Response of Overtopped White Oak to Release

Charles E. McGee

SUMMARY

Pole sized white oaks increase in volume growth

following release from overtopping trees, but the

response varies by size, age and appearance of

the oaks. Significant increases in epicormic sprouting, height loss by some released trees, and highly

variable stem volume growth make overtopped

white oak a very questionable source of future crop

trees. If overtopped trees are cut, those under 8

inches dbh and less than 80 years of age produce

vigorous stump sprouts and provide a source of

natural regeneration.

Millions of overtopped white oak arefound through

out the Cumberland Plateau region. Are these trees

which remain after commercial harvests an asset

or a liability? Will they respond favorably to release?

Can these trees become crop trees and desirable

growing stock? A a-year study of 240 released and

unreleased white oak provides early insight into

these questions (table 1). Some trees increased

in volume more than others following release from

overhead competition. Tree diameter, age, stem

form, crown development, and the degree of release were important factors. Dramatic increases

in the number and size of epicormic sprouts can be

anticipated on almost all released stems.

The white oaks in this study were significantly

overtopped by one or more larger trees. Most of the

sampled white oak were suppressed, but a few larger

ones were classed intermediate. Ages ranged from

30 to 100 years, and size ranged from 2 to 14 inches

dbh. The two study areas were typical of upland

hardwood land having been cut periodically during

the past 50 years or more. However, no cutting had

been done during the last 15 years and the stands

were fully stocked. Site quality on study areas ranged

from 80 to 70 for mixed oak.

Table l.-Average characteristicsot sample trees at t/me of

study initiation

Sample trek Age Height Diameter Volume

no. yra. ft. inches cu. ft.

Experiment l-released

High quality’ 42 53’ 51 6.0 5.5

Medium quality* 37 60 42 5.9 4.8

Low qualiv 25 62 35 0.4 4.3

Experiment II

Not released 40 50 45 6.2 6.2

Experiment Ill

Partially released 40 49 45 5.7 5.2

Not released 40 49 45 5.6 5.0

‘High quality-Straight stem, good crown.

Wedlum quality-Some sweep to bole, moderate crown.

sLow quality-Crook in bole or sparse crown or both.

The study was installed in three experiments.

Experiments I and II were located on the Domain

of the University of the South in Franklin County

and experiment Ill was located on Franklin-Marion

State Forest in Marion County.

Southern Forest Experiment Btation/T-10210 U.S. Postal Servicer Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Fore& Se&e, U.S. Department of Agriculture.

Serving Alabama Arkansas, Louisiana Mississippi, Eastern Oklahoma Tennessee, Eastern Texas.

1
Ixporlmont I

The purpose of this experiment was to determine

whether easily recognized tree characteristics of

overtopped white oak are related to response after

release. The 104 selected trees covered a range

of diameters, ages, and quality classes.

Forty-two trees were classified as high quality,

37 as Medium quality, and 25 as low quality, using

the following criteria:

High Quality-Large well formed crown and a

straight stem.

Medium Quality-Small but well formed crown,

stem having some sweep but

no major crooks.

Low Quality-Small or poorly formed crown,

crooked stem or stem with major

sweep.

An almost complete release of the sample trees

was achieved when most trees over 14 inches dbh

were commercially harvested, along with many

smaller trees. The remaining overstory trees near

a sample tree were cut. The average residual basal

area around the 104 sample trees was 30 square

feet per acre.

Measurements included a pre-release measure

of height and volume of the stem by Barr and Stroud

dendrometer. Quality estimates were made for each

stem and epicormic sprouts were tallied on the first

18 foot log by sprout size. After the second growing

season following release, the measurements were repeated. Height and volume determinations were

made from fixed relocatable points. The relationship

of diameter, age, and quality class to growth were

evaluated by regression analyses.

Total stem volume growth was predicted with the

iollowing equation:

Y=a+b(D)+b@

Where: D=Sample tree diameter breast height (in

inches)

A=Age of tree (in years)

Y=Total stem volume growth (cu. ft. per

2 years).

