WIND RISK MANAGEMENT INVIET NAM’S ACACIA SAWLOG TRANSITION

December 2018POLICY BRIEF

Key points Storms impose signifi cant risks on the economic performance of forest plantations dedicated to sawlog production, in the typhoon-exposed topography of Viet Nam. The assessment of wind exposure and the implementation of site-ad-apted silviculture are paramount in proactive forestry risk management. We combine state-of-the art wind risk assessment tools at regional level and supplement them with specifi c silvicultural management measures. The best strategy to reach tree sta-bility in high wind risk areas is the promotion of early diameter growth through timely thinning.

UNIQUE has developed business models for sustainable sawlog production. Together with IRENI, UNIQUE supported state forest enterprises and policy makers in overcoming the speci� c challenges as well as the piloting of the modelsII. � is work included asses-sing key barriers to large-scale implementation of sawlog production with Acacia and high-value native tree species. � e most prominent challenges are related to � nancingIII

the transition, managing wind damage risks, and building technical and silvicultural capacities. � is policy brief outlines our approach to mitigating the speci� c risk of storm damages in Acacia plantations for sawlog production through appropriate site selection and corresponding silvicultural treatments.

AcknowledgmentThis work was fi nanced by the Ger-man International Climate Initiative (IKI) by the German Federal Ministry for the Environment, Nature Conser-vation and Nuclear Safety (BMU).

f o r e s t r y a n d l a n d u s e

Forest Research

Nicolas Wittmann, Paul Jacovelli, Tommaso Locatelli,Ho Dac Th ai HoangUNIQUE forestry and land use GmbH

Viet Nam’s strategy to boost domestic sawlog production

Th e Government of Viet Nam has recog-nized the need and potential to increase the domestic production of sawlogs for its successful export-oriented processing in-dustry. Viet Nam’s natural forest resources are signifi cantly degraded and the domi-nant use of approx. 4 million ha of Acacia plantations is short-rotation chipwood pro-duction. Th e success of this business mo-del has helped regreening the country and signifi cantly reduced rural poverty. Howe-ver, this situation forces Viet Nam’s timber processing industry to import vast amounts of sustainably and legally produced tim-ber to satisfy its growing demandIV – cur-rently about 5 million m3 per annumIII&V.Th e government has issued policies which promote the transition, e.g. in its National Forestry Development Strategy 2006 – 2020 aiming at doubling domestic sawlog pro-duction to about 12 million cubic meters per year by 2020VI. In the meantime, this target has been supported by a number of

decisions and decrees. For example, deci-sion 5115/QD-BNN-TCLNVII of 2014 de-mands an increased value addition of 54% per m³ produced and that less than 40% of cultivated forests are used for chipwood pro-duction. Th e recently revised Law on Fores-try was adopted in December 2017. It puts a strong emphasis on promoting sustainable forest management and forest certifi cation in production forests. Both measures sup-port an increase in sawlog production.

Th e predominantly state-owned enterpri-ses have also realized that the profi tability of the currently prevailing short-rotation biomass production will further decrease due to rapidly increasing labour costs and price volatility for chipwoodVIII. However, despite the government’s eff orts to trigger the transition towards sustainable forest management, progress is still slow and this imposes signifi cant challenges for forest owners.

12 year old Acacia auriculiformisstand near Hue city

Figure 1: Acacia hybrid stand severely damaged by a tropical storm (Photo: Phong Dien FPD, 2016)

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Th e approach for mitigating wind risks for Acacia sawlog production

Acacia hybrid, a crossbreed of Acacia mangium and Acacia auri-culiformis, is a robust and fast growing species with good wood properties, high market demand and relatively straightforward silviculture. Th ese factors have led to its widespread and still growing use, and Acacia hybrid will remain the species of Viet-namese forest owner’s choice in the near future. However, in the exposed topography of Viet Nam, tropical storms pose a major risk to Acacia hybrid management. Th e North Western Paci-fi c Ocean is one of the world’s major tropical cyclones’ genesis areas. Many typhoons make landfall in Vietnam and cause seve-re economic damage, with gust wind speeds of >200 km/h ac-companied by heavy precipitationIX. Damage caused in planted forests ranges from branch and stem breakages to whole swathes of trees blown down.

