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i
iF o r e s t
F o r e s t
Biogeosciences and Forestry
Biogeosciences and Forestry
Influences of forest gaps on soil physico-chemical and biological
properties in an oriental beech (Fagus orientalis L.) stand of Hyrcanian
forest, north of Iran
Alireza Amolikondori (1),
Kambiz Abrari Vajari (1),
Mohammad Feizian (1),
Antonino Di Iorio (2)
Understanding the effects of silvicultural practices including single-tree selec -
tion on soil properties is essential for forest management in temperate broad-
leaved beech forests. Changes in physico-chemical and biological soil proper-
ties in 15 harvest-created gaps under single-tree selection and the adjacent
closed canopies, with five replications for each, were studied 6 years after gap
creation in an oriental beech (Fagus orientalis L.) stand of the Hyrcanian for-
est. Gaps were classified into three size classes: small (85-130 m2), medium
(131-175 m2) and large (176-300 m2). Soil cores were collected at the center
and at the edge of gaps, and under the adjacent closed canopy. Results indi-
cated that gap size significantly affected soil texture and bulk density,
whereas soil organic carbon (SOC), total nitrogen and pH showed a significant
gradient from the center to the edge of gap independently form their size.
SOC and total nitrogen at the center of gaps were also significantly lower than
closed-canopy, in particular for the medium-gap; contrastingly, the bulk den-
sity with the highest mean value was found at the center of the large-gap. Gap
size had no significant influence on soil microbial biomass. These results high-
lighted that similar conditions in terms of many soil properties were still
present among gaps and adjacent closed-canopy stands six years after logging,
though canopy openness triggered a reduction in carbon and nitrogen avail-
ability along with the related microbial activity at the center of gaps, indepen-
dently from their size. Therefore, if aimed at preserving an uneven aged
structure along with soil quality in temperate broadleaved deciduous forest as
the oriental beech stands in the Hyrcanian region, single-tree selection prac -
tice for harvesting trees can be recommended as sustainable forest manage-
ment type.
Keywords: Artificial Gap, Oriental Beech, Temperate Forests, Soil Properties
Introduction
Hyrcanian hardwood forests are charac-
terized by a significant set of characteris-
tics that make them ecologically and eco-
nomically attractive. On the other hand,
these forests suffered a lot of natural (e.g.,
wind) and artificial (e.g., logging) distur-
bance events, which frequently result in
the formation of canopy gaps. Forest gaps
are a critical factor of the disturbance
regime in Hyrcanian temperate forests.
Therefore, the understanding of the eco-
logical processes following the gap forma-
tion are essential for sustainable forest
management systems. Forest gaps are dif-
ferent sized spaces in the canopy and are
due to the damage or death of one or
more trees (Yamamoto 2000). Many envi-
ronmental variations take place after the
formation of a gap (D’Oliveira & Ribas
2011), among which the changes in the dis-
tribution of living and non-living resources,
whose impact is crucial on both above-
ground and belowground ecological pro-
cesses in forests (Liu et al. 2018). Indeed,
gaps influence the forest soil which is a vi-
tal part of the ecosystem functioning (Yang
et al. 2017). According to Scharenbroch &
Bockheim (2007), different elements may
influence soil processes including climate,
organisms, physiography, parent material,
time, and human activities. For example,
the soil microbial biomass plays an impor-
tant role in the nutrients cycle (Yang et al.
2010), resulting an important indicator of
soil fertility for the ecological research and
sustainable forest management (Ravindran
& Yang 2015). The canopy gap alters the mi-
croclimatic features of the soil and, conse-
quently, the soil microbial biomass and res-
piration (Bolat 2014). Knowing about the
amount of soil nutrients and its relation-
ship to gap dynamics can afford valuable
insights on forest ecosystem functioning.
