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Journal of Terramechanics 44 (2007) 423–428

ofTerramechanics

Effects of timber skidding on chemical characteristicsof herbaceous cover, forest floor and topsoil on skidroad

in an oak (Quercus petrea L.) forest

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

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

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

Received 27 June 2007; received in revised form 5 October 2007; accepted 7 December 2007Available online 28 January 2008

Abstract

This paper examines the effects of timber harvesting by skidding on some soil properties (sand, silt, clay, pH, organic carbon, bulkdensity and compaction), herbaceous cover (unit mass) and forest floor (unit weight) properties. Also N (%), P, K, Na, Ca, Mg, Fe, Zn,Cu and Mn (ppm) were determined in all herbaceous cover, forest floor and two soil depth (0–5 cm and 5–10 cm) on skidroad of an oak(Quercus petrea L.) stand in Istanbul Belgrad Forest – Turkey. In this study, obtained results are; the forest floor and the herbaceouscover amount on the skidroad have been found considerably lower than undisturbed area. There were some crucial changes in the char-acteristics of the soil which has been investigated down to 10 cm depth. Soil bulk density was found quite high in the samples taken fromthe skidroad subject to compaction compared to the ones on the undisturbed area. Nevertheless, no important difference had beendetected between the skidroad and the undisturbed area at both soil depths in terms of organic carbon contents. Moreover, the soil acid-ity (pH) values showed noteworthy differences in the analysis of soil samples taken from both soil depths on the skidroad and on theundisturbed area. Fe and Cu contents of herbaceous samples on skidroad were significantly higher than undisturbed area. Forest flooron skidroad had significantly higher K content, and significantly lower Zn, Mn and N content compared to undisturbed area. P, Fe, Znand Mn contents were found significantly lower in 0–5 cm soil depth on skidroad than undisturbed area. In 5–10 cm soil depth, concen-trations of N, P, Fe, Zn and Mn were significantly lower, while Mg and Cu contents were significantly higher than undisturbed area.Results indicate that long-term harvest using skidding techniques on these sites had adversely affected soil cation concentrations, physicalsoil conditions and mass of herbaceous cover and forest floor.� 2007 ISTVS. Published by Elsevier Ltd. All rights reserved.

Keywords: Harvesting impacts; Skidding; Chemical; Soil; Herbaceous cover; Forest floor

1. Introduction

Skidding or yarding on terrain requires the constructionof relatively dense network of forest roads including skid-roads, haul roads and landings [1,2]. Harvesting works

0022-4898/$20.00 � 2007 ISTVS. Published by Elsevier Ltd. All rights reserve

doi:10.1016/j.jterra.2007.12.001

* Corresponding author. Tel.: +90 (212) 2261100x25302; fax: +90 (212)2261113.

E-mail addresses: emak@istanbul.edu.tr (E. Makineci), mdemir@istanbul.edu.tr (M. Demir), acomez@hotmail.com (A. Comez), ersel@istanbul.edu.tr (E. Yilmaz).

being carried out in the forest areas cause losses, mixingand compaction of the soil to a great extent. Degradationin the soil after timber harvesting has also as much impor-tant effects on the contents of nutrients as it has impacton the physical properties of the soil [3–11]. Subject to this,plant development falls considerably [10–16]. Moreover,compaction and loss through erosion of the upper soil layerwhich is rich in organic matters and nutrients drops the effi-ciency of the forest [5,17–20]. Skidding works carried out inthe forests have negative impacts on the variety of the soil’sbiological communities and conditions thereof through

d.

424 E. Makineci et al. / Journal of Terramechanics 44 (2007) 423–428

effects such as decrease of organic matters, compaction,change in the flora and soil microclimate [3,12–14,21–23].Skidding of the harvested products directly on the groundcompresses the soil and results in changes in the structuralproperties of the soil. Such changes are directly affectingthe water holding capacity, soil aeration, drainage and rootdevelopment in the soil. Major deficiencies caused by theskidroads are determined as loss of organic matters fromthe forest floor and aboveground level, compaction andexposition to erosion of the soil.

