FAO_CIFOR_Forests and Floods_Drowning in Fiction or Thriving on Facts

RAP Publication 2005/03
Forest Perspectives 2

Forests and floods

Drowning in fiction or thriving on facts?

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RAP Publication 2005/03
F o r e s t Pe r s p e c t i v e s 2

Forests and floods
Drowning in fiction or thriving on facts?

The designations employed and the presentation of material in this publication
do not imply the expression of any opinion whatsoever on the part of the Food
and Agriculture Organization of the United Nations concerning the legal status
of any country, territory, city or area or of its authorities, or concerning the
delimitation of its frontiers or boundaries.
All right reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means, electronic,
mechanical, photocopying or otherwise, without the permission of the copyright
owner. Applications for such permission, with a statement of the purpose and
extent of the reproduction, should be addressed to the Senior Forestry Officer,
Food and Agriculture Organization of the United Nations, Regional Office for Asia
and the Pacific, 39 Phra Atit Road, Bangkok, Thailand.

ISBN 979-3361-64-6
© 2005 by FAO & CIFOR
All rights reserved. Published in 2005
Printed by Indonesia Printer
Cover photo:
Donkey riders wade through flood waters after
a heavy monsoonal downpour in Lahore, Pakistan, 2003
Published by
Center for International Forestry Research
Food and Agriculture Organization of the United Nations

Center for International Forestry Research
Jl. CIFOR, Situ Gede, Sindang Barang
Bogor Barat 16680, Indonesia
Tel.: +62 (251) 622622; Fax: +62 (251) 622100
E-mail: [email protected]
Web site: http://www.cifor.cgiar.org
Food and Agriculture Organization of the United Nations
Regional Office for Asia and the Pacific
Maliwan Masion, 39 Phra Atit Road
Bangkok 10200, Thailand
Tel.: + 66 (2) 697-4000; Fax: +66 (2) 697-4445
E-mail: [email protected]
Web site: http://www.fao.or.th

Contents

Acknowledgements

iv

Foreword

v

Introduction

1

Distinguishing fact from fiction

3

Policy implications

11

Taking an integrated approach

13

Towards more effective watershed management

16

Towards more effective floodplain management

19

Making rational policy decisions

25

Bibliography

27

iii

Acknowledgements
The preparation of Forest and floods: drowning in fiction or thriving
on facts? has been a collaborative venture. Numerous people have
contributed to this booklet by sharing their experiences and thoughts,
providing literature, assisting in distinguishing facts from fiction and in
drafting, commenting on and editing a progression of manuscripts. FAO
and CIFOR would like to thank in particular the following for participating
in the process:
Moujahed Achouri, Bruce Aylward, Kenneth N. Brooks, Neil Byron, Yvonne
Byron, Ian Calder, Bruce Campbell, Patrick C. Dugan, Patrick Durst,
Thomas Enters, Thierry Facon, Peter F. Ffolliott, Don Gilmour, Hans M.
Gregersen, Lawrence S. Hamilton, Thomas Hofer, Ulrik Ilstedt, Jack D.
Ives, David Kaimowitz, Benjamin Kiersch, Philip McKenzie and Kumar
Upadhaya.

iv

Foreword
The role of forests in sustaining water supplies, in protecting the soils of
important watersheds and in minimising the effects of catastrophic floods
and landslides has long been discussed and debated. The International
Year of Mountains (2002) and the International Year of Freshwater
(2003) re-emphasised that mountainous watersheds, land use and water
are inextricably linked. For decades this perceived link has served as
an important justification for promoting and implementing watershed
management.
Every year large-scale floods in the Asian lowlands affect the personal
and economic fortunes of millions of people. To many people involved in
developing disaster-reduction strategies and flood-mitigation management,
it appears that the intensity of floods has increased in the region in recent
decades. A common — and perhaps understandable reaction — is to blame
the mismanagement of Asia’s uplands and the clearing of forests in important
mountainous watersheds for the misery brought to the lowlands. To a large
extent, conventional wisdom — which is sometimes more fiction than fact
— about the benefits of forests has clouded the perspectives of decisionmakers, leading to an over-emphasis on reforestation and forest protection
at the expense of more holistic watershed and river-basin management.
The conventional wisdom is that forests act as giant ‘sponges’, soaking
up water during heavy rainfall and releasing freshwater slowly when it
is most needed, during the dry months of the year. The reality is far
more complex. Although forested watersheds are exceptionally stable
hydrological systems, the complexity of environmental factors should
cause us to refrain from overselling the virtues of forests and from relying
on simple solutions (e.g., removing people currently living in mountainous
watersheds, imposing logging bans, or implementing massive reforestation
programmes). Rather, the complexity of these processes should prompt us
to reassess our current knowledge of the relationship between forests and
water, and reconsider conventional responses to one of the most serious
disaster threats in the Asia-Pacific region — i.e., large-scale floods.
This booklet aims to separate fact from fiction on issues related to forests
and water and to dispel some of the commonly held misconceptions about
the role of forests in flood mitigation. It does not pretend to provide an
exhaustive overview on the subject; rather, it aims to brief policy-makers,
development agencies and the media, and so constructively contribute to
the development of sound watershed and river-basin management, and
flood-mitigation policies, for the region.
He Changchui
Assistant Director-General and
Regional Representative for Asia and the Pacific
FAO

v

A Chinese father and his daughter
wade through flood waters in
Jintang County, Chengdu, Sichuan
Province, June 29, 2004. The lowlying county along the Yangtze
River is frequently flooded by
heavy rains during the summer

Introduction

Every year, reports of large-scale flooding in the Asian lowlands
capture headlines and dominate newscasts. The 1980s and 1990s
will be particularly remembered for catastrophic floods and their
profound effects on people, property and economies in many Asian
countries.
Who doesn’t recall the flooding of the Yangtze River in 1998,
which devastated large areas of central China and resulted in
damage in excess of US$30 billion? Between January and August
2004, 46 million people were affected by floods in China. Floods
in 2000 affected 3.5 million people in Cambodia (one-third of
the population) and 5 million in Viet Nam, with associated costs
of US$145 million and US$285 million, respectively. In the same
year, floods in Bangladesh displaced more than 5 million people
and in India 30 million. A single flood in 1999 in the small, central
province of Thua Thien Hue, Viet Nam, led to the deaths of 400
people and damage to property worth US$120 million, or one-half
of the province’s annual GDP. Nearly every country in the region has
suffered the effects of catastrophic floods at one time or another.
Globally, floods affect the personal and economic fortunes of more
than 60 million people each year.
Much has been written about floods, their causes and impacts.
Debate has been intense about how to prevent, mitigate and
manage them. Each tragic event inevitably becomes a political
issue. Political survival demands that politicians are seen as
responding to each crisis in quick fashion. Thus, officials seek
immediate answers and short-term solutions. In many countries,
there is widespread belief — including among many foresters — that
forests can prevent or reduce floods. Therefore, an immediate,
frequently drawn conclusion is that floods occur because forests
have been cleared or degraded. Hence it is but a small step to
presume that the continuing deforestation of Asia’s watersheds is
the cause of the misery brought to millions of people every year.
The reality, however, is that direct links between deforestation and
floods are far from certain. Although the media attributes virtually
every flood-related tragedy to human activities — particularly to
agricultural expansion and timber harvesting (typically characterised

1

I n t r o d u c t i o n

by the press as ‘rampant illegal logging’ irrespective of legality
or harvesting methods employed) — hydrological systems are so
complex that it is extremely difficult to disentangle the impacts of
land use from those of natural processes and phenomena.
In the case of upland/lowland as well as forest and flood
relationships, existing ‘knowledge’ is frequently based more
on perceived wisdom, or myths, than on science. In the rush to
identify the culprits for the most recent disasters, assumptions
are made about processes in one region based on observations
from other regions which often have quite different environmental
characteristics, or by extrapolating from small to large scales.
Oversimplification is common, frequently leading to initiatives
such as logging bans or the resettlement of people residing in
watershed areas — often with minimal environmental benefits
but very definite negative social and economic implications. The
unfortunate outcome is that intended results are rarely achieved,
but scarce funds are misallocated and unnecessary hardships are
heaped upon those segments of society that become scapegoats for
flood-related disasters and damages.
All floods cannot and should not be completely prevented — flooding
is important for maintaining biodiversity, fish stocks and fertility of
floodplain soils. In many floodplains, certain crops (e.g., jute or
deep water aman rice in Bangladesh) depend on seasonal flooding.
However, steps can be taken to limit the adverse impacts of floods
and to ensure effective responses to flooding events. This requires
a far better understanding of the interactions between human
activities and floods, the limitations of watershed management and
the role of floodplain or river-basin management in reducing floodrelated impacts.
As a first step, decision-making needs to be supported by an
objective perspective of the relationships between forests and
water, in order to distinguish myths and conventional wisdom
from facts and sound science. Building on better understanding
of physical processes and the relationships between land use and
hydrology, more effective responses can be designed to reduce the
magnitude of disasters without repeating the mistakes of the past.

Recent flood in Cambodia
(courtesy of Mr Ty Sokhun,
Forest Management Office,
Department of Forestry and
Wildlife, Cambodia through
Water Resources Section,
UNESCAP)

2

Distinguishing fact from fiction

Are floods caused by nature or by human activities? This question
has been posed for decades and the issue has been researched
and discussed extensively in scientific circles. Surprisingly, in
many countries sound science has had relatively little impact
on people’s perceptions and beliefs. Partly, this is because the
general public finds it difficult to distinguish between good and
poor science, or between facts and plausible fiction. It may also
be that some people find it more convenient or advantageous to
perpetuate certain myths, rather than to address the issues in a
sound, scientific framework. Hamilton (1985) has characterised this
situation as ‘The 4 Ms: myth, misunderstanding, misinterpretation,
and misinformation.’
Although a great deal is known about hydrological processes and
the relationship between forests and floods, this knowledge is often
used to make generalisations that are frequently inappropriate or
misleading. There is a propensity to rely on simple cause-effect
relationships, when in reality natural environments are extremely
complex. Such complexity and the overlapping influences of human
activities on hydrological systems are frequently oversimplified,
particularly by the media and public officials seeking simple
explanations and solutions. Moreover, the inherent uncertainties
of many scientific findings and the absence of long-term research
are downplayed. Little distinction is made between what we know,
what we think we know or what we want to believe, contributing
substantially to the general confusion surrounding the effects of
forests on major floods. Also, while the hydrological processes are
well-established, the site-specific nature of the many interactions
leads to uncertainty in generalisations.
Much of this confusion has a long history and relates to the so-called
‘sponge theory’. Although the exact origin of the theory is unclear,
it appears to have been developed by European foresters at the end
of the 19th century. While it has never been confirmed, many people
have found it agrees with their own professional understanding and
intuition. According to the theory, the complex of forest soil, roots
and litter acts as a giant sponge, soaking up water during rainy
spells and releasing it evenly during dry periods, when the water
is most needed. Although the theory came under criticism as early

3

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as the 1920s, it continues to appeal to many people (foresters and
non-foresters alike). In many countries, it is firmly embedded in
national forest policies and programmes. The question is how much
of the sponge theory is fact and how much is fiction?

An early American view on forests and floods
Rain which falls over a bare slope acts differently. It is not
caught by the crowns nor held by the floor, nor is its flow into
the streams hindered by the timber and the fallen waste from
the trees. It does not sink into the ground more than half as
readily as in the forest, as experiments have shown. The result
is that a great deal of water reaches the streams in a short
time, which is the reason why floods occur. It is therefore true
that forests tend to prevent floods. But this good influence [of
forests on floods] is important only when the forest covers a
large part of the drainage basin of the stream. Even then the
forest may not prevent floods altogether. The forest floor, which
has more to do with the fallen rain water than any other part of
the forest, can affect its flow only so long as it has not taken up
all the water it can hold. That which falls after the forest floor
is saturated runs into the streams almost as fast as it would
over bare ground.
From: Gifford Pinchot, A Primer for Forestry, 1905

The Himalayan sponge
The Himalayan forests normally exert a sponge effect, soaking
up abundant rainfall and storing it before releasing it in regular
amounts over an extended period. When the forest is cleared,
rivers turn muddy and swollen during the wet season, before
shrinking during drier periods.
From: Myers 1986

