Complex sentence: For a tree seeding to grow into an adult tree it needs light and space, if seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing.
Split into simpler sentences: For a tree seeding to grow into an adult tree it needs light and space. If seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing.