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Influence of physiological condition
at the time of lifting on the cold
storage tolerance and field
performance of ash and sycamore
C. O’REILLY1, C. HARPER2 AND M. KEANE3
1
Department of Crop Science, Horticulture and Forestry, Faculty of Agriculture, University College Dublin,
Belfield, Dublin 4, Ireland
2 Eurofortech (European Network for Forest and Wood Industries), 39 Mountjoy Square, Dublin 1, Ireland
3 Research & Development Division, Coillte Teo, Newtownmountkennedy, Co. Wicklow, Ireland
Summary
The physiological condition of ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.)
seedlings sampled from the same nursery in Ireland was evaluated at periodic intervals from
September to May, and after cold (1ºC) storage from the time of lifting until May, in 1997/98. Shoot
water potential (WP), root electrolyte leakage (REL) and root growth potential (RGP) were assessed.
In addition, the survival and height increment of seedlings established in a field trial in tandem with
the physiology work was determined after one growing season. Shoot WP of freshly lifted ash
seedlings, but not sycamore, decreased to low values in the winter. REL and RGP values were
generally also lower in ash than in sycamore on most lift dates. Furthermore, sycamore became more
highly active earlier in the year (February/March) than ash (April/May). The effect of cold storage on
physiological responses was not consistent. The survival of seedlings in the field was close to 100 per
cent regardless of treatment. The height increment of freshly lifted sycamore was best for stock
planted from September to early March, whereas ash grew best when planted early
(October–November) or late (after February) in the lifting season, although differences between
most lift dates were small in ash. Under operational forestry conditions, planting during some of
these periods may not be advisable due to the potential effect of handling damage. Cold-stored ash
planted in May after cold storage performed well for seedlings lifted to the store from December to
February, but the physiologically more active sycamore performed best when stored from February.
Introduction
The afforestation programme in Ireland expanded from 5242 ha in 1985 to a peak of
23 460 ha in 1995 (Anon., 1998). Although the
annual area of afforestation has declined in recent
© Institute of Chartered Foresters, 2002
years, the area being planted annually is still relatively large (~15 000 ha). Reforestation accounts
for about another 7000 ha per year. The main
impetus for afforestation has been the incentives
paid by the Forest Service (also supported by the
EU) in the form of grants and premiums. The
Forestry, Vol. 75, No. 1, 2002
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F O R E S T RY
current target is to plant at least 20 per cent of
the new forests with broadleaves (Anon., 1996),
and it is likely that the proportion will increase in
the future. In particular, there is great interest in
the use of ash (Fraxinus excelsior L.) and
sycamore (Acer pseudoplatanus L.) because of
their relatively rapid growth rates, perhaps
making them economically viable forest species.
In addition, there has been a renewed interest in
the use of broadleaved trees for amenity and landscape purposes. The majority (>90 per cent) of
these seedlings are bare-rooted stock.
Unfortunately, the survival and/or growth of
broadleaved seedlings following planting are
sometimes poor, thus necessitating expensive
replanting and/or post-planting maintenance (e.g.
weed control). The quality of the planting stock
used may be contributing to these problems. The
cost penalty owing to plant failure may be higher
for broadleaves than for conifers since they are
more costly to produce and plant, and they are
usually planted at higher densities than conifers
(Joyce et al., 1998).
Seedlings used in the planting programme in
Ireland are usually lifted in the nursery from
about November to March, packed in coextruded polythene bags and dispatched for field
planting. The seedlings may be subjected to a
variety of stresses during this chain of events,
including the possibility of desiccation, rough
physical handling, lack of light (Tabbush, 1988;
McKay, 1997) and carbohydrate depletion during
storage prior to planting (Puttonen, 1986). In
addition, a significant proportion of seedlings are
now placed in cold or freezer storage for a period
before planting. The use of cold storage allows
flexibility in scheduling lifting operations, and the
stock is ready for dispatch for field planting when
field conditions are favourable.
Physiological quality is affected by dormancy
or stress resistance status at the time of lifting, but
cultural practices used in the nursery and plant
handling and storage practices also impact upon
this (Ritchie, 1984; McKay, 1997). The influence
of cultural or irrigation treatments in the nursery
(Farmer, 1975; Hipps et al., 1996, 1997, 1999),
physiological condition at the time of lifting (dormancy, frost hardiness, root growth potential)
(Calmé et al., 1994; McEvoy and McKay, 1997a;
Lindqvist, 1998), handling stresses (desiccation,
rough handling, root pruning) after lifting (Insley
and Buckley, 1985; Murakami et al., 1990;
McEvoy and McKay, 1997b; Symeonidou and
Buckley, 1997; McKay et al., 1999), and cold
storage (Webb and von Althen, 1980) on the
quality and/or field performance of various
broadleaved species has been described. However,
there is little information on the effect of physiological quality at the time of lifting on the cold
storage tolerance and field performance of ash
and sycamore, especially as it pertains to environmental conditions in Ireland.
The physiological status of ash and sycamore
seedlings at the time of lifting and/or following
cold storage were described in this study using
shoot water potential (WP), root electrolyte
leakage (REL) and root growth potential (RGP).
These parameters are important determinants of
stock quality (Ritchie, 1984; McKay et al., 1994).
