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Forestry and Wildlife
Research Series No. 1
Alabama Agricultural
Experiment Station
Luther Waters, Jr. Director
Auburn University
Auburn, Alabama
October 2000
4*
A
Planting
Morphological ly
Improved Pine
Seedlings to
Increase
Survival and
Growth
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Table of.Contents
Page
Factors ion..that ...In....uence...Seedling.....Survival..............................................................30 1
Laco SeedbedflDeniteSeedlng..... l....................................................................... 3
Root-weight Ratios............................................. eese aaeeess*e esa e****o *em4
Root Growth Potential ................................................................................ 4
Proper Planting Techniques............................................ 4
Growth of Morphologically Improved Seedlings ............................................................ 4
Predicting Per Acre Volume Gains .................................................... 5
Percent Gain............................................................................................ 5
A Shift in Site Index................................................................................. 5
The Establishment Quality Boost .................................................................... 6
The Age Shift Approach............................................................................... 6
How to Obtain a One Year Age Sit........ .............. 6
How to Obtain a Two Year Age Shift.......................................................................... 7
Predicted and Realized Gains ......................................................................sotsea**soas*s**8
Economic Advantages of Planting Morphologcially Improved Seedlings..........................969
Summary................................................................................. 9
References................................................................................................... 10
Information contained herein is available to all persons regardless of race,
color, sex, or national origin.

Planting Morphologically Improved Pine Seedlings
to Increase Survival and Growth
David B. South'
INTRODUCTION
Loblolly pine seedlings used by most researchers and
landowners are commonly grown at high seedbed densi-
ties (more than 25 plants per square foot of growing area).
These seedlings are classified as Grade 2 seedlings (Table
1) and typically have a root-collar diameter (RCD) that
averages 4 millimeters (mm). Since these seedlings have
small roots, survival under less-than-ideal conditions can
be a problem. As a result, landowners and researchers in
the South typically overplant to ensure adequate survival.
Researchers sometimes double-plant (planting two seed-
lings per spot) in order to ensure one seedling lives. Re-
searchers and landowners could also increase survival
lings grown at low seedbed densities because they haven't
been informed about the benefits of using these plants. In
fact, many landowners have been told that seedling mor-
phology is a poor indicator of seedling performance.
Some of those who say that seedling morphology is
a poor predictor of survival cite studies conducted in the
1930s when seedbed densities were high. Others cite more
recent studies that used seedlings from seedbeds with
densities greater than 45 plants per square foot (Dierauf
et al. 1993). Some studies confound seedling morphol-
ogy with other factors that affect survival. Although sev-
eral studies show positive correlations between RCD and
rates by planting large-di-
ameter seedlings (morpho-
logically improved seed-
lings), which have been
grown at low seedbed den-
sities (lessthan 20 plants
per square foot).
In the southern United
States, seedlings of
longleaf pine and various
hardwood species are com-
monly grown at low seed-
bed densities (less than 10
plants per square foot) to
increase their field perfor-
mance. However, the trend
of lowering the seedbed
density for loblolly and
slash pine has been slow to
occur. The primary reason
for this has been a lack of
demand for morphologi-
cally improved seedlings of
these species. Many land-
owners do not request seed-
TABLE 1. DEFINITIONS OF SEEDLING TERMS FOR BARE-ROOT LOBLOLLY PINE
Term
Cull seedling
Plantable seedling
Grade 2 seedling
Grade 1 seedling
Regular seedling
Target seedling
Morphologically
improved
Optimum seedling
Definition
An unacceptable seedling that does not meet a certain size standard
[e.g. has a root collar diameter (RCD) less than 3 mm]
A seedling that is slightly larger than a cull. Typically has a RCD
of 3 mm or more
A seedling that has a RCD ranging from 3.2 to 4.7 mm. This seed-
ling size is desired by most tree planters
A seedling that has a RCD greater than 4.7 mm
The average loblolly pine seedling planted by most researchers in
the South. Typically has an average RCD of about 3.9 mm
The seedling that the nursery manager would produce the most of
under ideal weather conditions. The target seedling at certain in-
dustry nurseries is much larger than at others
The seedling is only grown at low seedbed densities (< 20/ft
2
) and
at least half of the population has RCDs greater than 5 mm and
none less than 3 mm). This seedling has a higher root-weight ratio
and has been cultured to give more fibrous roots, but is not taller
than regular seedlings
The seedling size that will minimize overall reforestation costs while
achieving established goals for initial survival and growth. Although
the size of this seedling has not been defined, it might have a RCD
of about 8-10 mm
'South is a Professor in the Auburn University School of Forestry and Wildlife Sciences.
-- " '-- I--~
\,11II St~t~~lllll~ WII IlrlilL;L;C~I]Liil) I C; ?il
2 
ALABAMA AGRICULTURAL 
EXPERIMENT STATION
survival (Dierauf et al. 1993; South 1993; McGrath and
Duryea 1994), these studies are usually not cited by those
who claim that seedling morphology is a poor predictor
of field survival.
The general pattern, observed over the last 50 years,
however, has been that when large-diameter (morphologi-
cally improved) seedlings are properly planted, they typi-
cally survive better than smaller seedlings (South 1993).
Although all sites will not show this relationship, one site
in Georgia illustrates the relationship between RCD at
planting and seedling survival (Figure 1).
Some forestry companies agree. Their leaders believe
that seedling performance is related to RCD and that with
proper lifting and planting, seedlings with large diameters
tend to survive and grow better than small-diameter seed-
lings (Autry 1972; McGrath and Duryea 1994; South
1993). As a result, the target seedling RCD for some com-
panies is 6 mm (or greater); this is about 2 mm larger
than seedlings used by most researchers (Table 2).
The practice of growing pine seedlings at low seed-
bed densities has been used throughout the world to im-
prove the performance potential of pine seedlings. For
example, since the early 1970s, slash pine and loblolly
pine seedlings have been grown in bare-root nurseries in
South Africa at densities of 12 to 15 seedlings per square
foot. Likewise, for more than 20 years, nurseries in New
Zealand have been growing Monterey pine seedlings at
low seedbed densities. In fact, the recommended spacing
varies with site. For sites with low elevation, densities of
Figure 1. Relationship between seedling survival and
root-collar diameter at planting and survival (South and
Mitchell 1999).
100
90
80
70
% 60
. 50 t (2.42-0.207X)
=40/Y=100-10
a 30
20[
10
RCD at planting (mm)
15 seedlings per square foot are used; for more adverse,
high-elevation sites, lower densities (12 seedlings per
square foot) are recommended (FRI 1988). Currently, the
ideal size of a pine seedling in New Zealand is about 6 to
12 mm in diameter at the root collar (MacLaren 1993).
While seedling morphology is not a perfect predic-
tor of field survival, it is about the best tool available to
separate individual seedlings prior to planting according
to their potential for growth. This is much like the case
of genetically improved seedlings. Although knowing the
genotype usually does not help predict field survival,
TABLE 2. THE GROUNDLINE DIAMETER
1 
OR ROOT-COLLAR DIAMETER OF REGULAR BARE-ROOT
LOBLOLLY PINE SEEDLINGS USED IN RESEARCH STUDIES
State GLD
2  
Study State RCD
3  
Study
mm mm
GA 3.0 Sung et al. 1997
GA 2.8 Miller et al. 1995 GA 4.0 Harrington and Howell 1998
GA 3.0 Miller et al. 1995 GA 3.7 Kormanik et al. 1995
MS 3.0 Miller et al. 1995 GA 4.4 Kormanik et al. 1995
AL 3.0 Miller et al. 1995 SC 5.0 Barnard et al. 1997
LA 2.5 Miller et al. 1995 SC 4.2 Barnard et al. 1997
LA 3.6 Miller et al. 1995 SC 3.5 Barnett and McGilvary 1993
AL 3.6 Miller et al. 1995 SC 3.7 Barnett and McGilvary 1993
AR 3.6 Miller et al. 1995 SC" 3.6 Cram et al. 1997
TN 4.3 Miller et al. 1995 SC 4.1 Cram et al. 1997
LA 4.1 Miller et al. 1995 SC 3.3 Cram et al. 1997
AL 3.0 Miller et al. 1995 SC 3.6 Cram et al. 1997
GA 2.8 Miller et al. 1995 SC 3.7 Cram et al. 1997
VA 2.8 Miller et al. 1995 SC 4.3 Cram et al: 1997
VA 3.1 South et al. 1995 SC 4.3 Cram et al. 1997
AL 5.3 South et al. 1995 SC 4.2 Cram et al. 1997
Avg. 3.4 Avg. 3.9
Since seedlings are usually planted with the RCD below the groundline, the GLD is often measured at a higher point on
the stem than the RCD. 
2
GLD = groundline diameter. I RCD = root-collar diameter.
2 ALABAMA AGRICULTURAL EXPERIMENT STATION
PLANTING MORPHOLOGICALLY IMPROVED PINE SEEDLINGS TO INCREASE SURVIVAL AND GROWTH 
3
genetically improved seedlings are still planted to improve
the growth potential of a stand. As with genetically im-
proved seedlings, the main reason for using morphologi-
cally improved seedlings is to improve the growth poten-
tial of pine plantations.
FACTORS THAT INFLUENCE
SEEDLING SURVIVAL
Initial survival in the field is affected by several fac-
tors, including, in order of importance, environment, han-
dling, morphology, and physiology (Figure 2).
