UNIVERSITI PUTRA MALAYSIA

EFFECTS OF RIMBAKA FOREST HARVESTING TECHNIQUE ON

STREAM WATER QUALITY AND SOIL PHYSICAL PROPERTIES

OTHMAN BIN DERIS

FH 2009 4

i

EFFECTS OF RIMBAKA FOREST HARVESTING TECHNIQUE ON STREAM WATER QUALITY AND SOIL PHYSICAL PROPERTIES

By

OTHMAN BIN DERIS

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in fulfillment of the requirement for the Degree of Master Science

August 2009

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirements for the degree of Master of Science

EFFECTS OF RIMBAKA FOREST HARVESTING TECHNIQUE ON STREAM WATER QUALITY AND SOIL PHYSICAL PROPERTIES

By

OTHMAN BIN DERIS

August 2009

Chairman: Professor Dato’ Nik Muhamad bin Nik Ab. Majid, PhD Faculty: Forestry

Forest harvesting has raised public attention and has been blamed for

environmental problems especially land slide, soil erosion, flooding and

degradation of water quality. In Peninsular Malaysia, forest harvesting in the hill

forest mainly uses ground based system with the combination of crawler tractors

and winch. In an attempt to reduce soil disturbance and degradation of river

water quality, Rimbaka Timber Harvester (RIMBAKA) was introduced as an

alternative to the crawler tractor.

This study focused on the effects of forest harvesting using RIMBAKA technique

on river water quality index and soil physical characteristics. The study was

carried out at Hutan Simpan Gunung Benom, Raub, Pahang. This study is

important to determine the effects of using RIMBAKA for forest harvesting as it

can be considered as an alternative to the ground- based system which has

been proven to result in negative impact on soil properties such as soil

compaction, increased run-off and erosion and also caused degradation of river

water quality. The main objective of this study is to determine the forest

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harvesting effects on river water quality index and soil physical properties such

as texture, bulk density, particle density, porosity and moisture content.

Sampling of river water quality and soil physical characteristics were carried out

in the area that has been approved for logging at three stages namely before,

during and after forest harvesting. In order to determine forest harvesting effects

on water quality index, water samples were collected from the stream channel

site that flows through the forest harvesting area, logging road and virgin forest

area. In addition, river water quality index was also studied during the dry and

wet seasons for each site and also forest harvesting phases. The soil was

sampled randomly in the area approved for logging during each harvesting

phase.

Analysis of Variance (ANOVA) was used to detect significant differences in river

water quality index and soil physical characteristics for each forest harvesting

phase. Duncan Multiple Range Test (DMRT) was used to determine differences

between each phase. In order to determine significant differences between river

water quality during dry and wet seasons, a T-test was conducted. Meanwhile,

Pearson’s correlation coefficient was used to determine the turbidity and TSS

relationship. T-test was also used to determine differences between soil physical

characteristics at two altitudes (below and above 550 meters above sea level

(masl)).

It was found that RIMBAKA harvesting technique has adversely affected to

water quality index. Water quality slightly decreased during the wet season as

compared to the dry season. The decline in water quality index is caused by an

increase in Total Suspended Solid (TSS). During wet seasons, TSS value

before, during and after forest harvesting were 13.38 mg/L, 52.67 mg/L and

66.00 mg/L, respectively. The corresponding values during dry seasons were

7.58 mg/L, 33.08 mg/L and 27.83 mg/L, respectively.

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Stream crossing during road construction is the main factor in that increase TSS

concentration. During the harvesting phase in the wet season, TSS value in the

stream water at the road crossing is 71.07 mg/L compared to 34.5 mg/L at the

forest harvesting site and 28.83 mg/L at the control area. Meanwhile, after forest

harvesting, TSS value at the forest road site, harvesting area and the control

area are 88.75, 43.25 and 33.0 mg/L, respectively. However, an increase in TSS

value only resulted in a slight effect on water quality index value. Water quality

index before, during and after forest harvesting belong to Class I and II.

Turbidity and suspended solids showed strong linear relationship (r2 = 0.769).

The forest harvesting operation also changed the texture, increased the bulk

density and soil particle density. Indirectly, the changes had caused a decline in

the porosity and soil moisture (P≤0.05).

Based on this study, forest harvesting using RIMBAKA technique only resulted

in slight negative effects on water quality index and soil physical characteristics.

However, the negatives effects can be further reduced if the forest harvesting is

confined to dry season only. It is recommended that in future studies, more

sampling should be carried out in the logging area to provide a more complete

picture of the changes in soil and river water quality.

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Abstrak tesis yang dikemukakan kepada Senat Univeristi Putra Malaysia

sebagai memenuhi keperluan untuk ijazah Master Sains

Kesan Penuaian Hutan Kepada Ciri-ciri Fizikal Tanah dan Alur Kualiti Air

Oleh

Othman bin Deris

August 2009

Pengerusi : Professor Dato’ Nik Muhamad bin Nik Ab. Majid, PhD Fakulti : Perhutanan

ABSTRAK

Penuaian hutan telah menjadi perhatian umum dan dilihat sebagai penyebab

kepada masalah alam sekitar terutamanya tanah runtuh, hakisan tanah, banjir

dan kemerosotan kualiti air. Di Semenanjung Malaysia, penuaian hutan di hutan

bukit adalah berasaskan kepada sistem heretan pada permukaan tanah iaitu

kombinasi jentera berantai dan lori winch. Justeru itu Rimbaka Harvester

(RIMBAKA) telah diperkenalkan sebagai alternatif kepada penggunaan jentera

berantai untuk mengurangkan kerosakan tanah dan kemerosotan kualiti air

sungai.

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Satu kajian kesan penuaian hutan ke atas ciri-ciri fizikal tanah dan indeks kualiti

air sungai telah dijalankan di Hutan Simpan Gunung Benum, Raub, Pahang.

Kajian ini amat penting untuk menentukan samada kesan penuian hutan

menggunakan RIMBAKA boleh dijadikan alternatif kepada sistem heretan pada

permukaan tanah yang terbukti memberi kesan yang negatif kepada ciri-ciri

tanah seperti pemadatan tanah, peningkatan larian air permukaan, hakisan dan

juga kemerosotan kualiti air. Objektif utama kajian ini adalah untuk menentukan

kesan penuaian hutan terhadap indek kualiti air dan ciri-ciri fizikal tanah seperti

tekstur tanah, ketumpatan pukal, ketumpatan partikel, keliangan dan kandungan

kelembapan.

Persampelan ciri-ciri fizikal tanah dan kualiti air sungai dilakukan dikawasan

yang dilesen untuk pembalakan iaitu sebelum, semasa dan selepas penuaian

hutan. Untuk menentukan kesan penuaian hutan terhadap indeks kualiti air,

sampel air diambil dari alur sungai yang mengalir melalui lokasi penuaian hutan,

jalan hutan dan kawasan hutan dara. Sebagai tambahan, kajian juga dilakukan

pada musim kering dan musim hujan bagi setiap fasa penuaian hutan.

Persampelan ciri-ciri fizikal tanah pula dilakukan secara rawak bagi setiap fasa

penuaian hutan.

Analisa Varian (ANOVA) telah digunakan untuk mengesan perubahan yang

ketara indek kualiti air sungai dan ciri-ciri fizikal tanah bagi setiap fasa penuaian

hutan. DMRT pula digunakan untuk menentukan perbezaan bagi setiap fasa.

Ujian t pula telah digunakan untuk menentukan perbezaan yang ketara diantara

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kualiti air pada musim hujan dan musim panas. Sementara itu, Korelasi

Pearson’s coefficient telah digunakan untuk menentukan perhubungan dan

kekuatan diantara kekeruhan dan jumlah pepejal terampai (TSS). Ujian t juga

digunakan untuk menetukan perbezaan yang ketara diantara ciri-ciri fizikal tanah

pada paras ketinggian 350-550 dan 551-750 meter di atas paras laut

Daripada kajian yang dijalankan didapati penuaian hutan memberi sedikit kesan

negetif kepada indek kualiti air. Kualiti air sedikit menyusut pada musim hujan

dibanding pada musim panas. Penyusutan indek kualiti air adalah disebabkan

oleh peningkatan TSS. Semasa musim hujan nilai TSS pada fasa sebelum,

semasa dan selepas penuaian hutan meningkat kepada 13.38 mg/L, 52.67

mg/L dan 66.00 mg/L. Pada musim panas pula nilai TSS sebelum, semasa dan

selepas adalah 7.58 mg/L , 44.08 mg/L dan 27.83 mg/L.

Jalan hutan yang dibina merentasi alur sungai adalah merupakan antara faktor

utama peningkatan nilai TSS. Semasa fasa penuaian hutan iaitu pada musim

hujan, nilai TSS di kawasan alur sungai yang direntasi jalan hutan ialah 71.07

mg/L dibandingkan dengan 34.5 mg/L di kawasan penuaian hutan dan 28.83

mg/L di kawasan hutan dara. Walaubagaimana pun peningkatan TSS ini hanya

memberi kesan yang sedikit kepada indek kualiti air. Indek kualiti air sebelum,

semasa dan selepas penuain hutan masih dalam kelas I dan II. Ujian korelasi

diantara kekeruhan dan TSS menunjukkan kedua parameter tersebut

mempunyai hubungan linear yang amat kuat dengan nilai bacaan 0.769. Ini

menunjukkan peningkatan kekeruhan akan meningkatkan nilai TSS.

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Kajian juga menunjukan bahawa penuaian hutan memberi kesan yang negatif

kepada ciri-ciri fizikal tanah. Kesan tersebut ditunjukkan melalui perubahan

tekstur tanah, peningkatan ketumpatan pukal dan ketumpatan partikel. Secara

tidak langsung perubahan tersebut menyebabkan penyusutan keliangan dan

kelembapan tanah (P≤ 0.05).

Berdasarkan kepada kajian tersebut menunjukkan bahawa penuian hutan

menggunakan RIMBAKA hanya memberi sedikit kesan negetif kepada indek

kualiti air dan ciri-ciri fizikal tanah. Walaubagaimana pun kesan negetif tersebut

boleh dikurangkan dengan melaksanakan penuaian pada musim panas. Justeru

itu disyorkan agar kajian diteruskan dengan menggunakan lebih banyak sampel

di lokasi pembalakan agar dapat memberi gambaran yang lebih tepat terhadap

perubahan tanah dan kualiti air sungai.

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ACKNOWLEDGEMENT

In the name of Allah SWT, the most Benevolent and most Merciful

First of all I would like to express my heartfelt gratitude and appreciation to my

supervisor, Professor Dato’ Dr. Nik Muhamad bin Nik Ab. Majid for his invaluable

help, dedicated efforts, guidance, suggestions and construction criticisms

throughout this study.

I am also grateful and sincerely thankful to the other committee members,

Associate Professor Dr. Mohd Kamil bin Yusoff and Dr. Mohamad Roslan bin

Mohamad Kasim for their valuable advice, suggestions and constructive

comments.

The support given by Forestry Department Peninsular Malaysia particularly

Dato’ Seri Azahar bin Muda Director General, Forestry Department Peninsular

Malaysia.

I would also like to express my appreciation to the Mr. Zainuddin bin Jamaluddin

who is the former Raub District Forest Officer for allowing me to conduct my

studies in Gunung Benum, Forest Reserve. I also would like to acknowledge

Upaya Padu Sdn. Bhd for their permission to conduct this study.

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I would like to express my thanks and gratitude to Mr. Zahari Ibrahim, Mr. Puat

bin Dahalan, Mr. Jinis bin Abdullah, Mr. Abdul Wahid bin Salleh, Mr Mohd Armi

bin Abu Samah and Mr Mohd Hafiz bin Rosli for their help throughout my study.

Finally, I express my deepest appreciation to my wife Mrs. Sarimah Md Sharif,

my daughters (Nurazyyati, Nur Athirah, Nur Auni Syafiqah, Nur Alya Syakirah)

and my son Muhammad Ammar Farhan for their continued support and patience

during the entire study period.

May Allah SWT Bless You All.

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I certify that an Examination Committee met on date of viva voce to conduct the

final examination of Othman bin Deris on his Master of Science thesis entitled

“Effects of Forest Harvesting on Physical Soil Properties and River Water

Quality” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act

1980 and Universiti Pertanian Malaysia (higher Degree) Regulations 1981. The

committee recommends that the candidate be awarded the relevant degree.

