L1 to L3 trees have a time for harvesting, its about 20 seconds - somewhat less I think.
I only harvest L2 & L3 trees - I have a PH3 & its not worth the decay to harvest L1s.
Because of this limited time, it pays to get into position & only then start harvesting.
While its true that L3s only last a short time & you can only get one or two planks, sometimes you can get more - a lot more even.
I don't know if this is just like random loot mobs can drop - you get lucky, or, the longer a tree has not been harvested the more timber it gives,
It would be interesting to find out if reload increase works foe harvesting