Báo cáo khoa học: " Compaction and soil disturbances from logging in Southern Chile"

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Original article Compaction and soil disturbances from logging in Southern Chile A Iroumé J Gayoso Universidad Austral de Chile, Casilla 853, Valdivia, Chile Instituto de Manejo Forestal, (Received 2 July 1990; accepted le 13 november 1990) Summary — In an andesitic dystrochrept clay forest soil, the effect of a different number of passes of a rubber-tyred skidder on bulk density, total porosity and saturated hydraulic conductivity was studied. Soil samples were taken in undisturbed areas, and under skid trails with 1, 2, 3, 5 and 10 machine passes. Most compaction occurred after the initial few passes, but bulk density also in- creased significantly after more than 3 passes. Increases in bulk density were still important at the maximum sampling depth of 20 cm. Total porosity decreased for all treatments, associated with a re- duction of macropores. The saturated hydraulic conductivity became significantly reduced after the first initial passes. The effect of compaction on tree growth needs to be further studied and quanti- fied. ground-based logging / bulk density / saturated hydraul- soil compaction / soil disturbances / ic conductivity Résumé — Compactage et perturbation du sol après une exploitation forestière au Chili méri- dional. On a étudié l’influence du nombre de passages d’un débusqueur à pneus sur la densité ap- parente, la porosité totale et le coefficient de conductivité hydraulique d’un sol brun andésitique. Des échantillons de sol ont été prélevés dans des terrains non perturbés, et sous des chemins de débar- dage ayant 1, 2, 3, 5 et 10 passages. Le compactage le plus important s’est produit après les pre- miers passages, mais la densité apparente a encore augmenté significativement après le troisième passage. La densité apparente a aussi augmenté jusqu’à 20 cm de profondeur. La porosité totale a été réduite dans tous les cas, associée à une réduction des macropores. Le coefficient de conducti- vité hydraulique a été significativement réduit après les premiers passages. L’effet du compactage du sol sur la croissance des arbres doit être étudié et quantifié. compactage du sol / perturbation du sol / débusqueur à pneus / densité apparente / coeffi- cient de conductivité hydraulique 1 240 000 ha in 1986 (Instituto Forestal, INTRODUCTION 1987). Increased mechanization and the use of heavy machinery in logging opera- In Chile, forestry-related activities have in- tions have caused severe disturbances to creased substantially during the last 15 yr. forest soils, and compaction effects have This is partly due to the growth of the area been widely reported within the country under plantations at an average of 79 000 (Monrroy, 1981; Gayoso, 1982; Gayoso and Iroumé, 1984). ha yr since 1973, reaching more than * Correspondence and reprints
According to Beekman (1987) compac- THE STUDY AREA tion alters the soil’s physical and mechani- cal properties and leads to a less favora- study area is located a approximately The ble condition for plant growth, which in turn 39°44’ S and 73°10’ W, 15 km from the city leads to a decline in site productivity (Ges- of Valdivia in southern Chile. The site has sel, 1981) and reduces the present net a northern aspect with slopes varying be- worth of future timber harvests (Routledge, tween 5% and more than 60%, and eleva- 1987). tions ranging from 110 to 220 m above sea Compaction can extend to a considera- level. ble depth of the soil profile (Moehring, The area was covered with a 25-yr-old 1970) and the major compaction occurs Monterey pine plantation clear-felled dur- during the first passes of machinery (Ad- ing the last winter. A rubber-tired skidder ams and Froehlich, 1981). Upon compac- was used to transport uphill logs to land- tion, soil strength increases while total po- ings. rosity, available water, air content, infiltration rate and saturated hydraulic climate of the area is rainy- The conductivity decrease (Incerti et al, 1987). temperate with a Mediterranean influence As a consequence, tree growth can be re- (Fuenzalida, 1965). Annual rainfall in the duced because of restrictions in root de- city of Valdivia (9 m above sea level) rang- velopment, water supplyand aeration es from 1 752 to more than 2 936 mm (Corns, 1988; Vepraskas, 1988). In addi- (Fuenzalida, 1965). The period between tion, surface runoff may increase and soil May and August concentrates 70% of the erosion be promoted (Sidle, 1980; Stand- 2 340 mm long-term annual average rain- ish et al, 1988). fall (Reyes, 1981).Mean annual tempera- The extension of soil disturbances can ture is 12 °C with a maximum monthly be reduced by designing skid trails prior to mean of 16.9 °C in January, and a mini- harvesting (Froehlich et al, 1981).The in- mum of 7.6 °C in July. Predominant winds tensity can be reduced by harvesting dur- come from the north between April and ing the driest periods of the year, logging September, and from the west between downhill where possible and selecting low October and February. ground pressure equipment (Wingate-Hill geological substratum corresponds The and Jakobsen, 1982). Sometimes dam- "Piedra-Laja" formation, a coastal to the aged soils can be ameliorated by cultiva- metamorphic complex formed mainly by tion (Moehring, 1970). micaceous schists with intercalations of Chilean foresters have become aware quartz lenses (Illies, 1970). of soil alterations, but the degree and ex- to an andesitic dys- Soils correspond tent of the problem has not been widely forest type (Série Correltue) de- trochrept quantified. The objective of this study was veloped from pleistocene volcanic ash de- to assess compaction intensity and the ef- posited on the coastal metamorphic fects on soil dry bulk density, total porosity complex (Gayoso and Iroumé, 1984). and saturated hydraulic conductivity, fol- Apart from the high clay content (40-50%), lowing a clearcutting operation in southern they have a high porosity and high water Chile.