Previous studies have shown that soil
physic-chemical and biological features
were affected by gaps in different forest
types. In old growth northern hardwood-
hemlock forests (USA), Scharenbroch &
Bockheim (2007) reported that the value
of exchangeable cations in the 0-25 cm
mineral soil depth was lower in gaps than
© SISEF https://iforest.sisef.org/ 124 iForest 13: 124-129
(1) Faculty of Agriculture and Natural Resource, Lorestan University, Khorramabad (Iran);
(2) Department of Biotechnology and Life Science, University of Insubria, 21100 Varese (Italy)
@
@ Kambiz Abrari Vajari (abrari.k@lu.ac.ir)
Received: Jul 30, 2019 - Accepted: Jan 25, 2020
Citation: Amolikondori A, Abrari Vajari K, Feizian M, Di Iorio A (2020). Influences of forest
gaps on soil physico-chemical and biological properties in an oriental beech (Fagus orientalis
L.) stand of Hyrcanian forest, north of Iran. iForest 13: 124-129. – doi: 10.3832/ifor3205-013
[online 2020-04-07]
Communicated by: Giorgio Alberti
Research Article
Research Article
doi:
doi: 10.3832/ifor3205-013
10.3832/ifor3205-013
vol. 13, pp. 124-129
vol. 13, pp. 124-129
Amolikondori A et al. - iForest 13: 124-129
in closed canopy. In European silver fir
stands (Abies alba Mill) in Italy, Muscolo et
al. (2007a) reported the occurrence of
chemical and microbiological variations in
the soil of gaps. Other studies investigating
soil respiration (Saner et al. 2009, Pang et
al. 2013), microclimate variables (He et al.
2012), microbial community (Schliemann &
Bockheim 2014, Lewandowski et al. 2015),
microbial biomass (Arunachalam & Aruna-
chalam 2000, Muscolo et al. 2007b), en-
zyme activities (Yang et al. 2017) have also
confirmed the influences of forest gaps on
soil properties. The study of forest gaps dy-
namics is essential to understanding eco-
system function and predicting how forest
ecosystems respond to disturbance and to
forest management.
Oriental beech (Fagus orientalis L.) which
belongs to the family Fagaceae is one of
the most widespread broadleaved trees in
mixed and pure stands of the Hyrcanian
temperate forests. In these stands, differ-
ent gap sizes have been generated by us-
ing different silvicultural systems, espe-
cially the single-tree selection harvesting
method. Despite the importance of forest
gaps in the development of Hyrcanian tem-
perate forests, there is inadequate infor-
mation of their effects on soil properties.
This research aimed at determining the in-
fluences of forest gaps on soil features in
broad-leaf, deciduous beech stand. Specific
objectives of this study were: (i) to deter-
mine the effect of gap size on physico-
chemical and biological properties of soil;
(ii) to compare soil features among differ-
ent positions (center, edge of gap and
closed canopy); and (iii) to evaluate the
correlation between gap size and soil prop-
erties.
Materials and methods
Site description
The study was carried out in an uneven-
aged beech (Fagus orientalis Lipsky) forest
located in the Hyrcanian region, northern
Iran (36° 12′ N, 53° 24′ E), approximately
from 1000 to 1200 m a.s.l. This site covers
an area of about 40.4 ha on a 0-30% north-
facing slope. The climate is humid, with a
mean annual precipitation of 858 mm
mostly concentrated in autumn, and a
mean annual temperature of 10.5 °C. The
dominant soil types are pseudogleyic and
gley. Oriental beech trees occupy all forest
layers, from overtopped to dominant ones.
To a lesser extent, other tree species in-
cluding alder (Alnus subcordata C.A. Mey),
hornbeam (Carpinus betulus L.) and maple
(Acer velutinum Boiss.) are commonly pres-
ent. The broadleaved, multi-layered and
uneven-aged beech stand originated from
natural regeneration. The stand was man-
aged under the single-tree selection silvi-
cultural system in 2011. Under the current
silvicultural system, different canopy gaps
have generally been created within the
stand. These harvest-generated gaps were
randomly extended at the site. In total, 15
artificial gaps were sampled and catego -
rized in three size classes of five replicates
each: small (85-130 m2), medium (131-175
m2) and large (176-300 m2). The gap area
was measured using the formula for an el-
lipse: A = (πLW) / 4, where L is the longest
distance within the gap (m), and W is the
largest distance perpendicular to L (m –
Fig. 1). These distances were measured be-
tween stems of the trees at the border. All
gaps were oriented in north exposition
within forest (Fig. 1).