The most important factor is the environment where
the seedling is planted (called the site environment). This
includes such things as soil water content at time of plant-
ing, temperature and amount of rainfall soon after plant-
ing (a hard freeze or extended drought, for example), soil
texture, soil depth, competition from weeds, number of
insect pests, and amount of deer browse.
Seedling handling is also very important. The type of
lifting machine, the amount of cold storage, the temperature
of cold storage, the stripping of roots during lifting, the prun-
ing and washing of roots after lifting, the depth of plant-
ing-all can affect survival. In some cases, the way the tree-
planter handles the seedlings can make the difference be-
tween a plantation with 5% survival or 85% survival (Rowan
1987). In many years survival of machine-planted trees will
be higher than for inadequately supervised hand-planted
seedlings (South and Mitchell 1999b).
The next important factor is seedling morphology.
This includes, for example, root-weight ratio, root mass,
RCD, secondary foliage, and seedling height. In contrast,
presence of a well-formed terminal bud is not important
for survival.
Seedling physiology is also important and can be in-
fluenced by the nursery environment (fertilizer regime,
excessive rain, lack of soil oxygen, freezes, high tempera-
tures, photoperiod, pathogens, cultural practices, toxic
chemicals) as well as handling practices (condition of the
seedlings at lifting, amount of cold storage, desiccation
of roots, etc.). However, seedling physiology can be very
difficult to evaluate on individual seedlings at the time of
outplanting.
To a limited extent, the genetics of a seedling will
affect initial survival (through its effects on both seedling
physiology and seedling morphology). Although initial
survival is usually high for many progeny tests, the heri-
tability for survival can be 0.78 (NCSU 1995).
LOW SEEDBED DENSITIES
Seedlings grown at low seedbed densities usually
survive better than seedlings grown at high seedbed den-
sities. Seedlings grown at low seedbed densities have
Figure 2. A generalized model illustrating the relative
importance of four factors affecting survival of trans-
planted pine seedlings. Any one factor can be the major
cause of failure in a particular event.
PHYSIOLOGY
MORPHOLOGY
stronger first order lateral roots, more short roots, more
foliage, and a higher root-weight ratio (all part of a mor-
phologically improved seedling).
Contrary to popular belief, top-pruned seedlings pro-
duced from low seedbed densities are usually no taller
than seedlings grown at high seedbed densities. Proper
top-pruning in the nursery increases the root-weight ratio
and, therefore, increases the chance of survival when the
site enviornment is less than optimum (South 1998).
Several studies have demonstrated better survival
from seedlings grown at low seedbed densities (Table 3).
When average survival is less than 90%, morphologi-
TABLE 3. INCREASE IN SEEDLING SURVIVAL BY
USE OF LOBLOLLY PINE SEEDLINGS GROWN AT
Low SEEDBED DENSITIES
Study Low Medium Survival
density density gain
no/sq ft percentage
points
Rowan 1986 15 30 14
Shoulders 1961 14 38 12
Shoulders 1961 10 30 9
Rowan 1986 15 30 8
Leach et al. 1986 20 30 4
Shoulders 1961 13 35 3
Rowan 1986 15 30 2
Shoulders 1961 12 31 1
Shipman 1964 20 40 1
Carneiro 1985 15 26 -3
Average 5
Multiple listings for Shoulders (1961) and Rowan (1986)
due to multiple tests.
4 
ALABAMA AGRICULTURAL EXPERIMENT 
STATION
cally improved seedlings exhibit better survival than regu-
lar seedlings. Planting seedlings from low seedbed den-
sities usually increased survival by 4 to 10 percentage
points over that of seedlings grown at 30 plants per square
foot. Research has shown, however, that seedbed density
will have little or no effect on survival when average sur-
vival is greater than 96%.
Seedling height also has an effect on survival. When
grown at high seedbed densities, shorter seedlings are
more likely to survive than taller seedlings (Dierauf 1973;
Tuttle et al. 1988; Sluder 1991; Hitch et al. 1996). For
example, when grown at the same seedbed density, slash
pine seedlings which are 7 inches tall may survive better
(66% survival) than seedlings which are 13 inches tall
(35% survival) (Bengtson 1963). In fact, very tall seed-
lings grown at high seedbed densities (which produce low
root-weight ratios) survive pooly when planted on areas
with limited moisture.
Root-weight Ratio
Although low seedbed densities will result in seed-
lings with higher root-weight ratios, it is very important
that the root-weight ratio not be greatly decreased during
the lifting process in the nursery. If nursery managers are
not careful, injury to seedlings can result when using me-
chanical belt lifters (Green and Danley 2001). Less in-
jury has been observed on seedlings when lifting is done
by hand (Barnard 1980) or when a Fobro-type lifter is used
to assist in hand-lifting.
A number of studies demonstrate the balance between
roots and shoots is important to seedling survival, but some
researchers have implied that a morphological trait (such
as root-weight ratio) is not important for field survival.
