YELLOW-POPLAR ROOTING HABITS

JOHN K. FRANCIS

SUMMARY

Although the configuration of pole-sized yellowpoplar root systems in Tennessee is quite variable, a

branched taproot with several widely spreading laterals is typical. Rooting depth is particularly limited by

clayey texture, wetness, and firmness of subsoils.

Additional keywords: Liriodendron tulipifera L.,

taproot, water table.

YELLOW-POPLAR ROOT SYSTEMS

The rooting habits of yellow-poplar (Liriodendron

fulipifera L.) are not well known. Toumay (1929) described yellow-poplar seedlings as having rapidly

growing, deeply penetrating taproots with widespreading lateral roots. Steinbeck and Kormanik

(1968) observed that in sandy strata, roots of yellow-poplar seedlings were round, fleshy, and easily

separated from the soil. When roots grew into clay

lenses, they became flattened, somewhat flaccid,

and more likely to cling to fine soil particles. Coile

(1937) found that nearly all roots in a mixed yellowpoplar and sweetgum stand were in the upper 19

inches of the soil. Despite these observations, we

lack a clear idea of the structure of yellow-poplar root

systems and how they are affected by soil properties.

I have documented the rooting habits of 10 polesized yellow-poplars and tried to relate root development to soil properties.

METHODS

Ten soils in middle Tennessee were chosen for

their widely varying chemical and physical properties, topographic setting, and parent material. On

each soil a dominant or codominant yellow-poplar

about 4 inches in diameter was selected for study.

Trees chosen varied in age from 8 to 34.

After each tree was cut, a trench was dug up and

down slope with one face about 6 inches from the

stump. Trenches were long enough to expose most

of the root extension and as deep as the deepest

yellow-poplar roots. A full description was made of

each profile. Laboratory analysis of the chemical and

physical properties of each horizon was performed.

The soil was carefully picked away from the roots

of the tree until the trench face had been advanced 16

inches. After a 12-inch string grid was installed, the

root system was sketched and photographed.

RESULTS AND APPLICATION

Yellow-poplar root systems were quite variable.

Root size appeared to be governed by tree size, not

age. Although roots grew in response to soil horizon

conditions, much of the configuration of each yellow-poplar root system seemed to be a meandering

response to soil pores and structure. Both deep and

shallow root systems were present, but no sample

Southern Forest Experiment Station/T-10210 US. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
trees had abundant “feeder” roots at the interface

between the forest floor and mineral soil as do many

other forest species. The lack of abundant “feeder

roots” makes yellow-poplar less likely than many of

its associates to be weakened by disturbance of the

forest floor by logging or cultivation.

Taproot and heartroot systems both occurred, but

a several-branched taproot was more common (fig.

1). Lateral roots tended to grow parallel to the soil

surface, whether sloping or flat; taproots and sinker

roots grew down. The taproot or its branches extended much deeper into firm or wet subsoils than

descending branches of lateral roots.

Roots in coarse-textured soil were round, long,

little-branched, and fibrous. In clayey soil, roots were

weak, fleshy, flattened, and more crooked and

branched than in coarse soils. Clayey, wet subsoils

caused dieback and subsequent branching of root

tips (fig. 2). Dieback may have been caused by

anoxia. The importance of good aeration to yellowpoplar roots, especially lateral rocts, is illustrated in

figure 3. After being buried by sandy alluvium, lateral

roots of this yellow-poplar grew to near-surface positions and then spread out. However, the roots of

some yellow-poplars can grow for a short distance

into both seasonal and permanent water tables (fig.

4).

In shallow soils, yellow-poplars sometimes expanded their root systems laterally to make up for

lack of rooting depth. Roots penetrated fragipans and

other firm subsoils to a limited extent, but root growth

was clearly reduced. Managers should avoid planting

yellow-poplarwhere soils are wet and shallow, where

water tables are high, or where fragipans or very firm

subsoils exist.

Gravel in the soil did not alter root configuration

and did not noticeably contort individual roots. Yellow-poplar can do well in skeletal soils, if soil depth is

ample and the soil matrix is not hard. Old root channels were heavily used and may be important to root

extension in dense soils. Where possible, plant near

old stumps.

Although no changes were noted in rooting patterns, yellow-poplar generally did well where Ca and

base saturation were high. Poor growth was observed where exchangeable Al was high and both Ca

and base saturation were low. This pattern has been

reported in many other species (Foy 1974).

For growing yellow-poplar, a manager should

select a soil with no restriction to deep rooting, a soil

able to supply ample moisture while being well aerated and containing abundant Ca and other basic

cations.

6

0" ---------L+"

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24"

36"

IIB23t

Figure 2.-Excavated root system of a yellow-poplar

on Swain soil showing root tips which

have died back and branched.

This research was done by John K. Francis at the Sewanee Silvicultural Laboratory, maintained at Sewanee, Tennessee, by the Southern

Forest Experiment Station. Francis is now Associate Soil Scientist at the Southern Hardwoods Laboratory, which is maintained at Stoneville,

Mississippi, by the Southern Forest Experiment Station, Forest Service - USDA, in cooperation with the Mississippi Agricultural and

Forestry Experiment Station and the Southern Hardwood Forest Research Group.

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LITERATURE CITED

Coile, T. W.

1937. Distribution of forest tree roots in North

Carolina Piedmont soils. J. For. 35247-257.

Foy, C. D.

1974. Effects of aluminum on plant growth. In

R. W. Carson, ed. The plant root and its environment, p. 601-642. Univ. Press of Virginia,

Charlottesville.

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48" IIB22b

Figure 3.-Excavated root system of a yellow-poplar Figure 4.-fxcavated root system of a yellow-poplar

on an unnamed soil. After burial, lateral on Guthrie soil. The taproot and sinker

roots have grown to shallower, better roots have extended more than a foot

aerated positions. below the water table.

Steinbeck, K., and P. P. Kormanik.

1968. First-year root system development of two

clones of yellow-poplar. Ga. For. Res. Count.

Pap. 55.

Toumay, J. W.

1929. Initial root habits in American trees and its

bearing in regeneration. Int. Cong. Plant Sci.

Proc. 1: 713-728.

.S. GOVERNMENT PRINTING OFFICE 672-802 1979

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