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Forest Ecology and Management 232 (2006) 19–25
Mounding site preparation for forest restoration: Survival
and short term growth response in Quercus robur L. seedlings
Magnus Lof a,*, D. Rydberg b,1, Andreas Bolte c,2
a Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre,
P.O. Box 49, S-230 53 Alnarp, Swedenb Swedish Forest Agency, P.O. Box 234, S-291 23 Kristianstad, Sweden
c University of Gottingen, Institute of Silviculture, Department I, Buesgenweg 1. D-370 77 Goettingen, Germany
Received 19 December 2005; received in revised form 18 April 2006; accepted 1 May 2006
Abstract
Mounding site preparation for forest restoration: survival and short term growth response in Quercus robur L. seedlings control of natural
vegetation during afforestation and reforestation is necessary to avoid economical losses through growth reduction and mortality in seedlings. The
present field experiment, carried out on a ground-water influenced site with planted oak, included three site preparation treatments and undisturbed
control (C). The treatments were: repeated herbicide application (H), mounding site preparation (MSP), and mounding site preparation in
combination with repeated herbicide application (MSP + H). The mounds were 25 m long, 2 m wide and 20 cm high inverted mounds on humus,
and this method is sometimes also called bedding. Seedlings were monitored for 3 years and at the end of the experiment 90% of oak seedlings
survived in the various site preparation methods compared with 58% in the undisturbed control. The best growth was obtained when mounding site
preparation was combined with repeated herbicide treatment, producing five times greater seedling biomass compared with the control. Mounding
site preparation resulted in equal growth of seedlings compared with repeated herbicide application. Interference from vegetation had a strong
negative effect on seedling growth while mounding site preparation itself resulted in a positive seedling growth response. We conclude that
mounding site preparation is an efficient tool for forest managers in establishing oak stands and is a good alternative to herbicide treatment on
certain sites. On the other hand, a relatively large disturbance area and deep soil disturbances may impair recreational values and destroy
archaeological remains.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Conversion; Regeneration; Seedlings; Soil preparation; Weed competition
1. Introduction
European temperate broadleaved forest types previously
covered much larger areas than they do today (Hannah et al.,
1995; Bradshaw and Lindbladh, 2005) and restoration of these
forests is believed to be a step towards sustainable forestry (e.g.
Spiecker et al., 2004; Stanturf and Madsen, 2005). Since the
beginning of the nineteenth century, many original broadleaved
woodlands have been replaced by conifer plantations (Kenk and
Guehne, 2001). Although economically attractive for the forest
* Corresponding author. Tel.: +46 40 41 51 19; fax: +46 40 46 23 25.
E-mail addresses: magnus.lof@ess.slu.se (M. Lof),
dan.rydberg@skogsstyrelsen.se (D. Rydberg),
abolte@bfh-inst7.fh-eberswalde.de (A. Bolte).1 Tel.: +46 44 18 67 36; fax: +46 44 10 97 61.2 Tel.: +49 551 39 36 50; fax: +49 551 39 32 70.
0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2006.05.003
owner, these plantations have often proven to be unstable and
are subject to windthrow, drought damage and ultimately forest
decline (Oleskog and Lof, 2005). Other negative effects
associated with conifer plantations include enhanced accumu-
lation of organic material, abundant grass colonization of the
forest floor and decreased humus quality (Bolte, 1999; Prietzel,
2004; Jansen et al., 2005).
This study, conducted on a temperate forest site in the
southernmost part of Sweden, aims to increase the under-
standing of efficient establishment of oak stands. At the site, the
former forest stands of beech (Fagus sylvatica L.) and hybrid
Larch (Larix � Europlepis Henry) have repeatedly been storm-
felled. The oak species used in the present study, however, is
among the most wind stable tree species in European forestry
(Lupke von and Spellmann, 1999).
