Investigation of timber harvesting impac (5)

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Building and Environment 42 (2007) 1194–1199

Investigation of timber harvesting impacts on herbaceous cover,

forest ﬂoor and surface soil properties on skid road

in an oak (

Quercus petrea

L.) stand

Murat Demir

a,

, Ender Makineci

b

, Ersel Yilmaz

c

a

Department of Forest Construction and Transportation, Faculty of Forestry, Istanbul University, 34473 Bahcekoy, Sariyer, Istanbul, Turkey

b

Department of Soil Science and Ecology, Faculty of Forestry, Istanbul University, 34473 Bahcekoy, Sariyer, Istanbul, Turkey

c

Department of Forest Yield and Biometry, Faculty of Forestry, Istanbul University, 34473 Bahcekoy, Sariyer, Istanbul, Turkey

Received 13 October 2005; received in revised form 8 November 2005; accepted 11 November 2005

Abstract

In this study, we investigated the timber harvesting effects on some soil properties (sand, silt, clay, pH, electrical conductivity, ﬁne soil

o2 mm, coarse soil42 mm, root mass, organic carbon, moisture equivalent, total porosity, bulk density, moisture and compaction) at

soil depths (0–5 and 5–10 cm), herbaceous cover and forest ﬂoor (unit mass, organic matter and moisture) on skid road of an oak (Quercus petreaL.) stand in Istanbul Belgrad Forest of Turkey.

According to the results obtained, the forest ﬂoor and the herbaceous cover amount on the skid road have considerably decreased. There has been some crucial changes in the characteristics of the soil, which has been investigated down to 10 cm depth. The ﬁne soil weight and bulk density values were found to be quite high in the samples taken from the skid road subjected to compaction compared to the ones in the undisturbed area; also the porosity and moisture equivalent values decreased to a great extent. Nevertheless, no important difference has been detected between the skid road and the undisturbed area at both soil depths in terms of organic carbon rates. Moreover, the soil acidity (pH) values have shown noteworthy differences in the analysis of soil samples taken from both soil depths, on the skid road and in the undisturbed area.

Keywords:Harvesting impacts; Skidding; Skid road; Soil; Herbaceous cover; Forest ﬂoor

1. Introduction

Harvesting works being carried out in the forest areas causes losses, mixing and compaction of the soil to a great extent. Degradation in the soil after timber harvesting also has as much important effects on the contents of nutrients as it has impact on the physical properties of the soil[1–9]. Subject to this, tree development falls considerably [8–14]. Moreover, compaction and loss through erosion of the upper soil layer, which is rich in organic matters and

nutrients, brings down the efﬁciency of the forest[3,15–18]. The soil is a habitat for the plant roots and numerous viruses, bacteria, fungi, algae and other soil organisms. Skidding works carried out in the forests have negative impacts on the variety of the soil’s biological communities and conditions thereof through effects such as decrease of organic matters, compaction, change in the ﬂora and soil microclimate[1,10–12,19–21]. The dimension of the impact created by skidding of the products directly on the ground varies according to many factors such as slope, site characteristics, production methods used, planning of skid roads and production season. Skidding of the harvested products directly on the ground compresses the soil and results in changes in the structural properties of the soil. Such changes directly affect the water-holding capacity, soil aeration, drainage and root development in the soil. www.elsevier.com/locate/buildenv

_{Corresponding author. Tel.: +90 212 2261100/x25289;} fax: +90 212 2261113.

E-mail addresses:mdemir@istanbul.edu.tr,

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Major deficiencies caused by the skid roads are determined as loss of organic matters from the forest floor and aboveground level, compaction and exposition to erosion of the soil. These detriments also affect infiltration of water into the soil and pass through to the lower levels.

The aim of this study is to examine the impacts of production works, which have been carried out for many years, on some herbaceous covers, forest ﬂoors and soil properties on the skid road in a given oak (Quercus petrea

L.) stand in Istanbul Belgrad Forest of Turkey.

2. Material and methods

Belgrad Forest is located in Istanbul province in the Marmara geographical region between 411090_{N and} 411120_{N latitudes and 28}₁₅₄0_{E and 29}₁₀₀0_{E longitudes} and covers an area of 5441.71 ha (Fig. 1). The research area is in the boundaries of zone 82 of Belgrad Forest. According to the (long-term) data given by Bahcekoy Meteorology Station, the closest meteorology station to the research area, average annual precipitation is 1074.4 mm, annual mean temperature is 12.8₁C, mean high tempera-ture is 17.8₁C and the average low temperature is 9₁C. The climate of Istanbul Belgrad Forest is close to sea (ocean) climate with medium water deﬁcit in summers. Vegetation period maintains for 7.5 months (230 days) on average.

