Overview

• Globally,forestsandtheforestrysectorfacegrowingchallengesandrisksfromnaturaldisasters.Climate change is expected to increase the frequency and intensity of disaster events in the future, while greater and sometimes conflicting demands – driven by population expansion, economic development, and calls for environmental protection – are being placed on forests and forest land.

• Forestsandforestryhavecrucialroles–andlimitations–inmitigatingdisastersandtheirimpacts,andinpost-disasterreconstructionandrecovery. Evidence from the Asia-Pacific region demonstrates that forests, when appropriately planned and managed, can withstand and protect against natural disasters of varying degrees and types.

• Integratedapproachestodisasterriskreductionaremosteffective. Forestry can be one of many effective contributors to disaster risk management, especially when combined with appropriate land-use planning, mitigation measures and infrastructure, and early warning systems. Isolated measures are unlikely to be effective.

• Poorandmarginalizedpeopleremainthemostvulnerabletodisasters,oftenlivinginhighriskzonesandhavinglimitedaccesstoresourcesandsupportservices. The inclusion of villagers in planning and managing protection forests is important for improving not only their disaster-preparedness and resilience, but also for ensuring that such forests are effectively managed.

Forests and natural disaster risk reduction in Asia and the Pacific Policy brief

Key considerations in coastal forest rehabilitation following the 2011 Great East Japan Earthquake

Experiencesfromthetsunamitriggeredbythe2011GreatEastJapanEarthquakedemonstratedboththestrengthsandlimitationsofforestsindisastermitigation.* Coastal forests, primarily consisting of black pine, absorbed energy from the tsunami in many areas, reducing its speed and capturing debris. However, forests had little effect where wave height was greatest (20 to 30 meters according to some estimates). Wave force also flattened and uprooted trees or snapped their trunks in many coastal areas, contributing additional floating debris. Key considerations in rehabilitating Japan’s coastal forests include:

1. Constructionofartificialembankmentsallowstreesincoastalzonestobemorestronglyrooted.Limited soil thickness and a high water table inhibit tree-root growth in coastal zones, preventing strong soil bonding and increasing the risk of trees toppling in strong winds and waves. Construction of artificial embankments on which trees are planted may significantly improve disaster-mitigation functions.

2. Collaborationamongdifferentsectorscanensureavarietyofmutuallybeneficialoutcomes.Partnership between civil society organizations, private companies, academic institutions, government agencies, and the general public is essential to identify and incorporate the needs, interests, and strengths of various stakeholders into planning and implementation of forest rehabilitation.

3. Theuseoflocalknowledgeandforestresourcesinrecoveryeffortscansignificantlycontributetotheresilienceofdisaster-affectedpopulations. The construction of 8,000 temporary itakura shelters by local carpenters, using domestically sourced cedar, has so far received positive feedback from shelter inhabitants, and due to low costs has been considered a success. The experience provides a blueprint for the role that domestic forests and sustainable forest management – particularly the role of emergency ‘tree banks’ – can play in disaster recovery.

*Presented at the International Seminar on the Role of Forests in Natural Disasters and Revival of Forests and Forestry, organized by the Forestry Agency of the Ministry of Agriculture, Forestry and Fisheries of Japan on 5 February in Sendai, Japan. For further information, please visit: http://www.rinya.maff.go.jp/j/kaigai/natural-disasters.html.

Coastal forests and tsunamisAvarietyofcoastalforests–includingbeachforests,mangroves,andplantedforests–caneffectivelymitigatetheeffectsoftsunamisandstormwaves. Coastal forests can reduce the destructive power of tsunamis with wave heights up to 8–10 meters, by absorbing wave energy and stabilizing sand dunes and other elevated wave barriers along the coast. Additionally, coastal forests can decrease secondary damage by blocking drifting objects from washing inland.

Coastalforestscanprovidevaryingdegreesoftsunamimitigationdependingontheirdesignandmanagement. Factors include:

1. Widerforestbelts reduce tsunami impacts to a greater extent, as a tsunami’s hydraulic force is progressively dissipated by drag created by forest vegetation over distance.

2. Moderateforeststanddensities are most effective in absorbing a tsunami’s energy. If the density of trees and shrubs is too low, waves may pass relatively unimpeded. Forests that are overly dense can create excessive resistance and may be leveled by a large wave.

3. Highspeciesdiversityandamixedagestructurereduces structural uniformity of coastal forests and increases the density of roots, trunks, branches and foliage such that resistance to a tsunami is increased.

4. Maturestands (but not over-mature stands) are less likely to be toppled, uprooted or have trunks and branches snapped off by a tsunami.

Because social, economic and ecological conditions can constrain options for coastal forest development, it may be necessary to manipulate some of the above factors through forest design and management to compensate for a deficit in others.

Coastalforestscansometimesbecomealiability.Coastal forests can become a liability in the instance of very large tsunamis (e.g. greater than 10 meters in height). Even in cases where coastal forests could conceivably mitigate a tsunami, forest belts may be rendered ineffective if forest width, density, tree diameter, or soil substrate strength are insufficient and where broken material becomes debris to be carried further inland. Gaps in coastal forests – such as those located at river mouths, mangrove channel openings, settlements, beach access points and roads – can also act as funnels accelerating tsunami flows and increasing destructive force.

Forests and floodsForestscanreducefloodingriskinsmallandmediumcatchments.Forests and forest soils are capable of reducing runoff at small and medium scales for shorter-duration rainfall events, due to enhanced interception, infiltration and storage capacities relative to grasslands and bare lands. Evapotranspiration from forests also serves to reduce soil moisture content below that achieved by other vegetation types, creating a more substantial buffer against flooding when rainfall events occur.