The survival and first-year height increment of the
seedlings were evaluated in field trials established
in tandem with the physiology work. The objective of this study was to provide baseline information on the influence of physiological
condition (or ‘biological potential’) at the time of
lifting on the cold storage tolerance and field performance of carefully handled ash and sycamore
seedlings. Actual performance under operational
forestry conditions may deviate from this for
many reasons, but the effect of plant handling
stresses, as outlined above, may be the most
important factor influencing this (McKay, 1997).
Materials and methods
Plant material, sampling and cold storage
Ash (Irish seed source: 93(417), ID code HCN109-93) and sycamore (Irish seed source:
94(417), ID code HC-3212-94) 2 + 0 seedlings
from Ballintemple Nursery, Co. Carlow
(52°44N, 6°42W, 100 m a.s.l.) were lifted on
nine occasions from September to May, 1997/98
and dispatched to University College Dublin
(UCD) for study. The soil at Ballintemple is a
sandy loam of pH 5.7, having an organic matter
content of 6–8 per cent, and sand, silt and clay
fractions of 66, 19, and 15 per cent, respectively.
The ash seeds were drill-sown on 25 March 1996
at 51 kg m–2, while the sycamore seeds were sown
on 30 October 1995 at 30 kg m–2, achieving
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COLD STORAGE TOLERANCE OF ASH AND SYCAMORE
densities at the end of the first season of ~110 and
90 seedlings m–2, respectively. Phosphorus was
incorporated into the soil prior to sowing at
500 kg ha–1 (80 kg P) of 0-16-0, but the seedlings
received no other fertilizers in the first year.
Calcium ammonium nitrate with sulphur was
applied twice monthly from April to July in the
second year at 150 kg ha–1 (30 kg N ha–1). The
seedlings were undercut once at 15–17 cm in late
August of the second year, but were not
wrenched. In most other respects, the method of
nursery culture was similar to that described by
Mason (1994). The mean heights (and standard
errors) were 47 (1.1) and 52 (1.5) cm, and the
mean diameters (5 cm above cotyledon scars)
were 11.6 (0.28) and 10.1 (0.23) mm in ash and
sycamore seedlings at the time of lifting, respectively. The means are based upon a sample of 18
seedlings representing each of four lift dates
(seedlings from each lift date treated as a single
replicate).
On each lifting occasion, 150 plants of each
species were loosened by machine and lifted by
hand, then placed in polythene co-extruded bags
(50 seedlings per bag) and dispatched that day for
study to UCD. In an identical manner, three bags
containing 50 seedlings each (total 150) were dispatched for cold storage (1–2°C) once each
month from October to February. Upon removal
from the cold store in May, 100 seedlings (two
bags) were dispatched to the field trial, while 50
(one bag) were retained for the physiological
assessments. Another batch of seedlings was also
lifted and dispatched for field planting on most
lifting occasions, as described below.
Physiological observations and measurements
The physiological tests/assessments were carried
out within 2 days of the date of lifting or date of
removal from cold storage. The seedlings were
assigned at random to each test/determination. A
different sample was used each time and the
plants were held at 2–3°C until the time of
measurement/testing. Due to an inadvertent error
during processing, the shoot WP and REL data
are not available for either species freshly lifted in
November.
Shoot water potential The terminal 7–10 cm of
the leading shoot was excised from each of 15
3
seedlings per species and treatment (freshly
lifted/cold stored) to determine shoot water
potential (WP) using a Schölander type pressure
chamber (Skye Instruments; SKPM 1400) (after
Ritchie and Hinkley, 1975). When present, leaves
were removed before measurement of WP. The
shoots were pressurized using oxygen free
nitrogen.
Root electrolyte leakage The root electrolyte
leakage (REL) tests were carried out using a
method similar to that described by McKay and
Mason (1991). After washing the roots of 15
seedlings per species and treatment to remove
most of the soil, a 300–500 mg (fresh weight)
sample of fine roots (<2 mm diameter) was
removed from the central portion of the root
system of each plant and placed in beakers. The
excised roots were washed thoroughly three
times in tap water. After this, the roots were
rinsed twice in distilled water and placed in 28 ml
universal vials, and 17 ml distilled water was
added. The vials were capped, agitated and then
allowed to incubate at 27°C. The conductivity of
the bathing solution was measured after 18 h
using a conductivity meter with inbuilt temperature compensation (Delta Ohm, HD8706,
Padova, Italy). All root samples were killed by
placing the vials in an oven at 90°C for 2 h. The
samples were allowed to cool to room temperature before taking the second conductivity
reading. The initial 18-h conductivity reading
was expressed as a percentage of the second
reading.
Root growth potential This test was carried
out using an aerated hydroponics system. The
roots of the seedlings were washed to remove
most of the soil, and then pruned to ~12 cm
below the root collar. Any new white roots were
removed. On each occasion, five seedlings of
each lift/cold storage treatment per species
were placed in each of four plastic boxes
(35 60 90 cm), each containing about 150 l
tap water. Each group of five seedlings per treatment and species (total 20 plants each) was suspended in the water using a strip of polystyrene
(5 cm thick); the polystyrene was notched to
facilitate this process. Each group of five plants
was treated as a replicate for statistical purposes.
The boxes were placed in a heated greenhouse set
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F O R E S T RY
at 20°C (actual, 18–22°C day/15–18°C night).