The cubic volume growth of released trees was

directly related to tree diameter and to a ratio of

tree diameter over age. For a given diamet8r and

diameter/age ratio, high quality trees responded

more vigorously than medium or low quality trees

(fig. 1). The response of medium and low quality

trees was less predictable than high quality tree

response. The regression equation accounted for

over 80 percent of the variation in volume growth

when+appiied to.,the high. quality trees, but only

87 and 52 percenewhen applied to medium and low

qualiw trees.

The larger trees produced more volume when released than smaller trees. Additional analyses were

performed to determine whether percent volume

increases were related to tree characteristics. However, these analyses accounted for less than 50

percent of the variation. While some small trees

increased dramatically in volume percentage, generally small overtopped trees, particularly those with

low diameter/age ratios, were poor candidates for

rapid early development following release.

Height growth following release is highly variable

with no obvious link between height growth and tree

characteristics. The average annual height growth

in this experiment was about 0.4 feet in trees of each

class. However, 23 of the 704 trees actually lost

height after release. Most of the loss was due to

stem die-back. If the 23 trees that lost height are

deleted from the calculations, the average annual

height growth is about 0.7 feet per year.

The average number of epicormic sprouts on the

butt log of the 104 trees almost doubled following

release, and epicormic sprouts longer than 6 inches

increased from 5 to 15 per log (table 2).

3

TREE AQE-SO

-HlQH QUALITY STEM

Y~-0.8S+0.16(0)+7.1~ R2.01

--- MLDIUY QUALITY STEM

Y s -0.70 + 0.21(O) + 2.29 n2* 07

.

K

k

l ------ LOW QUALITY STEM

Y . -0.1. + 0.08(O) + 2.4# R2. 52

3 2-

2

Y s TWO YEAR OROWTW (CU. FT.1

0 . OiAMLtfR BREAST HLIOHT (IN.)

A * AOL (YEARS)

DIAMETf R (INCHES)

Figure 1. - Volume growth for high, medium, and low quality wi?ite

oak at age 50 in reletion to stem diameter Experiment 1.

Charles E. McGee is Principal Silviculturist, Sewanee Silviculture Laboratov, maintained at Sewanee, Te?nessee, by the Southern

Forest Experiment Station, Forest Service-USDA, in cooperation with the University of the South. ’

2
Table 2. - Epicormic sprouts on high, medium, and low quality’ white oak befor@ and &ter rg/easg Experiment /

Before release After release Percent

C3 in. 3-8 in. >8 in. Total e3in. 3-5in. Xin. Total increase

High quality 2.5 2.8 3.8 9.1 3.6 5.0 13.8 22.4 145

Medium quaiity 2.4 2.9 5.4 11.7 2.8 4.3 15.0 22.2 80

Low quality 2.8 2.3 5.9 11.0 2.0 3.1 14.3 19.4 75

Avg. Number Epicormic Sprouts . . . . . . . . . . . . . . , . . , . .

on butt log . * . . . . .,. 10.6 . . . . . . . . * iis ii;

I High quality-straight stem, good crown: medium quality-some sweep to bole, moderate crown: low qualitycrook in bole or sparse crown or both.

Exporlmont II

This experiment compared the response of the

high quality trees released in experiment I with a

similar population of high quality unreleased overtopped white oak growing nearby in a fully stocked

stand. Tree measurements and analyses were similar

to those described in experiment I.

Both released and unreleased trees made substantial gains in stem volume during the 2 year

period (fig. 2). However, the equations predicted

that a 30-year-old released tree, 6 inches dbh, will

average 0.75 cubic feet growth per year while a

similar unreleased tree will gain only 0.35 cubic feet

per year. As age increased in relation to stem size,

cubic volume increase declined.

Comparing released and unreleased trees provided more evidence that release may have an early

negative effect on height growth. Only 4 released

trees grew more than 2 feet in height in two years

while 11 unreleased trees grew over 2 feet. Seven

of the released trees actually lost height while only

one unreleased tree lost height. The average annual

height growth was 0.4 feet for released trees and

0.7 feet for unreleased trees.

