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Root morphology, stem growth and field performance of seedlings of two
Mediterranean evergreen oak species raised in different container types
M. Tsakaldimi
1
, T. Zagas, T. Tsitsoni & P. Ganatsas
Department of Forestry and Natural Environment, Laboratory of Silviculture, Aristotle University of Thes-
saloniki, University Campus, 54 124, P.O.Box 262, The ssaloniki, Greece.
1
Corresponding author*
Received 8 October 2004. Accepted in revised form 17 February 2005
Key words: container seedlings, outplanting performance, Quercus coccif era, Quercus ilex, root
morphology, stem growth
Abstract
Outplanting container-grown oak seedlings with undesirable shoot and root characteristics result in poor
establishment and reduced field growth. The objective of this study was to determine the influence of
container type on both above-and below-ground nursery growth and field performance of one-year old tap-
rooted seedlings Quercus ilex L. and Quercus coccifera L. The experiment was conducted in an open-air
nursery and the seedlings were grown in three container types. At the end of the nursery, growth period
seedlingsÕ shoot height, diameter (5 mm above root collar), shoot and root biomass, root surface area, root
volume and total root length were assessed. Then the seedlings were planted in the field and their survival
and growth were recorded for two growing seasons after outplanting. The results showed a difference
between the Quercus species in the effect of container type. Q. ilex seedlings raised in paper-pot had
significantly greater height, diameter, shoot and root biomass and root volume than those raised in the
other two container types. Similarly, Q. coccifera seedlings raised in paper-pot, had significantly greater
above-and below-ground growth than those raised in the other two container types. Both oak species
showed relatively low survival in the field; the mortality was mainly observed the first year afte r out-
planting, especially after the summer dry period. However, 2 years after outplanting, the paper-pot seed-
lings of the two oak species showed better field performance.
Introduction
In ecological studies, the evergreen sclerophylls
are regarded as one of most typical compo-
nents of the Mediterranean type vegetation
(Saleo and LoGullo, 1990). Many restoration
projects have established plantations of these
evergreen resprouting species (Vallejo et al.,
2000; Vilagrosa et al., 2003). Despite the great
efforts in oak regeneration research, the suc-
cessful planting of oaks is still fraught with
uncertainty (Pope, 1993). Early attempts to
introduce broad-leaved resprouting species to
the Mediterranean basin (e.g., Quercus spe-
cies) faced high seedling mortality, and until
recently, nursery and field techniques were
poorly developed for these two species (Pausas
et al., 2004). In eastern Spain as well as in
Greece, the field survival and growth of planted
Mediterranean oaks are frequently very low
(Hatzistathis et al., 1999; Pausas et al., 2004;
Tsakaldimi, 2001; Vilagrosa et al., 2003; Vi llar-
Salvador et al., 2004).
The poor development of Quercus seedlings
plantations, in some cases, could be attributed
to the low quality of the planted seedlings.
*E-mail: marian@for.auth.gr
Plant and Soil (2005) 278:85–93 Springer 2005
DOI 10.1007/s11104-005-2580-1
Nursery cultivation regimes can strongly deter-
mine the functional characteristics of seedlings
and their field performance (Landis et al.,
1990; Simpson, 1995; Villar-Salvador et al.,
2004). For instance, during the container seed-
ling production, container size, growing density
and design characteristics of the containers are
important determinants of seedling quality
(Landis et al., 1990). The volume of the cavity
is one of the most obvious and important
characteristics of a container because in gen-
eral, the larger the container the larger the
seedling that can be produced. However, the
optimum container size varies according to
many different factors, including species, grow-
ing density, environmental conditions and
length of the growing season. Pine species that
are tolerant of crowding, such as loblolly pine,
could be produced in small-volume containers
with a high growing density. In contrast,
broad-leaved species should be produced at
lower growing density because their leaves
intercept more water and nutrients and gener-
ate more shade (Landis et al., 1990). One of
the most serious problems in containers, espe-
cially in the case of seedlings with tap roots
such as oaks, is the tendency of seedling roots
to spira l around the inside of the container or
to concentrate at the base of the container
(Biran and Eliassaf, 1980; Landis et al., 1990).
Root spiraling is most serious in round,
smooth-walled plastic containers and can seri-
ously reduce seedling quality after outplanting.
In contrast, well-developed and well-structured
root systems with numerous first order laterals
are one of the most essential attributes of high
quality oak seedlings (Day and Parker, 1997;
Thompson and Schultz, 1995).