The photoperiod was extended to 16 h using
high-pressure sodium vapour lights. Relative
humidity was maintained above 50 per cent
using time-controlled fine mist nozzles. After 42
days, the number of new white roots (≥1 cm)
was recorded for each plant. Results from
previous research indicated that a shorter test
period was not sufficient to give reliable results
(Mortazavi, 1999).
Field performance
This trial was established in tandem with the
physiology work. At 4–6 week intervals from
October 1997 to May 1998, and after cold
storage until May, additional seedlings were dispatched for planting at a farm field-trial site at the
Coillte Tree Improvement Centre, Kilmacurra,
Co. Wicklow (52°56N, 6°09W, 120 m a.s.l.).
All seedlings were cold stored (2°C) and planted
within 2–4 days of lifting. The soil characteristics
were: pH 5.7, 7 per cent organic matter, and sand,
silt and clay fractions of 40, 32 and 27 per cent,
respectively. The site was rotovated in August
1997 to create a fine tilth. The site was cleared of
weeds using Roundup at 2 l/ha (720 g glyphosate)
and thereafter weeds were removed by hand at
regular intervals.
The trial was laid down as a randomized block,
split-plot factorial design. Species was the main
plot and storage treatment (freshly lifted, cold
storage until May) was the (split) subplot.
Seedlings representing eight lift dates for the
freshly lifted stock and five lift dates for the cold
stored stock were planted in each main plot. The
seedlings were planted in row plots containing 20
seedlings, each plot representing one of the 13
treatments. Each of the four blocks contained one
replicate of each treatment. Spacing was approximately 50 cm between rows and 30 cm within
rows.
Survival and height increment data were
recorded at the end of the first growing season.
Because initial planting stock size varied significantly with lift date (although differences
were small), the height increment data were
analysed as percentage of initial height. Initial
height was measured before growth began in
the spring. Subplot means were used in all data
analyses.
Data analysis and presentation
Analyses of the shoot WP and REL (after arcsin
square-root transformation) values were carried
using an analysis of variance (ANOVA) in SAS
(1989) to test for the effects of species and lift date,
carried out separately for each storage treatment
(no storage, or storage until May). In addition, the
REL values for before and after cold storage until
May for each lift date and species were compared
using a t-test. The RGP data were transformed to
square-root values to standardize variation.
Since environmental conditions in the greenhouse varied slightly with season, lift date effects
on RGP were not subjected to statistical tests for
the freshly lifted seedlings. The effect of species
on RGP for freshly lifted stock was examined for
each lift date separately using a t-test.
The field survival (after arcsin square-root
transformation) and percentage height increment
data were subjected to an ANOVA (SAS, 1989)
according to a split-plot design to test for block,
species, lift date and the interaction between
species and lift date, carried out separately for
each storage treatment. Means within species and
treatment (freshly lifted/cold stored) were compared further using LSD tests. Following this, the
performance of cold stored stock was compared
with that of the freshly planted stock for seedlings
lifted on same date, carried out separately for
each species (five lift dates only). In some cases,
the variances were heterogeneous, but the
Wilcoxon non-parametric procedures gave
similar results to the parametric tests, so only the
results of the latter are reported.
The relationships between parameter responses
were examined using simple linear correlations. The
mean values for each lift/storage date were used.
Results
Shoot water potential
Highly significant differences in shoot water potential due to species, lift and the interaction of these
factors were found for freshly lifted stock (all P <
0.001). Shoot WP showed a clear seasonal trend in
ash, but was less clear in sycamore (Figure 1). The
minimum WP in the winter was –1.43 MPa in
ash compared with –0.64 MPa in sycamore. In
ash, shoot WP was higher (less negative) from
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COLD STORAGE TOLERANCE OF ASH AND SYCAMORE
September until early December (–0.22 to
–0.50 MPa), then decreased greatly to low values
in January to early March (–1.43 to –1.24 MPa).
Shoot WP increased rapidly in April (–0.69 MPa)
and in May (–0.26 MPa). In sycamore, shoot WP
decreased from high values in September and
October (–0.34 to –0.40 MPa) to relatively low
values in December and January (–0.59 to
–0.64 MPa). Thereafter, WP fluctuated (–0.56 to
–0.29 MPa) over the February–May period.
Species differences alone were not significant
for cold stored stock, but lift date alone and its
interaction with species influenced shoot WP
(both P < 0.001). The effect of cold storage on
shoot WP was not consistent (Figure 1). In ash,
WP was higher after storage than at the time of
lifting (when values were low) for seedlings lifted
in January and February, but were about the same
for those lifted in December, and slightly lower
for plants lifted in October. In sycamore, cold
storage had no effect on shoot WP, except for
seedlings lifted in February (lower after storage).
Few of these differences were significant.
5
Seasonal differences in REL were relatively
small in ash. REL was relatively high in September (16 per cent) and October (19 per cent), but
then declined to a low in January and February
(11 per cent) (Figure 2). REL remained low in
March (12 per cent) and April (13 per cent),
before increasing in May (21 per cent). In contrast, in sycamore REL was very high in September (53 per cent), then declined to low values in
December and January (~17 per cent). Thereafter,
REL increased in February (33 per cent), then
declined slightly in March (26 per cent) and April
(23 per cent). REL increased again in May (50 per
cent).
In general, REL was a little higher after cold
storage than at the time of lifting in ash, except
for seedlings stored from October, when it was a
little lower (Figure 2). Most of these differences
were significant. In sycamore, REL was about the
same or higher after storage than at the time of
lifting. In particular, REL was higher after storage
(35, 48 per cent) than at the time of lifting for
sycamore lifted in December and January (~17
per cent).
