The distribution and frequency of damage to roadside trees in low-volume road construction

Majid Lotfalian·Mehran Nasiri

Introduction

Forest road networks are important in transportation of timber and forest management.Road construction in forest areas especially in mountains typically causes the destruction of natural habitats(Bernhardt-Romermann 2006;Spooner and Smallbone 2009;Farhig and Rytwinski 2009;Mullerova et al.2011;Bargali et al.2014,2015).Some adverse effects are direct and immediate(Joshi et al.1997;Kittur et al.2014;Rana et al.2015).The loss of the part of forest on which the road is built causes direct and immediate consequences such as damage to tree stands and grass cover(Benitez et al.2010;Avon et al.2013),damage to hydrology and increasing sediment delivery(Croke et al.2005),slope instability and landslide creation(Borga et al.2005),soil mass wasting and creep.Additional gradual and indirect effects can be caused by forest roads.Habitat fragmentation(Benitez et al.2010),water and soil pollution due to forestry machinery traf fic(Cornish 2001),and avoidance by birds due to increased noise are the most frequent examples.

Road construction on natural hillsides requires earthworks.Despite careful engineering of hillside length,slope gradient,and right of way,the loss of habitat causes public discontent and criticism.One of the main sources of adverse impact is steep slopes(Cao et al.2010;Melemez 2013).On highslopestheef ficiencyofmachinessuchasbulldozersand hydraulic excavators is reduced(Parsakhoo 2008;Ozturk et al.2010;Caliskan 2013).Working on steep or rock slopes can reduce operator ef ficiency,cause failure to comply with design standards,andultimatelyresultinfaulty construction(Heralt2002;Parsakhoo2008).Increasingoperatorerrorcan increase rock fall due to rock mass collapse and soil mass movement during road construction.Several studies have been accomplished aboutformation,rock mechanics(Marquinezetal.2003;Dorrenetal.2005;Perretetal.2004)and preventing rock falls conditions(Brauner et al.2005;Stoffel et al.2006).They stated that analysis and simulation of rockfall to investigate rockfall trajectories and management of rock fall using predictive GIS-based model can reduce the environmental destruction.In other studies,the effects of earthwork on tree stands during forest road construction were examined(Gumus et al.2009;Ozturk et al.2010;Caliskan 2013;Melemez 2013).In these studies,the amount of damage(bending,crushing and wounding)to the trees were studied according to the distance from fillslope,hillside gradient and road construction machinery such as hydraulic excavator and bulldozer.Gumus et al.(2009)stated that 90.48%of damaged trees were in the first 10 m afterthebeginningofthe fillslopeslope.Averageinjuryarea ofthedamaged trees wascalculatedas1081 cm2forthe first 10 m from the fillslope slope and an injury area of 1463 cm2was calculated for between 11 and 23 m on the fillslope slope.Hillside gradient and materials are very effective in treesdamageonroadside.Cohesionofsoilandrockparticles canincreasetheslopestability(BehniaandTabatabai2009).Also,thegradientofslopeisveryeffectiveinspeedoffalling rock and soil masses.Due to the importance of the slope gradient and hillside materials,the purpose of this study was to investigate the distribution and frequency of various damage(bending,crushing and wounding)to the trees adjacent to forest roads according to the type of hillside materials involved(soil and rock)and hillside gradient.

Materials and methods

and sliding of construction material were studied(Fig.1).Plots with variable width(due to damaged trees)and 50 m length(due to road slope)were considered in 17 km constructed road.Forty plots were systematic randomly selected for hillside with clay soil and also 40 plots for rock slopes.To measure the environmental damage,damaged tress(diameter at breast height(DBH)more than 8 cm)on the roadside were counted.To investigate the slope gradient on the rate of damage,plots were chosen in slope classes of 0–15%,15–30%,30–45%and more than 45%.Plot width was considered variable to determine the damaged trees distribution.Therefore,the distance from fillslope(out of earthwork area)to damaged trees were measured with a tape and damage frequency were recorded(Gumus et al.2009).The results were analyzed by SPSS and JMP4 software.So the effect of materials type(soil or rock)and slope classes on the rate of environmental damage for each treatment(type of damage)were studied using t-student test and One-way ANOVA analysis in SPSS,respectively.In order to investigate the distribution of treatments(damaged trees according to the distance from the fillslope)the Distribution command of JMP4 software was used and the results were analyzed.

Results

The result of frequency data indicated that earthwork caused fewer damage to adjacent trees and most of the damage was wounding.Also the frequency of tree wounding and crushing on the verge of rock slopes was more than clay soil hillsides(Fig.2).There was a

Study area

This study was conducted in a road of Caspian forests(in northern forests of Iran).Trees on the roadside were mostly Alder and Hornbeam.The study area was located in mountainous regions,general slope was normally less than 60%and the altitude was between 1100 and 1820 m.In these regions,construction of roads is dif ficult due to changes in topography.The type of soil was brown soil and in high altitude the soil depth w about 5–10 cm.In these region the road construction progress would be slow due to the presence of stone walls.Also the use of advanced machinery is not recommended due to economic reasons(low work volume)and environmental concerns.Therefore,most of the earthwork is performed by Komatsu D135 bulldozer and in some circumstances hydraulic excavator.

