I must admit I have the advantage of being the descendant of multi generational farmers..
and having spent half my life (the first of course) growing up on a farm, learning first hand, as well as university study in horticulture ..

monoculture : def. by cambridge dictionary:
noun:
meaning: the practice of growing only one crop or keeping only one type of animal on an area of farm land.
: an area of farm land on which only one crop is grown or one type of animal is kept, or the crops grown or animals kept there.
: a culture that is the same in many different places.

a monoculture is an imposed human construct.
diversity is not allowed in a monoculture. It defeats the purpose of it.

The lake that is drying up is a natural process...
the invading species which are doing so in the lake bed ..are a natural process...
that is a natural process.
simply because hogweed is beginning to invade ...is invading or has invaded an ecosystem...doesn't make "it" the monocultural ecosystem...nor does not mean it becomes or automatically is a monocultural environment.
It is an oxy***** (really?? this is not a derogatory word to censor..) to call something a moncultural ecosystem...it is in fact anathema to one another.

That isn't how nature works.