Seedling stands (in which the trees' stems are less than 1 inch in diameter) typically have large numbers of very small trees that face fierce competition from herbaceous and woody plants, extreme weather, pests, and heavy equipment operations in the stand. Herbaceous plants, shrubs, and trees compete with the tree seedlings for sunlight, moisture, and nutrients. Removing or reducing this competition may be necessary to ensure seedling survival and growth.
Seedling release can be done manually by hoeing or mulching, mechanically by mowing or cultivating, or chemically by using herbicides. For any of these, you must be able to locate the tree seedlings among their competition. If you are planting seedlings where you may need to do follow-up weed and brush control within a year, place a wire flag next to each seedling or periodically along the tree rows to help you locate the seedlings later.
Mowing is practical on old field plantations where trees are in straight rows with regular spacing, but mowing must be done frequently and it still allows weeds and woody brush to survive. Some form of cultivation offers better weed control than mowing. Hand hoeing weeds is practical only when you have just a few seedlings to manage. Cultivate field plantings with a tractor-drawn rotary hoe, harrow, disk, or in-row tiller such as a Weed Badger, Kimco, or Green Hoe. Seedling damage may occur if the tillage equipment cuts any seedling roots or if the equipment runs over seedlings due to operator carelessness or irregular tree spacing. Wet ground may prevent either mowing or cultivating when they are needed the most. You can use a hand-held brush hook or motorized brush saw to cut small woody shrubs and trees in small areas, but remember that many species, especially hardwoods, will resprout after cutting.
Mulch is usually effective at controlling weeds and conserving soil moisture. Its moisture conserving benefit is most helpful on the prairie and woodland fringe where precipitation is a limiting factor for tree growth. Many types work, including sheets of plastic or woven fabric, wood chips, straw, ground corncobs, paper sacks, or other organic materials. Mulch is difficult to transport and apply, so it may be appropriate only for relatively small plantations in open fields. Organic mulches may provide habitat for small rodents that can eat bark off trees in the winter.
The most common method of releasing seedlings from herbaceous or woody competition is to use herbicides. Usually a single application provides season-long control. Herbicides may be applied aerially or from the ground. Ground application using backpack or hand-held sprayers is more common on small plantations. For larger plantations, spray equipment can be mounted on skidders or other large equipment. Herbicides may be applied in spots around trees, in bands down tree rows, or be broadcast across an entire area. Spot and band treatments leave some herbaceous vegetation to help control soil erosion.
Select an herbicide labeled for the types of plants to be killed and those to be protected. Read the label carefully and follow the directions for application rates, timing, and precautions to take. Different herbicides kill vegetation in different ways. Some are growth regulators, while others destroy chlorophyll or essential plant tissues. Herbicides must be applied at a time when the target species are most susceptible. When applying herbicides by hand in hardwood plantings, hold a shield around important seedlings to prevent herbicide contact. To protect hardwood seedlings that resprout readily (such as oak), cut them off at ground level before applying herbicide to the area. They will sprout again after the herbicide danger has passed.
Use caution when applying herbicides so that spray does not drift onto adjacent areas or contaminate surface or ground water. Use drift-control additives if there is any possibility of wind-drift. Soil-activated herbicides can flow downslope and kill nontarget vegetation. Carefully observe environmental protection warnings on the label and maintain adequate buffer strips near water and nontarget areas.
Seedlings and saplings also may need liberation–?the removal or killing of large, undesirable trees that would interfere with the development of a new stand beneath the canopy. (See ?"Deadening Unmerchantable Trees?" on pg. 50.)
Tree shelters are hollow tubes about 4 to 6 inches in diameter and 2 feet to 6 feet tall that are placed over seedlings and held in place by stakes. Each seedling requires its own shelter, so they are expensive and cumbersome to install, but you can remove and re-use them.
Plastic shelters create a miniature greenhouse over each seedling that raises the humidity and carbon dioxide levels to increase the rate of tree height growth. They also may increase tree survival on difficult planting sites with low rainfall. When held snug to the ground, they keep rodents away from seedlings. Tall shelters prevent deer browsing?\one of their most useful purposes. Hollow tubes may attract birds that fall inside and cannot escape, but placing a plastic net over the top of the tube will keep birds out. Shelters should be left in place until trees have grown through the top of the shelter. Shelters designed (and installed) to prevent rodent damage near the ground should be left until bark is thick enough to resist rodent damage. However, non-biodegradable shelters must be removed once trees have outgrown them in order to prevent damage or even tree death.
Woven wire shelters held in place by stakes protect seedlings from deer and rabbit browsing, but do not modify the atmosphere around the seedlings. Where equipment will be operated to harvest mature trees, desirable tree seedlings must be protected from damage as much as possible. Strategies to protect the seedlings might be to: