Forest Pests: Insects, Diseases & Other Damage Agents

Improper Tree Planting Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

Taproot handling at planting affects stem quality of loblolly and slash pines. Planting pine seedlings is a difficult and time-consuming job, and many things can go wrong without careful attention to details. If a landowner is able to acquire vigorous stock of dimensions appropriate to his method of planting, then it is up to him to ensure that seedlings are handled and planted properly. Proper handling of pine seedlings includes cold storage prior to planting and protecting them from desiccation or injury during planting. There is no reason for the planter to trim roots since this is accomplished at the nursery during lifting. Proper hand-planting techniques include opening a hole that is deep enough for straight, vertical placement of the seedling’s roots 1-2” deeper than it grew in the nursery and closing the hole from the bottom up to remove air pockets. Proper machine-planting techniques include setting the colter blade at a depth that places the seedling root collar 1-2” below ground and maintaining a machine speed that minimizes the formation of “swept” roots. A swept or L-shaped taproot occurs when the planting machine is going too fast and actually drags the roots in the planting trench. Figures 168-173 illustrate root configurations resulting from machine planting.

Figure 168 - Bent taproot with a balled configurations, notice the girdling roots photo by Jason Gatch

Figure 169 - Bent multiple taproots, notice the girdling roots photo by Jason Gatch

Figure 170 - Bent taproot with a balled configuration photo by Jason Gatch

Figure 171 - A swept taproot photo by Jason Gatch

Figure 172 - A swept taproot photo by Jason Gatch

Figure 173 - Bent taproot with balled configuration and girdling roots photo by Jason Gatch

Much has been written about the influence of taproot handling at planting on subsequent survival and growth of southern pines. Almost 50 years ago, Philip C. Wakeley, an early forest regeneration scientist in the South, cautioned that shallow planting reduces survival more than all of the other planting errors combined. Most of the past research has shown that planting pine seedlings with bent taproots has little or no effect on their survival and growth, while removing their lateral roots can severely limit their survival. Until recently, the question of whether taproot handling at planting affects stem quality had not been addressed. Field observations suggested that seedlings planted with bent taproots tended to have greater levels of “sinuosity,” an oscillating curvature of the stem (Figure 174). In 1996, the Georgia Forestry Commission and the Daniel B. Warnell School of Forest Resources, University of Georgia began a series of retrospective and experimental studies to research this potential problem for loblolly and slash pines. Much has been written about the influence of taproot handling at planting on subsequent survival and growth of southern pines. Almost 50 years ago, Philip C. Wakeley, an early forest regeneration scientist in the South, cautioned that shallow planting reduces survival more than all of the other planting errors combined. Most of the past research has shown that planting pine seedlings with bent taproots has little or no effect on their survival and growth, while removing their lateral roots can severely limit their survival. Until recently, the question of whether taproot handling at planting affects stem quality had not been addressed. Field observations suggested that seedlings planted with bent taproots tended to have greater levels of “sinuosity,” an oscillating curvature of the stem (Figure 174). In 1996, the Georgia Forestry Commission and the Daniel B. Warnell School of Forest Resources, University of Georgia began a series of retrospective and experimental studies to research this potential problem for loblolly and slash pines.

Figure 174 photo by Terry Price

Retrospective Studies

In the retrospective approach, 24 machine-planted stands, ages 3 to 10 years, were selected for each species. Loblolly pine stands were located in the Piedmont of northeastern Georgia and had been planted under the Conservation Reserve Program (CRP). Slash pine stands were located in southeastern Georgia and were being managed by either Georgia-Pacific or Union Camp. At 3 plots within each stand, two trees were located, one with a low and one with a medium to high level of stem sinuosity. An 8-point index was then developed for scoring the severity of stem sinuosity for each tree. Then each of the 144 trees per species was excavated to determine whether it had a bent or straight taproot.

The results clearly show that percentage of trees for a given level of stem sinuosity was not independent of their taproot shape. Of the trees with bent taproots, 73% to 77% had medium to high levels of stem sinuosity, while 71% to 78% of those with straight taproots had low levels of stem sinuosity. This indicates that stem quality was not independent of taproot shape, and therefore, was linked to the way in which the taproot was handled at planting. For trees with bent taproots, the horizontal direction of the taproot was measured and found that it corresponded closely with the direction of the planting row. This confirmed that the trees had bent taproots from machine planting and not from a soil obstruction.

On the 8- to 10-year-old pines (nine sites per species), we estimated the effects of stem sinuosity on the volume of potential sawtimber. Using plumb bobs attached at a height of eight feet; we measured the diameter of the straight core within each tree (i.e., the cylinder remaining after chipping off the curves from sinuosity) (Figure 175). When the volume of straight trees in each stand was compared with the volume of the sinuous trees, it was found that sinuosity had caused reductions in potential sawtimber of 26% to 28%.

Figure 175 photo by Jason Gatch

Conclusions and Implications

This research has identified a correlation between taproot handling at planting and subsequent stem quality of loblolly and slash pines. Increased incidence and severity of stem sinuosity were linked directly to planting seedlings with bent taproots. Stem sinuosity also was visually detectable within the first three years after planting. In contrast, survival and growth were not affected greatly when seedlings were planted with bent taproots, but they decreased when seedlings were planted with trimmed taproots.

Alternative planting practices should be considered if levels of stem sinuosity are to be reduced. One remedy is to reduce the speed of the planting machine to minimize the degree to which the taproot is swept in the trench. When hand-planting pines, simple insertion of the root into the planting hole may not ensure its straight, vertical placement. It may be advantageous for the planter to use his hand to fully insert and straighten the root prior to closing the planting hole.

Before the first thinning of young stands that are being considered for sawtimber management, the incidence and severity of stem sinuosity should be assessed. If an insufficient number of crop trees of high stem quality is projected to remain after an operational thinning, then the stand should be managed as pulpwood and harvested when its value growth has culminated.

Proper handling of taproots at planting should be an important consideration for any reforestation project. Perhaps with a small amount of extra effort and cost, moderate to high levels of stem sinuosity can be avoided, and future management options will not be limited by taproot handling at planting.

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