Forest Ecology and Management, 26 (1989) 207-213 207 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Impact of Logging Equipment on Water Infi ltration Capacity at Olmotonyi , Tanzania

R.E.L. OLE-MEILUDIE and W.L.M. NJAU 1

Department of Forest Engineering, Faculty of Forestry, Sokoine University of Agriculture, P.O. Box 3012, Morogoro (Tanzania)

(Accepted 18 November 1987)

ABSTRACT

01e-Meiludie, R.E.L. and Njau, W.L.M., 1989. Impact of logging equipment on water infiltration capacity at Almotonyi, Tanzania. For. Ecol. Manage., 26: 207-213.

Assessment and comparison of the influence of compaction caused by two types of logging equipment, a farm tractor and a manually pulled sulky, on water infiltration capacity was made in two Cupressus lusitanica compartments, under wet conditions.

There were significant increases in soil bulk density for wheel-rutted and log-compacted sites during tractor extraction, with very small changes in density for the sulky-logged areas. Water infiltration rates were more significantly reduced in the tractor than the sulky-harvested areas, with more reduced rates in the wheel ruts than log-compacted sites. Infiltration rates decreased compared to increased bulk density, suggesting increased erosion potential with the degree of compaction.

There was a significant positive correlation between infiltration rate and litter depth, with higher rates for the light (sulky) than for the heavy (tractor) logging equipment. The results suggest that the use of heavy logging equipment, especially on soils with low bearing strength, increases soil compaction and may lead to increased erosion potential.

INTRODUCTION

The use of heavy logging equipment , especially g round-based equipment , in th inn ings has been cri t icized pr imar i ly because of damage caused by such equipment , to residual t rees as well as to the soil. Damage to the trees may cause actual reduct ion of po ten t ia l growth or actual loss of wood due to wood- ro t t ing fungi in t roduced as a result of s tem or root wounds crea ted (Fries, 1973; Aulerich, 1976; Heij and Leek, 1981 ). Soil damage is due bo th to compac t ion and to removal of soil organic mat ter . These soil d i s turbances result in changes

1Present address: Forest Division, Ministry of Natural Resources and Tourism, P.O. Box 426, Dar es Salaam, Tanzania.

0378-1127/89/$03.50 © 1989 Elsevier Science Publishers B.V.

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of soil properties which often cause reduction of tree growth (Aulerich, 1976; Lockaby and Vidrine, 1984; Jakobsen and Greacen, 1985).

The degree of soil compaction following mechanized harvesting will vary with soil texture, soil moisture, ground pressure, and vibration of the vehicle (Shoulder and Terry, 1978; Heij and Leek, 1981). Compaction increases soil bulk density and decreases macropore space. The increase in soil density is associated with slow movement of water, poor aeration and greater mechanical resistance to root growth (Hatchell et al., 1970; Moehring, 1970; Wackentin, 1971; Dickerson, 1976 ). The increased bulk density can also result in increased erosion potential, due to reduced infiltration capacity (Patric, 1980).

Most of the compaction is due to the weight of the machine and the shear force required to skid the load, although compaction under the skidded logs themselves is relatively minor. Studies carried out in the United States, for rubber-tired skidders, have reported that for loamy sand to silt clay loam the bulk densities of wheel-rutted soils increased an average of 20% to 1.55 g cm -3, while the increase was 10% for the soils between the ruts which were com- pacted by the movement of logs (Dickerson, 1976). Furthermore, percolation has been shown to decrease with increase in bulk density (Gumbs and Wack- entin, 1972; Dickerson, 1976). Organic matter, which can sometimes influence infiltration rate, tends to become depleted during skidding hence reducing in- filtration rate.

Only limited information exists on soil compaction and disturbance during harvesting operations in Tanzania (e.g. Maganga and Chamshama, 1984). Furthermore, no information is available on the influence of soil compaction on water infiltration under forest soil conditions following harvesting opera- tions. This information is important since most forest plantations are located in water catchment areas (Lundgren, 1978). This study was to assess and com- pare the influence of compaction caused by logging vehicles on water infiltra- tion capacity under different logging conditions.

MATERIALS AND METHODS

The study was conducted in Sokoine University of Agriculture (SUA) Training Forest, at Olmotonyi, Arusha, Tanzania. The forest is located ap- proximately 1400-2000 m above sea level, and the mean annual rainfall is about 1000 mm. The soils are of volcanic origin, and can be generally described as very fertile and highly erodible when disturbed. They are extremely powdery and dusty during the dry season. The soil texture is sandy loam (Lundgren, 1978). Data were collected in February/March, 1985 at the beginning of the rainy season, under fairly wet conditions.