Low survival and growth of seedlings results in economic
losses through extended rotation times and the cost of
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–2520
Table 1
Chemical soil properties of the organic layer and the rooted mineral soil
Organic layer (Oh horizona)
pH (KCl) 4.2
C/N ratio 17.8
Mineral soil at 0–10 cm (Ah horizona)
pH (KCl) 3.8
C/N-ratio 17.9
CEC (mequiv. g�1) 71
Al (% CEC) 63.7
K + Ca + Mg (% CEC) 17.4
Mineral soil at 10–27 cm (Bv horizona)
pH (KCl) 4.1
CEC (mequiv. g�1) 30
Al (% CEC) 84.9
K + Ca + Mg (% CEC) 8.6
Mineral soil at 27–58 cm (Bv/Go horizona)
pH (KCl) 4.1
CEC (mequiv. g�1) 24
Al (% CEC) 87.0
K + Ca + Mg (% CEC) 7.8
Means from two samples.a Classification according to Ad-hoc-AG Boden (2005); Oh: humified organic
layer containing amourphous organic material; Ah: humified mineral top soil
horizon; Bv: cambic mineral soil horizon; Bv/Go: cambic/gleyic mineral soil
horizon.
replacement of dead seedlings (Margolis and Brand, 1990).
Typically, it is necessary to control the natural ground
vegetation during forestation on open sites and this is usually
achieved by using herbicides, mechanical site preparation,
mulching or prescribed burning (e.g. Orlander et al., 1990).
Numerous studies show a positive correlation between all these
methods of vegetation control and growth and survival of
seedlings (e.g. Davies, 1988; Munson et al., 1993; Brose and
Van Lear, 1998; Lof et al., 2004). In general, forest managers
select herbicides because of their effectiveness and relatively
low cost compared with available alternatives. However,
increased environmental awareness has prompted public and
industry concern over herbicide use in forests (Willoughby,
1999). The European commission aims to make a decision on
many herbicides before the end of 2008 and forest managers
may have to look for alternative management practices.
Since the use of herbicides on forest land is restricted in
Sweden, mechanical site preparation such as soil scarification is
carried out on approx. 150,000 ha each year to control
vegetation and to facilitate manual planting (Anonymous,
2005). Mounding site preparation is an old mechanical site
preparation method that has attracted new attention (Sutton,
1993). It has become an alternative to other methods such as
soil scarification, especially in northern boreal coniferous forest
sites, where low soil temperature, high water table and high
competition are serious problems (Hawkins et al., 1995;
Hallsby and Orlander, 2004; Pennanen et al., 2005). Little
research has been done on mounding site preparation in the
temperate forest zone.
Site preparation influences many environmental conditions
simultaneously and the direct cause of any positive effect on
regeneration is often unknown (Margolis and Brand, 1990).
Moreover, there is a great variation among sites, and the growth
response of seedlings due to mechanical site preparation has
seldom been separated from other effects, such as simulta-
neously altered interference from natural ground vegetation
(Munson et al., 1993) or pine weevil herbivory (Hylobius
abietis L) (Lof, 2000a). Although the positive effect of
mechanical site preparation on survival and growth of conifer
seedlings is well established, the same cannot be said for
broadleaves.
This study investigates the influence of mounding site
preparation on the establishment of young oak seedlings. The
specific objectives of this study were: (1) to evaluate survival and
growth response of oak seedlings following mounding site
preparation and to compare site preparation using repeated
herbicide application with the plantation in undisturbed soil and,
(2) to examine whether any positive growth response following
mounding site preparation was a result of reduced competition
from natural vegetation or from the mounds themselves.
2. Material and methods
2.1. Site description
The study site was located in the Skarhult experimental
forest (558500N/138240E, 90 m above sea level) in the south-
ernmost part of Sweden, where a 32-year-old hybrid Larch
(Larix � Europlepis Henry) stand of 4.3 ha had been wind-
thrown in December 1999. The Larch stand had been planted in
1970 following a European beech (F. sylvatica L.) stand that
was wind-thrown in 1967. The parent soil material at the site
was formed by loose moraine sediments and the soil type can be
described as gleyic cambisol (Gleyic B) according to FAO
(1988). The lower soil levels from approx. forty to 60 cm soil
depth are intermittently water saturated and the soil texture is
sandy loam consisting of 25–43% sand, 40–50% silt and 17–
25% clay content (Ad-hoc-AG Boden, 2005).
