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## A Trillion Trees .....

How much land use is a trillion trees for the afforestation slider?

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So, I'm taking a stab at this from an article I read here:  https://reason.com/2020/02/13/republican-lawmakers-introduce-trillion-trees-act-to-combat-climate-change/ and the Science article.

Reading further in other places, there are optimal spacing for trees, and, of course, the amount of land used depends on how far apart you space the trees. Optimal spacing of anywhere from 10 (small trees) to 50 feet (oaks), with tree separation up to 100 feet, depending on how the forest will look.

This article claims 400 tress per acre, which is trees spaced 10 feet apart, or 20x20. That's 988 trees/hectare. To make the math easy, let's call it 1000 trees/hectare. So, 1 trillion trees divided by 1000 trees/hectare = 1 billion hectares.

According to the Science article,  "there is room for an extra 0.9 billion hectares of canopy cover".

In En-ROADS terms, you can go to afforestation detail and view the graph on "Land for Carbon Dioxide Removal" . The highest I could get to was 0.7 billion hectars by 2100. That only does 700 Billion trees. That changed a scenario I was working on about -0.2 C.

Thank you, Mark!

You did some heavy lifting with the calcs!

To boil it to relatable terms, to plant one trillion trees would take 1 billion hectares of land which is approximately the land mass of the entire United States including Alaska and Hawaii!

USA Land Mass (including Alaska & Hawaii) = 3.797 million mi²

1 billion Hectares = 3.861 million mi²

Is that about right?

Thank you again,  Laura

I looked at some other articles regarding the "Trillion Tree Planting" campaign assumes that 600 Billion trees will last until maturity so we are perhaps getting close to the En-Roads maximum setting for tree cover.

Still not a big effect on reducing the CO2 in the air as you indicated, Mark.  -0.2 Deg C.

Laura : Your estimates look good.

There's a lot of smoke and mirrors in this climate denier's solution. Given the estimates from the model, I think that the audience can figure this one out.

One more thing that occurred to me, this is a fairly dense forest. Where my trees are 10 feet apart, the crowns (leaf area) are packed together. This, along with root competetion, limits growth, which limits the amount of CO2 sequestered.

When I presented last weekend - we simulated a world the "news" regarding one trillion trees and CO2 sequestration were being thrown out as a "solution."

Some one other than me (best scenario!) pointed out that this does nothing to the energy demand chart - (chart on the left.)  So En-Roads led the conversation to "ya really need to STOP  pumping GHG into the atmosphere, too ...."

There is a good article on this here:

https://www.sdentertainer.com/uncategorized/what-would-happen-if-we-planted-1-trillion-trees/

'2.5 billion acres of forest to the world could drastically halt global warming to 2.7 degrees by 2050. To do so, the planting of roughly 1 trillion trees...'

Basically the Climate interaction slider on afforestation on this is completely wrong and needs fixing. It looks like lots of countries are going for 10 billion trees, Indian over 100 and China over 100 billion.

Also 'The Great Green Wall is an African-led movement with an epic ambition to grow an 8,000km natural wonder of the world across the entire width of Africa.'

The hidden point with this is that a lot of countries will not be meeting their C02 targets anytime soon, but with these planting projects they can do over 100% to balance out inadequacies elsewhere.

Thanks, Cassie.  I looked at the article you referenced to see the source and it seems the referenced paper has an "Erratum" - May 29, 2020 to the report “The global tree restoration potential” by J.-F. Bastin, ...

En-ROADS has a really good write up addressing Afforestation.  Always tricky to address during workshops because, of course, trees are a great thing for the earth and we want more but the expectation that it is a big player in addressing climate change in the time frame we need must be managed.

Hello Laura,

I looked at the Erratum and the paper What role can afforestation play in addressing climate change? By Andrew Jones

I would like to make some criticisms about that paper.

- It considers past and future emissions alleviated by growing trees up to the year 2100 from many decades ago. A much more useful metric would be to look at the short term period how much difference would it make by the 2030, 40, 50 etc to current levels. Saying that trees can reduce co2 by x percent over a large historic and future period is absolutely meaningless as regards the reality of what percentage of current CO2 emissions could be reduced each year in the near future which is the crunch time.

- It is a mistake to not consider tree plantations, many of which are harvested every 35 years, not 70 years.

- The profit from the tree plantations can also be used for other CO2 reducing technologies or more plantations.

- the graph dipping off after 2080 is entirely incorrect as it assumes lack of sequestration by forestation eg it makes the incorrect assumption that 0% of the reforestation will be harvested?

- I take issue with the 13 year lead in period for afforestation. Does Nuclear have a 5 year lead in for Korea and a 15 year lead in for the UK. I think it is mendacious to include the lead in period in the graphs and very much so in the models when nuclear apparently has zero lead in time! It has to compare like with like and this tragically has not been fed into the model.

Given the interactive tools are widely used I urge that this be corrected.

I've only spent 15 minutes or so on this, so there may be errors in my assessment, especially on percentage of wood harvesting which is mentioned in passing  and opaquely by the Royal society, if you require a more in depth assessment let me know.

Given that many countries will not do their bit, the cost effectiveness of forestation should also perhaps be noted.

Cassie -  Did you check out all the different assumptions that can be adjusted when it comes to tree planting within En-ROADS? Check under the menu item "Assumptions" in the Simulation menu. As you note tree planting can come in different forms. En-ROADS is global so things like delays are estimates of the global average.