Hacker News Reader

Comment by GhostVII | Hacker News Reader

I don't think this should be too surprising. Forests don't destroy carbon, just store it in the form of trees. When the trees decompose, or burn down, it is released again. So for a mature forest you would expect it to have around net 0 emissions. As far as I know the main way a forest can be a carbon sink is if it is expanding, which I don't think Canada's forests are doing.

View on HN

A study from 2008 shows that mature forests still store some carbon. https://www.nature.com/articles/nature07276 "We find that in forests between 15 and 800 years of age, ... forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral."

Not sure about Canada, but my understanding is that for the US we’ve gained forests compared to 50 or 100 years ago due to replanting, repurposing land and having dedicated paper pulp tree farms.

At least in BC, replanting and tree farming are alive and well and have been for many decades. There are in fact many places where second generation has been logged and third generation is in growth.

We're still nowhere near we were before the lumber boom of the mid to late-1800's. Tens of thousands of square miles were clearcut for lumber and cities are in their place now.

Also fire suppression. That's become a bit of a problem, as the forests are a lot more flammable now than they were historically.

While you bring up an important forestry mgmt issue (overgrowth of underbrush) I don’t think they count individual trees but rather surface area coverage.

That really depends on the state/region. You can see in this [1] report that states like Florida and Georgia are burning millions of acres a year in prescribed burns, while California burns a few ten thousand.

[1] http://www.stateforesters.org/sites/default/files/publicatio...

When trees decay, a certain portion of the material remains solid and eventually becomes part of the soil layer. Also when trees burn, a certain amount stays as carbon/charcoal/ash in the ground. So while some of the carbon is released when trees decay or burn, not all of it is. So I would expect a mature forest to be a carbon sink, though not necessarily a huge one.

Apparently most people don't understand this!

There's a net loss of planting new trees, but then as you say you get stasis.

You don't get stasis, but the rate of carbon absorption drops, when trees die in the forest some of the carbon that was sequestered gets retained in the soil, most will decompose back into the atmosphere but the slow growth of soil in a forest is tied to nutrients that are being isolated out of the environmental cycle.

Most forests in North America are not mature. Consider how tall redwood trees can get. Also, trees are converted into wood and paper. Generally that wood isn't burned and returned to the atmosphere.

Why not suggest the whole planet is carbon neutral at that point? It is meaningless because we only care about the carbon in the atmosphere.

A very small fraction is sequestered as topsoil.

You'd think large forest fires would have an impact though in terms of the regrowth.

Tree growth and forest fires are just moving carbon back and forth between the air, soil, and trees. You can’t simply “destroy” the carbon, you have to keep it somewhere. Similarly, humans aren’t “creating” carbon, we are just taking it out of the oil it was in and putting it into the air.

is it ? I thought it was mostly digested by fungi / bacteria / insects without re-emitting it

Digestion breaks things down for energy which means producing CO2. You can simplify organic chemistry on these scales as spending energy to store carbon or gaining energy to release it.

In some situations you can get net carbon storage which is how we got fossil fuels in the first place, but this is really slow. On the order of 1 Billionth the total fossil fuels stored per year.

I asked below but maybe you'll know the answer. Basically insects/bacteria cellular respiration produces CO2 just like us ?

update: found some answer https://www.amentsoc.org/insects/fact-files/respiration.html

I never considered that.

Also, how unlikely that this CO2 is reabsorbed by the plants (granted that can only occur after winter when leaves are back) ?

Yeah, of course. Bacteria, insects, fungi, and any animal break down plant matter (fruits, salads, wood), releasing CO2 in the process. Fire does the same, only the energy is emitted as heat and light, not movement and wasting time on HN.

CO2 + sunlight is again converted into organic material by plants (and some bacteria). It really doesn’t matter if it’s the „same“.

This is the basic carbon cycle.

You'll get a residue of organic materials that don't immediately return to the atmosphere, and eventually accumulate into fossil fuels, but that's a very slow accumulation, a fraction of the carbon that is initially captured when a unit of forest grows from scratch.

Carbon is an element. Most organisms to a lot of chemical rearrangement of the element, but the element is not created or destroyed in biological processes. Any carbon kept during life is released at death.

But not necessarily released as CO2, which is what "re-emitted" means to me. If it goes atmosphere -> tree -> fungus -> bits of fungus buried in the ground for millions of years, that's effective sequestration.

It may well be, but that's not what happens to most of the wood in trees— most of it rots (CO2 released slowly by the organisms consuming the wood) or burns (CO2 released by combustion).

As said below, it's not C, but CO2 we were worried about. Also I admit that I don't know if humus organism produce CO2 from wood remains.

This is true only in part.

We have found shells, made of Calcium carbonate, still relatively intact more than 3000 years after the death of the animal. Some shells had last for 500000 years (See Nature 2014-dec-03)

Under the sea there are entire ecosystems based in dead shells.

> As far as I know the main way a forest can be a carbon sink is if it is expanding, which I don't think Canada's forests are doing.

The way you keep a forest expanding is by logging it.

Serious question, ignoring the other environmental impacts of logging old growth forest:

Is logging carbon negative?

depends on what those logs are for. if they are for building houses, then probably yeah

A quick google suggests that this is an active research topic. I have only skimmed this paper, but they find that logging is net emitter of CO2:

https://cbmjournal.biomedcentral.com/articles/10.1186/s13021...

Interestingly, they account for carbon emission from the wood produced by logging ("sawnwood"):

Sawnwood decay is approximated with an exponential decay [with a half-life of] the normal distribution truncated at zero with mean equal to 30 and standard deviation equal to 15, according to IPCC guidelines. So far, no life cycle analysis has yet been done for woody products in the tropics and adapting the framework developed in Europe and North America in tropical countries remains challenging.

So they assume that the average bit of timber lasts thirty years before giving up its carbon, and only about one in six lasts longer than 45 years. I suppose the lifecycle of wooden manufactured items tends to end with them being burnt when they're worn out.

If i am reading the graphs correctly, then wood going to the sawmill is only a small part of the carbon emitted by forestry, and they mention that only one-third of the wood entering a sawmill leaves as sawnwood, the rest being lost as sawdust, so even if you could preserve wooden items for ever, it might not move the needle much.

On the other hand, if you could collect all the sawdust from the mill and bury it, or make it into biochar and then use it as a soil amendment, that might.

Anyway, that is one paper amongst many, go forth and read if you're interested!

There needs to be more talk about biochar...

> So they assume that the average bit of timber lasts thirty years before giving up its carbon, and only about one in six lasts longer than 45 years. I suppose the lifecycle of wooden manufactured items tends to end with them being burnt when they're worn out.

That seems like a pretty bizarre set of assumptions. Wood doesn't just disappear in 45 years unless you leave it in the open untreated.

As i wrote in the paragraph you quote, my assumption is that this models wooden items being burnt at the end of their useful lives.

But hey, don't take my word for it - in the paper, that bit references this:

Penman J, Gytarsky M, Hiraishi T, Krug T. Good practice guidance for land use, land-use change and forestry. Intergovernmental Panel on Climate Change (IPCC), chapter 3, Appendix 3.A.1.3. UNEP; 2003. p. 268–70.

Which you can read here:

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf...

So dive into the gory details of harvested wood products, and the basis for their future methodological development to your heart's content!

It sounds like the answer basically depends on how we log and what we do with the produce, but it could be made carbon neutral or even negative with the right approach.

Makes me wonder just how much polymer use we could replace with wood, and what kind of disposal techniques for it we could develop to increase carbon sequestration (e.g. instead of burning it, bury it deep?).

Reply on news.ycombinator.com