Assessment and demarcation of trail degradation in a nature reserve, using GIS: case of Bukit Timah Nature Reserve

land degradation & development

Land Degrad. Develop. 18: 500–518 (2007)

Published online 7 March 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ldr.793

ASSESSMENT AND DEMARCATION OF TRAIL DEGRADATIONIN A NATURE RESERVE, USING GIS: CASE OF BUKIT

TIMAH NATURE RESERVE

K. CHATTERJEA*

National Institute of Education, Nanyang Technological University, 1, Nanyang Walk, Singapore 637616

Received 4 May 2006; Revised 15 November 2006; Accepted 17 November 2006

ABSTRACT

With a significant rise in popularity of nature areas, particularly in urban settings like Singapore, Nature Reserves are beingincreasingly opened for public recreational use. In the Bukit Timah Nature Reserve (BTNR), the only remnant primary rainforest reserve in Singapore, trail networks are being expanded to meet this growing public demand. The physical condition of thepresent trail networks was assessed by monitoring the changes in surface compaction, soil moisture, infiltration rates, soilorganic matter content, root density, litter cover and rill development. These parameters were compared with similar dataobtained from undisturbed forested slopes to analyse the degree of changes brought about by trail usage. Significant changesoccurred in all measured parameters, indicating observable degradation of the trails, particularly on vulnerable slopes. Thesechanges are due to the heavy and increased use of the forest by visitors. Penetration resistance and shear strength of the topsurface layers of the trails are important indicators of trail degradation status and these have been plotted, using GIS, todemarcate trails under different levels of stress. This field monitoring provides a relevant local assessment of trail conditions.It has potential for use in decision-making in future planning and forest management under similar site conditions.Copyright # 2007 John Wiley & Sons, Ltd.

key words: forest trail degradation; surface penetration resistance; surface shear strength; hazard mapping using GIS; trail monitoring;

recreational use of forests; forest management; Singapore

INTRODUCTION

Across the globe, the demand for eco-based tourism and intensive use of recreational areas has increased due to

expanding populations, increased income, leisure time, mobility and consumer demands and choices (Dotzenko

et al., 1967; Poon, 1990; Sutherland et al., 2001). This evolution of tastes has produced growing pressures on

natural landscapes, adversely affecting the natural habitat conditions and causing degradation. The increasing

popularity of outdoor recreation has led to greater and more widespread ecological impacts on natural ecosystems

(Lynn and Brown, 2003). The fastest growing recreational activities are associated with trail use (Lynn and Brown,

2003). Trail degradation is one of the most evident consequences of expanding visitor numbers in nature parks.

While trails help to confine visitors to selected sites thereby minimising negative impacts, additions to the trail

network are an inevitable response to the increased movement of people within the forest. Trampling on trails alters

the soil surface characteristics, mechanical properties and hydrophysical behaviour which lead to greater on-trail

erosion and changes in the micro-climate of the forest under-storey. Over time, the concentration of such activities

on pre-defined trails results in extensive surface degradation and wildlife habitat disruption. As the recreational

value of nature trails grows with public engagement in outdoor activities (Bhuju and Ohsawa, 1998), both nature

trail users and park managers need to understand the effects of human trampling. They will then be more able to

*Correspondence to: Dr K. Chatterjea, National Institute of Education, Nanyang Technological University, 1, Nanyang Walk, Singapore637616.E-mail: [email protected]

Copyright # 2007 John Wiley & Sons, Ltd.

ASSESSMENT AND MAPPING OF TRAIL DEGRADATION IN A NATURE RESERVE 501

protect the forest ecosystem byminimising the negative impacts of trail usage. Hence, it is important to examine the

impact of recreational hiking on soil hydrophysical variables as well as to identify indicators that can be used by

land managers to assess the degree of stress imposed by recreational impacts (Sutherland et al., 2001).