Root electrolyte leakage
Species, lift and their interactions influenced REL
of both freshly lifted (all P < 0.001) and cold
stored stock (all P < 0.05).
Root growth potential
The effect of species on RGP of freshly lifted stock
was significant (most P < 0.05). The effect of lift
Lift date
Shoot water potential (MPa)
0.0
S
O
N
D
J
F
Lift date
M
Sycamore
–0.4
A
M
0.0
D
J
F
#
–0.8
* Ash
–1.2
# data missing
Freshly lifted
Cold stored
–2.0
Ash
0.0
–1.2
N
–0.4
–1.6
–0.8
O
O
N
D
*
J
F
#
–0.2
–0.4
–1.6
Freshly lifted
–2.0
–0.6
–0.8
Sycamore
*
Figure 1. Shoot water potential at the time of lifting and after cold storage until May in seedlings of ash
and sycamore in 1997/98. Arrows indicate approximate dates of terminal bud flushing. Vertical lines on
symbols are standard errors (some smaller than symbol). Values for the freshly lifted seedlings differed
(P < 0.05) from the cold stored stock on dates indicated (*).
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F O R E S T RY
60
Root electrolyte leakage (%)
# data missing
Freshly lifted
Freshly lifted
30
20
50
Sycamore
Ash
Cold stored
*
*
*
*
10
40
#
0
O
30
50
N
D
F
Sycamore *
40
20
J
*
30
Ash
10
20
10
0
S
O
N
D
J
F
M
A
Lift date
M
#
0
O
N
D
J
F
Lift date
Figure 2. Fine root electrolyte leakage at the time of lifting and after cold storage until May in seedlings
of ash and sycamore in 1997/98. Arrows indicate approximate dates of terminal bud flushing. Vertical lines
on symbols are standard errors (some smaller than symbol). Values for the freshly lifted seedlings differed
(P < 0.05) from the cold stored stock on dates indicated (*).
date was not examined because environmental
conditions in the greenhouse were not identical for
seedlings lifted on each date. In general, root
growth potential at the time of lifting was low
from September to November in ash (10–20 new
roots) and in sycamore (22–24 roots) (Figure 3).
Thereafter in ash, RGP declined and remained
near zero in December and January. From February onwards, RGP increased but remained low
(<15 roots) until early March, then increased to
high values in April and May (~45 roots). In contrast, in sycamore RGP increased in December (37
roots) and January (56 roots). RGP then increased
greatly and remained high (>100 roots) from February until April, but declined greatly in May (15
roots). RGP was higher in sycamore than in ash
during much of this period (most P < 0.05).
During the period of highest RGP, sycamore produced ~170 roots compared with 46 in ash.
For cold stored stock, species had a highly significant effect on RGP (P < 0.001), but the effects
on lift date and its interaction with species were
not significant. Variation in RGP was higher for
cold stored stock than for freshly lifted stock in
both species. RGP in ash was highest for seedlings
placed in storage in November and December
(~70 roots), compared with a maximum of 46
roots produced by stock freshly lifted in May
(tested at the same time as the cold stored stock)
(Figure 3). In sycamore, seedlings had very high
RGP after storage (~200 roots) regardless of lift
date.
Field performance
All of the ash and ≥98 per cent of the sycamore
seedlings survived after one growing season in the
field.
Species and lift effects on the percentage height
increment of freshly lifted stock were not significant, but the interaction of these factors was
highly significant (P < 0.001), indicating that lift
date effects varied greatly with species. Lift date
differences were a little larger for sycamore than
for ash. In ash, height increment was lowest for
seedlings lifted in December (19 per cent) and
January (25 per cent) and greatest for those lifted
on other dates (34–63 per cent) (Figure 4). Height
increment in sycamore was greater for stock lifted
from October to early March (44–67 per cent)
compared with those lifted in April (12 per cent)
and May (20 per cent).
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COLD STORAGE TOLERANCE OF ASH AND SYCAMORE
7
Freshly lifted
Freshly lifted
200
Sycamore
Number of new roots
Cold stored
120
100
80
Ash
60
40
20
0
150
O
100
300
N
D
J
F
D
J
F
Sycamore
200
50
Ash
0
S
O
N
D
J
F
M
100
A
0
M
O
N
Lift date
Lift date
Figure 3. Root growth potential at the time of lifting and after cold storage until May in seedlings of ash
and sycamore in 1997/98. Arrows indicate approximate dates of terminal bud flushing. Vertical lines on
symbols are standard errors (some smaller than symbol). Values for the freshly lifted seedlings were not
compared with those for the cold stored stock because conditions in the greenhouse were not identical for
each treatment.
e
Freshly lifted
Freshly lifted
70
5 0 Ash
Cold stored
Sycamore
40
Height increment (%)
60
*
*
O
N
30
50
20
40
10
30
7 0 Sycamore
20
Ash
10
0
S
O
N
D
J
F
M
Lift date
A
M
60
50
40
30
20
10
0
*
*
O
N
D
J
F
D
J
F
Lift date
Figure 4. End-of-season height increment as a percentage of initial height for ash and sycamore seedlings
freshly lifted or cold stored until May and planted 3 or 4 days later in 1997/98. Arrows indicate approximate dates of terminal bud flushing. Vertical lines on symbols are standard errors (some smaller than
symbol). Values for the freshly lifted seedlings differed (P < 0.05) from the cold stored stock on dates indicated (*).