With regard to sawlog production many practitioners worry that longer rotation lengths will lead to greater losses compared to short-rotation chipwood production. In response UNIQUE, IREN and Forest ResearchX have developed a wind risk mitiga-tion strategy for long-rotation Acacia plantation management. It consists of two major steps: In step one high risk areas are iden-tifi ed using the ForestGALES model and Air fl ow modelling, in a second step appropriate silvicultural management decisions and treatment strategies are derived for the diff erent areas and production goals.

Step 1: Critical wind speed modelling and plantation zoning

One of the best and most widespread models for predicting wind damage risk is ForestGALES, developed by Forest Rese-arch in windy Scotland. ForestGALES uses engineering princi-ples to calculate critical wind speeds at which a tree or a stand breaks or is uprooted. It was originally developed to model for a range of conifer species under growing conditions in the United Kingdom. In the meantime, it has been adapted to and applied in half a dozen countries on four diff erent continentsXI.

In order to map wind damage risk, ForestGALES needs fi rst to be parameterized for a specifi c species through mechanical tests on wood samples and a number of uprooting experiments. Th en, ForestGALES can be fed with inventory data from which it calculates critical wind speeds. Key input variables are:

Height of the tallest tree(s) in a stand; Mean diameter at breast height (1.3 m); Stocking density; Predominant soil type in a stand; Predominant depth of rooting system in a stand; Size of largest upwind gap adjacent to the stand.

Together with historical local wind climate data, ForestGALES calculates the average return period in which the critical wind speeds occur. Th e larger the diff erence between a planned rota-tion period and the specifi c return period of the critical wind speed, the lower is the wind damage risk.

Due largely to the rough topography in Viet Nam, wind micro-climate may vary considerably depending on the degree

of exposure to the main wind direction. Th erefore, ForestGA-LES’ predictions require that the localised air fl ow is modelled. Th e airfl ow model WAsP (Wind Atlas Analysis and Application Program) has successfully been coupled with ForestGALES to account for the infl uence of topography on meso and micro sca-les (fi gure 2). By applying these two models wind damage risk can be modelled for any given site as well as for any given stand structure. Th e results can then be used for silvicultural planning and practical management guidelines – i.e. identifying zones in which high-value, long-rotation management is feasible at ac-ceptable risk levels.

Figure 2: WAsP air fl ow model for 400 ha plantation area near Hue city. Dark colours indicate low average wind speeds, bright colours high average wind speeds.

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Step 2: Wind risk adapted silviculture

Mitigating wind damage risk is closely linked to the silvicul-ture applied, and so far there is little practical experience with regard to sawlog management in Viet Nam. In short-rotation biomass production, silvicultural interventions such as thinning and pruning are almost negligible. However, they are key for the successful production of high-value sawlogs.

Silvicultural interventions shape the appearance of single trees and plantation stands, especially with regard to sawlog manage-ment. Th ey infl uence a number of core factors determining wind risk vulnerability: Very dense stands limit the penetration of downbursts though the stand canopy, and provide strong mu-tual tree support, resulting in a high stand stability. On tree level sturdy trees with large diameters show a high single tree stability.

Optimising stand stability in sawlog management is challen-ging. Sawlog stands need to be thinned in order to promote the diameter growth. Th e gaps produced by thinning interventions increase wind penetration in the stand, which temporarily lo-wers the stand stability. In contrast, promototing single tree sta-bility is needed to achieve sawlog management goals. Diff erent to chipwood management, sawlog production should therefore focus on optimising single tree stability of future crop trees in order to mitigate wind damage risks.

Th inning interventions should be implemented intensively and early in the rotation because young stands typically show stron-ger growth dynamics than older stands, hence stand gaps crea-ted by thinnings are closed in a comparably shorter time. Th is way, single tree stability is promoted and stand stability main-tained to the highest degree possible.

First ForestGALES application in Viet Nam

In 2017 and 2018 a team of UNIQUE, IREN and Forest Rese-arch staff explored the potential of modelling wind damage risk. Th e fi rst phase of the study aimed at gauging the feasibility of adapting ForestGALES as a wind damage risk prediction tool in the Vietnamese context. During the second phase the team progressed in the development of a ready-to-use risk mitigation tool for Acacia hybrid in Vietnam.