However, the influence of container type
on seedling quality and the outplanting per-
formance of Mediterranean oak species has
received almost no attention and to the best of
our knowledge, no study on root morphology
of seedlings of these species has been reported.
Thus, the objective of this study was to
determine the influence of container type on
both above- and below-ground nursery growth
and field perfor mance of two tap-rooted seed-
lings, Quercus ilex and Quercus coccifera.
Materials and methods
Nursery phase
Experimental treatments The experiment was con-
ducted in an open-air nursery of Forest Service
(N. Chalkidona, North Greece). Acorns of Quer-
cus ilex L. and Quercus coccifera L. were sown in
mid-March. Three container types were selected to
provide a wide range in container volumes, density
of plants, and design characteristics as these have
been shown to have a strong influence on the mor-
phology and field performan ce of seedlings (Jones
et al., 2002; Landis et al., 1990; Salonius and Be-
aton, 1994). The container types used for the tap-
rooted seedlings production were: (a) paper-pot FS
615; made of biodegradable paper, planted with
the seedling, each cavity is hexagonally shaped,
bottomless, 482 · 10
3
mm
3
in volume and 150 mm
in depth, and (b) and (c) two rigid re-usable plastic
containers from which the seedlings are removed
before planting: (b) quick pot T18; each cavity is
of square shape, tapered from top to bottom, has
interior vertical anti-spiralling ribs and open cros-
sed base and is 650 · 10
3
mm
3
in volume and
180 mm in depth, and (c) plantek 35F; each cavity
has similar design features to quick-pot but air
root pruning is achieved from the sides of the
walls and from the base, and is 275 · 10
3
mm
3
in
volume and 130 mm in depth. All cavities were fil-
led with sphagnum Lithuanian peat of medium
structure and coarse perlite (3:1, v/v). This potting
medium is commonly used in Greek forest nurser-
ies. The potting med ium was fertilized with 1.3 kg
mixed fertilizer (N:P:K 15:30:15 + micronutri-
ents), 0.6 kg potassium sulf ate, 1.0 kg superphos-
phate (0-20-0), 0.4 kg magnesium sulfate and 2 kg
lime (CaO) per m
3
of peat.
The three treatments were arranged in a ran-
domized complete block design with three repli-
cations for each of 2 species · 3 container types.
There were 24 seedlings per container type, in
each block (total 216 seedlings per species) and
all seedlings were identified with a number. All
seedlings were irrigated with an overhead irriga-
tion system, as ne eded.
Growth measurements and destructive sampling At
the end of the growth pe riod in the nursery, on
86
November, the shoot height, the diameter
(measured 5 mm above the root collar) of all
seedlings were measured with an accuracy of 1
and 0.1 mm, respectively. Twelve randomly se-
lected seedlings per treatment (4 seedlings · 3
replications) of each species, were collected for
destructive sampling and they were transferred to
the Laboratory for biomass measurements. From
these selected seedlings, five random root samples
per treatment were used for the root morphology
estimations prior to biomass measurements. The
root system was separated from the soil, under a
gentle water jet, using a sieve to collect any root
fragments detached from the system. Then, each
root system was put into a glass box and covered
with a white plastic sheet to keep it in a fixed
position and improve the contrast of the root im-
age. The box was placed on a scanner (Hewlett
Packard, ScanJet 6100C) connected to a com-
puter, and an image analysis system (DT-Scan,
Delta T-Devices) was used to determine the total
root length, the root surface area and the total
root volume (Barnett and McGilvray, 2001;
Fitter et al., 1991). For biomass measurements
the seedlings were divided into two parts: shoot
(stem + needles) and root system. Both parts
were oven-dried at 70 C for 48 h and then they
were weighed (Thompson, 1985).
Field experiment
In early December, eight-month-old Q. ilex and Q.
coccifera seedlings were outplanted to the field in
ÔKassandraÕ Peninsula, Chalkidiki (North Greece),
which is located 80 km south-east of Thessaloniki
at 2530¢ Eand40 N. According to the climatic
data (period 1978–1997) from the meteorological
station of the Forest Service, the climate of the area
is of the Mediterranean type with mild winters and
dry hot summers. The mean annual rainfall reaches
581 mm, while the mean annual air temperature
goes up to 16.3 C and the mean maximum air
temperature of the warmest month (July) is
30.1 C. The dry period begins in the middle of
April and lasts until the middle of September (Tsa-
kaldimi, 2001; Tsitsoni, 1997). The vegetation of
the area belongs to Quercetalia illicis floristic zone.
