The sprouting and seeding potential of hardwoods is significant and can generally be relied upon to naturally regenerate stands. While hardwood stands are self regenerating, hardwood owners should be concerned about the quality and potential value of the regeneration. For many of our important and highly valued species their successful regeneration requires opening the canopy allowing partial or full sunlight to reach the forest floor. This influx of light spurs regeneration. Most regenerating hardwood stands can easily produce 2000-3000 sapling sized trees 10 years after a regeneration harvest. However, hardwood management is about producing a limited number of high valued trees per acre, not a large number of low quality trees. A fully stocked stand of 3,000 sapling sized trees of a low valued species results in a low value forest. While the same regenerating stand, containing 100 to 200 competitive saplings of a high valued species provides the basis for reaping significant benefits in the future. The goal for hardwood regeneration is to ensure that 10 to12 years after the regeneration harvest the stand contains adequate numbers of saplings, typically between 100 and 200, that are of a preferred species and that are as tall, or taller than, competing trees. At this point, crop-tree release, followed by commercial thinning, can be used further enhance their growth and development. In the end this condition leaves a hardwood owner with a fully stocked stand of 50 to 60 high value sawtimber sized trees per acre.    

There are occasions when supplemental planting is required to maintain good species composition. However, due to the cost of artificial regeneration the majority of forest forest owners rely upon natural regeneration for establishing their next hardwood forest. It is therefore important that hardwood owners recognize that assessing the natural regeneration potential prior to scheduling a regeneration harvest is important. The assessment provides information that is necessary to make intelligent decisions regarding whether a regeneration harvest should be undertaken at the present time. It also helps determine if any pre- or post-harvest treatments are needed to change species composition of the regenerating age class. The key is to make sure that adequate numbers of the proper species are naturally regenerated and evaluation of the regeneration potential prior to a harvest is required.       

How Hardwoods Regenerate

Successful regeneration of hardwoods using natural reproduction requires that stands are capable of providing an adequate number of regenerating trees of the proper species. While this goal applies to any forest type including pine, the manner in which it is achieved varies by forest type. Hardwood species can successfully regenerate new trees through:

• sprouts from stumps that were produced from the cutting of trees 2 to 10 inches in diameter (stump sprouts)
• the release of seedlings and saplings there are present in the stand prior to the regeneration cut (advance regeneration)
• sprouting of roots (root suckers)
• the development of new seedlings from seed already present in the forest floor prior to harvest (seek bank)
• seed that is deposited onto the site after the regeneration harvest.

Each hardwood species uses one or more of these reproduction types to create new trees in the regenerating stand. However, there is a difference in the success rate of each of these reproductive types that is species dependent. For example, yellow-poplar can easily regenerate from seed that accumulates in the duff layer for 3 to 7 years before a harvest and seed that is deposited onto the site directly after a regeneration harvest. Oaks do not accumulate seed in the forest floor (acorns must germinate right away or they perish). The probability that a seeding developing from an acorn at the time of harvest will survive to become a canopy tree in the next forest is close to zero. Oaks must have advance regeneration or stump sprouters present in the stand to successfully regenerate (see Forest Landowner 63(4) for a full explanation of oak regeneration).

Assessing and Predicting Hardwood Regeneration

If the forest owner wishes to know or control the species that the stand will contain after a regeneration harvest, then a thorough assessment of the regenerative potential, by species, must be accomplished prior to a harvest. Table 1 provides a list of common species and the type of reproduction that is generally required for that species to regenerate new trees capable of competing and growing into canopy trees in the next forest.        

Assessing the stand for its regenerative potential requires that data on each of the regenerative types, numbers of stump sprouters, advance regeneration, and seeding potential by species is obtained. The table indicates what regeneration type needs to be assessed for the species that are present.

In some cases an experienced visual inspection of the stand can provide a good assessment of the regeneration potential. In other cases plots must be established and data collected to assess the regeneration of the site. Typically, these plots are 1/100 acre in size and distributed throughout the stand, generally one or more per acre. In each plot a tally by species is completed of all:

• advance regeneration (typically trees from 2 feet in height up to 1.5 inches in dbh in bottomland sites and 4 feet in height to 1.5 inches dbh on upland sites)
• trees 2 to 10 inches in dbh that could stump sprout (stump sprouters).

Information is also recorded on the presence of species in the stand, or directly surrounding the stand, that could provide seed that has the capability of germinating and developing a competitive seedling. This could come from seed build up in the forest floor, seed from residual trees left in the stand after the regeneration harvest, or seed that is deposited from surrounding trees by wind or animals (mainly birds). Yellow-poplar is an example of wind deposited seed and black cherry is an example of bird disseminated seed, both species capable of developing competitive seedlings at the time of harvest. The occurrence of species in the stand that root sucker is also required.