Acacia hybrid plantations are considerably more prone to stem breakage then to uprooting. Th erefore, we parameterized Fo-restGALES to model Acacia hybrid stem breakage by perfor-

ming mechanical tests on wood samples of a number of age strata. Th en we modelled wind damage risk in a 400 ha plan-tation area near Hue city, in North Central Viet Nam. For each stand in the area the team assessed the wind damage risk for two diff erent scenarios. In a business-as-usual scenario (chipwood management) we assumed a high planting density and no thin-ning interventions. Th e second scenario (sawlog management) assumed for all stands lower stand densities and higher average tree diameters due to thinnings. Th e results show a considerably lower wind damage risk for the sawlog scenario (fi gure 3).

Figure 3: Comparison of the chipwood (left) and the sawlog scenario (right); wind risk rangesfrom low (dark green) to high (dark red) on 400 ha plantation area near Hue city

Conclusions & Outlook

Vietnamese government policies promote a transition towards sustainable forest management and sawlog production in large parts of the approx. 4 million ha of plantations which to a large extent are still managed in short-rotations for woodchip pro-duction. This confronts forest owners with severe wind risks in the exposed topography of Vietnam, which must be adequately assessed and addressed to achieve the desired economic perfor-mance.

Against this background, the consortium of UNIQUE, IREN, and FR has applied for the first time the ForestGALES model on

Acacia hybrid in Vietnam. ForestGALES is a powerful predicti-on tool which can be applied at different levels (stand, enterpri-se, landscape). Combined with respective silvicultural strategies the modelling allows for effective reduction of wind damage risk of Acacia hybrid stands for Vietnamese forest owners and land use planning. The tools and principles applied can be translated to other species and management systems in the future, e.g. rub-ber production. UNIQUE and its partners seek to accompany the development of the presented approaches to an applicati-on-ready wind risk mitigation strategy for Viet Nam.

UNIQUE forestry and land use GmbHSchnewlinstraße 1079098 Freiburg, GermanyTel.: +49 761 208534 0unique@unique-landuse.de

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ReferencesI Institute of Resources and Environment (IREN) of Hue University

II Pistorius, T., Ho Dac Thai Hoang, Tennigkeit, T., Merger, E., Wittmann, N., Conway, D. (2016): Business Models for the Restoration of short-rotation Acacia plantations in Vietnam, available online (EN & VI): https://www.unique-landuse.de

III Gromko, D., Pistorius, T., and Pham, T.L.H. (2017): Financing options for enhancing the value and productivity of production forests in Viet Nam, available online (EN & VI): https://www.unique-landuse.de

IV Phuc, X., and Canby, K. (2011): Baseline study 3, Vietnam: Overview of Forest Governance and Trade. Forest Trends FLEGT Asia Regional Programme. Forest Trends. Washington DC, USA

V VIBIZ. 2018. Import and export timber of Vietnam in (2017): Timber production. Vietnam business monitor & Insti-tute for brand and competitiveness strategy, available online (VI only): http://vibiz.vn/upload/17604/20180416/BaO-CaO-Go_compressed_1.pdf

VI MARD (2007): Forestry Development Strategy 2006–2020

VII MARD decision 5115/QD-BNN-TCLN (dated Dec. 1, 2014); other important regulations are MARD decisions 1565/QD-BNN-TCLN (dated July 8, 2013) and 919/QD-BNN-TCLN (dated May 5, 2014)

VIII Government of Viet Nam (2018): Việt Nam xuất nhập khẩu gỗ và sản phẩm gỗ, available online (VI only): hhttp://goviet.org.vn/upload/aceweb/content/Bao%20cao%20tong%20quan-final.pdf

IX Nguyen, K.C., Hoffmann, P., Abbs, D., Chattopadhyay, M., Nguyen, H.Q.T. and Tory, K. (2014): Climate features and extremes. In: Katzfey, J.J. McGregor, J.L. and Suppiah, R. (eds). High-resolution climate projections for Vietnam: Technical report. CSIRO, Australia

X Forest Research (FR) is a UK-based public forestry research institute

XI Locatelli, T, and Nicoll, B. (2017): Wind damage risk for Acacia plantations in Thua Thien Hue province of Vietnam, available online (EN): https://www.unique-landuse.de