Update:
Forest 1: After 3 years of Tokyo summers the larches called it quits.
This year in particular was the perfect storm. It was super hot, there was almost no rainy season to speak of, and the larches were attacked by a fungus that I couldn't get rid of despite my best efforts.
What started as 2 trees gone progressed to 3 more, and before I know it the whole group was toast. Pretty sad for me as it's one of the projects I've been working on the longest. Needless to say I won't be trying them again in this climate. RIP
Forest 2: The tridents on the other hand have been doing fine. I lost one of the original trees to a pervasive root fungus thing, but other than that growth has been fine. I let the trees in the colanders run, as well as the two that germinated last year. Seems a few of the cuttings in the long colander survived the whole summer as well. We are still clearing 30 degrees C nearly every day and the trees are still growing. I plan on repeated last year, but cutting back to another new trunk leader and taking winter cuttings where I can.
Then, this coming spring, I'm planning on assembling the first iteration of the actual forest.