2-YEAR DEVELOPMENT OF SOUTHERN PINE-SEEDLINGS AND ASSOCIATED VEGETATION FOLLOWING SPRAY-AND-BURN SITE PREPARATION WITH IMAZAPYR ALONE OR INMIXTURE WITH OTHER HERBICIDES

Eight herbicide combinations containing imazapyr alone or in mixture w ith glyphosate, triclopyr, or picloram+2,4-D were applied July-August 1991 at each of three upland sites in the southeastern U.S., with or w ithout a subsequent broadcast burn in September. Seedlings of loblolly (Pinus taeda L.) or slash (P. elliottii Engelm. var. elliottii) pine were planted that winter. Second-year (August 1993) vegetation respons es indicate that broadcast burning, in combination with herbicides, wa s associated with increased abundances of grasses, forbs, and shrubs a nd decreased abundances of vines and hardwood trees. In the presence o f burning, imazapyr-in-mixture treatments were associated with a high abundance of grass (53% cover) and a mean size of pines less than that of seedlings growing in imazapyr-alone treatments. In the absence of burning, imazapyr-alone treatments were associated with a high abundan ce of blackberry (21% cover), an average height of hardwoods (131 cm) exceeding that of pines (71 cm), and a mean size of pines less than th at of trees growing in imazapyr-in-mixture treatments. Hardwood height in the absence of burning was less when imazapyr was combined with gl yphosate (75 cm) than with triclopyr (102 cm). Regardless of the prese nce or absence of burning, size of pines and abundance of shrubs and h ardwoods did not differ between imazapyr rates of 0.56 and 0.84 kg aci d equivalent/ha or among herbicides applied in mixture with imazapyr.