Soil sampling
Soil samples were taken in October 2017,
six years after gap creation. After removal
of the litter layer, soil samples were col-
lected by hand soil corer (8 cm diameter)
from the shallower rooted soil layer up to
20 cm depth. The sampling protocol fol-
lowed the scheme reported in Fig. 1. For
each gap, 4 soil samples were collected at
the cardinal points of the gap border and 4
at the adjacent closed canopy at a distance
of 20 m from the gap (Fig. 1). The four gap-
edge-cores were mixed to produce one
composite sample (hereafter named gap-
edge-core); the same was done for closed
canopy cores (hereafter named close-
canopy-core). One more core was col-
lected at the center of the gap (hereafter
named gap-center-core), so that soil sam-
ples totaled three per gap. Each composite
soil sample was air dried and sieved to 2
mm mesh size, and any living plant material
was removed manually from the sieved soil
to accomplish physico-chemical analysis. A
subsample of each soil was stored at 4 °C.
Physico-chemical analysis of soil
Physico-chemical properties of soil were
analyzed based on Page (1992). Soil pH was
determined using a pH meter after shaking
the soil:water (1:1, w/v) suspension for 1
hour. Bulk density (BD, g cm-3) at air-dried
moisture content was calculated by clod
method; soil bulk density was measured by
calculating soil mass and volume using
paraffin wax using the following steps. In
clod method, soil bulk density is calculated
through computing soil mass and volume
by using paraffin wax and going through
these steps: at first, the weight of a clod is
determined and its volume is measured by
covering it in paraffin wax heated up to 65-
70 °C and the clod is plunged in the wax
bath for roughly 24 h. The waxed clod is
first weighed in the air and then weighed in
the given volume of water where the wa-
ter temperature is measured and the mass
is checked yet again (Al-Shammary et al.
2018). Soil texture (sand, silt and clay) was
determined using the Bouyoucos hydrome-
ter method. In the case of hydrometer
method, the methodology described in the
work of Bouyoucos (1962) and Papuga et
al. (2018) was applied. Soil moisture (%)
was obtained by drying soil samples at 105
°C for 24 h. Water content was obtained by
dividing the difference between wet and
dry masses by the mass of the dry sample.
Soil organic carbon (SOC, %) was assessed
using Walkley & Black (1934) method which
involves oxidation of organic matter by
K2Cr2O7 with H2SO4 heat of dilution and
then titrated with ferrous ammonium sul-
fate. Total N content was determined by
the Kjeldahl method (Brookes et al. 1982).
Phosphorus (P, mg kg-1) was obtained by
the method of Olsen et al. (1954). This
method used a 2.5-g sample shaken with
50 ml 0.5 m NaHCO3, buffered at pH 8.5,
for 30 minutes and filtering extracts
through Whatman no. 42 filter paper. P
concentration was determined by induc-
tively coupled plasma atomic emission
spectroscopy (ICP-AES); blank and stan-
dards were prepared in Olsen P extracting
solution (Chaouqi et al. 2017).
Soil microbial biomass C, N and P
Soil microbial biomass carbon (MBC), ni-
trogen (MBN) and phosphorous (MBP)
were obtained using the chloroform fumi-
gation-extraction method based on Broo-
kes et al. (1982, 1985) using K2SO4 (0.5 M)
and NaHCO3 (0.5 M) as extracting solution
in MBC, MBN and MBP, respectively. Brief-
ly, weighed portions of moist soil were put
into a desiccator containing wet filter pa-
125 iForest 13: 124-129
Fig. 1 - Sketch of
location of the
sampling points
within gap and
adjacent closed
canopy. Capital
letters indicate
cardinal points.
iForest – Biogeosciences and Forestry
Soil responses to forest canopy gaps
per and alcohol-free liquid CHCl3. The desic-
cator was evacuated on a water pump until
the CHCl3 had boiled vigorously for 5 min.