For each species, twenty seedlings per treatment
per replication were planted in a randomized
complete block design with three replications; the
identity of nursery blocks was maintained in the
field. Experimental blocks (500 m
2
each) were lo-
cated on three independent sites of W, NW and
N aspects and of moderate slopes (15–30%) and
they were not irrigated. The distance between the
sites was approximately 300 m. The soil of the
three sites, where the experiment was conducted,
is characterized as deep, sandy-clay loam, neutral
to moderate alkaline and rich in organic matter
at the surface horizons (Tsakaldimi, 2001).
The seedlings being hand planted in pits
(0.30 · 0.30 m) and they were spaced 2 m apart.
The survival was recorded for each seedling for
two successive years after planting. Furthermore,
2 years after planting, height and diameter
growth of each seedling were assessed (with an
accuracy of 1 and 0.1 mm, respectively). The rel-
ative growth rates (RGR) for both height and
diameter, after a period of 2 years, were calcu-
lated as the difference between the natural loga-
rithms of final and initial height or diameter
respectively, divided by time between the begin-
ning and the end of field experiments (in years)
(Elvira et al., 2004; Villar-Salvador et al., 2004).
Statistical analysis
All statistics were calculated with SPSS software.
Distribution was tested for normality by Kolmogo-
rov--Smirnov criterion and the homogeneity of
variances was tested by LeveneÕs test. The percent-
ages were transformed to arsine square root values,
before analysis. Significant differences between
treatment means were tested using analysis of vari-
ance (one-way ANOVA). Wherever treatment ef-
fects were significant, the DuncanÕsMultipleRange
Test was carried out to compare the means (Noru-
sis, 1994; Snedecor and Cochran, 1988).
Results
Nursery performance
Both species were affected by the type of con-
tainer. Q. ilex seedlings grown in paper-pot were
significantly taller, had greater diameter and
shoot biomass than seedli ngs grown in quick-pot
and plantek (Table 1). Also, the root biomass,
the shoot/root mass ratio and the total root vol-
ume found to be significantly greater in seedlings
87
grown in paper-pot than in seedlings grown in
quick-pot and plantek. The total root surface area
and root length did not show signifi cant differ-
ences among the paper-pot and quick-pot seed-
lings, but were significantly greater than those of
plantek seedlings.
Similarly to Q. ilex seedlings, Q. coccifera
paper-pot seedlings exhibited the greatest height,
diameter and shoot biomass (Table 2). On the
contrary, the seedlings grown in quick-pot did
not differ from those grown in plantek but both
were found significantly smaller than paper-pot
seedlings. The container type significantly
affected the root morphology. Paper-pot seed-
lings had a more extended ro ot system; their root
surface area and the total root length were signif-
icantly greater than that of seedlings raised in
plastic containers, and were twice or more great-
er than those of plantek seedlings. The root vol-
ume, and the root biomass allocation did not
differ between paper-pot and quick-pot seedlings
but remained greater than that of plantek seed-
lings. The shoot/root mass ratio was significantly
greater in seedlings grown in paper-pot.
Field survival
One year afte r outplanting (on November), the
survival rate presented significant diff erences
among the treated seedlings of Q. ilex, and it was
Table 1. Effects of container type on Q. ilex seedling characteristics at the nursery phase
Container type
Paper-pot Quick-pot Plantek
(FS 615) (T18) (35 F)
Above-ground seedling characteristics
Shoot height (mm) 401 (12.1)
a
208 (9.1)
b
240 (8.1)
b
Root-collar diameter (mm) 5.1 (0.12)
a
4.3 (0.09)
b
4.2 (0.09)
c
Shoot dry weight (g) 8.3 (0.80)
a
4.2 (0.44)
b
3.8 (0.24)
b
Below-ground seedling characteristics
Root dry weight (g) 4.6 (0.43)
a
3.5 (0.30)
b
2.9 (0.23)
b
Root surface area (mm
2
) 13 168 (1110)
a
11 806 (1536)
a
8057 (896)
b
Root volume (mm
3
) 6630 (890)
a
4220 (570)
b
4240 (610)
b
Total root length (mm) 7376 (701)
a
8144 (863)
a
4440 (502)
b
Shoot dry weight/Root dry weight 2.0 (0.1)
a
1.2 (0.1)
b
1.3 (0.1)
b
Values are means ± standard error (in parenthesis). Within a row, means followed by different letters, are significantly different
(P < 0.05).