This paper analyses the degree of trail degradation in Bukit Timah Nature Reserve (BTNR) of Singapore, a forest

that has over the years gained popularity as a leisure destination. Taking the forest soil surface as the original,

undisturbed condition of BTNR, the changes in surface conditions along the forest walking trails and the degree of

degradation along the designated, well-used forest paths are examined. Measured values of penetration resistance

and shear strength, infiltration rate and organic carbon content (Gardner and Chong, 1990) of the top surface soil are

analysed to test the hypothesis that an increase in trail use leads to increased surface soil compaction. Using analysis

of variance (ANOVA), the paper examines soil responses to trampling, determining if there is a significant difference

in the degree of soil degradation between trail, trail-side and forest. Finally, the paper also seeks to identify and map

the areas of high impact using GIS, to assist action on trail management by park managers.

The 164 ha BTNR is mostly lowland dipterocarp forest, some of which is primary rainforest. The actual forested

area of 75 ha has a network of 11 trails totalling 8 km in length running through the forest, sometimes across steep

slopes, leaving little of the area untouched (Figure 1). Many of these trails are soil covered, although in the course of

surface management by the rangers, some parts have been hardened with rocks, steps, or even covered with

boardwalks. On stretches with natural surface covers, degradation is visible and trails are widening into the

adjoining forest. During rainfall events, high infiltration rates occur on the forested slopes while the compacted

parts of trails act as ephemeral headwater streams, with high soil erosion.

METHODOLOGY

To assess the extent of trail degradation, trail surface conditions were observed from three perspectives: (a) surface

protection indicators, (b) stress impact factors and (c) response indicators. Using these indicators, individual trails

were assessed in terms of their hazard gradation.

Fieldwork was conducted between July 2004 and January 2006, which included two Northeast monsoon seasons.

Maximum daily temperatures commonly reached 298C and relative humidity within the study site remained close

to 100 per cent. To quantify the impact of hiking on soil properties, a post-impact, systematic transect-oriented

sampling framework covering forest, trail-side and trail segments was employed. Following park-designated hiking

trails, measurements were taken along transects through forest, trail and trail-sides, mostly at regular 100m

intervals. At each of the sites, where possible, three measurements were collected—on-trail, trail-side and forest.

The occurrence of excessive tree roots or gravel (bedrock outcrops), however, led to minor deviations from the

regular 100m sampling interval. Sampling was not possible at some sites due to constraints such as steep slopes and

inaccessible terrain (e.g. rocky paths). Table I summarises the types of data collected to assess the condition of the

trail, trail-sides and forest segments in the study area.

This study analyses the post-impact changes in the physical characteristics of the surface conditions and argues

that in comparison with the forest sites (used as a control), on-trail and trail-side sites have been and/or are in danger

of being severely degraded.

Protection of the forest surface was determined through observation and measurements of canopy covers along

forest paths through photogrammatic records of the overhead canopy cover. Surface litter covers on trails were also

determined through the use of surface grids. Together these provided indications of protection against surface

disturbance from either exposure or trampling.

To record surface compaction shear strength of the soil surface was measured using the hand-held Pilcon Vane

Tester. The BS1377 calculation, which divides the torque required to shear the soil by the surface area of the

cylinder of soil sheared by the vane blade (New Zealand Geotechnical Society, Inc., 2001), was adopted. The dial

readings were recorded and the absolute shear strength values were later determined by multiplying the readings

taken from the Pilcon Vane Tester by the given constants from the BS1377 calculation. Theoretically, the forest

sites should present the least resistance and hence lower shear strength while trails and trail-sides should record

higher values. Sutherland et al. (2001) reported that this strength increase comes about through a combination of

Copyright # 2007 John Wiley & Sons, Ltd. LAND DEGRADATION & DEVELOPMENT, 18: 500–518 (2007)

DOI: 10.1002/ldr

Figure 1. Bukit Timah Nature Reserve and the trails


DOI: 10.1002/ldr

502 K. CHATTERJEA

Table I. Data collected to measure trail degradation in Bukit Timah Nature Reserve

Observation Location Sites Method/instrument used

Surface protection indicatorsCanopy cover (%) T 33 Photogrammatic methodLeaf litter cover (%) T 36 Grid for calculating percentage of litter cover on surface

Surface stress indicatorsPenetration resistance (kPa) Total 116 Cone penetrometer

F 34TS 40T 42

Vane shear strength (kPa) Total 111 Hand vane shearF 36TS 36T 39

Response indicatorsOrganic carbon (%) Total 30 Loss-on-ignition

F 10TS 10T 10

Infiltration capacity (cmmin�1) Total 69 Double-ring infiltration methodF 5TS 22T 42


processes such as compaction by trampling and/or erosion with the removal of the surface horizon, and exposure of

a more resistant subsurface horizon. This would reduce the infiltration rates and increase the frequency of overland

flow generation that may overcome the increased surface strength and lead to rill incision.

