Turkish Journal of Agriculture and Forestry
http://journals.tubitak.gov.tr/agriculture/
Research Article
Turk J Agric For
(2016) 40: 109-119
© TÜBİTAK
doi:10.3906/ tar-1406-61
Impacts of two spatially and temporally isolated anthropogenic fire events
on soils of oak-dominated Zagros forests of Iran
Javad MIRZAEI*
Department of Forest Science, Faculty of Agriculture, University of Ilam, Ilam, Iran
Received: 11.06.2014
Accepted/Published Online: 06.08.2015
Final Version: 01.01.2016
Abstract: Anthropogenic fires have varying effects on the oak-dominated forests of the Zagros Mountains in western Iran. The objective
of this project was to investigate the effects of fire on various components of soil. For this purpose three homogeneous and neighboring
sites were inspected. Site A was the unburned control. Sites B and C experienced fires about 2 and 8 years prior to the study, respectively.
In comparison to the control, site B showed a decline in organic matter content (1.69 ± 0.24 vs. 1.13 ± 0.17), N amount (0.40 ± 0.05 vs.
0.19 ± 0.03), litter depth (1.20 ± 0.214 cm vs. 0.087 ± 0.044 cm), germinated seedlings (272 ± 40 vs. 75 ± 25), earthworm biomass (3.4
g/kg vs. 0.26 g/kg), and plant diversity (1.95 ± 0.30 vs. 1.35 ± 0.34). An increase was observed for pH (7.41 ± 0.11 vs. 7.72 ± 0.15), Ca
(569.09 ± 34 vs. 855 ± 38.17), bulk density (1.17 ± 0.05 vs. 1.66 ± 0.18), the number of arbuscular mycorrhiza (AM) spores, and stump
sprouting (1645 ± 533 and 3425 ± 491). Site C showed a similar decrease in organic matter content, N amount, litter depth, germinated
seedlings, and earthworm biomass. However, plant diversity was greatly increased at site C, demonstrating that the conditions were
better for plant life 8 years after the fire event. Thus, the number of germinated seedlings was lower than that of the control, while stump
sprouting (4170 ± 452 per ha) was the greatest. The AM spore count was higher at site B in comparison to site C, indicating that fire had
caused a long-term loss in this essential component of the soil. An increase in pH was a characteristic feature of the burnt sites. Levels
of macronutrient K were greatly increased at site C. In fact, K content was much higher than the other two sites (A, B, and C: 51.81 ±
3.69, 59.75 ± 8.18, and 72.55 ± 20.66, respectively), indicating that increased K content is a long-term effect of fire. Bulk density (1.80
± 0.14) increased at site C, which may be due to the insufficient earthworm biomass. Thus, 8 years were not enough to improve the soil
conditions for soil fauna.
Key words: Earthworm, forest fire, mycorrhiza, soil, Zagros forest
1. Introduction
The Zagros forests are located in western Iran, occupying
more than 40% of the country’s forests. The region features
a Mediterranean climate pattern with oak-dominant
deciduous forests. Human-induced wildfires, fueled by the
semiarid climate, hot winds, and dry underbrush, are an
annual phenomenon.
Fire is an important abiotic factor that causes
substantial changes to the soil profile and characteristics
depending on the severity and the duration of burning
(Amaranthus, 1989). The most affected soil properties
are texture (Scharenbroch et al., 2012; Norouzi and
Ramezanpour, 2013), organic matter (OM) content
(Novara et al., 2013), nutrient availability (Scharenbroch
et al., 2012), porosity, pH (Certini, 2005; León et al.,
2013), and electrical conductivity (EC) (León et al., 2013;
Norouzi and Ramezanpour, 2013). Fire leads to burning
of OM and this in turn affects the nutrient status of soil
(Hart et al., 2005). Nutrient losses by fire can be due to
*Correspondence: [email protected]
oxidation of compounds to a gaseous state that are solid
at normal temperatures (Fischer et al., 2000). In contrast,
fires can also increase nutrients through the process of ash
production. Forest fires are associated with large amounts
of ash production typically ranging from 2 to 15 Mg ha–1
(Raison et al., 1985). Fernandez et al. (1997) found that
although the amount of OM decreased after fire, the net
level of pH increased. All these physical changes further
affect the life intimately associated with soil.
