Transportation Research Part D 12 (2007) 453–459

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Chemical characteristics of the surface soil, herbaceouscover and organic layer of a compacted skid road in a fir

(Abies bornmulleriana Mattf.) forest

Ender Makineci a,*, Murat Demir b, Aydin Comez c, Ersel Yilmaz d

a Istanbul University, Faculty of Forestry, Soil Science and Ecology Department, 34473 Bahcekoy, Sariyer, Istanbul, Turkeyb Istanbul University, Faculty of Forestry, Forest Construction and Transportation Department, 34473 Bahcekoy, Sariyer, Istanbul, Turkey

c Research Institute for Forest Soil and Ecology, 26160 Eskisehir, Turkeyd Istanbul University, Faculty of Forestry, Forest Yield and Biometry Department, 34473 Bahcekoy, Sariyer, Istanbul, Turkey

Abstract

This study looks at the impacts of timber skidding in a pure fir plantation forest. It compares properties of herbaceouscover, organic layer and surface soil on the skid road and on adjacent undisturbed area. N, P, K, Ca, Mg, Na, Fe, Zn, Mnand Cu are quantified and the mass of herbaceous cover and organic layer, and sand, silt, clay rates, bulk density, com-paction and pH of soils were assessed. Both the herbaceous cover and organic layer mass on the skid road were signifi-cantly lower than the undisturbed area. The soil of the skid road also had higher bulk density and compaction, andlower organic carbon rates producing much denser and compacted soils. Only P concentration in herbaceous cover sam-ples from skid road was significantly higher, while Ca and Mg contents were considerably lower than undisturbed area.There were no significantly differences in N, K, Na, Fe, Zn, Cu and Mn concentrations of herbaceous cover. Comparedto the undisturbed area, the organic layer of the skid road had particularly low K, Na, Fe, Zn, Cu and Mn contents. At 0–5 cm soil depth, P and Fe contents were significantly lower than for undisturbed area but there were no major differences atdepth of 5–10 cm.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Timber skidding; Soil disturbance; Logging; Herbaceous understory; Soil conservation

1. Introduction

Skidding, or yarding, on terrain requires the construction of relatively dense network of forest roads includ-ing skid roads, haul roads and landings (Ketcheson et al., 1999). The logs are skidded on the ground or loadedon a cart, sledge or hauled by a crane is mounted on a farm tractor, or a portable cable-way. Man-power andanimals are also still being used in Turkey for that purpose. Ground based skidding, timber harvesting andlogging operations in forest ecosystems cause reductions and redistributions of organic matter, changes in

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doi:10.1016/j.trd.2007.06.001

* Corresponding author.E-mail address: emak@istanbul.edu.tr (E. Makineci).

454 E. Makineci et al. / Transportation Research Part D 12 (2007) 453–459

plant cover, the organic layer and soil properties, and modifications to the microclimate (Buckley et al., 2003;Godefroid and Koedam, 2004). It can also cause significant and wide-spread soil disturbance, includingremoval, mixing and compaction of various soil layers. Soil compacting typically alters soil structure andhydrology by increasing bulk density, breaking down aggregates, decreasing porosity, reducing aerationand infiltration capacity and increasing soil strength, water runoff, erosion, water logging and, possibly, pro-ducing inappropriate soil nutritional status (Kozlowski, 1999). This nutrient availability impacts plants andanimals that live in the soil (Ponder and Mahasin, 2002). The degree of compacting and loss of organic matterfrom the organic layer of soil can also have direct influences on the weathering rates of minerals, nutrient min-eralization and, ultimately, on plant growth. The work linking compaction and nutrient availability, and theeffects of compaction exists and is often confounding (Arocena, 2000). Sustained forest productivity stronglydepends on the maintenance of soil nutrients and, therefore, the effects of forest management practices on soilnutrient status are important (Knoepp and Swank, 1997).

This study looks at the impacts of ground based timber skidding activities since 1956 on the herbaceouscover, organic layer and soil properties at two depths (0–5 cm and 5–10 cm) in the skid roads of a fir (Abies

bornmulleriana Mattf.) plantation.

