Vegetative Reproduction
Vegetative reproduction, also called vegetative regeneration, is an important source of regeneration among hardwood species. There three types of vegetative reproduction: stump sprouts, seedling sprouts, and root suckers.
Stump Sprouts
Sprouts, i.e., sprouts originating from cut stumps of trees at least 2 inches in dbh., can arise from several different origins. Some shoots arise from dormant buds that originate at the pith, and grow just under the bark. Sprouts of this origin may appear at the root collar at the side or base of the stool. Others develop from adventitious buds formed in the cambium. These emerge from callus that forms along the cut surface around the top of the stump, just inside the bark.(Nyland 1996)
Stump sprouts are an important source of regeneration in Appalachian hardwoods. It is not uncommon for stump sprouts to account for half the stems in young stands (Johnson 1976; Wendel and Trimble 1968). This mode of regeneration has long been considered to produce poor quality stems compared to seedlings of the same species, mainly because of a high incidence of decay and breakage in stump sprouts.Decay organisms can enter stump sprouts through heartwood connections with either the decaying parent stump or dead companion stems. However, it is now clear that all stump sprouts do not suffer equally from this problem, and many of the fine trees in second-growth stands originated as sprouts. It has been shown that stump sprouts can produce sawlogs as high in quality as those from seedlings--and usually in a shorter time (Johnson and Rogers 1983). The incidence of decay and breakage increases with the size of stump and the height on the stump from which the sprout originates, with the latter being the more important factor. Sprouts that originate at or near the ground line have less decay and are likely to survive to maturity with the potential of producing a high quality stem (Wendel 1975; Lamson 1976). Sprouts are a more reliable source of reproduction in upland oak stands on sites of medium or lower quality because of the relatively large number of small trees present. Stump sprouts, however, play a less important role in reproducing most mature cove hardwood stands. (Kelty 1988)
Seedling Sprouts
"Seedling sprouts are another form of vegetative reproduction; they are biologically identical to stump sprouts, with the only distinction being that they originate from small stumps (less than 2 inches in diameter). While this exact size is arbitrary, the distinction is quite important, because the small stumps are quickly covered with callus tissue, such that no open wound is present for infection. Because they often develop after the seedling stem dies or is broken off at ground level, there is no problem of sprouts originating high on the stump. Thus, seedling sprouts tend to be free of the bad qualities that can occur with sprouts from large stumps. In fact, they are best considered in conjunction with advance-regeneration seedlings, since they usually occur in abundance when seedlings are damaged during logging operations. They tend to be even more desirable than seedlings, because seedling sprouts have established root systems and grow faster than the original seedling shoots, so the stems are often straighter. This characteristic has led to trials of mowing advance growth just before overstory removal in order to produce sprouts, but enough are usually created during logging that this generally does not appear to be necessary." (Kelty 1988)
Root Suckers
A few species sprout from adventitious buds produced on roots; these sprouts are generally referred to as root suckers. Suckers may also arise from shallow roots, and generally as single stems at multiple points of origin (loci) along the root system. Root suckers are of minor importance in Appalachian hardwood stands, limited to two commercial species--beech and black locust. Beech is a minor commercial species in Appalachian hardwood stands. Black locust normally is short-lived and is valuable for local post products and fuelwood. (Lamson 1988)
Factors Affecting sprouting
Lamson (1988) summarized several characteristics that affect sprouting frequency, such as the species, age, and diameter of the parent tree as well the season of cutting, site quality, and residual density of the stand:
| Species | Very high sprouting capacity: basswood, black cherry, and yellow-poplar High sprouting capacity: white ash, red maple, and red oak Medium sprouting capacity:sugar maple, white oak, white elm, black oak Low sprouting capacity: yellow birch, sweet birch |
| Age | Sprouting frequency usually decreases as age increases, i.e., cut stumps from older trees produce fewer sprouts than those from younger trees (Johnson and Godman 1983; Stroempl 1983). However, for most species, sprouting frequency remains fairly high for stumps of cut trees up to 60 years old. Except for basswood, sprouting frequency generally is low for cut stumps of trees over 100 years old. The best age for sprouting varies among species; for example, red maple continues to produce sprouts at a larger diameter than sugar maple (Solomon and Blum 1967). The decline in sprouting with size and age apparently results either from a thickening of the bark over dormant buds at the cambium, or from breaking the connection between the dormant buds and the pith.(Nyland 1996) |
| Diameter | Larger cut stumps generally produce few sprouts than smaller stumps. One-third or less of cut stumps from trees more than 20 inches in dbh can be expected to produce sprouts. For most species, sprouting frequency is at least 50% for trees up to 16 inches in dbh (Stroempl 1983). |
| Season of Cutting | Most trees cut in the dormant season produce more sprouts than those cut in the growing season (Johnson and Godman 1983). However, after age 10 season of cutting has little effect on sprouting frequency (Wendel 1975). This variation may result from hormonal fluctuations within the trees, or from the greater concentrations of carbohydrates in root systems during periods of dormancy (Kramer and Kozlowski 1960). (Nyland 1996) |
| Site Quality | Trees of similar dbh and species produce more sprouts on higher quality sites. |
| Residual Stand Density | Sprouting is less frequent in thinned stands than in clearcuts. Most cut stumps in thinned stands do not produce sprouts and those that do occur usually die from suppression (Johnson and Godman 1983). |
Encyclopedia ID: p1455
