22 May 2020

Trees for Climate Change

Carbon dioxide is a greenhouse gas. Increases in atmospheric carbon dioxide, due mostly to burning of fossil fuels, are responsible for about two-thirds of the total energy imbalance that is causing Earth's temperature to rise. Growing plants remove carbon dioxide from the atmosphere (carbon sequestration) through photosynthesis. Why don’t we just plant lots of trees?

Welcome back. Last February, I blogged about the World Economic Forum’s annual meeting, “Davos 2020,” whose theme was climate and sustainability (see Davos Focuses on Climate). One meeting announcement I mentioned was financial support for the forum’s global reforestation initiative. 

I mistakenly referred to the initiative as One Trillion Trees; that’s another trillion-trees project. Unbeknownst to me, quite a few nonprofit organizations and governments have begun large-scale tree-planting projects for a host of social, ecological and aesthetic reasons.
A Trillion-Trees effort in Western Australia (from www.landcarewa.org.au/news/trillion-trees-has-inspiring-global-landcare-vision/).
Is Tree Planting the Way to Go?
While endorsing the benefits of well-planned tree-planting projects, a recent commentary in Science Magazine warns against a simplistic view of tree planting as a solution to climate change.

Coauthored by an environmental scientist with the University of California, Santa Cruz, and a forest scientist with the University of São Paulo, Piracicaba, Brazil, the commentary points out that tree planting can have negative as well as positive outcomes depending on how and where trees are planted. 

Negative consequences might include reduced water supply, destruction of native grasslands, spread of invasive tree species, increased social inequity, displacement of farmland and increased deforestation.

The authors emphasize the importance of involving stakeholders, noting that tree-planting projects imposed by governments and external investors without engaging stakeholders have repeatedly failed. The planted trees are not maintained, farmers use the land for livestock grazing or the land is re-cleared. 

Ethiopia celebrates planting 350 million trees in one day to combat climate change and desertification (from www.rte.ie/news/newslens/2019/0730/1066005-ethiopia-plants-350-millions-trees/).
There are many reasons to plant trees--reforestation, sequestering carbon, providing income from timber harvesting and more. It’s not uncommon for the goals to conflict. 

Planning Tree-Planting Projects
The commentary offers guidance for new tree-planting projects.

Reduce forest clearing and degradation: Protecting and maintaining intact forests is more efficient, more ecologically sound and less costly than planting or replanting trees.

Treat tree planting as one element of multifaceted environmental solutions: Enhancing tree cover is one of the best options to offset greenhouse gas emissions, yet it addresses only a small portion of the needed carbon reductions. The estimates of how much vary more than tenfold.

Balance ecological and social goals: Acknowledge competing land uses and focus on landscapes with the potential to generate large-scale benefits. As an example, they suggest the Atlantic Forest in Brazil, where regional planning of tree-planting initiatives can lead to three times the conservation gains at half the cost.

Plan, coordinate and monitor: Work with local stakeholders to resolve conflicting goals and ensure maximum long-term effectiveness. Simply planting trees is not enough. Millions of dollars were spent to plant mangrove trees in Sri Lanka following the 2004 tsunami. Some five years later, most of the monitored restoration sites experienced tree losses of more than 90% because of poor project planning and lack of seedling maintenance.

Wrap Up
Growing trees is a long-term endeavor. It is not a substitute for, nor should it overshadow, actions that have greater potential for rapidly reducing greenhouse gas emissions, such as converting from fossil fuels to renewable energy technologies.

We should also recognize that the direct and indirect effects of climate change on tree mortality make it difficult to forecast how much carbon trees will sequester in the future.

That said, I’m all for planting, growing, restoring and conserving many trillions of trees. Of course, it must be done right. Thanks for stopping by.

Reforestation in Burkina Faso (USDA photo from commons.wikimedia.org/wiki/File:Burkina_Faso_-_Tolotama_Reforestation.jpg).
Commentary on tree planting for climate in Science: science.sciencemag.org/content/368/6491/580
University of California, San Cruz press release on commentary: news.ucsc.edu/2020/05/holl-trees.html
Study on planting 1 trillion trees in Science: science.sciencemag.org/content/365/6448/76
Three different trillion-tree projects:

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