A list of the problems:

• Grass cannot grow or spread.
• Trees cannot grow unless bonemeal is used.
• Leaves do not decay unless broken by the player.
• Neither water sources nor rain can hydrate farmland.
• Crops do not grow unless bonemeal is used.
  Below y=128 all of these mechanics work perfectly fine.
  (could only include screenshot for farmland issue, the others are difficult to prove unless you try them yourself.)