Forests, regulation of stream flow and flood prevention
It is commonly believed that forests are necessary to regulate
stream flow and reduce runoff, and to some extent this is true.
But, in reality, forests tend to be rather extravagant users of water,
which is contradictory to earlier thinking (FAO 2003). Considerable
quantities of rainfall (up to 35 per cent) are commonly intercepted
by the canopies of tropical forests and evaporated back into the
atmosphere without contributing to soil water reserves. Much of the
water that does soak into the soil is used by the trees themselves.
This should put to rest the belief that extensive reforestation or
afforestation will increase the low flows in the dry season (Hamilton
and Pearce 1987). Therefore, replacing forest cover with other land
uses almost always results in increased runoff and stream flow.
Runoff and stream-flow patterns will gradually return to original

4

A N D
F L O O D S

Contrary to popular belief, forests have only a limited influence
on major downstream flooding, especially large-scale events. It is
correct that on a local scale forests and forest soils are capable of
reducing runoff, generally as the result of enhanced infiltration and
storage capacities. But this holds true only for small-scale rainfall
events, which are not responsible for severe flooding in downstream
areas. During a major rainfall event (like those that result in massive
flooding), especially after prolonged periods of preceding rainfall,
the forest soil becomes saturated and water no longer filters into
the soil but instead runs off along the soil surface.

F O R E S T S

levels if an area is left to revert back to forest. Converting forest to
grasslands, however, will normally result in a permanent increase
in total water runoff.

Studies in America (Hewlett and Helvey 1970), and South Africa
(Hewlett and Bosch 1984) were amongst some of the first to question
the importance of the link between forest conversion and flooding.
Studies in the Himalayas indicate that the increase in infiltration
capacity of forested lands over non-forested lands is insufficient
to influence major downstream flooding events (Gilmour et al.
1987; Hamilton 1987). Instead, the main factors influencing major
flooding given a large rainfall event, are: (i) the geomorphology of
the area; and (ii) preceding rainfall (Bruijnzeel 1990, 2004; Calder
2000; Hamilton with King 1983; Kattelmann 1987).

Yielding insights into water yields
No experiments, with the exception of perhaps one, have
resulted in reductions in water yield with reductions in cover,
or increases in yield, with increase in cover.
From: Bosch and Hewlett 1982

Even at the local level, the regulating effect depends mostly on
soil depth, structure and degree of previous saturation. Thin soils
produce ‘flashy’ flows (quick responses). Massive programmes of
forestation that have often been proclaimed as ‘the answer’ to
preventing floods simply will not do the job, although there may
be many other benefits from reforestation (Hamilton and Pearce
1987).

Erosion and sedimentation
It is widely perceived that forests can control erosion and sediment
processes. While forest cover does tend to check erosion, it is not
the tree canopy that is directly responsible for this; rather it is
the undergrowth and forest litter. Experiments indicate that the

5

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erosive power of raindrops under trees actually tends to be very
high because the raindrops merge before dripping off the leaves
and therefore hit the ground with greater force (Wiersum 1985;
Hamilton 1987; Brandt 1988). This sometimes leads to particularly
serious erosion problems in plantations where the soil has been
cleared of vegetation and litter to reduce fire hazard or where
litter is collected for livestock bedding or fuel. If the soil surface is
adequately protected by a well-developed litter layer and complete
vegetative cover, other vegetation types can offer equivalent
protection against erosion, but with the added advantage of lower
water use.
Land degradation and soil erosion that are often associated
with the loss of forest cover are not necessarily the result of
the forest removal itself, but of the poor land-use practices
(overgrazing, litter removal, destruction of the organic matter,
clean weeding) implemented after forest removal (Bruijnzeel
1991, 2004; Hamilton with King 1983). Also, much of the erosion
that occurs after timber harvesting is due to the movement of soil
during logging operations (e.g., road construction, skidding, etc.).
Compaction results in lower water storage capacity of the soil and
increased surface runoff. Many of these negative effects can be
significantly diminished by applying reduced impact logging (RIL)
techniques.

Environmental benefits of reduced impact logging (RIL)
• On average, RIL results in 41 per cent less damage to
residual stands when compared with conventional logging
systems.
• The area covered by skid trails in RIL operations is almost 50
per cent less than in conventional logging, even for similar
volumes extracted.
• The area damaged by road construction is about 40 per cent
less with RIL than with conventional logging.
• Overall site damage (compaction, exposure of soil, etc.) in
RIL operations is generally less than half that in conventional
logging.
• Canopy opening is generally about one-third less in RIL
compared with conventional harvesting practices (16 per
cent versus 25 per cent).
From: Killmann et al. 2002

Landslips, too, may occur due to the loss of forest cover. Tree roots
play an important role in slope stability and can indeed give the
soil a certain amount of mechanical support, but this is limited to
shallow (<1m) mass movements (Bruijnzeel 1990, 2002; O’Loughlin
1974). This type of landslide is quickly stabilised and does not usually
result in high amounts of sediment entering the surrounding rivers.

6

F L O O D S

Research on the effects of land-use changes on flooding is usually
conducted in small headwater catchment areas (e.g., 100-1,000
hectares) and frequently considers the effects of only a single change
in vegetative cover (e.g., from forest to grassland), such as the
landmark Coweeta experiments in the United States (Douglass and
Swank 1975). Such experiments do not adequately take into account
the multiple land uses found over entire watersheds. Therefore,
extrapolation of research results obtained in sub-watershed areas
to entire watersheds is inappropriate and misleading. A review
of past research indicates that land-use effects on flooding were
observable only in relatively small basins (Table 1). In basins larger
than 50,000 hectares, the effects of flooding tend to be averaged
out across the different sub-basins as storms pass over. Since the
flood waves from the different sub-basins do not usually reach the
main basin area simultaneously, there may be little or no cumulative
effect from the individual flood waves.

A N D

Impacts of scale on flooding

F O R E S T S

Deep-seated (>3m) landslides, on the other hand, are not noticeably
influenced by the presence or absence of a well-developed forest
cover (Bruijnzeel 1990, 2002). Such events are most influenced by
geological, topographical and climatic factors, rather than by forest
cover (Ramsay 1987).

Experts agreeing on what is needed
Much is known about hydrological processes in forests at a small
catchment scale. However, there is a critical need to initiate and
strengthen long-term eco-hydrological monitoring for further
research to improve understanding of large-scale interactions
and the influence of forests on dry season flows, flood mitigation
and groundwater recharge in a range of environments in line
with paragraph 27 of the WSSD Plan of Implementation.
From: Shiga Declaration on Forests and Water, 2002

When major floods do occur, it is most often towards the end of
the rainy season, when heavy rain falls in a number of sub-basins
(simultaneously) and usually on soils that are already saturated
and therefore incapable of soaking up additional water. The extent
and severity of wide-scale flooding can be further intensified by
the occurrence of torrential rains in the floodplains or the river
surfaces themselves during vulnerable periods. This can be further
exacerbated by high tides, which frequently happen in Bangkok,
Dhaka and other low-lying cities.

7

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Table 1: The spatial dimension of land-use effects
Impact
Average flow
Peak flow
Base flow
Groundwater recharge
Sediment load
Nutrients
Organic matter
Pathogens
Salinity
Pesticides
Heavy metals
Thermal regime

0.1
x
x
x
x
x
x
x
x
x
x
x
x

1
x
x
x
x
x
x
x
x
x
x
x
x

Basin size [km2]
10
100
1,000
x
x
—
x
x
—
x
x
—
x
x
—
x
x
—
x
x
x
x
x
—
x
—
—
x
x
x
x
x
x
x
x
x
—
—
—

10,000
—
—
—
—
—
—
—
—
x
x
x
—

100,000
—
—
—
—
—
—
—
—
x
x
x
—

Legend: x = Observable impact; — = no observable impact
Adapted from Kiersch (2001).

Frequency of floods
Although some studies have shown apparent increases in flooding
over time, such studies have tended to look at relatively short
timeframes and limited data sets (Bruijnzeel 1990). When
considering longer timeframes, cycles are revealed within which
major flooding tends to occur at fairly regular intervals. These
cycles appear to be driven by major climatic patterns (e.g., those
resulting from the influence of cyclical warm ocean currents).
Examining the historical patterns of catastrophic events reveals that
floods, as well as droughts, are not a recent phenomenon by any
means. For example, major floods in the Bangkok metropolitan and
adjacent areas have been recorded regularly for the last 200 years.
Large-scale floods in the Chiang Mai valley in northern Thailand
are well documented for events in 1918-1920 and again in 1953.
These floods all occurred when lush forests were still abundant in
Thailand. Eight major floods were recorded in Bangladesh between
1870 and 1922. A study on floods in Bangladesh concluded that
‘there is absolutely no statistical evidence that the frequency of
major flooding has increased over the last 120 years’ (Hofer and
Messerli 1997).

Perceptions of the destructive power
and severity of floods
Settlements have always been established on floodplains, despite
the risk of periodic flooding. The numerous social, economic and
environmental benefits of living near water have historically

8

A N D
F L O O D S

The development of urban areas also transformed formerly
vegetated land to impermeable surfaces, with little or no water
storage capacity. Extensive areas of wetlands that once acted as
natural retention and storage areas for floodwaters were drained,
filled and built upon. Natural stream channels were straightened
and deepened, and structures such as dams and embankments were
commonly built to reduce local flood risks.

F O R E S T S

outweighed the risks of floods. Most early settlements were located
on the higher areas of floodplains, which helped to minimise risks
and potential damage from floods. As towns and cities grew,
however, new housing areas and commercial estates expanded into
the more flood-prone areas that had previously been avoided.

These ‘solutions’ may have served to help reduce flood impacts
locally but have often had the effect of shifting the problem
further downstream, rather than solving it. This pattern has been
exacerbated by the removal of the natural storage functions of
the floodplain. Today’s floodplains bear little resemblance to
yesterday’s floodplains, and it should not be a surprise therefore
that even minor floods can nowadays cause major damage.
The severity of floods is often measured and described in terms of
economic losses rather than physical parameters. This approach
can easily give the impression that flooding has become much
more severe in recent times. In reality, the huge economic losses
attributed to flooding in recent years are mainly a reflection of
expanding economic growth, increased investment in infrastructure
and rapidly growing floodplain populations. Although the escalating
economic costs of floods underscore the urgent need for improved
floodplain management and disaster mitigation, it is incorrect to
conclude that floods are any more frequent (in physical terms) now
than in the past.

Recognising the dilemma!
Within river systems, flooding is the natural way for the system
to discharge the water arising from the occasional large rainfall
event. There is no problem at all until man decides to use
some of the natural flood plain for his own use, and chooses
to protect against inundation. We then face the dilemma of
protecting against a natural hazard for the benefit of mankind
that has chosen to live and work in flood plain areas.
From: Learning to live with rivers, Institute of Civil Engineers, 2001

Although humans do not directly cause floods, we have sometimes
greatly exacerbated the problems caused by floods. Not only do
many cities have inefficient water-drainage systems, local land
subsidence makes recent floods appear worse than past events. For

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For intensively developed urban
areas and floodplains, land-use
planning and control measures
have an important role to play
in flood mitigation (Moosan
City, Kyungkido Province,
Republic of Korea) (courtesy of
the Farmland Rearrangement
Division, Ministry of Agriculture
and Forestry, Republic of
Korea through Water Resources
Section, UNESCAP)

10

example, due to excessive and long-term groundwater withdrawal,
Bangkok is sinking at an average of 2 cm every year. Since the city’s
elevation is between 0 and 1.5 m above sea level, it is not surprising
that high tides can inundate major parts of the city, especially
when they coincide with heavy rains. Other cities suffer similar
problems. Moreover, the large increase in non-absorbing surfaces
that goes with urban growth exacerbates the problem, speeding
surface runoff, and allowing less infiltration.

Going under
Pumping of groundwater is one of the main causes for land
subsidence, which has resulted in deeper flooding and longer
water logging.
From: Pramote Maiklad 1999

The media also plays a significant role in shaping perceptions of
the intensity, frequency and severity of flooding. Modern television
news networks, in particular, can record and broadcast news of
catastrophes far more quickly and comprehensively than anytime
in history. While major flooding events of the past often went
completely unreported, or were described only sketchily, perhaps
months after their occurrence, modern media has the capacity to
report extensively on flood disasters occurring anywhere in the world
within hours. This capacity of the media, coupled with journalists’
penchant for sensationalising news events — particularly disasters
— can easily lead people to conclude that floods are occurring more
frequently and with greater severity than in the past. Scientific
evidence, however, does not support such conclusions.

