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.

No abstract

No abstract

The effects of shoot damage on starch concentrations in large roots and lower boles of the tropical timber tree, Cedrela odorata, were measured over a 30-day period following mechanical shoot removal. The degree of damage was based on amounts typically destroyed by Hypsipyla grandella, a serious lepidopteran pest of C. odorata. From 14-monthold plantations at La Selva Biological Station, Costa Rica, three treatments were established based on the length of shoot and number of leaves removed: controls (no tissue removed), moderate damage, and severe damage. Initial starch concentrations were compared with concentrations observed 18 to 30 days following shoot removal using enzymatic starch hydrolysis and colorimetry. Root starch concentrations increased in undamaged trees, decreased slightly in the moderately damaged trees, and decreased markedly in severely damaged trees during the sampling period. Starch concentrations in lower boles did not decrease following shoot damage, suggesting a specific role of root starch reserves in responding to aboveground carbon requirements. The dry weights of regrown shoots were similar for the moderately and severely damaged trees, but severely damaged trees produced numerous basal shoots while moderately damaged trees produced only one or two terminal shoots near the point of excision. Decreases in root starch concentrations following shoot damage and rapid shoot regrowth suggest that starch remobilization in roots of C. odorata might provide a survival mechanism after attack by H. grandella.

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.