In December 2004, two soil pits were dug to ground water
level and samples were taken from each horizon and analyzed
for chemical properties (Table 1). All samples from the organic
layer and the mineral soil were oven-dried at 40 8C, sieved
(2 mm), and pH was measured with a digital pH-meter (glass
electrode, WTW GmbH Weilheim, Germany) in 1 mol L�1
KCl (1:2.5). Sub-samples were milled for total N and C
analysis; for the measurements, an automated C and N analyzer
(Carlo Erba NA 1500, Milan, Italy) was used. The mineral soil
samples were further analysed for cation exchange capacity
(CEC) and exchangeable cations (Ca2+, Na+, K+, Mg2+, Al3+,
Fe2+, Mn2+). The cation exchange capacity (CEC) was
determined by percolating (6 h) 2.5 g of the dried and sieved
soil material with 1N NH4Cl. Cations in the percolate were
determined with an atomic absorption spectrophotometry
(AAS, Varian Spectra 300A, Varian, Darmstadt, Germany).
The H+ saturation of the exchange complex was calculated
from the difference of the percolate pH before and after
percolation. The results were corrected by the hydrolyse
reaction of aluminium cations according to Meiwes et al.
(1984), depending on the Al3+ concentration. The CEC results
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–25 21
from the concentration sum of H+ and all measured cations
expressed in units of microequivalents per gram of dry soil
(meq g�1). The CEC saturation of the base cations K+, Ca2+,
Mg2+ and the acid cation Al3+ are given as percentage values
(Table 1).
The soil was acidic, occurring in the aluminium (Al) buffer
range (Ulrich, 1983) with a moderate to low CEC and moderate
CEC saturation of the base cations K, Mg and Ca (Table 1).
With respect to this and the medium status of C/N ratio (AK
Standortskartierung, 2003), overall site nutrition of the topsoil
within the range of seedlings’ roots can be characterised as
moderate.
The mean monthly air temperature and precipitation
measured in January and July at the climate station in Lund,
located 15 km west of the experimental site, averaged�0.3 and
17.9 8C and 67 and 87 mm, respectively, over the 3 years
(Anonymous, 2002–2004). The mean air temperature was high
in July 2003 and in August 2002–2004 (Table 2) and
precipitation was normal following planting in 2002. Pre-
cipitation was low in August 2002, May 2004 and in September
2002–2004 and was high in June 2002 and July 2004.
2.2. Experimental design
The experimental design was randomised blocks with four
treatments in each of the four blocks. The treatments were:
herbicide (H); mounding site preparation (MSP); mounding site
preparation plus herbicide (MSP + H); and untreated control
(C). Each treatment consisted of three randomly placed rows of
bare-root oak seedlings (Quercus robur L., 1/0, 15–25 cm,
Visingso-Herrangen, Sweden) in each block. Each row
consisted of 25 seedlings with a distance of 1 m between
seedlings. The distance between rows/treatments was approx.
2 m. Seedlings were planted manually in the end of April 2002
using a planting spade. Inverted mounds on humus about 25 m
long, 2 m wide, and 20 cm high were made by excavator in
early April 2002, an operation sometimes called bedding
(Sutton, 1993). The herbicide treatments were applied in early
June and in the middle of July each growing season during
2002–2004. The herbicide (glyphosate, 0.3 g m�2 active
Table 2
Monthly average air temperature (8C) and monthly precipitation (mm) during
the 2002, 2003 and 2004 growing seasons at Lund climatic station located
approx. 15 km south-west of the experimental site (Anonymous, 2002–2004)
Month 2002 2003 2004 30-year-mean
Air temperature
May 13.5 12.9 12.0 11.5
June 16.7 16.9 14.3 15.4
July 18.6 19.3 15.7 16.8
August 20.6 18.5 18.4 16.5
September 14.7 14.3 13.9 13.1
Precipitation
May 55 59 17 45
June 96 60 83 56
July 69 65 128 70
August 21 49 76 65
September 21 36 40 64
gradient) was spread in approx. 25 m long and 1 m wide
strips along the planting rows with the seedlings in the middle
of the strips. A shield was used to protect the seedlings. The size
of each block was 27 m � 25 m (0.067 ha) and the distance
between blocks was 4 m. All blocks were located approx. 20 m
from the nearest forest edge. The site was fenced to exclude
larger herbivores.