2. Method of analysis

Belgrad Forest, in Istanbul province, Turkey, is between 41� 09 0 and 41� 12 0 N latitudes and 28� 54 0 and29� 00 0 E longitudes and covers 5441.71 ha. The study area is in zone 64 of the forest. According to the datagiven by the Bahcekoy Meteorology Station – the nearest meteorology station to the area – the average annualprecipitation is 1074.4 mm, with a mean temperature of 12.8 �C, a mean high temperature of 17.8 �C and anaverage low of 9.0 �C. The climate is thus similar to sea climate with medium water deficits in summers. Thevegetation period is about 230 days.

The study area is a pure fir (Abies bornmulleriana Mattf.) plantation forest at an altitude of 190 m, has aslope of 17% and is exposed to an east aspect. The canopy cover is about 70% with an average trees diameter(dbh) of 24.38 cm, height of 22.76 m and density of 1889 trees per ha�1. The skid road passes through the areain a south-north direction, and it has been used since 1956. Approximately 103 m�3 of timber has been skid-ded annually during harvest activities (Anonymous, 2005). Skidding works in the area have involved humanand animal power, and machinery. The dominant herbaceous cover plant species are Hedera helix L., Rubus

ssp., Galium odoratum (L.) Scop., Ruscus aculeatus L., Ruscus hypoglossum L., Viola ssp. L., Salvia forskahlei

L. and Trachystemon orientale (L.) G. Don. The impacts of skidding on the organic layer, herbaceous coverand surface soil layer to a depth of 10 cm were examined and compared with an undisturbed area.

The skid road and the undisturbed area, where there was no skidding impact and which was at least 30 mfrom the skid road were sampled at seven different points at 10 m intervals. Seven samples were taken from eachherbaceous cover, organic layer, and 0–5 cm and 5–10 cm soil layers. Herbaceous cover samples were taken bycutting aboveground parts of plant masses in a square meter area and the samples of the organic layer weretaken from a 0.25 m�2 area by collecting all the layer in that area. Soil compaction at the same points whereherbaceous cover and organic layer samples were taken, was measured at 0–5 cm and 5–10 cm depths usinga pocket penetrometer. Soil samples from each site were collected at 0–5 and 5–10 cm depths with the aid of100 cm�3 steel soil cores. Some 300 cm�3 soil samples were taken for each soil layer at sampling points in Sep-tember 2004. Herbaceous cover and organic layer samples were dried at 65 �C, and soil samples at 105 �C over24 h to determine moisture content. Weight values given in subsequent tables are oven dried values.

Soil samples were ground and passed through a 2 mm sieve before analysis. Particle size distribution wasdetermined by the hydrometer method of Bouyoucos (1962), actual acidity by a pH meter with glass electrodesin 1:2.5 distilled water (Jackson, 1962), organic carbon by wet combustion method of Wackley and Black(1934), N by semi-micro kjeldal method (Jackson, 1962) using a Kjeltec Auto 1030 Analyzer, P by Brayand Kurtz’s (1945) No.1 method using a Spectronic 20D spectrophotometer, K+, Na+, Ca2+, Mg2+, Fe2+,Mn2+ by the ammonium acetate method (Jackson, 1962) using a Jenway PFP 7 flame photometer for K+

and Na+, Perkin–Elmer 3110 atomic absorption spectrometers for Ca2+, Mg2+, Fe2+, Mn2+. Cu2+ andZn2+ were determined by double-acid (HCl + H2SO4) method using Perkin–Elmer 3110 atomic absorptionspectrometer equipment (Perkins, 1970).

E. Makineci et al. / Transportation Research Part D 12 (2007) 453–459 455

Oven-dried organic layer and herbaceous cover samples (for 24 h at 65 �C until constant weight) wereground and passed through a 1 mm mesh screen before chemical analysis. These samples were analysed forN by the semi-micro kjeldal method using Kjeltec Auto 1030 Analyzer equipment. For determination of P,K, Na, Ca, Mg, Fe, Mn, Cu, Zn, the samples were disolved in a solution of HNO3–HCl4. K and Na concen-trations were determined using a flame photometer, P by vanado-molybdophosphoric yellow color methodusing Spectronic 20D spectrophotometer equipment, Ca, Mg, Mn, Fe, Cu, Zn by Perkin–Elmer 3110 atomicabsorption spectrometer equipment (Kacar, 1972).