for 24 h to obtain dry bulk density and total po- infiltration rate. TableI presents some of rosity (Lee et al, 1983). the soil’s physical and chemical properties. From the top 12 cm of the soil profile, 6 un- disturbed core samples of 940 cm were also 3 collected in each plot. The samples were satu- METHODS rated and the saturated hydraulic conductivity was measured using a constant head permea- meter, according to Head (1982). Within the logging site, sampling plots were se- lected in undisturbed and disturbed areas. In All intact core samples were collected using this study, areas not used as trails or log land- a double-cylinder hammer-driven core sampler, ings were considered as undisturbed. In dis- and all sample points were randomly selected. turbed areas with a 10 and 20% slope, plots Traffic and sampling occurred during the wet pe- were chosen under skid trails with 1, 2, 3, 5 and riod. Soil water content in undisturbed areas 10 machine passes. In areas with a 10% slope, 84% in surface (0-10 cm deep) and 66% in was the logged volumes in each pass were 2 and 4 the 11-20 cm deep layer. cubic meters (3 and 6 logs respectively), while in areas with a 20% slope the logged volume was 2 m (3 logs). The skidder used to log uphill 3 RESULTS AND DISCUSSION whole trees was a rubber-tyred Caterpillar 518 with the following characteristics: weight: 10 250 kg; tyre sizes: 18.4 x 30", tyre pressure: 170 In areas with a 10% slope, the differences kPa. between the results of soil alterations un- In the top 5 cm of the soil profile of each plot, der trails where the skidder snig logged 2 9 undisturbed core samples of 100 cm were 3 and 4 m respectively, were statistically , 3 collected. In addition, 3 samples of 100 cm 3 non significant, and are presented as be- taken from each of the following depths in were longing to the same data population. the soil profile: 6 to 10, 11 to 15, and 16 to 20 cm. The soil samples were oven-dried at 105 °C Bulk density and total porosity The results in figure 1 show that in areas with a 10% slope, the bulk density in the top 5 cm of the soil increased by 11% after 1 pass, 15% after 2 passes, 21 % after 3 turns, 31% after 5 machine passes, and 45% under trails with 10 skid passes. Bulk density also increased in depth under the skid trails. For example, in areas with a 10% slope, the bulk density increased by 39% between 6 to 10 cm depth, by 34% between 11 to 15 cm, and by 32% be- tween 16 to 20 cm, after 10 machine pass- es. In with a 20% slope, the bulk den- areas sity in the top5 cm of the soil increased by 23% after 1 pass, 32% after 2 machine passes, 37% after 3 turns, 48% after 5 passes, and 60% under trails with 10 skid passes (fig 2). As occurred in areas with a
figures 1 and 2 it can be seen that 10% slope, bulk density also increased in From compaction occurred after the first depth under the skid trails with a 20% most few passes, although bulk density still in- slope. After 10 machine passes, the bulk density increased by 52% between 6 to 10 creased significantly after more than 3 cm depth, 46% between 11 to 15 cm, and passes for all layers. This is slightly differ- 43% between 16 to 20 ent from data presented by Froehlich cm. (1978) and Adams and Froehlich (1981). These increases differ from those pre- sented by Adams and Froehlich (1981) From data obtained in a clay loam soil and Incerti et al (1987) but can be ex- in the Oregon coast range, Sidle and Drli- plained by different soil types and condi- ca (1981) developed a regression equation tions, and logging equipment. Moehring to determine the impact of the number of and Rawls (1970) found that more severe passes and slope gradient on bulk density. compaction occurs from traffic on saturat- These authors found that the slope did not ed than on dry soils. significantly affect bulk density, but they In trails with a 20% slope, the increase concluded that it can be an important fac- in bulk density for all different numbers of tor in the potential level of compaction. machine passes and depths was signifi- This fact was proven in this study, and cantly higher as compared with those ob- the best relationship between bulk density served in trails with a 10% slope. This may (BD in Mg.m as dependent variable, and ) -3 be a consequence of the difficulties that number of machine passes (NP) and slope the skidder found when logging in steep gradient (SG in %) as independent vari- terrains. Under these conditions the ma- ables, for all 4 depths, were : chine slipped continuously and remained for a longer period of time in a given place, puddling and dragging the soil.