Members of the Examination Committee are as follows:

Name of Chairperson, PhD Name of Faculty Universiti Putra Malaysia (Chairman) Name of Examiner 1, PhD Name of Faculty Universiti Putra Malaysia (Internal Examiner) Name of Examiner 2, PhD Name of Faculty Universiti Putra Malaysia (Internal Examiner) Name of External Examiner, PhD Professor Name of Faculty Universiti Putra Malaysia (External Examiner) ____________________________ HASANAH MOHD. GHAZALI, PhD Professor/Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date: 5/8/2009

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This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirement for the degree of Master Science. The members of the supervisory Committee are as follows: DATO’ NIK MUHAMAD NIK AB. MAJID, PhD Professor Faculty of Forestry Universiti Putra Malaysia (Chairman) MOHD KAMIL YUSOFF, PhD Associate Professor Faculty of Environment Universiti Putra Malaysia (Member) MOHAMAD ROSLAN BIN MOHAMAD KASIM, PhD Faculty of Forestry Universiti Putra Malaysia (Member) ________________________ AINI IDERIS, PhD Professor/Dean School of Graduate Studies Universiti Putra Malaysia Date:

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DECLARATION I hereby declare that the thesis is based on my original research work except for quotations and citations, which have been duly acknowledge. I also declare that it has not been previously or concurrently submitted for any other degree at Universiti Putra Malaysia or other institutions. _______________ Othman Bin Deris Date:

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TABLE OF CONTENT Page

ABSTRACT ii ABSTRAK v ACKNOWLEDGEMENT ix TABLE OF CONTENT xiv LIST OF TABLES xvi LIST OF FIGURES xviii LIST OF PLATES xix LIST OF ABBREVIATION xx CHAPTER

I INTRODUCTION 1

1.1 Background 1 1.2 Problems Statement and Objectives of the study 3 1.3 Scope and Limitations of the study 6

2. LITERATURE REVIEW 7

2.1 Reduced Impact Logging 7 2.1.1 Forest Road 9

2.1.2 Log Landing 10 2.1.3 Buffer Zone 11

2.2 Effects of forest harvesting on soil properties 13 2.2.1 Soil Texture 16 2.2.2 Bulk Density and Porosity 17

2.2.3 Soil Moisture Content 19 2.3 Degradation of river water quality 20

2.3.1 Dissolved Oxygen (DO) 24 2.3.2 Biochemical Oxygen Demand (BOD) 25 2.3.3 Chemical Oxygen Demand (COD) 27 2.3.4 Ammoniacal Nitrogen (AN) 28 2.3.5 pH 29 2.3.6 Total Suspended Solid (TSS) 30 2.3.7 Turbidity 31 2.3.8 Water Quality Index 32

3 MATERIALS AND METHOD

3.1 Description of Study Area 36 3.1.1 Location of study area 36 3.1.2 Climate 37 3.1.3 Altitude and Geology 38 3.1.4 Vegetation 41 3.1.5 Harvesting 41

3.2 Physical Soil Properties 45 3.2.1 Soil Sampling 45

3.2.2 Soil Analysis 48

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a. Particle Size Analysis 49 b. Particle Density 49 c. Bulk Density, Porosity and Soil Moisture Content 51

3.3 River Water Quality Assessment 51 3.3.1 Sampling Locations 51 3.3.2 Water Analysis 54 3.3.2.1 In-situ analysis 54 3.3.2.2 Laboratory Analysis 54

a. Biochemical Oxygen Demand (BOD) 54 b. Chemical Oxygen Demand (COD) 55

c. Total Suspended Solid (TSS) 55 d. Ammoniacal Nitrogen (AN) 55

3.3.3 Calculation of DOE-WQI 56 3.4 Statistical Analysis 56

4. RESULTS AND DISCUSSION 4.1 Introduction 58

4.2 Effects of Forest Harvesting on Physical Soil Properties 58 4.2.1 Soil Texture 59 4.2.2 Particle Density 63 4.2.3 Bulk Density 66

4.2.4 Porosity 69 4.2.5 Soil Moisture Content 71

4.3 Effects of Forest Harvesting on River Water Quality 75 4.3.1 Impact of Weather Conditions on River Water 75

Quality in Different Forest Phases 4.3.1.1 Water Quality Index (WQI) 75

4.3.1.2 Turbidity and Suspended Solid 77 4.3.2 Comparison between Site Conditions 78 4.3.2.1 Water Quality Index 78

4.3.2.2 Turbidity and Suspended Solids 80 4.3.3 Correlation between Turbidity and Suspended Solid 85

5. CONCLUSION AND RECOMMENDATIONS 87 5.1 General 87 5.2 Summary 88 REFERENCES 90 APPENDICES 106

A. Appendix 1 106 B. Appendix 2 107 C. Appendix 3 114 D. Appendix 4 115 E. Appendix 5 124 F. Appendix 6 125

BIODATA OF THE AUTHOR 126

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LIST OF TABLES Tables Page

2.1

Recommended Width of Buffer Zone in Peninsular Malaysia

12

2.2

The classification of water quality according to DOE-WQI.