2.3. Data collection
The seedling diameter (at ground level) and height
(stretched distance from ground level to highest living bud)
were measured on all living seedlings at the beginning of April
in 2003, and 2004, and in the end of September 2004. In April
2004, seedlings were difficult to find in the control treatment
due to abundant ground vegetation. Seedling diameter at
ground level was only measured for the first 10 seedlings in
each row in September 2004. In September 2004, the
percentage of natural vegetation cover was estimated in
40 cm fixed radius plots close to the living seedlings, and
assigned to one of 11 categories, where 0 = 0%, 1 = 1–11%,
2 = 12–21%, 3 = 22–31%. . .10 = 91–100% vegetation cover.
Following growth measurements and estimation of vegetation
cover in September 2004, the percentage of seedling foliage not
shaded by natural vegetation was estimated. A similar scale was
used, where 0 = 0%, 1 = 1–11%, 2 = 12–21%, 3 = 22–
31%. . .10 = 91–100% non-shaded foliage that overtopped
the natural vegetation.
Soil water potential at 10 cm soil depth was measured in
August and September 2004 with gypsum blocks (5201
Soilmoisture Blocks, Soilmoisture Equipment Corp., CA,
USA) at one position in each treatment. The gypsum blocks
were buried down at random selected positions near the oak
seedlings within each treatment.
Photosynthetic photon flux density (PPFD) was measured
(LI-190SA, LiCor Inc., Lincoln NE, USA) at the seedling level
and above the herbaceous vegetation (0.3 and 1.5 m), in early
August 2004 on 2 randomly selected locations per treatment
and block. Measurements were made between 11.00 and
13.00 ha on a clear day.
In early December 2004, three randomly selected seedlings
from each treatment and block (seedling no 5, 6 and 7 in the first
row in each block) were carefully extracted from the soil.
Thereafter, the seedlings were washed under running water and
the dry mass of seedling components was determined after drying
at 70 8C for 72 h. Earlier the same year, all leaves from the same
seedlings had been sampled in the end of September. To
determine leaf area, a sub-sample of 10 leaves from each seedling
was photocopied and measured with a computer image system
(Image access, Micro Macro Bildanalys AB, Sweden). They
were then oven dried at 70 8C for 48 h to determine dry mass.
2.4. Calculations and statistical analysis
The leaf area per seedling (LA) was calculated using total leaf
dry mass and leaf dry mass to leaf area ratio of the sub-sample. To
account for size-related variations following 2003 and 2004
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–2522
Table 3
Mean environmental characteristics near the oak seedlings in four treatments and 3 years
Treatment Vegetation
cover (%)
Overtopping of vegetation
(%) of seedling leaves
Soil water potential
(MPa) (August 7)
Soil water potential
(MPa) (September 17)
Relative
light (%)
C 95.9 39.8 �0.09 �0.24 28.8
H 12.4 91.5 �0.05 �0.05 75.8
MSP 95.9 56.1 �0.04 �0.09 23.8
MSP + H 6.7 97.5 �0.05 �0.06 75.1
Undisturbed control (C), herbicide (H), mounding site preparation (MSP), and mounding site preparation plus herbicide (MSP + H). Light was measured 30 cm above
ground near the seedlings and soil moisture was measured at a depth of 10 cm. For further description of measurements see text.