Lift date had a significant (P < 0.05) effect on
height increment of cold stored stock, but species
and its interaction with lift date had no effect.
Height increment of ash and sycamore was
significantly smaller for the cold stored stock than
the freshly lifted seedlings for those lifted in
October and November (all P < 0.05), but were
not different for seedlings lifted on other dates
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F O R E S T RY
(Figure 4). The magnitude of these differences
was greater and more consistent for sycamore
than for ash.
Relationship between parameter responses
Few correlations between parameters were significant. In ash, shoot water potential was negatively correlated with root electrolyte leakage (r =
–0.73; P < 0.01), mainly due to the effect for
freshly lifted stock (r = –0.83; P < 0.05) rather
than that for cold stored stock (r = –0.32; n.s.).
Root electrolyte leakage was correlated with root
growth potential (r = 0.62; P < 0.05) in ash, but
the correlation was not significant when analysed
separately for each storage treatment. None of
the physiological parameter responses were significantly correlated in sycamore.
RGP was significantly correlated with height
increment one growing season after planting for
freshly lifted ash seedlings (r = 0.78; P < 0.05),
while the relationship for REL and height was
close to significant (r = 0.75; P = 0.054). WP was
significantly correlated with height increment (r =
0.92; P < 0.05) for cold stored sycamore
seedlings.
Discussion
Physiological responses and field performance of
freshly lifted stock
Shoot water potential may fluctuate seasonally in
trees (Ritchie and Schula, 1984). WP decreases
from autumn to winter and then increases
(towards zero) again in the spring, primarily
associated with the process of winter hardening
and dehardening (Ritchie, 1982, 1984; Ritchie
and Schula, 1984; Colombo, 1990). The seasonal
change in shoot WP in ash, but not in sycamore,
followed this pattern (Figure 1). For this reason,
shoot WP may be a good indicator of winter
hardiness and associated dormancy status in ash,
but is less reliable for sycamore. Shoot water
potential was a useful indicator of dormancy
status in several broadleaved species in other
studies (Lakso, 1990; Murakami et al., 1990;
Englert et al., 1993).
However, shoot WP also changes in response
to water stress (Ritchie and Hinkley, 1975; Cleary
and Zaerr, 1980). Therefore, the higher (less
negative) winter shoot WP and the highly variable
values in sycamore from March to May probably
reflect its higher usage of water. The buds of
sycamore flushed earlier than those of ash, and
REL and RGP values also were higher throughout the lifting season (except for RGP in May),
suggesting that the plants were more physiologically active.
Root electrolyte leakage varied seasonally in
ash and sycamore (Figure 2), similar to that
described previously for these species growing in
Ireland (Mortazavi, 1999; O’Reilly et al., 2000).
These changes probably reflect variations in the
levels of physiological activity associated with the
process of winter hardening (Zhao et al., 1995;
McKay, 1998). Therefore, REL may indicate
periods when activity levels are low and the
plants are more likely to withstand the stresses of
lifting and handling (O’Reilly et al., 1999a, b,
2000). However, REL was relatively low (≤21 per
cent) throughout most of the lifting season in ash,
perhaps suggesting that the test is of limited value
for this purpose in this species. REL was much
higher in sycamore. While the exact values are
not known, REL should be less than 25 per cent
at the time of lifting in sycamore otherwise it
might be damaged during handling. The REL test
is more commonly used to determine potential
damage due to desiccation or cold storage stresses
than to assess activity levels; high values are
generally associated with membrane damage
(McKay and Mason, 1991; McKay, 1992, 1993;
McKay et al., 1999). In this study, the very high
REL that occurred in sycamore in May was
associated with a reduction in RGP and field performance, indicating that the plants were probably damaged during handling. However, REL
was also very high in September, but this did not
result in poor performance for seedlings planted
at this time. Post-planting field conditions may
have been more favourable for recovery from
damage for seedlings planted early (when shoot
growth has ceased) than for those planted late
(after the buds had flushed). Perhaps high REL
values indicate that cellular activity levels are high
(see Folk et al., 1999; Harper and O’Reilly, 2000)
and that the seedlings are more likely to be
damaged during handling/planting, but it may
not predict actual field performance.
Root growth potential remains low in most
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COLD STORAGE TOLERANCE OF ASH AND SYCAMORE
broadleaved species throughout the winter period
(Farmer 1975; Webb 1976, 1977). In contrast,
RGP increases in December/January in most evergreen conifers (Ritchie and Dunlap, 1980;
Ritchie, 1982). Conifer leaves probably provide
photosynthate for root growth, thus allowing
higher winter RGP. Nevertheless, RGP was relatively high in sycamore throughout the winter in
this study, and increased earlier in the spring in
sycamore than in ash. The high RGP of sycamore
may be a major contributor towards its ability to
compete successfully with other tree species.
Shoot water potential and root electrolyte
leakage were negatively correlated in ash, indicating that both parameters probably responded
in a similar manner to seasonal changes in
weather conditions. However, this result is probably of little value from a physiological or practical viewpoint since the REL changes were small.