Apparently, these individuals still believe Wakeley (1954)
who did not include a shoot/root ratio along with his seed-
ling grades. Wakeley believed such ratios had "... never
proven useful in grading southern pine nursery seedlings
.. " Perhaps Wakeley was comparing the length of the
shoot with the length of the taproot (an invalid measure
of shoot/root ratio).
The balance between root mass and shoot mass is
especially important when seedlings are planted in areas
or in seasons when moisture stress is likely to be severe.
In fact, in cases where Grade 2 seedlings survived better
than Grade 1 seedlings (Blair and Check 1974; Venator
1983), the lower survival may have simply been due to
lower root-weight ratios.
Root Growth Potential
One reason that more roots improve survival is be-
cause the existing roots produce many new roots soon
after planting (Williams et al. 1992). This ability is re-
lated to a seedling's root growth potential, which is a
measure of the new root growth under controlled condi-
tions. Theoretically, seedlings that produce many new
roots within a few weeks of planting will survive better
than seedlings which produce only a few new roots.
Some researchers believe seedling morphology has
little to do with the ability of a seedling to quickly pro-
duce new roots. However, researchers have demonstrated
a positive correlation between root biomass and root
growth potential (Switzer 1962, Larsen and Boyer 1983,
Carlson 1986). Apparently, the more fibrous lateral roots
a seedling has, the more root-tips are available for new
root growth. Seedlings which produce more new roots
have a greater ability to take up more water (Carlson 1986).
Proper Planting Techniques
One tree planter stated, "I am a quality planter. I prune
the roots to fit the planting hole." This type of mentality
will result in pruning more roots from a large seedling
than from a small seedling. And it may explain, in part,
why some operational foresters have observed that Grade
1 seedlings do not survive as well as Grade 2 seedlings. It
may also explain why the results from research studies can
differ greatly from those of operational studies if unsuper-
vised tree planters strip and prune roots prior to planting.
The survival benefits of growing seedlings at low
seedbed densities will be destroyed if removing roots re-
duces the root-weight ratio (Wilder-Ayers and Toliver
1987). And the root growth potential of seedlings can be
reduced in half by the single act of stripping the roots
through a closed fist (South and Stumpff 1990). Without
a doubt, pruning roots decreases survival (Harrington and
Howell 1998). One way to reduce the likelihood of root
pruning is to have seedlings planted with machines (South
and Mitchell 1999b).
If seedlings with large root systems are planted too
shallow (usually because the planting hole is too small),
they will not survive well (South 1999). However, when
planted deep enough (either by machine or by using proper
hand-planting methods), seedlings with better root-weight
ratios and more intact fibrous roots will survive better
than seedlings which have less roots, less foliage, and
lower root-weight ratios (often a result of being grown at
high seedbed densities).
GROWTH OF MORPHOLOGICALLY
IMPROVED SEEDLINGS
Although proper planting of morphologically im-
proved seedlings can increase survival, the greatest and
most consistent benefit of planting morphologically im-
proved seedlings is an increase in growth (Table 4). In no
case, did Grade 1 seedlings grow less (on an individual
4 ALABAMA AGRICULTURAL EXPERIMENT STATION
PLANTING MORPHOLOGICALLY IMPROVED PINE SEEDLINGS TO INCREASE SURVIVAL AND GROWTH 5-
tree basis) than the Grade 2 seedlings. Lower per acre
production was attributable only to poorer survival, which
is likely a result of poorer root-weight ratios, taller seed-
lings, or inexperience in planting larger stock.
Increases in per acre volume gains can be made at
ages 10 to 15 by planting seedlings with large RCDs usu-
ally because these seedlings have better survival due to
higher root-weight ratios. In most cases, gains will 
result
from both better survival and better average tree growth.
PREDICTING PER ACRE
VOLUME GAINS
It is not enough to be able to say "if you want more
wood, carefully raise and carefully plant stock with large
diameters and root mass." What the practical forester needs
is an estimate of the expected volume gain. Estimates of
volume gain per millimeter increase in seedling diameter
have been calculated for the examples in Table 4.
For example, if we assume the average RCD for a
Grade 2 seedling is 4 mm and we assume the average for
a Grade 1 seedling is 6 mm, then we can divide the vol-
ume difference by two to get an estimate of the volume
gain per mm. If we exclude the 30-year row-plot data in
Table 4, the average gain in volume amounts to about
190 cubic feet per mm. This suggests that, on average,
stands 15 to 20 years old will have an extra 380 cubic feet
per acre if planted with 6 mm seedlings (as opposed to 4
mm seedlings). Without making any further assumptions,
this 380 cubic feet value may be the best way to forecast
volume gains from planting large seedlings. However, this
single value does not take site quality or age into account.
The question now is how to predict volume gains for vari-
ous ages and sites.