Soil compaction was determined in two Cupressus lusitanica Mill compart- ments, one for clearfelling and the other for second-thinning. The clearfelling compartment, 25 years old, had a stand density of 540 stems ha-1 (SPH); stem

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sizes averaged about 25 cm diam. at breast height (DBH). The surface was sparsely covered with vegetation and litter. On the other hand, the thinned compartment, 14 years old, with a stand density of 1200 SPH and stems aver- aging about 16 cm DBH, had more vegetation and litter cover. A rear-wheel- driven Ford 6600 farm tractor (equipped wi~h a rear-mounted double-drum winch) with an operational weight of 2737 kg was used to skid logs from the clearfelled compartment. In addition, a 25 kg manually pulled sulky was used to harvest logs from the thinned compartment. In each compartment, six skid trails were selected systematically, starting from one end of the compartment boundary. The skid trails were parallel to one another and perpendicular to the contour.

With core samplers, 8 soil samples (4 observation points, 2 samples from each ) for bulk-density determination were taken per skid trail 10 cm below the surface of mineral soil. The samples were collected at intervals of 30 m, from the wheel-rutted soil, log-compacted soil between the wheel ruts, and adjacent undisturbed soil (2 m from the skid trail). The core samples gave an estimate of volume. They were oven-dried at 105 °C for 24 h.

Water infiltration rate was determined, in each of the observation points where bulk density measurements were made, by driving a locally made core (10 cm diam., 15 cm height) into the ground to about 2.5 cm below the surface. A known volume of water, 450 ml, was poured into the core and the time taken for the water to infiltrate into the soil was recorded using a stopwatch; three measurements were taken in each point. Infiltration rate (cm min- 1 ) was de- termined as:

volume of water in the core (cm ~)

infiltration time (min) × core area (cm 2 ) ( 1 )

Ground disturbance along the skid trails was assessed based on the extent of organic matter depleted by measuring litter depth along a vertical cut made in the soil. Mean litter depth for the disturbed and undisturbed sites was determined.

RESULTS AND DISCUSSION

Data on logging equipment and operational characteristics are summarized in Table 1.

Bulk density

Average bulk density (Db) in wheel-rutted, log-compacted and undisturbed sites for both extraction equipment is summarized in Table 2.

Comparing the average Db for tractor and sulky wheel-rutted sites indicated a statistically significant difference, with an increase for tractor extraction. The study also indicated significant differences in Db for the wheel-rutted and

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TABLE 1

Logging equipment and operational characterist ics

Clearfelled compar tmen t T h i n n e d compar tmen t

Equipment used Ford 6600 t ractor Sulky Weight (kg) 2737 25 Extract ion method Shortwood skidding Shortwood skidding Driver 's experience, years 4 - - Average skid-trail 38 14

spacing (m)

TABLE 2

Average bulk density (Db; g cm -3) in wheel-rutted, log-compacted and undis turbed sites

Site Tractor extract ion Sulky extract ion

Db c v + Increase + + (To) Db c v + Increase (%)

Wheel-rut ted 0.710 8.47 28.9* 0.627 2.99 1.6 n.s Log-compacted 0.640 5.59 16.15" 0.619 2.80 0.32 n.s Undis turbed 0.551 6.60 - - 0.627 2.99 - -

+ cv, coefficient of variation, %. + +, percentage increase of bulk density in relat ion to undis turbed sites. *, significant at P < 0.05, paired t-test; n.s., not significant.

log-compacted sites for tractor extraction, suggesting the effect of vehicle ground-pressure and vibration on the soil. These findings are similar to those reported by Dickerson (1976).

Water infiltration rate

Mean water infiltration rates (I) for wheel-rutted, log-compacted and un- disturbed sites are shown in Table 3. Tractor extraction resulted in greater reduced I than did sulky extraction, with significant differences in reduced rates between the wheel-rutted and log-compacted sites. The reduced rates could be due to (i) increased bulk density (Table 2 ), as reported also by Gumbs and Wackentin (1972), and /or (ii) surface cementing due to formation of a sealed layer on soil surface which resists water movement across the surface. The variation of infiltration rate with bulk density is shown in Fig. 1, the re- lationship being t ransformed logarithmically as follows:

exp (16.56- 28.15Db) I = 0.457 × -0 .03 (2)

1 + exp ( 16.56 -- 28.15Db )

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T A B L E 3

Average water inf i l t ra t ion ra tes (I; cm m i n - 1 ) for wheel - ru t ted , log-compacted and und i s tu rbed si tes

Site T rac to r ex t rac t ion Sulky ex t rac t ion

I c v + D e c r e a s e + + ( % ) I c v + Decrease ++ (%)

Whee l - ru t t ed 0.060 51.0 83.8* 0.315 6.0 4.5 n.s. Log-compared 0.120 63.0 67.6* 0.319 6.3 3.3 n.s. U n d i s t u r b e d 0.370 19.0 - - 0.330 7.8 - -

+cv , coeff ic ient of var ia t ion, %. + +, percen tage decrease inf i l t ra t ion rate in re la t ion to und i s tu rbed sites. *, s ignif icant at P < 0.05, pa i red t- test; n.s., no t s ignif icant .