The aim of this study is to examine the impacts of timberproduction works, which have been carried out for manyyears, on some properties of herbaceous cover, forest floorand soil on the skidroad in a given oak (Quercus petrea L.)stand in Istanbul Belgrad Forest – Turkey.

2. Materials and methods

Belgrad Forest is located in Istanbul province in theMarmara geographical region between 41�090–41�120N lat-itude and 28�540–29�000E longitude in Turkey. The BelgradForest covers 5441.71 ha. The research area is in theboundaries of zone 82 of Belgrad Forest. According tothe (long-term) data given by Bahcekoy Meteorology Sta-tion, the nearest meteorology station to the research area,average annual precipitation is 1074.4 mm, annual meantemperature is 12.8 �C, mean maximum temperature is17.8 �C and the average minimum temperature is 9 �C.The climate of Istanbul Belgrad Forest is maritime climatewith medium water deficit in summers. General texturetype of soil in research area is loam. Vegetation periodmaintains for 7.5 months (230 days) in average. Researcharea is a pure sessile oak (Quercus petrea L.) stand. Canopycover has been estimated as 0.8. Average diameter at breastheight is 29.72 cm, average height is 22.94 m and standdensity has been measured as 900 trees/ha. It was estimatedthat 195 m3 timbers had been skidded annually in harvestactivities on the skidding road [24]. Altitude is 140 m, slopeis 10–15% and it is in the SW aspect. The skidroad passingthrough the stand in East–West direction has long beenused (since 1956) in the production works. Skidding worksin the research area have been carried out by manpower,animal power and machinery. Herbaceous vegetation spe-cies are Hedera helix L., Ruscus aculeatus L., Ruscus hypo-

glossum L., Rubus ssp., Viola ssp. L., Galium odoratum (L.)Scop., Salvia forskahlei L., Trachystemon orientale (L.) G.Don. on the skidroad and undisturbed area. In this studythe impacts of skidding on the forest floor, herbaceouscover and the surface soil layer (down to 10 cm depth) havebeen examined in comparison with the undisturbed area.The skidroad and correspondingly the undisturbed areawhere there is not any skidding impact and at least 30 maway from the skidroad (at least 1 tree length far awayfrom skidroad edge to reduce side effects) were sampledat 7 different points at 10 m intervals. For this purpose, 7samples were taken from each of herbaceous cover, forestfloor, 0–5 cm soil and 5–10 cm soil. Herbaceous cover sam-

ples were taken by cutting aboveground parts of all herba-ceous mass in 1 m2 area and the samples of the forest floorwere taken from 1/4 m2 (0.25 m2) area by collecting all theforest floor in that area. Soil compaction at the same pointswhere herbaceous cover and forest floor samples weretaken and measured at two different soil depths (0–5 cmand 5–10 cm) by using a pocket penetrometer. Soil sampleswere taken from 0–5 cm and 5–10 cm with the aid of100 cm3 steel soil cores. A total of 300 cm3 soil samplewas taken for each of the soil layers of the sampling points.All samples were collected in September 2004. Sampleswere put in polyethylene bags and labeled. Collected sam-ples, brought to the laboratory from the research area, her-baceous cover and forest floor samples dried under 65 �C,and soil samples dried under 105 �C over 24 h. Weight val-ues given in relevant tables about herbaceous cover, forestfloor and soil samples are oven-dried values.