Forest fires exert influences not only on the physical
and chemical properties of soil, but also on biological
components, such as microbes, plant diversity (Safford
and Harrison, 2004; Scharenbroch et al., 2012), natural
regeneration (Sewerniak et al., 2011), mycorrhiza (Dhillion
et al., 1988; Jonsson et al., 1992; Rashid et al., 1997; MartinPinto et al., 2005), and earthworm biomass (Callaham
et al., 2003; Scharenbroch et al., 2012). Soil microbes
have been a focus of many studies, especially in terms of
abundance, species composition, and biomass, and have
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MIRZAEI / Turk J Agric For
been investigated in association with fire in a number of
forest regimes (Ahlgren and Ahlgren, 1965; Widden and
Parkinson, 1975; Tiwari and Rai, 1977; Dunn et al., 1979;
Theodorou and Bowen, 1982; Deka and Mishra, 1983).
Other soil organisms, such as collembola and earthworms,
play important roles in modifying the soil by creating
habitats with widely varying aeration, moisture relations,
nutrient status, and penetrability (Mataix-Solera, 2009).
These factors directly influence the growth and health of
plants (Mataix-Solera, 2009). It is well known that loss
of biodiversity not only decreases genetic resources, but
also reduces the productivity of ecosystems and alters
their buffering capacity against disturbances such as fire
(Naeem et al., 1994).
Although the effects of fire on some aspects of forest
ecosystems have been studied in various parts of the
world, several gaps in our knowledge remain. Exploration
of fire regimes in many forest types, such as those found
in the Zagros Mountains, can improve our understanding.
However, little information exists on the effects of
anthropogenic wild fires on the soil and biological
components of oak-dominated (Quercus brantii) forests
of the Zagros Mountains, the ecological responses of this
unique system to the fire, trends in ecosystem development
after fire, or recovery over time after a fire event (short
versus medium duration). The objective of this paper is to
help fill these gaps. In this perspective, the present work
aims at determining the effects of two different fires that
took place in 2003 and 2009 in Zagros Mountain forests.
Moreover, the ecological responses of the forest ecosystem
to these events in 8 years after the first fire in 2003 and 2
years after the second fire in 2009 are investigated. These
responses include abiotic (soil texture, bulk density, pH,
EC, N, P, K, Ca, Mg, C, and OM) and biotic (natural
regeneration, earthworm biomass, and the number of
mycorrhizal spores) factors. The principal objective of
this study is to determine the extent to which the soil and
biological features of the forest ecosystem have changed 2
and 8 years after the fires.
2. Materials and methods
The present study was conducted in 2011 in Zagros forests
of Southwest Iran.
2.1. Study area
This study was carried out on the north-facing hill slope of
Manesht–Ghalarang region of Zagros forests with latitude
33°36′–33°45′ and longitude 46°18′–46°37′ (Figure 1).
The region is located at 1100–1200 m above sea level on
the northern aspect of Manesht–Ghalarang, with a slope
of 20%–40%. The dominant species in Zagros forests is
Quercus brantii, which occupies nearly 90% of the upper
story. Other species, such as Pistacia atlantica, Crataegus
pontica, and Acer monspessulanum, are companions in the
110
oak stands. The region is characterized by scanty rainfall
with a mean annual value of 520 mm. The mean maximum
temperature is 28 °C while mean minimum is 0.58 °C.
2.1.1. Description of sites
The study was carried out on three neighboring sites
(about 0.5 km distance) with homogeneous site conditions
(site A, B, and C). Site A was designated as the control. It
was the unburned area following natural succession. Site B
experienced intensive human-caused fires in 2009, while
Site C suffered human-caused fires of a similar intensity
in 2003, 8 years prior to the measurements. The area of
the three sites was approximately 400 ha each. Both the
2003 and 2009 fires could be classified as high severity
fires, based on dead trees, ash production, plant mortality,
and regeneration processes such as sprout clumps and
vegetation reestablishment.
2.2. Sampling plots
In each site, 10 sample plots (400 m2) with 400-m intervals
were selected randomly for investigation. The frequencies
of tree and shrub species were determined in each sample
plot. Within each sample plot, microplots (100 m2) were
designed and the number of seedlings/ha (sprout–seed
origin separately) were recorded. In order to determine
landscape diversity of herbaceous plant species at the
sites, we used 2-m2 subplots. Indices of diversity (applied
Shannon–Wiener and Simpson indexes), richness
(Menhinick index), and evenness (Pielou index) were
calculated (formulas 1–4).
Formula 1
s
H ʹ′ = −∑ PiLn(Pi)
i=1
Formula 2
s
Si =1− ∑(Pi)
2
i=1
Formula 3
J' =
H'
'
H Max
Formula 4
R=
S
N
where pi is the proportion of all observations in the ith
species category, S is the total number of species, and N is
the total number of individuals.H´ = Shannon’s diversity
index, Si = Simpson’s diversity index, J´ = Pielou’s evenness
index, H´Max = ln s, and R = Menhinick richness index.
635000
636000
637000
638000
639000
3730000
634000
<Double-click here to enter title>
N
3729000
W
E
3728000
3727000
0
0.5
634000
1
2
635000
636000
KM
3725000
3726000
3728000
3725000
3726000
3727000
S
3729000
3730000
MIRZAEI / Turk J Agric For
637000
638000
639000
Iran
Ilam
Province
Legend
A
B
C
Study Area
Sample Points
Figure 1. Location of the study area.
2.3. Soil sampling and analyses
Soil samples were collected from 10 sample plots at all three
sites during September 2011. Five composite soil samples
were collected from the top 10 cm of soil in each treatment.
Soil samples were air-dried and sieved (2 mm) and used
to measure physical and chemical properties. Soil EC and
pH were measured in deionized water (1:5 and 1:2.5 soil/
water ratio, respectively) (McLean, 1982). Soil texture
was measured hydrometrically while the bulk densities
were measured gravimetrically. Total N was determined
by the Kjeldahl method (Bremner, 1996). Available P was
determined according to the Watanabe and Olsen method
(Watanabe and Olsen, 1965). Exchangeable Ca, K, and Mg
were analyzed using inductively coupled plasma atomic
emission spectroscopy (Kalra and Maynard, 1991). Total
OM was determined using a wet oxidation technique
(Walkley and Black, 1934).
2.4. Mycorrhiza and earthworms
For mycorrhizal study, 100 g of dried soil from each
sample plot within the respective site was used. The soil
sample was thoroughly moistened for 1 h before sieving
and decanting for the arbuscular mycorrhizal fungal spore
extraction and finally counting the number of mycorrhizal
spores (Rashid et al., 1997).
Earthworms were collected by digging (25 × 25 × 40
cm3) in each sample plot at the three sites and hand sorting
the worms following Anderson and Ingram (1993).
Earthworm biomass was determined by weighing them
after oven-drying at 60 °C for 48 h (Joshi et al., 2010). 2.5. Data analysis
The Kolmogorov–Smirnov test was used for normal
distribution and Levene’s test was used to determine
homogeneity of variances. Regeneration and mycorrhizal
data were subjected to logarithmic transformation to
follow the normal distribution. The data was subjected
to ANOVA using SPSS 16. Duncan’s multiple range test
was used to assess the differences in soil properties and
biological parameters between the sites A, B, and C. For
principal component analysis (PCA), all the data were
standardized to zero mean and unit variance, and the
analysis was done on the correlation matrix. The first five
components were retained and rotated using Varimax
rotation (Kaiser, 1958); the latter redistributed the variance
in each variable so that each one contributed strongly to
one of the components and little to the others (Sharma,
1996). Finally, the Pearson’s coefficients were calculated to
assess the correlations between parameters.
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MIRZAEI / Turk J Agric For
3. Results
Our results revealed the various impacts of anthropogenic
fire events on soil components including soil properties
(soil texture, bulk density, pH, EC, N, P, K, Ca, Mg, C,
and OM) and biological parameters (natural regeneration,
earthworm biomass, and the number of mycorrhizal
spores).
3.1. Soil properties
Fire significantly changed the pH and bulk density of the
forest soil (P < 0.005). Fire also increased the pH (P ˂
0.005) and Ca (P ˂ 0.005) of forest soil. Statistically, it did
not affect Mg, clay, sand, silt, or EC (P > 0.05). Forest fire
had various effects on nutrients such as N (P ˂ 0.005), P (P
= 0.483), K (P = 0.517), and OM (P = 0.034). It decreased
the total nitrogen and OM of soil, but had no effect on P
or K (Table 1).
