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Tree planting: A key weapon against global warming

External Reference/Copyright
Issue date: 
Friday, 22 February 2008
Publisher Name: 
Carbon Positive
Ally Charlton, Ian Hamilton
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Tree-planting activities - reforestation and afforestation - have come in for criticism in recent times, giving rise to a debate over whether planting new forests in order to combat climate change is worthwhile, and whether it can be accurately reflected in a system of economic credits.

The criticisms focus on:

  • the validity and accuracy of methods used to calculate the climate change benefits,
  • the ethics of ‘offsetting’, that is, compensating for emissions rather than eliminating them at source, and
  • the social and environmental impacts of plantations.

Carbon Positive believes strongly that tree-planting can and will make a valuable contribution to the fight against global climate change, as well as providing a host of wider environmental and socio-economic benefits. We further believe that carbon markets in their various forms are key to providing an effective means of financing tree-planting activities on the scale needed to make a difference globally.

This article seeks to support this view by outlining the many benefits of reforestation projects, and responding to some of the most frequent criticisms made of them.

There are indeed a number of pitfalls to be avoided, by both project developers and buyers of the carbon credits which finance climate-related plantation projects. But these are not by and large fundamental to the planting of trees, and can largely be avoided through responsible practices and adherence to appropriate standards.

So what are the benefits of planting trees?

Planting trees is hugely beneficial to the world in the face of accelerating climate change. There is now a strong international scientific consensus that human activity is causing global warming. A substantial reduction in the planet’s forest cover over recent centuries is a major contributor to this climatic change.

As trees grow they absorb carbon dioxide (CO2), the main 'greenhouse gas' responsible for global warming, thereby reducing the concentration of this gas in the atmosphere. Forests are referred to as 'carbon sinks' for this function of CO2 absorption and storage. Planting trees to bolster carbon sink area, an example of what’s termed ‘carbon sequestration’, helps offset the loss of native forests and fights global warming.

At a local level, tree-planting on deforested lands creates further environmental benefits. Forests play a vital role in regulating water supplies, helping to minimise both water shortages in times of drought and damaging floods in heavy rains. Trees also reduce soil erosion, thereby conserving soil quality upstream and water quality downstream. Forests also provide habitats for a wide array of plant and animal species, a number of which are threatened with extinction by deforestation.

Socio-economic benefits of reforestation projects include direct employment, infrastructure development, skills-transfer and the creation of markets for related products and services. Certain plantation forest models may also provide local communities with additional products such as fuel-wood, fruit, nuts and herbs, and opportunities for agricultural activities (inter-cropping, livestock grazing) within the forest area.

Finally, sustainable forestry can provide additional climate change and local environmental benefits in the longer term. Once harvested, the wood from the trees may be used either as a source of renewable energy, thereby reducing the use of fossil fuels, or for construction materials or furniture-making, thereby reducing deforestation elsewhere.

What are the criticisms?    

Against the background of the general benefits of tree planting there are a number of specific criticisms. These are summarised below and then examined in detail.

1. Tree-planting doesn’t address the real issue of preventing emissions at source
2. Trees take too long to make a difference to climate change
3. Carbon credits from tree plantations aren’t properly verified
4. Trees don’t last forever so their climate change value isn’t permanent
5. Money for plantations would be better spent preventing deforestation
6. Tree plantations are bad for biodiversity and the local environment
7. Forests may actually contribute to global warming
8. Plantations often have negative social impacts

1. Tree-planting doesn't address the real issue of preventing emissions at source:
We cannot rely on planting trees to absorb our ever-increasing emissions of greenhouse gases. We must instead focus on reducing both our total energy consumption and our reliance upon ‘dirty’ technologies and fossil fuels.

Yes, absolutely.

But this does not mean that planting trees is a bad thing, merely that it should not be the primary focus of the global response to climate change. As with a new illness, where you treat the symptoms of existing cases whilst working on finding a vaccine against future cases, it is desirable to plant trees while we work on addressing the longer-term technological and behavioural challenges of emissions reduction.
This criticism is in fact made not just of tree-planting, but of the wider concept of 'offsetting', that is, paying for greenhouse emissions reductions elsewhere to counter-balance one's own emissions. A common variant of the argument adds a moral perspective, likening offsetting to the medieval practice of buying ‘indulgences’ – effectively licences to sin - from the Church.