Soil samples were air-dried, ground and sieved with2 mm screen before analysis. Particle size distribution wasdetermined by hydrometer method of Bouyoucos’ [25],actual acidity by a pH meter with glass electrodes in 1:2.5distilled water [26], organic carbon by wet combustionmethod of Wackley and Black [27], N by semi-micro kjeldalmethod [26] using Kjeltec Auto 1030 Analyzer (Tecator,Sweden), P by Bray and Kurtz No. 1 method [28] usingSpectronic 20D spectrophotometer, K+, Na+, Ca2+,Mg2+, Fe2+, Mn2+ by ammonium acetate method [26] usingJenway PFP 7 flame photometer for K+ and Na+, Perkin–Elmer 3110 atomic absorption spectrometer for Ca2+,Mg2+, Fe2+, Mn2+. Cu2+ and Zn2+ were determined bydouble-acid (HCl + H2SO4) method using Perkin–Elmer3110 atomic absorption spectrometer equipment [29].

Oven-dried forest floor and herbaceous samples (for24 h at 65 �C until constant weight) ground and passedthrough a 1-mm mesh screen before chemical analysis.These samples were analysed for total N by semi-microkjeldal method [26] using Kjeltec Auto 1030 Analyzerequipment (Tecator, Sweden). For determination of P, K,Na, Ca, Mg, Fe, Mn, Cu, Zn, the samples were digestedin the solution of HNO3–HCl4. K and Na concentrationsdetermined by flame photometer, P by vanado-molybdo-phosphoric yellow color method using Spectronic 20Dspectrophotometer equipment, Ca, Mg, Mn, Fe, Cu, Znby Perkin–Elmer 3110 atomic absorption spectrometerequipment [30].

The values found for the undisturbed area and for theskidroad were compared statistically at 0.05 significancelevel by using independent sample t-test statistical analysis.Mean values found for all properties are shown in relevanttables.

3. Results and discussion

3.1. Properties of herbaceous understory

Aboveground amount of the total herbaceous coverin unit area was 240.18 kg ha�1 on the skidroad and

E. Makineci et al. / Journal of Terramechanics 44 (2007) 423–428 425

702.60 kg ha�1 in the undisturbed area (Table 1). Theundisturbed area had considerably more amount of herba-ceous cover than the skidroad. It is estimated that thegreatest impact in decrease of herbaceous cover on theskidroad is sourcing from the damage the skidding timbers.Moreover, the changing properties of the soil and forestfloor after skidding can be effective on the decreasing her-baceous cover [31,32]. Soil compaction can also severelyreduce herbaceous plant growth by restricting root growth.

Compared to undisturbed area, herbaceous cover onskidroad had substantial higher Fe (3692.95 ppm) and Cu(16.50 ppm) contents (Table 1). Other investigated chemi-cal parameters (N, P, K, Na, Ca, Mg, Zn and Mn) didnot differ significantly (Table 1). A reduced absorption ofthe major nutrients by compaction soils may account forbetween species as some have higher nutrient requirementsthan others [6]. And changed physical and chemical soilproperties caused by skidding, less forest floor and herba-ceous cover mass may be effective on the chemical proper-ties of herbaceous plants on skidroad. Also, moreherbaceous plants on undisturbed area competite for soilcations. On the other hand, more adapted (especially to soilcompaction) and less herbaceous plant mass exist on skid-road. These differences also possibly affect the chemical sta-tus of herbaceous plants on skidroad compared toundisturbed area. On the other hand, the reason of the dif-ference on herbaceous cover values likely because of thedifferent herbaceous species between skid road and theundisturbed area. However, a comprehensive herbaceousspecies determination has not been made in this study. Sev-eral researches demonstrated the different effects of skid-ding on herbaceous and understory plants [4,6,8,15,22].