No correlation was found between these parameters in sycamore. Water potential was not
correlated with field performance for freshly
planted stock of either species. In ash, root electrolyte leakage and root growth potential were
correlated (when data from both freshly lifted
and cold stored stock were included). This result
might be explained as follows. While high REL
values frequently indicate cell membrane damage
(McKay and Mason, 1991; McKay, 1992, 1993;
McKay et al., 1999), moderately high values
sometimes indicate that the seedlings have
become more active (see Harper and O’Reilly,
2000). Active (undamaged) plants are likely to
produce more new roots than plants that are
more ‘dormant’.
Survival was close to 100 per cent regardless of
lift date, indicating that both species have a relatively high tolerance to the stresses of lifting and
planting. However, these stresses had a greater
impact on height increment. Sycamore was more
highly active than ash (Figures 1–3) and was
probably more sensitive to the stresses of lifting
and handling, especially during the post-flushing
period (from March onward) (see McKay et al.,
1999). This may explain the large decline in
height increment with date of lifting for sycamore
planted after early March. In contrast, activity
levels were generally low in ash and the seedlings
were probably not damaged during the 2–4 day
interval between the times of lifting and planting.
In general, the height increment of ash was better
9
for seedlings planted early or late in the lifting
season, although differences among lift dates
were relatively small (excepting May lift date).
Similarly, Mortazavi (1999) found that date of
lifting between October and April had little effect
on the height increment of ash planted in the two
previous lifting seasons at the same site. Ash
seedlings planted in May grew well (Figure 4), but
this result may be misleading. Ash planted in May
in the previous planting season at this site grew
poorly (Mortazavi, 1999), perhaps because they
were more active at the time of lifting (and subsequently damaged during handling). Under operational forestry conditions, however, seedlings
planted in May are even less likely to perform
well in the field since they probably would not be
handled as carefully as the stock used in these
studies. In addition, there is a higher risk that
post-planting conditions (e.g. drought) would
reduce height growth further for seedlings
planted late in the season.
Physiological responses and field performance of
cold stored stock
There was no consistent pattern for the effect of
lift date on shoot water potential after cold
storage (Figure 1). In addition, shoot WP was not
significantly correlated with RGP or other
physiological responses in either species. In contrast, Webb and von Althen (1980) found that
high WP (less negative) was associated with high
RGP in several broadleaved species. However,
low (more negative) WP values were associated
with greater height increment in sycamore
(Figure 4), contrary to expectation. Low WP
values usually indicate that the seedlings are
suffering from moisture stress (Cleary and Zaerr,
1980), possibly caused by water loss during
storage (see McKay, 1997). The most likely
reason for this apparent anomaly is that the
storage temperature induced and/or maintained
‘dormancy’ in sycamore. Low shoot WP values
occur in seedlings in the winter, associated with
the process of hardening (Ritchie and Schula,
1984). No relationship was found between shoot
WP and height increment in ash.
There was no clear relationship between poststorage REL and height increment in the field in
both species in this study. The REL test is generally considered to be a better indicator of survival
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F O R E S T RY
potential than height increment for conifers
(McKay, 1998), but it may predict both in some
cases (McKay, 1992). In ash, REL was higher
following storage than at the time of lifting,
except for seedlings lifted in October (which also
grew poorly in the field). In sycamore, however,
REL was higher or about the same following
storage as at the time of lifting. In general, these
results are contrary to expectation. However,
Harper and O’Reilly (2000) found that moderately high REL values in Douglas fir (Pseudotsuga
menziesii) were not necessarily associated with
deterioration. High REL may sometimes reflect
elevated metabolism rates rather than a decrease
in quality (Harper and O’Reilly, 2000).
Root growth potential following cold storage
was very high in seedlings of sycamore regardless
of lift date, but in ash it was high for those lifted
in November and December only. RGP may have
been enhanced because the long period of cold
storage satisfied chilling requirements, thus partially releasing the plants from dormancy (Webb,
1976, 1977; Webb and von Althen, 1980; Harris
et al., 1993). However, plants may deteriorate in
cold storage, especially when placed in storage
when not dormant (Ritchie and Dunlap, 1980;
Struve, 1990). This may explain the low RGP of
ash seedlings stored from October in this study.
However, despite the high RGP of sycamore after
cold storage, they generally grew more poorly
than stock freshly planted from October to
March. Results from recent research indicate that
moderate stress levels cause shoot dieback in
some broadleaved species, especially in oak (data
not shown), but RGP is sometimes enhanced or
unaffected.
The results of this study also provided information on the potential use of cold storage in
operational forestry and landscape planting in
Ireland, especially as a means of extending the
planting season. The results indicated that ash
could be lifted from December to February and
cold stored until May without greatly affecting
field height growth potential, compared with the
increment of stock freshly planted from October
to April. However, sycamore may be a more sensitive to cold storage. Mortazavi (1999) found
that sycamore cold stored in 1996/97 and planted
in May after storage at the same site as used in
this study also grew poorly, although lift date
effects were less clear. Based upon the results of
this study, and Mortazavi (1999), sycamore
should be stored in January or February for planting until May. Storage from February may be
preferable because the duration of storage is
shorter. Freshly lifted sycamore performs poorly
when planted after about early March, so the use
of cold stored stock is recommended during this
period. The shoot WP, REL and RGP data indicated that sycamore was relatively active during
the winter, perhaps explaining its greater sensitivity to cold storage.
