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Comment by triclops200 | Hacker News Reader

That only "fixes" climate change as long as the trees continue growing and do not die. When dead, trees release their CO_2 that they've sequestered back into the atmosphere due to decomposition. Therefore, assuming those forests stay around, you've only delayed the problem by sinking a fixed amount of CO_2 away into the living biomass of the trees. The only way to make that a permanent sink would be to biochar the trees as soon as they die, which would be a logistical nightmare.

Negative rant over, it's still not a bad idea for the fact that it'd slow down the worst effects of climate change for a while, buying time for other solutions like renewable energy and whatnot, but it's not a pancea.

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That's basically, well, not true. When trees break down they contribute to soil organic matter. Approx 58% of SOM is carbon (SOC) making soil one of the largest carbon sinks on the planet. See https://en.wikipedia.org/wiki/Soil_organic_matter

If soil continues to accumulate in a healthy form, as it did on the Great Plains over millennia of grazing by bison herds, then yes.

Old growth forests often grow on rocky land, and have little long-term depth accumulation.

Source: hiking old growth forests over decades, and being a farmer.

Lack of soil accumulation does not mean the soil evaporates into thin air; it is taken up by the watershed and redistributed downstream. The same carbon cycle is in effect; accumulation in any particular terrain has really nothing to do with it.

Literally survivor bias. The old growth forests that survived loggers were the ones they couldn’t get to for a profit. Those will be in or near geographic barriers like swamps or rocky terrain.

Hmmm?

I've rarely hiked in harvested and replanted forests; these are boring. I did most of my hiking in central/northern BC and Alberta, Canada. These are some of the largest tracts of old-growth timber in the world.

The many old-growth forests I've hiked (sample: >1,000km, mostly dominated by conifers), with last burn times ranging from decades to centuries, have rarely boasted deep soil levels. This hypothesis is supported by existing research: https://www.researchgate.net/publication/225314103_Soil_Carb...

Old-growth coniferous forests are great -- but they're not a big "carbon store".

If you want land-use based carbon storage, I'd recommend investigating where the continent-wide, massive, deep, healthy carbon-rich store of topsoil and humous came from -- grazed grasslands and scrub brush.

Oh, North Canada? That's some tricky terrain. Bedrock is very near the surface, and you're right, it's hard to build up. Short growing season, for one.

The article you link mentions softwood forests being problematic for carbon accumulation. Not hardwood forests. Old growth temperate hardwood forests are quite rare now, and some of the apex tree species in those forests have very serious pathogens keeping them from re-establishing, more's the pity.

Does soil continue to break down over time or does it permanently sequester into peat/coal/oil? As far as I knew, basically all of the tree's cellulose eventually gets released over time into CO_2 via biological activity.

There is an upper limit to the amount of CO2 that soil absorbs - it's clearly not infinite. There is an equilibrium in the Earth's natural Carbon cycle.

Once a soil matures (a process that might take many decades), the amount of CO2 retained vs emitted reaches equilibrium.

Some thoughts on finite CO2-absorbing capacity: - If these forests are sustainably logged, we can take some of the carbon out and sequester it in buildings (or even just bury it), allowing the forest to regrow and absorb more carbon. - I have a theory that presently discussed global climate change solution only needs to buy us a maximum of 100 years, and by then our tech for dealing with silly problems like excess carbon will have almost surely advanced beyond recognition. Given rates of progress in chemistry, physics, and materials science over the last two centuries, this isn't crazy.

Some trees takes years to fully decompose, even in contact with the soy, even on tropical climate. I say because I practice a kind of agriculture where we plant trees to feed to soil, we prune/cut the trees to cover the soil 4 times a year, the soil keeps increasing in organic matter (becoming darker and darker each year) and I notice some especies are very good at not decomposing, usually this are trees used for civil construction, which is another way of storing the CO2 I think. For me cutting trees down is not the problem, the real problem is not planting more... also where that energy of the tree ends up, burning wood I think is a waste.

I personally believe that forests provide a net positive in terms of CO2 scrubbing regardless of decay/decomposition. The only evidence I'd offer is a time lapsed NASA video[0] showing CO2 emissions heatmap over time. The areas like the Amazon clear up the CO2 on a daily and seasonal basis. The areas where forests are impossible like the Arctic, it does not. The sun drives the cyclical "heartbeat" effect you see from day to day on the video, where plants using photosynthesis in the day (and macroscopically, the summer) effects the intensity of scrubbing moreso.

Also, maybe it is my mind's desire to simplify of all of it, but it was eye opening for me, and seemed obvious upon seeing that video, that forests were the key player in air management globally, and industrialized nations were the main drivers behind CO2 production in the air globally.

[0]: https://m.youtube.com/watch?v=x1SgmFa0r04

I thought about this and had an idea that I don't know if it can work, but I couldn't find any major problem with it.

Specifically, what if we start burying dead trees or those who reached peak mass in places where conditions will transform them into coal in 100(00..) of years?

That way carbon is captured and stored until we burn them again.

I am not sure that coal can be made this way again. There are fungi and bacteria now which break down the lignin in cellulose, which there was not during the carboniferous period. That was 60 million years of dead trees not breaking down fully and being compacted underground to make that coal, and it won't happen next time because the lignin will be eaten.

If deforestation is still occurring (net result that we are cutting down more trees than we are planting) then cutting down more trees doesn't solve the problem.

We do in fact need people to just start planting trees.

Of course. My point was to answer to the parent comment that said planting trees cannot be a long term solution.

if you biochar fallen trees and litter, and then bury it, it stays sequestered for a long time.

