There was a new article in Science that caused a kerfuffle in the Twitterverse (is that a Twitterfuffle?), which may be of interest to us. The story is that Science published an article saying that “planting trees globally would be REALLY good for carbon”. Now you may say that that’s not really news, but the authors made lots of assumptions (!) and ran models (!) and came up with some big numbers (!) and made perhaps out-sized claims. What is of interest to me is the choice of scale, in this case, the world. It takes chutzpah, I think, to think you can model how people could plant trees all around the world, where, and what that would do for carbon, get meaningful results and not need to ground-truth your work.
As you all know, I am a proponent of planting trees. I especially think that planting trees post-fire (where natural regeneration isn’t working), is something most people would support, not just for carbon reasons. I had heard at one time that the Forest Service was going to make a major push on its reforestation backlog, but never heard what happened to that effort. Anyone reading from the FS, please let us know! Anyway, here’s the free info on the paper and a link:. There’s also a science op-ed that has a firewall here.
The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Bastin et al. used direct measurements of forest cover to generate a model of forest restoration potential across the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9 billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more than 500 billion trees and more than 200 gigatonnes of additional carbon at maturity. Such a change has the potential to cut the atmospheric carbon pool by about 25%.
The restoration of trees remains among the most effective strategies for climate change mitigation. We mapped the global potential tree coverage to show that 4.4 billion hectares of canopy cover could exist under the current climate. Excluding existing trees and agricultural and urban areas, we found that there is room for an extra 0.9 billion hectares of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally support woodlands and forests. This highlights global tree restoration as our most effective climate change solution to date. However, climate change will alter this potential tree coverage. We estimate that if we cannot deviate from the current trajectory, the global potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority of losses occurring in the tropics. Our results highlight the opportunity of climate change mitigation through global tree restoration but also the urgent need for action.
I don’t know how anyone could model “forest loss due to climate change” since we don’t know how the climate will change, nor how trees will respond.
There is an interesting twitter discussion started by (Dr.) Pep Canadell linked here.
Replying to @pepcanadell
Some concerns on methods: only 10-13 factors determine tree cover potential globally – major local and regional-scale constraints missing, e.g. permafrost, subsoil constraints (ex. depth to bedrock), nutrient limitations, var. forms of soil degradation, seasonal inundation.
Replying to @EikeLuedeling @pepcanadell
Very relevant in high-potential areas! They also assume grazing areas and production forests can reach same tree cover as protected areas. In my view, a gross overestimate of actual potential! And a lesson on how machine-learning algorithms still need a reality check.
So I’m not the only person out there concerned about reality checks.
8 thoughts on “A Model Too Far?: The global tree restoration potential, Bastin et al. paper in Science”
The Forest Service Reforestation Backlog remediation is a work in progress. Flagship targets haven’t helped, and neither has lack of staffing/inadequate hiring process. The BLM in western Oregon states in their new RMP that post-harvest areas will be restocked (through natural and planted trees) within 5 years and post-disturbance areas will be restocked within 10 years. While the 5 years after harvest is pretty standard in the Forest Service (and ties back to the NFMA), the 10 years after disturbance is not, and there seems to be a reluctance on the part of the Forest Service to embrace something similar – mostly because the Forest Service (IMHO) doesn’t want to “earmark” funds for anything. The only “earmarked” reforestation funding comes from the KV Act (most of the collected KV funds were fire-transferred in 2018 and will probably be fire-transferred again in 2019) and the Reforestation Trust Fund (which is capped at $30 million per year). Nearly $10 million of the reforestation trust fund goes to agency overhead expenses before it ever goes to the regions. That overhead expense has been decreasing. But reforestation needs have been increasing due to fires. Some regions use their “expanded KV” for reforestation, but that was also fire-transferred in 2018 and will probably be fire-transferred again in 2019, and most regions use that “expanded KV” for things other than reforestation (and especially for timber sales).
“…and most regions use that “expanded KV” for things other than reforestation (and especially for timber sales).”
With the ‘bundling’ of non-commercial tasks into timber sales, it seems appropriate to use KV dollars to prep those non-commercial units. In the past, I have seen some creative “Sale Area Boundary” designations in salvage sales. Including plantations into the Sale Area is a way to use KV dollars that is not quite kosher, IMHO. That money is supposed to go into areas harvested by the salvage logging.
Trees also consume much water, so from a water standpoint many tree will consume much water that fish in streams need, especially in low flow times of the year.
But they can also hold soil and keep it from sliding into streams. I think you’d probably have to compare trees to shrub or grass cover in terms of all these things (carbon, water, wildlife preference, soil holding and so on). Maybe someone has done that? I think it would vary by place.
He’s referencing that silly Roger C. Bales myth of less trees more water. For 4 or 5 years Roger Bales preached less trees more water in streams and rivers. All of this campaigning for less trees of course came during the worst drought years in California’s recent mega-drought history. Never once provided proof of 10s of 1000s of natural ocurring death of trees by bark beetle causeed water to miraculously appear in creeks and streams,just like trees thinned provided more water availability in streams and creeks. Went back every time to the fact there was extreme drought for all that lack of water. Until 2017 when the floodgates of the heavens opened up and water filled streams, creeks, rivers, and Reservoirs and only then he mention dead trees caused more water to flow, and totally ignored excessive rainy season flooding events that winter.
Still like above you will hear them parrot Roger C. Bales shtick on less trees more water.
“What is of interest to me is the choice of scale, in this case, the world. It takes chutzpah, I think, to think you can model how people could plant trees all around the world, where, and what that would do for carbon, get meaningful results and not need to ground-truth your work.”
“I don’t know how anyone could model “forest loss due to climate change” since we don’t know how the climate will change, nor how trees will respond.”
It’s one thing to criticize research methods and results (the twitter comments) and another to criticize even posing the question. Especially related to something as important as climate disruption. Even if you don’t think the answer is worth much, there may be value in stimulating different ways of thinking about the question. Maybe a project like this would lead to others working on the details.
I’m actually not critiquing posing the question “can reforestation be helpful in addressing climate change” I’m critiquing trying to answer the question by running models with assumptions and no apparent ground-truthing. I don’t think that it’s a different way of thinking about it.. there are hundreds of papers covering the same ground. I’d rather folks spent research $ figuring out how to solve problems, not stimulating thinking. For example, where in Colorado are there places where trees could be planted for carbon purposes? What are the reasons people aren’t doing it? What interventions might lead to more acres successfully planted? I’m thinking the answers to those questions would be different in Tibet, Ukraine, Ghana, and Ecuador. And any solutions will have to take those differences into account. Now if you did that for each country and added them up, that would help answer the question.
The paper is a thought experiment, not meant to answer all the questions.