3.2. Properties of forest floor

Total forest floor weight in unit area was 4532.76 kg ha�1

and 2886.86 kg ha�1 in the undisturbed area and on the skid-road, respectively (Table 2). The undisturbed area had con-siderably higher amount of forest floor. Less forest floor onthe skidroad shows that the forest floor has been moved out

Table 1Herbaceous cover properties

Characteristics Skidroad Undisturbed Asymp. Sig. 2-tailed

Mass (kg ha�1) 240.18 702.60b 0.006 **N (%) 1.812 1.666 0.617 NSP (ppm) 177.66 167.16 0.668 NSK (ppm) 6807.97 9205.60 0.086 NSNa (ppm) 188.53 142.48 0.197 NSCa (ppm) 10432.84 13740.62 0.886 NSMg (ppm) 2205.25 2419.01 0.775 NSFe (ppm) 3692.95 344.23 0.004 **Zn (ppm) 54.51 76.32 0.886 NSCu (ppm) 16.50 10.80 0.032 *Mn (ppm) 863.76 835.09 0.668 NS

Values are mean. Significance levels are NS non significant, *0.05–0.01and **0.01–0.001.

by skidding. In addition, some of the trees along the skiddingroute were cut during building of the skidroads in order toprevent any preclusion on skidding works and to have astraight skidroad. Therefore, the number of trees per unitarea on the skidroad decreases. It is also estimated that, sub-ject to the decreasing number of trees, amount of litter fall isalso decreasing [31].

K content (1381.99 ppm) of forest floor samples weregrater on skidroad versus undisturbed area (Table 2). Incontrast, Zn (59.43 ppm), Mn (1484.59 ppm) and N(1.100%) concentrations in forest floor on skidroad werefound significantly lower than undisturbed area (Table 2).Differences on Na, Ca, Mg, Fe and Cu concentrations werenot statistically significant between undisturbed area andskidroad (Table 2). Disturbances by skidding cause dis-placement, removal and mixing of forest floor, and changethe physical and chemical soil properties. And these effectsmay influence decomposition, mineralisation and chemicalcomposition of forest floor. Many researchers indicatedthat the effects of timber harvesting and skidding on forestfloor [3,8,12–14,21,23].

3.3. Soil properties

3.3.1. 0–5 cm soil depth

The soil samples taken from 0–5 cm depth showedimportant differences in the undisturbed area and on theskidroad with regard to some properties such as sand %,clay %, pH, compaction and bulk density values (Table3). Average compaction value on the skidroad has beenmeasured as 2.71 kg cm�2 on the skidroad and1.37 kg cm�2 in the undisturbed area (Table 3). Soil depth(0–5 cm) on the skidroad is substantially compacted incomparison with the undisturbed area. Depending on thecompaction of the soil, considerable difference was foundbetween the undisturbed area and the skidroad with regardto the soil bulk density (Table 3). Soil bulk density (1.028 gcm�3) on the skidroad because of compaction are quitehigher than those on the undisturbed area (Table 3). Thesoil acidity (pH 6.23) at 0–5 cm depth on the skidroad is

Table 2Forest Floor properties

Characteristics Skidroad Undisturbed Asymp. Sig. 2-tailed

Mass (kg ha�1) 2886.86 4532.76 0.011 *N (%) 1.100 1.508 0.004 **P (ppm) 55.50 73.21 0.063 NSK (ppm) 1381.99 1128.96 0.006 **Na (ppm) 117.81 109.73 0.185 NSCa (ppm) 14839.79 18228.05 0.086 NSMg (ppm) 1989.97 2002.73 0.775 NSFe (ppm) 7097.55 5202.56 0.253 NSZn (ppm) 59.43 87.33 0.007 **Cu (ppm) 14.84 18.13 0.317 NSMn (ppm) 1484.59 2872.18 0.007 **

Values are mean. Significance levels are NS non significant, *0.05–0.01and **0.01–0.001.

