I think you will find it difficult to kill all the volunteer loblolly with nothing but fire. I've got one area that I have burned 8 times in the past 12 years. There were several log landings on it that were just solid small pines when I started the burning program and they all still have solid stands of small pines. The fire thinned them out and the ones remaining have gotten bigger, but I haven't been able to kill them all. I think you will need to have a really hot fire during the growing season to wipe out all of them.

I have another area of about 5 acres that was clearcut in 1999 and grew up in a really thick stand of volunteer loblolly. I thinned the stand with a dozer and a chainsaw, but the stand is still thicker than it should be. I've run several hot fires through it over the past 5 years and the ground under it is very open now. It used to be great bedding for deer, but not now. Even if I hadn't thinned it, the understory would still be open now due to the fire and the shading by the trees. Of course, I wanted it to be open and wasn't concerned with deer bedding, but I think the same thing would happen on your spot if you just cool season fire.

To keep it good bedding, you either need to do like NH said and use herbicide, or you need to run a really hot fire through it during the growing season every few years. If you don't kill the trees, they are eventually gonna get big enough to start shading the ground and killing your good cover plants.

Good luck with it.