Watermellons have a thing that makes them suck water from the ground.
this is ok if animals are NOT around. but if animals eat the watermellon then it gets bad.

Watter ---) mellon ---) *animal eating* ---) poop ---) nitrogen

this makes nitrogen a semi-renuable resorce, GREAT! but there is a problem.
this will dry up the planet and kill every jungle specific thing.
ok you can use watter from a naother planet if you want to remain in the jungle biome.
BUT the amoatnt of water and oxygen is fixed on a save, and because you can´t convert nitrogen into watter you will just run out of watter at some point.

if you play loong enough you will end up with tiny water ,tiny oxygen and a bunch of nitrogen, iron and gold + a lot of dead things.
why NO water and NO oxygen? because you need some water to create a jungle and some oxygen to make stones. and why a lot of dead things? because dry spells will ravage the land, volcanoes will pop-up on every planet, and animals will suffocate without fresh air to breathe, and wildfires sparked by volcanoes will devoure almoast everything.

Conclusion? PLANT JUST ONE WATERMELLON AND KILL IT!