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

Characteristics Skidroad Undisturbed Asymp. Sig. 2-tailed

Sand (%) 73.37 67.77 0.032 *Silt (%) 18.04 16.28 0.508 NSClay (%) 8.57 15.94 0.000 ***Acidity (pH) 6.23 5.61 0.040 *Bulk density (g cm�3) 1.028 0.635 0.001 **Organic carbon (%) 7.97 9.75 0.162 NSCompaction (kg cm�2) 2.71 1.37 0.000 ***N (%) 0.285 0.341 0.565 NSP (ppm) 3.76 9.47 0.009 **K (ppm) 123.24 97.15 0.406 NSNa (ppm) 19.87 24.01 0.225 NSCa (ppm) 2139.09 1624.24 0.406 NSMg (ppm) 361.29 281.76 0.225 NSFe (ppm) 0.70 1.34 0.012 *Zn (ppm) 62.00 93.71 0.021 *Cu (ppm) 0.99 0.83 0.482 NSMn (ppm) 55.60 189.74 0.002 **

Values are mean. Significance levels are NS non significant, *0.05–0.01,**0.01–0.001 and ***0.001.

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

Characteristics Skidroad Undisturbed Asymp. Sig. 2-tailed

Sand (%) 58.04 73.52 0.003 **Silt (%) 25.74 10.86 0.000 ***Clay (%) 16.20 15.61 0.754 NSAcidity (pH) 5.80 5.25 0.042 *Bulk density (g cm�3) 1.235 0.784 0.000 ***Organic carbon (%) 5.72 7.53 0.085 NSCompaction (kg cm�2) 3.37 1.85 0.000 ***N (%) 0.124 0.253 0.007 **P (ppm) 0.31 6.55 0.001 **K (ppm) 85.04 68.36 0.456 NSNa (ppm) 18.88 18.08 0.805 NSCa (ppm) 1227.48 907.41 0.620 NSMg (ppm) 316.71 201.46 0.038 *Fe (ppm) 0.62 1.35 0.001 **Zn (ppm) 31.57 53.86 0.004 **Cu (ppm) 1.45 0.83 0.026 *Mn (ppm) 49.68 180.51 0.001 **

Values are mean. Significance levels are NS non significant, *0.05–0.01,**0.01–0.001 and ***0.001.

426 E. Makineci et al. / Journal of Terramechanics 44 (2007) 423–428

higher to a great degree than the one on the undisturbedarea (pH 5.61) (Table 3). In addition to the changes inthe soil properties and subject to the decreasing forest floorand herbaceous mass, changes in the properties of thedecomposing organic matter can be effective on the acidityof the soil. Moreover, it is estimated that possible surfaceflows and erosion carrying as well as accumulation becauseof sedimentation are also effective on the soil acidity [31].

In 0–5 cm soil depth, P (3.76 ppm), Fe (0.70 ppm), Zn(62.00 ppm) and Mn (55.60 ppm) were significantly loweron skidroad than undisturbed area (Table 3). Differenceson N, K, Na, Ca, Mg and Cu concentrations were not sta-tistically significant (Table 3).

3.3.2. 5–10 cm soil depth

Results for the soil samples taken from 5–10 cm depthare similar to the results we found for 0–5 cm depth exceptfor the silt and clay ratios (Table 4). Nevertheless, differentfrom the 0–5 cm soil depth, no considerable differencescould be found in the clay proportions between the undis-turbed area and the skidroad (Table 4). Furthermore, it hasbeen observed that the silt proportion of the skidroad wasquite higher compared to the silt proportion of the undis-turbed area (Table 4). Likely cause of these changes inthe sand, silt and clay proportions must be, subject to thesoil compaction, the change in the natural soil structurebefore the skidding works. Because of the soil compaction,much higher bulk density (1.235 g cm�3) values found onthe skidroad at 5–10 cm depth (Table 4). Because of thecompaction that occurred on the skidroad after skiddingsoil bulk density values increased. In addition to theseimportant changes in the soil properties, it is estimated thatthe variations in the decomposition conditions sourcingfrom decrease in the forest floor and herbaceous coverare also effective on pH of the soil [31]. Similar skiddingand production works in the forestry applications generally

increases compaction of the soil. Despite our findings atboth soil depths, it is generally claimed that the skiddingworks cause decreasing of organic matter amount in thesoil [9,11–13,21,23].