Compaction of the surface layers was also measured using a hand-held cone penetrometer, with standard cone

tips. Cone penetrometers have been extensively used for detection of compacted soil layers (Rowell, 1994; Ziegler

et al., 2001; Motavalli et al., 2003). The principal advantages of using this method are its ease and speed of use,

potential relationship with soil physical conditions for root elongation and capacity to measure spatial variation in

surface and subsoil compaction (Motavalli et al., 2003). The penetrometer provides an index of normal strength,

termed penetration resistance for the upper soil depths (Ziegler et al., 2001). Maximum cone index (CI) readings

were taken directly off the dial gauge and recorded at depths of 2.5 cm, 7.5 cm, 15 cm and 22.5 cm, although for this

analysis only the top 2.5 cm readings (representing the surface condition) will be considered. Soil penetration

resistance in general should increase with trampling intensity. Liddle (1975) observed a linear relationship between

penetration resistance and trampling intensity on soils in a subtropical dry sclerophyll forest near Brisbane (Talbot

et al., 2003). It is thought that there should be significant differences in penetration resistance on surface soils

between forest, trail-side and trail.

Surface compaction through trampling is expected to influence the infiltration rate of the surface soil. Infiltration

tests were conducted using the double-ring method to determine this rate on forest, trail and trail-side sites.

Forest, trail and trail-side samples were collected along the same transects at selected trails for testing of organic

carbon as well as soil textural characteristics. In total, 12 random soil samples were taken from Dairy Farm Loop,

North View Path, Catchment Path as well as Cave Path (Figure 1). These samples (six from the forest and six from

the trail) were taken at topsoil depths in order to determine the soil textural characteristics. A further 30 random

samples were obtained at topsoil depths (forest: 10, trail: 10, and trail-side: 10) to determine the amount of organic

carbon content in the soil. The trails, and the adjoining trail-sides in Bukit Timah, were also monitored for changes

in surface conditions and these changes were recorded.


DOI: 10.1002/ldr

Extent of canopy protection over trails in BTNR

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Mean cover: 84.6%

Figure 2. Extent of canopy protection over trails in Bukit Timah Nature Reserve

504 K. CHATTERJEA

DATA ANALYSIS

Surface Protection from Overhead Canopy Cover and Surface Litter Cover

Figure 2 shows the percentage of canopy cover observed from 33 locations along eight trails. Records show that

most of the trails are very well protected and covered (mean protection of 84�6 per cent), indicating that throughfalland raindrop impact are not effective stress factors in this forest environment.

Figure 3 on surface litter cover, however, shows a very different scenario. Of the 36 sites measured, an average of

64�3 per cent surface was exposed and bare, indicating movement of loose dry litter due to either surface

disturbance such as visitor movement or due to excessive surface runoff during rainstorms. Chatterjea (1994)

mentioned that there are instances of generated saturation overland flow on the Bukit Timah forest slopes. If that is

assisted by a compacted surface, the trails will be subjected to much surface wash. This is supported by

observations of cleared trail surfaces along the walking trails in BTNR, although they are very well covered by top

canopy (Figure 4). From 36 records, there are 10 sites (27�7 per cent) along the various trails that had less than

10 per cent litter cover protection, indicating regular movement of litter along the trails exposing the surface to

subsequent impacts, both from surface wash and from trail use.

Surface Stress Indicators

Penetration resistance analysis

Frequently, the evaluation of the soil physical state in response to trail use has been described by penetration

resistance. Compaction reduces the volume of air spaces in the soil and increases its dry bulk density. Hence, when

soils become compacted, they are poorly aerated, more resistant to the penetration of roots and less permeable to


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Litter Cover Protection on trails in BTNR

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Mean litter cover protection: 35.7%

Figure 3. Litter cover protection on trails in Bukit Timah Nature Reserve

Figure 4. Bare surface on trail


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Surface Penetration Resistance on Forest, Trails, and Trailsides at BTNR

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Mean Penetration Resistance:Forest: 426.4 kPaTrail: 1230.6 kPaTrail-side: 117.3 kPa

Figure 5. Surface penetration resistance on forest, trails and trail-sides at BTNR

506 K. CHATTERJEA

water and thus more vulnerable to erosion (McBride et al., 2000). Values of penetration resistance for the different

sampling locations are shown in Figure 5. The average trail PR value at 2�5 cm depth is close to three times that

recorded on the forest segments, with 75 per cent falling above the maximum resistance figure for forest segments.