Table 2. Effects of container type on Q. coccifera seedling characteristics at the nursery phase
Container type
Paper-pot Quick-pot Plantek
(FS 615) (T18) (35 F)
Above-ground seedling characteristics
Shoot height (mm) 283 (15.4)
a
136 (11.5)
b
139 (9.2)
b
Root-collar diameter (mm) 4.2 (0.12)
a
3.1 (0.11)
b
3.1 (0.09)
b
Shoot dry weight (g) 4.5 (0.69)
a
2.1 (0.25)
b
1.6 (0.11)
b
Below-ground seedling characteristics
Root dry weight (g) 3.6 (0.49)
a
2.8 (0.29)
a
1.7 (0.14)
b
Root surface area (mm
2
) 12 306 (1996)
a
7950 (888)
b
5839 (614)
b
Root volume (mm
3
) 6410 (1290)
a
4260 (460)
ab
3300 (480)
b
Total root length (mm) 6233 (963)
a
4148 (462)
b
2973 (353)
b
Shoot dry weight/Root dry weight 1.3 (0.08)
a
0.7 (0.05)
c
0.9 (0.07)
b
Values are means ± standard error (in parenthesis). Within a row, means followed by different letters, are significantly different
(P < 0.05).
88
(a)
a
a
b
b
b
b
0
10
20
30
40
50
60
70
80
90
100
1
Years after field planting
Seeding survival in the field (%)Seeding survival in the field (%)
paper-pot
quick-pot
plantek
(b)
a
a
b
b
b
b
0
10
20
30
40
50
60
70
80
90
100
Years after field planting
paper-pot
quick-pot
plantek
2
12
Figure 1. Effect of container type on Q. ilex (a) and Q. coccifera (b) seedling survival in the field; the first and the second year
after outplanting. For the same year, means followed by different letter are significantly different (P < 0.05). Error bars are not
shown because they are too small.
Table 3. Container type effects on height, root collar diameter and relative growth rates (RGR) for Q. ilex and Q. coccifera seedlings,
2 years after field planting
Field growth Container type
Paper-pot Quick-pot Plantek
(FS 615) (T18) (35 F)
Q. ilex
Height (mm) 473 (22.5)
a
315 (21.4)
b
362 (26.6)
b
Height RGR (mm mm
)1
year
)1
) 0.9 (0.12)
b
1.8 (0.26)
a
1.6 (0.39)
a
Root-collar diameter (mm) 8.4 (0.37)
a
6.3 (0.28)
b
6.4 (0.37)
b
Diameter RGR (mm mm
)1
year
)1
) 0.25 (0.02)
ns
0.20 (0.03)
ns
0.21 (0.03)
ns
Q. coccifera
Height (mm) 367 (23.6)
a
278 (28.7)
b
273 (24.2)
b
Height RGR (mm mm
)1
year
)1
) 1.6 (0.23)
b
2.7 (0.35)
a
3.1 (0.53)
a
Root-collar diameter (mm) 6.6 (0.32)
ns
5.8 (0.31)
ns
5.7 (0.47)
ns
Diameter RGR (mm mm
)1
year
)1
) 0.24 (0.03)
ns
0.28 (0.03)
ns
0.29 (0.05)
ns
Values are means ± standard error (in parenthesis). Within a row, means followed by different letters, are significantly different
(P < 0.05).
89
negatively affected by the summer drought peri-
od (Figure 1a). Seedlings grown in paper-pot pre-
sented significantly greater survival rate (73.3%)
than those grown in quick-pot (50.9%) and
plantek (42.9%). During the second year after
outplanting, the summer drought period caused
a further reduction of survival rate; 8.3% for
paper-pot seedlings, 5.3% for quick-pot seedlings
and 12.5% for plantek seedlings.
Q. coccifera seedlings had also difficulties
surviving in the field (Figure 1b). The first year
after outplanting, the survi val rate significantly
reduced. The survival of paper-pot seedlings
was 73.6%, while the survival recorded in the
quick-pot and plantek seedlings reduced at half,
and it was 47.9 and 47.7%, respectively. At the
end of the second growth period in the field, the
survival rate reduced to 71.7% for paper-pot
seedlings, 41.7% for quick-pot seedlings and
45.5% for plantek seedlings.
