I guess you used Dynamic Trees code to generate trees?
For sure, it looks awesome, but comes with cost of fps drop.
In open field, or in mist my fps aprox. 100-120. In a middle of forest it drops to 40-60.
Sure, it's not that big of a big deal, but if I want to make big modded base in Mist, i need every frame possible.

Not sure what You or I can do to this at this point. Maybe reduce amount of trees? But that would decrease awesomeness.

So.... it's not much a report, but a general complaint about this problem. Maybe you will adress this issue in 1.16.

Not. I am not using dynamic trees...
The trees of the misty world are my personal development.
Frame drops can be due to fog rendering or chunk updates.
Anyway, I hope that both will be fixed in new versions.