The desiccator containing CHCl3 was kept
at 25 °C until the fumigated soil was re-
quired for chemical analysis. Control, non-
fumigated soil was treated similarly, ex-
cept that the desiccator contained no
CHCl3 and was not evacuated.
Microbial biomass C was measured by ex-
tracting the fumigated soil immediately fol -
lowing CHCl3 removal by shaking for 30 min
with 0.5 M K2SO4 at a solution:soil ratio of
4:1. After filtration through a Whatman no.
42 filter paper, the filtrate was analyzed for
organic C using dichromate digestion. Mi-
crobial biomass C was calculated as fol-
lows: MBC = Ec · (2.64), where Ec is the dif-
ferent between organic C extracted by 0.5
M K2SO4 from fumigate and non-fumigated
soil (Vance et al. 1987) and also MBN was
calculated from the difference between
the amount of inorganic N extracted by 0.5
M K2SO4 from fresh soil fumigated with
CHCl3 and the amount extracted from unfu-
migated soil by dividing by 0.54 (Alef &
Nannipieri 1995, Joergensen & Mueller
1996). MBP was calculated from the differ-
ence between the amount of inorganic P
extracted by 0.5 M NaHCO3, (pH 8.5) from
fresh soil fumigated with CHCl3 and the
amount extracted from unfumigated soil
by dividing by 0.4 (Brookes et al. 1982).
Soil respiration
The CO2 emission from each soil sample
was estimated after incubation for 3 days
at 25 °C (55% water content) in a closed sys-
tem. CO2 was trapped in a NaOH solution,
which was then titrated with HCl (Alef &
Nannipieri 1995).
Statistical analyses
To compare the three gap-size classes, 5
artificial gaps (replicates) per size class
were established. Two-way ANOVA was
performed to evaluate the effects of gap
size and within-gap core position. Data
were transformed where necessary to
meet assumptions. One-way ANOVA fol-
lowed by the least significant difference
(LSD) test were performed among the
three closed-canopy controls to exclude
possible differences among them. To test
the difference between the gaps and the
closed-canopy, a second one-way ANOVA
followed by the Dunnett’s test (bilateral al-
ternative, P < 0.05) was applied to differ-
ences among the closed-canopy (reference
mean) and both center and edge cores for
each gap size.
Pearson’s correlation was performed to
examine the relationships within physico-
chemical or biological variables and the
gap size, this latter simply scaled in three
increasing levels. Significant levels were ac-
cepted at P<0.05 and P<0.01. All the analy-
ses were performed with the software
SPSS® version 20.0 (IBM, Armonk, NY,
USA).
Results
Soil physico-chemical characteristics
Forest gaps significantly affected some
properties of the soil (Tab. 1). For the physi-
cal characteristics, gap size affected the
clay (P = 0.011 – Tab. 1) and sand (P = 0.018
– Tab. 1) proportion, with the medium size
showing the lowest values for sand and the
highest for clay (Tab. 2). Moreover, inde-
pendently form the gap size, the sand per -
centage was significantly lower in the cen-
ter than the gap-edge (position effect, P =
0.022 – Tab. 1) the opposite for the clay
(position effect, P = 0.044 – Tab. 1). The
gap size affected the bulk density as well
(P = 0.008 – Tab. 1), increasing from the
smaller to the larger size (Tab. 2). For the
chemical properties, no significant differ-
ences occurred between the different gap
sizes, whereas a significant gradient (with-
iForest 13: 124-129 126
Tab. 1 - F and P values of ANOVA (GLM) for the effects of gap-size and within gap core
position for gaps cores only on soil physico-chemical variables. (SOC): Soil organic car-
bon; (Total N): Total Nitrogen; (P): Phosphorus; (BD): Bulk Density.