Research area is a pure sessile oak (Quercus petrea L.) stand. Canopy cover has been estimated as 0.8. Average diameter is 29.72 cm, average height is 22.94 m and stand density has been measured as 900 trees/ha. It was estimated that 195 m3 timbers was skidded annually in harvest

activities on the skidding road [22]. Altitude is 140 m, slope is 10–15% and it is in the SW aspect. The skid road passing through the stand in East–West direction has long been used (since 1956) in the production works. Skidding works in the research area are being carried out by manpower, animal power and machinery. Herbaceous vegetation species are Hedera helix L., Ruscus aculeatus

L.,Ruscus hypoglossumL.,Rubusssp,Violassp L.,Galium

odoratum (L.) Scop., Salvia forskahlei L., Trachystemon

orientale (L.) G. Don. on the skid road and undisturbed

area. In this study, the impacts of skidding on the skid road that has been used for a long time, the forest floor, herbaceous cover and the surface soil layer (down to 10 cm depth) thereof have been examined, in comparison to the undisturbed area. The skid road was sampled at seven different points at 10-m intervals for this purpose (seven samples were taken from each of herbaceous cover, forest floor, 0–5 cm soil and 5–10 cm soil). Moreover, for control purpose, soil, forest floor and herbaceous cover samples from seven different points were taken again at 10-m intervals (seven samples from each of the herbaceous cover, forest floor, 0–5 and 5–10 cm soil) from the undisturbed area where there is no skidding impact and at least 25–30 m away from the skid road (at least one tree length away to reduce side impacts). Herbaceous cover samples were taken by cutting aboveground parts of all herbaceous cover in 1 m2area and the samples of the forest floor were taken from1

4m

2_{(0.25 m}2

) area by collecting all the forest ﬂoor in that area. Soil compaction at the places where herbaceous cover and forest ﬂoor samples were taken was measured at two different soil depths (0–5 and 5–10 cm) by using a

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pocket penetrometer. Soil samples were taken from 0–5 and 5–10 cm with the aid 100 cm3 steel soil cylinders. A total of 300 cm3soil sample was taken for each of the soils depths of the sampling points. All samples were collected in September 2004 and put in polyethylene bags and labeled. Samples brought to the laboratory from the research area were promptly weighed (within 1 h) and percentage of moisture and weight values of oven dried samples were calculated from the difference between the values of wet and oven-dried samples after making the herbaceous cover samples dried under 651C and forest floor and soil samples dried under 1051C for 24 h in an oven. All weight values given in relevant tables about herbaceous cover, forest floor and soil samples are oven-dried values. Organic matter amounts of the herbaceous cover and forest floor samples were found by loss on ignition method after grinding and burning at 5501C. Soil samples were sieved through 2 mm sieves and thus, fine soil (o2 mm), root (roots were weighed after rinsing with distilled water and waiting under 1051C for 24 h) and coarse soil fraction (42 mm) weights were found. Sand, silt and clay ratio of soil samples in the laboratory were found by Bouyoucos hydrometer method. Organic carbon ratio was determined by Walkey and Black wet digestion method. Also weight of fine soil (o2 mm) and 42 mm soil fraction weight, bulk density, total porosity, moisture equivalence, pH and electrical conductivity values were measured in the laboratory as described in Karao¨z [23–25]. The values found for the undisturbed area and for the skid road were compared statistically at 0.05 significance level by using independent samplet-test statistical analysis. Mean values found for all properties are shown in relevant tables.

3. Results and discussion

3.1. Properties of herbaceous cover

Aboveground amount of the total herbaceous cover in unit area is 240.18 kg ha 1 on the skid road and 702.60 kg ha 1 in the undisturbed area (Table 1). The undisturbed area has considerably more amount of herbaceous cover than the skid road. It is estimated that the greatest impact in decrease of herbaceous cover on the skid road is sourcing from the damage the skidding timbers cause on the herbaceous cover. Moreover, the changing properties of the soil and forest ﬂoor after skidding may directly or indirectly can be effective in decreasing herbaceous cover. The mean organic matter rate in the undisturbed area and the skid road is considerably different (Table 2) and organic matter rate of the herbaceous cover (91.12%) on the skid road is considerably higher than that of the undisturbed area (86.26%). This situation may most probably source from the difference among the herbaceous plant species. Changing conditions on the skid road can be effective in decreasing and changing the kind of species, compared to the undisturbed area. Results of previous similar studies show that there is a

difference between the skid roads and undisturbed areas in the kind of herbaceous species [2,4,20]. However, a comprehensive herbaceous species determination has not been made in this study. Subject to both differences between the organic matter rates (%) and also differences in the aboveground masses of herbaceous cover, the organic matter amount in the herbaceous cover unit area is considerably different on the skid road and in the undisturbed area. Higher organic matter amount in unit area has been detected in the undisturbed area (615.95 kg ha 1) (Table 1). Noteworthy difference could not be found in terms of moisture rates (Table 1). Similar to our ﬁndings in this research, many researchers have also set forth the negative impacts of skidding on the herbaceous cover

[2,4,6,13,20].