Percent Gain
There are several ways to estimate future volume
gains. Geneticists sometimes predict the per acre volume
TABLE 4. EFFECT OF A 1 MM INCREASE IN ROOT-COLLAR DIAMETER
ON GAINS IN HEIGHT AND VOLUME
1
Study Age Plot shape Avg. height Height 
gain Volumn gain
ft ft/mm cu ft/ac/mm
Wakeley 1969 30 row 61.6 
0.0 120
30 row 54.8 2.7 970
30 row 57.8 2.1 1,770
30 row 55.2 1.0 -16
Clark and Phares 1961 21 block 31.8 
0.4 580
20 block 29.9 0.4 330
Dierauf 19932 20 3-row 46.8 
-0.07 60
Dierauf 19932 19 3-row 42 0.38 
130
Clark and Phares 1961 19 block 28.9 0.0 
590
Sluder 1991 15 block 41 
0.0 -95
Sluder 1979 15 block 48 
1.2 219
15 block 46 0.7 118
South et al. 1989 15 row 31 
120
South et al. 1985 13 block 57 0.5 
428
Blair and Cech 1974 13 row 
279
13 row 266
13 row 377
13 row 0
13 row -383
South et al. 1995 12 - 35 
0.3 100
12 - 35 0.3 171
Hatchell et al. 1972 10 block 29 
5.4 412
10 block 29 2.6 356
Bacon 1979 10 block 47 
0.5 286
Rayonier (unpublished) 10 block 33.8 
0.0 0
Silker 1960 10 row 21 
0.9 112
SAFCOL (unpublished) 9 block 48.7 1.0 
349
Hunt 1967 9 row 28.0 1.0 
71
9 row 29 1.0 59
' These values are not corrected for differences in survival.
2 Seedbed density very high (46 to 60 plants per square foot).
gains by calculating a per-
centage of the volume ex-
pected from a local, unim-
proved source. A 12% gain
in volume per acre might be
estimated for first genera-
tion seedlings (from a
rogued orchard) and a 30%
gain in volume might be
estimated for rouged sec-
ond generation orchards.
Although this is a
tempting method to use due
to its simplicity, it can mis-
lead the public since the
percent gain varies with
age. The percent gain in per
acre volume observed at
age eight will not be the
same as that for unthinned
plantations at ages 25, 30,
40, 50, etc. Therefore, not
only is it important to tell
at what age the predictions
are valid, it is also impor-
tant to know that the per-
centage gain varies with
stand age.
A Shift in Site Index
Some people use a
shift in site index to predict
the gains from genetics
ALABAMA AGRICULTURAL EXPERIMENT STATION
(Table 5). If this increase in site index is permanent, then
the carrying capacity (i.e. the maximum amount of pine
volume the stand can support when the current annual
increment [cubic feet per acre per year] reaches zero) will
be increased, and use of growth and yield models to project
this increase will be appropriate.
However, the lift in site index can either be tempo-
rary or it can be permanent (Sprinz 1987). If the lift is
temporary, then the maximum carrying capacity of the
site will not be increased. This method is not appropriate
to use when volume gains from planting morphologically
improved seedlings are considered since better planting
stock does not increase the maximum carrying capacity
of the site. When volume gains occur due to planting seed-
lings with larger diameters, the gain in growth is due to a
temporary lift; some call this a Type I growth response
(Snowdon and Khanna 1989).
The Establishment Quality Boost
One way to model a temporary lift is to use the es-
tablishment quality boost (EQB) option in the growth and
yield model PTAEDA2V. The EQB technique has been
used to model gains from planting large-diameter seed-
lings and from herbaceous weed control. For a one-year
EQB, the stand characteristics of a typical nine-year-old
stand are used as the input data for the initial eight-year-
old stand. Likewise, for a two-year EQB, the characteris-
tics of a typical 10-year-old stand are used as the starting
point. Yields from applying these establishment techniques
are derived by increasing the stand structure.
The EQB method is very different from the age-shift
approach. The EQB method appears to underestimate
early seedling-size gains (10 to 18 years) while overesti-
mating gains at later ages (35 to 50 years). The EQB
method also predicts a strong synergistic interaction be-
tween seedling size and herbaceous weed control (which
most empirical studies do not support). South (2000) rec-
ommends that the age shift method be used instead of the
EQB method.
TABLE 5. VOLUME GAINS FROM GENETICALLY
IMPROVED SEEDLINGS BY INCREASING THE SITE
INDEX BY 12%1
Site Site
Age index 70 index 78.5 Difference Percent
yrs cu fi/ac cu fi/ac cu ft/ac gain
15 2,319 2,915 596 25.7
25 4,437 5,647 1,210 27.3
50 5,443 6,560 1,117 20.5
'Using PTAEDA2V random seed number 68767 for an
unthinned stand.