Policy implications

Disentangling facts from fiction related to catastrophic floods should
point policy-makers towards a broader perspective than simply
focusing on the uplands. The most important policy conclusion
is a cautionary one. The role of forests in solving flood problems
remains uncertain, although the progress that has been made in
understanding upland-lowland interrelationships suggests that
forests are much less important than commonly perceived. However,
close to the forests in the uplands, they can reduce flooding from
frequent, low-intensity, short-duration storms (Hamilton 1986).
While it may be convenient to blame upland farmers and poor
forest management for problems that affect low-lying areas, it
unfortunately does not contribute to solving the problems.
Sound science provides little evidence to support anecdotal reports
of forest harvesting or rural land-use practices leading to lowerbasin catastrophic floods. When it comes to prevention of major
floods, the ‘sponge theory’ is a historical erratum — a fiction often
inappropriately used to justify soil and water conservation measures,
forest management controls and logging bans. Unfortunately, the
‘sponge theory’ has also been used inappropriately to secure funds
for various development and governmental projects. Simplistic
belief in the flawed approach to flood management distracts the
attention of policy-makers from two main points:
1.

2.

There are many good reasons — other than for avoiding floods
— for protecting soils in Asia’s uplands and for managing upland
forests sustainably.
Instead of pointing to distant uplands as the source of their
problems and dwelling on fictional cause-effect relationships,
lowlanders (including policy-makers) should learn to live
with rivers and manage the lowlands for what they are
— floodplains.

11

For several days
volunteers in boats
had to rescue men and
women trapped on roof
tops during Jakarta’s
devastating floods in
February 2002 (photo by
Arie Basuki)

Taking an integrated approach

Although forests can play a certain role in delaying and reducing
peak floodwater flows at local levels, scientific evidence clearly
indicates that forests cannot stop catastrophic large-scale floods,
commonly caused by severe meteorological events — the type of
events that are often blamed on forest harvesting or conversion
to agricultural uses. This in no way diminishes the need for proper
management and conservation of upland forests. But it does point
toward the critical need for integrated approaches in river-basin
management that look beyond simplistic forest-based ‘solutions’.
To be successful, such integrated approaches must combine various
measures in the uplands with those in the lowlands, and work with
natural processes and not against them.
An integrated approach to river-basin management recognises the
limitations of working only in the uplands to minimise floods or only
in the lowlands to reduce their damage. It takes into account that
soils of well-managed natural forests and plantations can maintain
a higher water-storage capacity than most non-forest soils under
similar conditions. They can thus slow the rate of runoff, which in
turn helps to minimise flooding in smaller watersheds and of more
frequent intermediate events. It also does justice to the multitude
of other environmental services that forests provide. Furthermore,
an integrated approach recognises that forest conservation and
appropriate management are not only important in the upper
reaches of Asia’s watersheds but also in the river basins, where
the forests form an important component of wetland ecosystems.
Moreover, it recognises the role of maintaining forests on key sites
to reduce sediment problems, such as on slip-prone soils and in
riparian zones.
This approach integrates land-use management in the uplands with
land-use planning, engineering measures, flood preparedness and
emergency management in the lowlands. It considers the social
and economic needs of communities living in both the mountainous
watersheds and the river basins. Integrated management has to
be based on the best available scientific knowledge of the causes
and the environmental, social and economic impacts of floods.
Essentially, this approach should prepare people to live with and
adapt to rivers and floods.

13

Objectives

Objectives are formulated for the management of the
entire basin (watershed and floodplain) on the basis
of local and national needs by means of intensive
stakeholder consultation.

Planning

A plan for the management of the basin is formulated on
the basis of the objectives, the land-use and resource
management needs of the area. This is done through
intensive stakeholder participation.

Implementation

The plan is implemented by all landowners and
concerned stakeholders under the guidance of a
management board supported by appropriate policy
instruments and innovative financing.

Monitoring

Implementation of the plan is closely monitored to
asses the impact of interventions and policies. If
necessary, interventions can be adapted on the basis of
the monitoring results.

Evaluation

The implementation of the plan is evaluated on a
regular basis to ensure that the objectives are being
achieved. If necessary, the objectives can be adjusted
in light of new knowledge or a change in user needs.

a p p r o a c h
Ta k i n g

a n

i n t e g r a t e d

Such an integrated management system is the result of an iterative
process (Figure 1), which without doubt has many challenges
resulting from the trans-boundary nature of major river systems
such as the Ganga-Brahmaputra-Meghna Basin. It is also complicated
by the large number of different stakeholders who often have very
different views on how the problem should be solved, and by the
many conflicting uses of the precious resources within a basin.

Figure 1: The iterative process of integrated basin management.
Under the integrated approach, the objectives for the management
of the basin are initially formulated for both the lower and upper
basin areas. These objectives should be based on local and national
priorities, prevailing land uses and the unique characteristics of
each basin’s natural resources. Based on the defined objectives,
management plans are formulated for entire basins — which may
cross national borders — in close consultation with all stakeholders.
The management plan details the activities required to achieve the
desired objectives. Planning is appropriately done at two levels —
watershed and floodplain — and then integrated to form a cohesive
overall management plan (see for example Easter et al. 1986).

14

F O R E S T S

The management plan comprises all the activities required to
organise land and other resource use within a watershed in the
course of providing the goods and services defined by the objectives,
while at the same time maintaining and supporting the livelihoods
of resident populations. The plan is implemented by all landowners
and concerned stakeholders under the guidance of appropriate
management bodies and supported by pragmatic policy instruments
and innovative financing mechanisms. Examples of such bodies
include several river-basin commissions in the United States of
America and the United Kingdom, the Murray-Darling River basin
Commission in Australia, the Rhine and Danube Commissions in
Europe, the Red River Basin Commission that links Canada with the
USA, and the Mekong River Commission whose member countries
are Cambodia, Lao PDR, Thailand and Viet Nam.

A N D
F L O O D S

Incentives need to be offered to encourage desired land uses and
land-management practices and to align private interests with
the public good. Compensation needs to be provided to land users
negatively affected by the plans. The results of the implementation
are monitored and impacts of various policy instruments and
interventions assessed, to ensure that the objectives are being
achieved and that costs and benefits are equitably shared. The
entire process is evaluated on a regular basis and, if necessary,
objectives or activities can be adjusted to meet new requirements
or expectations. Management objectives can change over time as
priorities and land-use practices evolve. This is a dynamic process
that ensures, through the various feedback mechanisms, that
objectives remain realistic and can be reached without causing
unacceptable and unmanageable environmental and socio-economic
impacts.

