How does green turn to brown?

Hi.  I have tons of chopped down trees.  Some have been there for a few weeks, and some are fresh.  Those which are fresh have copious green foiliage.  The others have copious brown foliage.

Question:
How do the green nitrogen-rich leaves turn into brown carbon-rich leaves.  They're the same thing, just two weeks apart.

Duncan

I think it’s all green at this point, and will rob your garden of available nitrogen until it breaks down.

That's a great question!

Bacteria will take advantage of any available moisture to quickly breakdown the protein (nitrogen) compounds into volatile ammonia, which then disperses into the air.

But it should be possible to retain the nitrogen by careful, low-heat drying. You might do this by laying the grass out on a tarp, only an inch or two thick, with constant stirring to keep the leaves from matting or trapping moisture.

Based on the comparable process in alfalfa, careful drying should retain 70% or so of the original nitrogen.

For the home gardener, the brown/green thing is a bit of an approximation. The little chemical kits that detect nitrogen don't work well with organic materials. If you try to get send away to a lab for testing, you'll note that they will either not test for organic nitrogen, or will charge more.

Mmmm  So the colour is a bit of a red herring, just as black coffee grounds are "green".  What prompted my question was the fact that two similar branches look quite different only two weeks apart.  The leaves have turned from green to dark brown - but as Scorpio Rising has pointed out, the colour is immaterial at this point.  Both are "green".  Not exactly intuitive, but that makes more sense than nitrogen-rich leaves suddenly becoming carbon-rich just by being left out on the lawn.

They are being shredded on a daily basis to be added to my 5m^3 pile of wood chips which were originally my row of trees on the driveway cut down by the arbourists and chipped with their industrial chipper.

In order to accommodate all these chips I'm goint to build a series of compost bins out of pallets (i.e. 1 metre cubed) along the bottom fence.  I'll turn each bin with a 150mm auger every week or so to ensure aeration. But that is a long-term project.  They can stay there slowly composting for a number of years - no hurry. In the meantime, my three rotating 220 litre compost bins will receive all the softer stuff, manure, grass, coffee, kitchen scraps and so on.  That's what will be used to supplement my raised bed mixture.

How long does it take to break down and become usable?