As Table II shows, there is an increase of 114 per cent PR value on trails, as compared to forest sites, and 71 per

cent of on-trail results exceeded the critical value of 1000 kPa cited by different authors as limiting value beyond

which plant root elongation is severely restricted (Quinn et al., 1980; Varela et al., 2001). Unlike the unaltered

forest soils, on-trail PR values tend to be higher on surface, decrease at a depth of about 7 cm and then increase in

PR again, with depth (usually at 15 cm sampling depths). This result reinforces Bhuju and Ohsawa’s (1998) claims

that the effects of trampling appear to be restricted to the surface soil. Table III gives the results of ANOVA analysis

of penetration resistance between forest and trail segments.

Table II. Analysis of surface penetration resistance on soils in BTNR: forest, trail and trail-side surfaces

Values of surface penetrationresistance (kPa)

Forest surface(n¼ 25)

Trail surface (n¼ 31)(% increase from forest)

Trail-side surface (n¼ 42)(% increase from forest)

Maximum 965�3 2068�4 (þ114%) 2309�7 (þ139%)Minimum 68�9 137�9 (þ100%) 68�9 (0%)Mean 426�4 1230�6 (þ189%) 1117�27 (þ162%)Percentage of sites withPR above mean value

58% 47�6%

Percentage of sites withPR above 1000 kPa value

71% 60%


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Table III. ANOVA results of PR between forest and trail at 0�05 level of significance

Sum of squares df Mean square F Sig.

Between groups 282954�7 1 282954�715 52�297 0�000Within groups 389556�4 72 5410�506Total 672511�1 73


ANOVA results show that there are statistically significant differences between the forest and trail surface

penetration resistances (at 0�05 significance level). This confirms that hiking/walking activities lead to significant

degrees of compaction in materials on trails and make them significantly different from the original, undisturbed

forest conditions (Figure 6).

PR readings were also gathered from the sides of the trails that have been extended through diversions and

detours made by joggers and walkers. These sections were originally outside the designated trails and, therefore, a

part of the forest with the characteristic forest floor conditions of uncompacted surface. However, these trail-sides

showed similar trends as trail surfaces at depths of 2.5 cm, with a 139 per cent increase in PR values from the

original forest conditions. Although the minimum value was the same as on forest soils, the mean recorded a 162

per cent increase, suggesting that certain trail-sides are more compacted than others. In fact the maximum PR value

for trail-sides is even higher than that measured on trails. This high resistance value was recorded on one of the most

degraded sites where the trail width was more than 3�3m and the surface was heavily compacted into steps. 47�6 percent sites recorded values higher than the mean value. But what is more significant is that 60 per cent of the

Figure 6. Typical forest and trail conditions in BTNR


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Table IV. ANOVA results of PR between trail and trail-side at 0�05 level of significance



508 K. CHATTERJEA

trail-sides recorded values above the critical 1000 kPa, making these sections impenetrable by roots. The similarity

of penetration resistance recorded on trails and trails-sides are statistically significant, as shown in Table IV.

Statistically, there is no significant difference between results from the trails and trail-sides at 0�05 significance

level, signifying that the degree of trail-side degradation is comparable to that on the trails. This translates to

progressive extension of the degraded surface conditions to the previously forested areas, thus affecting parts of the

forest where such impacts were not intended.

Table V shows the results of such analysis and confirms that the present trail-side locations are indeed

significantly different from the original forest surfaces.