Epicormic sprouts on the first 16 foot log increased

on both released and unreleased trees. However,

the increase averaged 13 per tree on released stems

and 8 per tree on unreleased stems. Epicormic

sprouts longer than 6 inches greatly increased on

the released trees.

Exporlmont 111

In this experiment four treatments were imposed

on 160 high quality but overtopped white oak.

Treatments consisted of either (1) removal of directly overtopping trees, (2) removal of directly overtopping trees plus cutting the sample tree, (3) no

release but cut sample trees, and (4) no release

and no cutting.

The release imposed in treatments 1 and 2 removed directly overtopping trees but left considerable side shade. The average basal area of residual

trees around the sample trees as indicated by prism

-ALLEASLO (AGE 30)

-*- RELEASE0 (AGE SO)

--- NO RELEASE (AGE 30)

.------ NO RELEASE IAGE 50)

Y * TWO YEAR QROWTM (CU. FT,)

0 . DIAMETER SREAST IIEIOHT (IN.)

A * AQL (YEARS1 /

DIAMETER (INCHES)

Figure 2.- Volume growth for reiaaaed and unreleased white oak

in fe/aHon to tree age and stem diameter Experiment

i and II.

counts was 60 square feet per acre. Therefore, the

partial release achieved in this experiment is comparable to the release that might follow selection

cutting or heavy thinning. Volume measurements

and counts of epicormic sprouts of the standing

oak trees were completed as in experiment I. After

each growing season, number and height of stump

sprout development has been monitored on the

sample tree stumps.

Both the partially released trees and the unreleased trees continued to grow, with little difference

in cubic volume increment between them. The partially released trees did not respond in the same

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manner as the completely released trees in experiment 1 . The difference in residual basal areas, 30

square feet per acre in experiment I compared with

60 square feet per acre in experiment Ill, probably

accounts for the growth difference. Height growth

was about 0.4 feet per year for both partially released

and unreleased trees. Epicormic sprouting increased

120 percent in partially released and 46 percent in

unreleased butt logs. Stump sprouting was prolific

on both released and unreleased stumps of trees

less than 8 inches and under 60 years of age (table

3). Of the 80 felled trees, all but 10 had stump

sprouts by the second year.

Table 3.-White oak stump sprouting one and two years afrer

telling Experiment 111~

Tree size

inches dbh

Partially released Unreleased

One year lkro year One year lb40 year

sprouts sprouts sprouts sprout3

perstump perstump pek9tump p&stump

---------------averagenumber- ______ e-m_ ____

1 B-1 .Q 0 6 1 4 10

2.0-3.9 1 2 1 0 14 1 5

4.Ck5.9 16 1 3 1 5 1 4

6.0-7.9 22 22 21 1 9

8.0+ 1 2 2 S

Avg. sprout8

per stump 1 1 1 1 1 4 1 3

‘One year data published as”Size and age of tree affect white oak

sprouting.” C. E. McGee, Research Note W-239,1978,2 p.

DIsaJsaION

The presence of millions of overtopped white oak

in the Cumberland Plateau presents diff icult choices

to area forest managers. To cut the mostly unmerchantable pole-sized trees sacrifices many years

growth and time before merchantable trees can

develop. However, early data from this study show

rather strongly that many of these overtopped trees

are not good choices for crop trees. Generally, the

indicated practice would be to fell all overtopped

and unmerchantable trees left after a heavy commercial harvest.

Occasionally, however, the presence of enough

8-l 2 inch dbh trees to restock a stand may provide

an opportunity to avoid completely starting over.

This study has shown that most trees in the 6-12

inch dbh category will increase diameter growth

rapidly following release. Some of these trees will

maintain their rate of height growth, but others will

initially lose height. Most of the released trees will

have large increases in the sire and number of epicormic sprouts. These trees will eventually produce

sawtimber, but the overall log quality will be low

and individual tree performance highly variable. The

critical factor is having enough good trees to fully

restock the stand and occupy the site. Many stands

will have a few good overtopped trees but not enough

for full restocking. Only a few stands will have

enough of the overtopped trees of the size and

quality to justify leaving them for crop trees.

Sr IUS. GOVERNMENT PRINTING OFFICE: 19SG-771.091