Measurements

Fig.1 Damaged trees due to road construction in forest areas

In this research,some environmental damage such as bending,crushing and wounding of trees due to con fliction signi ficant difference between trees crushing and wounding based on materials type(p＜0.05),but this difference was not signi ficant for trees bending(Table 1).

Hillside gradient has a large impact on the amount of damage to adjacent stands.With increasing the slope,the amount of damaged trees would be increased and its impact on trees crushing and wounding would be greater(Fig.3).So that there was a signi ficant difference(p＜0.05)between slope classes of more than 45%and other classes in terms of damage associated with crushing(except slope class of 30–45%)and wounding.But this difference is not signi ficant for trees bending in different slope classes.Damage to trees on the hillsides with a slope of＞45%were 2,8.5 and 2.3 times more than hillsides with a slope of＜15%for bending,crushing and wounding,respectively(Table 2).

By monitoring the distribution of damage and distance from the fillslope it could be found that damage range was different due to its types and the maximum distribution was allocated to trees wounding.So up to 8 m from fillslope wounded trees could be observed.The measurements indicated that most damage due to collision of material with trees at the edge of road had occurred in 4,5 and 8 m from the fillslope for tree bending,crushing and wounding,respectively(Fig.4).Statistical comparison of the damage distribution according to materials type(rock or clay soil)showed that there was a signi ficant difference for wounding treatment(p＜0.05).Meanwhile,there was no signi ficant difference in other two treatments(trees bending and crushing distribution) depending on materials types(Table 3).

Fig.2 The frequency of damaged trees according to hillside materials

Table 1 ANOVA table for statistical comparison of damaged trees on the roadside according to hillside materials

Discussion

Road construction in mountainous and forest areas will cause irreparable damage(Cao et al.2010;Mullerova et al.2011).Removal and movement of soil to construction of new path can cause environmental ruination.In most cases,damage to adjacent trees have occurred due to falling rock and mass of soil during road construction which is in agreement with Gumus et al.(2009),Ozturk et al.(2010),Melemez(2013)and Caliskan(2013).

During earthworks by hydraulic excavator or bulldozer,there is a high possibility of sudden segregation of stone stratum from the cut slope.Clay soil can be separated from hillsides smoothly.The collapse type of this stone stratum based on cleavage and fraction angle would cause tree crushing and wounding at the edge of rock slopes more than hillsides with clay soil component.

Rock and soil masses which are falling will increase in speed due to high slope and cause damage to adjacent trees by the road.Higher slope,coarse aggregates and larger stone could cause more trees crushing in close distances.The results showed that trees crushing on slopes more than 45%were more than lower slope.The possibility of various damage occurrence on higher slope is greater than lower ones because of more collision.Therefore,according to the results it could be found that by increasing the slope,damaged trees on the roadside will be increased.The result is consistent with Caliskan(2013).By examining the bulldozer and hydraulic excavator function on different slopes they have indicated that the damage to adjacent stands on higher slope were increased due to declining in operator accuracy.On hillside with slope of 30–50%,they measured 21 and 33%damaged trees for hydraulic excavator and bulldozer,respectively.This percentage of damage on hillside with slope of 51–80%has become 27 and 44%for hydraulic excavator and bulldozer,respectively.Thus,hillside gradient could be undoubtedly introduced as the major factor of nature destruction in road construction.

Damage distribution to the tree stands at the road buffer is highly affected by road construction machinery and operator accuracy,materials type and terrain slope.The type and intensity of damage will vary from road into the stands.During earthworks when rocks fall,after traversing some distance these materials would be stopped bycollision with different obstacles.At the beginning of the route due to the high speed and intensity of collision,the possibility of trees bending and crushing is high(in 4 and 5 m distances)and after traversing some distance(8 m)by decreasing in speed and finally kinetic energy and converting to potential energy(K=U)the collision intensity will decline and wounded trees will be more visible.The result is in agreement with Gumus et al.(2009).They stated that 90.48%of damage to the adjacent stand had occurred in the first 10 m of the fillslope.Also considering the effect of materials type(stone or clay soil)soil masses would collapse and stop after traversing some distances butthe stones could traverse longer distances due to more strength.Hence,stone could traverse longer distances than soil masses and cause more tree damage in further distances from the rock slopes.

Fig.3 The rate of damage to trees according to hillside gradient

Table 2 Statistical comparison of different types of damage to the trees according to hillside gradient

Fig.4 Distribution of tree damage according to the distance from fillslope:a Bending,b crushing and c wounding

Table 3 ANOVA table for statistical comparison of damage distribution depending on materials types

Conclusion

Road construction in mountainousareascan cause irreparable damage to the trees in a buffer of roadside.It must also be noted that according to the close to nature method(usual method in Iran),forest engineers emphasis that presence of road is essential for forest management.At least in the mountain forests of northern of Iran many operations related to industrial wood transportation are not possible without using roads.Therefore,to improve wood production and providing required timber for markets,the acceptance of damage could economically be justi fied.However,forest engineers by using various techniques of road designing and construction seek to minimize these bad consequences.In order to reduce environmental effects,routing and construction of roads in areas with low slope and terraces is recommended.Also,using suitable machines for earthworks and highly skilled operators are essential.If during routing of road some places were diagnosed as negative and dangerous points,it is better to use special tree covers or obstructions(wooden obstruction and synthetic holder)in order to prevent the collision of stones and soil masses.

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