In 5–10 cm soil layer N (0.124%), P (0.31 ppm), Fe(0.62 ppm), Zn (31.57 ppm) and Mn (49.68 ppm) concen-trations were found significantly lower compared to undis-turbed area. On the other hand, Mg (316.71 ppm) and Cu(1.45 ppm) contents were significantly higher on the skid-road (Table 4). K, Na and Ca concentrations did not showsignificant differences between skidroad and undisturbedarea (Table 4). As shown in Table 4, 5–10 cm soil layerof skidroad has more fine texture (more silt and less sandproportions) than undisturbed area. However, soil on skid-road was severely compacted. For these reasons, possiblysome of cations such as P, Fe, Zn and Mn can not leachinto the soil. In addition, alterations both on soil and forestfloor properties resulting by ground based skidding affectseveral main mechanisms (such as mineralisation, leaching,weathering, respiration, biological activity and oxidation)in different ways. And these complicated and undeterminedprocesses can change the chemical composition of soil. Infact, important difference determined with regard to thesoil acidity can also be interpreted as the conditions thatchange after skidding may also be effective on the soilchemistry. Similarly, many researches stated that the skid-ding impacts cause changes in the chemical properties ofthe soil [3,8,11–14].

4. Conclusions

In this study, we have tried to put forward the impactsof skidding works, which have been carried out for manyyears (since 1956) on a skidroad in an oak (Q. petrea L.)stand, on the properties of topsoil, forest floor and herba-

E. Makineci et al. / Journal of Terramechanics 44 (2007) 423–428 427

ceous cover. The skidding works caused decrease in the for-est floor and the herbaceous cover to a great extent. Fur-thermore, the skidding has been effective on both soildepths (0–5 cm and 5–10 cm) which were examined. Com-paction of soil with the impact of skidding has causedincreasing bulk density values on the skidroad. Negativeimpacts of soil compaction have been set forth with manyresearches. Compaction of soil causes decrease in the per-meability and infiltration capacity of the soil which leadspooling of water on the ground and therefore loss of mois-ture through evaporation [3–5,7,13–16]. Therefore rootdevelopment slows down and subject to this, water andnutrient uptake of the existing plants decreases. [3,14,21].Moreover, because of the increasing denitrification, nitratenitrogen is lost in the atmosphere. Thus, nitrogen lossesoccur in the soil by this way [3,13]. Decreasing of infiltra-tion and permeability in the soil in the slope areas becauseof compaction can cause erosion [5,16,17,19,20]. Lesseningof the herbaceous cover and forest floor after skiddingleaves the soil vulnerable against erosion and forest floordecomposition and mineralization also decreases becauseof unfavorable soil conditions. Thus, retardation occursin the nutrient cycle in the forest ecosystem [3,8,11–14,21,23].

Similarly or in contrary to our results, many researchesconducted to detect the effects of skidding or timber harvest-ing on soil, forest floor or herbaceous plants. And they con-cluded that effects are complicated and changeabledepending on a lot of factors such as, disturbances, microcli-mate, stand type and soil characteristics [4,6,8,14,15,31–33].

Briefly, the long-term skidding works carried out in anoak stand caused noteworthy losses in the herbaceouscover and forest floor on the skidroad. Additionally, soilproperties have also changed to a great extent. It is obviousthat particularly the changes which occur subject to the soilcompaction will cause negative impacts on the water andair economies of the soils on the skidroads. Prompt actionsshould be taken in order to prevent and minimize such neg-ative impacts of the skidroads. Especially, the skidroadsshould not be used for long periods without taking anyactions after they are built. Making rehabilitation works[7,34,35] on the skidroads of which soil properties havebeen drastically degraded and therefore lost their plantcover shall be very useful in terms of protection of theecosystem.

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