34

3.1

Geometry of the feeder road and skid trail in the harvesting area

43

3.2

Soil sampling plots based on altitude

48

3.3 The location and conditions of the study area 52

4.1 Soil texture in relation to harvesting phase for the two locations sampling

60

4.2

Soil particle density in relation to harvesting phase for the two locations sampling

64

4.3

Soil bulk density in relation to harvesting phase for the two locations sampling

66

4.4

Soil porosity in relation to harvesting phase for the two locations sampling

70

4.5

Soil moisture content in relation to harvesting phase for the two locations sampling

72

4.6

Statistical analysis for detecting changes mean of DOE-WQI

75

4.7

Statistical analysis for detecting changes mean of Turbidity

77

4.8

Statistical analysis for detecting changes mean of TSS

77

4.9

Mean Comparison of DOE-WQI in Undisturbed Forest, Logging Area and Road Crossing the Stream.

79

4.10

Mean Comparison of Turbidity value in Undisturbed Forest, Logging Area and Road Crossing the Stream.

81

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4.11

Mean Comparison of TSS value in Undisturbed Forest, Logging Areas and Road Crossing the Stream.

81

4.12 Correlation Between TSS (mg/L) and Turbidity (NTU) for before, during and after harvesting

86

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LIST OF FIGURES Figures Page

2.1

The types of forest roads

10

3.1

Location of the study sites in Compartment 35A, Gunung Benum Forest Reserve, Raub, Pahang.

37

3.2

Mean monthly rainfall at Gunung Benum Forest Reserve (1996-2005)

38

3.3

The three-dimentional view of the Compartment 35, Gunung Benum Forest Reserve, Raub, Pahang. (Sources: Googles Earth, 2007).

40

3.4

Plot layout for soil sampling (not to scale)

47

3.5

Plot layout for water sampling locations (not to scale)

53

4.1

Soil texture in relation to elevation and harvesting phase.

63

4.2

Particle density in relation to elevation and harvesting phase.

65

4.3

Bulk density in relation to elevation and harvesting phase.

69

4.4

Soil porosity in relation to elevation and harvesting phase.

71

4.5

Soil moisture content in relation to elevation and harvesting phase.

74

4.6

The means values of DOE-WQI in logging area, road crossing the stream and undisturbed forest.

80

4.7

The means values of Turbidity in logging area, road crossing the stream and undisturbed forest.

83

4.8

The means values of TSS in logging areas, road crossing the stream and undisturbed forest.

84

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LIST OF PLATES Plates

Page

3.1

Rimbaka Timber Harvester (Rimbaka)

43

3.2

“San Tai Wong”

44

3.3

Silt trap

44

3.4

Drainage system

45

3.5

Soil sampling for bulk density (before forest harvesting)

48

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LIST OF ABBREVIATIONS

AN Ammoniacal Nitrogen

ANOVA Analysis of Variance

APHA American Public Health Association

BOD Biological Oxygen Demand

COD Chemical Oxygen Demand

DO Dissolved Oxygen

dbh Diameter at breast height

DID Department of Irrigation and Drainage

DOE-WQI Department of Environment -Water Quality Index

FDPM Forestry Department Peninsular Malaysia

masl meter above sea level

mg/L milligram/liter

MUS Modified Uniform System

NTU Nephelometric turbidity Units

P Probability

PRF Permanent Reserve Forest

pH in unit pH

RIL Reduced Impact Logging

Rimbaka Rimbaka Timber Harvester

r Coefficient Of Correlation

SFM Selective Forest Management

SIDO Sub Index of Dissolved Oxygen

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SIBOD Sub Index of Biological Oxygen Demand