3.2. Natural regeneration
Data analysis revealed differences in stump sprouting (P
˂ 0.005) and seedling germination (P ˂ 0.005) at the three
sites. The results showed that the number of germinated
seedlings was the least at site B (the land that experienced
the recent fire), while at site C it was slightly less than
that of the control (A: 272 ± 40, B: 75 ± 25, C: 200 ± 36).
However, fire apparently enhanced stump sprouting at the
two burned landscapes. Stump sprouting exhibited peak
values 8 years after the fire at site C (A: 1645 ± 533, B: 3425
± 491, C: 4170 ± 452).
3.3. Landscape diversity
Landscape diversity for herbaceous species was
investigated at the three sites using different diversity
indices. The Shannon–Wiener diversity index did not
differ significantly (P > 0.05), but the lowest value was
obtained in site B and the highest in site C (Table 2).
Significant differences were observed in the other indices
of diversity, such as Simpson’s index (P ˂ 0.005), richness
(P ­˂ 0.005), and evenness (P = 0.012). Simpson’s index in
site C was significantly higher than the other two sites.
One more point is that the greatest amount of evenness
was observed in site A (Table 2).
3.4. Mycorrhiza and earthworm biomass
The number of spores differed significantly in control and
burned sites (P = 0.018). It increased 2 years after the fire
at site B, but dramatically decreased 8 years after the fire
at site C (Figure 2). The biomass of earthworms was the
greatest at site A (3.4 g/kg), whereas at site B it decreased
to 0.26 g/kg. Furthermore, a slight increase happened (1 g/
kg) at site C 8 years after the fire (Figure 3).
3.5. PCA
PCA was applied to the whole data set. The concentrations
of each parameter (both edaphic and biological) at sites A,
B, and C were treated as separate variables. The first two
principal components were selected; they accounted for
approximately 50% of the total variation. The components
were rotated using Varimax rotation; Table 3 gives the
Table 1. The significant differences in soil physicochemical properties between control and burnt sites. The data are
means ± standard error.
112
Parameters
Site A
(Control)
Site B
(2 years after fire)
Site C
(8 years after fire)
pH
7.41 ± 0.11 b
7.72 ± 0.15 a
7.76 ± 0.14 a
EC (mmho/cm)
463.20 ± 4 a
519.30 ± 9.20 a
449.20 ± 29.3 a
Ca (mg/kg)
569.09 ± 34 b
855 ± 38.17 a
819.50 ± 93.9 a
Clay (%)
27.80 ± 1.75 a
27.50 ± 2.82 a
29.80 ± 1.20 a
Sand (%)
34.72 ± 2.26 a
40.00 ± 1.64 a
38.60 ± 3.09 a
Silt (%)
37.40 ± 1.90 a
32.50 ± 1.54 a
31.60 ± 2.96 a
Bulk density (g/cm3)
1.17 ± 0.05 b
1.66 ± 0.18 a
1.80 ± 0.14 a
N (%)
0.40 ± 0.05 a
0.19 ± 0.03 b
0.21 ± 0.03 b
P (mg/kg)
20.36 ± 1.80 a
21.37 ± 2.61 a
24.00 ± 2.39 a
K (mg/kg)
51.81 ± 3.69 a
59.75 ± 8.18 a
72.55 ± 20.6 a
Mg (mg/kg)
23.18 ± 1.81 a
26.25 ± 3.75 a
23.50 ± 1.006 a
Carbon (%)
0.72 ± 0.15 ab
1.10 ± 0.06 a
0.63 ± 0.14 b
OM (%)
1.69 ± 0.24 a
1.13 ± 0.17 ab
0.88 ± 0.19 b
MIRZAEI / Turk J Agric For
Table 2. Duncan’s multiple range test analysis of diversity, richness, and evenness indexes of herbaceous plants from control and burnt
sites. The data are means ± standard error.