disturbed conditions can be expected 18 yr after compaction. However, Went and Thomas (1981) reported that compaction was still severe after 32 yr. Severely com- pacted soils could be retored by ploughing, disking and subsoiling. Due to the existence of the one-to-one The coefficients of determination for all correspondence between bulk density and equations were significant at the α 0.01 = percentage total porosity, total porosity de- level and the standard errors of BD estima- creased after a different number of ma- tions were 0.016 for Eq 1, 0.019 for Eq 2, chine passes associated with increases in 0.017 for Eq 3 and 0.017 for Eq 4. bulk density (figs 1 and 2). A value of 1.10 Mg·m for bulk density -3 for all The decrease in total porosity the top soil layer has been measured in on treatments must be associated with a re- the same area under logging roads and duction of macropores. For this soil, Gayo- landings (Gayoso and Iroumé, 1984). Al- so and Ellies (1984) determined that mac- though it is hazardous to use Eq 1 to ex- ropores (ie > 50 μm) decreased from 28.1 trapolate beyond 10 passes, it is possible to 9.2%, that the percentage of intermedi- to estimate that such bulk density is ate porosity (ie 0.2 to 50 μm) remained al- reached after 50 or 100 machine passes, most invariable, and that micropres (ie depending on the slope gradient. < 0.2 μm) increased from 30.5 to 40.4%, from undisturbed to severely compacted Close to the studied area, growth losses conditions. of up to 30% in tree height have been re- ported associated with severe compaction According to Baver et al (1972), a re- and bulk densities of 1.07 Mg·m (Gayo- -3 duction of macropores below 10% of soil so, 1982). According to Sidle and Drlica volume at matric potentials below 100 cm (1981), bulk density in trails with 4 to 11 water can be considered to be restrictive to passes can be considered as intermediate root growth because of poor aeration and compaction, and this level of compaction increase in soil strength. Jurgensen et al can affect site productivity. The limit of bulk (1979) found that major productivity losses density from which compaction can reduce are associated with poor oxygen availabili- non-capillary porosity and root develop- ty. ment to critical levels for tree growth must The decrease in total porosity is not a be determined for each individual soil type. clear indication of restrictions to root and As be observed from these results, tree growth, and it is certainly not critical can in all cases the major increases occurred for Monterey pine establishment; at least in in the top of the soil profile but they were a soil such as the one studied that has 75% total porosity. The determination of still important at 16-20 cm, suggesting that pore size distribution is essential for future compaction extended deeper. According to studies. this observation, compaction could affect the top 30-40 cm of the soil where a great- er part of the root system of Monterey pine Saturated hydraulic conductivity is distributed (Murphy, 1982). Bulk recover, especially in density can surface layers. Hatchell et al (1970) esti- The results for the saturated hydraulic con- mated by regressions that recovery to un- ductivity (K) of the top 12 cm of the soil are
presented in table II. According to Rogow- with K decreased by 90% af- 20% slope, a sky (1972), Talsma and Hallam (1980) and ter 1 pass, 94% after 2 machine passes, 97% after 3 passes, 98% after 5 passes, Incerti et al (1987) it is possible to assume log-normal and 99% under trails with 10 skid passes. distribution for the data of a each individual treatment. The geometric In spite of the variations of 1-2 orders of mean can then be calculated because it magnitude of K, the higher values of anti- equals the median value for a lognormal log S were not much greater than 2, and distribution, and the antilog of the standard for some of the individual treatments even deviation of the transformed data may be smaller than 2. This value (2) for the index used as an index of variability. of variability has been tentatively suggest- ed by Rogowsky (1972) as an upper limit