Floods after heavy rain
in May 2003, Ranna,
Hambantota District, Sri
Lanka (photo by Sophie
Nguyen Khoa, IWMI)

15

Towards more effective
watershed management

To date, watershed management has generally achieved only
partial success, largely due to the fact that biophysical factors
have been emphasised at the expense of socio-economic concerns
and the fact that hydrologic boundaries are not congruent with
political boundaries. To be seen as responding to flooding problems,
government officials and development agencies regularly launch new
watershed-management programmes and projects. The activities
under these initiatives typically focus on maintaining or expanding
forest cover and encouraging soil and water conservation practices
in agricultural areas. Attention is also usually given to curtailing
shifting cultivation and stabilising rural settlements. However,
sporadic short-term efforts in soil and water conservation and
reforestation on individual plots (selected on the basis of farmers’
willingness to participate or direct payments for co-operation) are
unlikely to have a discernible flood mitigation effect, even at the
level of a small watershed.
Although these types of projects can be beneficial on a local scale,
they are not likely to contribute significantly to flood mitigation as
a whole. They may, however, contribute to reducing sedimentation,
which has adverse effects on aquatic life, reservoir life, potable
water quality, irrigation quality and navigation (Hamilton and
Pearce 1986).
Watershed management that is heavily reliant on improved
farming technologies often ignores the many water resourcerelated problems that are caused by non-agricultural land uses.
Mining and physical infrastructure such as roads, for example,
can affect local hydrology far more than agricultural practices,
and can lead to uncontrolled runoff and sedimentation of rivers.
Effective watershed management identifies the main problem areas
or ‘hot spots’ of risk and sets appropriate priorities for mitigative
interventions. Under this approach, there is no pre-determined
assumption that agriculture and farmers (or forestry and loggers)
are the major sources of problems.
Effective watershed management is an iterative process of
evaluating, planning, restoring and organising land and resource
use within a watershed to provide desired goods and services while

16

A N D
F L O O D S

An important aspect of watershed management is land-use
classification and land-use planning. It is vital that the fragile
areas be identified and protected from inappropriate use, whether
forestry, agriculture or mining. However, even the ‘best’ plan will
have no impact if its implementation is not facilitated by supportive
policies, a regulatory framework providing guidance, and incentive
systems stimulating behaviour that benefits the watershed and
society at large.

F O R E S T S

maintaining and supporting the livelihoods of resident populations.
This process provides an opportunity for stakeholders to balance
diverse goals and resource uses, and to consider how their
cumulative actions may affect long-term sustainability of natural
resources. Embedded in the concept of watershed management is
the recognition of the interrelationships of many different activities
such as fisheries, urban development, agriculture, mining, forestry,
recreation, conservation and other human influences, as well as the
linkages between upstream and downstream areas.

What can be expected from forest and soil conservation?
Forestation of mountain watersheds and extensive soil
conservation measures are valuable for the sake of the hill
farmers, if appropriately carried out. It is potentially disastrous,
however, for foreign aid agencies and national government
authorities to undertake such activities with the conviction that
they will solve problems in the plains.
From: Lauterburg 1993

Although watershed classification, planning and management
are usually the domain of foresters (or soil conservationists), the
profession falls short in recognising that forest management itself
— if not practised appropriately — can produce substantial on- and
offsite costs. Poor logging practices generate massive quantities
of sediments and can substantially influence local stream-flow
patterns, especially through increased runoff from landings,
skidtrails and logging roads. Thus, effective watershed management
also means introducing reduced impact logging, enforcing logging
guidelines and adhering to codes of practice for forest harvesting.
In addition, riparian forests should be managed rigorously to protect
water quality. This is an area where unambiguous research results
point to significant environmental benefits.
Unfortunately, the benefits of these techniques are not fully
recognised and related practices are not utilised to their full
potential. Many logging companies still consider reduced impact
logging merely in terms of increased operating costs with no
additional economic gains. In the absence of rigorous regulation
and targeted incentives, such attitudes typically result in limited
application of improved logging practices.

17

m a n a g e m e n t
w a t e r s h e d
To w a r d s

m o r e

e f f e c t i v e

Effective watershed and forest management consistently yield
significant environmental services, including high-quality freshwater supplies. However, the influence of watershed and forest
management practices on stream-flow patterns is relatively small,
and is mainly limited to watersheds up to 500 km2 in area. As such,
forests alone will not be able to protect entire river basins from
catastrophic events. Even with the best intentions, no amount of
watershed management interventions will prevent major flooding
events, although there are some definite benefits at the local
scale.

Flooding in Tonle Sap area of Cambodia inundates agricultural lands
(courtesy of Mr Ty Sokhun, Forest Management Office, Department of
Forestry and Wildlife, Cambodia through Water Resources Section,
UNESCAP)

18

Towards more effective
floodplain management

Effective floodplain management, like watershed management, is
an iterative process of identifying and assessing alternative ways of
reducing the impact of floods (particularly of catastrophic events)
in flood-prone areas. Decision-making in floodplain management
involves compromises between the costs and benefits of alternative
actions. It also requires that upper catchment areas be considered
part of the solution and not as the ‘source’ of the problem.

What is floodplain management?
Floodplain management refers to all the actions society can
take to responsibly, sustainably, and equitably manage the
areas where floods occur and which serve to meet many
different social, economic, natural resource and ecological
needs. Since this includes reducing the hazard and suffering
caused by floods, floodplain and flood management consist of
many common activities. However, floodplain management
recognises explicitly that other factors of a social, economic,
natural resource management and ecological nature also have
to be taken into account in “managing” floods.
From: Mekong River Commission, 2001

In the past, structural responses (e.g., dams, levees, dikes, etc.)
were emphasised and, indeed, in the early- to mid-20th century
engineers prevailed in debates over the best means to tame the
awesome power of floodwaters. With ‘flood control’ as their explicit
objective, engineers around the world spent decades (and billions
of dollars) building dams, embankments and levees to prevent
floodwaters from inundating floodplains. These structures were
often combined with dredging to straighten and deepen stream
channels. According to the World Commission on Dams (WCD 2000),
some 13 per cent of all large dams, or over 3,000 worldwide, were
built with a specific flood-mitigation function.
Most flood defences were built as individual local schemes,
with little consideration of their impacts across the wider river
catchment, their impacts on the aquatic and coastal environments
or, indeed, even their broad economic impacts. The fact that