Figure 3. Hypothetical gains from a one-year advance
in stand development for loblolly pine (South 2000).
Gain (Cubic feet per acre)
500
400 Highsite
300 -- v r g st
200
0
5 9 13 17 21 25 29 33 37 41 45 49
7 11 15 19 23 27 31 35 39 43 47
Age
The Age Shift Approach
A simple way to model the gains from planting mor-
phologically improved seedlings is to advance the stand
age. In other words, getting the trees off to a faster start
could result in a 10-year-old stand that would have the
same stand structure and would grow the same as a nor-
mal stand at age 11. This method appears more appropri-
ate when a temporary lift in site index occurs. For loblolly
pine, this method would not show much gain in per acre
volume production at age 50.
A growth and yield model (Hafley et al. 1982) was
used to estimate volume gains from a 1-year advance in
stand development (Figure 3). This indicates that a 1-year
gain will result in more volume on high sites than on low
sites. On the high site, one might expect intensive man-
agement to increase productivity by about 400 cubic feet
per acre per year at year 12 and by 300 cubic feet per acre
at year 21. On low sites, a 1-year gain might only be 150
to 170 cubic feet per acre (at ages 15-20). Assuming the
difference in RCD is 2 mm (for example, planting 6 mm
seedlings vs. 4 mm seedlings), these values are similar to
those reported in Table 4.
HOW TO OBTAIN
A ONE YEAR AGE SHIFT
A one-year age shift can be obtained by several meth-
ods. One method would be to purchase seedlings from
the local nursery and grade out all seedlings that have a
RCD greater than 5 mm. The remainder could either be
thrown away (very expensive) or repackaged and sold
(possibly at the same price per thousand) to a contractor
who likes to plant seedlings with small roots.
The results from this method should be similar to past
studies where only Grade 1 seedlings were planted. How-
ever, the disadvantage of these seedlings is that since they
were grown at seedbed densities near 27 plants per square
foot, they would not be morphologically improved and
PLANTING MORPHOLOGICALLY IMPROVED PINE SEEDLINGS TO INCREASE 
SURVIVAL AND GROWTH
may not have a good root-weight ratio. In some cases,
there may be few seedlings with 5 or 6 mm RCD and the
development of the secondary foliage may also be mini-
mal. Any additional exposure during the grading process
might negatively affect survival. Therefore, their chance
of surviving a drought would be only marginally better
than in the past when densities greater than 45 plants per
square foot were used (Dierauf 1973).
The recommended method would be to contact a
nursery manager well before sowing and have the man-
ager contract grow seedlings at a low seedbed density (a
target density of 15 to 20 plants per square foot for loblolly
and slash pine). The seedlings should be cultured so that
they produce many fibrous roots and should be carefully
lifted to retain both a good root-weight ratio and fibrous
roots. The average seedling RCD should be 6 mm (or
greater). Any seedlings with RCD less than 4 mm should
be culled. This method should produce growth gains simi-
lar to those in Table 4.
HOW TO OBTAIN
A TWO YEAR AGE SHIFT
A two-year shift in age can be achieved by planting
morphologically improved seedlings and applying a her-
bicide application to control herbaceous weeds. In some
cases, applying several applications of herbicides (dur-
ing the first growing season) to regular seedlings can re-
sult in a 0.6 to 1.4 year shift in the height growth curve
(Lauer et al. 1993). Although the number of published
studies about the effects of applying herbicides to larger
seedlings is limited, it appears that early growth gains from
applying herbicides and planting morphologically im-
proved seedlings are additive (Mitchell et al. 1988; Britt
et al. 1991; South et al. 1995; South and Mitchell 1999a;
South et al. 2001).
Obtaining a two-year shift in age without the use of
herbicides is more difficult. The probability of actually
achieving such a two-year gain is less certain because it
requires a thorough under-
standing of interactions be-
Figure 4. A hypothetical interaction of stock size, planting time, and weed competition
on initial seedling growth (adapted with permission from Kimmins 1989).
Small seedlings
So 3-4 mm RCD
PP P P
Large seedlings
7-10mm RCD
=
TIME SINCE HARVEST
tween planting date, seed-
ling size, weed competition,
insect pests, and soil mois-
ture. For example, to avoid
competition from herba-
ceous weeds, the time be-
tween harvest and planting
may need to be shortened
(Figure 4).
To obtain a two-year
shift in age without the use
of herbicides would require
an integrated approach to
regeneration so that no
weak link spoils the efforts.
To begin with, nursery cul-
tural practices should be
followed to produce an av-
erage RCD of near 8 mm
without the seedlings being
too tall. The seedling cull-
ing standard should be
raised to at least 4 mm. In
order to be economical, this
will mean growing at low
seedbed densities and will
likely involve fall fertiliza-
tion with nitrogen.