Associated with an increase of bulk for uniformity of hydraulic conductivity with- a decrease in total porosity, density and in soil series. The values obtained in this the saturated hydraulic conductivity varied study for such an index suggest that Kwas for all treatments. In areas with a 10% relatively uniform. slope, the geometric mean value for K de- creased by 35% after 1 pass, 89% after 2 According to Incerti et al (1987) the me- machine passes, 90% after 3 machine dian and the range for each treatment can passes, 93% after 5 passes, and 99% un- indicate the difference between treat- der trails with 10 skid passes. In areas ments. In the skid trails with a 10 and 20%
with bulk density, the saturat- As the median and also the mean, geo- slope, occurs hydraulic conductivity can also recover. metric mean and the range decreased with ed Perry (1964) estimated that approximately increases in the number of machine pass- 40 yr are required to recover the initial infil- es. tration capacity. Considering that the usual The decrease in hydraulic conductivity rotation period for Monterey pine planta- is related to a decrease in total porosity. tions in Chile is about 25 yr, the recovery The best relationship found between the of Kcould be restricted. geometric mean of K (in m·day and total ) -1 The decrease in saturated hydraulic porosity (TP in %) obtained from the top 12 in increased run- conductivity should result cm soil samples is : off, which could promote erosion and nutrient losses while reducing soil water availability. These effects are now being The coefficient of determination of Eq 5 evaluated in experimental sampling plots. issignificant at the α 0.01 level. = The saturated hydraulic conductivity de- creased by 90% (ie from 2.078 to 0.216 CONCLUSION ) -1 m·day with a decrease in total porosity of only 5% (ie from 75 to 71%). This last The results show that logging operations at value of total porosity was achieved after 1 the studied site have a significant impact to 3 passes. A further decrease in K by on the soil’s physical properties. Increases 92% (ie from 0.216 to 0.018 m·day was ) -1 in bulk density and decreases in total po- associated with an additional decrease in rosity and saturated hydraulic conductivity total porosity of 20% (ie from 71 to 57%). were detected. Most compaction occurred This may be a consequence of a strong re- after the first few machine passes, al- duction of macropores during the first lev- though bulk density increased significantly els of compaction (after 1 to 3 machine after more than 3 passes. Increases were passes). After the initial passes, the reduc- still important at 20 cm depth suggesting tion of total porosity may be caused by a that compaction could affect the top 40 cm decrease of pores of all sizes, which re- of the soil, where a greater part of the root sults in a slower reduction of K. system of Monterey pine is located. Fur- saturated hydraulic conductivi- ther work in this area should at least con- Although sider the top 40 cm of the soil profile and ty is not the only factor that determines determine critical values of bulk density surface runoff, in a first approach it can be above which tree growth can be affected. said that runoff will occur when the rainfall In addition, the effect of high organic mat- rate exceeds K. From rainfall data for the ter content on soil compaction resistance studied area, rainfall events with a recur- under humid conditions must be quantified. rence interval of 20 yr can be estimated at 0.15 m·d and the soil is able to allow the , -1 The observed decrease in total porosity infiltration of such events in areas with less mainly be associated with a reduction must than 2 to 5 skid passes. Because hydraulic in macroporosity, shown by the decrease conductivity determined in situ can be an of hydraulic conductivity. This suggests order of magnitude smaller than results that poor oxygen availability can be the pri- measured from core samples (Topp and mary limiting factor to tree growth. Pore Binns, 1976), runoff may occur more often size distribution analysis is essential for fu- than predicted. ture studies.