However,forestshavelittledemonstrableinfluenceinmitigatingextreme,basin-wideeventsanddownstreamflooding,whichareoftentheresultofacombinationoffactors. Major floods often occur after prolonged periods of rainfall, such as during the late stages of the rainy season in monsoonal Asia when soil water retention capacities in connected river sub-basins are typically exceeded and incapable of soaking up additional water during a major rainfall event.

Forests and landslidesTreesandforestscanplaycriticalrolesinpreventinglandslidesandsoilerosiononhillsidesandmountainslopes. Deep-rooted trees and shrubs can reinforce shallow soil layers, anchor soil to bedrock, and form buttresses that resist soil movement. Forest cover and undergrowth also reduces soil moisture levels making landslides less likely to occur. Forests can also serve as an effective barrier against rock, debris and soil slips from higher elevations, as well as limit the distance of landslide run-out.

Forestcoverhasonlyamarginaleffectondeep-seatedlandslidesthataretypicallyinstigatedbyextremeeventssuchascontinuousheavyrainfallorearthquakes.Forests also impose a load on slopes and could increase susceptibility to land sliding where slopes are very steep or unstable.

Forestconversiontootherusesonslopinglandsgenerallyincreaseslandsliderisks. The removal of forests from sloping land can increase landslide risks even after regeneration, as rooting strength may take up to two decades to recover to previous levels. Land uses that increase slope instability and erosion include upland roads built without adequate engineering and drainage, poor logging practices and conversion of forest land to agriculture (although agroforestry lands that contain a significant proportion of trees can mitigate some risks).

Rehabilitationofslopinglandscanavertnegativeeconomic,socialandenvironmentalimpactsfromlandslideevents.Appropriate techniques to (re)establish vegetation on slope areas depend on the degree of soil disturbance and slopes must be sufficiently stable for the establishment of tree seedlings. The choice of species has both ecological and socioeconomic implications. Different species may be better suited to new conditions than previous ones, and species may also be chosen to provide goods and services to local people.

Conventional wisdom informing much of the discussion in Asia related to the role of forests in flood mitigation stems from the so-called ‘sponge theory’. According to the theory, the combination of forest soils, roots and undergrowth acts as a giant ‘sponge’ that regulates water flows by soaking up water during the rainy season and releasing it evenly during the dry season. While there is little empirical evidence to support this claim, related provisions remain embedded in many national forest policies and programs across Asia. Governments and the public are often quick to blame catastrophic floods on the clearing of forests by farmers and loggers in the uplands, although such links are not generally supported by scientific or empirical evidence. In many countries in Asia, the sponge theory has, nonetheless, provided justification to relocate populations from upland forest and watershed areas, implement massive reforestation programs and strict conservation measures, and also justifies current logging bans in China and Thailand. These initiatives have produced environmental benefits, but often at a high social and economic cost, particularly for local people residing in forest and watershed areas.

The ‘forest sponge’ theory and its inappropriate impacts on forest policy in Asia

Further reading

Braatz,S.,S.Fortuna,J.BroadheadandR.Leslie(Editors). 2007. Coastal protection in the aftermath of the Indian Ocean tsunami: What role for forests and trees? Proceedings of the Regional Technical Workshop, Khao Lak, Thailand, 28–31 August 2006. FAO, Bangkok.

FAOandtheCenterforInternationalForestryResearch(CIFOR). 2005. Forests and Floods: Drowning in fiction or thriving on facts? FAO, Bangkok; CIFOR, Bogor.

Forbes,K.andJ.Broadhead.2011. Forests and landslides: the role of forests and forestry in the prevention of landslides and rehabiliation of landslide-affected areas in Asia. FAO, Bangkok.

Forbes,K.andJ.Broadhead. 2007. The role of coastal forests in the mitigation of tsunami impacts. FAO, Bangkok.

All publications available at http://www.fao.org/asiapacific/rap/publications/en.

Further information

Please visit: http://www.rinya.maff.go.jp/j/kaigai/natural-disasters.html.

RecommendationsForestry can play an important role in mitigating the impacts of natural disasters in the Asia-Pacific region. Well-managed forests can provide a measure of protection to at-risk populations and property, as well as resources for reconstruction and recovery. However, mounting pressures on forest land and resources, combined with weak governance and rural poverty, pose serious challenges to managing forests in high-risk areas.

To ensure forestry remains utilized as an effective tool in disaster risk management and response systems, the following considerations are recommended:

Disasterriskreductionstrategiesshouldaimatmitigatingandadaptingto–ratherthanonsolelypreventing–disasters. Disaster risk strategies and management should aim to mitigate and minimize the impacts of disasters through implementing a variety of integrated measures that work with natural processes, rather than taking isolated measures that may be individually ineffective or relying solely on technologies and infrastructure to prevent adverse impacts.

Scientificevidenceisessentialindevelopingdisasterriskmanagementandresponsesystemsrelatedtoforestlandscapes. In many Asia-Pacific countries, disaster events have often triggered knee-jerk policy shifts in how forest landscapes are managed, rapidly and adversely affecting land-use practices and livelihood options for local people. Instead, disaster risk management plans and policies should be informed by the best available information, including both scientific evidence and empirical knowledge.

Potentialtradeoffsandopportunitycostsinimplementingdisasterriskmanagementshouldbefullyconsidered.Managing forests for protection may run counter to the interests of local stakeholders, including the rural poor, who due to poverty and economic considerations often have little choice but to live, or undertake activities, in high-risk areas such as coastal or steeply sloping zones. Therefore, assessments should involve local people and take their needs, interests and circumstances into account to ensure that any actions taken do not increase vulnerability by, for example, reducing livelihood options. In particular, the productivity and economic potential of protection forests for local people should be a major consideration.

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