great. soon it will be economically unfeasible to not cut down every forest.

It stands to reason that growing biomass sequesters CO2, at least until it is burnt again. Neither photosynthesis nor any other major chemical cycle in plants produces CH4. I suspect a small herd of cows generates more methane than an entire forest - not to mention the 100 billion m^3 of natural gas that is flared or vented each year by the oil industry.

IMHO, anything that turns waste streams into energy at reasonable cost is worth investigating. This is especially true of the logging and paper industries.

The Life of a Tree
When most people think about the effect of a tree on the environment, they only think of photosynthesis, the process whereby trees (and other green plants) convert CO2 and water into carbohydrate and oxygen. As long as the tree remains alive that is a valid model. Unfortunately, trees, like us, don't live forever.

Let us assume for the moment that when the tree dies, it dies with all the carbohydrate that it produced during its life in tact (ignore for now the secondary products produced from the carbohydrate). In other words, assume that the part of the tree that was perhaps consumed by animals or parasites and the leaves it may shed every autumn is a negligible part of the overall carbohydrate production.

So, when the tree dies, it has done the world this service: it has converted a large mass of CO2 to O2. In the process, it has also produced a lot of biomass. So far, the tree has been a huge benefit to everybody. Unfortunately, the story does not end there...

After its death the tree biomass is broken down. One way it breaks down is aerobic (in the presence of oxygen). This is basically a reverse of photosynthesis. If the entire tree breaks down this way (no biomass remains), it would consume all the oxygen that was produced during its life, and return all the CO2 that was captured. That is the good option, believe it or not.

The tree can also break down in the absence of oxygen (anaerobic conditions). Here the carbohydrate would basically break down 50:50 between CO2 and methane (CH4). If the entire tree breaks down this way, no oxygen is consumed. But a ton of CH4 is released. Since CH4 is 20 times worse ito GHG than CO2, this is a problem.

So there you have it: if the entire tree breaks down in aerobic conditions, its life cycle effect is zero. If the entire tree breaks down in anaerobic conditions, its life cycle contributed equivalent amounts of oxygen and CH4. You could even sum it up with a chemical reaction:
CO2 + 2H2O -> 2O2 + CH4

In the real world, a tree will break down partly aerobic, partly anaerobic. So, there will always remain some oxygen and some CH4. That is why Cervus got information indicating that reforestation (by itself)will increase global warming.

Now, this is where things get interesting. Take a step back and look at the bigger picture. The bigger picture contain these elements, in addition to growing (and dying trees):
1. Man needs energy.
2. Man burns oil for energy, releasing a lot of CO2.
3. CO2 levels in the atmosphere increase.
4. O2 levels decrease.
5. Is it getting hot in here?
6. Are we dead, yet?

Now, notice why CO2 levels are increasing: there are two sources of CO2: the rotting trees and the exhaust gases of man’s energy consumption. What if one of these sources could be eliminated? With apologies to eco-terrorists, peak-oilers and other depressive types, I am not going to propose we go beck to the Stone Age. Quite the opposite.

Eliminate rotting trees. OK, it will take decades, maybe centuries, but you’ve got to start somewhere. How do you eliminate rotting trees? By projects such as this one proposed by UMaine. That is you take the biomass from the trees and you use it to replace oil. Here is what you achieve:
1. You reduce and eventually eliminate (we hope) oil consumption.
2. By doing that you stabilize CO2 levels: all CO2 released is no part of a living carbon cycle - i.e. the carbon released is balanced by carbon absorbed by photosynthesis.
3. You also stabilize oxygen levels, as a nice side effect.
4. You eliminate all that CH4 release, thus reducing global warming significantly.

Bottom line: we need projects like this one to save our butts!

Nothing personal t, but what have you been smoking?

"The flaw here is that decomposition can take hundreds of years, but if you burn it you will concentrate the time frame in the near term to add even more co2 in the short term."
Hundreds of years? Where is that?

CO2 in the atmosphere is balanced the biomass and fuel that you keep in storage. Since these technologies would give a value to trees, it stands to reason that more trees would be cultivated, meaning more tree biomass, meaning lower CO2.

"We need to decrease co2 now."
Nice slogan/bumper sticker. Meaningless in practice.

"The other flaw is that we won't use trees as a substitute; we will use them as an addition. That is our nature; to consume everything in the largest quantities as quickly as possible. As long as we haven't set a mandatory cap on emissions, we will continue to increase our emissions regardless of the technology."
Repeat after me: the government will not save us. Mandotary CO2 caps is meaningless. Just like California's legislation did not in the end force EVs onto the roads, CO2 caps will not force technology ripe. Our best hope is the market.

We will eventually run out of oil. Nobody knows when, but our love affair with oil will eventually end. It may already be happening.

"As far as growing trees increasing global warming, that theory was thoroughly debunked by the realclimate.org people."
You have a specific link? Am I supposed to be impressed by the name realclimate?

In the real world, a tree will break down partly aerobic, partly anaerobic. So, there will always remain some oxygen and some CH4.

Where to begin?

There are several forms of anaerobic respiration, of which carbon disproportionation is by far the least efficient and is competitive only in anoxic conditions, like the bottom of a swamp (they call it swamp gas for a reason); in microbes in the guts of animals, like cows and termites and people; in landfills; and in beer bottles. In soils it's either aerobic respiration or denitrification. Even in highly anoxic conditions like peat bogs and ocean sediments most (though not all) of the respiration uses sulfate as an oxidant. Using O2 as an oxidant you get 478 kJ/mol C; using nitrate you get 398 kJ/mol C; using sulfur you get 126 kJ/mol C; and using carbon you get a pathetic 70 kJ/mol C. In a normal healthy forest very very little goes through C (although there's an intriguing lab study indicating that plants may produce methane as part of growth.)

You do get (abiotic) methane production in biomass burning, you may also get an increase in methanogenic bacteria, so deforestation is definitely associated with methane release, but forestation is not.

The problem is not CO2 or CH4, anyway; it's the fact that those species are radiatively important and currently exist in far higher concentrations than what we evolved under, biologically and socially. And the concentrations are increasingly rapidly.

Over a ~century or more timeframe, a tree will be carbon neutral, releasing as much CO2 (to respiration, of itself, of browsers, and of decomposers) as it takes in: the UoM's idea is that if reduced carbon in the form of lignin and other plant parts are going to oxidize to CO2 anyway, might as well use that energy to do useful work (by societal metrics, at any rate)

Am I supposed to be impressed by the name realclimate?

No, I hope you're not impressed by the name. OTOH, you should be impressed by the peer-reviewed literature put out by the authors of the site.