However, the analogy is flawed: whilst one can choose to sin or not to sin, in today's world it is simply not possible to stop emitting greenhouse gases immediately, or within a few years. Even with significant financial commitments and fundamental lifestyle changes, climate change will not be stopped within a few years.

So whilst in the long-term individual and corporate behaviour and the energy basis of the entire global economy must change, in the short-term it is better to purchase offsets than to do nothing at all. This is especially the case when considering the other environmental benefits that planting trees can bring beyond climate change.

It is also worth noting that in existing and emerging emissions trading schemes, it is not possible for emitters to cover all their emissions with offsets. In the EU Emissions Trading Scheme (EU ETS) and the Regional Greenhouse Gas Initiative (RGGI) in the US North East, for example, the use of offsets is limited to a small proportion of the overall emissions cap, typically 3 to 15 per cent. These limits are designed to keep the focus on reducing emissions at their source.

2. Trees take too long to make a difference to climate change:
It takes 50 or 100 years for trees to grow large enough to absorb significant amounts of carbon so accurate carbon crediting shouldn’t see any generated for decades.

This is not the case for plantation forests.

Carbon absorption rates in trees depend on the species and the location. Fast-growing species in tropical climates can sequester CO2 many times faster than the average European forest, and plantation projects aimed at earning carbon credits are typically designed to maximise the sequestration potential.

Over a 20-year lifecycle, the right species in the right conditions can absorb over 40,000 tonnes of CO2 per square kilometer. So a plantation of 100 square kilometers can absorb 4 million tonnes of CO2 over 20 years. That’s equivalent to taking 50,000 cars or more off the road during that time (based on annual emissions of 3 to 4 tonnes for the average car and its usage).

Even when allowing for other factors that reduce the net carbon effect of tree planting, such as the greenhouse-gas emissions from vehicles and machinery used during planting and maintenance, a sizable plantation makes a very significant positive contribution to the greenhouse problem.

Attracting deserved criticism, however, is the reported practice of some offset providers selling upfront, in one year, forest carbon credits for the total future CO2 absorption of trees over their lifetime. This is not good practice. However it is not permitted under the Kyoto Protocol’s Clean Development Mechanism (


); afforestation and reforestation credits are issued every five years, and only for the amount of carbon stored up until that point. Non-Kyoto carbon offset schemes are discussed below.

3. Carbon credits from tree plantations aren’t properly verified:
Reforestation credits are unreliable because there is little verification of trees grown or accurate accounting for credits generated.

This is a valid criticism of the ‘voluntary’ market currently, but not the ‘compliance’ market.

In the compliance market, offset credits are purchased to meet mandatory requirements under the Kyoto Protocol or other regional or national emissions trading schemes. The most widely used are


under the CDM. Carbon credits for compliance are highly standardised and regulated. Tight conditions govern what kinds of projects qualify for credits, strict monitoring and auditing is required, and centralised registration and issuance of credits prevents double-counting.

The fact that afforestation and reforestation projects have been slower to get off the ground in the CDM than clean technology projects is largely because of the commitment within the UNFCCC to ensure that the rules governing measurement and credit generation are credible.

So far, it’s a different story in the ‘voluntary’ market, where organisations and individuals buy carbon credits to offset their emissions by their own choice. There are no laws forcing them to do so, and hence a lack of common standards and regulatory oversight. Tree-planting is a common activity for generating offsets in this market.

While many providers of voluntary credits do adhere to robust verification and accounting principles, there have also been cases of inconsistent calculation of credits, sales of non-existent credits, and double-counting of credits. The lack of consistency has made it difficult for buyers of credits to be sure that emission reduction projects are actually carried out and do deliver their promised reductions.


There is certainly a need for greater standardisation and better regulation of this market to ensure that 'cowboys' cannot survive in it. Many providers of voluntary credits agree on this. International accreditation standards, such as the Voluntary Carbon Standard, VER+ and the Community, Climate and Biodiversity Alliance’s CCB Standard, are now emerging to address these concerns and provide buyers of credits with confidence that they are indeed getting their money's worth.

