Nature doesn’t work in the most optimal way, so it’s not always best to replicate it. Tons of things happen in nature that may wipe out important ecosystems. I suppose one could argue that at a long enough time scale it will even out but that time scale can be millennia. In the meantime, nature can wreak tons of havoc.
Nature (and by that I mean ecosystems because nature is a vague) also doesn’t behave in necessarily intuitive or easily observable ways either. What might seem “obvious” at first can be very wrong.
Nature (and again I mean ecosystems) also doesn’t exist in vacuums. What may have worked for centuries can be upset by even the most subtle of temperature shifts, and those might be caused by effects hundreds of miles away.
Unchecked nature is also not always going to be conducive to human needs either.
The entire field requires constant observation and inference. Even the ways of indigenous people that are fetishized as natures way by many, are scientific in nature. They’re the result of many years of observation, experimentation, learning and modifying how nature works to fit our needs.