Diversity indexes
Treatment
Richness (Menhinick) Evenness (Pielou)
Shannon–Wiener
Simpson
Site B (2 years after fire)
1.35 ± 0.34 a
0.23 ± 0.09 b
4.50 ± 1.16 b
0.36 ± 0.13 b
Site C (8 years after fire)
2.15 ± 0.17 a
0.72 ± 08 a
11.43 ± 1.44 a
0.58 ± 0.10 ab
Site A (Control)
1.95 ± 0.30 a
0.41 ± 0.06 b
10.42 ± 1.23 a
0.80 ± 0.05 a
B iomass of earthw orm (g/kg)
Number of AM spores/g
3
2.5
2
1.5
a
ab
1
b
0.5
0
Control
2 years after fire
8 years after fire
5
4
a
3
2
b
1
0
a
Control
2 years after fire
Treatment
8 years after fire
Treatment
Figure 2. Numbers of spores of AM fungal species recovered per
1 g soil from control and burnt sites by wet sieving. The data are
means ± standard error.
Figure 3. Biomass of earthworm species per 1 kg soil from site A
(control), site B (2 years after fire), and site C (8 years after fire).
The data are means ± standard error.
Table 3. Correlations between element concentrations and rotated principal components.
Factors
Axis 1
Axis 2
Factors
Axis 1
Axis 2
Litter
–0.31
0.09
P
0.08
–0.29
EC
0.11
0.25
Mg
0.11
–0.21
pH
0.14
–0.28
Spore
0.05
0.44
Clay
0.02
–0.02
Shannon–Wiener
–0.23
–0.18
Silt
–0.19
0.13
Evenness (Pielou)
–0.28
0.09
Sand
0.17
–0.11
Richness (Menhinick)
–0.34
–0.14
N
–0.25
–0.05
Diversity (Simpson)
–0.35
–0.05
C
0.11
0.38
Earthworm biomass
–0.24
0.11
OM
–0.08
0.36
Bulk density
0.26
–0.07
K
–0.06
–0.11
Stump sprout
0.01
–0.32
Ca
0.32
–0.01
Germinated seedling
–0.30
–0.11
113
MIRZAEI / Turk J Agric For
rotated loadings. The loadings on the first component
were large for germinated seedling, litter, N, Ca, bulk
density, earthworm biomass, and diversity indexes
concentrations in both horizons. The largest loadings
on the second component were for stumps sprouted,
EC, pH, C, OM, P, Mg, and the number of mycorrhiza
spores in both horizons. The interrelations among the
different regions and parameters are more evident in the
projections of components 1 and 2 (Figures 4a and 4b),
respectively. Figure 4a shows a cluster of sample plots of
three sites. The control plots were on the negative side of
the first axis; the cluster consisted of parameters such as
germinated seedlings, litter, N, earthworm biomass, and
diversity indexes (Figure 4a). Site B was on the positive
side of the first axis with Ca and bulk density as parameters
(Figure 4a). Site C was on the negative side of the second
axis with the cluster depicting a positive correlation with
stump sprouting, P, Mg, and pH (Figures 4a and 4b). The
Pearson correlations of all data sets are shown in Table 4.
The results of Pearson correlation are in accordance with
the results of PCA analysis (Table 4).
4. Discussion
The structure of the world’s landscape is changing rapidly
due to human-related activities (Nagendra, 2002). All fires,
whether natural or human-caused, are thought to have a
significant effect on the distribution and maintenance
of an ecosystem’s integrity (Boerner, 1982). Therefore,
quantification of the “impacts of fire and the subsequent
ecological responses” has become increasingly crucial in
landscape management (Boerner et al., 2009). The present
study addresses this issue in the fire-scorched landscape
of the Zagros Mountain forests. Fire alters the abiotic and
biotic characteristics of soil. In many cases, these impacts
Figure 4. PCA of the whole data set. Location of study sites (a); soil and biological factors (b) in the plane defined by the first two
axes in PCA.