Those looking to buy tree-planting credits in the voluntary market should be wary of projects that do not come with an internationally-recognised accreditation. If a project’s validity can’t be transparently demonstrated or independently verified, then the credits should not be bought.

4. Trees don’t last forever so their climate change value isn’t permanent:
You can never be sure how long the trees planted for carbon credits are going to remain in the ground.


Yes, and carbon crediting should reflect this.

A major difference between reforestation projects and other carbon credit projects is that tree planting takes CO2 out of the atmosphere. Forests are a carbon sink whereas most other carbon cutting projects directly prevent carbon going into the air in the first place – from sources such as factories, power plants and transport.

Unlike direct reductions in emissions, carbon sequestration through tree-planting is reversible. Trees could burn down in a forest fire, die from disease or insect attack, or be chopped down by those seeking to exploit their economic value, all of which will sooner or later release some or all of the stored CO2 back into the atmosphere.

The need to address this issue caused considerable debate and delay before afforestation and reforestation (A/R) projects were allowed to qualify for credits in the CDM. A/R projects were finally admitted in 2003, but with specific rules which differ from those for all other CDM credits. The A/R rules are complex but, in effect, credits have to be verified every five years. If the trees are not still standing, then the credits are no longer valid and replacements must be purchased. By contrast, all other credits under the CDM are valid in perpetuity once issued. As a result, A/R credits trade at significantly lower values per tonne of CO2 than other ‘permanent’ credits. 

Not many voluntary market projects apply this level of rigour in their carbon accounting as yet but, as described above, independent accreditation standards do exist. For example, the revamped

Voluntary Carbon Standard

(backed by The Climate Group, International Emissions Trading Association and the World Business Council for Sustainable Development) accounts for the possibility of carbon loss by requiring a proportion of carbon credits generated every year be held in a “buffer reserve” to cover potential losses.

So, it is now possible to ensure the long-term credibility of carbon credits from forestry projects in both the Kyoto-compliance and voluntary carbon markets. Buyers should use only those offset providers that have achieved the appropriate accreditation.


Forest carbon standards: Full rundown

5. Money for plantations would be better spent preventing deforestation:
Clearing of native forests results in large greenhouse gas emissions so investing in halting deforestation in the first place should be the priority.

We need to do both.

Slowing and halting the clearing of native forests is critical. Deforestation is the second largest source of global greenhouse gas emissions after power generation, according to the Global Canopy Programme, contributing to the release of up to 2 billion tonnes of CO2 into the atmosphere per year – significantly more than all the cars and trucks in the world.

Support for globally co-ordinated deforestation initiatives - involving paying developing countries and their communities not to clear vital tropical rainforests – is gaining momentum.

However, that solution is only just getting underway whilst deforestation continues apace. Until the significant political and technical obstacles to these initiatives are resolved, reforestation provides a valuable counter-balance to ongoing forest destruction. In the long-term, the ideal solution is that sound incentives be in place both to halt deforestation, and to encourage reforestation.

The Reduced Emissions from Deforestation and Degradation (REDD) initiative is already beginning to see

carbon credits paid

for the preservation of existing tropical rainforest – properly monitored and verified to the CCB Standard. This is further evidence that the evolving market system of carbon credits is set for a key role on both sides of the forests-climate equation - deforestation and reforestation.

6. Tree plantations are bad for biodiversity and the local environment:
Large mono-culture plantations of exotic species do not benefit native plants and animals, and native forests are sometimes cut down to make way for them.


This is true of some commercial timber plantation operations, but not of tree-planting overall, and particularly not of well-regulated carbon-financed projects.

The first element of this argument is addressed in a key requirement for most carbon offset tree-planting schemes; that they be located on land that was cleared or degraded some time previously. To be eligible for credits under the CDM, it is necessary to provide detailed proof that the land was cleared before 1990, when the idea of carbon-based financing for reforestation first emerged. Other standards also require clear evidence that benefits are not accruing to those responsible for the original land-clearing. These controls ensure that carbon credits do not provide incentives for further deforestation.

The second point is a valid criticism of purely commercial timber plantations of fast-growing tree-species, such as eucalyptus and certain types of pine, which certainly do not replicate the conditions of a natural forest.