3.2. Properties of forest floor

Total forest floor weight in unit area in the undisturbed area is 4532.76 kg ha 1 and on the skid road 2886.86 kg ha 1 (Table 2). The undisturbed area has considerably higher amount of forest floor. Less forest floor on the skid road shows that the forest floor has been moved out by skidding. In addition, some of the trees along the skidding route are cut during building of the skid roads in order to prevent any preclusion on skidding works and to have a straight skid road. Therefore, the number of trees per unit area on the skid road decreases. It is also estimated that, subject to the decreasing number of trees, amount of litter fall is also decreasing. There is no important Table 1

Herbaceous cover properties

Characteristics Skid road Undisturbed Asymp. Sig. 2-tailed

Herbaceous mass (kg ha 1)

240.18a 702.60b 0.006 ** Moisture (%) 67.67a _71.12a _0.371 _NS Organic matter (%) 91.12a _86.26b _0.030 _* Organic matter (kg ha 1_{) 218.87}a _615.95b _0.011 _* Values are mean. Significance levels are NS non-significant, *0.05–0.01 and **0.01–0.001, values within columns followed by the same letter are not statistically different at 0.05 significance level.

Table 2

Forest ﬂoor properties

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difference between the organic matter rates on the skid road (85.58%) and in the undisturbed area (89.37%) (Table 2). Depending on the considerable difference in the forest floor amounts, organic matter amounts (kg ha 1) in unit area also show important differences and the values in the undisturbed area (4037.76 kg ha 1) are much higher than the value taken from the skid road (2449.24 kg ha 1) (Table 2). The fact that there is no important difference between the forest floor organic matter rates can be explained as the presence of the last year’s leaves in the forest floor both in the undisturbed area and on the skid road for the reason of fast decomposing oak forest floor

[26,27]. Mean moisture rate of forest floor in the undisturbed area (48.45%) has been found considerably higher than that of the skid road (35.42%) (Table 2). The reason why there are crucial moisture differences in the forest floor of the undisturbed area and the skid road may be holding of less moisture subject to the decreasing forest floor. Another reason of this may be losing the rain waters because of rapid penetration down to the mineral soil without being held in the forest floor subject to the decreasing forest floor and thickness as well as loosing the same because of surface flows and evaporation. Impacts of skidding and production works on the forest floor characteristics show similar results in many researches

[1,6,10–12,19,21].

3.3. Soil properties

3.3.1. 0–5 cm soil depth

The sample soil taken from 0–5 cm depth showed important differences in the undisturbed area and on the skid road with regard to some properties such as sand %, clay %, pH, ﬁne soil (o2 mm) weight, moisture equivalent

%, total porosity %, compaction and bulk density values (Table 3). Average compaction value on the skid road has been measured as 2.71 kg cm 2 on the skid road and 1.37 kg cm 2in the undisturbed area (Table 3). 0–5 cm soil depth on the skid road is substantially compacted in comparison with the undisturbed area. Depending on the compaction of the soil, considerable differences were found between the undisturbed area and the skid road with regard to the soil bulk density, fine soil weight, total porosity and moisture equivalent values (Table 3). Soil bulk density (1.028 g cm 3) and fine soil weight (0.887 g cm 3) on the skid road because of compaction are quite higher than those in the undisturbed area (0.636 and 0.479 g cm 3, respectively) (Table 3). Similarly, the values of total porosity (47.84%) and moisture equivalent (22.58%) on the skid road subject to compaction are considerably lower than the total porosity (59.19%) and the moisture equivalent (28.88%) in the undisturbed area (Table 3). Mean sand rate (73.37%) on the skid road which is quite higher and the mean clay rate (8.59%) which is lower on the skid road than in the undisturbed area have been found (Table 3). The reason of the important differences in the sand and clay rates may be the changes in the natural structure of the soil subject to soil compaction along with possible surface flows and erosion effects. The soil acidity (pH 6.23) at 0–5 cm depth on the skid road is higher to a great degree than the one in the undisturbed area (pH 5.61) (Table 3). In addition to the changes in the soil properties, subject to the decreasing forest floor and herbaceous cover, changes in the properties of the decomposing organic matter can be effective on the acidity of the soil. Moreover, it is estimated that possible surface flows and erosion carrying as well as accumulation because of sedimentation are also effective on the soil acidity.

No important differences could be found between the skid road and undisturbed area values with regard to other soil properties we have examined characteristics such as silt %, electrical conductivity, soil fraction greater than 2 mm, root mass, organic carbon and moisture rates (Table 4).

