Just a note here, I didn't test what I'm about to say about pickaxes:

As soon as I got my bronze axe, I rushed back to the meadows hunting for birches and oaks to get a hand on the new birch seeds and acorns - I wanted to plant some around my base. I took down about 30 birches and a dozen of oaks, only one birch seed. No acorns.
I kind of gave up on the project. Later I casually crafted an iron axe, and stumbled upon an oak tree. Well I took it down just to see. Nice ! An acorn. So I looked for some more. The next 3 oaks I got acorns, and half of the birches I took down yielded their seeds as well.
SO I kind of have the theory that the higher tier tool you get, the more mats you harvest. I didn't confirm this with axes, just experienced it, and never paid attention to pickaxes since, but if it's true then that would have to be taken into account