Thirty percent forest or 70% agroforest: which will make an Indonesian watershed healthy?

Indonesia’s spatial planning law prescribes 30% of land needs to be set aside as forest for watershed functions. But this number was originally based on melting snow in Europe. Will it lead to healthy watersheds in the tropics?


By Meine van Noordwijk


Numbers can seem very definitive but that doesn’t mean they shouldn’t be questioned. One such case is Indonesia’s ruling that 30% forest cover will secure a healthy, well-functioning watershed. Where does this number come from? This value of 30% was first proposed in the 1920s, derived from research into a forest’s function in delaying snowmelt in the Swiss Alps and thus reducing the risk of floods. This finding is not directly transferable to the tropics.

Rather, based on our research at the World Agroforestry Centre it seems that some other numbers and issues are probably more relevant. For example, if a single numerical target is desired, then aiming for 70% land cover with agroforests is more realistic than 30% with forests. From a socioeconomic point of view, this is because farmers prioritize the maintenance of systems, such as agroforestry, that improve their livelihoods. And in situations where the opportunity costs don’t add up—for example, in oil-palm landscapes adjoining old complex rubber systems that act as buffer zones around national parks—then rewards’ schemes, such as those promoted by the World Agroforestry Centre and the International Fund for Agricultural Development through the Rewards for, Use of, and Shared Investment in Pro-poor Environmental Services project, which are being taken up by the Ministry of Environment and others, might tip the balance in favour of ‘conservation with benefits’.

Biophysical issues also underlie the inadequacy of the ‘30% forest’ value: even in the best possible condition an otherwise degraded watershed with 30% forest cover only leads to a buffer indicator of 30%. A ‘buffer indicator’ is derived from computer modelling of quantitative flow in streams; it can be used as a performance indicator for a watercourse. For example, degradation of a watershed that brings the buffer indicator below 70% usually means flooding problems. This can be seen in the case of riparian wetlands that are converted to other, non-buffering uses and where urbanization and road construction increase the fast-drainage (and low infiltration) fraction of land, directly reducing buffering and promoting floods. To achieve a buffer indicator of 70% or more, a corresponding 70% or more of the watershed needs to be in a high-infiltration condition. Agroforestry systems and dispersed trees in the landscape support high infiltration.

It is clear from our research that to properly manage watersheds to ensure that they are functioning well needs a focus on all land uses not just on a forest fraction. A full evaluation of the effect of different types and quantities of land cover on watershed functions needs to include the effects of tree cover on temperature, wind speed and rainfall, as well as technical engineering interventions in the flow pathways of water, such as drainage ditches and dams.

agroforest, Indonesia, watershed

Agroforests support watershed functions in Indonesia. Photo: World Agroforestry Centre/Meine van Noordwijk

Generally speaking, public policies that supposedly attempt to maintain, or restore, the services provided by well-functioning watersheds usually stay at the level of expressing objectives (‘healthy watersheds’), prescribe solutions (‘X% forest’) and governance instruments (‘carrots, sticks and sermons’) or focus on a socially valid process (‘multi-stakeholder participation’) or some combination of the above.

But implementable policies require clarity about what terms mean and how borderline cases are to be interpreted; otherwise everything will become a borderline case and absorb attention and energy that could be used in better ways. The closer a policy’s targets are to the function to be achieved, the more likely it is that the targets will actually be achieved.

So when land-use categories are used with reference to specific functions, the operational definition of the terms becomes of more than academic importance. ‘Forest’ is a notoriously fuzzy concept in this regard. Use of a fuzzy concept can be politically advantageous because more people think their interests are being taken into account but whether, when the fog clears, there is a well-functioning watershed or not remains to be seen.


This article is based on a presentation made to Indonesia’s National Watershed Health seminar in Malang, East Java, 30 September 2014.

For tracing the reference to snowmelt, see the Bibliography of Soil Science in Indonesia 1890–1963: Japing HW. 1930. Bosch hydrologisch onderzoek van den laatsten tijd. Recent forest hydrological research. Tectona 23:919–935 in which ‘the author reviews recent forest hydrological research done in Switzerland (Engler 1919, Burger 1928), USA (Bates and Henry 1928, Shuman 1929, Lowdermilk 1929) and Japan (Tokutaro Hirata 1929). He considers the results in connection with their significance to Java. Afterwards, he makes recommendations for further research on this subject (direct measurement, on a large scale, of the run off on small plots together with the exact measurement of discharges in some collection areas; soil physical analysis and laboratory experiments) in Java’.



Edited by Robert Finlayson



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This work is linked to the CGIAR Research Program on Forests, Trees and Agroforestry’s component on Landscape Management of Forested Areas for Environmental Services, Biodiversity Conservation and Livelihoods



Rob Finlayson

Robert Finlayson is the Southeast Asia program's regional communications specialist. As well as writing stories for the Centre's website, he devises and supervises strategies for projects and the countries in the Southeast Asia region, including scripting and producing videos, supervising editors and translators and also assisting with resource mobilization.

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