Fig. 1. Mean seedling survival in the four treatments during 3 years. Open
symbols denote treatments with herbicide and filled symbols denote treatments
without herbicide. Treatments followed by different letters are significantly
different ( p < 0.05). Mean � S.E. For descriptions of treatments see Table 3
and text.
growing seasons, the mean relative growth rate in diameter (RD,
mm mm�1 and year�1) was calculated using the formula:
RD ¼ ðlnðD2Þ � lnðD1ÞÞ=ðt2 � t1Þ (1)
where D1 and D2 denote root collar diameter in the end of each
growing season and t2 � t1 is 1 year.
The general linear model (GLM) procedure for the analysis
of variance was used to perform statistical tests on seedling
survival and growth after calculating treatment averages (SAS
Institute Inc., Cary, NC, USA). Before the survival rates of
seedlings were analyzed, frequencies were transformed
according to Zar (1984) using the formula:
p0 ¼ 1=2ðarcsinðX=ðnþ 1ÞÞ1=2 þ arcsinððX þ 1Þ=ðnþ 1ÞÞ1=2Þ(2)
where p0 is the transformed frequency, X denotes the number of
living seedlings at the end of the experiment, and n is the
number of planted seedlings at the beginning of the experiment.
Where significant F values occurred, Tukey’s multiple range
test was done for further analysis. In the comparisons, p < 0.05
was considered significant.
3. Results
Three years following start of experiment, the natural
vegetation cover was similar in the control and the MSP—
treatment (Table 3). Three growing seasons after planting in
April 2002, the vegetation cover near the seedlings was 96%. In
contrast, in the H- and MSP + H-treatments, the cover of
vegetation was only 12 and 7%, respectively. Even though the
vegetation cover was high in the control and MSP-treatment,
40% and 56% of seedling foliage overtopped the competitive
vegetation in the two treatments. In the H- and MSP + H-
treatments, most leaves were not covered by surrounding
vegetation.
Soil water potential values were high, except for control in
September (Table 3). The PPFD at seedling level (0.3 m) was
similar in the control and MSP-treatment and in the H- and
MSP + H-treatments and corresponded to 29%, 24% and 76%
and 75% of full light (PPFD at 1.5 m), respectively.
Three growing seasons following planting in April 2002,
there was a strong positive ( p < 0.001) effect of all site
preparation treatments on seedling survival (Fig. 1). In H-,
MSP-, and MSP + H site preparation treatments the survival of
seedlings was approx. 90%, whereas only 58% of seedlings
survived in the control (C). In the end of the second growing
season, there was a trend of reduced survival in both the control
(C) and MSP-treatment. Furthermore, we observed that many
seedlings were damaged by voles, especially in the control (C)
following the first growing season. Stem bark was stripped and
gnawing had been evident on the lower part of stems.
There was also a strong positive effect ( p < 0.0001) of the
different site preparation treatments on seedling growth of stem
base diameter (Fig. 2A). The difference was obvious as early as
the end of the first growing season. In September 2004, the
mean stem base diameter of seedlings in the MSP + H-
treatment was approx. twice as large as in the control (C). There
was also a positive effect of both MSP- and MSP + H-
treatments on seedling length compared with the control (C)
(Fig. 2B).
For seedling dry mass, there was a strong significant effect of
treatment in the end of 2004 ( p < 0.001) (Fig. 3A). The dry mass
of seedlings from the MSP + H-treatment was approx. twice as
high compared with the H- and MSP-treatments and five times
higher than in the control (C). The same trend was found for
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–25 23
Fig. 2. Mean seedling stem base diameter (A) and height (B) in four treatments
and 3 years. Open symbols denote treatments with herbicide and filled symbols
denote treatments without herbicide. Treatments in the same box followed by
different letters resulted in statistically significant differences ( p < 0.05).
Mean � S.E. For descriptions of treatments see Table 3 and text.
