Sources of Regeneration
On most hardwood sites, natural regeneration will be sufficient to replenish the stand. Go through a stand before the harvest cut to see if you have enough seedlings, seedling sprouts, root sprouts, or stump sprouts of the desired species to develop into an adequately stocked stand once the overstory is removed. Tolerance of species to shade, and whether the species is heavy or light seeded, will govern the steps to be taken to start a new stand.
Intolerant, light-seeded species such as yellow-poplar, ash and cottonwood will regenerate themselves from seed if the seedbed conditions are favorable and sunlight is available. Seed from species such as yellow-poplar and ash remain viable on the forest floor for several years and are usually plentiful if these species were present before harvest. Also, birds, animals, and wind transport seeds from nearby stands. Logging activity is usually sufficient to scarify the forest floor and provide the mineral seedbed needed for germination. Removal of the overstory and brush will enable sunlight to reach the forest floor, helping the light-seeded species to germinate and grow fast enough to compete with other plants. Usually, seed trees need not be left on hardwood sites.
When regenerating heavy-seeded species of intermediate shade tolerance, such as the oaks, well established seedlings should be in the understory at the time of harvest. These seedlings develop after germination under the shade of the forest canopy. Many seedlings die quickly, others die back and resprout, but some endure under closed canopies for several years, and are called advance regeneration. Their top growth may be very slow, but the root system continues to develop.
Advance regeneration is particularly important for oaks because new seedlings are produced sporadically, and grow too slowly to compete successfully with other species. Oak saplings, 4 to 5 feet in height, with well developed root systems, are most desirable as advance regeneration. These young trees will respond quickly and vigorously to sunlight after the harvest cut, and should grow fast enough to compete with other species. Logging usually does not harm advance regeneration because sprouts will grow vigorously from the root collars of saplings and seedlings that are broken or cut during harvest.
Young hardwood stands almost always contain some stump sprouts, and occasionally entire stands can develop from stump sprouts. Because of their vigorous early growth, stump sprouts often dominate other forms of reproduction. The quality and longevity of trees resulting from stump sprouts are sometimes questioned, but stems that start from small stumps below or near the ground line are usually good risks. Stump sprouts from yellow-poplar often produce the best trees in the stand. Most hardwoods also produce root sprouts. Species such as black locust and sassafras produce them prolifically and may regenerate almost entirely from root sprouts.
Cutting Methods
The total removal of the canopy in one cut, called clearcutting, is an effective and efficient method to naturally regenerate a hardwood stand. Clearcutting provides the best conditions for fastgrowing, shade-intolerant species that need full sunlight to develop rapidly. Some shade-tolerant species also do well under these conditions. Total canopy removal results in an even-aged stand.
The commercial timber harvest will remove much of the canopy - and the cleaner the logging job the better. In most cases, however, culls, low quality trees, undesirable species, and some small trees will be left. Cut or kill these remaining trees so they will not impede regeneration. You may control this unmerchantable material by several methods. A combination of felling and herbicide injection could be used. Trees of desirable species that produce sprouts could be felled, and undesirable species could be injected. Undesirable trees may be controlled before or after the commercial logging operation. The method and timing are less important than making sure that unwanted trees are treated, especially stems larger than 4 inches in diameter.
In some stands, grapevines may interfere with seedling growth. Grapevines are intolerant of shade and, if cut 3 to 4 years before the timber harvest they should not be a problem in the new stand.
The size of the regeneration opening depends on your overall management objectives. Areas as small as 1/2acre can be used, but development of such small tracts will be impeded by side competition and over-browsing by deer. Also, such small tracts are inefficient to manage. Openings several acres in size usually can be managed more efficiently and with fewer residual trees affected by degrade on the edge of the openings.
Good hardwood regeneration has developed from the shelterwood regeneration method. A series of treatments are involved: (1) partly cut the overstory to leave 50 to 60 square feet of basal area per acre, (2) cut, or inject herbicide in the unmerchantable understory trees at the time of the first cut, (3) a few years after the first cut, make a secondary cut - which would be a final harvest cut if regeneration is satisfactory, or cut the stand back to 40 to 50 feet of basal area again if regeneration needs to develop further under shelter. In the latter instance, a third, final harvest cut would be made.
The shelterwood method also produces an even-aged stand. The sources of regeneration can be the same as in a clearcut, but they depend somewhat less on seed and seedlings already in place before any cutting is done. In most cases, leaving a shelterwood has few biological advantages, but it can be used to help develop advance regeneration.
The shelterwood method of regeneration cutting should not be confused with the occasional removal of the biggest and best timber trees - or high grading. When you make partial cuts to regenerate a stand, treat unmerchantable understory trees, and remove the remaining overstory when regeneration reaches a satisfactory stage. High grading produces neither of these goals and badly detracts from long-range growth potential.
Removal of single trees scattered throughout the stand, as a regeneration method, generally has not proved to be an effective way to regenerate the hardwoods of the South. Most desirable southern hardwoods have little tolerance of shade. They will begin to develop under partial shade, but they should be released from overhead competition fairly early in life. The biggest drawbacks to single-tree selection are that the method fails to provide for quick and orderly removal of overhead competition and it promotes the development of shade-tolerant species, many of which are not desirable.
Planting Hardwoods
Hardwood seedlings account for about 1% of the total seedlings produced in southern nurseries. The highest species production is for black locust, sycamore, cottonwood, eucalyptus, sweetgum, black walnut, yellow-poplar, green ash, white ash, and water-willow oak.
Black locust is planted primarily for erosion control. The rest are planted most often by industry on clean tilled land where they are cultivated two to four times during each of the first 2 years in the field.
Black walnut and yellow-poplar are the two preferred species for planting on small ownerships in the Piedmont, the extreme upper Coastal Plain and farther north. Both species are quite site specific. Fastest growth occurs on stream terraces, in coves, and on lower north- and east-facing slopes. The soil should be deep, fertile, and well drained. If yellow-poplar trees of seed bearing age were present in the harvested stand, then planting is usually not necessary.
Hardwood seedlings should be large, with a root collar diameter of at least 1/8 inch, a live terminal bud, and a well developed root system. Black walnut and yellow-poplar can be planted with a bar or mattock, taking care to avoid doubling or twisting the roots. Control herbaceous plants until the tree seedlings have outgrown the weeds. Inject woody plants with a registered herbicide. Planting on a spacing of 10 by 10 feet permits cross cultivation where feasible. Yellow-poplar will prune itself at such a spacing unless many of the seedlings die. Start pruning the black walnut when it is about 5 years old.
The three most important points to remember when planting hardwoods are: (1) Selecting the planting site. Be sure that the species is suited to the site. (2) Plant only large, healthy seedlings, with an adequate root/top ratio. (3) Be prepared to control competing plants until your tree seedlings are well established and free to grow.
Direct Seeding Hardwoods
Another option for establishing oaks is direct seeding of acorns. Research indicates that oaks can be successfully regenerated from properly stored acorns sown any month of the year either by hand or machine.
Good results are reported from sowing freshly collected or properly stored untreated acorns of Nuttall, cherrybark, Shumard, and water oaks. Nuttall consistently gives the best results. Satisfactory results are generally expected from direct seeding these favored bottomland oak species if the following suggestions are heeded:
- Reduce animal predation by seeding 2-acre or larger forest openings or old fields relatively free of competing vegetation.
- Match species to site. Sow Shumard and cherrybark on welldrained sites. Sow Nuttall oak on heavy clay sites subject to flooding from January through mid-May. Water oak is more flood tolerant than cherrybark, but less than Nutall.
- Collect acorns soon after seedfall. They can be stored in 4 mil polyethylene bags at about 35F. Red oak acorns can be stored up to 3 years, but should be tested for moisture content every 3 or 4 months. Red oak acorns should be kept at 40-to 45-percent moisture content.
- Acorns can be sown at any time of the year.
- A sowing depth of 2 to 3 inches is best.
- Sow acorns by hand or with modified mechanical agricultural planters.
- Sowing rate should be about 1,500 acorns per acre at a spacing of 10 x 3 feet to facilitate between-row weed control if needed. Even without weed control, direct-seeded oak will continue to grow if they have direct overhead sunlight.