Conclusions
The results of this study indicate that sycamore is
physiologically more active than ash from
October to May. WP, REL and RGP were higher
in the former than the latter species on most lift
dates, and it was a little more sensitive to cold
storage. Survival after planting was excellent
(nearly 100 per cent) in both species regardless of
planting date. The height increment of ash was
best for seedlings planted early (September/
October) or late (after February) in the lifting
season, although differences between most lift
dates were small. Sycamore planted late (after
early March), when physiological activity was
highest, grew poorly, probably owing to damage
caused to the roots during handling. Ash lifted
from December to February, and sycamore lifted
in February, performed well in the field when
planted after cold storage until May. These results
largely corroborate the findings from earlier
unpublished work carried out in Ireland (Mortazavi, 1999).
Acknowledgements
The authors would like to thank the following for their
assistance in carrying out this work: R. Lowe, N.
Morrissey, and J. Fennessy from Coillte and A. Baraldi
and R. Cabral from UCD. Funding for this project was
provided by COFORD (Council for Forest Research
and Development) and Coillte Teoranta (Irish Forestry
Board).
References
Anon. 1996 Growing for the Future. A Strategic Plan
for the Development of the Forestry Sector in
Ireland. Department of Agriculture, Food and
01oreilly (ds)
17/1/02
9:53 am
Page 11
COLD STORAGE TOLERANCE OF ASH AND SYCAMORE
Forestry. Published by Stationery Office, Government Publications Office, Dublin.
Anon. 1998 1998 Forestry Yearbook. Irish Timber
Grower’s Association, Dublin.
Calmé, S., Bigras, F.J., Margolis, H.A. and Hebert, C.
1994 Frost tolerance and bud dormancy of containergrown yellow birch, red oak and sugar maple
seedlings. Tree Physiol. 14, 1313–1325.
Cleary, B.D. and Zaerr, J.B. 1980 Pressure chamber
techniques for monitoring and evaluating seedling
water status. N. Z. J. For. Sci. 10, 133–141.
Colombo, S.J. 1990 Bud dormancy status, frost hardiness, shoot moisture content, and readiness of black
spruce container seedlings for frozen storage. J. Am.
Soc. Hortic. Sci. 115, 302–307.
Englert, J.M., Fuchigami, L.H. and Chen, T.H.H. 1993
Effects of storage temperatures and duration on the
performance of bare-root deciduous hardwood trees.
J. Aboric. 19, 106–112.
Farmer, R.E. Jr 1975 Pruning northern red oak nursery
seedlings: effects on root regeneration and early
growth. Can. J. For. Res. 5, 381–386.
Folk, R.S., Grossnickle, S.C., Axelrood, P. and Trotter,
D. 1999 Seed-lot, nursery, and bud dormancy effects
on root electrolyte leakage of Douglas fir (Pseudotsuga menziesii) seedlings. Can. J. For. Res. 13,
1269–1281.
Harper, C.P. and O’Reilly, C. 2000 Effect of warm
storage and date of lifting on the quality of Douglasfir seedlings. New For. 20, 1–13.
Harris, J.R., Bassuk, N.L. and Whitlow, T.H. 1993
Effect of cold storage on bud break, root regeneration and shoot extension of Douglas fir, paper birch
and green ash. J. Environ. Hortic. 11, 119–123.
Hipps, N.A., Higgs, K.H. and Collard, L.G. 1996 Effect
of root wrenching and irrigation rate on the growth
and water relations of Castanea sativa and Quercus
robur seedlings in nursery beds and after outplanting.
Can. J. For. Res. 27, 180–188.
Hipps, N.A., Higgs, K.H. and Collard, L.G. 1997 The
effect of irrigation and root pruning on the growth of
sycamore (Acer pseudoplatanus) seedlings in nursery
beds and after transplantation. J. Hortic. Sci. 71,
819–828.
Hipps, N.A., Higgs, K.H. and Collard, L.G. 1999 Effect
of root wrenching on the growth and water relations
of Prunus avium and Castanea sativa seedlings in
nursery beds and after outplanting. Can. J. For. Res.
29, 696–704.
Insley, H. and Buckley, G.P. 1985 The influence of desiccation and root pruning on the survival and growth
of broadleaved seedlings. J. Hortic. Sci. 60, 377–387.
Joyce, P.M., Huss, J., McCarthy, R., Pfeifer, P.A. and
Hendrick, E. 1998 Growing Broadleaves. Silvicultural Guideline for Ash, Wild Cherry, Beech and Oak
in Ireland. National Council for Forest Research and
11
Development, National University of Ireland,
Dublin.
Lakso, A.N. 1990 Interactions of physiology with multiple environmental stresses in horticultural crops.
HortScience 25, 1365–1369.
Lindqvist, H. 1998 Effect of lifting date and time of
storage on survival and die-back in four deciduous
species. J. Environ. Hortic. 16, 195–201.
Mason, W.L. 1994 Production of undercut stock. In
Forest Nursery Practice. J.R. Aldhous and W.L.
Mason (eds). Forestry Commission Bulletin No 111.
HMSO, London, pp. 112–121.
McEvoy, C. and McKay, H.M. 1997a Root frost hardiness of amenity broadleaved seedlings. Aboric. J. 21,
231–244.
