Sounds like you probably have a Trimble?
I have a $400 hand-held Garmin to put trees (and stumps) into data bases for my consulting work. I still find that I have to match aerial photos with on-the-ground photos if I am to match tree numbers to the little green lumps in the aerial (for an illustration). I have gotten down to +/-10 ft. at times with the Garmin, but usually it is between +/-15-20--or even worse on steep ground. Then again, if you are collecting GPS coordinates to just get near the tree on the ground, and then walk up to it and visually check it's ID (by species, diameter, and perhaps a tag) it doesn't really matter.
For a recent job, I tried to use a laser (LaserAce) to triangulate the locations of trees, but it was way too slow, and nearly impossible on a steep slope with brush (where I was trying to make a stump map, for the most part for an appraisal after a fire and AFTER most trees had been cut, on steep brushy ground as well -- why do they wait to call until after cutting?!!:bang
. So I used the Garmin and took lots of photos with stakes by the stumps, and also sketched the scene with the stakes numbered; that way I could label photos shot on the ground, and my illustrations (maps) based on the aerial photos.