How exactly is a trunk like this formed?

[leatherback]

Really good trunks can be grown in 3-5 years.

in YOUR climate

Your annual growth is 5 years growing here

 

[Shibui]

Your annual growth is 5 years growing here

I'd be intrigued to compare growth rates with a few others from different areas.
Originally I assumed that our longer seasons would equal increased growth rates but have seen some pots from northern growers that appear to show comparable rates. Further north means shorter growing season but longer daylight should mean increased growth so maybe the 2 can cancel each other in some places?

I've been considering setting up some trials to compare growth rates between regular dig and prune V left in place and intact leader. Maybe start this winter if I can find some spaces....

 

[leatherback]

Further north means shorter growing season but longer daylight should mean increased growth so maybe the 2 can cancel each other in some places?

I think with tridents the big difference would be temperaturewise. Last year, we had 3 days where temps hit 30c/86F or above (considered hot days here). 2018 and 2019 were extremely hot here, and we hit 30c for 15 and 16 days. Normal summer temperatures get stuck at ~25C.