To establish whether trail-sides were significantly altered from their original forested counterparts, ANOVAwas

performed. When comparing the trail-sides with that of the forest, trail-sides obtained higher mean PR values than

that of the forest (increase of 162 per cent over forest values, significant at 0�05 level) (Table V). This also reinforcesthe view that the trail-side conditions are increasingly moving away from the unaltered state of the forest, implying

that deterioration of the surface conditions are extending beyond the designated trails into forest areas. On analyses

of individual trails, it is revealed that PR values obtained from some trail-sides (e.g. at Seraya Loop and North View

Path) are higher than or equal to those on the trails. This supports that hiking impacts are being extended beyond the

trails and that, with time, trail-side conditions will increasingly liken the trails and are hence under risk of

degradation. Table VI below shows some values of PR obtained from a 500m length of the Seraya Loop, a trail

under very heavy trampling. Figure 7 shows the present condition of the trail.

Again, the figures reflect similarly high degrees of compaction along trails, with moderate changes along the

margins. These data also point to severe compaction around root exposures (rootsteps), where hikers and bikers

tend to exert more force as they pass over them.

Table V. ANOVA results of PR between forest and trail-side at 0�05 level of significance



Table VI. Mean penetration resistance values (kPa) for trail, trail-side and forest segments along Seraya Loop

Forest Trail At rootsteps on trail Trail-side

Site 1 689�4 1323�65 1613�2 861�75Site 2 103�4 1116�8 1654�6 689�4Site 3 386�1 2171�61 2667�97 930�69Site 4 344�7 1034�1 1964�79 758�34Site 7 344�7 1447�74 1778�65 896�2Site 8 137�88 792�8 1916�53 654�93Site 9 193�0 2343�96 1378�8 978�94


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Figure 7. A badly impacted trail segment along Seraya Loop, BTNR


Surface shear strength analysis

The properties of matter that resist the stresses generated by gravitational force are collectively known as the shear

strength (Ritter et al., 2002) and this gives an indication of the surface resistance to erosion. The shear strength

values of the surface materials on trail, trail-sides and forest segments are shown in Figure 8.

The top surface of trails showed higher values of shear strength as compared to those of the forest. With the

exception of two samples, the forest yielded values of less than 80 kPa with more than 50 per cent of the results

falling under the forest mean of 40�7 kPa. The conditions of the forest appear to be similar as results reflect little

deviation from the mean (Figure 8). On-trail data presented a more varied pattern of results averaging at 102�4 kPa.On certain trails, the results obtained were comparable to that obtained from the forest. However, distinctively,

almost all trail results are above the forest mean of 40�7 kPa with 50 per cent of the results obtained showing shearstrength values greater than 100 kPa. Unlike the results obtained for the forest, the trail data show a large deviation

from the mean. However, statistically, these values are still significant. Hence, it may be concluded that the shear

strength of individual trails depends on the intensity of their use.

The increased strength of the trail will restrict root elongation and prevent seedling germination. Such compact

path surfaces act as source areas for overland flow generation (Sutherland et al., 2001). This occurs on the Bukit

Timah trails. The variations in shear strength values obtained from the trails can be attributed to possible differences

in visitor usage, while lack of alternative routes and lack of scope for lateral deviations (e.g. when trails are flanked

by steep slopes) may have led to the concentration of trail-use impacts on certain segments of trails as walkers are

confined to those pre-defined trails.

Response Indicators

Loss-on-ignition analysis

The percentage LOI between trail and trail-side shows no distinct pattern (Figure 9). Differences between these

losses vary from sample to sample. The values of less than 14 per cent LOI, however, are still distinctively less than

those obtained from the forest, thereby supporting the argument that trail-side environments are slowly degrading,


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Shear Strength on different surfaces in BTNR

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Forest: Mean: 40.7 kPa

Trail:Mean: 102.4 kPa(20 sites above mean value)

Trail-side:Mean: 86.6 kPa(20 sites above mean value)

Figure 8. Surface shear strength on forest, trails and trail-sides at BTNR

Figure 9. Percentage loss of organic matter in soils on forest, trails and trail-side surfaces at BTNR


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510 K. CHATTERJEA


mirroring to a closer extent the conditions of trails. Certain trail-side samples yielded results lower than those from

the trails indicating that these trail-sides are more affected than the adjoining trails, reinforcing the earlier

conclusion that hikers seeking to avoid badly degraded areas create new trail environments adjacent to the existing

trails. Similar more prominent signs of degradation were noticed in the PR values at certain trail-side locations. This

suggests that increasing amounts of forest tracts are slowly being encroached upon, transforming into barren,

compacted landscapes thereby threatening the biodiversity it supports. Furthermore, the low LOI values in both

trails and trail-sides suggest the loss of the main cementing agent of forest soils making it more susceptible to

erosion from the generated surface wash. Signs of such removal of topsoil is seen in Figures 11 and 14.