Fuenzalida H (1965) Clima. In: Geografía Saturated hydraulic conductivity was Económica de Chile. CORFO, Santiago, found to be markedly reduced with rela- Chile, 99-151 tively low decreases in total porosity, re- Gayoso J (1982) Pérdida de la productividad del sulting in an increased potential for runoff, sitio por efecto del madereo. Actas Reunión erosion and nutrient losses, which can fur- de Trabajo sobre Evaluación de la Productivi- ther affect site productivity. dad de Sitios Forestales, 22-24 April 1982, In Chile, large areas of man-made fo- Valdivia, 284-299 intensely managed. Increasing rests are Gayoso J, Ellies A (1984) Vorbelastung und Ver- mechanization and the use of heavy ma- formung als Folge unterschiedlicher Bewirts- chaftung von einigen Böden Südchiles. Z chinery in forest operations suggests the Kulturtechnik Flurbereinigung 25, 39-46 need to quantify the extension and intensi- Gayoso J, Iroumé A (1984) Soil disturbance ty of soil compaction, and the effect on from logging in Southern Chile. In: Proc tree growth. The natural rate of recovery Symp Effects of Forest Land Use on Erosion and the effect of some cultivation practices and Slope Stability. Environment and Policy must also be analyzed. Institute, East-West Center, University of Hawai, Honolulu, 203-209 Gessel S (1981) Impacts of modern forestry on ACKNOWLEDGMENT forest productivity. Proc XVII IU- continuing FRO World Congress, Japan, 3-19 Hatchell GE, Ralston GW, Foil RR (1970) Soil This work supported by Proyecto Fondecyt was disturbance in logging. J For 68, 772-775 0916-88. Head KH Laboratory Test- (1982) Manual of Soil Pentech, London, 123 p ing. Illies H (1970) Geologia de los Alrededores de REFERENCES Valdivia y Volcanismo y Tectónica en Márgenes del Pacífico en Chile Meridional. Adams PW, Froehlich HA (1981) Compaction of Universidad Austral de Chile, Valdivia, 64 p Forest Soils. USDA Pacific Northwest Ext Incerti M, Clinnick PF, Willatt ST (1987) Pub PNW 217,13 p Changes in the physical properties of a forest Baver LD, Gardner WH, Gardner WR (1972) soil following logging. Aust For Res 17, 91-98 Soil Physics. Wiley, New York, 4th edn Instituto Forestal (1987) Estadisticas Forestales Beekman F (1987) Soil strength and forest op- CORFO, Boletín 1, 100 p 1986. erations. Doctoral thesis, Dept For Tech- Jurgensen M, Larsen M, Harvey A (1979) Forest nique, Agricultural University, Wageningen, Soil Biology-Timber Harvesting Relation- The Netherlands, 168 p ships: A Perspective. USDA For Service Gral Corns IG (1988) Compaction by forestry equip- Tech Rep INT-69, 12 p ment and effects on coniferous seedlings Lee IK, White W, Ingles OG (1983) Geotechni- growth on four soils in the Alberta foothills. cal Engineering. Pitman, Boston, 508 p Can J For Res 18, 75-84 Moehring DH (1970) Forest soil improvement (1978) Soil compaction from low Froehlich H through cultivation. J For 68, 328-331 ground-pressure, torsion-suspension logging Moehring D, Rawls IW (1970) Detrimental ef- vehicles on three forest soils. Res Pap 36, fects of wet weather logging. J For 68, 166- Oregon State University, 12 p 167 Froehlich H, Aulerich D, Curtis R (1981) Design- Monrroy M (1981) Cambios fisico-mecánicos de ing skid trail system to reduce soil impacts los suelos de textura fina por efecto de mad- from tractive logging machines. For Res Lab, tracción animal y mecanizada. Te- Oregon State University, Res Pap 44, 15 p ereo con
PR, Smith RB Ing For Universidad Austral de Chile, Val- sis Commandeur Standish JT, divia, 126 (1988) Impacts of Forest Harvesting on Phys- p ical Properties of Soils with Reference to In- Murphy G (1982) Soil damage associated with creased Biomass Recovery - A Review. Inf production thinning. N Z J For Sci 12, 281- Rep BC-X-301 Pacific Forestry Centre, 24 p 292 Perry TO (1964) Soil compaction and Loblolly Talsma T, Hallam PM (1980) Hydraulic conduc- pine growth. USDA For Sevr Tree Planters tivity measurements of forest catchments. Notes 69, 9 Aust J Soil Res 30, 139-148 Reyes JC (1981) Caracteristicas de las precipit- Topp GC, Binns MR (1976) Field measurement aciones de Valdivia: 1960-1976. Tésis Uni- of hydraulic conductivity with a modified air- versidad Austral de Chile, Valdivia, 48 p entry permeameter. Can J Soil Sci 56, 139- Rogowsky AS (1972) Watershed physics: soil 147 variability criteria. Water Res 8, 1015-1020 MJ (1988) Bulk density values diag- Vepraskas Routledge RD (1987) The impact of soil degra- nostic of restricted root growth in coarse- dation on the expected present net worth of textured soils. Soil Sci Soc Am J 52(4), 1117- future timber harvests. For Sci 33, 823-834 1121 Sidle RC (1980) Impacts of Forest Practices on Went S, Thomas BR (1981) Effects of skid Surface Erosion. Pacific Northwest Extension roads on diameter, height and volume growth Publ PNW 195, 15 p in Douglas fir. Soil Sci Soc Am J 45, 629-632 Sidle R, Drlica D (1981) Soil compaction from Wingate-Hill R, Jakobsen B (1982) Increased logging with a low-ground pressure skidder in mechanisation and soil damage in forests - a the Oregon Coast ranges. Soil Sci Soc Am J review. N Z J For Sci 12 (2), 380-393 45, 1219-1224