Restoring longleaf pine wiregrass ecosystems: plant cover, diversity and biomass following low-rate hexazinone application on Florida sandhills

Abstract

A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wildfire, was treated with low-rate (1.1 or 2.2 kg/ha) applications of the herbicide hexazinone during the 1991 growing season. All applications successfully reduced oak in the overstory and understory, mortality ranging from 83 to 93%. The declining competition from oaks was associated with progressive increases in foliar cover of wiregrass, all graminoids and forbs over time. Plant species diversity declined in the initial year, but recovered by the second growing season. Species richness increased overall, while evenness declined with the continuing expansion of wiregrass. Initial increases in the standing biomass of wiregrass did not persist beyond the second growing season. The broadcast application method exposed a greater number of understory plants to contact with hexazinone, resulting in initial declines in forb cover, species richness and diversity. Although recovery was noted in subsequent years, because of lower selectivity this broadcast application method is not recommended as a restoration technique. Spot application of liquid hexazinone was generally more selective in its effect upon the plant community. The 1.1 and 2.2 kg/ha application rates, while producing an initial year reduction in diversity and evenness, resulted in increases in the cover of all graminoids and forbs and the highest species richness. While both application rates are useful, the 2.2 kg/ha application is most effective in controlling woody plant competition and stimulating increases in wiregrass and is therefore recommended for restoring xeric sandhills and similar longleaf pine wiregrass ecosystems.