It also improves the soil long term - particularly in sandy soils it helps water retention.

Obviously this is much more work that just planting and forgetting though.

> if you biochar fallen trees and litter, and then bury it, it stays sequestered for a long time. > It also improves the soil long term - particularly in sandy soils it helps water retention. > Obviously this is much more work that just planting and forgetting though.

If we used cross-laminated timber [1] to construct our buildings instead of concrete, there would be an economical incentive to keep a lot of timber forests around. For additional carbon-negativity (and soil quality!) the timber industry could be required to biochar and bury its litter. This way, without too much government coercion, maybe our building frenzy [2] could end up being carbon negative?

Much like modern diesel engines that make (polluted) air clean(er) [3].

[1] https://en.wikipedia.org/wiki/Cross-laminated_timber

[2] https://www.youtube.com/watch?v=tXNJa86tErQ

[3] https://newmobility.news/2019/08/28/can-new-diesel-engines-a...

You don't need to biochar them, in a forest ecosystem they take care of themselves.

Well, the main purpose would be to avoid tree death. And even natural death of trees can be allowed considering that an oak lives around 150 years. Regarding what you say about releasing the co2 they have stored, keep in mind that the tree is not a co2 sponge. It takes co2 and transforms a big chunk of it in other carbon-based components useful to the tree.

I recommend this article that clears some ideas about trees and co2: https://medium.com/the-philipendium/trees-and-carbon-dioxide...

I have to agree with the posted article, even if it is mixing acres and square meters in the explanations.

A sequoia sempervirens lives 1,500 years.

I am not deluding myself that we will mitigate climate change by covering Earth in sequoia, but still that gives some timescale on how long trees can live.

If we could mitigate climate change for another 1,500 years we would probably have found some other mitigations by then.

I do not see how the maximum age of the trees matters. There is no difference between 10 generations of trees that live for 150 years and one generation that lives for 1500 years. What matters is the amount of additional CO2 which can be bound in biomass per square kilometer (comapred to the biome we are replacing) and how many square kilometers which are available for this project.

I fully support any plan that ends in the forest moon of Endor. What are even the odds we'd have fossil fuels left to burn in 1,500 years? I feel like we can safely say we'd have reached peak oil by then.

I don't know the source other than Elon Musk stated it in one of his presentations, but according to him we have five times as much fossil fuel reserves as we would need to utterly destroy ourselves with climate change. If that's right, waiting until we run out is not a solution. I realize the context was mentioning some speculation that we could push the timeline out some by planting trees. That speculation aside, we can't just wait for the oil to run out and be fine.

I didn't intend argue we should wait until we run empty on Fossil Fuels. I just can't see any way in which we'll still be consuming them in 1,500 years - either we'll have moved off them, we'll have run out, or the world will have become not compatible with life (non-exclusive "or" in this case).

Great comment and even better concept.

It's worth mentioning that sequoia along with a few other species are outliers as far as longevity. Most trees do not live nearly that long.

FTR, many tree species can live for hundreds of thousands of years.

"FTR, many tree species can live for hundreds of thousands of years."

The oldest known tree in the world is 5000 years old.

No individual trees are known to live hundreds of thousands of years.

There are clonal trees, like aspens, that could live as a colony for hundreds of thousands of years, but that's not quite the same thing (and our oldest verified example is only 80k years old).

https://en.wikipedia.org/wiki/List_of_oldest_trees

Ok, you're right that it depends on what you count as a tree. An aspen "colony" is a living organism, and its "trees" visible aboveground are merely its stems. Such organisms may live as long as 1,000,000 years.

That's only one side of forest. Don't they contribute on thermal buffering, wind patterns and evaporation too ?

Also it may help sustaining the good chain.

But when the trees die, new trees will grow in the same area, sequestering more or less that CO2 that was emitted from the dying tree, no? Would this not turn the forests into a permanent CO2 sink, at least on a rough scale?

Or do they sequester less than they emit?

Once the forest grows to maximum height and density, it stops being a sink. It keeps being a storage though, which is still a benefit.

I unfortunately can't find a reference, but I heard that it takes about 20 years for a newly planted tree to peak with regards to absorption of carbon, and after about 100 years it reaches equilibrium where the forest emits about the same amount of carbon to the atmosphere as it absorbs (through decaying matter, fallen trees, and whatnot). It of course depends on the type of tree.

I think it's best to look at this as mass preservation problem. Trees absorb CO2 from air and store in their bodies. Once they die, the CO2 gets released.

Since there's a limited tree mass per area unit that the ground can support, once you reach that mass the input and output need to zero out, since there's nowhere to store any additional CO2.

I'm not an expert in this area, but from what I can tell:

Young rapidly growing forests sequester carbon more quickly than mature forests, but mature forests still sequester some carbon, possibly into the soil. (One source https://www.sciencedaily.com/releases/2008/09/080910133934.h... ) Separately, the regrown forest could be maintained in a state of peak carbon sequestration by doing selective logging from time to time, and as a bonus it would be profitable to do so.

Let's also not forget that forests burn. And they burn on a regular basis. You also run into tree-specific issues like beetles, which can kill off wide swaths of trees "naturally".

So, natural death and decomp is not the only things to worry about with using forests.

We can continue to plant trees until the end of time.

By end of time, I assume you mean entropic heat death of the universe. In which case no, planting trees will have become impossible trillions of human years previous to this, due to there not being and planets.

I don't mean that. I mean something closer to the end of humans on earth.

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