However, most carbon offset schemes include strict criteria on local environmental and biodiversity impacts in order to address these concerns. Species selected must be appropriate for the sites, and many schemes require a certain proportion of trees planted to be indigenous species or a certain proportion of the land to be devoted to native forest regeneration. And since offset projects are generally located on land that is already degraded, they still lead to an overall increase in ecosystem health and biodiversity.

It is finally worth noting that it is somewhat unfair to judge commercial timber plantations against the benchmark of natural forest. This imposes a higher standard than that faced by commercial growers of other non-indigenous monoculture crops, such as wheat or maize, and ignores the additional environmental benefits that plantation forests do provide.

7. Forests may actually contribute to global warming:
Recent studies have found evidence that some forests’ atmospheric warming effects may outweigh their cooling impact.  

Not the case in most carbon sequestration plantations.

One study released in late 2006 found that in addition to the ‘cooling effect’ due to absorption of CO2, forests have several other warming and cooling effects, which vary according to where the trees are planted. In temperate latitudes the dark foliage of trees absorbs more solar energy than the grasslands or open areas which they tend to replace, and trees also grow slowly, removing relatively low volumes of CO2 from the atmosphere per year.

In tropical climates, by contrast, the trees generally replace dense ground vegetation and thus have little impact on solar energy absorption. The trees grow fast and absorb high volumes of CO2, and higher evaporation levels add a further cooling effect.


study thus concluded

that whilst tree planting in the tropics has a net cooling effect, in temperate regions it can actually have a net warming effect.

While forest plantation activity goes on at most latitudes around the globe, carbon projects tend to be located in the tropics, where faster growth rates maximise the rate of carbon absorption and hence the volume of carbon credits generated.

Another study published in 2006 by scientists at the Max Planck Institute in Germany, claimed to have discovered that plants actually emit methane, a greenhouse gas with 23 times the global warming potency of CO2. This triggered an international debate on whether planting trees might actually worsen global warming rather than help to mitigate it.

Clarification provided by the authors of the study since, however, is that methane emissions from plants are very low and that the climatic benefits of forests far outweighed the negatives. The benefits gained by reforestation would be reduced by only 1 to 4 per cent due to methane emissions, said Frank Keppler, one of the authors.

Furthermore, in May 2007, scientists at Plant Research International in Wageningen in The Netherlands published the results of a study which tested the Planck findings in more controlled conditions. It found no evidence at all of methane emissions from plants and suggested that the methane detected in the original study may have come from elsewhere.

8. Plantations often have negative social impacts:
Many forest planting schemes are bad for surrounding local communities, for example, their operators pay exploitative wages or force people off their land.


Not a criticism of tree planting per se, but an important consideration.

All tree-planting projects, especially those in the developing world, should ensure that wages are fair, that land rights are respected, and that the views and needs of local communities are taken into consideration in project design and management. The socio-economic benefits of projects should far outweigh any genuinely unavoidable negative impacts.

The CDM and the emerging accreditation schemes for voluntary carbon projects include social as well as environmental criteria, and require detailed initial analysis and ongoing monitoring to ensure that these are met.  For CDM projects the host country government must confirm that it does contribute in all respects to national objectives for social, environmental and economic development. In the voluntary market, the ongoing strengthening and wider application of common project standards is certainly needed to assure buyers that their carbon credits do not come with hidden social costs.


In conclusion

In assessing the major arguments advanced against the practice of planting trees in order to mitigate climate change, Carbon Positive has sought to put the pros and cons into their proper perspective.

We are not saying that all tree plantation activity is positive, nor that those plantations that are positive are flawless and can't be improved in some aspects. We are saying that tree planting is an inherently positive activity, and that, when done right, it does offer substantial benefits for the climate, for the surrounding environment and for local people. We are saying that carbon financing is a valid and powerful means of achieving these benefits.

Getting it right, however, is not easy. As the industry evolves, there are wrong turns and mistakes being made and those involved must be ready to accept constructive criticism. But we hope this article demonstrates that tree planting is fundamentally desirable and that a major contribution to fighting climate change is achievable. As such, those that genuinely strive towards the appropriate environmental and social principles should be encouraged.


Extpub | by Dr. Radut