Variable Stats Gap size Within Gap
Position
Gap size ×
W-G Position
(df = 2) (df = 1) (df = 2)
SOC (%) F 1.589 5.1 0.174
P 0.227 0.034 0.841
Total N (%) F 1.822 5.451 0.268
P 0.183 0.028 0.767
P (mg kg-1) F 1.902 0.157 0.441
P 0.171 0.695 0.648
Clay (%) F 5.41 4.519 0.249
P 0.011 0.044 0.782
Silt (%) F 2.741 0.371 0.177
P 0.085 0.548 0.839
Sand (%) F 4.804 5.98 0.724
P 0.018 0.022 0.495
pH F 0.591 4.275 0.64
P 0.562 0.048 0.536
BD (g m-3) F 5.934 2.617 0.686
P 0.008 0.119 0.513
Moisture content
(%)
F 0.325 0.051 2.335
P 0.726 0.823 0.118
Tab. 2 - Physico-chemical variables for two within-gap position and three gap-size classes, and the adjacent closed canopy. Values
are the mean (± standard deviation) of 5 replicates, 15 replicates for the closed-canopy only. The letters a, b, and c indicate signifi -
cant differences between all positions (LSD, P<0.05); the letters x and y indicate significant differences between within-gap posi -
tions and closed canopy (Dunnet’s test, bilateral alternative, P<0.05) (SOC): Soil organic carbon; (Total N): Total Nitrogen; (P): Phos-
phorus; (BD): Bulk density.
Variable Small Medium Large Closed
canopy
gap-center gap-edge gap-center gap-edge gap-center gap-edge
SOC (%) 5.32 ± 1.47 6.41 ± 1.56 b3.86 ± 1.42 ax 5.52 ± 0.48 b4.81 ± 0.97 5.74 ± 2.06 b5.98 ± 1.36 y
Total N (%) 0.45 ± 0.13 0.55 ± 0.12 b0.33 ± 0.12 ax 0.47 ± 0.04 0.43 ± 0.08 0.49 ± 0.18 b0.51 ± 0.12 y
P (mg kg-1) 5.76 ± 1.95 4.92 ± 0.67 4.95 ± 2.72 4.24 ± 0.47 6.00 ± 2.96 6.68 ± 1.85 5.34 ± 2.54
Clay (%) 20.90 ± 4.92 15.50 ± 3.48 a25.10 ± 3.09 b22.80 ± 3.57 b19.10 ± 8.08 15.40 ± 4.57 a19.90 ± 5.83
Silt (%) 10.50 ± 1.37 11.10 ± 2.99 a7.55 ± 2.08 b8.80 ± 3.61 9.92 ± 3.22 9.80 ± 1.16 10.20 ± 3.34
Sand (%) 68.50 ± 3.64 b73.30 ± 1.91 a67.30 ± 2.12 b68.40 ± 2.77 b70.90 ± 5.27 74.80 ± 4.70 a69.70 ± 4.38
pH 6.83 ± 0.21 6.72 ± 0.40 7.09 ± 0.27 a6.72 ± 0.23 b6.85 ± 0.26 6.76 ± 0.21 6.87 ± 0.27
BD (g m-3) 1.28 ± 0.17 b1.27 ± 0.20 b1.53 ± 0.12 1.29 ± 0.23 b1.69 ± 0.32 ax 1.54 ± 0.23 1.33 ± 0.18 y
Moisture (%) 43.70 ± 9.95 38.60 ± 9.39 32.80 ± 6.98 43.20 ± 4.93 41.40 ± 13.4 38.30 ± 4.02 34.90 ± 5.90
iForest – Biogeosciences and Forestry
Amolikondori A et al. - iForest 13: 124-129
in-gap-position effect) was observed for
SOC (P = 0.034), total N (P = 0.028) and the
pH (P = 0.048) with the SOC and total N in -
creasing from the center to the edge, the
opposite for the pH.
The closed-canopy did not show any sig-
nificant difference with gaps for all proper-
ties, with the only exception of the lower
SOC and total N concentrations for the
medium sized and the higher BD for the
large sized gaps, both measured at the
center of the gap. Correlation highlighted
the relationship among those variables af-
fected by within-gap-position effect. More-
over, gap size correlated positively only
with BD (Tab. S1 in Supplementary mate-
rial).