Fig. 3. Mean seedling dry weight in 2004 (A), mean seedling leaf area in 2004
(B), seedling stem base relative growth rate from 2002 to 2003 (white) and
2003–2004 (grey) (C) and root:shoot dry weight ratio in 2004 (D) in four
treatments. Treatments in the same box followed by different letters resulted in
statistically significant differences ( p < 0.05). Mean � S.E. For descriptions of
treatments see Table 3 and text.
seedling leaf area (Fig. 3B). For relative diameter growth rate
there was no significant difference between treatments in 2004,
although there was a trend of higher relative growth rate in the
various site preparation treatments compared with the control (C)
(Fig. 3C). In 2003, the MSP + H-treatment had a higher
( p < 0.05) relative growth rate than the control (C) and MSP-
treatments (no letters signifying differences shown) (Fig. 3C).
Moreover, although there was tendency for lower root:shoot
ratios in MSP- and MSP + H-treatments, no significant
difference was found between treatments at the end of 2004
growing season (Fig. 3D).
4. Discussion
Mounding site preparation proved to be an efficient
reforestation method. In this study, seedling survival was high
(approx. 90%) when bare-root oak seedlings were planted in the
various site preparation treatment sites that included mounding
site preparation. In comparison, lower survival was found in the
undisturbed control and the result was clear from the first
growing season. This might have been a result of less
transplanting stress for seedlings planted following site
preparation. In this study, seedlings in the control were planted
into already existing natural ground vegetation having developed
over two growing seasons and abundant vegetation may decrease
soil water content (Lof et al., 1998) which might have enhanced
the internal water stress that seedlings undergo following
planting (Kozlowski and Davies, 1975). However, in this case,
after the seedlings were planted a period of high precipitation
followed. Furthermore, we observed much vole damage on
seedlings, especially in the undisturbed control, possibly causing
many to be missed from the first inventory. This agrees with
earlier research on broadleaved seedling survival and establish-
ment in herbaceous environments, where a substantial number of
the established seedlings can be damaged or consumed by rodent
herbivores, and thus disappear over time (Lupke von, 1987;
Manson et al., 2001; Lof et al., 2004; Hytonen and Jylha, 2005).
In 2003, lower survival was found in the MSP-treatment and
in the control (C) than in 2004. This was probably an effect of
when the inventory took place. Survival and growth during the
2002 and 2003 growing seasons were measured in early spring
2003 and 2004. In April 2004, natural vegetation in these two
treatments was abundant and some seedlings may have been too
difficult to find. In September 2004, when leaves were present
on the seedlings, more seedlings were found.
Interference from vegetation had a negative effect on the
growth of oak seedlings. This is similar to the results of numerous
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–2524
other studies (e.g. Davies, 1988; Cogliastro et al., 1990; Munson
et al., 1993; Lof, 2000b). Comparison of RD values in H- and
MSP + H treatments with the control (C) and MSP-treatment
shows a trend of reduced seedling growth for 2 or 3 years after
planting. However, the differences were not always significant.
Furthermore, interpreting relative growth rates may be difficult
since larger seedlings normally exhibit lower values of relative
growth rate than smaller ones (Brand et al., 1987).
Interference from vegetation was mainly below ground in
this study. For seedling foliage that was below competing
vegetation, the relative light level was approx. 24–29% of full
light. This is a light level that results in growth reduction of oak
(Oleskog and Lof, 2005). However, a large proportion of
seedling foliage in the control (C) and in the MSP-treatment
was above competing vegetation and thus had access to full
light. Hence, light was not the primary competitive constraint
between herbaceous vegetation and seedlings.
In accordance with earlier research on conifer seedlings,
mounding site preparation had a positive influence on the
growth of oak seedlings compared with the undisturbed control
(Sutton, 1993; Nilsson and Orlander, 1999; Hallsby and
Orlander, 2004; Pennanen et al., 2005). Stem base diameter
growth, seedling biomass and seedling leaf area were approx.
the same in the H- and MSP-treatments. In the present study, the
herbicide treated strips were only 1 m wide and root
competition may have occurred from the vegetation on both
sides. A much stronger effect of repeated herbicide application
is expected to be found when larger-sized experimental plots
are used (Davies, 1988; Munson et al., 1993; Lof, 2000b).
Seedling height was greater in MSP-compared with the other
treatments including H-treatment. However, it is well known
that biomass partitioning of seedlings shaded by trees and other
competing vegetation may change, i.e. that taller oak seedling
are found where relative light levels decrease (Ammer, 2003).