McEvoy, C. and McKay, H.M. 1997b Sensitivity of
broadleaved trees to desiccation and rough handling
between lifting and planting. Arboriculture Research
Information Note 139/97/SILN. Arboriculture
Advisory and Information Service, Wrecclesham,
Farnham, Surrey, 7pp.
McKay, H.M. 1992 Electrolyte leakage from fine roots
of conifer seedlings: a rapid index of plant vitality
following cold storage. Can. J. For. Res. 22,
1371–1377.
McKay, H.M. 1993 Tolerance of conifer roots to cold
storage. Can. J. For. Res. 23, 337–342.
McKay, H.M. 1997 A review of the effect of stresses
between lifting and planting on nursery stock quality
and performance. New For. 13, 369–399.
McKay, H. M. 1998 Root electrolyte leakage and root
growth potential as indicators of spruce and larch
establishment. Silva Fenn. 32, 241–252.
McKay, H.M. and Mason, W.L. 1991 Physiological
indicators of tolerance to cold storage in Sitka spruce
and Douglas fir. Can. J. For. Res. 21, 890–901.
McKay, H.M., Aldhous, J.R. and Mason, W.L. 1994
Lifting, storage, handling and dispatch. In Forest
Nursery Practice. J.R. Aldhous and W.L. Mason
(eds). Forestry Commission Bulletin No. 111.
HMSO, London, pp. 198–222.
McKay, H.M., Jinks, R.L. and McEvoy, C. 1999 The
effect of desiccation and rough-handling on the survival and early growth of ash, beech, birch and oak
seedlings. Ann. For. Sci. 56, 391–402.
Mortazavi, M. 1999 Impact of physiological status on
the quality of broadleaved planting stock. Ph.D.
thesis, National University of Ireland, University
College Dublin.
Murakami, P., Chen, T.H.M. and Fuchigami, L.H.
1990. Desiccation tolerance of deciduous plants
during postharvest handling. J. Environ. Hortic. 8,
22–25.
O’Reilly C., McCarthy N., Keane M., Harper C.P. and
Gardiner J.J. 1999a The physiological status of
Douglas-fir seedlings and the field performance of
01oreilly (ds)
17/1/02
12
9:53 am
Page 12
F O R E S T RY
freshly lifted and cold stored stock. Ann. For. Sci. 56,
297–306.
O’Reilly C., Harper C.P. and Keane M. 1999b Influence
of physiological status at the time of lifting on cold
storage tolerance and field performance of Douglas
fir and Sitka spruce. Ir. For. 56(2), 2–17.
O’Reilly, C., Harper, C.P., Mortazavi, M., Baraldi, A. and
Keane, M. 2000 The use of physiological indicators in
assessing readiness for lifting, cold storage and planting of important conifer and broadleaved species.
Report Submitted to Council for Forest Research and
Development (COFORD), UCD, Ireland.
Puttonen, P. 1986 Carbohydrate reserves in Pinus
sylvestris seedling needles as an attribute of seedling
vigor. Scand. J. For. Res. 1, 181–193.
Ritchie, G.A. 1982 Carbohydrate reserves and root
growth potential in Douglas-fir seedlings before and
after cold storage. Can. J. For. Res. 12, 905–912.
Ritchie G.A. 1984 Assessing seedling quality. In Forest
Nursery Manual: Production of Bareroot Seedlings.
M.L. Duryea and T.D. Landis (eds). Martinus
Nijhoff/Dr W. Junk, The Hague, pp. 243–249.
Ritchie, G.A. and Dunlap, J.R. 1980 Root growth
potential: its development and expression in forest
tree seedlings. N. Z. J. For. Sci. 10, 218–248.
Ritchie, G.A. and Hinkley, T.M. 1975 The pressure
chamber as an instrument for ecological research.
Adv. Ecol. Res. 9, 165–254.
Ritchie, G.A. and Schula, R. 1984. Seasonal changes of
tissue water relations in shoot and root systems of
Douglas-fir seedlings. For. Sci. 30, 538–548.
SAS Institute 1989 SAS Language: Reference, Version
6. 1st edn. SAS Institute, Cary, NC, 1042pp.
Struve, D.K. 1990 Root regeneration in transplanted
deciduous nursery stock. HortScience 25, 266–269.
Symeonidou, M.V. and Buckley, P.G. 1997 The effect of
preplanting desiccation on survival and growth of
Prunus cerasifera seedlings and the relationship of
physiological indicators at planting with field performance and survival. Russ. J. Plant Physiol. 44,
514–517.
Tabbush, P.M. 1988 Silvicultural systems for upland
restocking. British Forestry Commission Bulletin No
76. HMSO, London, 21pp.
Webb, D.P. 1976. Effects of cold storage duration on
bud dormancy and root regeneration of white ash
(Fraxinus americana L.) seedlings. HortScience 11,
155–157.
Webb, D.P. 1977 Root regeneration and bud dormancy
of sugar maple, silver maple, and white ash seedlings:
effects of chilling. For. Sci. 23, 474–483.
Webb, D.P. and von Althen, F.W. 1980 Storage of hardwood planting stock: effects of various storage
regimes and packaging method on root growth and
physiological quality. N. Z. J. For. Sci. 10, 83–96.
Zhao, S., Colombo, S.J. and Blumwald, E. 1995 The
induction of freezing tolerance in jack pine
seedlings: the role of root plasma membrane H+ATPase and redox activities. Physiol. Plant. 93,
55–60.
Received 26 June 2000