Soil microbial biomass C, N and P
As shown in Tab. 3, forest gaps had no in-
fluence on the biological properties of the
soil (P>0.05). MBP marginally missed the
significance for the variance of within gap
position (P = 0.061 – Tab. 3) with values at
the center always lower than at the edge,
significant only for the medium sized gap
(Tab. 4); MBN/total N marginally missed
the significance for the gap size × within
gap position interaction (P = 0.087) with
values at the gap center higher than those
at the edge except for the medium sized
gap. No differences occurred also between
the three controls, so that they were
pooled and treated as one. Although not
significantly, there was a general trend for
the gaps to have MBC, MBP, MBN concen-
trations and their ratios higher than the
closed-canopy plots. MBC directly corre-
lated with MBP and its own ratio to MBN
and SOC. In the microbial biomass, the C:N
ratio increased with decreasing N:P and
N:total N ratios (Tab. S1, Supplementary
material). Between physico-chemical and
biological variables, it is worth to note the
direct relationship between MBC and silt
percentage. Nitrogen in microbial biomass
(MBN) increased with increasing N and
SOC concentrations into the soil, whereas
an inverse relationship did occur with soil
pH and BD (Tab. S1).
Discussion
This work highlighted that changes in the
size of gap six years after logging may af-
fects soil physico-chemical characteristics
rather than the microbial biomass and soil
respiration. This outcome is particularly evi-
dent for the medium-sized gaps in this
study (131-175 m2). Moreover, some of the
soil chemical characteristics such as SOC
and total N showed a significant decrease
in the center of gaps, independently from
their size. Studies on the correlation be-
tween canopy gap size and BD have pro-
vided inconsistent results; correlation was
found positive in broad-leaved Pinus ko-
raiensis forests (Zhang & Zhao 2007) or ab-
sent in old-growth Tsuga canadiensis for-
ests (Schliemann & Bockheim 2014). The
lack of correlation of BD with the textural
component of the soil made this result
hard to fathom, but soil compaction due to
the seedling recruitment (Muscolo et al.
2010) cannot be ruled out.
Markedly higher soil moisture levels in
the artificial gaps compared to adjacent
closed-canopy were found for Danish Fa-
gus sylvatica forests (Ritter & Vesterdal
2006) and Turkish oriental beech, oak, and
chestnut stands (Sariyildiz 2008). This can
be related to the joint effects of an in-
creased rainfall and reduced transpiration
by plant uptake (Latif & Blackburn 2010,
Muscolo et al. 2010).
127 iForest 13: 124-129
Tab. 3 - F and P values of ANOVA (GLM) for the effects of gap-size and within gap core
position for gaps cores only on soil biological variables. (MBC): Microbial Biomass Car-
bon; (MBP): Microbial Biomass Phosphorus; (MBN): Microbial Biomass Nitrogen.
Variable Stats Gap size Within Gap
Position
Gap size ×
W-G Position
(df = 2) (df = 1) (df = 2)
MBC (mg kg-1) F 0.091 0.968 0.574
P 0.914 0.335 0.571
MBP (mg kg-1) F 0.176 3.853 0.912
P 0.839 0.061 0.415
MBN (mg kg-1) F 1.802 1.226 1.301
P 0.189 0.281 0.292
MBC/MBN F 2.364 0.341 0.583
P 0.121 0.566 0.567
MBC/MBP F 0.241 2.008 0.474
P 0.787 0.169 0.628
MBN/MBP F 1.012 0.418 0.858
P 0.379 0.524 0.436
MBC/SOC% F 0.366 0.235 0.067
P 0.698 0.633 0.935
MBN/Total N F 2.116 0.29 2.749
P 0.146 0.596 0.087
MBP/P F 0.045 2.436 1.164
P 0.956 0.134 0.333
Respiration
(mg CO2-C g-1 soil d-1)
F 0.847 0.201 1.118
P 0.441 0.658 0.343
Tab. 4 - Biological variables for two within-gap position and three gap-size classes, and the adjacent closed canopy. Values are the
mean (± standard deviation) of 5 replicates, 15 replicates for the closed-canopy only. The letters a, b, and c indicate significant differ -
ences between all positions (LSD, P<0.05); the letters x and y indicate significant differences between within-gap positions and
closed canopy (Dunnet’s test, bilateral alternative, P<0.05). (MBC): Microbial Biomass Carbon; (MBP): Microbial Biomass Phospho-
rus; (MBN): Microbial Biomass Nitrogen; (SOC): Soil Organic Carbon; (Total N): Total Nitrogen; (P): Phosphorus.