114
–0.29
–0.11
–0.09
0.47**
0.2
–0.47** 0.12
0.29
–0.23
–0.17
–0.42*
0.01
0.49**
0.29
–0.29
0.50**
0.24
–0.23
–0.08
–0.27
–0.09
–0.41*
–0.41*
Li
GS
EC
pH
Cl
Si
Sa
N
C
OM
K
Ca
P
Li
BD
Mg
Sp
Sh
Ev
Ri
Si
EW
0.28
–0.01
–0.32
0.34
–0.17
0.24
–0.06
0.06
–0.12
1
GS
0.29
0.26
0.58**
0.23
0.37*
–0.15
–0.16
–0.26
–0.35
0.01
0.08
–0.11
–0.31
–0.13
–0.26
–0.38*
–0.12
0.25
0.33
–0.08
0.32
–0.17
0.08
0.15
–0.39*
–0.31
0.42*
–0.11
–0.15
1
EC
–0.22
–0.26
–0.17
–0.14
–0.13
–0.40*
0.09
0.19
–0.22
0.21
0.35
0.22
–0.34
–0.31
–0.12
0.21
–0.3
0.09
1
pH
0.07
0.02
–0.02
0.14
–0.27
–0.11
0.00
0.08
–0.03
0.05
0.16
–0.04
0.09
0.08
–0.01
–0.44*
–0.31
1
Cl
0.31
0.48*
0.26
0.21
0.17
0.01
–0.23
–0.16
–0.04
0.01
–0.08
0.29
0.12
–0.00
0.06
–0.71
1
Si
–0.35
–0.47*
–0.23
–0.30
0.04
0.06
0.21
0.09
0.06
–0.05
–0.03
–0.24
–0.18
–0.05
–0.05
1
Sa
0.04
0.55*
0.35
0.45*
0.16
–0.14
0.04
–0.39*
–0.42*
–0.02
1
OM
–0.26
–0.28
–0.32
–0./8
–0.23
0.67**
–0.06
0.34
0.01
–0.15
0.11
–0.32
0.39*
–0.11
–0.22
–0.57** 0.39*
–0.37*
0.07
0.08
0.46*
1
C
–0.51** 0.14
–0.09
–0.11
–0.32
–0.14
0.03
–0.09
1
N
–0.04
0.01
0.14
–0.14
0.21
–0.29
–0.06
0.00
–0.34
0.17
–0.19
1
K
–0.27
–0.27
–0.28
–0.25
–0.14
–0.05
0.02
0.47**
–0.00
0.14
1
Ca
–0.14
–0.13
–0.08
–0.33
–0.04
–0.41*
0.41*
0.06
–0.31
1
P
–0.37*
–0.17
–0.07
0.17
1
BD
–0.01
–0.29
–0.40*
–0.43*
–0.52** –0.27
0.01
–0.55*
0.83**
–0.18
–0.18
1
Li
–0.29
–0.05
–0.08
–0.24
0.00
–0.19
1
Mg
0.00
–0.19
–0.22
0.09
–0.30
1
Sp
0.03
0.51**
0.75**
0.20
1
Sh
0.46*
0.46*
0.56**
1
Ev
0.27
0.66**
1
Ri
0.34
1
Si
SS = stump sprout, Li = litter depth, GS = germinated seedling, Cl = clay, Si = silt, Sa = sand, BD = bulk density, OM = organic matter, Sp = number of spore, Sh = Shannon–Wiener diversity index, Ev = evenness index, Ri = richness
0.33
0.36
0.40*
–0.38*
0.25
0.13
–0.13
–0.45*
–0.05
–0.13
–0.58** –0.39*
0.03
0.42*
0.03
0.44*
–0.07
–0.05
–0.22
–0.2
0.66**
1
1
SS
Li
SS
Table 4. Pearson correlation between all data used in PCA. Significance levels are reported (*: P < 0.05; **: P < 0.01).
MIRZAEI / Turk J Agric For
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MIRZAEI / Turk J Agric For
are either negligible or short-lived. However, long-term
impacts do exist and significantly influence an ecosystem’s
functioning (Nagendra, 2002).
4.1. Soil properties
Fire has profound effects on the pH, bulk density,
macronutrients, OM, and litter layer of soil.
During the combustion process, several previously
bound nutrients are released in their elemental or radical
form. In the ash form, these substances are subsequently
leached into the soil, resulting in an increase in pH (Molina
et al., 2007; Boerneret al., 2009; Schafer and Mack, 2010;
Tufekcioglu et al., 2010; Aref et al., 2011; Scharenbroch et
al., 2012). Our results also revealed an increase in soil pH
after the fires at sites B and C. Site C (8 years after fire) had
slightly elevated pH values (7.76), showing that change in
pH is a long-term ecological effect. A higher pH is typically
associated with enhanced nutrient cycling, especially of
elements that are critical for plant growth, such as N and P
(Boerner et al., 2009).