There was a positive growth response of oak seedlings
following mounding site preparation itself. Although the
vegetation cover in year 3 in the control (C) and in the MSP-
treatment was the same and resulted in the same light level at
30 cm from ground, seedling growth was greater in the MSP-
treatment than in the control (C). This growth effect can
somewhat be attributed to less competition and transplanting
stress for seedlings in the MSP-treatment since competitive
vegetation was not present at the time of planting, as it was in
the control (C). Furthermore, although the same vegetation and
light pattern were found in the H- and MSP + H-treatments,
seedling growth was higher in the MSP + H-treatment than in
the H-treatment. This is in contrast to findings of Sutherland
and Foreman (2000) where planting in mounds resulted in less
growth of Picea Mariana (Mill.) BSP seedlings compared with
those in a repeated herbicide treatment. Munson et al. (1993)
did not find any substantial effect of mechanical site preparation
on conifer seedling growth compared with a repeated herbicide
treatment but they used blade scarification and not mounding.
According to Carlquist (2000), working in boreal forest sites,
mounding creates a positive microclimate for planted seedlings
by increasing heat absorption, which results in better root growth
of planted seedlings and a longer growing season. He also stated
the importance of fine soil texture for good water storage in the
mound. In the present study, the soil consisted of a large fraction
of silt and clay, which is why mounding was a good choice of
method. Such sites are prone to surface frost which is negative for
seedlings and elevated planting positions may have reduced the
influence from frost in this study. Others have stated that
mounding improves the short-term nutrient supply to seedlings
due to a stimulation of humus mineralization by mechanical
disturbance (Orlander et al., 1990). However, there is a risk that in
a later stage of stand development, growth may be retarded due to
the fact that the leached elements had previously been lost from
the ecosystem. Furthermore, on ground-water influenced sites,
mounding increases the part of the rooting zone without
groundwater influence and associated reduced conditions.
Hallsby and Orlander (2004) have pointed out that elevated
planting positions may cause water stress in seedlings during
periods with little precipitation. We experienced such periods
during the study but did not find low water potential in the MSP-
treatment. Soil water potential was not measured continuously
during the three growing seasons and therefore an influence of
soil drought on seedling growth cannot be excluded. However,
we found a trend of lower root:shoot ratio following mounding
site preparation which is in contrast to expected biomass
partitioning following drought conditions and perhaps soil
drought was not important in the mounds in this study.
5. Conclusions
We conclude that mounding site preparation is an efficient
tool for forest managers in establishing oak stands and is a good
alternative to herbicide treatment on ground-water influenced
sites. In the present study, survival and growth of seedlings
following mounding site preparation were equally as high as in
the repeated herbicide treatment over three growing seasons.
However, such high effort in herbicide application is seldom put
into practice. Mounding site preparation results in a relatively
large disturbance area and deep soil disturbance, which is
negative for recreational values and sustainable nutrient
management. In addition, mechanical site preparation such
as mounding may destroy hidden archaeological remains and
therefore, careful site selection is needed.
Acknowledgements
We appreciate the assistance of Ulf Johansson at Tonnersjo-
hedens and Skarhults experimental forests. Our thanks also to
Georg Andersson, Rolf Overgaard and Oriana Pfister (SLU,
Southern Swedish Forest Research Centre) as well as to Tomasz
Czajkowski and Heiko Rubbert (Gottingen University, Institute
of Silviculture) for their help with field work, and to Michelle
Slaney for linguistic improvements. We thank R.F. Sutton and
one anonymous reviewer for constructive comments. Financial
support was received from the Lidellska foundation, the Swedish
Research Council for Environment, Agricultural Sciences and
Spatial Planning and the research program Sustainable manage-
ment in hardwood forests. The root and soil studies were
M. Lof et al. / Forest Ecology and Management 232 (2006) 19–25 25
supported by the German Federal Ministry of Science and
Technology (Junior Professorship A. Bolte).
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