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I still don't fully grasp the climate impact of lumbering (unless its purpose is burning the wood for energy or making space for pastures which is obviously bad). Is cutting down trees and making or constructing something from them good or bad for the climate? Deforestation is supposed to be detrimental for the environment, but Finnish researchers suggest we shift from steel and concrete to wood in our building construction. It's gonna cost us all trees in the world considering the population growth and urbanisation, isn't it?

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  • It's a matter of perspective; a mature forest holds lots of carbon, so chopping it down and replacing with seedlings reduces the capacity of an existing carbon sink. It will take a very long time before it can store the same amount of carbon again. But using wood for building is also creating a new carbon sink. Calculating the net effect is difficult as you often don't know how effective replanting is and how long the new "wood-building" carbon sink will last.
    – THelper
    Nov 19 '21 at 11:43
  • I would be surprised if replanting efficiency was anywhere below 100%. In fact, efficiency of only 99% would be very surprising. I live in a country where every forest has to be replanted by law (Finland), and failures of replanting just do not happen. If a forest is planted where forest was previously chopped down, it's a rule of nature that the replanting succeeds. It won't fail.
    – juhist
    Nov 23 '21 at 16:42
  • @juhist replanting itself usually isn't the problem (unless a mono-culture is introduced), the issue is that a mature forest can sequestering carbon better than a newly planted one. On the other hand there's also research that says the exact opposite. My take on this is that it depends on other circumstances than just old and new.
    – THelper
    Nov 24 '21 at 8:13
  • A middle-aged forest grows the fastest. It is true that in the very start of the lifetime of a forest, it is very slow in capturing carbon but the growth in the very start is exponential. An old forest won't capture any carbon, it's in equilibrium. If we want to have many middle-aged forests, we need to plant many new forests and don't care about the inefficient carbon capture in very young forests, realizing that as the forest becomes slightly older, its carbon capture massively increases.
    – juhist
    Nov 25 '21 at 17:54
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Oh yes it is very useful.

Let's consider you have an old forest, something in which the trees have grown very large so if you choose to chop them down, you get a very high share of sawlog and very low share of pulpwood.

There are three sustainable things you can do to it:

  1. Leave the forest there. The trouble is, the forest is already at equilibrium, so any carbon sequestered is matched by carbon dioxide from decomposing. Climate benefit of that particular forest is exactly zero.
  2. Chop down the forest, and use all of the wood as pulpwood. Financially this is a very poor decision, because pulpwood has a far lower price than sawlogs. However, this is still more sustainable than leaving the forest there, because at least the pulpwood substitutes for packaging materials that would have otherwise been made out of oil (plastics). However, the packaging materials created from the pulpwood are rapidly burned for energy, so they don't retain their carbon for long. So the only climate benefit is from substituting for oil use. At least you get some climate benefit.
  3. Chop down the forest, attempting to make the sawlog percentage as high as possible. The sawlogs are maximally used for creating permanent carbon sinks and used for furniture, houses, etc. You can expect them to retain the carbon for 100 years. You will still get a small pulpwood share, but that has climate benefits too: it substitutes for oil use. Also you will get sawdust etc that can be burned for energy (substitutes coal use in heating in cold climates), or be used to make biochar (it retains most of the carbon while still producing some energy for heating although less than if it was burned directly to energy).

In cases 2 and 3, you will obviously plant a new forest that during its rapid growth stage is a very efficient carbon sink. By removing the old forest, you retained its carbon maximally, while at the same time created room for new forest to grow. Forest is always limited by room: if there was infinite room on this planet, there would be no climate crisis as we would just plant exponentially increasing amounts of new forest to capture emissions from exponentially increasing fossil fuel use.

So you can see that chopping down the forest and maximizing the sawlog percentage, building something from the wood, maximizes the climate benefit.

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Deforestation per se, without replanting trees to compensate for the trees felled, is bad for the environment.

Replacing steel and concrete with lumber/timber from trees for construction purposes is an old concept of sustainability. The manufacturing of steel and concrete is very energy intensive and the manufacturing of both currently produces a lot of carbon dioxide.

In producing steel, currently carbon, in the form of coal, is added to the molten iron ore to remove oxygen from the melt. Basically the chemical equation is iron oxides + carbon gives iron + carbon dioxide:

FexOy + C -> Fe + CO2

There are new processes to produce green steel/iron by using hydrogen instead of coal (carbon) to remove the oxygen from the melt. Such a process would produce water vapor instead of carbon dioxide.

FexOy + H2 -> Fe + H2O

Getting the hydrogen is the tricky part. Currently plans are in place to use electricity from renewables, and hydro electricity to produce hydrogen and oxygen via the electrolysis of water.

The process of manufacturing cement for concrete involves roasting limestone (CaCO3). This produces carbon dioxide.

Using lumber from trees, instead of steel and concrete, avoids the production of vast quantities of carbon dioxide. The tree plantations that were felled to produce construction lumber can eventually be replaced by replanting the forest plantation. This is a more sustainable and less environmentally damaging way of producing construction material.

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