19

m a n a g e m e n t
f l o o d p l a i n
e f f e c t i v e
m o r e
To w a r d s

Can floods be controlled?
“Flood control” is a common expression... But one cannot control
floods; at best one can manage their detrimental effects. The
words “flood control” are therefore not used in this report.
From: Mekong River Commission, 2001

embankments and other engineering structures were most
effective only for small- to medium-sized flood events was often
not recognised. Also, river, road and other embankments sometimes
inhibited the discharge of rainwater from water-logged areas into
the river system (particularly where the number of sluices in
the embankments is insufficient) and accordingly increased the
dimension of flooding.
The available water storage of a typical reservoir is generally much
less than the volume of a major flood surge. Moreover, structural
solutions often have spill-over effects, shifting problems from one
location to the next. For example, emergency releases of water
during periods of high rainfall can dramatically and dangerously
increase water levels immediately downstream of dams.

Experiences with embankments in Bangladesh
The Brahmaputra embankments channel the flood waters of the
river, preventing the river from overflowing. In 1987, however,
this had serious consequences for the left, unembanked side of
the river: The water spread out and inundated large areas, and
erosion on the left river bank increased dramatically.
From: Hofer and Messerli 1997

It should be evident that individual flood alleviation schemes
cannot be considered in isolation and that a solution in one part of a
river basin may be detrimental for other areas further downstream.
Recently, numerous restoration projects have been implemented to
reverse the impacts of earlier engineering works such as the Rhine
Action Plan on Flood Defence adopted in 1998 after major floods in
1993 and 1995 (Leentvaar 1999). Increasingly, management of flood
risks is moving away from structural engineering solutions toward
programmes that work with natural processes. The impetus for this
shift came from a number of major destructive events over the last
50 years, including:
• 1953 coastal flooding in the Netherlands that led to the Delta
works;
• 1988-9 floods in Bangladesh that led to the Flood Action Plan and
the National Water Management Plan;

20

F L O O D S

The new approach weighs alternative actions in floodplain
management in the context of whether overall flood effects are
positive or negative. Although attention is usually focused on the
negative effects of floods, there are highly important positive
effects that warrant recognition and consideration. Flooding in
many low-lying areas in Asia is a vital element of the culture and
economy of the people. Annual floods along many rivers carry fine
sediments and nutrients that renew the fertility of the land and
aquatic habitats, and the continuous flow of silt-bearing irrigation
water helps control diseases in many areas. In a region where
agriculture and fishing remain vitally important, the loss of these
beneficial effects could potentially lead to unacceptable economic
and social disruption. However, what is beneficial to some may
inflict heavy economic costs upon others. The challenge is to
balance costs and benefits.

A N D

the upper Mississippi floods of 1993;
the Rhône floods of 1993;
the Rhine floods of 1993 and 1995;
the Yangtze floods of 1998 in China; and
the Elbe floods in Europe in 2002 — which once again drew
attention to the important role of non-structural catchment
measures.

F O R E S T S

•
•
•
•
•

The positive effects of flooding
During a normal flood [in Bangladesh] the fields are inundated
and alluvial organic matter is deposited. Normal floods are
necessary for important monsoon crops.
From: Hofer and Messerli 1997

New flood management approaches are steadily introducing or
expanding the role of non-structural measures within integrated
floodplain management programs. Key measures include the
identification of natural storage areas, such as swamps and
wetlands, where excess water can be directed and temporarily
stored during periods of flooding. The World Commission on Dams
(WCD 2000) categorises the components of an integrated approach
to floodplain management according to those which reduce the
scale of floods, those which isolate the threat of floods and those
which increase people’s capacity to cope with floods (Table 2).
A similar approach is also evident in the Mekong River Commission’s
(MRC 2001) promotion of ‘Integrated Floodplain Management’,
which comprises a mix of four types of management measures.
These reflect the flooding, flood risk and flood hazard characteristics
of a particular floodplain, the specific social and economic needs
of flood-prone communities, and the environmental and resource
management policies for the floodplain.

21

m a n a g e m e n t
f l o o d p l a i n
e f f e c t i v e
m o r e
To w a r d s

Table 2: Complementary approaches of integrated flood management
Reducing the scale of
floods
Better catchment
management
Controlling runoff
Detention basins
Dams
Protecting wetlands

Isolating the threat of
floods
Flood embankments
Flood proofing
Limiting floodplain
development

Increasing people’s
coping capacity
Support traditional
strategies
Emergency planning
Forecasting
Warnings
Evacuation
Compensation
Insurance

Source: World Commission on Dams (2000)

Integrated Floodplain Management on the Mekong River
Land-use planning measures are aimed at “keeping people
away from the floodwaters.” Land-use measures on the
floodplain aim to ensure that the vulnerability of a particular
land-use activity is consistent with the flood hazard on that
area of land.
Structural measures are aimed at “keeping floodwaters away
from the people.” Typical structural measures include flood
mitigation dams, embankments and flood detention basins.
Flood preparedness measures recognize that — no matter
how effective the above types of management measures are
— an overwhelming flood will eventually occur. These measures
embody flood forecasting, flood warning, and raising the general
flood awareness of the potentially affected population groups.
In a number of cases, flood preparedness and emergency
measures may be the only type of management that is feasible
or economically justified.
Flood emergency measures deal with the aftermath of major
events by “helping affected people to cope with floods.”
Flood emergency management, like floodplain management,
is a process that typically encompasses preparation, response
and recovery. The process embodies evacuation planning and
training, emergency accommodation planning, flood cleanup,
restitution of essential services, and other social and financial
recovery measures.
From: Mekong River Commission, 2001

The importance of regional co-operation has also been stressed by
the South Asian Floods Project (SAF) of the International Centre
for Integrated Mountain Development. The project facilitates
information exchange in the Hindu Kush-Himalayan region (http:
//www.southasianfloods.org). It stresses that one of the most
cost-effective means of reducing the impact of floods is the nonstructural approach of providing people with sufficient advance
warning for them to escape from approaching disasters. It further

22

F O R E S T S

points out the importance of timely and reliable information on
weather and river flows, and the open exchange of information
among countries. Priority needs to be given to the development of
such information gathering and dissemination networks in countries
where no such systems currently exist.

