You misunderstood the options. Option 1 involves no new trees, it just keeps the old one.
Now that does make some sense. It is unfortunate that for it to be carbon neutral we have to screw up the forest eco-system. Decaying wood is an important part of a healthy forest and supports many species.
The point that isn’t being stated explicitly is that the neutrality comes from the creation of a tree. It isn’t the absoptive power of the tree that’s interesting. It’s the fact that the tree is build out of carbon. If you leave a tree standing there, you haven’t locked up any new carbon. The neutral situation is burning a tree (releasing that mass of carbon) and then growing a new one from scratch (requiring that mass of carbon.) Other than via the addition of mass of the tree, a tree doesn’t remove any net carbon from the atmosphere.
Old trees don’t grow indefinitely. They die. Then they rot and turn into carbon dioxide anyway. Burning fossil fuel just introduces more carbon dioxide into the cycle. An old forest absorbs no carbon dioxide since it isn’t changing in density.
In fact that is directly the opposite of what actually happens. A fully mature tree won’t grow much, whereas a sapling (with enough light and water) will be growing every year.
The example I specifically mentioned has trees reaching maturity after 1 year. At that point, they’re as big as they’re going to be. Thus, they’re not absorbing carbon anymore. If you keep burning fossil fuels with Option 1, you’re going to keep having to plant more and more trees every year. The only way for Option 1 to “involve no new trees & just keep the old one” is if you’re going to assume a single tree can grow infinite feet tall. That does not exist in real life.
Wrong. Option 1 involves adding no new trees. How do I know? Because I defined option 1 :D.
It may be artificial to focus on just one tree, and yes it will die eventually, but averaged over all trees it is fine I think. There is nothing at all in option 1, by definition, which calls for 10 or 1000 trees.
How about conservation of mass? Think about it this way- you burn X kgs of carbon per year, sending it into the atmosphere. For a tree to absorb all this, it needs to get X kgs of carbon larger.
If the carbon comes from an outside source (fossil fuels), then after a thousand years you need 1000 * X kgs of total carbon locked inside a tree to ensure that no additional carbon is sent to the atmosphere. A single tree cannot hold 1000 *X kgs of carbon, so you’re going to have to have a pretty decent size forest instead.
Contrast that to option 2. If you just burn X kgs of carbon from a tree, then your new tree only needs to be X kgs of carbon total. It never needs to get larger than X, even after 1000 years.
I remember someone–don’t remember who–saying on these boards a while back that saplings sequester much more carbon than mature trees. It struck me as counter-intuitive; looking at the rings on a tree stump, they seem to grow by roughly the same increment (on average). Given the relationship between radius and volume or surface area, I can’t see how this works.
I would appreciate any elaboration you can provide.
I don’t know if this is why you heard what you heard, but I can think of two reasons saplings sequester more carbon than mature trees.
One reason is growth rate - it’s advantageous for a tree to grow faster at the begining of it’s life, so that it can get above everything else to get sun.
The other reason is that the saplings are much more densely spaced. If you start from a clear field and allow it to go through succession, it’ll go from grass to scrub trees, to fast growing hardwoods like poplar, then on to the good hardwoods like maple and cherry. (YMWV with climate and soil conditions) Initially the trees are so close together that you can’t even walk through them. Gradually most of the trees will die out due to competition. A mature tree will shade out a lot of area. The carbon in the saplings is locked out of the atmosphere for a shorter time than that in large trees, but there is much more of it. With a good sized tree, there may be a 30’ circle of nothing else but mushrooms growing under it. You can fit loads of 1-2" diameter saplings in that area.
I have a 14 acre woodlot that was cut flat about 28 years ago. I take 4 cord of firewood off of that land a year, and I can’t even get through all of the standing dead. All that I burn is on it’s way to atmospheric carbon anyway, and there’s plenty of dead wood left for wildlife.
I’m no expert on trees by any means, but I think this is wrong. The growth rings vary in size, not surprisingly, with the amount of growth. Hell, archeologists can describe the weather in 3000 BC just by analyzing the size of the growth rings in trees from that area and time period. I’m pretty sure if you look at any tree’s rings, the ones in the middle will be thicker than the ones towards the edge.
Look at the area of the growth ring. An eighth inch of growth on a two foot diameter tree is much more than even a quarter inch diameter new growth on a half inch diameter sapling. The fact that there are so many more branches and limbs on a large old tree all growing in size also beats out the small tree of the same species. Like I said it’s not simple.
It’s because trees don’t get infinitely big. A 200-year old tree is not twice as big (by mass) as a 100-year old tree, right? In most cases, a 100-year old tree isn’t twice as big as a fifty year old tree, either.
Sure, depending on the conditions and the species, trees are going to grow fastest on an absolute basis at some point after the first couple of years, but that growth can’t continue forever. It will slow down at some point (if nothing else, because the tree will eventually die and decay, releasing the carbon).
The specific growth curve of a tree is a bit tangential to the original carbon neutrality claim.
If you repeatedly:
(1) plant a bunch of trees,
(2) let them grow to some fixed height,
(3) cut them down and burn them
then you will not be adding any carbon to the atmosphere(*). That’s the long and short of the argument. Anything beyond this steady-state picture (perhaps involving starting with existing trees) will shuffle some carbon around initially, but that’s not within the scope of the claim.
(*) except for things like diesel burned during logging and transport.