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What is a Forest Worth – Explicitly?

How much is this worth? Photo: Tripp Burwell

By Tripp Burwell

A major focus in the conservation world today is finding (and perhaps creating) economic incentives to perform acts of conservation.

This method has its detractors, but proponents assert that if we can find additional motivations for conservation, that can only help the conservation effort.

If you follow conservation news, or even the Pope’s encyclical on climate, you may have heard of ecosystem services.

Essentially, functioning ecosystems provide positive benefits to people. To name a few services: healthy ecosystems sequester carbonstop erosion, and purify air and water.

People frequently cite water purification as one of the most economically valuable aspects of ecosystems services. Water that passes through a healthy ecosystem is less contaminated, and it thus costs less to treat.

People are also willing to pay for water.

The best known case of an economically motivated land conservation action to purify water occurred when New York City opted to restore watersheds in the Catskill Mountains rather than build a new multi-billion dollar filtration plant in the 1990’s.

It was generally understood that land restoration in the headwaters would be cheaper than the cost of the plant.

How much cheaper though? How great were the benefits of conserving forest compared to the cost of treating water?

New York City headwaters. Photo: Tripp Burwell

These questions are difficult to answer for a variety of reasons, but mostly because these benefits are hard to quantify.

However, as some have recently noted, we are entering “the cost-benefit state” – and knowing these precise values is becoming more and more important.

Previous researchers who have tried to examine exactly how beneficial healthy forests are for water purification, however, have mostly focused on the effect of the quality of the water going into a water filtration plant.

They haven’t been as concerned with, or able to tease apart, the central question of what the effect of forest cover is on water treatment cost (did the Catskills conservation effort provide an economically efficient solution to the problem?).

This is an understandable oversight.

Water quality is relatively straightforward thing to measure. It’s a measurement that is done often and can be easily replicated. However, analyzing such data tells us very little about the actual forest performing the service.

To appropriately value the service, we need to understand some information about the forest for a few reasons.

First, ecosystems are not homogeneous. Some forests likely do a better job of water filtration than other forests. Secondly, to explicitly value the contributions of these different types of forest to water filtration, we need to know the forest condition (intact, logged, degraded, etc.) and size.

Conducting such a comprehensive analysis requires a large set of detailed data – both on forest cover conditions and on water filtration expenses.

Land-cover in various parts of the New York City headwaters. Photo: Tripp Burwell

A team of researchers at Duke’s Nicholas School of the Environment and the Forest Research Institute of Malaysia examined this issue in a recently published paper in Environmental and Resource Economics, titledValuing Water Purification by Forests: An Analysis of Malaysian Panel Data.

We used econometric models to examine monthly water treatment costs across 41 treatment plants throughout Malaysia from 1994-2007. Fortunately, Malaysia has exceedingly good data on forest cover and water treatment costs – allowing us to address several questions for the first time.

Additionally, we could control for a lot of factors that may have otherwise made our analysis less robust – such as the varying amount of rain present in the monsoon-driven climate of Malaysia.

We looked at three key questions:

1. How much forest do you need?

2. How do the benefits provided by the forest compare with the cost of water treatment?

3. How do the economic benefits of providing water purification compare with the economic benefits of converting the land to some other use (e.g. agriculture)?

Is this enough forest? Photo: Tripp Burwell

1) How much forest is enough?

Developing countries generally have much higher deforestation rates than developed countries, and often poorer quality drinking water too.

Some programs have been established, particularly in Ecuador and Vietnam, to pay people to conserve the water quality service that forests provide, but there has been little established evidence about their effectiveness or value.

Conservatively estimating, we found that protecting virgin and logged forests against conversion to nonforest land uses can reduce the operating costs of water treatment plants.

Specifically, averaging across the 41 treatment plants, we found that avoiding the conversion of 1% of a catchment from forest to nonforest land use reduced treatment cost by 1.16% in the case of virgin forest and 0.85% in the case of logged forest.

The author explores untreated water. Photo: Kamal Medhi

2) How do the benefits provided by the forest compare with the cost of water treatment?

We defined marginal value as the annual reduction in treatment cost that results from the conversion of 1 ha of virgin forest to a non-forest land-use.

Our research suggests that the forest’s value to the treatment plants was equivalent, on average, to more than a third of the plants’ aggregate expenditures on priced inputs (labor, energy, chemicals, maintenance).

Overall, the marginal value trendline was downward, in keeping with textbook marginal benefit curves.

The marginal values varied greatly across the treatment plants (forest cover was more valuable to some treatment plants than others) – highlighting the importance of many factors in the environment to water treatment cost.

In one case, the overall benefit to a treatment plant was greater than the expenditure on all priced inputs.

Alternative land-use: oil palm. Virgin forest behind. Photo: Tripp Burwell

3) How do the economic benefits of providing water purification compare with the economic benefits of converting the land to some other use (e.g. agriculture)?

Maintaining virgin forest also incurs an opportunity cost, or the cost of otherwise pursuing some other opportunity with the land. In this case, virgin forest would likely be converted to rubber or oil palm plantations.

The annual economic return from these plantations was much higher than the return we found from maintaining a high quality forest for the water treatment plants.

Initially, this suggests that the value of water purification does not justify protecting the forests from agricultural conversion, as that would result in a higher economic return for the community.

However, we felt that this comparison exaggerated the gap between the purification service’s marginal benefit and its marginal cost for a few reasons.

  • We used conservative methods to estimate the marginal benefit, which likely underestimated such a benefit.
  • Establishing rubber and oil palm plantations requires substantial investments in infrastructure, terracing, and drainage, which we were not able to factor into our calculations. Additionally, our estimates of plantation returns were nationwide averages across Malaysia, including many highly productive lowland plantations.
  • These lowland sites offer superior growing conditions to and lower investment costs than creating plantations in the headwaters above the treatment plants. Thus, we overestimated the opportunity cost by an unknown, but surely large, amount.

Overall, this suggests that water purification services would more likely justify protection of virgin forests in locations where the main threat comes from logging (i.e., degradation), not conversion to plantation crops (deforestation).

Water purification can justify protection against logging. Photo: Tripp Burwell

This is the first econometric study to estimate directly the effects of tropical forest characteristics on water treatment cost. Generally, economically-motivated decisions about forest protection and use have previously not been able to take such important services into explicit account.

Maintaining virgin forest creates real and quantifiable benefits to both the Malaysian government and the Malaysian people. These benefits vary significantly across water treatment plants, highlighting the fact that there are likely many situations where protection of virgin forests could be justified just for the economics alone.

Additionally, water purification is just one of the services that tropical forests can supply. It is the only one that we have quantified here. Protection decisions that appear to be economically unjustified when only water purification is considered might turn out to be justified when a broader range of services is taken into account.

Tripp Burwell is on the Board of Directors for SCB’s North America Section and an MBA/MEM candidate at UNC’s Kenan-Flagler Business School and Duke’s Nicholas School of the Environment. 


  1. Beth King
    Smithsonian Tropical Research Institute, Panama
    September 16, 2015, 11:12 am

    We are studying exactly this question in a 700ha area of the Panama Canal watershed. Read more about the Agua Salud Project at: http://www.stri.si.edu/sites/tropicos/pdf/TROPICOS_Mar_2015.pdf

  2. Sharl Heller
    Plymouth, MA
    September 16, 2015, 6:23 am

    As a member of the Plymouth Massachusetts Open Space Committee, we are always looking for information that justifies efforts to preserve natural areas. While I find it sad that we must quantify in dollars the value of preserving forests, your article provides exactly the kind of information we need. Thank you.