A N D
F L O O D S

Finally, there is a clear need to develop improved capacities
for river systems to respond to flooding in both rural and urban
environments, and by balancing land use more carefully. Agricultural
and forestry policies, practices and incentive schemes need to be
redirected towards reduction of flood risks and the restoration of
the roles of formerly undeveloped floodplains for storing water
and reducing peak flows downstream. Indeed, flood storage could
become a recognised land use in development plans, which should
be encouraged and compensated through government incentives.
For example, over 25,000 homes have been relocated from the
Mississippi floodplain since 1993, and thousands of hectares of
marginally productive low-lying areas have been reconverted from
agriculture to natural areas (Galloway, Jr. 1999).

Reversing the past
In the future, drainage design should reverse the past 200
years of engineering practice. Storage should be maximized
and conveyance minimized. Post-modern drainage design
should mimic the form and performance of the pre-settlement
drainage system.
From: Hey 2001

Urban flood in Bangkok,
Thailand (courtesy of
the Royal Irrigation
Department of
Thailand through Water
Resources Section,
UNESCAP)

23

A healthy mountain watershed
in Kashmir, Indian Himalaya
(photo by Thomas Hofer)

Making rational policy decisions

Flood processes in Asia are highly complex. Only integrated
approaches take this complexity sufficiently into account and
lead to adaptive and effective flood management. An improved
approach to watershed and floodplain management integrates land
management in the uplands with land-use planning, engineering
solutions, flood preparedness and emergency management in the
lowlands. This requires good understanding of all the physical
processes involved, as well as the social behaviour and culture of
local residents. Furthermore, this approach should draw upon the
best available scientific knowledge about the environmental, social
and economic impacts of floods and the environmental, social and
economic effects of interventions.
The myths and misperceptions about the causes of flooding that
have misguided decision-makers, planners and managers alike need
to be replaced by rational understanding based on facts. Too many
local, national and international agencies have used ‘conventional
wisdom’ and unsupported claims to advance their own institutional
interests and because it has been politically advantageous to channel
aid funds to upland reforestation and conservation projects. The
media has unfortunately perpetuated many of the myths regarding
forests and floods out of a well-intentioned, but ill-informed,
desire to protect the environment, especially the forests of upper
watersheds.
It should be clear that large-scale reforestation programmes, the
adoption of soil and water conservation technologies in agriculture,
logging bans and the resettlement of upland people to lowland
areas will not significantly reduce the incidence or severity of
catastrophic floods. Positive environmental impacts from these
interventions will be of a local nature, while the negative social
and economic impacts are likely to be more widespread.
Importantly, the habit of blaming upland inhabitants for catastrophic
floods of whole river basins must be abandoned. Instead, practical
solutions are needed to redress watershed degradation caused by
unsustainable land-management practices, including poor logging
practices and inappropriate infrastructure development. While
refraining from exaggerating the negative impacts that mountain

25

d e c i s i o n s
p o l i c y
r a t i o n a l
M a k i n g

people have on the environment, we should also not overstate the
positive impacts of their participation in watershed management
programmes, as is happening with some recent attempts to develop
markets for the environmental services that forests may provide.
Moreover, policy-makers and development agencies have a moral
and ethical responsibility to ensure that regulatory and project
approaches are based on the best available scientific knowledge
and do not unnecessarily place upland communities at risk of
further impoverishment.

The scope of forestry in mitigating floods
…the scope for forests to reduce the severity of major floods
that are derived from an extended period of very heavy rainfall
is rather limited.
From: UK Forestry Commission, 2002

While the ability of forests to prevent catastrophic floods is limited,
watershed management should definitely not be abandoned. Forests
provide a variety of environmental services, which need to be
protected and nurtured for the benefit of today’s and tomorrow’s
upland and lowland populations. Watershed management needs to
consider the needs and interests of local populations, but should
also account for the needs of the wider society.
The most effective approaches to reducing damage caused by
catastrophic floods require a strong focus on downstream areas and
floodplains. People in these areas need to ‘learn to live with rivers’,
as the UK Institution of Civil Engineers entitled its 2001 report on
flood mitigation measures. At the same time, politicians and policymakers need to abandon their belief in quick fixes for flood-related
problems. While the high costs of floods in the lowlands of Asia
are evident, it is important that the beneficial aspects of floods
are also acknowledged. It is only by promoting and supporting
comprehensive integrated watershed and floodplain management
that the needs and aspirations of all residents — uplanders and
lowlanders — can be adequately addressed.

26

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Forest Perspectives Series
1. - Fast-Wood Forestry: Myths and Realities. 2003.
Christian Cossalter and Charlie Pye-Smith
- Fast-Wood Forestry: Myths and Realities (Japanese edition). 2005.
Christian Cossalter and Charlie Pye-Smith

There is a tendency to blame all natural disasters on human abuse of the natural
environment. This is no more evident than in the case of devastating floods and landslides
that affect the personal and economic fortunes of millions of people every year. Each
disaster is followed by a predictable response. Upland farmers and loggers are blamed
for clearing and degrading forests. In many people’s minds the use and abuse of forests in
upland watersheds represents the main cause of massive lowland floods.
Forests and floods: drowning in fiction or thriving on facts? explores the scientific
evidence linking floods and forests. The booklet reveals that much of what is ingrained in
people’s minds cannot be substantiated by science and is often little more than myth or is
patently incorrect. Such conventional wisdom has often led decision-makers to implement
misguided policies that adversely affect the livelihoods of millions of people living in
upland areas.
Forests and floods distinguishes fact from fiction and recommends alternative approaches
for effective watershed and floodplain management. This authoritative overview has
been produced by a suite of renowned experts, but it should appeal to everyone with
an interest in escaping the quagmire of stale and dated paradigms. Ultimately, Forests
and floods aims to better inform policy-makers, development agencies and the media,
and so constructively contribute to the development of sound watershed and river-basin
management and improved flood-mitigation policies.

Forest Perspectives are published to promote discussion and debate on key forest
issues. They are published by CIFOR as a service to encourage dialogue and information
exchange among the international forest community. Electronic versions can be
downloaded from CIFOR’s web site (www.cifor.cgiar.org) and from FAO’s web site
(www.fao.or.th)