Variable Small Medium Large Closed
canopy
gap-center gap-edge gap-center gap-edge gap-center gap-edge
MBC (mg kg-1) 405.60 ± 256.1 371.70 ± 169.6 294.50 ± 138.8 463.70 ± 271.8 370.30 ± 180.4 466.40 ± 237.6 295.50 ± 191.4
MBP (mg kg-1) 5.20 ± 3.18 5.63 ± 2.33 3.87 ± 1.80 a 8.85 ± 4.47 b 5.21 ± 2.08 7.74 ± 5.47 1.94 ± 0.61
MBN (mg kg-1) 102.90 ± 47.0 106.40 ± 81.9 51.70 ± 24.8 116.30 ± 39.1 63.20 ± 47.2 58.50 ± 38.4 83.90 ± 55.9
MBC/MBN 2.87 ± 1.70 1.94 ± 0.98 6.69 ± 4.07 4.82 ± 4.84 4.71 ± 2.74 6.03 ± 4.16 1.80 ± 0.80
MBC/MBP 110.70 ± 74.2 66.48 ± 21.6 90.30 ± 57.6 54.90 ± 25.5 83.60 ± 66.2 82.30 ± 44.7 77.70 ± 51.9
MBN/MBP 44.10 ± 40.2 21.50 ± 20.2 18.60 ± 17.9 23.60 ± 21.5 17.70 ± 21.2 17.60 ± 22.1 26.30 ± 28.8
MBC/SOC 72.30 ± 33.9 65.90 ± 37.8 79.80 ± 42.0 67.00 ± 40.3 59.80 ± 24.7 59.20 ± 27.4 49.40 ± 32.4
MBN/Total N 260.90 ± 138.1 a 135.10 ± 107.8 151.70 ± 44.3 239.70 ± 67.6 130.20 ± 105.4 109.50 ± 81.22 b 168.90 ± 105.8
MBP/P 0.90 ± 0.43 1.13 ± 0.36 0.63 ± 0.36 1.39 ± 0.38 0.96 ± 0.48 0.93 ± 0.89 0.93 ± 0.61
Respiration (mg
CO2-C g-1 soil d-1)
0.10 ± 0.06 0.10 ± 0.04 0.09 ± 0.05 0.13 ± 0.03 0.14 ± 0.03 0.11 ± 0.04 0.09 ± 0.05
iForest – Biogeosciences and Forestry
Soil responses to forest canopy gaps
The openness of the canopy induced a
significant decrease of soil pH at the edge
of the gap, independently from its size, but
no difference occurred in comparison to
the closed canopy. Zhang & Zhao (2007)
found no significant difference for soil pH
between canopy gaps and closed-canopy
sites in broad-leaved Pinus koraiensis for-
ests. Kooch et al. (2010) reported a higher
amount of pH for the large gaps in compar-
ison to the medium gaps. Interestingly, the
inverse pattern occurred for SOC and total
N, resulting in a significative negative cor-
relation with soil pH. Many factors could
affect soil pH, such as salt base saturation,
soil redox state, soil water content, and
CO2 partial pressure in soils. The increase of
soil respiration with the gap opening,
though not observed in this study with the
only exception for the large gaps, in-
creases HCO32- concentration resulting in
higher pH (Pujia et al. 2014).