After recording survival rates we excavated
five dead seedlings of each treatment and species
and found that their roots were restricted to the
space of the nursery roo t plug and none of them
had developed new roots out of it.
Growth in the field
At the end of the second year in the field, 23
months after outplanting, the Q. ilex seedlings
shoot height and diameter presented significant
differences among the treatments and followed
the same trend as in the nursery (Table 3). The
larger and thicker seedlings were those that had
grown in paper-pot and the smaller seed lings
were those that had grown in quick-pot and
plantek. However, quick-pot and plantek seed-
lings showed significantly greater height RGR
than paper-pot seedlings, while the diameter
RGR did not differ amon g treated seedlings.
Similarly, the larger Q. coccifera seedlings had
grown in paper-pot while the smaller ones had
grown in quick-pot and plantek. The quick-pot
and plantek seedlings again showed significantly
greater height RGR than the paper-pot
seedlings
while their diameter and diameter RGR did
not show significant differences among treated
seedlings (Table 3).
Discussion
The seedlings of both oaks produced in the three
container types, were healthy, none of them
showed root spiraling and all of them approxi-
mately reached the appropriate dimensions for
planting. According to EU legislation (Council
Directive 71/161/EEC, 1971) Quercus seedlings, 1
or 2 years old, are considered suitable for planting
when their height is 150–250 mm and root-collar
diameter is 4 mm. Concerning the Mediterranean
oaks, Nardini et al. (2000) found that two-year
old Q. ilex seedlings, raised in containers, were
much smaller than those of our study; their stem
diameter was only 2.7 mm, height 420 mm, total
root dry weight 0.5 g and root surface area was
3680 mm
2
. Also, Villar-Salvador et al. (2004),
found that 10-month-old Q. ilex seedlings, grown
in forest-pot 300 containers and fertilized with
slow-release fertilizer N:P:K (15:7:15), 1 kg m
)3
peat, were only 141 mm in height and they allo-
cated shoot dry weight 1.72 g and root dry wei ght
3.39 g. In our study, seedling dimensions of the
two oak species were much differentiated among
the container types used. In both oak species,
seedlings raised in paper-pot were superior to seed-
lings raised in the other two plastic containers.
Contrary to what has been reported for large r
containers with lower growing densities (Aphalo
and Rikala, 2003; Landis et al., 1990; Tanaka and
Timmis, 1974), the paper-pot although it is smaller
in size and create higher seedling densities than
quick-pot, it increased shoot height, diameter, bio-
mass allocation and enhanced the root morphol-
ogy of the oak seedlings. A possible explanation for
this, is the construction material of the paper-pot;
the paper is permeable and allow water and solu-
ble salts to move late rally between the cavities of
the container. This positively affected the water
and nutrient availability for each seedling and thus
enhanced the seedlingsÕ growth (Tsakaldimi,
2001). Moreover, although there are no measure-
ments, the quick-pot and plantek, which are plastic
and black- colored containers, may absorb more
solar radiation which can increase the root tem-
perature. High soil temperatures were especially
reported for black plastic containers (Whitcomp,
1989). The high root temperatures can inhibit root
growth and may even result in seedling mortality
(Landis et al., 1990).
90
In the field, both oak seedlings had difficulties
to survive, but the mortality was much higher in
Q. ilex seedlings. Similarly, Villar-Salvador et al.
(2004) report that Q. ilex seedlings have lower
survival and grow th when compared with other
Mediterranean woody species. This indicates that
this species is more susceptible to stress factors
during its early life stages and especially during
the first summer period. In this study also, the
mortality was mainly observed at the end of the
first year after outplanting and after the summer
dry period, and varied considerably among the
container seedlings. The survival rate of paper-
pot seedlings was much greater (73.3 % for Q. ilex
and 73.6% for Q. coccifera) than that of the
other container seedlings, while the survival rate
of the plantek seedlings was only 42.9% for
Q. ilex and 47.7% for Q. coccifera. At the end of
the second year after outplanting, there was a
further reduction of seedling survival. However,
the survival of seedlings grown in paper-pot
remained higher (65 and 71.7% for the Q. ilex
and Q. coccifera , respectively) while the survival
recorded for plantek seedlings was 45.5% for
Q. coccifera and only 30.4% for Q. ilex. Villar-
Salvador et al. (2004) found that 2 years after
outplanting, the mortality of Q. ilex seedlings
reached to 42% and tended to occur during the
summer period. Hatzistathis et al. (1999) found
that Q. ilex grown in paper-pot, had very low
survival (33.7%), 18 months after outplanting in
the Kassandra, northern Greece.