The values found for the undisturbed area and the skid road were compared at a 5% significance level usingindependent sample t-test statistical analysis.

3. Results

3.1. Properties of herbaceous cover

Significantly higher herbaceous cover mass in unit area was detected in the undisturbed area (Table 1),while the herbaceous cover mass in the skid road was less because of the deleterious effects of skidding, chan-ged soil conditions, and especially compacting, and organic layer properties. Similarly, Mariani et al. (2006)reported that the organic layer removal reduced levels of herbs and shrubs. Soil compaction can also severelyreduce plant growth by restricting root growth due to oxygen stress, and lower the percentage of water and airspace in the soil (Barzegar et al., 2006). Kozlowski (1999), also mentions reduced photosynthesis when soilsbecome increasingly compacted, because of smaller leaf areas.

The t-test showed that P, Ca and Mg concentrations of herbaceous cover significantly differ between theskid road and the undisturbed area: the former had much higher P and lower Ca and Mg concentrations thanin the undisturbed area. There were no significant differences in N, K, Na, Fe, Zn, Cu and Mn concentrationsof herbaceous cover between the areas. In contrast, soil compaction typically decreases absorption of majornutrients by roots, especially N, P and K, while mineral uptake is reduced by a combination of nutrient lossesfrom the soil, decreased access of roots to nutrients and a lowered capacity of roots for mineral uptake(Nadian et al., 2005). Changed physical and chemical soil properties caused by timber skidding, less organiclayer and herbaceous cover mass may affect the chemical properties of herbaceous plant cover of the skid road.On the other hand, more adaptable plants with less herbaceous plant mass may exist on the skid road.

3.2. Properties of organic layer

Average organic layer mass in undisturbed area was much higher than the skid road (Table 2). Substantialless organic layer in skid road showed that skidding of logs decreased the amount of organic layer. Timberharvesting and skidding can dramatically alter organic layer properties, and temporarily destroy the organiclayer by mixing with the mineral soil and/or displacement surface organic material in forest ecosystems (Fisher

Table 1Herbaceous cover properties

Characteristics Unit Skid road Undisturbed Asymp. Sig. 2-tailed

Herbaceous cover mass (kg ha�1) 488.46a 1125.11b 0.000 ***N (%) 2.030a 2.000a 0.482 NSP (ppm) 120.58a 97.66b 0.035 *K (ppm) 6620.46a 5539.54a 0.337 NSCa (ppm) 12,155.77a 19,476.81b 0.002 **Mg (ppm) 2574.04a 3768.26b 0.006 **Na (ppm) 166.50a 115.53a 0.335 NSFe (ppm) 1472.04a 368.75a 0.565 NSZn (ppm) 49.71a 48.00a 0.798 NSCu (ppm) 11.53a 9.87a 0.084 NSMn (ppm) 531.21a 832.52a 0.180 NS

Values are mean. Significance levels are NS non significant, *0.05–0.01, **0.01–0.001 and ***0.001>, values within columns followed bythe same letter are not statistically different at 0.05 significance level.

Table 2Organic layer properties

Characteristics Unit Skid road Undisturbed Asymp. Sig. 2-tailed

Organic layer mass (kg ha�1) 4799.17a 8598.94b 0.005 **N (%) 1.443a 1.452a 0.949 NSP (ppm) 56.83a 54.68a 0.798 NSK (ppm) 1230.45a 1545.50b 0.013 *Ca (ppm) 10,830.96a 15,994.44a 0.110 NSMg (ppm) 3033.21a 2334.38a 0.338 NSNa (ppm) 127.71a 151.93b 0.033 *Fe (ppm) 7944.43a 11,213.75b 0.035 *Zn (ppm) 85.00a 99.86b 0.048 *Cu (ppm) 20.22a 25.32b 0.009 **Mn (ppm) 1350.59a 1837.75b 0.025 *

Values are mean. Significance levels are NS non significant, *0.05–0.01, **0.01–0.001 and ***0.001>, values within columns followed bythe same letter are not statistically different at 0.05 significance level.

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and Binkley, 2000; Tan and Chang, 2007). Smith and Wass (1985), indicated that humus characteristics in skidroad would tend to have a low rate of decomposition and mineralization. In addition, some of the trees alongthe skidding route are cut during building of the skid roads in order to prevent any preclusion on skiddingworks and to have a straight skid road. Therefore, the number of trees per unit area in the skid road decreases.It is also found that, subject to the decreasing number of trees, the amount of litter fall is decreasing and, dueto annually skidding and the long-term use of the road, there is the possible presence of last year’s shed litter inits organic layer (Makineci et al., 2007).

K, Na, Fe, Zn, Cu, and Mn contents of organic layer samples were significantly grater in undisturbed areaversus skid road. Differences on other investigated chemical parameters (N, P, Ca and Mg) were not statisti-cally significant. Possibly changed conditions in soil and herbaceous cover after skidding and the effects of her-baceous based skidding on organic layer affected the chemical properties of organic layer.

3.3. Soil properties

3.3.1. Soil depth (0–5 cm)

Some soil properties such as sand rate and pH did not show significant differences in the undisturbed area andin the skid road (Table 3). However, other investigated soil properties in 0–5 cm depth such as silt and clay rates,organic carbon, compaction and bulk density showed significant differences between undisturbed area and skidroad. The average compaction was measured as 3.71 kg cm�2 for the skid road and 1.55 kg cm�2 for the undis-turbed area, indicating that at 0–5 cms soil depths the skid road had been substantially compacted. The organiccarbon rate in the skid road was found quite lower than the undisturbed area but the soil bulk density was quitehigher. Mean silt rate was quite higher and the mean clay rate was lower in the skid road than the undisturbedarea. The reason of the important differences in the silt and clay rates might be due to the changes in the naturalstructure of the soil because of soil compaction with possible surface flows and erosion effects. In addition to thechanges in the soil properties, decreasing amounts of organic layer and herbaceous cover and changes on theproperties of the decomposing organic matter can be effective on the soil properties (Makineci et al., 2007).

In the 0–5 cm soil depth, P and Fe concentrations in skid road were significantly lower than undisturbedarea. Differences on N, K, Na, Ca, Mg, Zn, Cu and Mn concentrations were not statisticaly significant (Table3). Herbauts et al. (1996) indicated that soil compaction generates reduced forms of irons and induces a strongleaching of iron hydroxides. McNabb et al. (1997) also reported P as one of the most pronounced elementswhen skid trail versus non-skid trail samples were compared with a tendency for P to vary inversely with soildisturbance intensity suggesting decreased mineralization of P, or increased uptake for P.

3.3.2. Soil depth (5–10 cm)

Unlike the 0–5 cm soil depth, no large differences were found in the clay and silt rates at greater depthsbetween the undisturbed area and skid road. Compacting, bulk density and organic carbon, however, showed

Table 3Investigated soil properties in 0–5 cm soil depth

Characteristics Unit Skid road Undisturbed Asymp. Sig. 2-tailed

Sand (%) 52.13a 48.84a 0.292 NSSilt (%) 27.55a 21.99b 0.001 **Clay (%) 20.32a 29.17 0.027 *pH pH 5.89a 5.69a 0.398 NSBulk density (g cm�3) 0.908a 0.706b 0.033 *Organic carbon % 4.22a 13.24b 0.001 **Compaction (kg cm�2) 3.71a 1.55b 0.000 ***N (%) 0.345a 0.386a 0.406 NSP (ppm) 1.88a 5.17b 0.013 *K (ppm) 146.83a 165.45a 0.749 NSCa (ppm) 2003.55a 2020.68a 0.749 NSMg (ppm) 295.54a 318.09a 0.848 NSNa (ppm) 25.72a 25.09a 0.655 NSFe (ppm) 0.34a 1.32b 0.002 *Zn (ppm) 95.29a 84.43a 0.848 NSCu (ppm) 0.83a 0.61 a 0.406 NSMn (ppm) 134.92 a 175.57 a 0.180 NS

Values are mean. Significance levels are NS non significant, *0.05–0.01, **0.01–0.001 and ***0.001>, values within columns followed bythe same letter are not statistically different at 0.05 significance level.