3.3.2. 5–10 cm soil depth

Results for the soil samples taken from 5 to 10 cm depth are similar to the results we found for 0–5 cm depth except for the silt and clay ratios (Table 4). Nevertheless, different from the 0–5 cm soil depth, no considerable differences could be found in the clay rates between the undisturbed area and the skid road (Table 4). Furthermore, it has been observed that the silt rate of the skid road is quite higher compared to the silt rate of the undisturbed area (Table 4). Likely cause of these changes in the sand, silt and clay rates must be, subject to the soil compaction, the change in the natural soil structure before the skidding works. Because of the soil compaction, much higher bulk density (1.235 g cm 3) and ﬁne soil weight (0.784 g cm 3) values and also much lower total porosity (45.52%) and moisture equivalence (21.57%) were found on the skid road compared to the undisturbed area because of soil compaction on the Table 3

Investigated soil properties in 0–5 cm soil depth

Sand (%) 73.37a 67.77b 0.032 * Silt (%) 18.04a 16.28a 0.508 NS Clay (%) 8.59a 15.95b 0.000 ***

pH 6.23a 5.61b 0.040 *

Electrical conductivity (mhos cm 1)

86.57a 88.35a 0.899 NS Fine soil (o2 mm) weight

(g cm 3)

0.887a 0.479b 0.000 *** Coarse soil (42 mm)

weight (g cm 3₎

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skid road at 5–10 cm depth (Table 4). Because of the compaction that occurred on the skid road after skidding, the ﬁne soil weight and bulk density values increased. Depending on the decrease in the total porosity after compaction, the moisture equivalent decreased. These consequences are the impacts that directly affect and decrease water and air economy of the soil. In addition to these important changes in the soil properties, it is estimated that the variations in the decomposition conditions sourcing from decrease in the forest ﬂoor and herbaceous cover are also effective in affecting pH of the soil. This important difference determined with regard to the soil acidity can be interpreted as the conditions that change after skidding may also be effective on the soil chemistry. In fact, many researches state that the skidding impacts cause changes in the chemical properties of the soil[1,6,9–12].

Soil properties which we have examined 5–10 cm depth (electrical conductivity, soil fraction42 mm, root, organic carbon and moisture) do not show noteworthy differences between the skid road and the undisturbed area (Table 4). Similar skidding and harvesting activities in the forestry applications generally increases compaction of the soil. Crucial changes may occur on the physical factors that affect the higher bulk density, lower porosity and water-holding capacity of the soil because of compaction of the soil [1–10,13,16,28]. Despite our ﬁndings at both soil depths, it is generally claimed that the skidding works cause decrease in organic matter amount in the soil.

[7,9–11,19,21].

4. Conclusions

In this study, we have tried to put forward the impacts of skidding works, which have been carried out for many

years on a skid road in an oak (Quercus petreaL.) stand, on the topsoil properties, forest floor and herbaceous cover. The skidding works that have been carried out caused decrease in the forest floor and the herbaceous cover to a great extent. Furthermore, the skidding has been effective on both soil depths (0–5 and 5–10 cm) which were examined. Compaction of soil with the impact of skidding has caused increase in fine soil weight and bulk density values and decrease in total porosity and moisture equivalent rates on the skid road. Negative impacts of soil compaction have been set forth with many researches. Compaction of soil causes decrease in the permeability and infiltration capacity of the soil, which leads pooling of water on the ground and therefore loss of moisture through evaporation [1–3,5,11–14]. Therefore, root development slows down and subject to this, water and nutrient uptake of the existing plants decreases. Decrease in the total porosity and worsening of soil aeration negatively affect aerobe soil organisms and are also effective on the life activities of other organisms[1,12,19]. Moreover, because of the increasing denitrification, nitrate nitrogen is lost in the atmosphere. Thus, nitrogen losses occur in the soil by this way[1,11]. Decreasing of infiltration and permeability in the soil in the slope areas because of compaction can cause erosion[3,14,15,17,18]. Lessening of the herbaceous cover and forest floor after skidding leaves the soil vulnerable against erosion and forest floor decomposition and mineralization also decreases because of unfavorable soil conditions. Thus, retardation occurs in the nutrient cycle in the forest ecosystem[1,6,9–12,19,21].

Brieﬂy, the long-term skidding works carried out in an oak stand caused noteworthy losses in the herbaceous cover and forest ﬂoor on the skid road. Additionally, soil properties have also changed to a great extent. It is obvious that particularly the changes which occur subject to the soil compaction will cause negative impacts on the water and air economies of the soils on the skid roads. Prompt actions should be taken to prevent and minimize such negative impacts of the skid roads. Especially, the skid roads should not be used for long periods without taking any actions after they are built. Making rehabilitation works[5,29,30]

on the skid roads to retain soil properties which have drastically degraded and which have undergone erosions and, therefore lost their plant cover shall be very useful in terms of protection of the ecosystem.

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pH 5.80a _5.25b _0.042 _*

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