The most important
factor would be to avoid
late winter planting (late
February and March). In
7
8 ALABAMA AGRICULTURAL EXPERIMENT STATION
fact, if the soil moisture is adequate, the two-year shift in
age would be easier to achieve if seedlings could be
planted and established in late October or early Novem-
ber. This would require little or no storage between lift-
ing in the nursery and outplanting. In the past, however,
planting in October was successful on an operational scale
(St. Regis in Florida and Union Camp in Georgia).
Proper depth of planting would also be very important.
Seedlings should be provided with a sufficiently deep hole
and should be planted at least 3 inches deeper than the level
at which they were grown in the nursery. Machine planting
would likely be less stressful than hand- planting.
Although planting large-diameter seedlings of
Douglas-fir appears to achieve an establishment boost of
two or more years (Blake et al. 1989), a two-year boost
with loblolly pine has not yet been documented (since
studies comparing 10 mm RCD seedlings with 3 mm RCD
seedlings have not been in-
stalled). However, one Figure 6. Realized 
volume g
study with slash pine seedlings that average 5.3 n
(South and Mitchell due to planting slightly large
1999a) found 
that early 
convert the 
values to an 
abs
treatment. From this site, pr
growth gains from planting the more intensive treatmen
10.5 mm RCD seedlings Herb = herbicide; 
SPD = Sh
exceeded that 
of applying
double-bedding and a her-
bicide to 3.5 mm seedlings 700
(Figure 5). Studies like this 600
suggest that many land- 500
owners are using morpho- 
400
logically inferior seedlings 
300
(Table 2). 
200
100
PREDICTED AND 0
REALIZED GAINS (100)
Models can 
be useful 
control
for making management 
DAP
decisions but rarely do they
predict the results for an in-
dividual site. For example,
Figure 6 shows the realized
gains (black bar) for planting seedlings that averaged 5.3
mm at the groundline at time of planting. The control plot
included only minor site preparation (inject hardwoods
with herbicide followed by a burn) while the best response
was observed on an area with a shear, pile, and disk (South
et al. 1995). The gray bars show the estimated volume
gain from planting seedlings that averaged 6.4 mm RCD
(or 1.1 mm larger at the groundline). Although the mea-
surements were real for the 6.4 mm seedlings, the vol-
ume gains per acre were estimated (volume per acre was
derived using both measured survival gains and measured
individual tree volume gains).
Figure 5. Effect of seedling size and intensive silvicul-
ture on early growth of slash pine seedlings (South and
Mitchell 1999).
4th-yr biomass Index 
(dinm
2
)
10
8
61-
3.5 10.5
RCD at planting (mm)
SSingle bed 
Double bed
e d +Herbicide
ains (age 12) for various silvicultural practices using
mm at the groundline (black bars). Predicted volume gains
r seedlings (6.4 mm) are represented by gray bars. To
solute basis, add 1,260 cubic feet per acre to each
edicted gains from planting larger stock are greater for
ts (South et al. 1995). DAP = diammonium phosphate;
iear, Pile, and Disk.
feetlacre)
...
.........
Herb
DAP+Herb
SPD SPD+Herb
SPD+DAP SPD+DAP+Herb
5.3amm m6.4mm
Real BE Projected
While this could be an exaggerated estimate (South
et al. 1995), it does suggest the early gains from planting
large diameter seedlings are potentially greater when
growth is accelerated by applying intensive silviculture.
In other words, economic gains from planting morpho-
logically improved seedlings will be greater for
short-rotation, intensively managed plantations than for
long-rotation, less intensively managed plantations. In one
example (Figure 6), the estimated gains (due to planting
larger seedlings) at age 12 for the most intensive treat-
ment (shear + pile + disk + diammonium phosphate + the
herbicide hexazinone) was 245 cubic feet per mm.
PLANTING MORPHOLOGICALLY IMPROVED PINE SEEDLINGS TO INCREASE SURVIVAL AND GROWTH
ECONOMIC ADVANTAGES
OF PLANTING MORPHOLOGICALLY
IMPROVED SEEDLINGS
In the past, landowners have purchased genetically
improved seedlings, which cost more than seedlings that
had no genetic improvement. In some cases, the differ-
ence between unimproved seedlings (called woods run
seedlings) and genetically improved seedlings was $8 per
thousand plantable seedlings. However, even when using
the wrong genetic provenance, the landowner was usu-
ally willing to pay extra for genetically improved seed-
lings. Landowners considered the additional cost to be
minimal compared to the expected additional growth.
Likewise, additional volume growth can be expected
from morphologically improved seedlings but they also
cost more to produce. In some cases, a nursery manager
may charge $10 to $30 more for a thousand seedlings
grown at low seedbed densities (15 plants per square foot)
than at higher densities (27 plants per square foot).
The economic advantage of using morphologically
improved seedlings will vary depending on how the plan-
tation is managed. The economics depend on both spac-
ing in the plantation and the timing of the first thinning.
Since the use of morphologically improved seedlings does
not cause a permanent lift in site index, their use for
unthinned plantations on very long rotations is not rec-
ommended. In contrast, the economics can be very favor-
able if all the additional volume gains, due to using mor-
phologically improved seedlings, are harvested during the
first commercial thinning (age 12 to 15). The present net
value of an additional 100 to 400 cubic feet of wood har-
TABLE 6. PROJECTED MERCHANTABLE V4
AND SUBSEQUENT GAINS IN PRESEN
Year Dominant height Harvest age Volu
advance (age 15) cu
One 60 15
60 20
50 15
50 20
40 15
40 20
Two 60 15
60 20
50 15
50 20
40 15 .
40 20
'Gains made by achieving a one- and two-year advance in
2 Volume gain per acre calculated from the NCSU Plantatic
upper-coastal plain sites. Assumes planting 360 trees pera
stumpage value of $0.60/cubic foot; and a 26% tax bracket.
vested at age 15 can easily exceed an additional $10 -$20
per acre cost in seedlings (Table 6: South et al. 1985;
Caulfield et al. 1987).
The economics will also be affected by planting den-
sity. Some researchers (Bailey 1986; Borders et al. 1991)
recommend outplanting up to 1,300 trees peracre (TPA)
while others (Vardaman 1989; Bowling 1987) recommend
outplanting 300 to 400 TPA. Therefore, the additional cost
per acre for morphologically improved seedlings can vary
from less than $10 (at 300 TPA) to $39 (at 1,300 TPA).
Due to density-related competition, merchantable volume
production at age 20 to 25 is not strictly proportional to
the number of trees planted. In fact, on some sites, mer-
chantable volume may even be the same for trees planted
at 300 TPA and 1,200 TPA (Harms and Lloyd 1982;
Sarigumba 1985). Therefore, the incremental gains (due
to planting morphologically improved seedlings) will not
be proportionally increased by planting four times as many
trees. As a result, the economic advantage of using mor-
phologically improved seedlings is much lower when
outplanting densities are high. In some cases, machine
planting 500 morphologically improved seedlings per acre
will be less expensive than planting 726 regular seedlings
(South and Mitchell 1999b).
SUMMARY
Loblolly and slash pine seedlings grown at low seed-
bed densities (less than 20 plants per square foot) are con-
sidered to be morphologically improved if they (1) are
larger in diameter (half or more of the plantable seed-
lings have RCDs greater than 5 mm and none less than 3
mm), (2) have a higher
root-weight ratio, (3) have
OLUME GAINS been cultured to produce
T VALUE
1  
more fibrous roots, and (4)
n gain Gain/acre are not taller than seedlings
Sf/aic $ raised at higher densities.
Survival of properly
300 $74 planted morphologically
260 $48 improved seedlings will
260 
$36 usually 
be greater than
150 $28 
seedlings grown at high
170 $24 seedbed 
densities. Al-
800 $148 though there may be no dif-
770 $106 ference in survival when
530 $98 conditions for survival are
320 $59 favorable (greater than 9Q%
330 $46 survival), an increase of 4
to 10 percentage points is
stand development, possible when survival of
on Management Simulator for regular seedlings is less
Lcre; a 6% real interest rate; athn7%
10 ALABAMA AGRICULTURAL EXPERIMENT STATION
Machine planting is recommended when planting
morphologically improved seedlings. Because they have
larger roots, morphologically improved seedlings may
require more time to plant properly by hand. Therefore,
supervision will be essential to keep tree planters from
(1) reducing the root-weight percentage by pruning and
stripping roots prior to planting, (2) cramming the large
roots in a shallow planting hole, or (3) failing to plant the
root-collar 3 to 5 inches below the groundline.
When planted properly, morphologically improved
seedlings can advance stand development by one year. A
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12 ALABAMA AGRICULTURAL EXPERIMENT 
STATION

Alabama
Agricultural
Experiment
Station
Outlying
Units
Tennessee Valley Research and Extension Center (TVREC)
Sand Mountain Research and Extension Center (SMREC)
North Alabama Horticulture Research Center (NAHRC)
Upper Coastal Plain Research Center (UCPRC)
Chilton Area Research and Extension Center (CAREC)
Black Belt Research and Extension Center (BBREC)
Piedmont Research Center (PRC)
Prattville Research Field (PRF)
E.V. Smith Research Center (EVSRC)
Lower Coastal Plain Research Station (LCPRS)
Monroeville Experiment Field (MEF)
Wiregrass Research and Extension Center (WREC)
Brewton Experiment Field (BEF)
Ornamental Horticulture Station (OHS)
Gulf Coast Research and Extension Center (GCREC)
Main Agricultural Experiment Station (AAES)
at Auburn University and Alabama A&M University