From the U.S. Forest Service Jellico Vegetation Management project documentation:
CROP TREE RELEASE
This treatment releases desired trees in the dominant and co-dominant crown classes that are vigorous, exhibit healthy crowns, and have good form. The number of crop trees is determined on a stand-by-stand basis, as older stands generally have a lower number of crop trees per acre than younger stands. The species preference for crop trees in order is as follows: white oak, northern or southern red oak, chestnut oak, post oak, hickories, black oak, black walnut, yellow poplar, other hardwoods. Undesirable competing vegetation within four feet of the crowns of desired trees would be cut and left on the ground and/or treated with herbicide.
PRE/POST HARVEST SITE PREPARATION
This treatment consists of preparing a stand for natural regeneration and/or planting. It is conducted immediately before or after all clearcuts, two aged shelterwoods, and deferment harvests. All undesirable species (e.g., red maple), trees not selected for retention, non-merchantable material (i.e., trees smaller than 8 inches diameter at breast height), and any trees competing with desired regeneration are cut and/or treated with herbicide.
MIDSTORY REMOVAL
Midstory control is a treatment whereby trees in the midstory that are preventing sunlight from reaching desired regeneration on the forest floor are cut and/or treated with herbicide. This allows for increased growth of desired regeneration.
GRAPEVINE CONTROL
Where the presence of excessive grapevine is inhibiting tree growth across a stand, this treatment is employed. Grapevines are cut and/or treated with herbicide. This treatment is usually carried out in conjunction with other intermediate treatments such as site preparation, midstory removal, crop tree release, and invasive species control. It can also be independent.
INVASIVE SPECIES CONTROL
This treatment consists of manual and/or chemical treatment of native and non-native invasive species wherever they are detected. This treatment is carried out independently and in conjunction with other intermediate treatments. High priority areas would be roadsides and stands proposed for treatment.