Our results demonstrated an increase in bulk density
at both sites B and C. Previous studies indicate that bulk
density nearly always increases as a consequence of fire
(Seymour and Tecle, 2004; DeBano et al., 2005). Bulk
density is the mass of dry soil per unit bulk volume and
is related to porosity, which is the volume of pores in a
soil sample (nonsolid volume) divided by the bulk volume
of the sample. Its increase after fire is associated with the
collapse of aggregates and clogging of voids by the ash; as
a consequence, soil porosity and permeability decrease
(Certini, 2005). These changes result in various indirect
impacts, including increased hydrophobicity (water
repellency), leading to decreased infiltration and increased
runoff and often preceding increased erosion (DeBano,
2000).
Macronutrients are essential for plant growth and
nutrition and substantially affect the productivity and
vegetation dynamics of an ecosystem (DeBano, 2000;
Kumar et al., 2013). In the present study, the forest fire
apparently decreased N at both sites B and C, while it did
not affect the soil concentrations of P, K, or Mg. Many
authors have reported a considerable loss of the total
amount of N after a fire (Knight, 1996; Sahajo, 1999;
Arocena and Opio, 2003; Neff et al., 2005; Kumar et al.,
2013). Although various nutrients can become more
available during and after a fire, others such as N may
be volatilized and thus lost during a fire (Fischer et al.,
2000). Volatilization, which is temperature-dependent,
most commonly affects N and, to a lesser extent, P and
C. Even though volatilization removes nutrients from a
system, it can also convert them to a more available form.
For example, N is often converted to the more available
form ammonium during the volatilization process. Thus,
N seems to decrease in a site, but the amount of available N
116
to plants may increase or decrease, depending on the site.
In our case, the increase in seed germination,
resprouting, and subsequent plant diversity at site C
indicates the efficient delivery of available N to on-site
plant species. However, if anthropogenic fires are quite
frequent, especially on N-deficient sites such as semiarid
rangelands, N may actually be lost.
In our study, fire had no effect on P, K, or Mg
concentrations in soil. DeBano (1990) reported that,
compared to N, Mg was less sensitive to fires. Similar to
our research, Neff et al. (2005) showed that P and K did
not change after forest fire. On the other hand, our study
showed an increase in Ca after fire. Neff et al. (2005)
showed that burned soils have higher Ca than unburned
soils. The increase in Ca can probably be ascribed to ash
(Arocena and Opio, 2003).
Our results showed a significant decrease in the OM
component of the soil as a direct consequence of fire.
Rather than improving, the loss was further aggravated 8
years after fire. These results are in accordance with the
findings reported by Sahajo (1999).
OM is critical for ecosystem sustainability in that it
provides a protective soil cover that mitigates erosion.
It also aids in regulating soil temperature and provides
habitat and substrates for soil biota. Furthermore, it can be
a major source of readily mineralizable nutrients (Neary et
al., 1999) and therefore supplies the plants with most of the
available P and S, and virtually all of the available N. Soil
OM’s role in N storage is especially important in forests
because their continued high productivity depends, to a
large extent, on large supplies of available N. In contrast,
Novara et al. (2013) showed that there was no significant
difference between burned and unburned sites as far as
OM was concerned.
Litter layer significantly declined in depth after fire
(Table 5), especially at site B (2 years after fire). This
decline had probably two effects on plant life with respect
to (1) seedling germination and (2) stump sprouting. The
effects are discussed in the next section.
4.2. Biological parameters
Our results showed that fire decreased the number of
germinated seedlings (more effective in site B than in
site C, Table 5). Factor interaction was very important in
this regard. Bulk density and litter depth were two factors
associated with seedling germination. Fire increased bulk
density and decreased litter depth (Table 5). Thus, the fire
created unsuitable conditions for seedling establishment.
Moreover, fire directly injured the acorns and natural
seedlings in this region. In contrast, stump sprouting
increased after fire. Abiotic stresses are known to stimulate
hidden sprouts. Therefore, the increase in sprouting is
relatively predictable. Most of the stump sprouts belonged
to Quercus brantii. This species is known to have a high
MIRZAEI / Turk J Agric For
Table 5. Duncan’s multiple range test: litter depth and natural seedlings at three study sites. The data are means ± standard error.
Treatment
Litter depth (cm)
Site B (2 years after fire)
Natural seedlings (ha)
germinated seedling
stump sprouting
0.087 ± 0.044 b
75 ± 25 b
3425 ± 491 a
Site C (8 years after fire)
0.43 ± 0.08 b
200 ± 36 a
4170 ± 452 a
Site A (control)
1.20 ± 0.214 a
272 ± 40 a
1645 ± 533 b
stump sprouting ability compared to other tree species in
the Zagros region (Mirzaei et al., 2007). However, there
are other studies (Hutchinson et al. 2005) showing that
Quercus seedlings are nonresponsive to forest fires.
Our study revealed that plant diversity of the floor
species initially declined (up to 2 years after fire). However,
a rapid increase was observed 8 years after fire. When a
fire burns out canopy cover, it helps light reach the forest
floor. Meanwhile, with passing time, more herbaceous
plants find opportunities for growth and establishment.
Therefore, this increases plant diversification (Coroi et al.,
2005). Evenness index of herbaceous species decreased
significantly after forest fire. Thus, fire caused some species
to dominate in this ecosystem.
Mycorrhizal spores showed an increase in site B (2 years
after fire). However, the number at site C was relatively
low. This immediate increase may be explained by the fact
that the mycorrhiza ascospores are thermotolerant and
their germination is stimulated by fire stress, as shown
in previous studies (Warcup and Baker, 1963; Dhillion
et al., 1988). However, the decline at site C (8 years after
fire) was perhaps a long-term effect of fire. Jonsson et al.
(1992) demonstrated that fire caused a significant loss of
fungal biomass in the organic horizons of the soil. Several
authors have observed a dramatic negative effect of forest
fires on fungi (Ahlgren and Ahlgren, 1965; Widden and
Parkinson, 1975; Tiwari and Rai, 1977).
Forest fire also decreased earthworm biomass
(Figure 3). Fire usually has long-term impacts on the
soil environment, consequently affecting the welfare
of the associated biological organisms. These impacts
include competition for habitat and food supply that
affect the reestablishment and succession of plants and
animals (Verma and Jayakumar, 2012). Thus, a number of
studies show a decline of earthworm biomass in scorched
landscapes (Ahlgren and Ahlgren, 1965; Dunn et al., 1979;
Theodorou and Bowen, 1982; Deka and Mishra, 1983).
4.3. Summary and conclusion
The main conclusions of this study are summarized as
follows:
1. In the Zagros forests, fire decreased litter depth, while
it increased the bulk density and the level of pH in the
soil. This might result in a decrease in infiltration and
increase in soil erosion.
2.Fire caused a reduction in the amount of some
important macronutrients (i.e. total N) of forest soil.
On the other hand, low levels of precipitation and
high soil compactness are the most important factors
that hinder the capacity of soil to recover from the
negative effects of fire in a short period of time in this
region. In other words, 8 years are hardly enough for
improvement of N content in Zagros forests, whereas
in other regions of the world even 1 year may be
enough (Seki et al., 2010).
3. Earthworms were severely affected by fire, as their
recovery even 8 years after fire was not satisfactory.
4. Fire decreased germinated seedlings due to its effects
on litter depth, pH, and bulk density because these soil
properties are important for seedling germination. In
contrast, stump sprouts increased, indicating they may
have been stimulated by fire.
5. Mycorrhizal spores were also negatively affected by fire.
They increased 2 years after fire, perhaps because of
high temperature stress that led to spore germination.
However, the number of spores declined in the long
run. The main reason is probably an interruption in the
symbiotic relationships.
6. Plant diversity of floor species increased in the 8 years
since the first fire event. Fire decreased overstory
canopy cover and increased the penetration of light
to the forest floor and so the herbaceous plant species
diversity increased.
Acknowledgments
We are grateful to the University of Ilam for financial
support of the research and extend our appreciation to the
natural resource office for the technical support and data
collection. Thanks are due to Dr Farrah Zaidi (University
of Peshawar, Pakistan), Dr M Norouzi, Dr HR Naji, Dr M
Mirab-balou, Dr M Pourreza, Dr M Moradi, Dr O Karami,
and M Mirzaei for their helpful comments and suggestions
regarding the manuscript.
117
MIRZAEI / Turk J Agric For
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