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significant differences (Table 4) indicating that the skidding effects had impacted up to 10 cm down. The rea-sons of lower organic matter at the 5–10 cm soil depth might be similar to 0–5 cm soil depth. Furthermore,changed soil properties in lower depths of the skid road might lead to both lower biological activity anddecomposition of organic compounds at 5–10 cm soil depth. Differences in sand, slit, clay rates and pHbetween skid road and undisturbed area were not significant.

None of the element concentrations (N, P, K, Ca, Mg, Na, Fe, Zn, Mn and Cu) in the 5–10 cm soil layershowed significant differences between the skid road and the undisturbed area. Concurring with Knoepp andSwank (1997), it seems saw-log harvesting using cable-yarding techniques had not adversely impacted soil cat-ion concentrations. However, the results run contrary to Wang (1997), who reported that many more nutrientelements (N, P, K) in the skidding trail soils had been lost due to heavy disturbances. Arocena (2000) addi-tionally found that when the organic layer was retained and soil was not compacted, the amounts of Ca+2,

Table 4Investigated soil properties in 5–10 cm soil depth

Characteristics Unit Skid road Undisturbed Asymp. Sig. 2-tailed

Sand (%) 48.44a 48.01a 0.908 NSSilt (%) 27.04a 29.65a 0.257 NSClay (%) 24.52a 22.34a 0.373 NSpH pH 5.63a 5.49a 0.570 NSBulk density (g cm�3) 0.983a 0.866b 0.017 *Organic carbon (%) 3.12a 9.01b 0.000 ***Compaction (kg cm�2) 3.35a 1.98b 0.000 ***N (%) 0.279a 0.234a 0.180 NSP (ppm) 0.00a 0.15a 0.060 NSK (ppm) 130.77a 128.93a 0.949 NSCa (ppm) 1673.80a 1243.44a 0.085 NSMg (ppm) 262.72a 251.06a 0.749 NSNa (ppm) 24.35a 20.07a 0.110 NSFe (ppm) 0.48a 1.00a 0.195 NSZn (ppm) 45.66a 41.00a 0.655 NSCu (ppm) 0.71a 0.96a 0.277 NSMn (ppm) 129.97a 114.85a 0.338 NS

Values are mean. Significance levels are NS non significant, *0.05–0.01, **0.01–0.001 and ***0.001> values within columns followed bythe same letter are not statistically different at 0.05 significance level).

458 E. Makineci et al. / Transportation Research Part D 12 (2007) 453–459

K+1, Mg+2 and Al+3 in soil solution were higher. On the other hand, many studies have found that increasesof denitrification were possibly due to soil compaction – nitrate nitrogen was lost into the atmosphere (Nugentet al., 2003).

In addition, alterations in soil and organic layer properties resulting by ground based skidding can haveeffects through a number of mechanisms (such as mineralization, leaching, weathering, respiration, biologicalactivity, oxidation, and diffusion) and these complicated and undetermined processes can change the chemicalcomposition of soil.

4. Discussion

The findings indicate that timber skidding can cause a decrease in the mass of the organic layer and her-baceous cover in skid road and that these effects go down at least 5–10 cm. Herbaceous cover in skid roadhad grater P, and significantly lower Ca and Mg content than those of undisturbed area. The organic layerof the skid road had lower K, Na, Fe, Zn, Cu and Mn contents than undisturbed area and in terms of chemicalproperties, only P and Fe concentrations in 0–5 cm soil layer differed significantly between the skid road andthe undisturbed area. Concentrations of chemicals in the 5–10 cm soil layer were not significantly differentbetween locations.

Changes from soil compaction cause negative impacts on the water and air status of the soils on the skidroads. Prompt actions should be taken to prevent and minimize such negative impacts of the skid roads. Espe-cially, the skid roads should not be used for long periods without taking any remedial actions – the long-termutilization of the same road increases the damage. Rehabilitation works, including mulching, of skid roads,the soil properties of which have been drastically degraded, should be implemented. The rehabilitation of skidroads is, however, bound to be costly and its effectiveness has not been adequately demonstrated. Reduction ofskid road disturbance is thus a prime objective. Displacement of the upper soil or the FH horizon alone shouldbe avoided to lessen such negative impacts, and to limit organic layer and herbaceous cover losses on the soilcaused by compaction fitting a conical skid cap at the end of the timber, during the skidding, or usage of slides,may be environmentally beneficial.

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