Undo debug edit.
Up the scan radius minimum a bit more.

This is just to prevent underscanning ... 8 is still the
min radius we can get which may still be a bit too small.
Spruce: only grow "tall" spruces in dense taiga.

This isn't a minecraft thing, but a natural observation - in
nature when pine trees grow close together, they lose all their
side branches except the ones on top. We can easily recreate
this growth pattern in minecraft by making plants grow "tall" in
dense forests. Over time, the non-dense variants will lose their
ground and forests will become much more like real forests.

This should only effect Taiga's - in Ice plains and Extreme hills
we will likely never grow these since spacing is so large.