Infiltration rates

With high degrees of compaction and loss of organic matter, it is assumed that the infiltration capacity on trail-sides

would also be reduced.

Infiltration rates after 15 min show that there is some difference between the highest infiltration rates obtained on

forest, trail and trail-side locations (Figure 10), although there is little variation in the mean rate of both trail and

trail-side location classes. A large extent of the trail and trail-side results show low infiltration rates of less than

10 cm h�1 after 15 min. These correspond to the results obtained from other experiments and it may be concluded

that due to excessive trail use, surface soils are highly compacted and hence infiltration on both trails and trail-sides

are negatively affected.

Trail Degradation Zone Map Using GIS

The combination of surface compaction and loss of infiltration capacity on the trail surfaces results in generation of

surface wash during rainstorms, when the entire trail system behaves as a network of surface drainage system. With

slopes ranging from 15 to 20 degrees such surface wash leads to substantial sediment movement, albeit for a short

distance (Chatterjea, 1994), scouring topsoil, creating potholes, exposing roots and washing out entire layers of

topsoil and thus exposing an even more compacted subsurface layer higher in clay content (Figure 11), as also

observed by Sutherland et al. (2001). The trails soon get degraded and trail users create detours through forested

areas at the verges of the trails. This entire process of degradation occurs in stages, with some trail segments being

affected more than others. This progressive degradation of the trails poses a challenge to forest management as

demand on trail use is high. This study devised a system of Degradation Hazard Zoning for all trails in BTNR, based

on measured values of compaction (Penetration resistance and Shear Strength) of trail surfaces. This mapping is

aimed at providing information to forest managers on the status of trails as well as to maintain records of changes in

the state of all trails over time.

Data regarding surface penetration resistance and surface shear strength are used to plot the values along

surveyed trails in the nature reserve in order to spatially locate the zones of high degradation hazard on trails. The

output in the form of a set of GIS maps demarcating hazard zones supported by field data sets is meant to assist the

Park Managers in decision-making regarding the timing and scope of trail monitoring and management.

Hazard Classification of Trails

Two parameters, penetration resistance and shear strength, are used to assess the severity of trail deterioration using

GIS system and maps are generated using ArcMap. Data of each of the parameter are classified based on observed

data in the entire database and a hazard classification is devised specifically customised to the trails observed. Data

range covering those from the Forest segments, are taken as areas of No Hazard, and all trail segments falling in the

same range of readings for Penetration resistance and Shear Strength are shown in blue (colour code demarcating

areas of No Hazard category). Each demarcated section of a trail is delineated either as no hazard (NH), low hazard

(LH), shown in green, medium hazard (MH), shown in yellow, or high hazard (HH), showing in red. Each level of

higher hazard classification is based on an increasing value of the parameter chosen for the query. Although the

number of data sites is not numerous, the classification shows a trend which can be further investigated through

collection of similar data from more number of sites.


DOI: 10.1002/ldr

10.00

90.00

190.00

290.00

390.00

490.00

590.00

690.00

790.00

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Time (hr)

Infi

ltra

tio

n R

ate

(cm

hr-1

)

F1 F2 F3 F4 F5

Forest: Highest initial infiltration: 750 cm hr-1

15 Minute Infiltration rates (cm hr-1) on Trails and Trailsides

0.00

10.00

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30.00

40.00

50.00

60.00

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80.00

Trail-sideTrail

Locations

Infi

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ates

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Trail: Highest infiltration rate: 45.91 cm hr-1 Mean rate: 11.72 cm hr-1 Trail-side: Highest infiltration rate: 72.50 cm hr-1 Mean rate: 12.51 cm hr-1

Figure 10. Infiltration rates at forest, trails and trail-sides after 15 min


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512 K. CHATTERJEA

Figure 11. Exposed subsurface on degraded trail in BTNR


Hazard Classification for Penetration Resistance Parameter

Based on all the penetration resistance data, the average Penetrometer value for forest is 426�4 kPa and the

maximum limit of kPa above which root penetration is impossible is 1000 kPa. So the classification for Hazard

grades is based on the understanding that any station recording less than 1000 kPa is under ‘No Hazard’. Judging

from the minimum and maximum values derived from the field data for all stations, a classification scheme

(Table VII) is derived.