SICOD Sub Index of Chemical Oxygen Demand

SIAN Sub Index of Ammoniacal Nitrogen

SIPH Sub Index of pH

SISS Sub Index of Suspended Solid

SMS Selective Management System

TSS Total Suspended Solid

α Alpha

1

CHAPTER ONE

INTRODUCTION

1.1 Background

In 2000, the world forest cover was estimated at 29.6% of the total land area or

3,869 million hectares which can be divided into four broad categories, namely

temperate, boreal, subtropical and tropical forests. Temperate, boreal and

subtropical forests occupy about 1.86 billion hectares and tropical forests occupy

2.01 billion hectares (Food and Agriculture Organization [FAO], 2005). Twenty

nine countries have more than half of their land covered with forest. Malaysia is

one of the countries having more than 50% of the land area covered with forest.

The Malaysian tropical rain forests are one of the twelve mega-biodiverse

countries in the world. The forest contains 14,500 species of flowering plants

and trees, 600 species of birds, 286 species of mammals, 140 species of snakes

and 80 species of lizards (Forestry Department Peninsular Malaysia [FDPM],

2004).

In 2006, the total forested land in Malaysia was 19.52 million hectares (59.50%

of total land area), with 5.88 (44. 7 %) million hectares in Peninsular Malaysia,

4.40 (59.7%) million hectares in Sabah and 9.24 (75.1%) million hectares in

Sarawak. From the 19.52 million hectares of forested land, 17.40 million

hectares are dry inland forest or dipterocarp forest while the remaining 1.54

million hectares and 0.58 million hectares are swamp forest and mangrove

2

forest, respectively. In order to preserve the forest resources as a renewable

resource, 14.39 million ha or 73 % of the forest areas have been gazetted as a

Permanent Reserved Forest (PRF) for sustainable management. The area of

PRF in Peninsular Malaysia, Sabah and Sarawak are 4.70 million hectares, 3.59

million hectares and 6.10 million hectares, respectively (Abdul Rahman, 2008).

The PRF in Malaysia has been systematically managed since the beginning of

the century. The forests are managed into three broad forest types such as

dipterocarp forest, swamp forest and mangrove forest. There are two

management systems for dipterocarp forest in Peninsular Malaysia, namely

Modified Malayan Uniform System (MUS) and Selective Management System

(SMS). The aim of MUS and SMS is to manage the forest on a sustainable

basis. However, the principle behind the system is different. Under the selective

logging system there is an intention to harvest the timber at the end of the 30

years cutting cycle while under the uniform system one has to wait a complete

rotation of 55 years or more until the regeneration has grown into harvestable

trees (FDPM, 2003b).

The MUS consists of removing the matured crop in a single felling of all trees

below 45 cm diameter at breast height (dbh) for all species while SMS entails

selection of optimum management regimes based on pre-felling inventory data

with the minimum cutting regime of 50 cm for dipterocarps, except Chengal

3

(Neobalanocarpus heimii) where the cutting limit would be above 60 cm dbh and

45 cm for non-dipterocarps (FDPM, 2003b).

The total forested areas to be managed under SMS and MUS are estimated at

1.3 million hectares and 1.54 million hectares respectively or 2.84 hectares of

productive forests of the PFR (FDPM, 2005a). To ensure that the forest is better

conserved and sustained, the annual coupe in Peninsular Malaysia has been

scaled down under the 6th Malaysia Plan (1991-1995), 7th Malaysia Plan (1996-

2000) and 8th Malaysia Plan (2001-2005) to 52,250 ha, 46,040 ha and 42,870 ha

per annum, respectively (Azmi and Yap, 2004).

1. 2 Problem Statement and Objectives of the study

The forestry sector has significantly contributed to the socio-economic

development of the country. In 2005, the forestry sector and wood products

(including wood and rattan furniture) contributed about RM21.5 billion of the

Malaysian Gross Domestic Product. This accounted for 4.0% of the total gross

export of Malaysia at freight of board (f.o.b) of RM533.8 billion (FDPM, 2005a).

However, harvesting in the hill forests draws public attention and has been

blamed for environmental problems especially land slide, soil erosion, flooding

and degradation of water quality. Currently, most of the harvesting operation is

in the hill forests because of the reduction in areas of the lowland forests had

been cleared for agriculture, industrial and urban expansion since the1960s