Most young tree saplings spend their early decades under the shade of their mother's canopy. Limited sunlight means they grow slowly.
Slow growth leads to dense, hard wood.
But something interesting happens if you plant a tree in an open field: free from the shade of bigger trees, the sapling gorges on sunlight and grows fast.
Fast growth leads to soft, airy wood that didn't have time to densify.
and soft, airy wood is a breeding ground for fungus, disease, and ultimately a short life.