Table VII shows the frequencies of class sizes in each hazard category from the measured data points. With this

classification, 48�3 per cent of the measured sites fall under medium and low hazard; 27�6 per cent require regular

monitoring (MH); 27�6 per cent site under severe threat of degradation and require immediate attention.

Table VII. Classification of hazards and frequency of class sizes, based on penetration resistance data (N¼ 29)

Hazard class and colour code Parameter value class (kPa) Frequency

High hazard (HH) (Red) 1600–2000 8Medium hazard (MH) (Yellow) 1300–1599 8Low hazard (LH) (Green) 1000–1299 6No hazard (NH) (Blue) 0–999 7

Table VIII. Classification of hazards and frequency of class sizes, based on shear strength data (N¼ 24)

Hazard class and colour code Parameter value class (kPa) Frequency

High hazard (HH) (Red) 130–160 5Medium hazard (MH) (Yellow) 100–129 5Low hazard (LH) (Green) 64–99 6No hazard (NH) (Blue) 0–63�99 8


DOI: 10.1002/ldr

Figure

12.Mappingofsurfaceconditionsontrailsin

BTNR

Copyright # 2007 John Wiley & Sons, Ltd. LAND DEGRADATION & DEVELOPMENT, 18: 500–518

DOI: 10.1

514 K. CHATTERJEA

(2007)

002/ldr


Hazard Classification for Shear Strength Parameter

Based on all the shear strength results, the average shear strength value for forest is 40�7 kPa while the maximum

value for forested sites is 64�6 kPa. The classification for Hazard grades is based on the understanding that any

station recording less than 64 kPa (the maximum recorded at forest sites) is under ‘No Hazard’. Judging from the

minimum and maximum values derived from the field data for all stations, a four-category classification scheme

was derived (Table VIII).

From the given data, 33�3 per cent of the sites need no immediate attention, but 45�8 per cent of the sites are undermedium and low hazard; 20�8 per cent require regular monitoring (MH), while 20�8 per cent sites are under severethreat of degradation and require immediate attention.

After defining the levels of hazard for the two parameters showing surface compaction, GIS is used to map the

locations with the different levels of hazards along the different sections of the trails, using either of the two

Figure 13. Mapping of trail degradation using superimposed values of surface penetration resistance and surface shear strength


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516 K. CHATTERJEA

parameters or both superimposed to generate mapped information on impacted trails under stress (Figures 12

and 13). These maps can be used by park managers for easy detection of the areas under stress and subsequent

amelioration work. The overlay map delineating areas of high stress help the decision for prioritising management

procedures.

Based on the data and hazards classification, the following hazard zone map was produced using ARCGIS 9 with

both parameters (Penetration resistance and Surface Shear Strength on trails) plotted together.

CONCLUSION

Areas with superimposed grades of hazard indicate status of the trails. Any segment with two superimposed high

hazard status indicates an area that requires urgent management. From this generated map segments of Dairy Farm

Loop, Seraya Loop, Catchment Path, Cave Path, and Tiup Tiup Path can be demarcated as heavily impacted and

hence requiring urgent attention. As 76 per cent of the 400 000 annual visitors prefer to go on the trails (Chatterjea,

2007), such severely impacted trails are expected to show signs of overuse.

Based on the changes of both physical and hydrophysical properties of the soil and the surface conditions, it is

evident that hiking on the trails of BTNR has led to significant degradation. Compaction from overuse leads to

reduction in infiltration, thereby causing infiltration excess surface overland flow to occur, resulting in features such

as rills, gullies and potholes due to surface wash erosion and sediment movement (Figures 14 and 15).