7

g

H

0.49

0.40

0.31

0.22

0.12

0.03 Cj , , i u i i I

0.49 0.56 0.62 0.69

-J Bulk density g cm

Fig. 1. Variation of infiltration rate as a function of bulk density.

' 0.76

The decreasing I with increasing DB could be due to possible changes in the volume, size, shape and distribution of voids caused by compaction.

Organic matter

Organic matter/litter depth was greater for sulky than for tractor-logged areas (Table 4 ). Water infiltration rate increased linearly with litter depth, as

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TABLE 4

Average litter depth (L; cm) for tractor and sulky extraction

Sites Tractor extraction Sulky extraction

L cv + L cv +

Wheel-rutted 0.14 21.4 4.57 40.9 Log-compacted 1.16 26.7 4.87 43.5 Undisturbed 5.03 47.5 5.10 54.5

+ cv, coefficient of variation, %.

follows:

I = 0.067+0.056Db; r 2 ---- 0.89 (3)

The increase could possibly be due to increased porosity, and reduced surface ceiling with increased organic content of the soil. Removal of organic matter could also result in reduced site productivity.

CONCLUSIONS

The following main conclusions can be drawn from this study: Soil compaction, in skid trails, due to tractor-extraction caused significant

increases in soil bulk density, especially on wheel ruts. The resulting compaction substantially reduced water infiltration rates. The extent of soil surface disturbance, especially removal of organic matter,

may result in greater erosion potential due to reduced infiltration rate. Site productivity may also be reduced as a result of surface disturbance.

The use of less-heavy logging equipment would be desirable, particularly in soils with a low bearing strength.

REFERENCES

Aulerich, D.E., 1976. A survey of horse loggers in Oregon. Forest Engineering Department, Oregon State University, Corvallis, 4 pp.

Dickerson, B.P., 1976. Soil compaction after tree-length skidding in northern Mississippi. Soil Sci. Soc. Am. J., 40: 965-966.

Fries, J., 1973. Thinning - - why and how? In: Thinning in the Forestry of the Future: Royal College of Forestry, Stockholm, Res. Notes No. 69, pp. 1-18.

Gumbs, F.A. and Wackentin, B.P., 1972. The effect of bulk density and initial water content on infiltration in clay soil samples. Soil Sci. Soc. Am. Proc., 36:720 pp.

Hatchell, G.E., Ralston, C.W. and Foil, R.R., 1970. Soil disturbance in logging. Effects on soil characteristics and growth of Loblolly pine in the Atlantic coastal plain. J. For., 68: 772-775.

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Heij, W. and Leek, N.A., 1981. Impacts of wood harvesting technology on soil and vegetation. In: Proc. XVIIth IUFRO World Congress, 6-17 September 1981, at Kyoto, Japan. Japanese IUFRO Congress Council, Interdivisional vol., pp. 21-32.

Jakobsen, B.F. and Greacen, E.L., 1985. Compaction of andy forest soils by forwarder operations. Soil Till. Res., 5: 55-70.

Lickaby, B.G. and Vidrine, C.G., 1984. Effects of logging equipment on soil density and growth and survey of young Loblolly pine. South. J. Appl. For., 8: 109-112.

Lundgren, B., 1978. Soil conditions and nutrient cycling under natural and plantation forests in Tanzanian highlands. Dept. of Forest Soils, Swedish Univ. of Agricultural Sciences, Rep. For. Ecol. For. Soils, 31: 1-426.

Maganga, S.L. and Chamshama, S.A.O., 1984. Impacts of wood harvesting on soil and the residual trees in plantations on Mount Meru, Tanzania. Morogoro,.Tanzania, Div. For. Rec. No. 32, 13 pp.

Moehring, D.N., 1970. Forest soil improvement through cultivation. J. For., 68: 328-331. Patric, J.H., 1980. Some environmental effects of cable logging in Appalachian forests. USDA For.

Serv. Northeast. For. Exp. Stn. Gen. Tech. Rep., NE-55. Shoulder, E. and Terry, T.A, 1978. Dealing with site disturbances from harvesting and site prep-

aration. In: T. Tippin (Editor), Principles of Maintaining Productivity on Prepared Sites. Mississippi State Univ. Press, New Orleans, pp. 85-97.

Wackentin, B.P., 1971. Effects of compaction on content and transmission of water in soil. In: Compaction of Agricultural Soils. Proc. ASAE, 126: 146-147.