These findings are partially compatible
with those of Ritter & Bjørnlund (2005)
who indicated that gap had no influence
on the amount of organic material of the
soil in Fagus sylvatica stands. In fact, in this
study the canopy openness affected any-
how the amount of SOC and N available
into the soil in the central area of the gap,
particularly for the medium size gaps. The
lack of significance for the smaller and
larger gaps might be related to the small
number of soil samples in comparison to
the high soil heterogeneity. The lack of no-
ticeable changes among gaps in this study
could be also attributed to resistance of
forests to small scale disturbances (Ritter
& Bjørnlund 2005).
Regarding the soil biological variables,
the slight changes observed among gaps,
although not statistically significant, may
be attributed to vegetation type (Ravin-
dran & Yang 2015), changes in the microcli-
matic properties of the soil (Bolat 2014),
and gaps age. Microbial biomass changes
according to soil temperature, moisture,
and depth of soil (Ravindran & Yang 2015).
In addition to microclimate conditions, vari-
ations of soil biological characteristics may
also be related to soil compaction and re-
duction in woody residuals (Lewandowski
et al. 2015). In fact, discrepancy in the
quantity and quality of leaf and root litters
can be an essential factor affecting the mi-
crobial biomass of the soil (Yang et al.
2010). The significant direct correlations
observed between nitrogen concentration
in microbial biomass (MBN) and N and SOC
concentrations into the soil highlighted
this essential factor, though independent
form the size of gaps. In this study, micro-
bial biomass markedly increased from
closed-canopy to gaps (Tab. 4). Micro-envi-
ronmental conditions that benefit micro-
bial activity, including temperature of air
and soil, solar radiation and soil moisture,
have been found more favorable in gaps
than in adjacent closed-canopy stands, so
that gaps could have higher rates of de-
composition than the closed forest (Schlie-
mann & Bockheim 2014, Adachi et al.
2006). Although soil respiration is a valu-
able indicator to study decomposition sta-
tus, it is variable in nature and changes in
response to moisture, available resources,
and temperature (Bolat 2014). In this study,
soil microbial biomass in terms of MBC,
MBN, MBP and their ratios were higher in
gaps than in closed canopy highlighting the
higher nutrient concentrations in the gaps,
though their values were lower at the cen-
ter than at the edge. Moreover, the ratio of
MBC to soil organic matter (MBC/SOC) is
used to compare the quality of soil with
different organic material concentrations
(Chandra et al. 2016). The higher MBC/SOC
ratios observed in gaps and in particular at
the center highlighted the higher availabil-
ity of organic matter provided by the litter
of herb-tree layer plants in this position.
Likewise, MBN/total N and MBP/available P
indicate the availability of N and P. A de -
crease in MBN with increasing gap size
(Tab. 4) might be related to the influence
of soil temperature and moisture on de-
creasing microbial biomass and decomposi-
tion of organic matter (Muscolo et al.
2010). According to our results, correla-
tions observed between some of the
physico-chemical and biological investi-
gated variables highlighted the occurrence
of a gradient from the edge to the center
of the gap responsive to the openness of
the canopy, and such gradient is indepen-
dent from the size of gap.
Conclusions
This research examined the influence of
artificial gaps created under single- tree se-
lection in oriental beech stand on some soil
properties and its comparison with undis-
turbed adjacent stands. According to re-
sults, it can be concluded that there are rel-
ative similar conditions in terms of many
soil properties among gaps and adjacent
closed-canopy stands six years after log-
ging, though canopy openness triggered a
reduction in carbon and nitrogen availabil-
ity at the center of the gaps, independently
from their size. Therefore, if aimed at pre-
serving an uneven aged structure along
with soil quality in temperate broadleaved
deciduous forest as the oriental beech
stands in the Hyrcanian region, single-tree
selection practice for harvesting trees can
be recommended as sustainable forest
management type.
Acknowledgements
We would like to express our gratitude to
Lorestan University, Lorestan, Iran to pro-
vide us with financial supports.
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Supplementary Material
Tab. S1 - Pearson’s correlation between gap
size, soil physico-chemical and biological
variables.
Link: Amolikondori_3205@suppl001.pdf
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