling treatments. We predicted that plant species richness and densities of herbaceous groundcover life forms would increase according to the percent hardwood reductions. Predictions were not supported by treatment effects for species richness because positive responses to fire best explained increases in plant richness, whereas ULW ® effects accounted for the largest initial decreases. Legumes, non-legume forbs, and graminoids did not respond to treatments as predicted by the hypothesis. Again, positive responses to fire dominated the results, which was supported by greater herbaceous densities observed in reference plots. Overall, we found that the least effective and least expensive hardwood midstory reduction method, fire, resulted in the greatest groundcover improvements as measured by species richness and herbaceous groundcover plant densities.
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