The reduced penetrability of the surface soil results in the significant loss of vegetation as existing vegetation is

lost to trampling and new seedlings are unable to establish themselves in the highly compacted soils. This results in

the reduction of surface organic litter and subsurface organic content thereby implicating the loss of significant

microbial activity within the soils. Further, the inability for roots to penetrate the compacted soils results in less

aerated soils and reduced infiltration, therefore, discouraging the growth of plants.

The lack of sufficient litter cover on most parts of the intensively used trails increases the vulnerability of the soils

to raindrop/leaf drop impact. The lack of surface organic matter further amplifies the problem. As a result trails are

exposed to heightened erosion.

Figure 14. Potholes and roots on a degraded trail segment in BTNR


DOI: 10.1002/ldr

Figure 15. Overland flow along trail surface during one rainstorm in BTNR


Statistical analysis has shown that while there is distinct variation between forest and trail conditions, the

trail-side conditions are fast mirroring conditions on the compacted trails. This process, if left unattended, will

encroach upon the boundaries of the trails, thus effectively extending areas of stress well into the forested segments

of the forest.

The obtained values of stress and impact indicators in this study and their spatial locations through the maps are

aimed at providing some insight into the effects of increasing visitorship to this small patch of forest. The results

call for further study into the other impacts on the forest environment as well as the establishment of a more detailed

and coordinated monitoring and management strategy to maintain the forest conditions at BTNR.

references

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Chatterjea K. 2007. Development and environment: the constant battle. In Geographies of a Changing World, Global Issues in the Early 21stCentury, Ooi GL, Chatterjea K, Chang CH and Lim K. Prentice Hall: Singapore; 252.

Chatterjea K. 1994. Dynamics of fluvial and slope processes in the changing geomorphic environment of Singapore. Earth Surface Processes &Landforms 19: 585–607.

Dotzenko AD, Papamichos NT, Romine DS. 1967. Effects of recreational use on soil and moisture conditions in Rocky Mountain National Park.Journal of Soil & Water Conservation 22: 196–197.

Gardner BD, Chong SK. 1990. Hydrological responses of compacted forest soils. Journal of Hydrology 112: 327–334.Liddle MJ. 1975. A selective review of the ecological effects of human trampling on natural ecosystems. Biological Conservation 7: 17–36.Lynn Natasha A, Brown Robert D. 2003. Effects of recreational use impacts on hiking experiences in natural areas. Landscape & Urban

Planning 64: 77–87.McBride RA, Joose PJ, Wall G. 2000. Risk of soil compaction in soil quality. In Environmental Sustainability of Canada Agriculture: Report of

the Agri-Environmental Indicator Project. McRae T, Smith CAS, Gregorich LJ (eds). Agriculture & Agri-Food Canada: Ottawa; 224.


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Motavalli PP, Anderson SH, Pengthamkeerati P, Gantzer CJ. 2003. Use of soil cone penetrometers to detect the effects of compaction and organicamendments in claypan soils. Soil & Tillage Research 74: 103–114.

New Zealand Geotechnical Society, Inc. 2001. Guidelines for Handheld Shear Vane Test, New Zealand Geotechnical Society, Inc., August 2001.Poon A. 1990. Competitive strategies for a ‘‘new tourism’’. In Progress in Tourism, Recreation & Hospitality Management, vol. 1, Cooper CP(ed.). Belhaven Press: London; 91–102.

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Ritter DF, Kochel CR, Miller JR. 2002. Process Geomorphology, 4th edition. McGraw-Hill: NY.Rowell DL. 1994. Soil Science: Methods & Applications. Longman: Essex.Sutherland RA, Bussen JO, Plondke DL, Evans BM, Ziegler AD. 2001. Hydrophysical degradation associated with hiking trail use: a case studyof Hawai’iloa Ridge Trail, O’Ahu, Hawai’i. Land Degradation & Development 12: 71–86.

Talbot LM, Turton SM, Graham AW. 2003. Trampling resistance of tropical rainforest soils and vegetation in the wet tropics of North EastAustralia. Journal of Environmental Management 69: 63–69.

Varela ME, De Blas E, Benito E. 2001. Physical soil degradation induced by deforestation and slope modification in a temperate-humidenvironment. Land Degradation & Development 12: 477–484.

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Documents

Assessment and demarcation of trail degradation in a nature reserve, using GIS: case of Bukit Timah Nature Reserve