The better survival of paper-pot seedlings can
be attributed to their initial morphologic al char-
acteristics. Villar-Salvador et al. (2004) reported
that, Q. ilex seedlings with largest shoots and
with a higher S/R ratio had lower mortality than
those with opposite attributes, 2 years after out-
planting. Cortina et al. (1997) found that shoot
height was also positively correlated with field
survival of Q. ilex seedlings. Also, in a previous
study, Tsakaldimi (2001) found that diameter
was a good predictor for field survival of
Q. coccifera seedlings; the thicker the seedlings
the higher the survival. Similarly, in our study,
the paper-po t seedlings of both oak species, that
exhibited the lower mortality, had much greater
shoot height, root-collar diameter, shoot dry
weight and S/R ratio at the time of planting. The
poor performance of smaller seedlings may be
due to an unbalanced carbon economy during
their establishment phase and the summer period
(Villar-Salvador et al., 2004). Root characteristics
may also have contributed to the better survival
of paper-pot seedlings. The greater root volume
and root surface area (as well as the great er total
root length only in the case of Q. coccifera
)of
paper-pot seedlings, may have resulted in a better
water and nutrient uptake during their early
stages after outplanting and especially during the
summer drought. When growth or survival is
limited by water (as is observed in the Mediterra-
nean basin) or nutrient availability, immediately
after outplanting, roots play a more important
role in the performance of container seedlings
(Aphalo and Rikala, 2003). Furthermore, it may
be important that paper-pot seedlings were plan-
ted with pots, thus, they had their roots pro-
tected not only during the planting work but the
whole first year after outplanting until the roots
increased and penetrated the soil. In contrast,
quick-pot and plantek seedlings, which were plan-
ted without the cavity, had their roots unpro-
tected and moreover their roots had difficulty
crossing a textural discontinuity from a light, fri-
able grow ing medium to natural soil (Tinus,
1986). According to Ruehle and Kormanik
(1986), oak seedlings must develop new roots
soon after planting if they are to survive and
grow. This seems to be confirmed in our study
since all the excavated dead seedlings had devel-
oped no roots out of the nursery plug.
The differences in seedlings size in the nursery
phase, of both oak species, persisted 2 years after
the outplanting in the field. Paper-pot seedlings
remained significantly taller than the other con-
tainer seedlings, although the height relative
growth rate (RGR) was greater in quick-pot and
plantek seedlin gs. Q. ilex seedlings raised in
paper-pot also had the greatest field diameter,
while their diameter relative growth rate (RGR)
did not differ from that of the other container
seedlings. In the case of Q. coccifera, although
quick-pot and plantek seedlings had smaller diam-
eter at planting they grew as well as the larger
paper-pot seedlings. However, Villar-Salvador
et al. (2004), reported that Q. ilex seedlings with
larger shoots and with a higher S/R ratio had
larger stem volume increase, 2 years after out-
planting. In contrast, studies among many other
91
species concluded that, differences in seedlings
size at planting disappeared after one or two
growth periods in the field (Jones et al., 2002;
Simpson, 1995). Actually, growth following out-
planting is more complex than mere survival and
is related to the planting environment, the genet-
ic potential and the physiological and morpho-
logical status of the seedlings, at the time of
outplanting (Mexal and Landis, 1990).
Conclusions
The results of this study suggest that the con-
tainer type has a strong influence on seedling
quality and outplanting performance of Q. ilex
and Q. coccifera seedlings. The paper-pot contrib-
utes to the production of taller, thicker and hea-
vier seedlings with a more extended root system.
The better quality of these seedlings in combina-
tion with the fact that the paper-pot seedlings
have their roots protected from transplanting
shock, results in better field performance. Also, it
is suggested that larger oak seedlings have better
survival and they remain greater 2 years after
outplanting. Grading criteria for oak seedlingsÕ
shoot height and root-collar diameter will be
important for sites where environmental stress
may be high.
Acknowledgement
We would like to thank the anonymous referees
for their comments and suggestions on an earlier
version of the manuscript.
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