The data and information collected in this procedure would include plot information on the number of advance regeneration that are large enough to potentially produce a sapling sized tree in the regenerating stand and stump sprouters, and the occurrence in the entire stand of species that can contribute competitive regeneration from seed or root sprouts. Foresters can use this information to estimate the dominate species (usually up to five species) that will be present in the regenerating stand and also the number of interfering trees that need to be either removed from the stand so that they do not interfere with the growth and development of the regenerating forest. Foresters can also use this data to determine if there will be an adequate number of high valued species present in the regenerating stand. This is really the important issue, ensuring that the stand will regenerate at least a minimum number of preferred species that can be competitive and occupy a dominant canopy position at age 10 to 12.  

Example of the Use of a Regeneration Assessment

The following is an example of a regeneration assessment prior to the harvest of a 20 acre tract. Approximately 10 acres is comprised of an oak dominated hillside and hill top area and 10 acres is a mixed yellow-poplar, red oak, and beech hollow and bottom site. Twenty regeneration plots, one per acre, are distributed through the tract. The yellow-poplar present in the hollow and bottom will ensure adequate yellow-poplar regeneration in these areas if the canopy is fully removed. However, in every plot in this area there were found at least one beech tree between 2 and 10 inches in size representing at least 100 beech trees per acre that can overshadow the regenerating trees, or if cut their sprouts can interfere with the regeneration of preferred species. There were also noted at least 10 large beech trees in this area that can produce trees from root suckers. Based on this it was decided to go in prior to the harvest and chemically deaden both the large and the 2 to 10 inch beech trees. This will reduce the stump and root sprouting of this species and provide more growing space for preferred species. Even though the overstory in this part of the tract contained good red oak there were only a few small advance regeneration sized seedlings and no stump sprouting sized trees. This indicates that red oak will not regenerate at this time. The forest owner then must decide if a yellow-poplar dominated stand is acceptable for this area. If not, then the regeneration harvest must be postponed to provide time to develop adequate oak advance regeneration to ensure that red oak is maintained in the stand (See Forest Landowner 64(2) and (3) for an overview of the oak shelterwood system.). In the oak hillside and hilltop area 4 of the plots contained at least one 2 to 10 inch oak. If cut during or after a regeneration harvest these stumps will yield vigorous sprouts that can be counted on to produce competitive saplings. The data indicate 40 of these saplings will be present per acre. Four of the plots also contained at least one black cherry advance regeneration sized tree. The forester estimated that half of these advance regeneration trees will produce competitive saplings for a total of 20 per acre. The data also indicated that another 40 saplings per acre will be produced through a combination of ash, yellow-poplar and sugar maple. This is a total of 100 saplings per acre of oak, black cherry, ash, yellow-poplar and sugar maple. Based on this estimate the forester recommends regeneration. However, the data also indicated that a large number of red maple and elm stump sprouters and advance regeneration exist. Also sassafrass trees are present in an around this part of the tract. It was determined that after the regeneration harvest the remaining red maple and elm trees would be surveyed and if enough were present to hinder regeneration they would be chemically treated to prevent them from interfering with the preferred regeneration. It was determined that the sassafras trees would be chemically treated prior to harvest to reduce stump sprouts.

The end result of the regeneration assessment indicates that if a regeneration harvest was to be completed then chemical treatment of beech and sassafras prior to the harvest was in order and the tract assessed for interfering red maple and elm after harvest. The result would be a 10 acre stand of yellow-poplar with 10 acres of mixed oak, ash, cherry saplings that could be released after the stand reached sapling size. The landowner realizes that by implementing the regeneration harvest now the amount of high quality red oak regenerating in the hollow and bottom will be minimal.

While natural hardwood regeneration is plentiful, quality hardwood regeneration can not be taken for granted. Assessment of the natural regeneration potential and estimation of the species composition of the regenerating stand should be undertaken. The data from this evaluation can be used to provide options to the hardwood owner on the timing and treatments, if any, needed to produce a successful high value hardwood stand.

Clatterbuck, W.K. 2004. Guidelines for managing trees that develop from sprouts. Forest Landowner 63(3):14-15.

Dubois, M.R.1996. Management of Hardwood Forests for Timber in Alabama. Alabama Cooperative Extension Program. Auburn University ANR-0581: 4pp.   

Morehead, D.J., and K.D. Coder. 1994. Southern Hardwood Management. USDA Forest Service, Management Bulletin R8-MB 67. 142pp.

Stringer, J.W. 2004. Assessing Oak Regeneration. Forest Landowner 63(4): 27-29.

Stringer, J.W. 2005. Oak Shelterwood: the basics of a new system used to naturally regenerate oak. Forest Landowner 64(2):48-49.

Stringer, J.W. 2005. Oak Shelterwood: how to apply the system to stimulate oak regeneration. Forest Landowner 64(3): 27-29.

Figure Caption:

14-year-old red oak tree originating from a low cut stump. The 6 inch tree that was present prior to the regeneration harvest was cut and the stump sprout has produced a high quality crop tree that will cultivated to the end of the rotation.